Smithsonian Institution

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Smithsonian Institution

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smithsonian contributions to paleobiology • number 100 0

The Geology and Vertebrate 

Paleontology of Calvert Cliffs, 

Maryland, USA

Edited by

Stephen J. Godfrey
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The Geology and Vertebrate 

Paleontology of Calvert Cliffs, 

Maryland, USA

Edited by

Stephen J. Godfrey

smithsonian contributions to paleobiology • number 1 0 0

WASHINGTON, D.C.

2018
ABSTRACT

Godfrey, Stephen J., editor. The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA. Smithsonian Contributions to 

Paleobiology, number 100, iv + 274 pages, 93 figures, 63 body restoration images, 11 tables, 2018.—The last comprehensive review of the fossil 

vertebrates from the Miocene of Calvert Cliffs was published more than 100 years ago. This volume is a collection of papers that updates some 

of the geological features of Calvert Cliffs and provides reviews of the fossil biota that include representatives from the following taxonomic 

groups: chondrichthyans (chimaeras, shark, skates, and rays), actinopterygians (ray-finned fishes), crocodilians (crocodiles), and sirenians (sea 

cows). Peter Vogt, Ralph E. Eshelman, and Stephen J. Godfrey document how the 20–40 m [65–130 ft] high Calvert Cliffs along the western 

shore of the Chesapeake Bay continue to yield insights into 18–8 mya (Miocene) geology, marine and terrestrial vertebrate fauna, and the origin 

and evolution of Chesapeake Bay and Calvert Cliffs up to the present. These exposures rank high among the best-known fossiliferous deposits 

of any age. Bretton W. Kent describes the cartilaginous fish (the chondrichthyan) fauna, consisting of 54 species—3 chimaeras (ratfishes), 39 

sharks, and 12 skates and rays—a fauna rich in large macrophagous sharks and large neritic rays. In an addendum to Kent’s chapter, he and 

David J. Ward describe a new species of giant thresher shark with serrated teeth. Giorgio Carnevale and Stephen J. Godfrey present an account 

of the 38 actinopterygian taxa known from osteological remains and a diverse otolith assemblage of at least 55 taxa. These actinopterygians 

show an affinity for well-oxygenated muddy and sandy substrates dominated primarily by shallow-water species characteristic of the inner shelf 

and secondarily by epipelagic taxa. Robert E. Weems details the crocodilians referable to the tomistomine Thecachampsa. The closest living 

relative is Tomistoma schlegelii, the false gharial of Southeast Asia. Two species are present: Thecachampsa sericodon and T. antiquus. These 

tomistomines are found in shallow marine coastal deposits, indicating that they inhabited coastal waters. Daryl P. Domning reports that fossils 

of the Miocene marine fauna include rare sirenians of the family Dugongidae. Three taxa are known: the halitheriine dugongid Metaxytherium 

crataegense, the dugongine dugongid Nanosiren sp., and another dugongine, aff. Corystosiren. The St. Marys Formation contains remains that 

may be referable to Metaxytherium floridanum, but confirmation awaits the discovery of more complete specimens.

Cover image: Calvert Cliffs at Warrior’s Rest Sanctuary; view looking north. These 12–15 million-year-old sediments from the Miocene epoch 

comprise the upper portion of the Calvert Formation and the overlying Choptank Formation. Photo by Stephen J. Godfrey. 

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Library of Congress Cataloging-in-Publication Data

Names: Godfrey, Stephen J., editor. | Smithsonian Institution Scholarly Press, publisher.

Title: The Geology and vertebrate paleontology of Calvert Cliffs, Maryland / edited by Stephen J. Godfrey.

Other titles: Smithsonian contributions to paleobiology ; no. 100. 0081-0266.

Description: Washington, D.C. : Smithsonian Institution Scholarly Press, 2018. | Series: Smithsonian contributions to paleobiology, ISSN 0081-0266 ; 

 number 100 | Includes bibliographical references and index.

Identifiers: LCCN 2017059091

Subjects: LCSH: Geology, Stratigraphic--Miocene. | Geology--Maryland--Calvert Cliffs. | Paleontology--Miocene. | Paleontology--Maryland--Calvert Cliffs. | 

 Vertebrates, Fossil. | Biology--Classification.

Classification: LCC QE694 .G46 2018 | DDC 566.09752/44--dc23 | SUDOC SI 1.30:100

LC record available at https://lccn.loc.gov/2017059091 

ISSN: 1943-6688 (online); 0081-0266 (print)

ZooBank registration: 28 August 2018 (LSID urn:lsid:zoobank.org:pub:806B4214-CD38-41EC-BDFF-7A6F913F9324) 

Publication date (online): 25 September 2018

The paper used in this publication meets the minimum requirements of the American National Standard for Permanence of Paper for Printed Library 

Materials Z39.48–1992. 
Contents

INTRODUCTION by Stephen J. Godfrey 1

1 Calvert Cliffs: Eroding Mural Escarpment, Fossil Dispensary, 

and Paleoenvironmental Archive in Space and Time 3

Peter Vogt, Ralph E. Eshelman, and Stephen J. Godfrey

2 The Cartilaginous Fishes (Chimaeras, Sharks, and Rays) 

of Calvert Cliffs, Maryland, USA 45

Bretton W. Kent

Addendum 157

Bretton W. Kent and David J. Ward

3 Miocene Bony Fishes of the Calvert, Choptank, 

St. Marys, and Eastover Formations, Chesapeake Group, 

Maryland and Virginia 161

Giorgio Carnevale and Stephen J. Godfrey

4 Crocodilians of the Calvert Cliffs 213

Robert E. Weems

5 Fossil Sirenia (Mammalia) of the Miocene Chesapeake 

Group, Eastern United States 241

Daryl P. Domning

INDEX 267

Introduction

Stephen J. Godfrey

The naturally eroding sea bluffs along Calvert Cliffs rank high among the bestknown and long-studied fossiliferous deposits of any age on the planet, yet 

they continue to yield insights into the Miocene marine and terrestrial biota 

that thrived there between approximately 18 and 8 mya (million years ago). 

Along the Potomac River on the Maryland side, and elsewhere in Virginia, the age of the 

Miocene sediments reaches back to 23 mya (Kidwell et al., 2015). All of these shallow marine to coastal sediments comprise only a small part of the vast thickness of sediments that 

have been shed from the eroding Piedmont and Appalachian Mountains, an ongoing process that began with tectonic breakup of Pangaea and the consequent separation of North 

America from Africa ca. 175 mya. At the time of the 1904 Maryland Geological Survey 

publication on the systematic paleontology of the Miocene deposits of Maryland (Case et 

al., 1904), the fossilized remains of more than 600 different species were documented, the 

majority of which were of marine invertebrates. Although a detailed survey of the invertebrate fossils found along the cliffs is beyond the scope of this volume, they, in addition to 

the vertebrate fossils reviewed here (more than 110 vertebrate species are reviewed in this 

volume), and the sediments in which they are entombed give us a picture of the environment and the organisms that lived in the Mid-Atlantic region of North America during the 

Miocene epoch. 

The last comprehensive review of the fossil vertebrates from the Miocene of Calvert 

Cliffs was published more than 100 years ago, and since then, a great deal has been discovered, researched, and published. This volume updates some of the geological features of 

Calvert Cliffs and provides reviews for the following taxonomic groups from the Miocene 

Chesapeake Group: chondrichthyans (chimaeras, shark, skates, and rays), actinopterygians 

(ray-finned fishes), crocodilians, and sirenians (sea cows). It is anticipated that a second 

volume will include additional contributions on the geology of the cliffs as well as reviews 

of the other vertebrate groups known from the Chesapeake Group in Maryland and Virginia: turtles, birds, terrestrial mammals, seals, toothed whales, and baleen whales.

Upon hearing of my ambitious hopes to help compile, in a single volume, an update 

on the Miocene geology and vertebrate paleontology of Calvert Cliffs, David J. Bohaska 

(collections management, vertebrate paleontology, Smithsonian Institution) told me, “It 

will be wrong the day it’s published.” As a contributing editor to several of the Geology 

and Paleontology of the Lee Creek Mine, North Carolina volumes (Ray and Bohaska, 

2001; Ray et al., 2008), he understood the nature of science and wanted my expectations 

to be realistic. (Thank you, Dave!) This effort is by no means the final word on the geology 

and vertebrate paleontology of Calvert Cliffs. It is a reflection of our collective curiosity 

Curator of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, 

USA. Also, Research Associate, Department of 

Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 

20013-7012, USA.

Correspondence: 

Stephen.Godfrey@calvertcountymd.gov

Received 1 May 2015; accepted 25 August 2017.
2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

that allows us to update what is currently known. Bohaska deserves special thanks for responding to countless requests from 

me for help and information throughout my 20 years here at the 

Calvert Marine Museum.

Daryl Domning of Howard University (and author of chapter 5) once said to me, “Do something now as opposed to everything never.” This volume is the “something now”; hopefully, it 

will inspire excellence in collecting and research so that future 

generations of paleontologists, both avocational and professional, can revise this work to further deepen our understanding 

of the world that used to be.

This work is dedicated to the landowners along Calvert 

Cliffs and along other tributaries flowing into the Chesapeake 

Bay, who have so generously allowed professional paleontologists to quarry fossils from their cliff-front properties. Permission 

to quarry is only half the equation, however. The majority of the 

finds along the cliffs are made by amateur/avocational collectors; 

they donate many of their finds to public museum collections—

principally those of the Calvert Marine Museum (CMM) and the 

Smithsonian Institution’s National Museum of Natural History 

(NMNH). At the time of this writing, fully 70% of the fossils 

in the permanent paleontology collection of the CMM were donated by avocational paleontologists. Consequently, most of the 

fossils illustrated herein were also collected by amateurs. And so 

I extend the dedication of this volume to include avocational collectors, for without their generosity this volume would be poorer 

indeed. They are our eyes and scouts along the cliffs, regularly 

reporting the presence of newly exposed bones therein.

A WORD OF WARNING TO FOSSIL HUNTERS

“Digging in the cliffs is dangerous and is prohibited on all 

state and federal lands” without obtaining permits. “On private 

land, permission must be obtained from the owners before digging. If you see a skull, bone, or unusual fossil in the cliffs, please 

report it to the Calvert Marine Museum in Solomons, Maryland 

(410-326-2042). The museum appreciates getting this information and, if justified by the importance of the find, will make 

every effort to obtain the necessary permission and have trained 

personnel collect the specimen, giving full credit to the finder” 

and the property owner (Ashby, 1979:16).

ACKNOWLEDGMENTS

I express my gratitude to James O. Farlow, who first approached me during a coffee break at an annual meeting of the 

Society of Vertebrate Paleontology to ask if I had an interest in 

editing a volume on the geology and paleontology of Calvert Cliffs 

for Indiana University Press (IUP). And so the project began with 

guidance from Robert J. Sloan, editorial director at IUP. When 

it became obvious that the contributions far exceeded a single 

volume, he very graciously dissolved our agreement, allowing 

for submission to Smithsonian Institution Scholarly Press (SISP). 

Ginger Minkiewicz, director of SISP, was willing to publish this 

effort, and Stephanie Summerhays (formerly of SISP) cheerfully responded to many queries on my part; thank you both very much. 

Other members of the SISP team include Meredith McQuoidGreason, Julie Beals, and Tshawna Byerly. I am very grateful for 

your attention to detail. This volume benefitted greatly from constructive reviews by Nicholas D. Pyenson (NMNH) and David J. 

Bohaska (NMNH).

I also express my appreciation to the contributing authors 

for their wonderful chapters and extraordinary patience. The artistic excellence of Tim Scheirer (CMM) is evident throughout; 

he has drawn all the life restorations of the Miocene vertebrates 

illustrated herein with the same expertise that characterizes all 

his work. John Nance (paleontology collections manager at 

CMM) also helped in many ways.

I am also indebted to C. Douglass Alves (former director, 

CMM) and Sherrod Sturrock (director of CMM) for also recognizing the value of a comprehensive work like this. Ralph 

Eshelman, first director (now research associate) at CMM, had 

the vision to create a curatorial position in paleontology at the 

fledgling CMM. He along with James A. Kaltenbach, David J. 

Bohaska, and volunteers including Norm Riker, Wally Ashby, 

and Linda McGilvery began the fossil collections that continue 

to grow with no end in sight. The curatorial position at CMM is 

made possible with funding from the citizens of Calvert County, 

Maryland, and the Calvert County Board of County Commissioners. Additional funding for the Department of Paleontology 

comes from the Clarissa and Lincoln Dryden Endowment for 

Paleontology at CMM. 

REFERENCES

Ashby, W. L. 1979. Fossils of Calvert Cliffs. Calvert Marine Museum Special Publication 2. Solomons, Md.: Calvert Marine Museum.

Case, E. C., C. R. Eastman, G. C. Martin, E. O. Ulrich, R. S. Bassler, L. C. Glenn, 

W. B. Clark, T. W. Vaughan, R. M. Baggs Jr., A. Hollick, and C. S. Boyer. 

1904. “Systematic Paleontology of the Miocene Deposits of Maryland.” In 

The Miocene Deposits of Maryland, ed. W. B. Clark, G. B. Shattuck, and W. 

M. Dall, pp. 1–543. Baltimore: Johns Hopkins Press.

Kidwell, S. M., D. S. Powars, L. E. Edwards, and P. R. Vogt. 2015. “Miocene Stratigraphy and Paleoenvironments of the Calvert Cliffs, Maryland.” In Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015, ed. D. K. Brezinski, J. P. Halka, and R. A. Ortt Jr., pp. 231–279. 

Geological Society of America Field Guide 40. Boulder, Colo.: Geological 

Society of America. https://doi.org/10.1130/2015.0040(08).

Ray, C. E., and D. J. Bohaska, eds. 2001. Geology and Paleontology of the Lee 

Creek Mine, North Carolina, III. Smithsonian Contributions to Paleobiology 

90. Washington, D.C.: Smithsonian Institution Press.

Ray, C. E., D. J. Bohaska, I. A Koretsky, L. W. Ward, and L. G. Barnes, eds. 2008. 

Geology and Paleontology of the Lee Creek Mine, North Carolina, IV. 

Virginia Museum of Natural History Special Publication 14. Martinsville, 

Virginia.
ABSTRACT. The Calvert Cliffs are a series of bayside bluffs, typically 20–40 m high, 

that form a 40 km long shoreline escarpment on the western shore of the Chesapeake 

Bay in Calvert County, Maryland. These cliffs expose fossil-rich shallow marine sediments deposited between about 18 and 8 mya, during the Miocene epoch at times when 

relative sea level was higher than today. In ascending order, the Miocene strata exposed 

in the cliffs belong to the Calvert, Choptank, and St. Marys Formations. These formations are overlain along the southern portion of the cliffs by “upland gravels,” fossilpoor fluvial deposits that accumulated at times in the latest Miocene or Pliocene when 

sea level was only slightly higher than today. The Calvert Cliffs we see today began to 

form about 5,000 years ago during the most recent rise of sea level that followed the 

last glacial event, called the Wisconsinan. The slopes of these cliffs, mostly between 45° 

and 60°, make them unstable and prone to collapse. Whenever the toe of a cliff becomes 

stabilized through formation of sand bars, sand spits, or human intervention, the overlying cliff face erodes back until it reaches a stable slope of about 30°–35°. Ongoing cliff 

erosion causes long-term shoreline retreat, which averages about 5–30 cm/yr along the 

central and northern cliffs where the semi-consolidated marl of the Plum Point Member 

is exposed at beach level. Erosion rates are much higher along the southern cliffs, where 

sandier, less consolidated Choptank and St. Marys Formation sediments are exposed at 

beach level. There the rate of shoreline retreat locally averages 50–100 cm/yr. The ongoing cycle of erosion and shoreline retreat exposes the abundant and diverse Miocene 

fossils entombed within the cliffs, which wash out and become scattered across the underlying beaches. The Calvert Cliffs constitute a regional scenic landmark with relatively 

high topographic relief very rare along the tidal shoreline between the northern New 

Jersey Highlands and Kill Devil Hills in North Carolina. They also are regarded as one of 

the three most important deposits of Miocene fossils in the world.

1 Calvert Cliffs: Eroding 

Mural Escarpment, 

Fossil Dispensary, and 

Paleoenvironmental Archive 

in Space and Time

Peter Vogt,1,2 Ralph E. Eshelman,2 and 

Stephen J. Godfrey3*

1 Research Associate, Marine Science Institute, 

University of California, Santa Barbara, Santa 

Barbara, California 93106, USA.

2 Research Associate, Calvert Marine Museum, 

P.O. Box 97, Solomons, Maryland 20688, USA.

3 Curator of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, 

USA. Also, Research Associate, Department of 

Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 

20013-7012, USA.

* Correspondence:

Stephen.Godfrey@calvertcountymd.gov

Received 1 May 2015; accepted 25 August 2017.
4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

INTRODUCTION

As the chapters in this volume demonstrate, the 20–40 m high 

Calvert Cliffs (Figures 1.1, 1.2) have yielded extremely significant 

insights into the Miocene world that was present in the region 

from approximately 18 to 8 mya. On the outcrop-poor Southern 

Maryland Coastal Plain, the Calvert Cliffs stand out as a premier 

example of local geology (Glaser, 1971) and paleontology (e.g., 

Ward and Powars, 1991). The Calvert Cliffs cap a 750 m thick 

stack of sediments near the landward edge of an enormous wedge 

of debris deposited on the eastern margin of North America since 

its breakup from Africa around 175 mya. Without an outcrop like 

the Calvert Cliffs, our knowledge of the Miocene world would be 

limited to what could be gleaned from a sediment core not more 

than 5 cm in diameter (e.g., Hansen and Wilson, 1984). 

The cliffs expose the lower half of the Miocene Chesapeake 

Group, including much or all of the marine Calvert, Choptank, 

and St. Marys Formations (Figure 1.3). Shattuck (1904) 

FIGURE 1.1. Chesapeake Bay region, showing the Calvert Cliffs, with its named communities, facilities, and 

beaches, and other coastal bluffs greater than 15 m high. Letters locate selected photos shown in Figure 1.2 of the 

Fairhaven Cliffs (Figure 1.2A) and the Calvert Cliffs (Figure 1.2B–F). The western border of the Atlantic Coastal 

Plain, marked by the Fall Line (Weems, 1998), is taken from Powars (2013).

Breezy Point

F

Choptank River

Patuxent River

Kent

Island

Eastern

Bay

Potomac River

Ν

Piedmont

Coastal Plain

Drum

Cliffs

Holland

Cliffs

Lyons

Creek

Popes

Creek

Cliffs

Horsehead Cliffs

Stratford Cliffs Nomini Cliffs

Fairhaven

Chesapeake Beach

Camp Roosevelt

Plum Point

Parkers Creek

Scientists Cliffs

Governor Run

Matoaka Cabins

 Calvert Beach

Flag Ponds

Calvert Cliffs Nuclear Power Plant

Cove Point

Drum Point

Langleys

Bluff

Little Cove Point

Anderson’s

Camp Kaufmann

Dares Beach

Bayfront Park

Chancellor

Point Windmill

Point

Fall Line

Rocky Point

Naval Research Lab C

alv

ert Clis Holland Point

Driftwood Beach

CHESAPEAKE

BAY

A

B

C

D

E

N38 ̊ 30’

77 ̊W 

_N38 ̊ 30’ _

_

_

_ _

N39 ̊

VIRGINIA

MARYLAND

MARYL

VIRGINIA

AND

WASHINGTON, D.C.

ANNAPOLIS
NUMBER 100 • 5

subdivided the entire lower Chesapeake Group into two dozen 

“zones,” which we here call “beds” to avoid confusion with paleontological zones. Shattuck’s numbering system is still widely 

used today, with the exception of his zone 16, which later mapping has shown to be only a local unit. Overlying these shallow 

marine Miocene strata in the middle and especially the southern 

Calvert Cliffs are fluvial strata informally called upland deposits 

by Schlee (1957). With rare exceptions (e.g., McCartan et al., 

1990), these upland deposits are nearly devoid of fossils and thus 

are not a focus of this volume. Although poorly dated, these sediments were generally deposited by the ancient Potomac and its 

tributaries during the late Miocene through Pliocene and perhaps 

early Pleistocene times. Even during maximum Pliocene warmth 

(Miller et al., 2012), however, the Atlantic did not return to the 

area of the Calvert Cliffs. Tidewater in the form of estuaries, producing the modern and earlier Calvert Cliffs by shoreline erosion 

(e.g., Hobbs, 2004; Vogt et al., 2010) only reappeared after the 

middle Pleistocene (since ca. 1 mya). During repeated major glaciation and very low sea levels, rivers such as the Susquehanna 

carved deep valleys to enable formation of later estuaries and 

cliffs such as those described in this volume.

Calvert Cliffs expose shallow marine to coastal nonmarine 

sediments that were derived from the eroding Piedmont and Appalachians during the Miocene and probably Pliocene epochs. 

The marine Miocene exposures of the Calvert Cliffs rank among 

the best-known and longest-studied fossiliferous deposits of any 

age on the planet. Largely for this reason, the cliffs are among 

the 100 most significant geologic outcrops in northeastern North 

America (Vogt and Eshelman, 1987) and are extremely popular 

with amateur fossil collectors, including both serious museum 

volunteers and casual fossil hunters (e.g., Ashby, 1979; Powell, 

1986; Dickas, 2012). Diverse species of invertebrate marine fossils—a review of which is outside the scope of this volume—are 

exposed in the eroding cliff faces, and abundant specimens of 

them litter the shoreline below the cliffs. As the following chapters in this volume demonstrate, the cliffs provide a window into 

not only the marine but also the terrestrial Miocene vertebrate 

faunas of the Mid-Atlantic region.

There are many other stories to be told about the 42 km 

long series of eroding coastal cliffs and intermittent stream valleys found along portions of the western shore of the Chesapeake Bay. They include conflicting human interactions with the 

cliffs and the role of the cliffs as regional scenic and recreational 

landmarks—the subject of photography, art, and fiction. Geomorphology and modern erosional processes (driven by wave 

erosion that is enabled by wind, exceptionally high tides during 

storms, and rising sea level) maintain the cliffs as ever-changing 

outcrops that are eroding back at rates typically ranging 0.1–0.5 

m/yr. The cliffs also constitute an unusual ecological transition 

zone, called an ecotone, which is rich in ephemeral microhabitats 

lying between land and sea. 

DIVERSITY OF FOSSILS FROM 

THE CALVERT CLIFFS

The nonvertebrate fossil record is readily subdivided into 

(1) the plant kingdom, (2) single-celled and other tiny animals 

best studied under the microscope, and (3) macroscopic invertebrates such as mollusks. Vertebrates, the focus of much early 

research (e.g., Whitmore, 1971b), include marine sharks, rays, 

chimeras, bony fishes, turtles, crocodilians, sea birds, and marine 

mammals, as well as occasional examples of freshwater and terrestrial vertebrates that washed into the Miocene sea. To reach 

out to a wider readership, we will use common English names 

for these Miocene creatures because most have modern relatives, 

at least at the family or genus level and in some cases even at the 

species level.

Microscopic plant remains from the Calvert Cliffs include 

diatoms (a major group of photosynthetic algae with at least 23 

species identified to date; Andrews, 1978, 1988) and radiolarians 

(Shattuck, 1904), both of which have shells, called tests, which 

are made of silica. There are also abundant remains of many 

species of another biostratigraphically important phylum of single-celled organisms called dinoflagellates (De Verteuil and Norris, 1996), some of which can both photosynthesize and ingest 

other microbes. Microscopic pollen grains, although produced 

by macroscopic land plants, are another abundant component of 

the marine plant microflora that tells us most of what we know 

about the onshore flora. The pollen from the Calvert Cliffs remains largely unstudied, but Bryan Landacre (in Weems et al., 

2017) reported pollen assemblages from beds of similar age in 

the nearby Westmoreland County cliffs of Virginia (Figure 1.1). 

These pollen assemblages (called palynofloras) come from the 

Plum Point Member of the Calvert Formation, the Choptank 

Formation, and the Little Cove Point Member of the St. Marys 

Formation. The palynofloras from all three of these units are 

dominated by species of oak (Quercus), hickory (Carya), and 

pine (Pinus). Secondary elements, however, can vary considerably from unit to unit. In the Plum Point Member, the secondary 

elements consist mainly of hardwood taxa such as alder (Alnus), 

ash (Fraxinus), elm (Ulmus), holly (Ilex), hornbeam (Ostrya/

Carpinus), sweetgum (Liquidambar), and wingnut (Pterocarya, 

an exotic). Cypress trees (Taxodium type) are the most common and persistent warm-temperate to tropical taxon present 

in the Plum Point, followed by Momipites (an extinct exotic in 

the walnut family). In the Choptank Formation, the mix of secondary forest elements was somewhat different and consisted of 

ash (Fraxinus), beech (Fagus), birch (Betula), hornbeam (Ostrya/

Carpinus), and sweetgum (Liquidambar). Cypress (Taxodium

type) again is present throughout the Choptank Formation but 

in reduced numbers compared to the Plum Point time. Also 

represented in the Choptank Formation are grasses (Poaceae), 

sedges (Cyperaceae), and herbaceous taxa, including representatives of Amaranthaceae and Asteraceae. Yet another palynofloral 

assemblage is found in the Little Cove Point Member, where the 
6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

bed 19

A B

C D

E F

Fairhaven South of Bayfront Park

North of Parkers Creek Western Shores

Rocky Point North of Driftwood Beach

bed 11

bed 12

bed 13

bed 17

bed 15

beds 21-23

post-Miocene

bed 18

bed 14

bed 14

bed 10

beds 4-9

bed 3B

bed 3B

bed 14

bed 20

beds 21-23

bed 19
NUMBER 100 • 7

FIGURE 1.3. Ages and stratigraphic correlation chart for the Miocene part of the Chesapeake Group. The dark bracket 

within the group column designates the part of the Miocene Chesapeake Group represented by the sediments along the 

Calvert Cliffs. The Eastover Formation is preserved only in Virginia and northern North Carolina. Modified from R. E. 

Weems (Calvert Marine Museum, personal communication) and Powars (2013).

FIGURE 1.2. (Facing page) (A) Cliffs south of Fairhaven, Anne Arundel County, Maryland (approximately 38°44′32.43′′N, 76°33′23.75′′W). 

(B) The Calvert Cliffs south of Bayfront Park, Calvert County, Md. (approximately 38°40′28.76′′N, 76°31′52.22′′W). (C) The Calvert Cliffs 

north of Parkers Creek, Calvert Co., Md. (approximately 38°32′33.23′′N, 76°31′2.50′′W). (D) The Calvert Cliffs at Western Shores, Calvert Co., 

Md. (approximately 38°29′31.62′′N, 76°29′54.67′′W). (E) The Calvert Cliffs at Rocky Point, Calvert Co., Md. (approximately 38°25′29.69′′N, 

76°25′41.37′′W). (F) The Calvert Cliffs north of Driftwood Beach, Calvert Co., Md. (approximately 38°21′17.16′′N, 76°23′31.02′′W). Numbers in the photos indicate beds (zones) first defined by Shattuck (1904).
8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

secondary hardwood forest elements include beech (Fagus), cypress (Taxodium type), hemlock (Tsuga), wingnut (Pterocarya), 

and sweetgum (Liquidambar). Grasses (Poaceae), sedges (Cyperaceae), and herbaceous taxa (Amaranthaceae and Asteraceae) 

again are well represented. All of the terrestrial palynofloras 

from the Westmoreland Cliffs have their greatest similarity to the 

palynofloras being produced today in Florida and the southern 

Atlantic and Gulf Coastal Plains. 

Macroscopic remains of land plants include carbonized 

small logs, twigs, cones, fruits, and nuts of trees that originated 

from the nearby warm temperate to nearly subtropical coastal 

forests growing to the west. No modern comprehensive review 

of these plant remains has been undertaken; however, macrofossils from various kinds of pine (Stark, 1987), cypress, oak, and 

elm represent parts of forest associations that grew along nearby 

coasts and riparian venues (e.g., Berry, 1916). Vogt and Parrish 

(2012) suggested that rare erratic pebbles found in the Calvert 

Formation (along Calvert Cliffs) were rafted into the sea as ‘driftwood dropstones’ trapped in tree roots. These dropstones are 

most abundant in beds 12 and 14, both of which contain carbonized wood. 

At least 23 species of foraminifera, tiny calcareous planktonic animals, have been identified to date (e.g., Shattuck, 1904; 

Gibson, 1983; Buzas and Gibson, 1990). Also known are calcareous shells from at least 25 species of ostracods (Malkin, 1953), 

which are tiny clam-like crustaceans. Larger invertebrates include 

echinoderms (Shattuck, 1904), with at least one species each of 

sand dollar (Kier, 1983), sea urchin, starfish, and brittle star; two 

hydrozoans (Shattuck, 1904); at least one species of coral (Shattuck, 1904); one brachiopod (Shattuck, 1904; superficially clamlike, they lived directly on the substrate); bryozoans (Shattuck, 

1904; colonial organisms sometimes called moss animals); and 

several species of barnacles (Zullo, 1984) and other crustaceans, 

one of which is thought to have produced the abundant trace fossil Gyrolithes sp. (infilled helical burrows seen in vertical section 

along the cliffs; Uchmana and Hanken, 2013). Notable among 

many crabs collected is the giant spider crab Libinia amplissimus

from the St. Marys Formation, which is nearly twice the size of 

its living relatives (Feldmann and Schweitzer, 2016).

Mollusks are by far the most common macrofossils found 

and are generally much more abundant on the beaches below 

the cliffs than are shells of modern species inhabiting the Chesapeake Bay (Figure 1.4). The paucity of shells of modern Chesapeake mollusks (such as oysters, mussels, and soft-shell and razor 

clams) is due in part to much lower abundance of these animals 

today than in the late nineteenth century. More than 400 Miocene species (e.g., Shattuck, 1904; Schoonover, 1941; Vokes, 

1957; Ward, 1992; Petuch, 2005; Petuch and Drolshagen, 2010) 

are known from the Calvert Cliffs, including a scaphopod (a 

burrowing marine mollusk popularly known as a tooth or tusk 

shell), snails, clams, oysters, and pectens (scallops). The pectens 

are often especially well preserved, particularly in the Choptank 

Formation. Nance et al. (2015) recently reported on the presence 

of intact proteinaceous shell-binding material in Ecphora snail 

shells from along the Calvert Cliffs. These original proteins represent some of the oldest and best-preserved examples of proteins 

ever found in a fossil shell. Many of the mollusks found in the 

Calvert Cliffs are preserved in their life positions, a fossil association called a biocenosis. In contrast, most vertebrate remains 

are broken and scattered and often show bite marks made by 

sharks. Bone fragments are most abundant in the so-called Parkers Creek Bone Bed (bed 12), where they are typically found at 

10–100 m intervals. This bed contains an association of remains 

typical of a fossil death assemblage (called a thanatocoenosis), 

but the remains are too scattered to qualify as a true “bone bed” 

because the bones, although abundant, are not tightly packed 

into dense clusters like they are at localities discussed in Rogers 

et al. (2007). 

Fossil shark teeth (Figure 1.4; Kent, this volume) are probably the single greatest attraction the cliffs offer to the fossilcollecting public (e.g., Glaser, 1979; Powell, 1986; Kent, 1994; 

Dickas, 2012). Most shark teeth are found as “float” on the 

beach and, for some species, are abundant (Visaggi and Godfrey, 

2010) because sharks continually shed teeth during their lifetimes. Miocene species—closely related to modern ones—include 

angel, bramble, bull (gray), cow, hammerhead, lemon, mako, 

sand tiger, sharpnose, snaggletooth, thresher, tiger, and whale 

sharks. The largest sharks in this fauna (Carcharocles chubutensis, C. megalodon, and Parotodus benedenii) are all now extinct. 

A front tooth of C. megalodon may measure more than about 

13 cm (5 inches) on edge. For many collectors, the discovery of 

such a tooth is a find of a lifetime. Carcharocles megalodon traditionally has been considered to be related to the modern great 

white shark (Applegate and Espinosa-Arrubarrena, 1996), but 

now it appears likely that the modern great white shark is more 

closely related to Carcharodon (also known as Isurus or Cosmopolitodus) hastalis (Ehret et al., 2012; Kent, this volume), one of 

the extinct broad-toothed mako species found along the Calvert 

Cliffs. Shark vertebral centra also are occasionally found, but 

otherwise, the cartilaginous skeletons of sharks generally do not 

fossilize. 

Other fossil fish remains include many species of skates and 

rays (Kent, this volume), as well as a wide variety of bony fishes 

(Leriche, 1942; Carnevale and Godfrey, this volume), including 

sturgeons, gars, bowfins, shad, freshwater and marine catfishes, 

hakes, cods, brotulas, toadfishes, anglerfishes, garfishes, sea robins, poachers, sea bass, tilefishes, bluefishes, cobias, pinfishes, 

scups, croakers, black drums, red drums, tautogs, stargazers, 

barracudas, wahoos, bonitos, tunas, blue marlins, sailfishes, lefteye flounders, burrfishes, and ocean sunfishes. Although some of 

the fossil fishes from the cliffs are different from living species 

(because of evolutionary change), others are practically indistinguishable from extant species and show how little many bony 

fishes have evolved in the last 10–20 million years.

Two amphibian taxa (both Caudata) have been reported 

from the Calvert Formation at the Pollack Farm fossil site near 

Cheswold, Kent County, Delaware (Weems and George, 2013), 

but as yet no amphibian fossils have been found along Calvert 
NUMBER 100 • 9

A B

C

D

E

50 mm

2 inches

FIGURE 1.4. (A–D) Selected Miocene fossils and (E) the living Puritan tiger beetle. (A) The muricid 

gastropod Ecphora gardnerae gardnerae, Maryland’s state fossil. (B) Carcharocles megalodon lower anterior tooth, lingual view. (C) Carcharodon hastalis upper anterior tooth in lingual view, showing where 

the base of the enameloid cutting edge was notched on both sides by Native Americans for use as a tool, 

projectile point, or pendant; this is one of four comparable shark teeth recovered from Wheatley Point 

midden site 18DO371 in Dorchester County, Maryland (Lowery et al., 2011: figs. 10–12). (D) Scallop 

shell (Chesapecten nefrens) festooned with barnacles (Balanus concavus chesapeakensis; Pilsbry, 1916; 

Zullo, 1984). (E) Extant tiger beetle (Cicindela puritana), federally listed as threatened, which requires 

eroding cliff in which to lay its eggs (Knisley, 2011); photo courtesy of B. Knisley.
1 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Patuxent R

 iver

3000 BCE

shoreline

5000 BCE

shoreline

Kent Is.

Cape Charles

Paleochannel

Eastville

Paleochannel

Tilghman Is.

Fairhaven Clis

Plum Point

Parkers Creek

Flag Ponds

Cove Point

Drum Point

Holland Point

Battle

Creek

N38 ̊ 30’

76 45’W _76 30’W _

_

_

0 5 10 miles

0 10 kilometers

A

C B
NUMBER 100 • 1 1

Cliffs. In contrast, sea turtles are represented by at least three species of cheloniid sea turtles plus a hefty leatherback turtle (Collins and Lynn, 1936; Weems, 1974; Lapparent de Broin, 2001; 

Chesi et al., 2007). Nonmarine turtles are very rare but include a 

side-necked turtle, a musk turtle, a painted turtle, a pond turtle, 

a slider turtle, two kinds of softshell turtle, and five kinds of tortoise from the Calvert and St. Marys Formations of Delaware, 

Maryland, and Virginia (Weems and George, 2013). Teeth and 

scutes of two species of presumably saltwater crocodiles (some 

of which produced some of the larger coprolites found in the 

cliffs) are prized finds (Weems, this volume). Among the known 

birds (Olson, 1984; Rasmussen, 1998) are two species of jaegers, 

two auks, a duck, three gannets, an albatross, several shearwaters, a loon, a tropic bird, a quail-like bird, a pheasant-like bird 

(the chachalaca), a turkey, and a dove. The most impressive bird 

remains are those of the giant false-toothed bird (Pelagornis), 

which is an extinct relative of the pelican and the world’s largest 

marine bird with a wingspan up to about 6.4 m (21 ft; Mayr and 

Rubilar-Rogers, 2010). As many as three separate species of this 

flying marvel may have been present in the region of Maryland 

at one time or another during the Miocene.

Land animal remains (Emry and Eshelman, 1998; Eshelman et al., 2007; see also Dooley, 2007), presumably washed 

into the Calvert Sea as methane-inflated carcasses (known 

as “bloat and float” taphonomy), include an extinct wolf, a 

bear-dog, a large extinct cat, at least four species of peccaries, 

fanged deer, a protoceratid (an extinct group of antelope-like 

browsers with elaborate horns), at least two species of camel, 

a tapir, two species of rhinoceros, up to five species of threetoed horses, and a large elephant-like animal called a gomphothere. The odds were heavily stacked against the remains 

of any terrestrial animal being carried into the Miocene shallow marine environment. The vicissitudes of fossilization and 

preservation (the study of which is called taphonomy) mean 

that, for most of these prehistoric creatures, a few bones or 

teeth (but never entire skeletons) have been recovered. The 

Calvert Sea was well oxygenated, which was good for 

life but bad for fossilization. In contrast, the modern 

Chesapeake Bay has bottom waters that are often hypoxic or 

even anoxic because of wasteful and adverse human activities. 

One of the world’s richest records of fossil marine mammals 

has come from the Calvert Cliffs. It includes some of the world’s 

oldest known true seals and also sea cow remains, representing 

at least three species (Kellogg, 1966; Domning, 1984, 2006, this 

volume). More than 30 species of cetaceans are known (Gottfried et al., 1994, and numerous references therein), including 

both baleen whales and toothed whales. Toothed whales include 

both large and small sperm whales, shark-toothed dolphins, and 

a variety of long- and short-snouted “dolphins.” Representatives 

of the family Delphinidae, true dolphins, have never been found 

within the Calvert Cliffs. 

HUMANS AND CALVERT CLIFFS

The actively eroding Calvert Cliffs as presently configured 

began to form about 5,000 years ago (Figures 1.5, 1.6). About 

that time, rising sea levels flooded the originally narrow freshwater lower Susquehanna River valley, inundating and eroding 

shorelines that caused the Chesapeake Bay to eventually lap up 

against cliffs abandoned when sea levels fell at the end of the 

last interglacial (marine isotope stage [MIS] 5e), around 125,000 

years ago. The long-abandoned cliffs of the Chesapeake Bay 

that existed during the previous interglacial had by then been 

reduced by erosion to gentle forested escarpments in the more 

than 100,000 years that had passed. This means that the PaleoIndian and early to middle Archaic natives that lived in this area 

prior to 5,000 years ago did not see the steep cliffs we see today 

because they did not yet exist.

In the absence of written records, we cannot know with any 

certainty how the earliest Native Americans interacted with the 

cliffs, but archeology confirms that fossil Miocene shark teeth 

were prehistorically traded (from around 500 bce to around 

1300 ce) as far west as central Ohio (Lowery et al., 2011) and 

that at least some of these teeth probably were collected along 

the Calvert Cliffs. Examples have been found of fossil shark 

teeth that were modified into scrapers and projectile points (see 

Figure 1.4C), and possibly, others were collected simply as curiosities and ornaments.

It seems plausible that prehistoric Native Americans also 

herded game, notably white-tailed deer, over the Calvert Cliffs, 

where they could easily be killed on the beach below. Even today, 

FIGURE 1.5. (Facing page) The Calvert Cliffs region in relation to later Pleistocene and Holocene geomorphology, with estimated 3000 and 

5000 bce shorelines indicated by thin dark lines. The modern Calvert Cliffs shoreline is indicated by the thick solid line. The thick dashed line (A) 

shows the present Chesapeake–Patuxent drainage divide that separates modern Battle Creek (B) from its previous headwaters, which were captured by the Susquehanna River and now flow in the opposite direction toward Chesapeake Bay as Parkers Creek (Vogt, 1991). The Last Glacial 

Maximum Cape Charles paleochannel (about 24,500 bce) and the MIS 6 Eastville paleochannel of the Susquehanna River (about 140,000 bce) 

are indicated (Colman et al., 1990). The location of a +6–7 m terrace (stippled area, C) shows areas that are now land but were submerged at 

the peak of the last interglacial (MIS 5e, 125,000 years ago). The landward edge of this terrace indicates MIS 5e shorelines, including “paleo” 

cliffs now covered by vegetated escarpments.
1 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Calvert Clis

Late Miocene-Pliocene

uvial deposits

Shipping Channel

Present-day Chesapeake Bay

Erosion

Miocene 

Shallow marine{

Eastern Shore

Paleochannels under present Chesapeake: Eastville Cape Charles 

Holocene estuarine deposits

Middle & Later Holocene, 5 ka *

Many 125 ka (C) sea clis reoccupied

Cli shoreline erosion resumes 

Erosion

* 1 ka = 1000 years ago

Pleistocene sedimentation

Later early Holocene, 7 ka

Rapid widening of bay

Early Holocene, 8 ka

Early narrow Chesapeake

Archaic Indian cultures

First tidewater o Calvert 9 ka; Megafauna extinctions ca. 12.8 ka

Clovis culture 13.3-12.8 ka. First humans here 14-15 ka?

Late Wisconsinan, 20 ka

Last Glacial Maximum (LGM)

Early Wisconsinan Chesapeake, 80 ka “Super – Chesapeake”, 125 ka 

Formation of estuarine terraces +5-7 m

along Patuxent and other tidal “rivers”

Cli erosion

Interglacial

Sea level 6m higher than today

Penultimate Glacial

Rapid sea-level rise, 133-130 ka

Erosion 

Calvert “Superclis”, 135 ka

Upland Deposits

Early Homo sapiens appear in Africa

Oldest Paleochannel under present Chesapeake 

Susquehanna River

Erosion of the Eastville Channel

Erosion

Susquehanna River

H

I

G

F E

D C

B A
NUMBER 100 • 1 3

dogs sometimes chase deer over the cliffs, causing broken bones 

and likely death for most of them. It is also highly likely that 

Late Archaic and Woodland Indians used the promontories on 

the cliff edges to scan the bay for friendly or hostile canoes. 

Similarly, earlier Archaic and Paleo-Indians must have stood on 

the edge of the remnant escarpment, east of the modern Calvert 

Cliffs, scanning the forested plain below for signs of game and 

perhaps also for enemy or friendly campfires near the Susquehanna River several kilometers to the east.

In 1525 the Spanish, under the pilot and explorer Pedro de 

Quexós, were likely the first Europeans to discover and enter 

the Chesapeake Bay, which they called Bahia de Santa María 

(Cumming, 1982:274). The first Europeans known to have explored the full length of the bay to its northern limits sailed on 

the 1588 Vicente Gonzales expedition (Cumming, 1982:278). 

That is likely to have been the first time the cliffs were seen 

by Europeans; however, no mention of them was made in the 

expedition’s reports (see also Scisco, 1945, 1947). The cliffs were 

first definitely documented by Captain John Smith (Smith, 1986 

[1608]) as he sailed north up the bay on his exploratory shallop 

voyage in June of 1608.

Upon departing Jamestown on the first of two discovery 

voyages, Smith and his men had been following the eastern side 

of the Chesapeake, 

but finding this easterne shore shallow broken isles, 

and maine for the most part without fresh water, we 

[sailed] for the weasterne shore. So broad is the bay 

here, that we could scarce perceive the great high 

Cliffes on the other side. By them, wee ancored that 

night, and called them Richards Cliffes. 30 leagues 

[about 167 km] we sailed more Northwards, not finding any inhabitants, yet the coast well watred, the 

mountains very barren, the vallies very fertile, but the 

woods extreame thicke, full of Woolves, Beares, Deare, 

and other wild beasts (Smith, 1986[1608], vol. 2:165).

It is not clear what “mountains very barren” meant, unless 

it was a change made by editors. Perhaps Smith was referring to 

the eroded, bare character of the cliffs, which would stand out 

in an otherwise thickly vegetated landscape. The Calvert Cliffs 

part of the Chesapeake shoreline was therefore largely or entirely 

uninhabited in 1608, and no archeological evidence for earlier 

Native American settlements––other than temporary hunting 

camps—has been discovered. However, it must be kept in mind 

that any evidence for settlement activity within roughly 100 m of 

the present cliff shoreline (including interspersed valleys where 

freshwater streams debouched into the bay) would have been destroyed over the last several centuries by cliff erosion, a process 

discussed elsewhere in this chapter.

The name “Richards” or “Rickards” Cliffs, after Smith’s 

mother-in-law’s family, obviously did not stick. Maps from the 

eighteenth to nineteenth centuries label the feature with names 

like “Clifts,” “Cliffs,” or “Cliffs of Calvert,” with “Calvert 

Cliffs” eventually becoming standard in the twentieth century. 

However, since the Calvert Cliffs Nuclear Power Plant went into 

operation on the southern cliffs during 1975–1976, the term 

“Calvert Cliffs” is often used in reference to the power plant. 

Smith may well have noticed the speckled white shell marl 

exposed in the cliffs, but if so he did not record this observation. 

However, in one of his accounts he did note “mountains of a 

diverse nature, Marle, Fuller Earth,” which likely referred to materials he observed in the Calvert Cliffs. (Smith, 1986[1612:3]).

The first historical European notice of vertebrate 

fossils from the Chesapeake Bay area appears in John Winthrop’s 

journal entry of 3 August 1636, reporting fossils found along 

the James River in southeastern Virginia (discussed in Hosmer, 

1908:185–186): 

Samuel Maverick, who had been in Virginia near 

twelve months, now returned...It is strange, what 

was related by him and many others, that, above 

sixty miles [about 97 km] up James River, they dig 

nowhere but they find the ground full of oyster shells, 

and fishes’ bones, etc; yes, he affirmed that he saw the 

bone of a whale taken out of the earth (where they 

digged for a well), eighteen feet [about 5.5 m] deep.

After English colonists, who first settled in Maryland at St. 

Mary’s City off the Potomac River, had begun to cross the Patuxent River in the later 1630s and especially after the first plantations appeared along the Calvert Cliffs, probably starting in the 

later 1650s, locals surely explored the shoreline at the foot of 

the cliffs and collected fossils as curiosities. By the time of Augustine Herrman’s 1670 (published 1673) map (available online 

at Library of Congress, https://www.loc.gov/item/2002623131/) 

of the Chesapeake Bay, the Calvert Cliffs shoreline is shown 

FIGURE 1.6. (Facing page) Evolution of topography and sea level along an east–west profile across the central Calvert Cliffs from around 

140 ka (when the Susquehanna River flowed in the Eastville paleochannel) to the present (A–I). Seismic reflection profiling mapped these paleochannels in the mid-1980s (Colman et al., 1990); higher-resolution but lower-penetration chirp sonar profiles show more detailed structure 

in the channel fill (e.g., Cronin et al., 2007; Shah et al., 2012). Late Pleistocene paleochannels like the two shown were carved during the major 

Laurentide ice sheet advances described by Balco and Rovey (2010). More speculatively, the southward shift of the Coastal Plain Susquehanna, 

Potomac, and Delaware rivers (e.g., Higgins et al., 1974) was possibly caused by southward migration of the forebulge of the first major glaciation (e.g., Balco et al., 2005).
1 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

sprinkled with more than two dozen plantations. After Hugh 

Jones became minister and naturalist to Christ Church in Calvert 

County—not far inland from the central cliffs—he began to collect plant and animal remains starting in July of 1696 and also 

fossil remains that he shipped to collectors back in England. Out 

of all of the material that he collected, only his pressed botanic 

specimens, three tooth plates of the ray Aetobatus, and a partial odontocete atlas can be presently located (Reveal, 1987; Ray, 

2001). Reverend Jones may well have collected fossils from the 

Calvert Cliffs or from the beaches along their base until his death 

in 1702.

Among the fossils that are found in the Calvert Cliffs is a 

four-ribbed extinct muricid snail called “Ecphora,” which was 

long considered to be the earliest illustrated fossil from North 

America (supposedly in 1685; Shattuck, 1904). This attribution is now known to be incorrect (Ray, 1987; also see Conrad, 

1832). More recent research suggests that the first illustrated fossil from North America came from Virginia (Figure 1.7B) and 

that the Ecphora illustration, probably dating from 1770, was 

drawn from a fossil collected by Hugh Jones from the Calvert 

Cliffs. The present location of this Ecphora shell is unknown, 

but a 1786 auction catalog of the Portland Museum (UK) lists 

item #3516 as “a very curious and rare species of Buccinum (a 

genus of snail) in a fossil state, having four high sharp ridges, 

from Maryland, very rare” (Lightfoot, 1786:137). Ecphora

continues to be the most celebrated Miocene mollusk from the 

Calvert Cliffs. For example, the Calvert Marine Museum Fossil 

Club, the American Fossil Federation, and the Paleontological 

Research Institution include an Ecphora as part of their logos, 

and the state of Maryland adopted the Ecphora as its state fossil 

shell in 1985 (Figures 1.4A, 1.7A).

The earliest known reference to a vertebrate fossil from what 

is certainly the Calvert Cliffs is in Samuel Latham Mitchill’s 1818 

review of fossils from North America: “I remember, that petrified bones, apparently of a whale, were brought from the shore 

of the Chesapeake Bay, near the place where the river Patuxent 

enters it, to the City of Washington, by Mr. O’Neale” (Mitchill, 

1818:394).

The well-known British paleontologist Thomas Say described 

fossil shells collected by John Finch (Finch, 1833) in 1824 from 

Maryland and Virginia. This pioneering work (Say, 1824) marks 

the beginning of scientific interest in the rich fossil deposits of the 

Atlantic Coastal Plain. One of us (REE) was privileged to view 

these fossils, which are still in the collections of the Natural History Museum in London (formerly the British Museum of Natural History). Say’s 1824 observations are still appropriate today: 

“Many of these shells appear to the eye nearly perfect, in every 

respect, with the exception of color, as the recent ones of the coast, 

and not a few of the bivalves have both bivalves attached...; circumstances which indicate an undisturbed deposition in the waters in which they lived” (Say, 1824:124).

The American Timothy A. Conrad developed a keen interest 

in the molluscan fossils from the Chesapeake region. Beginning 

in 1830, Conrad published more than 30 scientific papers describing many fossils from the Calvert Cliffs (see, e.g., Conrad, 

1832). 

The first detailed geological description of the Calvert Cliffs 

(with measured stratigraphic sections) is that of the state geologist 

of Maryland, Julius Timolean Ducatel, whose Report on the New 

Map of Maryland, 1836 (Ducatel and Alexander, 1837) devotes 

fully 25 of 59 pages to Calvert County (Figure 1.8). Ducatel’s favorite geological outcrop was the short section of high cliffs between 

twentieth century developments at Governor Run and Scientists 

Cliffs. Ducatel (in Ducatel and Alexander, 1837:11) wrote,

B

A

FIGURE 1.7. Two of the earliest illustrated fossils from North 

America. (A) “Ecphora sp., collector and formation unknown; from 

Maryland... (first published in... Lister, Huddesford edition, 1770, 

pl. 1059, fig. 2)” Ray (1987:3). (B) “Chesapecten jeffersonius (Say, 

1824), right valve (thought to have been collected by John Banister 

from the Yorktown Formation of Virginia; first published in Lister, 

1687, p. 167: . . . from Huddesford edition, 1770).” Ray (1987:4). 

Both images edited in Photoshop from Ray (1987).
NUMBER 100 • 1 5

But perhaps the most interesting spot at which to 

determine the geological features of the county, is 

on the north side of Governor’s [sic] Run, on the 

plantation of Mr. Frazier [probably either James or 

Charles Frazier]. In this locality the cliffs are upwards of one hundred feet [about 30.5 m] high and 

afford a luminous view of all the strata containing 

fossils [what later became known as zones 14, 17, 

and 19 of Shattuck, 1904] as well as many of the intermediary ones, thus furnishing useful directions for 

research of those beds that are sought after for marl. 

Ducatel promoted the mining of fossil shells, outcropping 

also in deep ravines, for use by farmers to lime fields and to 

help sanitize outhouses. Referring to soil quality, Ducatel also 

noted “this good soil rarely extends beyond one mile [~1.6 km] 

from the bay side, after which it becomes very sandy and sour, 

throwing up a thick growth of pine.” This observation shows 

that Ducatel recognized the connections between geological substrates and vegetation. From early colonial times through the 

first half of the nineteenth century, local farmers on occasion 

limed their fields with mollusk-rich fossil marl, as well as oyster 

shell mounds left by Native Americans (Ducatel and Alexander, 

1837:9; Miller, 1907).

Richard Harlan (1842), sometimes characterized as America’s first professional vertebrate paleontologist (Simpson, 1942), 

published the first formal scientific description of a fossil vertebrate from the Chesapeake Bay region, an extinct dolphin collected by Francis Markoe Jr. in 1841 from the southern end of 

the Calvert Cliffs. Timothy Conrad assisted Markoe in collecting 

these dolphin bones. Harlan named the dolphin Delphinus calvertensis, in recognition of the fact that the collection site was in 

Calvert County. Markoe was the cofounder and corresponding 

secretary of the National Institute for the Promotion of Science 

in Washington, the predecessor of the Smithsonian Institution. 

Sir Charles Lyell (1845), the most famous geologist of his day, 

also published descriptions of the Miocene geology and fossils of 

Maryland. In 1867 the famous dinosaur hunter and vertebrate paleontologist Edward Drinker Cope placed Harlan’s fossil dolphin in 

a new genus. That same year Cope (1867) described a fossil tooth 

from the Calvert Cliffs that he referred to as a shark-toothed whale. 

This specimen later proved to be a canine tooth from the extinct peccary Cynorca, now known from more diagnostic material (Wright 

and Eshelman, 1987). Although peccary bones might not have been 

expected in the Calvert Cliffs marine deposits, Harlan (1842) had 

already reported on the occurrence of a fossil proboscidean (gomphothere) tooth from the “Miocene of Maryland.” Cope (Osborn, 

1931:148) also surely knew that land mammal fossils sometimes 

turned up in Maryland Tertiary marine deposits, for he wrote in a 

letter to his father (1867), 

I accepted the invitation of a Marylander interested in 

science to examine with him the Eocene and Miocene 

beds in the South part of the state, between the Potomac and Patuxent. One object was to examine, and 

if possible to procure a collection of fossil vertebrata 

and Mollusks in possession of an old man [James T. 

Thomas] not far from the latter river. I examined the 

latter and found it of value to science. Of the vertebrates 

were remains of 26 or more species, of which seven are 

cetaceans. One is a whale of large size; among other 

parts is the whole lower jaw—7 ft. [about 2.1 m] long 

is there...and singularly enough two land vertebrates—

a small peccary and a carnivore the size of a fox.

The relative importance of the Miocene vertebrate record 

from Calvert Cliffs, in contrast to outcrops in North Carolina and Virginia, is evident in the modern assessment by Ray 

(1983:8–9): 

Perusal of...publications on fossil vertebrates of the 

Chesapeake Series reveals very little on the Yorktown 

Formation and relatively little on North Carolina. 

The reasons are readily apparent; in spite of the occasional notice of large whale skeletons since early colonial times and the superabundance of invertebrates, 

natural exposures have produced an unreliable crop 

of vertebrate material. Of that, very little of adequate 

quality reached the hands of researchers, as compared, 

for example, to the abundance of good specimens from 

the Calvert Formation of Maryland [emphasis added].

Although good Miocene vertebrate remains have been recovered 

from the Lee Creek phosphate mine in North Carolina (Ray, 

1983) and the Pollack Farm quarry in Delaware (Emry and Eshelman, 1998), the Calvert Cliffs remain unequaled in the abundance and quality of their fossil materials.

The historical era of Calvert Cliffs research can be thought 

of as terminating with the papers of Harris (1893) and particularly with Shattuck (1904), who published numerous drawings 

of vertebrate and invertebrate fossils (see also Vokes, 1957), 

and who, on the basis of measured sections along the cliffs, assigned numbers to the strata (“zones,” here called beds) exposed 

in the cliffs and other areas. Shattuck’s work is still referenced 

in modern publications, even though many of his taxonomic 

identifications have been revised and some of his stratigraphy 

refined or rejected (e.g., Vokes, 1957). With the close proximity 

of the cliffs to the Smithsonian Institution and the U.S. Geological Survey, it is not surprising that many curators and researchers from these institutions continued to conduct research at the 

Calvert Cliffs (Figure 1.9). Among them were Frederick W. True, 

C. Lewis Gazin, Alexander Wetmore, Remington Kellogg, Lauck 

W. Ward, and Frank C. Whitmore Jr. 

THE CALVERT CLIFFS AS A MIOCENE 

PALEOENVIRONMENTAL ARCHIVE

The modern era of lithostratigraphic and biostratigraphic interpretation of the Miocene strata exposed along the Calvert Cliffs 

began with regional mapping of the Calvert Formation by Lincoln 

Dryden (1930, 1936), followed by Schoonover’s (1941) stratigraphic study of mollusks in the Calvert and Choptank Formations. Renewed paleontological and paleoecological interest after 

World War II led to Gibson’s (1962) study of benthic foraminifera 
FIGURE 1.8. Ducatel’s 1836 map (in Ducatel and Alexander, 1837) showing the topography of 

Calvert County with notes on local geology. Note indication of “fossils,” “blue clay,” “clayey 

loams,” etc. North is to the left.
NUMBER 100 • 1 7

in the Mid-Atlantic middle Miocene, Gernant’s (1970) study of 

the paleoecology of the Choptank Formation, Andrews’ (1978, 

1988) Calvert Cliffs and then regional study of Miocene diatoms, 

and Wetmore and Andrews’ (1990) biostratigraphy of silicoflagellates and diatoms in the Mid-Atlantic Coastal Plain. Buzas and 

Gibson (1990) described the various foraminifera at the Calvert 

Cliffs Nuclear Power Plant site. The work of De Verteuil and 

Norris (1996) added dinoflagellates to the list of biostratigraphically important Miocene microfossils. Among the many studies 

of Mid-Atlantic middle Miocene mollusks, including those found 

in Calvert Cliffs, are the self-published works of Petuch (2005) 

and Petuch and Drolshagen (2010). Also important are the benchmark mollusk-based biostratigraphic syntheses of Ward (1992) 

and Ward and Andrews (2008) and also Kelley’s (1983) attempt 

to test the theory of punctuated equilibrium using mollusks from 

the Chesapeake Group, including the Calvert Cliffs.

A comprehensive biostratigraphic and lithostratigraphic 

study was initiated by Susan Kidwell in her Ph.D. dissertation 

work conducted in the early 1980s, which focused mainly on the 

middle Miocene strata exposed in the Calvert Cliffs. Her work, 

later expanded and formally published (e.g., Kidwell, 1989, 

1997), included along-strike profiles of the Calvert Cliffs that 

FIGURE 1.9. Smithsonian staff and affiliates conducting research at the Calvert Cliffs south of Plum Point, ca. 1905: from left to right, Norman 

H. Boss up on the cliff face, unknown individual digging, and William Palmer and his wife, Arminia Palmer, collecting fossils below the cliffs. 

Image courtesy of the Smithsonian Institution. 
1 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

are shown here as Figures 1.10 and 1.11 Using Kidwell (1997) 

as their basis, Vogt and Parrish (2012) proposed that the Parkers 

Creek Bone Bed (bed 12) was deposited during the peak of the 

Middle Miocene Climatic Optimum and that the Governor Run 

channel of Kidwell (1997) at the base of the Choptank Formation was carved into the top of the Calvert Formation as the 

result of a significant sea level fall caused by Antarctic ice sheet 

expansion around 13.9 mya.

Research has been undertaken to correlate the strata preserved in the Calvert Cliffs with core holes on the nearby New 

Jersey continental margin (Browning et al., 2006, 2008) and in 

the buried Chesapeake impact crater (Poag, 1999; Browning et 

al., 2009). Although the correlations proposed have not been 

universally accepted, they form the basis for incorporating the 

Calvert Cliffs stratigraphic record into a broader Atlantic margin 

stratigraphic record. As suggested by Boulila et al. (2011) and 

by Vogt and Parrish (2012), the New Jersey borehole sediment 

record may provide evidence for a 1.2 Ma obliquity modulation influence on Antarctic ice sheet volume and thus on global 

eustatic sea level fluctuations. Imprecise dating of sediments, 

however, currently limits the reliability of these correlations. Recently, a shorter-term, 405 ka Milankovitch cyclicity (controlled 

by orbital eccentricity) has been proposed as the explanation for 

the pervasive, fining-upward cycles that are seen throughout the 

Calvert Cliffs and age-equivalent Miocene strata in the Westmoreland County, Virginia, region (Weems et al., 2017). Should 

future work confirm this cyclicity, then exceptionally precise age 

control and levels of correlation will be possible for the beds 

exposed in the Calvert Cliffs that will greatly enhance the importance of the Calvert Cliffs record for global correlations and the 

Miocene climate record.

COMMERCIAL, RESIDENTIAL, MILITARY, 

AND INDUSTRIAL DEVELOPMENT 

ALONG CALVERT CLIFFS

Because of the steep cliffs and shallow, often rough nearshore waters, early settlement was very limited along the Calvert Cliffs because there are no natural harbors and few suitable 

landing sites. The first and only major lighthouse along the cliffs 

was installed on the Cove Point spit in 1828, and although unmanned and automated in 1986, it is still operational today. From 

the colonial period up to the late nineteenth century, landings 

were used to transport freight between the shore and commercial ships. With the advent of larger and more powerful steamboats, larger-scale wharves were needed to replace the earlier, 

smaller-scale landings in order to make loading and unloading of 

these larger ships possible. An additional consideration was that 

these newer wharves, built to accommodate the new steamboats, 

had to be long enough to reach navigable deep waters. An approximately 97.5 m (~320 ft) long L-shaped wharf was built in 

1872 at Governor Run, where there was a prominent gap in the 

FIGURE 1.

cliffs; it remained in use until about 1928. Lodging, somewhat 

10. Along-strike (south to north) lithostratigraphic profile of the Calvert Cliffs based on Kidwell (1997) with the addition of the postulated Moran Landing reverse 

fault (see also Powars, 2013), which offsets the Chesapeake Group strata.
NUMBER 100 • 1 9

like modern bed and breakfast lodging, was provided near the 

Governor Run wharf by 1896 or earlier, attracting tourists to 

fish and also probably to collect fossils along the nearby beaches. 

A second wharf was built at Cove Point as early as 1896 (Eshelman, 1996).

From the early nineteenth through the early twentieth centuries, almost all level land in Calvert County was farmed. Prior 

to cheap modern fertilizers, exhausted land was left to regrow 

forest for some years until its fertility recovered sufficiently to 

allow it to be recleared for further farming. Many fields extended 

to the very edge of the cliffs, and these, according to geologist J. 

T. Ducatel, afforded great bay views from nearby farms “commanding an extensive prospect of a magnificent sheet of water” 

(Ducatel and Alexander, 1837:8).

Tourist interest in the Calvert Cliffs began with steamboats 

from Baltimore bringing city people to rural waterfront inns. 

Bayside steamboat landings promoted fishing, swimming along 

sandy beaches, and good seafood. The opening of the Chesapeake Beach Railway from Washington, D.C., on 9 June 1900 

brought thousands of visitors each year to the Chesapeake Beach 

Amusement Park just north of the northern end of Randall 

Cliffs, which are the northernmost cliff segment of the Calvert 

Cliffs. The land above the northern end of Randall Cliffs today is 

part of what is now known as Bayfront Park (formerly Brownie’s 

Beach). To judge from postcards and tourist brochures printed in 

the early 1900s, this northernmost part of the Calvert Cliffs was 

then known as the “Great Bluff,” and it apparently was a popular attraction. The railway era ended in 1935, a victim of the 

private automobile. The amusement park lingered on much longer, but it too finally closed in 1972. One of the authors (REE) 

found his first fossil shark tooth while swimming at Chesapeake 

Beach. In those days, it was not unusual for scores of children to 

be holding cherished shark teeth in their hands after a full day 

on the beach.

With the advent of cars and roads, opportunities expanded 

for people to see Ducatel’s great bay views, as well as to find recreational water and beach access for boating, swimming, fishing, 

and fossil collecting. From the 1920s through the 1960s, summer camps and vacation cabins sprang up all along the Calvert 

Cliffs. By far the largest was Chesapeake Ranch Estates, which 

had more than 6,000 lots plotted between 1957 and 1967, all 

of which were located along and near the southern end of the 

Calvert Cliffs. By the 1980s, nearly 20 other named towns and 

developments were clustered along the Calvert Cliffs from Chesapeake Beach in the north to Drum Point in the south.

The most famous of the summer camps was Camp Roosevelt, located on the northern cliffs. This was the first permanent Boy Scout Camp in Maryland and possibly the first in the 

United States. Camp Roosevelt, first leased by the Boy Scouts of 

America in 1914, was originally called Camp Archibald Butts, 

but it was renamed after President Theodore Roosevelt soon 

after his death in 1919. One of the authors (REE) attended this 

camp several times in his younger years and recalls that it was 

customary for each troop to make a plaque showing its troop 

number. These plaques were hung from the log rafters of the 

dining hall. Many of those plaques were decorated with gluedon fossil shark teeth collected from the beach. Since those days, 

the camp has largely disappeared. Attempts (involving author 

PV) were made to preserve the Camp Roosevelt tract as a county 

park, but these efforts failed largely because of opposition from 

neighboring landowners. In the late 1970s the camp became a 

large-lot subdivision. This and other new cliff-side developments 

appeared along the Calvert Cliffs. The developments expanded 

0 4 8

km

Disconformities

Key fossil beds

South NorthMeters

Boston Clis Drumcli Camp Roosevelt

Kenwood Beach

Parkers Creek

Mean

Sea

Level

10

20

30

St. Marys Fm.

beds 21-24

Choptank Fm.

beds 16b-20

Calvert Fm.

beds 1-15/16a

bed 19

14

12

17

GRC

10

FIGURE 1.11. Simplified alongstrike profile of the Calvert Cliffs, 

showing the Choptank and Calvert 

Formations at high vertical exaggeration and modified from Kidwell 

(1997). GRC refers to the filled Governor Run channel. Not shown here 

are the St. Marys Formation beds 

and the overlying nonmarine upland 

deposits exposed in the southern 

Calvert Cliffs.
2 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

and spread during the later twentieth century; by the twenty-first 

century, the 305 m (1,000 ft) wide “Maryland Critical Area” 

along the Chesapeake shoreline was the most densely developed 

strip of land running the length of Calvert county. This was in 

sharp contrast to Smith’s (1608) observation that the entire native population was clustered in tiny hamlets along the Patuxent 

River well to the west of the cliffs.

The Calvert Cliffs made military and industrial contributions during the middle and later twentieth century. During World 

War II (1941), the Naval Research Laboratory acquired approximately 1,220 m (4,000 ft) of cliff-front property at Randall Cliffs 

near the northern end of the Calvert Cliffs. The elevation of the 

cliff top overlooking the Chesapeake provided an excellent location for radar research, as it approximated the heights of naval 

shipborne radars above the water. Later, an amphibious training 

base was established at Solomons (1942–1944), just south of the 

southern end of the cliffs. This site was chosen because the beach 

at Cove Point and adjacent cliffs served as a training venue for 

troops preparing for similar amphibious landings at the bluffs of 

Normandy along the French coast in 1944.

In 1966, the Baltimore Gas and Electric Company purchased about 400 ha (986 acres) along the southern cliffs on 

which to build their Calvert Cliffs Nuclear Power Plant. A portion of the cliffs was removed in order to build the two reactors, which went on line in 1975–1976. The total size of the site 

has expanded since then to about 840 ha (2,076 acres), and the 

power plant is currently owned and operated by Exelon. The 

reactor site was placed on the southern cliffs in the 1960s because it was a safe distance from population centers in case of an 

accident; land was available at a relatively low cost, public opposition was low, and water for cooling was abundant. In 2000, 

the two reactors were recertified for operation through 2034 and 

2036, with aboveground (dry cask) storage of radioactive waste 

to continue. In 2005, a 1,600 MW third reactor was proposed to 

be located inland from the cliff edge. Many hearings were held to 

try to assuage public opposition to this expansion, but the effort 

ultimately failed; several years later Exelon finally withdrew its 

application for a third reactor.

One positive outcome of the initial permitting negotiations 

for construction of the plant by Bechtel Corporation was a granting of permission to conduct a multidisciplinary paleoecological excavation on a portion of the cliff-edge area that had to be 

removed for construction of the reactor foundations. Principal 

funding was provided by the National Science Foundation, with 

additional financial support coming from the Ford Foundation 

and the National Geographic Society. The grant was administered by the Maryland Academy of Sciences, with participation 

from the National Museum of Natural History of the Smithsonian Institution. During a two-year excavation study in 1968 and 

1969, scientists from around the world (including REE) completed what was at the time the most in-depth paleoecological 

and paleontological study of the cliffs ever undertaken, primarily 

in the Choptank Formation. Unfortunately, with a few exceptions (e.g., Whitmore, 1971a; Buzas and Gibson, 1990; Shideler, 

1994) none of the results were ever published, although data 

from the project did influence subsequent work of others (e.g., 

Ward, 1992).

During 1970–1972 Columbia Gas System acquired about 

412 ha (1,017 acres), including parts of the Cove Point marsh 

area, just to the south of the nuclear power plant; a liquefied 

natural gas (LNG) terminal (currently operated by Dominion 

Energy) was installed approximately 1.6 km (1 mi) offshore to 

accommodate deep-draft tankers. For financial reasons, the terminal was mothballed for many years, but it reopened in 2003. 

By 2012, new U.S. natural gas discoveries and improvements in 

hydraulic fracturing (“fracking”) technologies had made it economical for the United States to become an exporter of LNG, 

so Dominion Energy filed for permits to expand its Cove Point 

facility for that purpose, with plans to be operational by 2018. 

Both the nuclear power plant and the LNG facility took 

parts of the Calvert Cliffs shoreline that had been suggested for 

a bayside nature park as early as 1945. However, a legal challenge in 1972 by the Maryland Conservation Council and the 

Sierra Club resulted in preservation of much of the remaining 

Cove Point marsh region as well as some adjacent woodland 

containing a section of overgrown paleocliffs (i.e., a section of 

previously eroding cliffs now shielded from wave erosion by spit 

development). This preservation was possible because by then 

LNG could be delivered to the onshore liquefaction facility by 

pipeline under the Chesapeake Bay, so the new facility did not 

need to expand its industrial area into the adjoining (and now 

preserved) part of the property.

Three other major unrealized projects involving the area 

around the Calvert Cliffs have been proposed over the years. In 

1963, Maryland state senator Louis Goldstein proposed a scenic 

“dream highway” from Annapolis to Drum Point (Evening Star, 

1963), in part following the abandoned Drum Point rail rightof-way.1

 Along its length, this parkway would have offered motorists views of the Chesapeake Bay at various locations. Louis 

Goldstein also promoted construction of a third bridge across 

the Chesapeake Bay, from Cove Point to Dorchester County on 

the Eastern Shore. This site was reevaluated along with several 

others by a 2005–2006 task force, but no action was taken on 

a third Bay Bridge.2

 About 2008, the Potomac Electric Power 

Company (PEPCO) proposed constructing a high-voltage transmission line extending from Virginia through southern Maryland to the Delmarva Peninsula through a buried direct current 

cable that would pass under the Chesapeake Bay starting at a 

site at Western Shores on the Calvert Cliffs. This project was 

canceled in 2012, primarily for economic reasons.3

The Calvert Cliffs might have made a great national monument or even a national park, but even by 1940 the rapid development of vacation housing would have made that difficult. By 

1950, when Klingel ([1951] 1984) described the scenic beauty of 

the Calvert Cliffs shoreline, he realized that it was already too 

late to preserve much of this shoreline (see also R. Mansueti, 

“Natural History Wonders of Calvert County in Southern Maryland, Md.,” 1954, unpublished). A Calvert Cliffs State Park 
NUMBER 100 • 2 1

finally became a reality in 1966, eventually preserving about 530 

ha (1,312 acres) and about 1.7 km (1 mi) of cliffs in their natural eroding (and fossil-producing) state. This was considerably 

smaller than the 850 ha (~2,100 acres) that was recommended 

by the State Planning Commission in 1945. The park cliffs expose the uppermost Choptank Formation and most of the St. 

Marys Formation. By the time that the northern part of the Cove 

Point spit and adjoining marsh and woods came to be preserved 

next to the LNG terminal, cliff erosion and outcrop exposure 

had already been arrested by spit development many centuries 

earlier. Similar cliff stabilization is found at Flag Ponds Nature 

Park, where a smaller prograding spit complex (called a cuspate 

foreland) has formed. This property was acquired by Calvert 

County in 1988, along with wooded paleocliffs and forestland 

behind the spit. The stabilized and forested cliffs at Cove Point 

(Beardslee, 1997) and Flag Ponds show what the Calvert Cliffs 

region looked like when, at the end of former interglacial times, 

sea levels began to drop and the cliffs slumped and grew over as 

world climate cooled and ice sheets expanded (Figures 1.5, 1.6).

No preservation progress was made along the middle Calvert Cliffs until 1995 and 1998, when The Nature Conservancy 

acquired—for subsequent resale to the state of Maryland—two 

large parcels that included cliff shoreline totaling about 2.5 km 

(1.5 mi) on both sides of Parkers Creek in addition to the beach 

at the mouth of the creek. This cliff segment is of special importance because the vertebrate-rich upper Plum Point and Calvert 

Beach Members (particularly beds 12 and 14) are exposed here 

just above sea level. Farther north, except for the tiny Bayfront 

Park (formerly Brownie’s Beach; Figure 1.2), none of the cliffs in 

this region have been preserved, although a few privately owned 

segments, some including cliff sections up to about 1 km long, 

still remain undeveloped and could perhaps be preserved if funding and/or landowner generosity resulted in permanent preservation. Meanwhile, geoscientists have access to these sites only 

through the generosity of private landowners. Long sections of 

cliff face in this region have already been armored to protect 

property located immediately above and behind the cliffs, and 

the remaining segments not already preserved probably will be 

armored over during the next few decades in response to sea 

level rise and continuing wave and storm erosion along the base 

of the remaining unprotected cliffs. 

Out of the approximately 40 km (25 mi) of Calvert Cliffs 

shoreline (including ravines and stream valleys such as Parkers 

Creek and Plum Point Creek), only about 7 km (4.3 mi) have been 

preserved in a natural state. If the preserved spit shorelines at Cove 

Point and Flag Ponds are subtracted, along with the salt marsh 

gap between cliff segments at Parkers Creek, then only 10% (~4 

km or 2.5 mi) of actively eroding cliff faces (including ravines) are 

permanently protected. This leaves rather slim pickings for future 

paleontologists. It is especially ironic that none of the five type 

sections for various Chesapeake Group formations and members 

located within the Calvert Cliffs have been protected.

THE RELATIONSHIP BETWEEN ONGOING SEA 

LEVEL RISE AND CLIFF EROSION

Sea Level Rise

The Calvert Cliffs are maintained by several processes of erosion and, unlike a cliff made of granite or other very hard rock, 

would revert to more gentle forested slopes within several decades 

if erosion were to cease (e.g., Clark et al., 2004). The overall rate 

of cliff erosion is controlled by the rate of cliff toe erosion, which 

eventually causes oversteepening of the cliff face, so that its upper 

part collapses at intervals in a perpetual gravity-driven cycle. Cliff 

toe erosion thrives on continuing relative sea level (RSL) rise, 

which is regularly measured by tide gauges that show the rate of 

land subsidence plus the rate of global sea level rise. If RSL were 

to fall, cliff recession would erode back at ever lower rates until 

an angle of repose is reached, after which erosion would more or 

less cease. During the last century, RSL rise in the Chesapeake Bay 

region has reflected the net sum of ocean water warming (which 

produces thermal expansion), global glacier and ice sheet melting, isostatic effects resulting from an increasing ocean volume, 

and subsidence of remnants of a glacioisostatic forebulge (flexural arch; peripheral bulge) that persists from the last glaciation 

of North America when the weight of the massive Laurentide ice 

sheet caused the continental crust just south of the glacial front to 

warp upward. The contribution of forebulge subsidence (called 

glacial isostatic adjustment) adds about 1 mm/yr to the ongoing 

Chesapeake RSL rise because the region more or less occupies 

the crest of the residual forebulge just south of the maximum 

front of the last (Wisconsinan) North American glaciation (e.g., 

Engelhart et al., 2011; Raymo et al., 2011). Depending on the 

mantle viscosity structure, models predict that about 6–12 m of 

forebulge uplift left to subside remain before the crust in this region is again in equilibrium with the mantle below it (e.g., Raymo 

et al., 2011; J. Mitrovica, Harvard University, personal communication, 2013). Long-term tectonic and sediment-loading effects 

are comparatively minor and need not be considered (Pazzaglia 

et al., 2010). An additional recent and future factor adding to 

land surface subsidence is caused by extraction of groundwater, 

which creates land subsidence concentrated in cones of depression around major pumping areas. If the Gulf Stream weakens, as 

some models predict (Sallenger et al., 2012), additional sea level 

rise would occur along the U.S. East Coast.

Tide gauges record only RSL rise, which is the parameter 

to which the cliffs are responding. Boon et al. (2010) averaged 

tide-gauge-derived RSL rates that have been recorded since the 

gauges were installed. Largely because of short-period sea level 

noise (e.g., El Niño–Southern Oscillations and year-to-year variations), the formal errors for average RSL are higher for gauges 

with shorter observation histories. The Baltimore tide gauge, 

which has the longest record, has documented a 1903–2009 average sea level rise rate of 3.09 ± 0.1 mm/yr, and there is no strong 

evidence to suggest any recent acceleration in the rate of rise. 

Annapolis, closer to the cliffs, has documented an average of
2 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

3.37 ± 0.16 mm/yr from 1930 through 2009, whereas Solomons, 

just south of the Calvert Cliffs, has documented an average of 3.49 

± 0.19 mm/yr from 1940 through 2009. Directly across the bay 

from the cliffs at Cambridge the tidal gauges have documented 

sea level rise at a rate of 3.34 ± 0.46 mm/yr. Tide gauges located 

farther to the northwest at Washington, D.C., have documented 

a lower average rate of RSL rise of 2.96 ± 0.24 mm/yr, whereas 

gauges farther south and east in the Chesapeake region have documented higher RSL rise rates: 5.48 ± 1.67 mm/yr at Ocean City, 

Maryland; 4.12 ± 0.30 mm/yr at Gloucester Point, Virginia; and 

5.82 ± 0.68 mm/yr at the south end of the Chesapeake Bay Bridge 

and Tunnel near Norfolk, Virginia. These figures suggest that the 

average RSL rise for the Calvert Cliffs has been about 3.4 mm/

yr. This value is reasonably consistent with the results of Froomer 

(1980), who, on the basis of a study of sediment cores taken in the 

Parkers Creek marsh at a gap in the middle of the Calvert Cliffs 

(Figure 1.1), estimated that there has been an average RSL rise 

of 2.74 mm/yr from 1650 through 1975. This somewhat lower 

average RSL rise, based on a record more than 300 years long, 

may indicate that there has been an increase in the rate of sea level 

rise within the last century. Although not statistically significant, 

this conclusion is reinforced by comparing 1944–1975 tide gauge 

RSL data with 1976–2007 RSL data from the Chesapeake region 

(Boon et al., 2010). Although Boon et al. have concluded from tide 

gauge records that the eustatic sea level rise recorded in the Chesapeake region over recent decades to a century has been close to the 

1.70–1.80 mm/yr global average for the twentieth century, radar 

altimetry has measured an apparent acceleration of global sea 

level rise to 3.0–3.1 mm/yr during the years 1993 through 2010, 

which is still a short interval of observation time. Using a different 

type of analysis, Ezer and Corlett (2012) inferred an even more 

dramatic acceleration, from a range of 1–3 mm/yr in the 1930s to 

4–10 mm/yr in 2011.

Cliff Erosion Processes

A variety of processes are at work on the Calvert Cliffs, 

sculpting and eroding them constantly. For regional treatments 

of global coastal cliff erosion processes, see Emery and Kuhn, 

(1982) and Hampton and Griggs (2004). Various erosion processes specific to Calvert also are discussed by Leatherman 

(1986), Schweitzer (1993), Clark et al. (2004), and, especially, 

Miller (1995), who has by far the most comprehensive treatment, based largely on measurements taken from 1990 through 

1994 at 22 boreholes created to monitor groundwater near the 

Naval Research Laboratory, Scientists Cliffs, Calvert Cliffs State 

Park, and Chesapeake Ranch Estates. It seems that the Calvert 

Cliffs may have become just as much of a laboratory for estuarine cliff erosion as they are for Miocene fossil studies.

Understanding erosion along the Calvert Cliffs comes in 

part from understanding the lithology and related geotechnical 

properties (especially permeability and cohesiveness) of the stack 

of Miocene sedimentary strata in the cliffs, which resembles a 

slightly tilted layer cake (Figures 1.10–1.12) that has its layers 

dipping gently toward the southeast (Shattuck, 1904; Kidwell, 

1997). Physical properties vary far more from one bed to another 

than they do along any particular bed (Figures 1.10, 1.13, 1.14), 

but even so geotechnical properties do vary slightly even within 

any particular bed. The only major departure from this tilted 

layer cake pattern is the Governor Run channel, which was cut 

about 6 m into preexisting Calvert Formation strata at the beginning of Choptank time (Figures 1.10, 1.11; see Kidwell, 1997). 

The trend of this unique channel incised within the Calvert Cliffs 

remains unknown, but its cross section in outcrop extends from 

Governor Run to just south of Parkers Creek, which is a region 

that includes all of Scientists Cliffs, where the filled channel typically lies between 4 and 8 m above sea level. The fill primarily is 

fine to medium sand (hence the term Governor Run sand), with 

some clay present at its base and on its flanks. Because of its low 

cohesive strength and high permeability, Miller (1995:42) called 

the Governor Run sand “the single most important stratigraphic 

unit along Scientists Cliffs.”

Cliff profiles generally are more complex than simple slopes, 

and they vary both along the length of the cliffs and over time. 

Miller (1995; Figure 1.15A,B) proposed that there is a relationship between the shape of a cliff slope profile and the dominant 

erosional processes that act upon it (Figure 1.16) Many of the 

cliff erosion processes either cause or are caused by slope oversteepening, but slope oversteepening is ultimately controlled by 

the rate of toe erosion caused by wave action at the base of the 

cliffs (Wilcock et al., 1998; Figure 1.16A) or by wintertime cycles 

of freezing and thawing (Figure 1.16C,D), both of which keep 

the lower slopes steep except where and when they are covered 

by debris shed from above (Zwissler et al., 2014; Figure 1.16B). 

The uppermost part of the cliffs is also generally nearly vertical 

or even undercut, with soil bound by roots, forming the equivalent of a caprock at the top. 

The middle slopes of the cliffs are commonly somewhat gentler and dominated by relatively frequent shallow translational 

slides. Miller (1995) measured the midslope angles at 12 sites 

along the Calvert Cliffs and found (from north to south) that 

their slope was 70° and 48° near Naval Research Laboratory and 

Randle Cliff (Leatherman, 1986, reported 40°–50°); 48°, 49°, 

and 49° where the Governor Run sand occupies the midslope 

from north of Scientists Cliffs to Governor Run; 41° (Rocky 

Point), 68°, 53°, and 49° around Calvert Cliffs State Park; and 

53°, 47°, and 57° along the cliffs at the Chesapeake Ranch Estates. Much steeper slopes do occur locally, however, on the lower 

and upper middle to upper slopes (e.g., 70°–80° and nearly 90°, 

respectively) between Scientists Cliffs and Parkers Creek (Miller, 

1995:45). Shell marl beds (beds 17 and 19) project slightly from 

the cliff face at many sites, even forming short vertical outcrops, 

except at beach level, where the shell beds are undercut by waves 

to form overhangs. 

Loosening of the underlying, more cohesive clay-rich intact 

Miocene sediments can be caused by freeze–thaw cycles, desiccation, and vegetation root penetration, among other processes. 

Average slopes at 25 sites on the middle and southern cliffs (from 
FIGURE 1.12. South (lower left) to north (upper right) profile, in three parts, of the Calvert Cliffs (adapted from fig. 2 of Vogt and Eshelman, 1987) constructed from 

Calvert County topographic map contours, with numbered biostratigraphic beds (zones of Shattuck, 1904) and modern place-names along the cliffs. Capital letters B to F show locations of photographs in Figure 1.2. Note that Governor Run channel (Figures 1.10, 1.11; Kidwell, 1997) and Moran Landing Fault are not identified on this generalized profile. The original (pre–late Quaternary) land surface along this cliff profile must have been above the level of the present highest Calvert County topography in this region (approximately along the watershed) west of the modern cliffs (upper profile, mostly along Maryland Route 4). The reason is because streams flowing west from a once higher upland, now eroded away from an area now occupied by the Chesapeake Bay, removed the upland gravel materials that once covered this region but are now gone (Vogt, 1991). Along other stretches of cliffs in the Chesapeake Bay region, for example, the Westmoreland Cliffs in Virginia and the cliffs around Popes Creek, Maryland, as well as along the southern Calvert Cliffs, overlying upland gravels are everywhere present along the tops of cliffs. The loss of the unconsolidated upland deposits (Schlee, 1957) is sufficient to account for most of the now missing, eroded material. 
2 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

23

22

21

20

19

18

17

15-16A

14

13

12

11

10

9

8

7

6

5

4

3

2

1

15.6?

17

23?

40 Eocene

Piney Point and

Nanjemoy Formations

Governors Run sand fills

channel - incised valley

Unconformity (wavy lines 

show two of several 

points where the record

may be missing)

Parkers Creek bone bed

Fine sand and shells 

(representative example)

Fine sediment few shells

Diatomite (remains of

siliceous phytoplankton)

Major unconformity - more

than 20 million years not

recorded in this area.

Lag deposit (reworked

bones and pebbles) 

Glauconitic (greenishcolored) sand

Upland Deposits; fluvial 

sand, silt, clay, and gravel; 

fossils very rare

8 24

8 - 2.7?Ma

16B

Burrowed firm ground

16

Estimated

millions of

years ago (Ma)

Shattuck zone (bed)

number

13.9?

14.5?

St. Marys

Formation

Choptank

Formation

Calvert

Formation

11?

Miocene seas retreat ca.

8 Ma, exposing land to

erosion from rivers and

streams

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+ +

+

+

+

+ + + + + + +

+ + + + +

+ +

+ + +

+

+ + +

+

+

+

+ +

+

+

+

+

+

+

+ + +

+ +

+ +

+

+ + +

+

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Present dissected land

surface develops starting

ca. 2.7 million years ago,

especially in last 150,000

years

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FIGURE 1.13. Composite section of the Miocene Chesapeake Group strata along the Calvert Cliffs that unconformably 

overlie the Eocene Piney Point and Nanjemoy Formations and underlie late Miocene(?) and Pliocene upland deposits. This 

section was originally constructed by Gernant et al. (1971), modified by Vogt and Eshelman (1987), and further modified 

here. Approximate depositional ages are generalized from Vogt and Parrish (2012).
NUMBER 100 • 2 5

Scientists Cliffs to Chesapeake Ranch Estates) were measured by 

Zwissler et al. (2014) starting in 2003 and later using lidar-based 

topographic contour maps (measurement uncertainties were not 

given). Only sites without toe erosion by waves were chosen. All 

but one of the slope angles were between 35° and 55°, with a median slope angle of around 44°. This is somewhat lower than the 

midslope values measured in the field by Miller (1995). Leatherman (1986) measured similar slopes near the northern end of the 

Calvert Cliffs in the vicinity of the Naval Research Laboratory. 

Some cliff slopes fall above this range. For example, Clark et 

al. (2004) reported slopes as high as 65° near Calvert Beach, 

whereas Zwissler et al. (2014) measured an 88° slope in that 

same vicinity. There appears to be no systematic difference between average slopes in the southern Calvert Cliffs and average 

slopes in the northern cliffs, even though there is a considerable 

difference between the lithology and physical properties of the 

Choptank and St. Marys Formations in the southern cliffs and 

the lithology and physical properties of the Calvert Formation in 

the northern cliffs. This conformity perhaps reflects the fact that 

the average slope angles are primarily controlled by noncohesive 

material on the middle slopes and (where debris covers the Miocene toes) also on the lower slopes. 

Probably most of the Calvert Cliffs that have slopes greater 

than 35° to 40° are unstable. Clark et al. (2004) measured 47 

slopes of stabilized and forested fossil cliffs that are naturally 

protected by foreland spit complexes at Flag Ponds and Cove 

Point. Forty-two of the stabilized slopes ranged between 26° and 

36°, with a mean slope of about 31°; measurement errors were 

not estimated. Where the toe of the cliff face has been artificially 

protected for decades (for example, at the Naval Research Laboratory and at South Beach in Scientists Cliffs; see below), the 

lower slope of the cliffs, formed of debris, has a slope that is 

<35° and is covered with vegetation (e.g., Miller, 1995). In round 

numbers, we can predict that reducing an average Calvert Cliff 

slope by around 15° (from 45° to 30°) would turn most of the 

cliff into a forested escarpment with greatly diminished erosion 

rates but also with greatly diminished geological exposures and 

fossil yields. The slope at which a cliff slope becomes stabilized 

can differ from one locality to another because factors such as 

lithology and groundwater hydrology differ from one section of 

the cliffs to another. 

The pace of cliff erosion varies with season and with weather 

and also from north to south along the cliffs and vertically within 

the cliffs from one stratum to another. Nearly all of the destructive processes are erosional because the clay, silt, and sand that 

compose the cliffs are chemically stable at the Earth’s surface. 

Some chemical weathering occurs, but it is limited mostly to 

acidic rainwater dissolving fossil carbonate shells and to nearsurface oxidation of ferrous iron to ferric iron, which turns the 

unweathered gray silty mudstones of the three formations to 

shades of red or yellow. Where there is groundwater penetration 

of the Miocene strata, it generally is limited to existing joints. 

Salt crystallization can occur where brackish bay water persistently wets the sediments, and heating of near-surface voids can 

promote sediment disintegration if there is thermal expansion of 

gases within the voids (Hampton and Griggs, 2004:21).

Precipitation of gypsum and calcium carbonate on the surface of a cliff can locally cover and thereby temporarily armor 

small patches or ledges of Miocene outcrop. Similarly, ferric iron 

oxide (hematite and limonite) may locally cement and protect 

patches of overlying upland deposits by forming reddish sandstone blocks that are usually about 10–20 cm thick but locally 

up to 1 m thick. These are locally collected and utilized for fireplaces, exterior building stonework, and yard decoration. They 

can be locally protective, but these chemical precipitates are generally too small and scattered in their occurrence to significantly 

affect the overall rate of erosion along the Calvert Cliffs. A notable exception occurs at Rocky Point in Calvert Cliffs State Park 

(Figure 1.2E), where bed 19 (the Boston Cliffs Member of the 

Choptank Formation), which forms the toe of the cliff there, has 

become indurated (cemented) by ferric iron oxide (Miller, 1995). 

Some iron cementation also occurs in the Plum Point Member 

just north of Parkers Creek. It has been proposed that the iron 

was first leached out of near-surface sediments (probably gravels 

of the upland deposits) by very acidic water associated with decaying vegetation. This iron later became redeposited when and 

where the acidic groundwater that contained it became exposed 

to oxygen, such as in the originally permeable bed 19 shell marl 

at Rocky Point. Similarly, at Cove Point there are abundant large 

iron-cemented blocks of post-Miocene(?) upland deposit material exposed in the upper part of the cliffs. Many of these have 

completely eroded out and litter the beach.

The erosional attack against cliff toes by waves is particularly 

efficient, although episodic (e.g., Wilcock et al., 1998), along the 

southern cliffs, where the sandier, less consolidated sediments of 

the Choptank Formation are exposed at or near the base of the 

cliffs. Erosion there is especially severe if winds and waves come 

from the southeast. Miller (1995) concluded that the rate of wave 

undercutting depends on tide level and the cohesive strength of the 

toe material. When tide levels are high and the cohesive strength 

of toe material is relatively low, wave erosion generates the highest rates of toe erosion observed along the cliffs. Among the sites 

examined by Miller, the highest rates of erosion were found along 

the cliffs just south of Parkers Creek (Figure 1.16A) and near 

Calvert Cliffs State Park. When high storm surges combine with 

easterly storm winds, significant wave erosion (tens of centimeters) can occur in a matter of just a few hours where less cohesive 

beds are exposed to the waves. The longest fetches, and thus the 

greatest damage, occur when winds are blowing from the NNE 

(70–105 km) or from the SSE (150–175 km). Annual maximum 

wave heights along the Calvert Cliffs regularly exceed about 1.2 

m (4 ft; Zabawa, 1989: tbl. 1), and these can occur either during 

tropical storms (late summer and fall) or during late fall, winter, 

and spring storms called nor’easters. Some of the greatest historical storm surges along the Calvert Cliffs (~1.2–1.5 m or ~4–5 ft) 

occurred during the Chesapeake–Potomac hurricane of 23 August 

1933 and Hurricane Isabel on 18 September 2003.
2 6 

• SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Naval Research Lab

GRAIN - SIZE

DISTRIBUTION

Sand

Silt

Clay

CUMULATIVE PERCENT

20 40 60 80

SL

5

30

25

20

15

10

Dry, green-gray, clayey silt with sparsley

scattered shell lenses in ne sand matrix

Dry, green clayey, sandy silt with

sparsely scattered shell lenses

Moist, gray-green, silty, clayey sand with

sparsely scattered lenses of shells;

shells slightly more dense near base

Saturated shell bed in gray sand matrix;

some silt present

Dry, gray, silty, sandy clay

with sparse shell lenses

Moist, gray-green, clayey, sandy silt

Dry, gray-green, silty, sandy clay

with traces of shells

Moist, tan, silty, clayey, ne sand

with layers of oxidized iron

Moist, tan, ne sand

with traces of silt and clay

Moist to dry, tan, silty, clayey, ne sand

with layers of oxidized iron

Soil horizons and root zone;

moist, brown, sandy, silty clay

A Scientists Clis

GRAIN - SIZE

DISTRIBUTION

Sand

Silt

Clay

CUMULATIVE PERCENT

40 60 80

SL

-5

5

30

25

20

15

M

10

Soil horizons and root zone; dry, orange,

silty, very ne sand

Dry, tan, ne sandy clay

Moist, gray, silty sandy clay

Moist to dry shell bed with brown,

medium sand matrix

Dry, brown, medium sand

Dry, gray, silty sand with some clay

Dry, gray, clayey, sandy silt

Moist shell bed with brown

medium to ne sand matrix

Moist, gray-green to olive-green medium

to ne sand; saturated at base

Dry, greenish-gray, clayey,

silty, very ne sand

Dry, dark gray, silty, very ne sand

B

FIGURE 1.14A,B. Lithologic and grain size distributions within four shallow boreholes drilled just inland from the Calvert Cliffs. From north to south they are (A) the Naval 

Research Laboratory, (B) Scientists Cliffs, (C) Calvert Cliffs State Park, and (D) Chesapeake Ranch Estates. Adapted from Miller (1995), with Shattuck zone numbers and formation limits estimated by comparison of lithology with Figure 1.10. (Figure 1.14C,D on facing page.)
NUMBER 100

• 2 7

Calvert Clis State Park

GRAIN - SIZE

DISTRIBUTION

Sand

Silt Clay

CUMULATIVE PERCENT

20 40 60 80

SL

-5

5

201510

M

Soil horizons and root zone; moist,

orange – brown, medium sand

Slightly moist, tan, medium sand

with traces of pea gravel and traces

of sti white clay

Slightly moist, light gray, silty clay

with lenses of coarse sand

Moist, light gray/tan, mottled, silty,

clayed ne sand (predominantly ne

sand); saturated at base of unit

Saturated, dark gray, ne sand

with traces of silt and clay

Slightly moist, gray, silty clay

with lenses of ne sand

Slightly moist, gray, clayed silt

with traces of ne sand

Saturated, gray, very ne sand

with traces of shells

C Chesapeake Ranch Estates

GRAIN-SIZE

DISTRIBUTION

Sand

Silt

Clay

CUMULATIVE PERCENT

20 40 60 80

Soil horizons and root zone; moist,

brown, silty, clayey sand

Moist brown to yellow brown, medium

to coarse sand with traces of pea

gravel and thin clay laminations;

saturated at base

Saturated, medium to coarse yellow/tan

sand with lenses of pea gravel

Saturated, tan/yellow, silty sand

Slightly moist, tan/gray clay

Saturated, interbedded sands and clay

Moist, dark gray, very clayey,

silty, very ne sand

Several saturated cycles of shell fragments in ne sands ning upwards to

shell-free silts

Moist, gray, clayey silt with a 0.2 m

thick bed of shells in a saturated,

very ne sand matrix

Moist, gray, silty, clayey, ne sand

35302520

M

1510

5

SL

D

FIGURE 1.14C,D. Lithologic and grain size distributions within four shallow boreholes drilled just inland from the Calvert Cliffs. From north to south they are (A) the Naval 

Research Laboratory, (B) Scientists Cliffs, (C) Calvert Cliffs State Park, and (D) Chesapeake Ranch Estates. Adapted from Miller (1995), with Shattuck zone numbers and formation limits estimated by comparison of lithology with Figure 1.10. (Figure 1.14A,B on facing page.)
0 20 40

M

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

TYPE I

TYPE II

TYPE III

TYPE IV

A 0 20 40

M

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

20

M

0

TYPE I

TYPE II

TYPE III

TYPE IV

A

TYPE I T TYPE II TYPE III YPE IV

(non- steady state only)

vegetation

eect

slide debris

wedge

R - RATE OF TOE RECESSION

R - RATE OF DEBRIS DELIVERY TO SLOPE

R - RATE OF MIDSLOPE RECESSION

b

d

m

Rd Rb > ≈ Rd Rb < Rd Rb < Rd Rb

Rm Rb > Rm Rb Chesapeake Ba ≈ y

B TYPE I T TYPE II TYPE III YPE IV

(non- steady state only)

vegetation

eect

slide debris

wedge

R - RATE OF TOE RECESSION

R - RATE OF DEBRIS DELIVERY TO SLOPE

R - RATE OF MIDSLOPE RECESSION

b

d

m

Rd Rb > ≈ Rd Rb < Rd Rb < Rd Rb

Rm Rb > Rm Rb Chesapeake Ba ≈ y

B

FIGURE 1.15. (A) The four types of Calvert Cliffs cliff-face slope profiles based on relative rates of toe recession, debris delivery to slope, and 

rate of midslope recession (Miller, 1995). (B) Four simplified examples of slope profile for each of the four slope types (Miller, 1995). See also 

Miller et al. (2006).
NUMBER 100 • 2 9

The more indurated (cohesive), massive, sparsely fossiliferous silt-clay beds (for example, beds 11 and 13 of the Plum Point 

Member) resist wave erosion where they are locally exposed near 

sea level along the middle and northern cliffs and can locally act 

as natural bulkheads, reflecting waves back out into the bay. This 

bulkhead effect can also serve to inhibit cliff base sand accumulation and beach formation, for example, north of Parkers Creek 

(Figure 1.2C). This particular environment essentially has a bimodal stability. There is a “beach state,” which can occur because 

of a storm or persistent wind/wave pattern and can persist for 

some time, but most of the time there is a “no-beach” (natural 

bulkhead) state that is more normal. This bimodal stability is 

reflected both in anecdotal observations and in historical maps 

that show long intervals of time when a beach is present in these 

regions followed by long intervals of time when there is no beach 

at all. Man-made bulkheads (e.g., at the Naval Research Laboratory) create a permanent no-beach state that prevents erosion but 

also the formation of offshore sandbars (Miller, 1995). 

Where they are at beach level, the interbedded, much sandier Plum Point Member shell marls (especially beds 12 and 14) 

are far more susceptible to wave erosion during high tides than 

beds 11 and 13. Waves quarry out mollusk shells contained in 

those beds, creating cavities that are then enlarged by hydraulic 

plucking (the toilet plunger effect). Where mollusk-rich bed 14 is 

exposed at sea level (from southern Scientists Cliffs to Kenwood 

Beach), such natural quarrying creates linear notches (undercuts) 

along the cliff face. When these notches are cut back 20–40 cm, 

slabs of the overlying bed 15 collapse (spall away). This usually 

happens along near-vertical, cliff-parallel fracture lines called exfoliation joints. The resultant collapsed blocks can be up to a 

meter thick and several meters tall and consist of parts of upper 

bed 14 and lower bed 15. These blocks, similar in appearance 

to the collapsed blocks shown in Figure 1.16A, are helpful for 

paleontologists because they create fresh exposures along cliff 

toes that are otherwise often hidden behind slide debris, moss, or 

vascular plants (Figure 1.16B).

A similar situation exists between the north end of Scientists 

Cliffs and the south end of Parkers Creek beach, where bed 12 

(Parkers Creek Bone Bed) is exposed near sea level. This section 

of cliff is part of the Parkers Creek Preserve (Warrior’s Rest Sanctuary) and is allowed to erode naturally. Wave erosion of bed 12, 

which is a sandy shell marl about 30–50 cm thick that contains 

broken small shells, locally produces linear undercut notches that 

create overhangs of bed 13 and, at the same time, forms benches 

on the top of bed 11. Large intact blocks of beds 13 and 14 often 

collapse onto the beach, providing access to strata derived from 

portions of the cliff face normally out of reach without ladders.

When slide debris accumulates along the toe of cliffs, it 

protects the Miocene strata at the base of the cliff from further 

erosion, sometimes for years. This debris (called colluvium) also 

can buttress the lower part of the cliff, reducing the likelihood 

of further sliding, although further sliding can and does occur 

on exposed surfaces in the upper part of the cliff above the 

slide debris. If the slide debris arrives on the beach with rooted 

vegetation (e.g., Figure 1.16B), particularly if there is time to 

grow new vegetation, the unconsolidated debris acquires some 

additional resistance to wave erosion and can develop miniature 

“undercliffs.” Debris slides, which may be composed of one or 

more successive slides at the same site, can create a kind of cyclicity to the cliff erosion process in which the period of the cyclicity 

is determined by how long it takes the bay waves to remove the 

slide episode debris protecting the “Miocene toe.” The longer it 

takes to erodes away the debris apron, the more time there is for 

deep-rooted vegetation to establish itself on the slopes above.

Groundwater moves through some strata in the Calvert 

Cliffs, flowing rather rapidly through the relatively permeable 

upland deposits, more slowly through the strata of the Choptank 

and St. Marys Formations, and only very slowly or not at all 

through the Calvert Formation, which is mostly impermeable 

layers (aquiclude or confining bed). Along parts of the Calvert 

Cliffs, the presence of alternating permeable and impermeable 

beds has created what are known as perched water tables (e.g., 

Leatherman, 1986; Miller, 1995). Groundwater seeping out at 

the base of these perched beds commonly creates horizons of 

darkened (wet) sediment, lines of vegetation, and, in winter, 

horizons of ice buildup (Figure 1.16C). Groundwater will exit 

from the cliff faces most often along the disconformity between 

the impermeable Calvert and more permeable Choptank Formations, perhaps most dramatically at the base of the Governor 

Run sand in the area of Scientists Cliffs. Locally, seepage erosion (called sapping) may occur (e.g., Leatherman, 1986; Miller, 

1995), and water seeping along plant roots or joints also tends 

to weaken the sediments. A water-hose-like flow of water from 

about bed 17 levels of the cliff, observed on 6 August 2016 just 

after a massive sediment failure in Scientists Cliffs (discussed 

below), was likely caused by a sapping effect.

The more cohesive, wave-resistant beds (e.g., beds 11 and 

13) are eroded in a different manner—primarily through intermittent cycles of freeze and thaw (Miller, 1995; Zwissler 

et al., 2014). The interstitial water freezes during winter cold 

snaps, prying apart the grains and shells in the sediment. 

When these icy shells thaw, the sediment turns to mud and 

falls off as flakes or is rinsed away by rains. The loose material initially accumulates next to the cliff toe but then is washed 

away during high tides and storms. When and where the gently seaward-sloping Miocene sediments are exposed near the 

cliff toe, the freeze–thaw cycle can also remove material from 

that surface, speeding up disintegration of intact sediment 

blocks on the beach. Typical winter cold spells will remove 

1–2 cm from the cliff face, but during long, exceptionally cold 

periods up to 10 cm may be removed (Figure 1.16D). Repeated, 

separate cold spells degrade the cliff faces more rapidly than a 

single protracted cold spell. Miller (1995) concluded that the 

freeze–thaw cycle is the primary cliff retreat process at sites 

where the toes are not being undercut by waves, for example, at 

Calvert Cliffs State Park, where Zwissler et al. (2014) concluded 

that 65% of the toe recession at those six Calvert Cliffs study 

sites is due to the freeze–thaw cycle.
3 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

B

A

C D

bed 11

bed 12

bed 13

bed 14
NUMBER 100 • 3 1

Desiccation, a diffusion-type process similar to but less 

important than the freeze–thaw cycle, can also loosen cohesive 

beds (for example, beds 11, 13, and 15) during long summer 

droughts, such as the one that occurred in 2002. As interstitial 

water evaporates from the surface of the exposed beds, the dried 

crust spalls off in thin flakes. Desiccation has been observed to 

remove several millimeters of sediment during droughts, but no 

systematic study has been conducted.

Erosion processes above the cliff toes continuously play 

catch-up in response to the oversteepened lower slopes. Freeze–

thaw cycles, desiccation, and prolonged soaking rains are very 

effective at loosening sediment higher up on the cliffs, with gravity, wind, and flowing water doing the rest. Exposed Choptank 

and St. Marys Formation strata can be eroded into rills and small 

gullies in heavy rains, with their eroded clay, silt, and fine sand 

entrained in suspension flows and deposited as thin layers on 

adjacent sandy beaches.

Vegetation to some degree protects the Miocene strata from 

many erosional processes, but plant roots also tend to penetrate 

and loosen the strata to depths of 50 cm and sometimes more. 

It is notable that the rapidly receding, unvegetated cliffs between 

Parkers Creek and Scientists Cliffs stand at the same midslope 

angles (48°–50°) as the slowly receding, heavily vegetated cliffs 

of nearby northern Scientists Cliffs (47°–49°; Miller, 1995:187). 

This similarity suggests that vegetation has only a temporary effect on the long-term erosional cycle of the cliffs.

It seems likely that the typical 20–40 cm thickness (Miller, 

1995) of shallow translational slides on the midslopes of vegetated cliffs (e.g., at Scientists Cliffs; Figure 1.16B) is determined 

largely by the thickness of Miocene sediment loosened by plant 

roots. These translational slides commonly begin near or slightly 

below the top of the cliff and tend to happen during and up to 

24 h after protracted heavy rains (>5 cm/d; P. Vogt, personal 

observations; see also Miller, 1995; Miller et al., 2006). Brief but 

heavy summer thunderstorms produce water that comes down 

too fast to penetrate, whereas protracted rains saturate the sediment, thereby increasing the weight of the surface material and 

at the same time reducing its shear strength. Relatively more rain 

is needed to saturate soil on a sloping surface than on a more 

level surface. For example, a 5 cm rain falling vertically on a 

typical 45° will be equivalent to only 3.5 cm of rain falling on 

horizontal ground.

Typical translational slides are about 10–20 m in width (Figure 1.16B). The age of small trees carried down to the beach 

from slides on the cliff faces provides a measure of how long a 

cliff face has been stable. According to local conventional wisdom, large trees growing on the slopes or on top of the cliff actually promote cliff retreat because of the large root balls pulled 

out by these trees when they are uprooted in storms and because 

of the high “sail area” of tall trees, which makes them especially 

vulnerable to the power of strong winds. This idea is interesting, 

but there have been no studies undertaken on the long-term effect that large trees might have on cliff stability.

Among the less commonly observed processes that operate 

along the Calvert Cliffs, in the southern cliffs where they are 

occupied by Choptank, St. Marys, and younger fluvial strata, 

rotational slumps can locally occur that indent the cliff face by 

up to a few meters during single failures. Large-scale liquefaction 

is also a process not documented along the cliffs, except during a 

1979 slide in southern Scientists Cliffs when the sediment above 

the Calvert–Choptank contact liquefied as a result of frozen and 

broken water pipes at an unoccupied cliff-edge house. All Miocene sediment back to the house foundation flowed down onto 

and across the beach, demonstrating that liquefaction is possible 

in at least some sediment of the Choptank, St. Marys, and upland 

gravels units but only under exceptional, probably man-made, 

circumstances. A similar, larger event occurred at Scientists Cliffs 

during August 2016 and is discussed in detail below.

Bioerosion includes scattered nesting holes slightly less than 

10 cm in diameter created by rough-winged swallows and belted 

kingfishers, as well as minuscule holes a few millimeters in diameter that are excavated several decimeters into the cliff by insects, 

including Puritan tiger beetle larvae. Dens excavated by groundhogs occasionally can contribute to local sediment failure near 

cliff tops. Fossil quarrying by humans, usually for vertebrate remains near the cliff base, produces scattered small cavities that 

are typically 10–20 cm across. These cavities can be much larger, 

however, when remains of large vertebrates such as whales are 

removed. These larger cavities, which may be a cubic meter or 

more in volume, are too infrequent in space and time to accelerate the rate of cliff failure. In most cases, they are no longer visible within a year or two along the rapidly eroding southern cliffs, 

although farther north they may remain visible for some years in 

the more slowly eroding marls of the Plum Point Member. All 

these types of bioerosion have no significant impact on the rate 

FIGURE 1.16. (Facing page) Examples (at Scientists Cliffs and at cliffs between there and Parkers Creek) of cliff erosion processes: (A) Undercut 

columnar blocks from bed 11 (lower) and bed 13 (upper) in the process of falling into the water. Note that storm waves are preferentially eroding the less resistant, ~50 cm thick bed 12 to create a ledge and undercutting of bed 13. (B) Section of cliffs in northern Scientists Cliffs, showing 

recent “wet rug” slide scars triggered by protracted heavy rains. (C) Winter view south of Parkers Creek, showing slide scars on middle cliff and 

icicle formation at the base of the Choptank Formation, where groundwater seeps out and freezes. (D) Calvert Formation (bed 14) just above 

the beach, showing an approximately 8 cm thick frozen surface that is still attached in some places (light gray) but already fallen off in other 

places (dark gray, with fresh exposure of bed 14 mollusks). Frozen sediment turns to mush as soon as the interstitial ice holding it together melts.
3 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

of erosion along the Calvert Cliffs; however, industrial-scale cliff 

removal (e.g., during construction of the Calvert Cliffs Nuclear 

Power Plant) is another matter and will be discussed separately.

Man versus Cliff Erosion

Cliff erosion has long been observed (e.g., Shattuck, 1904; 

Schoonover, 1941), but apparently, it was not considered to be 

a problem worthy of mitigation until the expansion of housing 

and other high-value property developments near the cliff edges 

during and after World War II. In succeeding decades, more and 

more of the Calvert Cliffs shoreline has become variously modified from its natural state for the purpose of reducing erosion. 

It is the human perception of this problem, and not the natural erosion rate, that has changed, however. A study by Miller 

(1995:193) of early aerial photographs, mapping, and other observations led him to conclude “the slopes were eroding in much 

the same way nearly a century ago as they are today.” However, 

land clearing for agriculture, beginning in the later seventeenth 

century, increased sediment delivery to the Chesapeake and 

helped nourish sand beaches along the Calvert Cliffs.

The Naval Research Laboratory Randall Cliffs facility, built 

atop the northern cliffs in 1941 for radar research purposes, 

was probably the first example of cliff erosion control: A 1.4 

km long section of cliffs was armored by a steel bulkhead (seawall) in 1945, causing the beach below the cliff to disappear. 

In the early 1970s, a wooden bulkhead was constructed outside 

the deteriorating steel structure. Although toe retreat was arrested, the upper parts of the cliff have continued to erode (e.g., 

Leatherman, 1986). The Naval Research Laboratory bulkhead 

has significantly slowed the rate of cliff erosion there, but it has 

done so at the cost of destroying the underlying beach and also 

preventing the development of offshore sand bars (Miller, 1995). 

Similar bulkheads also have been constructed along the Dares 

Beach–Wind Cliffs shoreline and next to the Calvert Cliffs Nuclear Power Plant.

In 1993, the Calvert County Board of Commissioners appointed a Calvert County Cliff Policy Task Force to address the 

complex management issues involving the Calvert Cliffs. The 

task force (which included authors REE and PV) examined the 

cliffs from many perspectives: as a regional landmark and fossil 

repository; as the home of a species of federally listed endangered tiger beetle; and as a threat to cliff-edge developments due 

to the ongoing erosion that maintains the cliffs. The task force 

recommended a mandatory policy of setting new developments 

well back from the cliff tops (Calvert County Cliff Policy Task 

Force, 1993, unpublished report), and this policy was in part 

adopted by Calvert County in 1996. Under this policy, properties 

already built near the cliffs were grandfathered in and thus not 

directly subject to this new rule. A recommendation that was not 

adopted, however, was the requirement that prospective buyers 

of cliff-edge properties be warned of the erosion issue. It was not 

until 2008 that Calvert County printed a small brochure on this 

subject (Calvert County Department of Planning and Zoning, 

2008). As a result, until 2008 cliff-edge homeowners could 

truthfully claim that they had never been told of the risk that 

was inherent to their properties (Property Owners Association 

Chesapeake Ranch Estates, 2010). 

Through the years, various cliff-edge developments have 

tried different approaches to stopping cliff erosion, and some 

have simply let the cliffs erode. According to a 2010 tabulation 

by the Calvert County government, 234 houses were located 

within about 30 m (100 ft) of the cliff edge in 2003. Of these, 

1 at that time was actually overhanging the cliff edge, 19 were 

within about 1.5 m (5 ft) of the cliff, 20 others were within about 

3 m (10 ft), and 43 more were within about 6 m (20 ft) of the 

cliff. Lumping together all of these various houses along the cliffs 

is somewhat misleading because cliff retreat is slower along the 

middle and northern cliffs, where the Calvert Formation crops 

out at the base of the cliff, than it is along the southern cliffs, 

where the less cohesive Choptank and St. Marys Formations are 

exposed at beach level. For example, a house about 8 m (25 

ft) from the cliff edge in the Scientists Cliffs community might 

have 50 years of remaining life before it succumbs to cliff erosion, whereas a similar house at the same distance in parts of 

Chesapeake Ranch Estates might succumb to cliff erosion in just 

a decade or two.

The grandfathered cabin development of Scientists Cliffs, 

which had been laid out beginning in 1936 south of Parkers 

Creek, by 2003 had come to include 79 cliff-edge houses, of 

which 40 were wholly or partly within about 6 m (20 ft) of the 

cliff edge. In an attempt to protect these properties, the Scientists 

Cliffs Association constructed a groin jetty perpendicular to the 

approximate 1.9 km (1.2 mi) of shoreline in 1946 and a second one in 1948. Many more were built in the 1950s and later. 

Such structures (Schultz and Ashby, 1967) were less effective 

than bulkheads at slowing cliff toe retreat, but they did maintain 

and widen the beach by trapping sand moving southward under 

longshore drift (Downs, 1993). The beaches at the Scientists 

Cliffs community and elsewhere along the cliffs have long been 

a major recreational asset for boaters, swimmers, sunbathers, 

fishermen, fossil collectors, hikers, and others. By the 1970s, the 

early Scientists Cliffs groins (variously built of wood, old tires 

impaled on steel rods, and well casings) began to be replaced by 

gabions (wire cages filled with rocks about 20 cm in size, which 

individually are too small to stay in place under Chesapeake 

wave climates without the cages). The longest groin, progressively lengthened over the years, comprises boulders (“rip-rap”) 

too large to be moved by Chesapeake storm waves. This groin 

eventually built up an approximately 300-m-long northwardnarrowing permanent beach on its north (up-drift) side. On its 

southern down-drift side, however, cliff toe erosion actually was 

facilitated because the beach there was starved of sand. 

Similar efforts were made at other places along the Calvert 

Cliffs, in which groins or jetties were constructed to control 

shoreline processes. The Flag Harbor marina, created by dredging out the lower part of Calvert Beach Run, eventually required 

regular effort to keep its boating channel open to the waters of 
NUMBER 100 • 3 3

the Chesapeake. Shoreline modifications were added between 

1950 and 1980, including several groins, to protect nearby housing developments (Clark et al., 2004), and a jetty was built at the 

mouth of Kings Creek (Calvert Beach development) in 1975. All 

these shoreline modifications have impeded southward transport 

of beach sand, causing starvation and beach erosion along the 

northern part of the popular Flag Ponds Nature Park.

On the basis of questionnaire responses from cliff-edge 

cabin owners, Vogt in 1979 estimated the average long-term recession rate of the cliff face at Scientists Cliffs to be about 5–10 

cm/yr. Although newer estimates suggest the long-term rate is 

closer to 5 cm/yr, by the 1990s, some owners began to construct 

toe revetments in the form of gabions to slow erosion. At the 

same time, however, the gabion construction reduced the already 

narrow beach width, required repair when the wires broke, and 

obviously had an unnatural and unsightly appearance. Also they 

were hazardous once gabions began to break: the insulation is 

damaged during storms, giving the saline bay water the opportunity to corrode and break the metal wire core.

Concerns about a possible acceleration of cliff erosion rates, 

exacerbated by the exceptional storm surge associated with Hurricane Isabel in 2003 and by several anomalously heavy, protracted rains that occurred during 2009–2010 (discussed by 

Property Owners Association Chesapeake Ranch Estates, 2010), 

led to the formation of an ad hoc Calvert Cliffs Stabilization 

Committee (Steering Committee, 2010), which included representatives from a number of the developments bordering the 

Calvert Cliffs. Only one geologist was appointed to this committee. A central goal of this committee was to help cliff-edge 

owners and their associations obtain the various county, state, 

and federal permits needed to construct additional cliff erosion 

control measures. In the community of Scientists Cliffs, new permits issued in 2013 cleared the way to construct an additional 

500 m (~1,650 ft) of gabions that year as toe revetments that 

were located at various places where the toe of the Miocene cliff 

was exposed and thus eroding. More robust and expensive toe 

revetments composed of boulders (riprap), similar to one constructed by Western Shores in 1996, were proposed for about 

490 m (~1,600 ft) of cliff base at Chesapeake Ranch Estates, 

where an earlier experiment in 2005 had deployed concrete “reef 

balls” along about 175 m (~580 ft) of shoreline to absorb wave 

energy but without notable effect. Similarly, a shoreline stone 

revetment was constructed in Calvert Beach during 2014–2015, 

and others have just been completed at Western Shores and at 

Chesapeake Ranch Estates. 

Critics of the more aggressive erosion control measures 

(termed “hard armoring”) decry the resultant loss of a scenic 

landmark, beaches, tiger beetle habitat, and fossil-producing exposures. Skeptics of these efforts further point out that cliff erosion will continue above the revetments at least for a few decades 

(e.g., Leatherman, 1986; Clark et al., 2004) as the cliff top continues to erode back until the entire slope reaches a relatively stable 

angle of repose. This angle is different for different sections of the 

cliff because it depends on the type of sediment that is present at 

each site. Curiously, the cliff edge above Rocky Point, which is the 

only site along the Calvert Cliffs that has not significantly receded 

in 150 years, exhibits a relatively low 41° midslope angle. This 

suggests that although shore retreat is not significant there, slope 

erosion is continuing nonetheless (Miller, 1995).

Skeptics also point out that revetment, especially the riprap 

type proposed for Chesapeake Ranch Estates that extends up to 

about 9 m (30 ft) from the cliff toe, would reduce or even eliminate the already relatively narrow beaches, which are enjoyed by 

those who live inland from the cliffs in the same communities. 

Cliff stabilization supporters argue that continuing cliff erosion 

increases bay siltation and turbidity, but revetment critics counter by pointing out that cliff erosion is a perfectly natural process 

that contributes at least some sand to the beaches.

In 2012, the ad hoc Calvert Cliffs Stabilization Committee succeeded in obtaining Maryland Emergency Management 

Agency and Federal Emergency Management Agency funding for 

the 2013 purchase and 2014 demolition of the 10 most threatened cliff-top houses: two in the Scientists Cliffs community, 

two in the Kenwood Beach community, one in the Calvert Beach 

community, and five in Chesapeake Ranch Estates. Once the 

houses had been demolished, their sites were returned to their 

natural condition. Thus, the years 2013–2014 marked a turning 

point for grandfathered cliff-top developments, which undoubtedly will have to sacrifice additional houses in the future, even in 

some places where recession of the Miocene cliff toes is already 

blocked by revetments. 

Occasionally, broken water pipes in cliff-edge structures 

have triggered landslides on a scale not previously observed 

even after heavy rains and high tides. One such slide occurred 

in southern Scientists Cliffs in about 1979, when the plumbing 

in an unoccupied cliff-edge home froze and cracked during a 

cold spell. Water from the cracked pipes flooded the basement 

of the house and then ran outside and saturated the surrounding 

soil and much of the underlying Miocene Choptank Formation 

sediment between the house and the cliff edge. The saturated 

sediment liquefied and failed, creating a slide headwall that lay 

directly below the outer part of the foundation. The liquefied toe 

of the slide, about 2 cm thick, spread out across the beach into 

the bay. The house was saved by constructing concrete beams 

across the slide scar, which also were used to support a new deck 

that projected out across the subsequently vegetated slide scar. 

Since then, only some relatively minor failures have occurred on 

the edges (shoulders) of the slide scar. An even more dramatic 

failure—possibly the largest historic landslide along the middle 

and northern portion of the Calvert Cliffs—began on 6 August 

2016 in front of an unoccupied cliff-edge home atop an approximately 25-m-high (80–85 ft) cliff in the middle part of the Scientists Cliffs community. The owners had been there over the 

Fourth of July holidays, but a week or two later, the connection 

between the incoming water line and the house plumbing failed. 

Water flowed continuously into and just outside the basement 

and from there soaked into the ground below and next to the 

foundation. According to a neighbor (E. Dodsworth, personal 
3 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

communication, 2016), seven slides occurred over a three-week 

period, even long after the water had been shut off. Several other 

slides occurred in the following weeks. According to the neighbor, until the water was turned off, it actually flowed as if from a 

hose out of the cliff about 10–12 m below the cliff top (probably 

out of the sandy shell marl of bed 17 of the Choptank Formation). The final headwall of the slide, its outer cliff-edge corners 

forming a reentrant 21 m (70 ft) wide, did not stabilize until it 

lay under the foundation of a house that, before the slide occurred, had been located about 9 m (30 ft) from the original 

cliff edge. There was no choice except to have the house condemned and demolished. In this remarkable event, the cliff edge 

had retreated in three weeks by an amount that under natural 

conditions would have taken one or two centuries. The sole of 

this slide appears to follow the base of bed 17, a shell marl. The 

community manager (S. Dean, Scientists Cliffs Association, personal communication, 2016) compared daily water use by the 

community on the same dates in 2015 and 2016 and, from this 

comparison, concluded that the water leak averaged approximately 106 m3

/d (28,000 gal/d) beginning about 21 July, and 

totaled approximately 1,800 m3

 (~475,000 gal) of water during 

the 17 days preceding failure. If we assume that the Choptank 

Formation at this site had an available porosity of about 40%, 

then the leaked water would likely have been stored within a 

volume of sediment about 10 m wide × 15 m deep × 22 m long. 

This is roughly the same magnitude of sediment volume present 

in the slide at the time of failure.

Measuring the Rates of Erosion and Recession

along the Calvert Cliffs

Using a representative 30 km section of eroding Miocene 

cliffs and assuming an average shoreline retreat rate of 30 cm/

yr (~1 ft/yr) and an average cliff height (allowing for sediment 

“missing” in ravines) of about 15 m, we can estimate that an 

average of about 135,000 m3

 of sediment is removed from the 

cliffs annually and deposited on the beaches and in the adjacent 

Chesapeake Bay. This provides a reasonable estimate of the overall rate of erosion along the cliffs, but it tells us nothing specific 

about particular areas along the cliffs. Quantitative estimates of 

average shoreline erosion rates along particular portions of the 

Calvert Cliffs apparently were not attempted until after World 

War II (Singewald and Slaughter, 1949), when such estimates 

came to be of vital importance for long-term planning purposes 

such as imposing setback restrictions for new construction, for 

possible mitigation measures, and for the assessment of risk (and 

life expectancy) for structures near the cliff tops. 

The position of the top edge (lip) of a cliff and the position 

of its toe are the two most obvious and consistently measurable 

points that can be made on the Calvert Cliffs. However, even 

after compiling a table of these measurements, deriving a meaningful numerical rate of cliff recession is still difficult because 

cliff erosion is highly variable over both short periods of time 

and small scales of distance. A particular cliff top may remain 

nearly stable for many years, then recede 1 m or more because 

of a single failure. Periods of fast erosion during unusual episodes of heavy rains (e.g., in 2009–2010), hurricanes (e.g., Isabel 

in 2003), or severe winters (e.g., 1976–1977, 2013–2014, and 

2014–2015) can have a much larger impact on cliff erosion than 

the long-term average. Further complicating estimation efforts is 

the fact that although a numerical average of 0.3–0.6 m/yr (1–2 

ft/yr) is numerically accurate for the Calvert Cliffs as a whole 

(Zabawa, 1989), the erosion rate along the northern and central 

Calvert Cliffs is consistently less than along the southern cliffs. 

Even within each of these regions, differences in local shoreline 

conditions create further differences in the local rates of erosion. 

Along much of the Calvert Cliffs, sedimentary debris shed 

from the cliffs accumulates to form an apron along the foot of 

the cliffs, covering the toe of the cliffs and protecting their Miocene sediments from erosion for lengthy intervals of months or 

even years. This means that the average long-term retreat of the 

Miocene toe is significantly less in these areas than what is seen 

at times when the toe of the same cliff is exposed to cycles of 

freezing and thawing or to hydraulic plucking. Debris aprons are 

composed mostly of very loose materials, so when they are occasionally subjected to storm wave damage, they can be removed 

quickly in very large volume. Such storm losses create an appearance of very rapid cliff retreat that does not reflect the long-term 

trends important to planning policies. 

A third obvious but ephemeral measurement that can be 

taken along the base of the cliffs is the landward edge of the 

water of Chesapeake Bay. The edge of the bay is constantly moving in and out beneath the cliffs with tides and weather, which 

over time can create and destroy sand beaches. This measurement provides valuable information about the health of the 

beaches along the Calvert Cliffs, but it does not tell much about 

the cliffs themselves. 

Shoreline retreat rates can be measured on the ground or, 

much more practically, by remote sensing or surface mapping. 

Measuring cliff retreat on the ground has been done by use of 

a fixed reference marker (e.g., Leatherman, 1986) or by driving rows of rebar stakes (pins) into the lowermost cliff face and 

measuring the increasing length of the protruding part of the 

stakes over time (Miller, 1995) as erosion progresses. Leatherman (1986) reported an average cliff retreat rate of 15 cm/yr 

at Randle Cliff Beach Benchmark #7 from December 1951 to 

April 1978 near the northern end of the cliffs. During the period 

1992–1994, pin fields were installed and measured at three cliff 

toe sites along Scientists Cliffs in the central part of the cliffs and 

one site at Calvert Cliffs State Park at localities where wave undercutting was not taking place (Schweitzer, 1993; Miller, 1995). 

Although the observation time was short, the results (Miller, 

1995) are generally consistent with what is known about processes where freeze–thaw cycles are a major factor in the erosion 

rate and no undercutting takes place. The results of this study 

indicate long-term average rates of cliff retreat are slow at Scientists Cliffs, where they average about 5 cm/yr, and much faster 

at Calvert Cliffs State Park, where erosion rates were 31 cm/yr 
NUMBER 100 • 3 5

during a mild winter with little or no erosion except in winter. 

During cold winters, the erosion rates are even higher. 

The Maryland Geological Survey initiated a long-term and 

ongoing investigation of the state’s tidewater shoreline erosion 

rates. The first study (Singewald and Slaughter, 1949) compared 

the 1847–1848 U.S. Coast Survey maps with 1938 aerial photographs. Man-made structures identified on both images were 

used as reference points for cliff shoreline locations, a technique 

basically still used today (e.g., Zwissler et al., 2014). The accuracy of the 1949 study was limited, partly because of difficulties 

in consistently identifying the cliff edge and the Miocene cliff toe 

and also partly because of inaccuracies inherent in the 1847–

1848 maps, which were based on plane table surveying at scattered locations. The Maryland Department of Natural Resources 

(DNR) updated and continued this work, eventually publishing a 

four-volume atlas of Maryland tidal shorelines and erosion rates 

that was based on comparison of temporally successive aerial 

photographs (Maryland Coastal Zone Management Program, 

1975). By the 1990s, geographic information system (GIS) mapping software and inexpensive GPS navigation tools were greatly 

improving shoreline and cliff mapping accuracy, so that the latest 

Maryland coastal erosion rates and background data now are 

available online (Maryland Geological Survey, 2018a, 2018b).

According to the Maryland coastal zone website (Maryland 

DNR, 2013), the state has 12,330 km (7,660 mi) of tidal shoreline. Of this, 65% (including Calvert Cliffs) has eroded, on average, 0–0.6 m/yr (0–2 ft/yr) from around 1940 to around 1998. 

Accurate measurements of erosion rates less than 0.3–0.6 m/yr 

(1–2 ft/yr) were not possible. “Shorelines” were defined as the 

water’s edge seen in the photographs. Some parts of Maryland’s 

eroding tidal shoreline are eroding even faster, with 11% of the 

state’s tidal shoreline eroding at 0.6–1.2 m/yr (2–4 ft/yr), 3% 

at 1.2–2.4 m/yr (4–8 ft/yr), and 1% eroding at a rate of 2.4 m 

(8 ft) or more per year. Overall, 69% of Maryland’s coastlines 

have been retreating due to erosion. The most rapidly eroding 

parts of the Chesapeake Bay shoreline are along the edges of 

low Pleistocene terraces that are composed of poorly compacted 

sediment and exposed to the open bay on the Eastern Shore. The 

slowly or noneroding shorelines are mostly along narrow estuaries and sheltered coves. The Calvert Cliffs, accounting for only 

0.35% of Maryland’s total tidal shoreline, are exceptional in that 

they combine relatively slow rates of erosion with full exposure 

to the open Chesapeake. The difference in erosion rate under 

very similar circumstances between poorly compacted Pleistocene sediment and well-compacted Miocene sediment shows the 

importance of the relatively indurated (cohesive) nature of the 

Miocene sediments at the base of the cliffs in resisting erosion, 

particularly the nature of the Plum Point Member of the Calvert 

Formation, which is the unit directly exposed to wave erosion 

along the middle and northern cliffs. 

Erosion (cliff retreat or recession) rates provided on the 

Maryland coastal zone website (Maryland DNR, 2013) vary 

substantially along the Calvert Cliffs. Some of the rates and their 

variations are artifacts, depending on various uncertainties and 

on the interval of time considered, that is, between successive 

aerial photographs. For example, for the northern half of the 

cliffs, included in the U.S. Geological Survey Prince Frederick 

and North Beach quadrangles, the most recent rates are based 

on the interval 1960 to 1993. For the southern half of the cliffs 

(Cove Point and Solomons quadrangles), the most recent rates 

are based on the interval 1942 to 1993. In general, the erosion 

rates along the middle and northern cliffs located north of Flag 

Ponds Nature Park, where the Plum Point Member of the Calvert Formation is exposed at beach level, are mostly in the 10–30 

cm/yr range, consistent with the local 15 cm/yr (1951–1978) 

measurement at Randle Cliff reported by Leatherman (1986). 

The unprotected cliffs immediately north and south of Parkers Creek have been eroding somewhat faster than this average 

rate (about 40 cm/yr). To the south of Flag Ponds, eroding cliffs 

have been retreating at about 50–150 cm/yr, with more spatial 

variability than seen to the north. Exceptionally, the formerly 

eroding cliffs behind the Flag Ponds and Cove Point sand spits 

(cuspate forelands) have become stabilized wooded slopes (e.g., 

Clark et al., 2004) and so are not eroding at all at present, although the nearby shoreline sands are being eroded north of the 

spit tips and deposited just south of the tips, accreting new land 

(Beardslee, 1997).

By comparing aerial photographs, Miller (1995:194) independently estimated historic cliff recession rates at sites he 

studied. He determined a cliff recession rate of 10 cm/yr for the 

Scientists Cliffs segment, 80 cm/yr for the cliffs just north of Scientists Cliffs, 40–120 cm/yr for sites near Calvert Cliffs State 

Park (except for the very anomalous rate of <10 cm/yr at Rocky 

Point), 30–35 cm/yr around the Naval Research Laboratory and 

Randle Cliff, and <10–60 cm/yr for the Chesapeake Ranch Estates cliffs.

To estimate what fraction of Calvert Cliff recession is due 

to freeze–thaw cycles, Zwissler et al. (2014) analyzed accurate 

aerial photographs of the Calvert Cliffs from 2003, 2006, 2007, 

and 2011, which were taken more than a decade after the 1993 

baseline photographs used by the Maryland DNR. They measured the distances from cliff-adjacent houses to the nearest cliff 

edge at nine sites in Scientists Cliffs and four sites each in Calvert 

Beach, Calvert Cliffs State Park, Park Chesapeake, and Chesapeake Ranch Estates. The specific measurement sites were not 

chosen at random, but rather were selected to avoid cliffs where 

wave erosion was occurring. From data at 25 sites, Zwissler et al. 

(2014) calculated average recession rates for 75 different individual locations, which ranged from nearly 0 to 158 cm/yr. Almost 

half of these values were between 25 and 75 cm/yr. On the basis 

of the average rates for each locality, Chesapeake Ranch Estates 

(71 cm/yr) and Calvert Cliffs State Park (65 cm/yr) in the south 

had the highest rates of land loss, four sites in northern Scientists 

Cliffs had little or no loss over this period, and the remaining 

sites had rates of land loss clustered in the middle (26–35 cm/yr). 

These data are also consistent with the observation that there was 

relatively higher short-term erosion loss during the extreme rain 

events that occurred in 2009 and 2010. The dramatic difference 
3 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

between recession rates in northern versus southern Scientists 

Cliffs (<5 versus 35 cm/yr) probably reflects the physical properties of the strata exposed to Chesapeake wave erosion. The cohesive clay-rich bed 13 stratum along the base of the northern cliffs 

at Scientists Cliffs is much less susceptible to erosion than the 

easily wave erodible shell marls of bed 14 that form the base of 

the southern cliffs at Scientists Cliffs. Zwissler et al.’s 2003–2011 

cliff recession rates, which were determined at specific localities 

chosen deliberately, are roughly consistent with the more regionally estimated rates for the period 1960–1993 that are reported 

on the Maryland DNR (2013) coastal erosion website.

Offshore Sand Bars

Sand beaches and offshore sand bars (see, e.g., Shea, 1994) 

play a significant role in slowing Calvert Cliff erosion, but their 

multiyear and multidecadal trends are poorly known. Beach 

sand is typically of medium-grained particle size, with finer 

sand concentrated offshore (Figure 1.17). The 1847 Coast Survey map and the 1938 aerial photographs (see Singewald and 

Slaughter, 1949) are the earliest depictions of beach locations in 

this area, and their distribution is rather different from where 

we see beaches today. For example, the cliff between Governor 

Run and Scientists Cliffs was bordered by a narrow sand beach 

for a number of years until 1991, when the beach completely 

disappeared and left the toe of the cliff prey to continuous wave 

erosion (Miller, 1995). After Hurricane Isabel struck in 2003, 

however, a new beach formed and remained until 2016, when 

the Miocene toe of the cliff was reexposed in some areas.

Four or more sand bars, arranged nearly parallel to the 

shoreline, may be present along parts of the cliffs provided 

enough sand is available to sustain them. Multiple sand bars 

are not unusual in places where littoral depth gradients are very 

gentle, which is often the case along the Calvert Cliffs. The gentle gradients and shallow offshore water depths have resulted 

from the presence of underlying, relatively consolidated Miocene 

strata, which Chesapeake Bay surf is unable to excavate to a 

depth of more than about 0.5–1 m below sea level in the littoral zone. The resultant multiple sand bars (Shea, 1994) absorb 

wave energy, and sometimes waves even break on the nearshore 

bars before they reach the beach if winds and tides are favorable. 

Sand bars thus help to decrease the rates of cliff erosion when 

tides and water levels are in the normal range, although during 

high water levels and storm surges, wave energy can still become 

concentrated on the cliff toe. 

Conventional wisdom attributes beach nourishment to cliff 

erosion, but in fact the Miocene strata exposed in the cliffs are 

primarily composed of fine sand (the primary constituent in 

most beds; Downs, 1993; Miller, 1995), silt, and clay, none of 

which remain on the beach under the Chesapeake’s extant wave 

climate. The fine sand that washes out can help to nourish the 

offshore bars (Figure 1.17), but suspended finer material ends 

up farther offshore or, in the case of clay, probably is deposited 

in the deep central offshore channel. Sand sufficiently coarse to 

be stable along the beaches of the northern and central Calvert 

Cliffs beaches probably originates largely from the fluvial upland 

deposits that are being carried to the beaches from more inland 

areas via ravines and streams. Along the southern cliffs, however, 

the upland deposits that cap the cliffs do contain large quantities of medium to coarse sand that help to replenish the beaches 

there. This abundance of sand helps explain why the exceptionally large sand accumulations at Flag Ponds and Cove Point are 

there and nowhere else along the cliffs. A 2015–2016 study of 

zircon age distributions (McCormick et al., 2017) also supports 

the conclusion that most of the sand along modern Calvert Cliffs 

beaches originated by erosion of fluvial late Miocene to Pliocene 

upland deposits and not primarily by erosion of the Miocene 

marine sediments exposed in the Calvert Cliffs. 

TECTONIC INFLUENCES ON THE 

CALVERT CLIFFS

The Calvert Cliffs and the Miocene strata they expose can 

be explained by depositional and erosional processes ultimately 

driven by eustatic sea level variations caused by climate change 

and attendant fluctuations in global ice sheet volume (Ruddiman, 2008). There are, however, some joints of possible tectonic 

origin in the Plum Point Member, and one reverse fault penetrating the entire Choptank Formation. The nearly vertical, eaststriking joints, spaced about 20 cm apart, are prominent in beds 

11 and 13 south of Parkers Creek. These joints may reflect thermal contraction and expansion of cohesive sediments within several decimeters of the cliff face. However, studies in the coastal 

plain of northern Virginia have attributed similar features to a 

subtle but pervasive tectonic stress field in the early part of the 

late Miocene that was related to the forces that uplifted the modern Appalachian Mountains (Newell, 1985; Weems et al., 1996, 

2017). The preferred joint trends in the Northern Neck region 

in Virginia closely match the trends of the creeks there, suggesting that the creeks became preferentially incised along the joint 

trends. This may also be the case for ravines and stream valleys 

interrupting the Calvert Cliffs. However, vertical cliff-parallel 

joints 25–50 cm inside the cliff face are almost certainly caused 

by the cliffs themselves changing the stress field after removal 

of once-continuous layers located where the Chesapeake Bay is 

today.

The only other tectonic feature so far recognized along the 

Calvert Cliffs is a fault that, although noted as an offset in earlier biostratigraphic research, is most evident in the along-strike 

cliff profile of Kidwell (1997) and reproduced here as Figure 

1.10 (also see Powars, 2013). At Moran Landing, between the 

Calvert Cliffs State Park and the Calvert Cliffs Nuclear Power 

Plant, the Miocene strata do not project directly across a small, 

semicircular gap in the cliffs but instead show an offset of about 

3 m, indicating the presence of a high-angle reverse fault (here 

called the Moran Landing Fault) with its south side upthrown 

relative to its north side. The offset of these beds is not likely to 
NUMBER 100 • 3 7

be due to a mapping error and likely is related to a contortion 

of the bed 15–17 interval into a tight anticline at Conoy Landing, just to the north of Moran Landing. Both the fault and the 

presence of the anticline indicate that these strata were disrupted 

after deposition of the Choptank Formation. Whether the fault 

continues into the overlying nonmarine sediments has not been 

determined because the overlying upland deposits are very variable in their lithology and have very discontinuous layers (Figure 

1.10; see also Schlee, 1957). The strike of this fault is poorly 

constrained, and no younger limit has been established for its 

activity, but the structure may have been formed by the same 

regional tectonic event documented in Virginia that occurred 

in the early part of the late Miocene. The unusual, semicircular 

valley at Moran Landing is probably related to the fault and its 

effect on the strength of sediments in its immediately surrounding area. Hansen and Edwards (1986) identified a structure that 

they believe to be a NE-trending reverse fault with the south 

side upthrown, in the same sense as the Moran Landing Fault 

but crossing the Calvert Cliffs about 10 km north of it. It is 

quite possible that the Moran Landing Fault is related to a similar deep structure and is rooted at great depth in the basement 

rocks below the Coastal Plain. Numerous faults and other structures of many ages lace this Pre-Jurassic basement (Hansen and 

Wilson, 1984) underlying the area of the Calvert Cliffs. Some 

of these ancient structures may have become reactivated and 

have penetrated the sediment wedge deposited since formation

and growth of the modern Atlantic Ocean (e.g., Mixon and 

Newell, 1977; Hansen, 1978, 1988; Powars and Horton, 2010).

THE CALVERT CLIFFS AS A REGIONALLY 

SIGNIFICANT COASTAL PLAIN LANDMARK

Most famous scenic landmarks (for example, the Grand 

Canyon and Yosemite Valley) have been created by erosion. The 

Calvert Cliffs are a lesser example of that process, but lesser is 

a relative term. Although 50 or 100 Calvert Cliffs would have 

to be stacked together to equal the relief of many U.S. western 

landmarks, the 42 km length of the cliffs is a respectable dimension. Moreover, on the otherwise flat and even monotonous 

Atlantic Coastal Plain that runs from Long Island, New York, 

south through Florida and then wraps around the north shore of 

the Gulf of Mexico as the Gulf Coastal Plain, the Calvert Cliffs 

stand out as a major natural landmark (Mansueti, unpublished), 

most easily appreciated from a small boat (such as the view seen 

in Figure 1.2). The Calvert Cliffs are featured in paintings, photographs, and fiction (e.g., Vogt, 2009). In the early seventeenth 

century John Smith, a man raised in the lowlands of southeastern 

England, could rightly call them “great high cliffs.” Old-growth 

forest capped the cliffs until the end of the seventeenth century, 

and its presence made the cliffs look about twice their actual 

height until they were later deforested for agriculture. Had the 

cliffs been owned by the U.S. government, as much of the land 

west of the Mississippi River was, it is almost certain that given 

their prominence as a regional landmark and because of their 

unexcelled fossil wealth, there would now be a “Calvert Cliffs 

National Monument” or perhaps even a “Chesapeake National 

Park,” with the Calvert Cliffs as a prime attraction, competing in 

PERCENT OF SAMPLE

PHI UNITS

2 1 0.5

MM

0.25 0.125 .0625

30

20

10

0

-1 0.5 0 0.5 1 1.5 2 2.5 3 3.5 4

BEACH

NEARSHORE

CLIFFS

FIGURE 1.17. The size distribution of sand particles in beach sand, nearshore bar sand, and cliff sediment at Scientists Cliffs (Downs, 1993). 

Coarser sand is to the left, and finer sand is to right. Note that most sand from the Calvert Cliffs at this locality is too fine to remain in the beach 

sands, so erosion from the cliffs can serve only to replenish sand in the sand bars. Along the southern Calvert Cliffs, the overlying sandy and 

gravelly upland deposits do yield medium and coarse sand fractions that are heavy enough to remain on the adjacent beaches.
3 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

fossil wealth with Dinosaur National Monument and the Florissant Fossil Beds in Colorado. Even today, the largest remaining 

natural segment of the Calvert Cliffs on either side of Parkers 

Creek deserves recognition as a national natural landmark.

Unlike most well-known landmarks, the Calvert Cliffs are 

best appreciated from the perspective of a boat located some 

hundreds of meters to several kilometers to their east, out in the 

Chesapeake Bay. Standing on the naturally forested cliff edge, 

one can see only a small part of the cliffs. If one tries to access 

them along the shore, they still can be difficult to fully appreciate 

because of landslide debris and trees shed from the cliffs and because the beach is narrow or, in many places, nonexistent. From 

either their top or their base, there is a very real and ever-present 

danger of landslides, as can be seen in Figure 1.16A,B, particularly after protracted heavy rains. Two fatalities occurred during 

the second half of the twentieth century, both along the southern Calvert Cliffs. In both cases, beach walkers simply were at 

the wrong place at the wrong time. The southern Calvert Cliffs 

truly are the most dangerous section because that is where the 

rapidly eroding Choptank and St. Marys Formations are present 

at beach level, and the only modestly compacted upland gravels 

overlie them (Figure 1.10). Indeed, the threat of cliff collapse is 

so great in this area that the beach south of the cliffs at Calvert 

Cliffs State Park is off limits to visitors.

Some segments of the Calvert Cliffs remain in a precarious 

legal state, developed neither for housing nor for industry yet 

at the same time not preserved. A striking example is the cliff 

just north of Governor Run, which is the second highest cliff 

along the Calvert Cliffs. This cliff was described by Ducatel and 

Alexander (1837:12) as “perhaps the most interesting spot at 

which to determine the geological features,” one which “affords 

a luminous view of all the strata containing fossils.” Ironically, 

the senior author of this chapter has since 1981 been a 1/15 

shareholder in a corporation that owns the roughly 28 ha (70 

acre) forested tract that lies above this cliff and extends back 

from it about 1,200 m from the 243-m (800-ft)-long segment of 

cliff and beach. Despite several efforts led by this author and the 

availability of a market value payment for it, this famous cliff remains unpreserved. Until 1981, it was one of the few spots along 

the cliffs where the public could collect fossils for a small fee 

(Glaser, 1979:54–66). Road access to this site is now closed to 

all but local cottage owners, who want to prevent trespassing on 

their long pier. This change illustrates the continuing challenges 

to preservation efforts along the Calvert Cliffs. 

BEACHES AND BLUFFS ALONG THE 

CALVERT CLIFFS: A DYNAMIC AND 

EVER-CHANGING ENVIRONMENT

Quite apart from, and in some ways at odds with, their 

value as a rich repository of fossils, the Calvert Cliffs and adjacent shoreline area also constitute a narrow, unusual, complex, 

and constantly changing ecological niche. Although this chapter 

naturally emphasizes the cliffs themselves and their relationship 

to their adjacent shoreline, it also needs to be noted that the Calvert Cliffs are part of a narrow belt of steep dissected land and an 

adjacent shallow littoral zone. Landward of the cliffs, Holocene 

and earlier interglacial shoreline erosion of semi-indurated Miocene sediments has steepened eastward topographic gradients, 

causing the cliffs to be incised with numerous steep-sided ravines 

that are steadily extending westward by headward erosion. The 

resultant steep topography, formed just inland from the actual 

faces of the cliffs, has created many ecological niches that would 

not be present without erosion driven by the adjacent Calvert 

Cliffs and Chesapeake Bay. Seaward of the cliffs the bay remains 

shallow for 100 m or more offshore, and in many areas this shallow shelf locally hosts four or more nearly shore-parallel sand 

bars. Such bar systems require a low seafloor gradient to form, 

which has been possible because of the resistance of the Miocene 

strata to downward erosion in the littoral zone under present 

wave climates. In contrast, unconsolidated Quaternary sediments on the Eastern Shore are rapidly eroded down to 1.5–2 m 

below sea level, even near the water’s edge.

Until Europeans arrived, there were only a few eroding 

outcrops other than the Calvert Cliffs, and these were located 

only along some of the larger tributaries of the bay such as the 

Choptank, Patuxent, and Potomac. All of these eroding outcrops supported, and still support, an ever-changing mix of microhabitats. For example, when a new slide occurs, even across 

an area with dimensions of just a few square meters, it exposes 

fresh Miocene strata on the cliff face. The resultant scar on the 

cliff face is then rapidly colonized by seeds or by regrowth of 

plants surviving in the slide mass or from the roots whose tops 

were sheared off. Concurrently, at the base of the cliff where 

slide debris piles up, the debris is itself rapidly recolonized. The 

beach surrounding the slide debris, where present, is also constantly changing and supports its own array of narrow ecological 

niches. To date, no scientific study has been done on the natural revegetation of slide scars and slide debris along the Calvert 

Cliffs. The wealth and diversity of wildlife made possible by the 

ever-changing face of the Calvert Cliffs is commonly overlooked. 

One documented example is the case of certain tiger beetles that 

lay their eggs in small holes made in bare cliff exposures (Figure 

1.4E; discussed below). 

The cliffs and their adjacent beach form a natural transition 

zone, called an ecotone, between what was once continuous forest to the west of the cliffs and the open water of the Chesapeake 

Bay to their east. This border region creates a sunlit “edge habitat” similar to what modern man creates when roads are built or 

fields are cleared but which in nature was very rare until European settlement. The sunlit aspect of this edge habitat must have 

supported thick vegetation, accounting for John Smith’s 1608 

(1986, vol.2:165) observation that the woods he saw from the 

water were “extreame thicke.” At that time and for the next half 

century, when large trees collapsed onto the beach because of 

slides, their presence made the shoreline remain wild and impassable. Even two centuries later, access to the beach below the cliffs 
NUMBER 100 • 3 9

must have been arduous without a small boat except where plantation owners had built farm roads down to landings or piers.

In the modern world, most subdivisions along the Calvert 

Cliffs remove or trim fallen trees to make their beaches passable. There are no professional botanists among the authors of 

this paper, but the senior author notes that flora growing on the 

cliffs near Scientists Cliffs and on the debris cones sloughed off 

the cliffs commonly include many native species that are mostly 

fast growing and shade intolerant, such as black locust (the most 

common), bayberry, sycamore, black willow, slippery elm, tulip 

poplar, black cherry, and others. Oaks, hickories, and conifers, 

all characteristic of the forest habitats above and behind the 

cliffs, are rare in this environment.

Many alien species (mostly invasive) also easily establish 

themselves on the cliffs or, in some cases, were deliberately 

planted to try to help slow cliff erosion. These species, mostly of 

East Asian origin, include kudzu, Oriental bittersweet, ailanthus 

(tree of heaven), weeping willow, autumn olive, Japanese honeysuckle, mimosa, multiflora rose, English ivy, and various grasses. 

A native species of equisetum (horsetail rush), cattail (Typha

spp.), and Phragmites (possibly including the native American 

variety), as well as various types of moss, successfully colonize 

the very moist environments—even tiny microswamps—perched 

on slide debris or on ledges formed on the top surface of impervious Plum Point Member strata. European coltsfoot, generally 

absent from the acidic soils of the Coastal Plain, exploits the 

Miocene shell beds and shelly slide debris because they offer a 

geologically limed neutral or even alkaline pH.

A different and less diverse flora inhabits the sandy beaches 

above normal high tide. The most common natives of this environment are the brackish-tolerant orach (also called orache) and 

sea rocket, although invasive Japanese knotgrass has also become established locally on the back beaches. Older and higher 

beaches, inundated only during rare storm surges, occur at only 

a few places along the Calvert Cliffs shoreline. Examples include 

the older spit beaches at Flag Ponds and Cove Point and the 

barrier beach that separates the Chesapeake Bay from the salt 

marsh of Parkers Creek. Common floral inhabitants of this habitat, mostly native, include loblolly and Virginia pine (especially 

at Flag Ponds), persimmon, eastern “red cedar” (actually a juniper), greenbrier, bayberry, prickly pear cactus (Opuntia spp.), 

and, of course, poison ivy.

Chesapeake waves periodically wash ashore abundant dead 

or dying fishes, crabs, driftwood, subaquatic vegetation, and 

other organic debris that quickly attracts a food chain of consumers. Before European settlement, black bears and wolves such 

as those seen by John Smith in 1608 were surely common diners 

on this bountiful food supply. Today, the bears and wolves are 

gone, and the largest remaining consumers are primarily birds 

and raccoons. Bald eagles and ospreys scout for fish by routinely 

riding along updrafts created by air moving over the Calvert 

Cliffs, whereas great blue herons stand patiently below in shallow waters, waiting for unwary prey. Turkey vultures and black 

vultures help to clean up what the more active predators leave 

behind. The cliffs are also important to wildlife in other ways. 

Here and there, rough-winged swallows and belted kingfishers 

peck nesting cavities into the cliffs. In spring, cow-nosed rays 

mate close to shore and scour the shallow sandy bay floor for 

mollusks, and horseshoe crabs come ashore below the cliffs to 

spawn. In summer and early fall, vast schools of menhaden hug 

the shoreline to evade their finny predators. Some of the human 

efforts to reduce shoreline and cliff erosion, notably the emplacement of groins, have provided otherwise rare hard substrates for 

sessile biota such as algae, barnacles, and blue mussels, whereas 

crabs find safe hideouts among the nonnative rocks. Natural 

hard substrates along the beaches bordering the Calvert Cliffs 

are relatively rare but include driftwood, large fossil pecten shells 

and vertebrate bones, and blocks of iron oxide–cemented sandstone, derived largely from post-Miocene fluvial deposits topping the cliffs. It is a fascinating fact that beachcombers can find 

13 million-year-old pecten shells from the Choptank Formation 

that are encrusted with both Miocene and modern barnacles! 

The waters immediately offshore of the Calvert Cliffs have 

been (and often still are) an important food source for humans. 

Commercial fishing, formerly important, has mostly passed into 

history, although a pound net fishery still survives locally off parts 

of the southern Calvert Cliffs. Until modern times, oyster beds 

existed along much of the Calvert Cliffs shoreline. They and the 

oyster boats (called bugeyes) that dredged for them are gone now, 

victims of overfishing and two oyster diseases. Crabs are still 

present, however, and crab pots are still emplaced every summer 

and fall in long, parallel lines offshore from the Calvert Cliffs. 

Two tiny beetles—species of the carnivorous genus Cicindela—have in recent years emerged, by their rarity, as the bestknown biota inhabiting the cliff environment (e.g., Vogler et al., 

1993; C. Barry Knisley, Randolph-Macon College, “Studies of Two 

Rare Tiger Beetles (Cicindela puritana and C.d. dorsalis) in Maryland, 2010,” unpublished). Cicindela puritana, the Puritan tiger 

beetle (Figure 1.4E), requires eroding sandy cliffs for its reproduction. This beetle was first scientifically collected in Maryland near 

Chesapeake Beach in 1911. The other species, Cicindela dorsalis 

dorsalis, the Northeastern Beach tiger beetle, requires an undisturbed sandy beach for reproduction. Along the Calvert Cliffs, this 

beetle was first collected at Flag Ponds and Kenwood Beach in the 

1950s (Knisley, personal communication, 2012). In the mid-1980s, 

Knisley began to study these beetles along the cliffs and at a few 

other sites where they exist. Sampling along transects, he began 

to monitor population densities along the cliffs, first in 1986 and 

then annually starting in 1988. Having established their rarity, 

Knisley had them successfully added to the federal list of threatened species in 1990. This designation has put legal constraints 

on human cliff-edge and beach modifications, particularly those 

reducing cliff erosion. This restriction has become a problem

for about half of the 234 houses located within 30.5 m (100 ft) 

of the cliff edge that were discussed above because as of 2007 

Puritan tiger beetle populations had been discovered at the base 

of the cliff below those houses. This situation has not served to 
4 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

make cliff-edge property owners friends of Puritan tiger beetles, 

but paleontologists are happy that these beetles help to keep at 

least portions of the cliffs in their natural eroding state. Efforts 

at the preservation of these beetles do not seem to be going well, 

however, because Knisley’s annual beetle counts show a longterm decline in both species, especially in C. d. dorsalis. Some of 

the sites along the cliffs that supported beetle populations during 

the late 1980s and early 1990s no longer do.

THE FUTURE OF THE CALVERT CLIFFS

The history of previous predictions about the future of the 

Calvert Cliffs shows that most of these predictions have been 

far from what has actually happened. However, because the 

future of the Calvert Cliffs is tied to the future of RSL rise, 

to ongoing efforts to restore the water quality and ecosystems 

of the Chesapeake Bay, and most particularly to the efforts of 

cliff-top landowners to armor the cliff shoreline against erosion, we can hazard some fairly conservative and well-justified 

predictions. First, residential and other development along the 

Calvert Cliffs has slowed drastically since the 1980s, in large 

part due to environmental concerns that shoreline housing and 

other development on land near the Chesapeake Bay have a 

disproportionately negative effect on Chesapeake water quality 

due to resultant sediment, nutrient, and other runoff. 

Nowhere is the conflict between Calvert Cliffs shoreline 

development and protecting the Bay better illustrated than in 

Scientists Cliffs in the Maryland Critical Area about midway 

along the cliffs. As of this publication, 287 houses plus buildable lots currently exist on about 113 ha (280 acre)—three 

fewer, due to imminent or actual loss of houses to cliff erosion, than cited in Scientists’ Cliffs History Book Committee 

(2010). If today these 113 ha were still farmland or forestland, 

only 14 buildable lots would be allowed because of the Critical 

Areas legislation enacted by Maryland in 1984 and adopted 

by Calvert County in 1989. The legislation reduced building 

density, absent wastewater treatment plants, for land within 

305 m (1,000 ft) of tidewater to improve water quality in the 

Chesapeake and its connected estuaries. In addition, Calvert 

County now requires setbacks of three times the cliff height for 

new cliff-side houses other than those in grandfathered subdivisions like Scientists Cliffs.

According to Boon et al. (2010), the U.S. Army Corps of 

Engineers and National Research Council estimate that RSL in 

the Chesapeake Bay region will be about 50 to 150 cm higher 

than today by the early twenty-second century. This value 

is based on an estimated RSL rise of 5 to 15 mm/yr, which 

will be considerably higher than the 3.4 mm/yr rate that prevailed during the last century. This much higher RSL rise will 

mean increased shoreline erosion rates, particularly along unprotected segments of the Calvert Cliffs, which lie across the 

Chesapeake Bay from the low-lying salt marshes of Dorchester 

County. These marshes, already rapidly eroding today, will almost certainly be lost to future sea level rise. The loss of these 

marshlands will increase the fetch of easterly storm winds, and 

these will create wave energies that are higher on average than 

today and will attack the cliffs more strongly than today. The 

only countervailing factor that can be expected is that a warming climate and warmer winters probably will reduce the effects 

of freeze–thaw cycles on cliff erosion during the winter months.

Because the formations, members, and beds differ in their 

resistance to wave erosion, future sea level rise will change the 

rate and character of erosion at any place over decades and centuries. For example, at RSL rise of 3–6 mm/yr, the 25-cm-thick 

Parkers Creek Bone Bed (bed 12) will take only 83–42 years, 

respectively, to pass through sea level. Active wave erosion of 

this sandy layer is the primary reason for the rapid cliff retreat 

and fossil release between Scientists Cliffs and Parkers Creek, 

where the cliffs are allowed to erode naturally. In the adjacent 

northern Scientists Cliffs, cohesive bed 13 retards cliff erosion, 

while the cliffs just north of Parkers Creek are protected at sea 

level by cohesive bed 11. The gentle, apparent southward dip 

(around 1:1000) of Miocene strata exposed along the middle 

and northern cliffs (Kidwell, 1997) indicates that an intersection between the stratigraphy and sea level migrates north at 

3–6 m/yr. We can thus predict that by the twenty-second century, rapid cliff erosion and fossil release will be shifting north 

of Parkers Creek as rising sea levels bring bed 12 within reach of 

Chesapeake waves, while the cliff south of this creek will then 

be naturally armored by bed 13. In the same way, the Choptank–

Calvert boundary will migrate north along the cliffs, increasing 

wave erosion where the Choptank Formation will also likely 

be exposed.

An increase in future rates of cliff erosion along unprotected parts of the Calvert Cliffs probably will mean increased 

rates of fossil exposure and continuing favorable habitats for 

the Puritan tiger beetle Cicindela puritana. At the same time, 

however, the increasing value of shoreline real estate will probably motivate ever more aggressive and expensive engineering 

efforts on the part of landowners to arrest or slow shoreline 

erosion, using methods such as boulder or gabion-type revetments, reef balls, offshore T-shaped groins, bulkheads, and 

even cliff face armoring. Over long periods of time, this alternation of armored and naturally eroding cliffs will turn 

today’s relatively straight coastline of the Calvert Cliffs into 

a strongly crenulated pattern of projecting armored segments 

and indented unprotected segments. Cliff erosion along the 

unprotected segments will eventually produce arcuate coves 

that will have wider beaches and reduced cliff erosion. At the 

same time, abandonment and demolition of threatened cliffedge structures (which began in 2014) might eventually return 

some strips of cliff-front terrane back into their predevelopment natural state.

The Calvert Cliffs constitute one of the greatest natural 

assets of Calvert County and southern Maryland. The fossils 

and sediments exposed in the eroding Calvert Cliffs are silent 

witnesses to how the environment and its ecological response 

have changed during the course of approximately ten million years (ca. 18–8 Ma). This ten-million-year-long history 
NUMBER 100 • 4 1

“book” likely has pages or even a chapter or two missing (as 

recorded by disconformities—e.g., Kidwell, 1997) and lacks 

death-assemblage “snapshots” (e.g., Tucker et al., 2014). The 

knowledge gained from more than a century of studies of the 

paleoenvironmental information recorded in the Miocene 

strata of the Calvert Cliffs adds to knowledge obtained from 

geological deposits of other places and times. Taken together, 

these studies will lead humankind to a better understanding of 

how and why the Earth’s surface environment and the life it 

supports have changed over “deep time.”

 Apart from its Middle Miocene paleoenvironmental archive, the Calvert Cliffs and adjacent beaches as they exist now 

present a natural laboratory for study of littoral and masswasting processes associated with dynamic shoreline changes 

forced by rising sea levels. Although the Calvert Cliffs will no 

doubt continue to inform future generations of earth scientists, 

so too will they generate controversy as society wrestles with 

whether and how much the cliffs should be fortified against 

the natural processes of erosion. The result of this struggle will 

greatly affect the fate of the Calvert Cliffs in coming years.

ACKNOWLEDGMENTS

We thank Milan Pavich (U.S. Geological Survey) and Inga 

Clark for valuable discussions. Under Pavich’s direction, Clark 

processed lidar topography along a strip of land along the Calvert Cliffs. The topographic analysis was originally intended, 

with their coauthorship, for this chapter, but length limitations 

dictated that it be treated in a later publication. We extend many 

thanks to Rachel Reese (Calvert Marine Museum [CMM]) and 

Michael Godfrey (formerly CMM) for helping draft Figures 1.6 

and 1.14. We thank Mark Lay (National Museum of Natural 

History) and Thomas Jorstad (National Museum of Natural 

History) for providing information about Figure 1.9. This chapter benefitted from constructive reviews by Nicholas D. Pyenson 

(National Museum of Natural History [NMNH]), David J. Bohaska (NMNH), and Robert E. Weems (CMM).

Funding for the Department of Paleontology at the Calvert 

Marine Museum is provided by the citizens of Calvert County, 

the Calvert County Board of County Commissioners, and the 

Clarissa and Lincoln Dryden Endowment for Paleontology at the 

Calvert Marine Museum.

NOTES

1. The Evening Star newspaper published “Dream Road Realized for 

Maryland’s Western Shore” on 26 September 1963.

2. A new bridge across the Chesapeake Bay running from Lusby (Cove 

Point) to Taylor’s Island (6.3 miles) as proposed by Louis Goldstein 

(actual proposal not seen) was formerly studied by contract from 

State Roads Commission in 1964. During 1985–1986 local papers 

report Goldstein again promotes such a bridge, but Calvert Board 

of County Commissioners and other politicians including Thomas 

Rymer oppose the plan, and the State Highway Commission decided that the bridge was not feasible at that time. In 2003, then 

Governor Robert Ehrlich appointed a local task force that included 

Maryland state delegates Sue Kullen and Tony O’Donnell, who 

both opposed the bridge, as reported in Calvert Recorder, 27 May 

2005.

3. The Mid-Atlantic Power Pathway (MAPP) proposal was formally 

presented to the Calvert Board of County Commissioners (BOCC) 

on 16 October 2010. It was opposed by the BOCC majority and 

others. On 27 August 2012, PEPCO Holdings International was 

notified that Pennsylvania–New Jersey–Maryland Interconnections 

cancelled the MAPP project.

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ABSTRACT. The Miocene sediments of Calvert Cliffs contain a remarkable fauna of 

cartilaginous fishes, with a total of 54 species. Of these, there are 3 species of chimaeras 

(ratfishes), and the remaining 50 are elasmobranchs (39 species of sharks and 12 species of rays). This number of species is slightly larger than the Holocene chondrichthyan 

fauna of the Middle Atlantic states of 46 species (28 sharks and 18 rays). The sharks 

of Calvert Cliffs are particularly diverse and contain two complex assemblages, both 

of which had their evolutionary roots in the Paleogene. One assemblage consists of the 

newly emerged, largely mesotrophic carcharhiniforms spreading from the tropics into 

more temperate, middle-latitude habitats of the northwestern Atlantic. The other assemblage represents an essentially simultaneous diversification of gigantic, macrotrophic species, principally among the lamniforms. Included within this assemblage is a previously 

unnamed giant thresher shark (Lamniformes, Alopiidae) with serrated teeth. Taken as a 

whole, the Calvert Cliffs chondrichthyan fauna is richer in large, free-ranging macrophagous sharks and large, neritic rays than the Holocene fauna of the Middle Atlantic states.

INTRODUCTION

Shark and ray teeth are perhaps the signature fossils collected along Calvert Cliffs, 

drawing thousands of collectors to the fossil-strewn beaches of the western shore of the 

Chesapeake Bay each year. Isolated teeth are extremely abundant and can range in size 

from not much larger than a grain of sand to that of a man’s hand. Color is likewise 

varied, from light ruddy or grayish browns to nearly black. Their popularity has led to a 

number of publications documenting the diversity of Calvert Cliff chondrichthyans. The 

oldest was published by the Maryland Geological Survey on the fossils of the Maryland 

2 The Cartilaginous Fishes 

(Chimaeras, Sharks, and Rays) 

of Calvert Cliffs, Maryland, 

USA

Bretton W. Kent

Instructor, College of Computer, Mathematical 

and Natural Sciences, 3142 Plant Sciences Building, University of Maryland, College Park, Maryland 20742, USA.

Correspondence: bkent@umd.edu

Received 1 May 2015; accepted 25 August 2017.
4 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Miocene (Eastman, 1904). Later works included Leriche (1942), 

McLennan (1971), Ashby (1986), Kent (1994), Müller (1999), 

Vokes et al. (2000), and Visaggi and Godfrey (2010). 

Historical Context

Elasmobranchs have a long, complex evolutionary history 

(Compagno, 1990b; Maisey et al., 2004; Wilga et al., 2007). 

Following the loss of a number of elasmobranch genera at the 

end of the Cretaceous, elasmobranchs reradiated during the 

early Paleocene (Danian) and attained a high diversity by the 

Eocene, which was correlated with elevated global temperatures. 

Elasmobranch diversity then declined during the late Paleocene 

(Guinot et al., 2012), coinciding with a prolonged period of severely depressed global temperatures in the middle Oligocene. 

During the late Oligocene and early Miocene changes in oxygen 

isotope readings are consistent with rapidly increasing global 

temperatures. Simultaneously, global CO2 levels increase until 

they are comparable to those of the Holocene (Zachos et al., 

2001; Thomas, 2008; McGowran et al., 2009; Potter and Szatmari, 2009). The sediments of Calvert Cliffs were deposited during this period of increasing temperature and represent the most 

recent period of evolution in elasmobranch communities (Guinot 

et al., 2012). The end of the Neogene began with an episode of 

global cooling 3.6–2.0 mya in the Pliocene (McGowran et al., 

2009) and ended with a major turnover in marine biotas 2–1 

mya (Chapman, 2000; Jackson and Johnson, 2000). 

During the Neogene chondrichthyan faunas underwent 

two fundamental changes, driven by morphological diversification in the elasmobranchs. The first of these is a modernization 

of neritic and pelagic elasmobranch faunas. Prior to the Neogene diversification of sharks, these faunas are dominated by 

FIGURE 2.1. Temporal changes in tooth morphology from the Late Cretaceous through the Holocene of the Mid-Atlantic states of the 

eastern United States based on the presence or absence of cusplets and serrations. Data were compiled from Cappetta (1987), Kruckow and 

Thies (1990), Kent (1994), Müller (1999) and from unpublished data collected by Meredith Phillips (Master of Chemical and Life Sciences 

Program, University of Maryland, College Park). 
NUMBER 100 • 4 7

sharks with tearing-type dentitions consisting of teeth with tall, 

slender crowns and accessory cusplets. Teeth of this morphology are adapted for grasping and restraining small, active prey 

(Cappetta, 1987; Kent, 1994; Williams, 2001). By the late Oligocene and early Miocene shark faunas have a more complex 

mixture of tooth morphologies comparable to that of the Holocene (Figure 2.1). This change is partially correlated with a 

fundamental shift from faunas dominated by lamniforms to one 

dominated by carcharhiniforms (Leriche, 1942; Maisey, 1984; 

Purdy, 1998b; Visaggi and Godfrey, 2010). Diversification in the 

carcharhiniforms was particularly pronounced in the carcharhinids, a family with a number of medium to large sharks that rose 

to prominence in tropical littoral habitats. The carcharhinids 

first appeared in the early Eocene and diversified during the explosive adaptive radiation of marine invertebrates and teleosts 

during the Paleogene (Musick et al., 2004; Alroy et al., 2008; 

Santini et al., 2009; Friedman, 2010; Vermeij, 2011; Sorenson 

et al., 2014). Many carcharhinids have a cutting-clutching-type 

dentition, with serrated, bladelike teeth in the upper jaw and 

slender, erect teeth in the lower jaw. Such dentitions are better 

at gouging chunks of flesh from prey and are more versatile, allowing sharks to handle a broader range of prey types and sizes 

(Cappetta, 1987; Kent, 1994; Williams, 2001). Others, such as 

the tiger sharks (Galeocerdo) evolved specialized cutting dentitions with acutely notched distal margins of the crowns that are 

capable of efficiently handling many different prey types (Motta, 

2004). Carcharhinid teeth also represent a shift in the biomechanical properties of the teeth from the taller, narrower teeth 

of lamniforms that functioned like cantilevered beams in both 

puncture and draw movements to lower, wider teeth of many 

carcharhiniforms with notches in the cutting edges that concentrated forces on prey tissues during lateral head shaking (Whitenack et al., 2011). 

By the early Neogene the carcharhinids had become increasingly diverse and numerically abundant, although the lamniforms maintained a substantial presence, particularly among the 

largest species (Purdy et al., 2001; Musick et al., 2004; Visaggi 

and Godfrey, 2010). The shift toward a carcharhiniform-dominated fauna continued well after the Neogene, with the blue 

shark, Prionace glauca (carcharhiniform), eventually replacing 

the shortfin mako, Isurus oxyrinchus (lamniform), as the most 

abundant open-ocean shark within only the last few thousand 

years (Litvinov, 2007).

The second revolution in Neogene shark faunas was a 

burst of gigantism among large, macrophagous sharks. In this 

context, gigantism and giant species refer to the evolution of 

the largest species in a clade (McClain et al., 2015; Vermeij, 

2016; Ferrón et al., 2017) and are not without precedent in 

chondrichthyan faunas. Similar bouts of gigantism have previously occurred among the eugeneodontid “sharks” (Edestus, 

Helicoprion, Parahelicoprion) in the Permian (Merino-Rodo 

and Janvier, 1986; Grogan and Lund, 2004; Mutter and Neuman, 2008; Lebedev, 2009; Tapanila et al., 2013) and the lamniform sharks in the Cretaceous (Cardabiodon, Cretolamna, 

Cretoxyrhina, Leptostyrax, Squalicorax; Shimada, 1997, 2007; 

Siverson, 1999; Rothschild et al., 2005; Siverson and Lindgren, 

2005; Cappetta, 2012; Frederickson et al., 2015) and the Paleogene (Carcharocles, Jaekelotodus, Macrorhizodus, Otodus, Palaeocarcharodon; Renz, 2002; Cappetta, 2012; Shimada et al., 

2016). Gigantism in Neogene macrophagous sharks differs from 

the previous ones by the independent evolution of large body 

size in a number of genera belonging to distantly related orders, 

including the hexanchiforms (Hexanchus), lamniforms (Alopias, 

Carcharocles, Carcharodon, Isurus, Megalolamna, Parotodus), 

and carcharhiniforms (Galeocerdo, Hemipristis; Renz, 2002; 

Gallagher, 2006; Mutter and Neuman, 2008; Lebedev, 2009; 

Cappetta, 2012; Shimada et al., 2016). Neogene elasmobranch 

gigantism was also characterized by the evolution of the largest 

known macrophagous shark, Carcharocles megalodon. As with 

the diversification of the carcharhiniforms, gigantism in Neogene 

sharks had its origins within the Paleogene, when all of these 

genera of large sharks first appeared. 

Gigantism is typically correlated with elevated levels of benthic and planktonic diversity (Pyenson and Vermeij, 2016; Vermeij, 2016; Slater et al., 2017). This pattern appears to be the 

driving force for the Neogene giant sharks as well, where gigantism is correlated with a corresponding diversification of large 

prey (i.e., cetaceans; pinnipeds; sirenians; scombrid, xiphiid, and 

istiophorid teleosts; and lamniform, carcharhinid, and myliobatiform elasmobranchs; Domning, 1978; A. P. Martin, 1995; Fierstine, 1998; Purdy et al., 2001; Walsh and Naish, 2002; Musick 

et al., 2004; Ehret, 2010; Boessenecker, 2011, 2013; Cappetta, 

2012; Gottfried et al., 2012; Maisey, 2012; Santini and Soreson, 2013; Sorenson et al., 2014; Aguirre-Fernández et al., 2016; 

Valenzuela-Toro et al., 2016). However, much of this proliferation of giant sharks appears to be due to two specific groups of 

large prey, the advanced cetaceans and pinnipeds. Both of these 

groups radiated and diversified from the Oligocene through the 

early Pliocene in middle latitudes. Beginning in the late Pliocene, 

diversity in both of these groups shifted to higher latitudes (Deméré et al., 2003; Arnason et al., 2006; Adnet and Martin, 2007; 

Marx and Uhen, 2010; Klimley, 2013:38; Kelley and Pyenson, 

2015; Collareta et al., 2017a). The giant sharks of the Neogene 

were principally inhabitants of temperate oceans and of pelagic, 

rather than benthic, ecomorphotypes. Fast, pelagic sharks must 

swim continuously to ventilate the gills and, to accommodate 

these demands, have metabolic rates 5 to 10 times higher than 

those of comparable benthic sharks. The colder, largely oligotrophic polar waters would make the fast, pelagic lifestyle energetically unsustainable and prevent these sharks from expanding 

their ranges into higher latitudes (Priede et al., 2006; Seibel and 

Drazen, 2007; Aronson et al., 2007). Cold temperatures certainly do not preclude the presence of all large sharks since the 

sleeper sharks (Somniosus) are quite successful in polar seas. 

Sleeper sharks are at least as large as extant great white sharks 

(Carcharodon carcharias, maximum length of about 6 m; Castro, 2010), with the largest of the species, the Greenland shark 

(S. microcephalus), reaching at least 6.4 m and perhaps as much 
4 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

as 7.3 m (Compagno et al., 2005). But unlike C. carcharias and 

other fast, pelagic sharks, sleeper sharks are epibenthic and exceptionally sluggish, with maximum swimming speeds of about 

0.7 m/s (Watanabe et al., 2012). 

The inability of the fast, pelagic Neogene giant sharks to 

follow the geographic shift of cetaceans and pinnipeds toward 

the poles reduced the availability of suitable prey and was likely 

associated with their eventual decline and extinction (Adnet and 

Martin, 2007; Pimiento et al., 2016; Collareta et al., 2017a). 

This scenario is supported by research on extant C. carcharias

along the coast of Argentina. White sharks were abundant during the Pleistocene and Holocene in the temperate marine waters of the southwestern Atlantic but are rare today, a change 

attributed to extensive harvesting of pinnipeds by humans in 

these waters in the nineteenth and twentieth centuries. Pinnipeds 

are still abundant farther south in Patagonia, but these waters 

are too cold to support C. carcharias, which is limited to temperatures of 15°C–23°C (Cione and Barla, 2008). This thermal 

limit is consistent with the known contractile properties of mesothermic shark aerobic muscles (e.g., the shortfin mako, Isurus 

oxyrinchus), which become less efficient below 15°C–16°C than 

the muscles of ectothermic sharks (Donley et al., 2007). But this 

reduced efficiency of muscles in mesothermic sharks does not 

prevent them from brief excursions into colder water (Bonfil et 

al., 2005; Nasby-Lucas et al., 2007; Weng et al., 2007; Domeier 

and Nasby-Lucas, 2008; Johnson et al., 2009; Block et al., 2011; 

Jewell et al., 2013; Hoyos-Padilla et al., 2016; McAuley et al., 

2017). These studies have helped distinguish between resident 

and transient sharks that exhibit very different behaviors. Resident sharks engage in behaviors that are associated with active 

foraging, including relatively slow, area-restricted swimming and 

repeated, brief vertical dives. Conversely, transient sharks exhibit 

relatively rapid, directed swimming and make only infrequent 

changes in depth. The differences between these behaviors are 

important because resident sharks will have a significant impact 

on local prey communities, whereas transients will not. For example, detailed analysis of telemetry data on C. carcharias in 

the northwest Pacific (Block et al., 2011, figs. 3a, 4c) found that 

resident white sharks occur between 25°N and 35°N latitude. 

Records at higher latitudes were due to the occasional transient 

individual. Later studies (Jewell et al., 2013; Hoyos-Padilla et al., 

2016; McAuley et al., 2017) have reached similar conclusions 

in other geographic regions, including Australia, Mexico, and 

South Africa. 

Giant sharks also may have been precluded from higher 

latitudes by the evolution of the killer whales (Delphinidae; Orcinus) during the early Pliocene. The distribution of Orcinus extends farther into the colder waters near both poles than that of 

fast, macropelagic sharks. Further, they feed opportunistically on 

a variety of large prey, including cetaceans and pinnipeds, and 

can hunt cooperatively in social groups (Heyning and Dahlheim, 

1988; Lindberg and Pyenson, 2006; Pimiento and Balk, 2015; 

Vermeij, 2016). 

Unlike earlier, Mesozoic elasmobranch diversifications, the 

complex selachian faunas of the Neogene arose during a period 

of comparative stasis in higher elasmobranch taxa (Guinot et 

al., 2012). Instead, during the Neogene speciation and adaptive 

radiation occurred within genera that had already become established by the late Paleogene taxa (Guinot et al., 2012: fig. 3). 

Conversely, the end of the Neogene is characterized by the loss 

of relatively few, species-poor lamniform genera and the retention of species-rich carcharhiniform genera (A. P. Martin, 1995; 

Cappetta, 2012). 

Relevance of Calvert Cliffs Chondrichthyans

The Calvert Cliffs fossil beds were deposited during the 

transition from the early, expansive phase of the Neogene diversification in the early Miocene (early Burdigalian) to the more 

established chondrichthyan faunas of the middle and late Miocene (Langhian–early Tortonian). During this period, the combination of gigantism and modernization produced a complex 

chondrichthyan fauna that clearly foreshadowed the modern 

fauna while simultaneously containing a number of unique elements. The roughly 10-million-year (my) interval encompassed 

by the Calvert Cliffs fossil beds is eminently suited to examining 

a number of unresolved issues related to the Neogene chondrichthyans, including the mechanisms for the evolution of large size 

in sharks, trophic interactions in complex faunas, and speciation 

and adaptive radiations in different taxa. 

Evolution of Elasmobranch Gigantism

The evolution of gigantism in a diverse range of elasmobranchs in the Neogene is remarkable for both the size of the 

largest species and the diversity of genera involved but also raises 

a number of essential issues. The most obvious is that the evolution of large body size requires fundamental changes in scaling 

relationships and developmental pathways. Exactly how these 

changes came about has never been fully documented. 

In organisms, the relationship between size and functionality is nonlinear, producing a fundamental trade-off between 

shape and function. So to maintain function as size increases, 

shape must change, whereas to maintain shape, function must 

change (Schmidt-Nielsen, 1984; Koehl, 2000). This scaling of 

shape in most biological systems is fundamentally limited by the 

ability to deliver nutrients to, and remove wastes from, metabolically active tissues (Banavar et al., 2002) using fractal circulatory 

systems in large organisms (West et al., 1997, 2003; Brown et al., 

2005). These vascularization networks arise by iterative branching, with the number of capillaries in the circulatory system increasing as the three-quarter power of mass. With extinct sharks 

we are limited almost exclusively to teeth, so the evolution of 

tooth vascularization at very large sizes is an important consideration. Following this circulatory scaling relationship with 

body mass, the tooth of a hypothetical descendant species that 

was 4 times taller than those of its ancestral species will require 
NUMBER 100 • 4 9

almost 23 times as many capillaries as those of a smaller-toothed 

ancestor. Such a dramatic increase in the complexity of the capillary beds will require a substantial elaboration of tooth vascularization beyond the comparative simplicity of the ancestral 

species. Further, different lineages of sharks would be expected 

to independently solve the problem of large tooth size by evolving unique patterns of vascularization, which are most readily 

apparent as the distribution of nutrient foramina on the root 

surface of a tooth. At present, the complex interplay of scaling 

issues related to gigantism in the various taxa of giant Neogene 

sharks is little studied and poorly understood. The one study that 

has examined at least some aspects of these scaling issues found 

that Carcharodon and Carcharocles evolved fundamentally distinct ontogenetic solutions to the problems of larger tooth sizes 

(Nyberg et al., 2006: figs. 6,7). 

Trophic Interactions

Holocene shark communities lack the diversity of giant species present in Neogene paleocommunities and provide few insights into the question of how so many large shark species could 

be accommodated in the same area. Understanding the trophic 

interrelationships of Neogene giant sharks with each other and 

with the rapidly diversifying carcharhiniform sharks requires a 

fundamentally different approach. Several sources of information can be used to reconstruct feeding relationships, including 

(1) analogies with living species, (2) bite marks on prey species, 

and (3) associations of teeth with prey remains. All of these 

provide useful information, although each must be interpreted 

somewhat differently.

Tooth morphology analogies provide a means of directly 

comparing an extinct species with a living one (Siverson, 1992; 

Welton and Farish, 1993; Purdy et al., 2001), although there are 

two specific problems with such interpretations. First, the teeth 

will be similar, but not identical, in morphology, and even subtle 

differences can be important. The extant tiger shark (Galeocerdo 

cuvier) is a large, eurytrophic shark capable of eating an exceptional range of prey types (Compagno, 1984, 2002; Compagno 

and Niem, 1998). The tiger shark from Calvert Cliffs (G. aduncus) is so similar in morphology that Purdy et al. (2001) listed it 

as a junior synonym of G. cuvier. But it differs in two important 

respects; the teeth of G. aduncus are roughly half the size of 

those of G. cuvier and exhibit a higher degree of heterodonty 

than those of the living species. The difference is size would seem 

to be relatively inconsequential, except that the deflection force 

at the tip of the crown is proportional to the length of the crown 

raised to the fourth power (Koehl, 2000). Consequently, assuming geometric similarity, the teeth of the extant G. cuvier would 

have a deflection force 16 times greater than that of the extinct 

G. aduncus. This difference would have considerable consequences for diet choice in these two species. The more extensive 

heterodonty in G. aduncus further complicates any dietary reconstructions. Although many teeth in G. aduncus have broad 

crowns and resemble small versions of those of G. cuvier, other 

teeth are somewhat more delicate, with narrower crowns. Apical stress applied to food is inversely proportional to the radius 

of curvature of the coronal tip, so that narrow-crowned teeth 

will concentrate stress in a smaller area and more readily pierce 

compliant tissues than teeth with broader tips (Lucas, 1982; 

Evans and Sanson, 2003; Freeman and Lemen, 2007). Obvious 

differences exist in functional morphology between the broad 

and narrow tooth forms of G. aduncus, but how these ultimately 

affected prey selection remains unknown since the disposition 

of these teeth within the dentition (i.e., gradient monognathic 

heterodonty, dignathic heterodonty, or gynandric heterodonty) 

is unresolved. 

Bite marks are reasonably common on fossil bones, usually taking the form of deep incisions or gouges on prey hard 

tissues (Deméré and Cerutti, 1982; Mapes and Hansen, 1984; 

Cigala-Fulgosi, 1990; Schwimmer et al., 1997; Bianucci et al., 

2000, 2010; Neumann, 2000; Noriega et al., 2007; Cicimurri 

and Knight, 2009a; Kallal et al., 2010). Such marks can be difficult to assign to a specific species, although there are exceptions. 

Deméré and Cerutti (1982) were able to match the spacing of 

parallel grooves in the bite marks on a cetotheriid whale fossil 

with the serrations on the teeth of co-occurring Carcharodon 

sulcidens (junior synonym of C. carcharias). Bite marks produced by unserrated teeth are more difficult to assign to species, 

although with detailed analysis, plausible inferences are possible. 

Bianucci et al. (2010) examined smooth bite makes on a Pliocene 

cetacean. They artificially produced bite marks of Carcharodon 

hastalis (or C. plicatilis?) and Isurus oxyrinchus teeth but were 

unable to consistently distinguish between these two species. The 

size of the skeletal bite marks and their disposition in a dental arcade were more informative and were consistent with the larger 

Carcharodon species. In some rare cases, bite marks on softer 

materials can be definitively assigned to a shark species; Godfrey 

and Smith (2010) were able to match tooth marks on a crocodilian coprolite with the extinct tiger shark Galeocerdo aduncus. Govender (2015) examined bite marks on cetacean bone 

fragments and was able to distinguish bite marks produced by 

serrated teeth (C. carcharias and Carcharocles megalodon) and 

unserrated teeth (Isurus spp. and C. hastalis). 

Teeth embedded within prey skeletal elements (usually 

bones) are more informative since the teeth can be more easily identified to species (Rothschild and Martin, 1993; Everhart 

et al., 1995; Schwimmer et al., 1997; Shimada, 1997; Shimada 

and Everhart, 2004; Shimada and Hooks, 2004; Rothschild et 

al., 2005; Cicimurri and Knight, 2009a; Ehret et al., 2009b). If 

the entire tooth is present, identification is comparatively simple. 

Unfortunately, during feeding and fossilization the tooth may 

fracture, leaving only the tip of the crown embedded within the 

bone. This fracturing complicates tooth identification but still is 

more definitive than identifications based on bite marks alone. 

In some rare cases, prey parts may be preserved in shark teeth. 

A particularly intriguing example (Figure 2.2A,B) is a C. hastalis tooth (CMM-V-3990) from Calvert Cliffs completely penetrated by a myliobatiform caudal spine. What is unusual about 
5 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

this tooth is that the spine must have penetrated very early in 

the formation of this tooth, as the enameloid on both faces is 

thrown into folds around the spine. Further, a micro-computed 

tomography (micro-CT) scan (Figure 2.2C) shows no internal 

evidence of the spine within the osteodentin of the crown, although the medial vascular tubule normally present in this species (Figure 2.2D) has bifurcated around the original position 

of the spine. Presumably, prior to the final mineralization of the 

tooth, the material from the spine was resorbed and remodeled 

within the osteodentin, leaving only the remnants embedded in 

the enameloid of the labial and lingual faces and the modified 

vascularization pattern. 

Associations of shark teeth with prey skeletons are also 

well documented in the paleontological literature (Cione and 

Medina, 1987; Repenning and Packard, 1990; Druckenmiller 

et al., 1993; Bigelow, 1994; Schwimmer et al., 1997; Shimada, 

1997; Bianucci et al., 2000; Cicimurri and Knight, 2009a). The 

presumption is that these are teeth shed during feeding. In situations where the associated teeth are consistent with the species 

inferred from bite marks or embedded teeth (e.g., Cicimurri and 

Knight, 2009a) this interpretation is plausible. But in the absence 

of such corroborating evidence it is difficult to know whether the 

teeth were functionally associated with the skeleton or present 

by coincidence. Background data on the abundance and diversity 

of shark teeth in the same stratum as the skeleton could help 

such difficulties but are rarely available. A notable exception is 

a study on the Cretaceous lamniform Squalicorax (Schwimmer 

et al., 1997); Squalicorax teeth were uncommon components of 

the local shark fauna but became numerically dominant adjacent 

to vertebrate skeletal remains. Unfortunately, other factors, such 

as predators attracted to the swarm of scavengers around the 

carcass or the postmortem deposition of teeth by hydraulic sorting, could also produce a concentration of teeth near a skeleton. 

The problem with all of these sources of biological evidence 

is that it is frequently difficult to distinguish between active predation and the scavenging of carcasses. Certainly, the presence of 

small shark teeth or bite marks with a large prey would preclude 

predation and be more consistent with scavenging. Large teeth 

and bite marks associated with a skeleton are more difficult to 

interpret but can be deduced with careful observations. Ehret et 

al. (2009b) interpreted a Carcharodon tooth embedded in a mysticete mandible as the result of scavenging, as this body region is 

normally avoided by extant white sharks during attacks on living 

cetaceans. More direct evidence is sometimes present where the 

bite is not immediately fatal and the prey survives long enough 

to physiologically respond to skeletal damage. Rothschild et al. 

(2005) were able to attribute shark bites in mosasaur caudal 

vertebrae to a failed attack by Cretoxyrhina because the bite 

marks and an embedded tooth tip are spatially associated with 

abscesses in the bone produced by an inflammatory response. 

Likewise, Kallal et al. (2010) attributed similar bone damage in 

a Pliocene cetacean to an attack by a lamniform shark. 

A C B

D

FIGURE 2.2. (A–C) Carcharodon hastalis left upper anterior tooth penetrated by a myliobatiform spine (CMM-V-3990; beds 3/4, Pamunkey 

River, Virginia; images provided by Stephen Godfrey; 1 cm scale bar). (A) Labial view. (B) Lingual view. (C) Single-image micro-CT scan of 

CMM-V-3990 tooth interior. (D) Single-image micro-CT scan of undamaged C. hastalis tooth. CT images courtesy of the University of Texas 

High-Resolution X-ray Computed Tomography facility.
NUMBER 100 • 5 1

Species Recognition and Identification

The diversification of the elasmobranchs, especially the carcharhiniforms, during the Neogene creates numerous difficulties 

in understanding speciation events and in identifying individual 

species. Biologists have an enormous advantage in this regard 

when studying extant species. Not only can they examine wholebody morphology, they can directly observe reproduction and 

feeding and more easily document geographic ranges. These 

observations produce species descriptions that are both comprehensive and detailed. Further, when there are doubts about 

species identity, molecular techniques can be used to separate 

closely related species. These techniques are particularly useful, 

as they allow researchers to define biological species on the basis 

of the degree of interbreeding that has occurred. Paleontologists 

must work with far less information, typically limited to morphological features. As a result, paleontologists work with morphologically defined species (i.e., morphospecies), rather than 

true biological ones. 

The most rigorous interpretations of fossil chondrichthyans are based on articulated skeletons and dentitions (e.g., Shimada, 2007; Ehret et al., 2009a), as these provide evidence of 

the whole-body morphology. These specimens are exceptionally 

rare, as the tesserate cartilage that makes up the chondrichthyan 

skeleton is easily crushed and dissociated during fossilization 

(Maisey, 2012). Even under ideal conditions, these specimens 

are usually incomplete but can still provide useful information 

about hard tissues and allow more rigorous reconstructions of 

the missing soft tissues. They can also help correct misconceptions about higher taxonomic assignments of extinct species 

(Shimada, 2005; Shimada et al., 2009). 

In the absence of intact skeletons and dentitions, wholebody reconstructions of fossil sharks and rays (Gottfried et al., 

1996; Kent, 1999c; Shimada et al., 2010) are fraught with difficulties. Unfortunately, since the majority of extinct species are 

known only from isolated teeth, reconstructions must rely on 

analogies with extant species. Measurements on extant species 

can provide more rigorous evaluations of morphology that can, 

in turn, be used to predict the most likely morphology of extinct species. But relying too heavily on extant forms produces 

an intellectual “keyhole” through which we obtain a severely 

restricted view of the possible morphologies and lifestyles available to extinct forms (Bengtson, 1987, 2001) and constrains extinct animals to be generic versions of extant ones (Pagel, 1991). 

Further, this approach overlooks critical evolutionary innovations not evident in the extant analogs. As discussed above, this 

modern bias is particularly troublesome where extinct species 

are substantially larger than extant ones. Research on the Late 

Cretaceous shark Cretoxyrhina mantelli (Shimada, 1997) demonstrates the dangers of ignoring the admonition against relying 

too heavily on extant analogs. Earlier dentition reconstructions 

of this shark were based on analogies with the extant lamniform, 

Lamna nasus (Eastman, 1895; Welton and Farish, 1993). The 

teeth of C. mantelli are also substantially larger than those of 

L. nasus (2 versus 6 cm; Cappetta, 1987). The developmental 

problems of producing both these larger teeth and the sharks 

with larger bodies cannot be simply ignored and may require 

evolutionary innovations not present in the extant species. 

The abundance of isolated teeth present in the unconsolidated sediments of Calvert Cliffs greatly simplifies collecting, 

so that huge samples can be obtained surprisingly quickly. The 

ease of collection means that the range of morphological variability within a species is easily documented, even for relatively 

rare species. But because the teeth are almost entirely collected 

as isolated specimens, this variability in form can be difficult to 

interpret in an unambiguous way. 

Smith (1994:20–22) proposed a two-step process for critically evaluating and documenting fossils where sample sizes 

large enough for statistical analysis are available. The first step is 

to use a range of bivariate plots of morphological features to assess variability. By testing various morphological features against 

each other informative characters can be identified. When performed over a sufficiently large size range, these plots can also 

detect ontogenetic changes and sexual dimorphism. Smith’s second step was to compare the values for this sample with other 

samples to assess the number of species present. This comparison 

establishes the degree of morphological overlap and provides objective criteria for documenting and interpreting morphospecies 

in the fossil record.

Figure 2.3 is a bivariate plot of data for teeth from three 

alopiids, the small-toothed Alopias cf. A. vulpinus and two giant 

species, A. grandis and an unnamed species with serrated cutting 

edges (see this chapter’s Addendum) based on teeth housed in the 

Smithsonian Institution’s National Museum of Natural History, 

the Calvert Marine Museum, and the author’s reference collection at the University of Maryland at College Park. Figure 2.3A 

compares teeth of these three species with respect to tooth height 

and root width. Not unexpectedly, the teeth of the two giant 

species are noticeably larger than those of the small-toothed A. 

cf. A. vulpinus. There is no overlap between A. cf. A. vulpinus

and the two giant species but extensive overlap between the two 

giant species. The height-width regression line for A. cf. A. vulpinus (dashed line), when extended to larger tooth sizes, demonstrates that the teeth of the giant Alopias species are consistently 

taller for a given tooth width than would be expected by simple 

allometric scaling. But extensively extrapolated data should always be viewed with some suspicion since even slight changes in 

the data for A. cf. A. vulpinus could produce a marked change in 

the regression line and interpretations about the tooth morphology in the giant species. 

A more direct approach to compare the three species is to 

use derived metrics that have higher information content. Figure 2.3B compares teeth of these three species on the basis of 

relative elevation (i.e., the ratio of the tooth height to the root 

width) and relative coronal width (the ratio of the mid-crown 

width measured at the height of the inflection point on the distal 

cutting edge to the root width of the tooth). Both metrics are 

based on ratios, and size has been suppressed as a confounding 
5 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

variable. Teeth of A. cf. A. vulpinus are morphologically very 

distinct from each of the giant species in both elevation (oneway analysis of variance [ANOVA] with pairwise Tukey honestly 

significant difference [HSD] tests; F2,29 = 17.2, P < 0.0001; HSD 

P < 0.01) and relative coronal width (F2,29 = 33.3, P < 0.0001; 

HSD P < 0.01), although differences are less pronounced than in 

Figure 2.3A. The teeth of the serrated species tend to be somewhat taller and more bladelike than those of A. grandis, although 

variability clouds for these two species broadly overlap, and neither relative elevation nor relative coronal width is statistically 

different between the two giant species (HSD P > 0.05). 

This discussion of tooth morphology in Alopias is overly 

simplistic in several respects. The most obvious is that the teeth 

for the two giant species represent a substantial, but incomplete, 

subset of their size range, as no teeth from smaller individuals 

are included. Of particular importance are morphological comparisons between similarly sized teeth of A. cf. A. vulpinus and 

juveniles of the two giant species. A second complication is that 

alopiids have relatively mild heterodonty, and teeth from different positions in the jaws can be compared with little difficulty. 

Sharks with more extensive heterodonty have teeth with several 

different morphologies that must be analyzed separately. Finally, 

the alopiids are not particularly speciose compared to other 

families, such as the carcharhinids. So although bivariate plots 

can provide considerable clarity when only a few species are involved, the presence of numerous species with high morphological overlap is more troublesome. 

Part of the difficulty in more diverse species complexes is 

that not all morphometric measurements are equally informative 

and it is not always obvious by visual inspection of teeth which 

metrics will be the most useful. To be practical, the bivariate 

plot technique relies on using a large number of morphometric 

measurements in order to determine which are most informative. 

Reinecke et al. (2005, 2011) have successfully employed this 

technique to rigorously test differences between closely related 

species of Oligocene and Miocene sharks. Unfortunately, simple 

measurements on teeth may not provide clear resolution in some 

cases, and more sophisticated metrics must be used to generate 

the bivariate plots (e.g., Naylor and Marcus, 1994; Adnet, 2006; 

Chandler et al., 2006; Nyberg et al., 2006; Shin, 2010; Whitenack and Gottfried, 2010). 

Two closely related species are likely to share some similarities in morphology, so simply finding some specimens from 

different samples that appear to be nearly identical in form is 

FIGURE 2.3. Bivariate plots of tooth morphology in Calvert Cliffs alopiids. A cross (×) = Alopias cf. vulpinus; solid circle (•) = A. grandis; 

open circle (°

) = serrated Alopias (see this chapter’s Addendum). (A) Tooth height versus root width. Reduced major axis regression (dashed 

line) extrapolated from A. cf. vulpinus; tooth height = 0.77(root width) + 0.76, R2

 = 0.922, N = 9. (B) Relative elevation versus relative coronal 

width; see text for details.
NUMBER 100 • 5 3

not unexpected. The real problem is in determining the extent of 

morphological overlap. Extensive overlap would be indicative 

of a single species and would justify placing a fossil species and 

an extant species in synonymy. A reduced level of overlap would 

increase the likelihood that two species were present, and the 

application of the extant species name to the fossil species would 

be inappropriate. This distinction is essentially a statistical one 

(Hammer and Harper, 2006:8–19); what is the probability that 

a sample of fossil teeth and a sample of extant teeth are from 

the same species? Unfortunately, the application of extant names 

to fossil specimens typically has been based on a visual inspection of specimens to assess the degree of morphological overlap. 

This procedure is adequate only where the relevant characters 

are based on the presence or absence of a specific structure (e.g., 

the serrations of the previously unnamed giant Alopias). Where 

differences are based on magnitude, delineating species is far 

more difficult. In these cases, the most reliable method is to utilize morphometric procedures.

For much of the history of research on fossil elasmobranchs, 

species names have been erected on relatively meager evidence. 

The complex interactions of ontogenetic, sexual, and positional 

differences in morphology produced numerous situations where 

a single species was identified by multiple names. The problem is 

compounded by species being erected with a limited number of 

specimens, so that multiple names may have been erected for the 

same species; for example, Marsili et al. (2007) list seven junior 

synonyms for the specific name of Parotodus benedenii, a species with relatively mild heterodonty. This synonymy produced 

a confusing proliferation of species names and undoubtedly produced numerous examples of having too many species names 

for the number of species actually present. In reaction to this 

taxonomic nightmare, a recent trend in the taxonomy of Neogene fossil sharks has been to suppress most fossil specific names 

in favor of placing these in synonymy with extant species (e.g., 

Purdy et al., 2001; Ward and Bonavia, 2001; Marsili, 2007a,b). 

This practice is conservative and minimizes the perpetuation of 

unnecessary names. It also reduces a number of species names to 

junior synonyms and helps clarify the broad evolutionary framework for the extant sharks. This practice also produces a new 

set of problems since it implicitly assumes that Neogene sharks 

have exhibited evolutionary stasis. A rapidly growing body of 

evidence suggests that such stasis is unlikely and that numerous taxa have diversified during the Neogene and Quaternary: 

Squatina (two bursts of speciation 18–15 mya and 3.5–2.9 mya; 

Stelbrink et al., 2010), orectolobids (three bursts in the early late 

Miocene, late Miocene to early Pliocene, and late Pliocene to 

early Pleistocene; Corrigan and Beheregaray, 2009), Mustelus

(Miocene; Boomer et al., 2012), Carcharhinus (23–9 mya; A. P. 

Martin 1995), Negaprion (about 14 mya; Schultz et al., 2008), 

sphyrnids (late Miocene to middle Pliocene; Lim et al., 2010), rajids (late Miocene to Pleistocene; Valsecchi et al., 2005; Pasolini 

et al., 2011), and Potamotrygon (relatively recent and ongoing; 

Toffoli et al., 2008).

When the last major reviews of Calvert Cliffs chondrichthyans (Kent, 1994; Müller, 1999) were published, the available 

research on fossil chondrichthyans was largely descriptive and 

qualitative. This information provided extensive and detailed 

documentation of stratigraphic and geographic ranges, as well as 

relevant diagnostic characters for distinguishing different taxa. 

But such research was inherently limited by problems of sorting 

through the immense clouds of variability to determine which 

tooth attributes are informative and which are not. Over the past 

two decades, newer technologies and methodologies have produced data that are more quantitative and rigorous on a broad 

range of fossil vertebrates, including chondrichthyans. When 

coupled with the large body of earlier descriptive work, these 

analytical tools have triggered an almost explosive growth in our 

understanding of the remarkable fossil record of chondrichthyans, including those of Calvert Cliffs. 

The following represents the current state of our knowledge 

of the fossil cartilaginous fishes of Calvert Cliffs. This record is 

extensive, detailed, and part of an ongoing, wide-ranging effort 

by numerous individuals to more fully understand this dramatic 

period in chondrichthyan evolution. 

Museum Abbreviations

CMM Calvert Marine Museum, Solomons, Maryland, USA

NHMUK Natural History Museum, London, UK

UMCP author’s reference collection at the University of 

Maryland, College Park, Maryland, USA

USNM National Museum of Natural History (formerly U.S. 

National Museum), Smithsonian Institution, Washington, D.C., USA

Statistical Analysis

Statistical analyses were based on the recommendations in 

Sokal and Rohlf (1995) and Hammer and Harper (2006). Basic 

statistical calculations (t-test, analysis of variance, reduced major 

axis regression) were performed using the PAST (Palaeontological Statistics, version 3.01) statistical computation software 

(http://folk.uio.no/ohammer/past/). The Crawford-Howell modified t-test, an adaptation of that proposed by Sokal and Rohlf 

(1995:227–229) for comparing a single specimen with a sample, 

was computed using the downloadable Singlims_ES.exe calculator (http://homepages.abdn.ac.uk/j.crawford/pages/dept/psychom.

htm; Crawford et al., 2010). Statistical results are expressed as 

exact, two-tailed probabilities, except as noted in the text.

Taxonomy

Taxonomy follows that of Stahl (1999) for holocephalans 

and Cappetta (2012) for elasmobranchs, except where noted in 

the text. 
5 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

SYSTEMATIC PALEONTOLOGY

Subclass Holocephali Bonaparte, 1832

Order Chimaeriformes Obruchev, 1953

Ratfishes – Chimaeriformes

The chimaeroid fishes are an ancient group of cartilaginous 

fishes. Extant chimaeroids, or ratfishes, are found worldwide in 

deepwater marine habitats, although the group was more widespread on continental shelves during the Mesozoic and early Cenozoic (Averionov and Popov, 1995). The fossil record consists 

primarily of isolated dental plates, which occur in three pairs, with 

two pairs (vomerine and palatine) in the upper jaw and one pair 

(mandibular) in the lower jaw. Each plate is composed of acellular bone with pleromin-reinforced areas, referred to as tritors. 

Pleromin is a unique hard tissue found only in chimaeroids that 

strengthens the tritors, which are the functional surfaces for processing food (Lund et al., 1992). The pleromin in tritors can be 

either laminated (=tightly packed sheets of pleromin) or vascular 

(=less compact masses of pleromin). The number and distribution 

of tritors, along with their pleromin structure (laminated versus 

vascular) on different dental plates, are diagnostic for chimaeroid 

taxa. Terminology for identifying and describing tritors is based 

on Ward and Grande (1991), Patterson (1992), and Stahl (1999). 

Unfortunately, isolated chimaeroid tooth plates can be difficult to correctly identify, as they can be quite variable. Extant 

species that have been examined in detail have been found to 

have a high level of intraspecific variation, including that between individuals and ontogenetic changes resulting from feeding-related wear (Stahl, 1999:15–16). 

Dorsal spines and egg cases of chimaeroids are also occasionally collected but are difficult to assign to a specific species 

unless found in association with dental plates. 

Family Callorhynchidae Patterson, 1965

Chimaeroids in the family Callorhynchidae from Calvert 

Cliffs are known only from isolated dental plates of two genera, 

Edaphodon and Ischyodus. The two genera can be separated by 

several characters, including the number and disposition of tritors and the presence or absence of a descending lamina. Unfortunately, these characters are somewhat variable, and additional 

variation during ontogeny, evolutionary changes over the history 

of these genera, and due to tritoral wear can complicate identifications of these two genera (Stahl, 1999:127). 

Genus Edaphodon Buckland, 1838

Edaphodon cf. E. sweeti Chapman 

and Pritchard, 1907

FIGURE 2.4A,B

Synonymy follows Kemp (1991) and Stahl (1999).

Description. The description of Edaphodon in Calvert 

Cliffs is based on two well-preserved mandibular plates (CMMV-1386 and USNM 546145). The plates are thick, robust, and 

anteroposteriorly elongated into a beak. The symphyseal surface is narrower adjacent to the beak and broadens distally. A 

laminated tritor is typically present on the beak of Edaphodon

mandibular plates but is not present in either of the specimens 

examined. Three principle tritors are present, anterior and posterior outer tritors and a middle tritor. The middle tritor is divided longitudinally, a condition known to occur in this genus 

(Stahl, 1999:138). The sizes and shapes of the tritors of the two 

illustrated specimens are quite varied and likely result from differences in premortem wear; Figure 2.4A is largely intact and has 

little wear, whereas wear is much more extensive in Figure 2.4B. 

Discussion. Edaphodon fossils occur from the Cretaceous through Pliocene of Africa, Australia, Europe, and North 

America. They are particularly abundant during the Cretaceous 

and Paleogene, but by the Neogene only a few Edaphodon species have been described, including E. antwerpiensis Leriche, E. 

mirabilis Chapman and Cudmore, E. pliocenicus Carraroli, and 

E. sweeti Chapman and Pritchard (Stahl, 1999). On the basis of 

only a few specimens, any identification of Calvert Cliffs Edaphodon is tentative, but they appear to be closest to E. sweeti 

(Kemp, 1991: pl. 40C; Stahl, 1999: fig. 144B). 

Stratigraphic and Geographic Ranges. Edaphodon tooth plates are very rarely collected from Calvert Cliffs 

and are known only from the two specimens shown in Figure 

2.4A,B. The only other records of E. sweeti are from the late Miocene to the early Pliocene of Australia (Kemp, 1994; Stahl, 1999). 

Genus Ischyodus Egerton, 1843

Ischyodus sp.

FIGURE 2.4C

Description. The illustrated specimen is a robust plate 

with two oblong, closely spaced tritors. The plate, although 

fragmentary and worn, is consistent with the triangular palatine plate of the genus Ischyodus, with both the outer tritor and 

middle tritor present. 

Discussion. Many chimaeroid tooth fragments from 

Calvert Cliffs are much less complete than the mandibular plates 

in Figure 2.4A,B. The specimen in Figure 2.4C is more typical 
NUMBER 100 • 5 5

and can be difficult to identify to genus. This thick specimen is 

comparable with those of Ischyodus (e.g., Stahl, 1999: fig. 138, 

E2 and E3; Otero et al., 2012: fig. 3 V1). Ischyodus fossils are 

known from the Middle Jurassic through the Pliocene. Like Edaphodon, Ischyodus has reduced diversity by the Neogene, and 

only two species (I. dolloi Leriche and I. mortoni Chapman and 

Pritchard) are known (Stahl, 1999). 

Stratigraphic and Geographic Ranges. Plates 

such as the one shown are only very rarely collected from Calvert Cliffs, and only the illustrated specimen was available for 

detailed study. Too few specimens are known to determine any 

distributional patterns.

Family Chimaeridae Bonaparte, 1831

Genus Chimaera Linnaeus, 1758

Chimaera sp.

FIGURE 2.4D

Description. Plate fragments are thin and fragile. The 

occlusal surface is undulating with comparatively thick tritoral 

ridges alternating with thin intertritoral dentine. There is little 

wear on either the tritors or the intertritoral dentine. The latter 

has obvious incremental growth lines. 

Discussion. The two tooth plate fragments tentatively assigned to the genus Chimaera are quite thin and fragile, compared to the very robust tooth plates of Edaphodon

and Ischyodus. The growth lines, which are quite obvious on 

these fragments, have not been observed on either Edaphodon

or Ischyodus from Calvert Cliffs. Their assignment to Chimaera

is based on their general resemblance to this genus (e.g., Stahl, 

1999: fig. 161B; Laurito Mora, 2008: fig. 1). The fragmentary 

nature of the available specimens precludes assigning them to a 

specific jaw position. 

Stratigraphic and Geographic Ranges. Only 

two specimens are known for this species, although the illustrated 

fragment (Figure 2.4D) was found in situ (bed 14). The genus Chimaera is extant with seven species but does not presently occur 

in the Mid-Atlantic region. The diet consists of crustaceans, mollusks, and small teleosts and in at least one species changes with 

larger body sizes (Didier, 2002, 2004; Moura et al., 2005). 

Subclass Elasmobranchii Bonaparte, 1838

Superorder Selachimorpha Nelson, 1984

Order Hexanchiformes de Buen, 1926

Family Hexanchidae Gray, 1951

Cow Sharks – Hexanchidae

The hexanchids, or cow sharks, are generally considered to 

be relatively primitive sharks that have only a single, posteriorly 

A B

C

D

FIGURE 2.4. Chimaeroid tooth plates (1 cm scale bar). (A) Edaphodon cf. sweeti right mandibular plate; oral view (CMM-V-1386; Parkers 

Creek, Maryland). (B) Edaphodon cf. sweeti right mandibular plate; oral view (USNM 546145; Scientists Cliffs, Md.). (C) Ischyodus sp. right(?) 

palatine plate; oral view (CMM-V-1588; Scientists Cliffs, Md.). (D) Chimaera sp. indeterminate position; oral view (CMM-V-1385; Parkers 

Creek, Md.). 
5 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

positioned dorsal fin, an anal fin, six or seven pairs of gill slits, 

and weakly calcified vertebral centra. The dentition has very 

distinctive teeth and pronounced dignathic heterodonty. The 

subterminal mouth has large, comblike lower teeth with an acrocone and numerous accessory conules that become progressively 

reduced distally. The teeth of the upper jaw are smaller and exhibit monognathic heterodonty with substantial changes in morphology along the jaw (Cappetta, 1987, 2012). The distinctive 

teeth of hexanchids have relatively poor cutting ability compared 

to other sharks, such as carcharhinids, but have greater durability (Corn et al., 2016). 

The identification of fossil hexanchids is complicated by 

extensive ontogenetic and individual variability (Kemp, 1978; 

Cione and Reguero, 1994; Herman et al., 1994a). A detailed 

morphometric analysis of fossil and Holocene Hexanchus anterolateral teeth (Adnet, 2006) has helped clarify ontogenetic 

and phylogenetic variation in this genus and provides a practical 

means of evaluating other hexanchids. 

There are two hexanchid genera known from Calvert Cliffs, 

a seven-gilled cow shark (Notorynchus) and a six-gilled cow 

shark (Hexanchus). 

Genus Notorynchus Ayres, 1855

Notorynchus primigenius (Agassiz, 1843)

FIGURE 2.5A–E

Synonymy follows Reinecke et al. (2011).

Description. The distinctive saw- or comblike lower anterolateral teeth (Figure 2.5A) are broader than high, with an acrocone and five or six distal conules of progressively smaller size. 

The acrocone is only slightly larger than the adjacent first distal 

conule and has recurved serrations basally on the mesial cutting 

edge. The root is rectilinear and compressed, with a weakly concave mesial margin. In profile, the root is wedge shaped, thickest 

at the coronal base, and tapering to a thin basal margin. Both 

the labial and lingual root faces are flat, but although the labial face is smooth, the lingual face typically has numerous, fine 

vertical grooves. Pathological lower anterolateral teeth are occasionally collected, and these teeth frequently have larger, more 

pronounced mesial serrations (Figure 2.5B).

Lower, medial teeth also have multiple conules but are 

nearly symmetrical (Figure 2.5C). The central conule is the largest on the tooth but is inclined laterally. Lateral to the largest conule there are three to five additional conules of decreasing size 

on each shoulder. The root is compressed, with a beveled profile 

and fine vertical grooves on the lingual face. 

Upper teeth are more variable in morphology. Upper anterior teeth (Figure 2.5D) have a crown consisting of a single 

conule that is erect to weakly distally inclined. The root is robust 

and quadrate. In profile, the crown is lingually arched, and the 

lingual face of the root is steeply beveled. Upper anterolateral 

teeth (Figure 2.5E) retain the enlarged principal conule. Anterolateral row groups close to the anterior teeth have only a single 

distal conule, whereas more posteriorly positioned teeth become 

progressively broader with two to five distal conules. The mesial cutting edge is somewhat variable but usually has a series of 

basal serrations or, on some teeth, a single small conule. The root 

is similar to that of the lower anterolaterals, although the mesial 

margin is weakly convex, rather than concave. 

Discussion. Purdy et al. (2001) regarded N. primigenius

as a junior synonym of the extant N. cepedianus on the basis of 

the overall similarity in tooth morphology, although, as yet, no 

detailed morphometric analysis has been performed to test this 

assertion. However, the geographic distribution of N. cepedianus

is quite unlike the Neogene N. primigenius, with the former species generally restricted to cool temperate waters, whereas the 

latter is also widely distributed in warm temperate and tropical 

waters (Reinecke et al., 2011). On the basis of these geographic 

differences, Miocene Notorynchus from Calvert Cliffs are, for 

the present, retained in N. primigenius. 

The largest lower anterolateral teeth of N. primigenius are 

about 30 mm wide. On the basis of comparisons with the extant 

species N. cepedianus Purdy et al. (2001:84) estimated the body 

length for teeth of this size to be 3–4 m. This size compares to 

a maximum length of 2.9 m for N. cepedianus (Van Dykhuizen 

and Mollet, 1992; Ebert, 2002; Compagno et al., 2005). 

Stratigraphic and Geographic Ranges. This is 

the more common of the two cow sharks in the Chesapeake Group 

with more than 40 specimens examined for this study. Like most 

fossil hexanchids, it is represented primarily by the large lower anterolateral teeth. Notorynchus primigenius is most common along 

the northern end of Calvert Cliffs and has been collected in situ 

for beds 3–5, 8, and 10–14. This species is also known from MidAtlantic exposures of the slightly older bed 1 of the Calvert Formation. This species (sometimes listed as N. cepedianus) has been 

reported from the late Oligocene (Chattian) through late Miocene 

(Messinian) of Florida(?), Maryland, North Carolina, and Virginia, as well as Australia, Austria, Azores, Belgium, Denmark, 

France, Germany, Japan, the Netherlands, Poland, Portugal, Slovakia, Spain, and Switzerland (Radwański, 1965; Antunes and Jonet, 

1970; van den Bosch et al., 1975; Cappetta, 1987, 2012; Kemp, 

1991; Kent, 1994; Yabumoto and Uyeno, 1994; Müller, 1999; 

Hulbert, 2001; Purdy et al., 2001; Reinecke et al., 2008, 2011; 

Visaggi and Godfrey, 2010; Ávila et al., 2012; Bor et al., 2012). 

The extant N. cepedianus is a wide-ranging, littoral eurytrophic shark of cool temperate, coastal waters worldwide, with 

the exception of the North Atlantic and Mediterranean. These 

robust, strong-swimming sharks are known to feed on a diverse 

range of prey (elasmobranchs, teleosts, pinnipeds, and carrion), 

with an ontogenetic shift in dietary preferences from teleosts 

to elasmobranchs to pinnipeds with increasing body size. The 

maximum body length of N. cepedianus is at least 2.9 m (Compagno, 1984, 1990b, 2002; Last and Stevens, 1994; Ebert, 2002; 

Compagno et al., 2005).
NUMBER 100 • 5 7

Genus Hexanchus Rafinesque, 1810

Hexanchus gigas (Sismonda, 1857)

FIGURE 2.5F,G

Description. The lower anterolateral teeth superficially 

resemble those of N. primigenius but can be larger, are considerably broader, have seven or more distal conules, and have basal 

serrations on the mesial cutting edge. The root, like that of N. 

primigenius, is compressed, with a wedged-shaped profile, fine 

vertical grooves on the lingual face, and a concave mesial margin. 

Medial teeth (Figure 2.5G) are again comparable to those of 

N. primigenius but are larger (width of at least 25 mm) and have 

five or more conules on each shoulder. 

Several worn and fragmented teeth possibly representing 

other H. gigas tooth positions were examined, but none could be 

unambiguously assigned to this species, and they may fall within 

the variation inherent within N. primigenius. 

Discussion. Hexanchus lower anterolateral teeth occur 

in two different morphologies (Ward, 1979): (1) grisiform teeth 

with mesial serrations that are either small or completely lacking 

and a low acrocone only slightly larger than the first distal conule and (2) vituliform teeth with large serrations and a tall acrocone of noticeably larger size than the remaining conules. These 

differences were later attributed to gynandric heterodonty, with 

the grisiform teeth representing females and the vituliform teeth 

representing males (Kent, 1994; Purdy et al., 2001). A detailed 

morphometric analysis found that this difference is ontogenetic, 

rather than genderal. Vituliform teeth are associated with sexual 

maturity, and their prevalence in males may simply reflect the 

maturation of males at smaller body sizes (Adnet, 2006). 

The teeth of H. gigas are similar to, but larger than, those of 

the extant bluntnose sixgill shark, H. griseus (Adnet and Martin, 

2007), and as yet it is unclear whether they represent separate 

A B

C

D

E

F

G

FIGURE 2.5. Notorynchus and Hexanchus teeth (1 cm scale bar). (A) Notorynchus primigenius right lower anterolateral tooth; lingual view 

(CMM-V-773; bed 14, Governor Run, Maryland). (B) N. primigenius pathological right lower anterolateral tooth; lingual view (CMM-V422; Parkers Creek, Md.). (C) N. primigenius lower medial tooth; lingual view (CMM-V-2270; Parkers Creek, Md.). (D) N. primigenius right 

upper anterior tooth; lingual view (CMM-V-416; bed 12, Parkers Creek, Md.). (E) N. primigenius right upper anterolateral tooth; lingual view 

(CMM-V-1629; Scientists Cliffs, Md.). (F) Hexanchus gigas right lower anterolateral tooth; lingual view (CMM-V-3776; Windmill Point, Md.). 

(G) H. gigas lower medial tooth; lingual view (USNM 609547; Willows Beach, Md.). 
5 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

species or are conspecific. The extant H. griseus is a large benthic 

shark with a maximum length of at least 4.8 m and possibly 5.5 

m. Hexanchus griseus is a versatile, eurytrophic shark of tropical 

and temperate marine shelf and upper slope habitats, occurring 

to depths of at least 1,875 m. The diet is very broad and includes 

a variety of teleosts, elasmobranchs, cephalopods, crustaceans, 

pinnipeds, and carrion. Adnet and Martin (2007) correlate the 

evolution of large body size in Hexanchus species, such as H. 

gigas and H. griseus, with the inclusion of cetaceans and pinnipeds in the diet; large fossil Hexanchus teeth of these species are 

particularly abundant in formations with large concentrations of 

marine mammals (Fordyce, 2009). The large H. gigas tooth (Figure 2.5F) was associated with a cetacean skeleton (Cephalotropis 

coronatus Cope, CMM-V-3277) from the St. Marys Formation, 

although it is unclear whether this represented active predation 

or scavenging. 

Stratigraphic and Geographic Ranges. The 

teeth of H. gigas are far less commonly collected from Calvert 

Cliffs than those of N. primigenius, and only four specimens 

were available for study. The rarity of H. gigas teeth from Calvert Cliffs precludes a detailed assessment of the distribution of 

this species in different horizons. Beach specimens are from the 

northern end of Calvert Cliffs, suggesting derivation from the 

Calvert Formation. The tooth shown in Figure 2.5F was collected from bed 24 of the St. Marys Formation. Fossils of very 

large Hexanchus teeth comparable with those of H. gigas have 

been widely, if rarely, collected from the Miocene and Pliocene 

of Belgium, Chile, Italy, Japan, Malta, Peru, Portugal, Spain, and 

California and North Carolina in the United States (Antunes 

and Jonet, 1970; Itoigawa and Nishimoto, 1974; Muizon and 

DeVries, 1985; Cappetta, 1987; Nolf, 1988; Yabumoto and 

Uyeno, 1994; Müller, 1999; Purdy et al., 2001; Ward and Bonavia, 2001; Adnet and Martin, 2007; Reinecke et al., 2011). 

Order Echinorhiniformes Shirai, 1996

Family Echinorhinidae Gill, 1862

Genus Echinorhinus Blainville, 1816

Bramble Sharks – Echinorhinidae

The bramble sharks (Echinorhinus) are large, distinctive 

squaliform sharks that attain a maximum length of about 4 m. 

Their most conspicuous diagnostic character is the presence of 

numerous enlarged, thornlike dermal denticles embedded within 

the skin. The denticles are scattered over the body surface, although adjacent denticles may become fused into irregular plates. 

Bramble sharks are epibenthic in deeper (400–900 m), temperate and tropical marine environments. They occasionally venture 

into water as shallow as 11 m, and much of what is known about 

their biology is derived from sharks in these more accessible habitats. They have a relatively generalized diet of small sharks and 

bony fishes, as well as benthic invertebrates, such as cephalopods 

and crustaceans (Silas and Selvaraj, 1972; Taniuchi and Yanagisawa, 1983; Compagno, 1984:25–27; Aguirre et al., 2002; Dawson and Starr, 2009). Echinorhinus are present but exceptionally 

rare in the Holocene fauna of the Mid-Atlantic states. The only 

known specimen is an E. brucus captured off the coast of Virginia in 187 m of water (Musick and McEachran, 1969). 

The Echinorhinus dentition is homodont with uniquely 

shaped teeth. Each tooth is highly compressed, with a crown 

strongly inclined distally. One or more cusplets are also present 

on each shoulder in teeth from Neogene species, although they 

are typically absent on posterior and juvenile teeth. The root is 

compressed and rectangular in outline. 

Echinorhinus blakei Agassiz, 1856

FIGURE 2.6A–6C

Synonymy follows Pfeil (1983:205) and Reinecke et al. (2011). 

Description. As is typical of Echinorhinus teeth, the 

low crown is compressed, smooth edged, and distally inclined. 

Only a single well-developed cusplet is typically present on each 

shoulder and is so strongly divergent as to be nearly horizontal. On some specimens (Figure 2.6A) a weak secondary cusplet 

may also be present. Posterior teeth (Figure 2.6B) may have low, 

rounded mesial and distal heels, rather than cusplets. The root 

is highly compressed and rectilinear. The lingual face of the root 

has two or three medial nutrient grooves, and a large number 

of small nutrient pores are scattered along the root immediately 

adjacent to the basal margin of the enameloid. 

Presumed dermal thorns of Echinorhinus have been collected from Calvert Cliffs (Figure 2.6C). The base is ovoid with 

radial grooves extending from an enameloid-capped apex to the 

margins. 

Discussion. Purdy et al. (2001) suggested that 

E. blakei is conspecific with the extant prickly shark, E. cookei

Pietschmann, although there are some differences. Most large 

teeth of E. cookei have two distinct cusplets on each shoulder, 

whereas similarly sized teeth of E. blakei normally have only 

one. The crown of E. blakei is also lower than that of the extant species but appears to be more conspicuous because of the 

less prominent cusplets (Pfeil, 1983:205–211). In his exhaustive 

review of the echinorhiniforms Pfeil (1983:180–212) lists these 

two forms as separate species, although noting that there are 

obvious similarities between them. 
NUMBER 100 • 5 9

The Calvert Cliffs dermal thorns attributed to E. blakei

resemble those of the extant bramble shark, E. brucus (Bonneterre), in having radial grooves. But the composite thorns arising 

from the fusion of two or more individual thorns that occur in 

E. brucus (Pfeil, 1983: pl. 65, fig. 4) have not been observed in 

Calvert Cliffs specimens. In this respect, the Calvert Cliffs dermal thorns resemble those of E. richiardii Lawley from the early 

Pliocene of Italy (Pfeil, 1983: pl. 66, figs. 4 and 6), although 

Cappetta (2006) considers this a junior synonym of E. brucus. 

Stratigraphic and Geographic Ranges. Echinorhinus blakei is one of the rarest sharks from Calvert Cliffs 

and is reliably known only on the basis of a single intact tooth, 

a few tooth fragments, and two presumed dermal thorns from 

the northern end of the cliffs. This scarcity of specimens is understandable, given the preference of bramble sharks for waters 

deeper than those represented by the Calvert Cliff strata. This 

scarcity is exacerbated by the delicacy of the thin, compressed 

teeth, which are easily damaged by wave action. 

This species has been previously reported from California, Oregon, Maryland, and North Carolina (Case, 1973; Pfeil, 

1983; Cappetta, 1987, 2012; Kent, 1994; Purdy et al., 2001). 

Order Squaliformes Goodrich, 1906

Family Squalidae Blainville, 1816

Genus Squalus Linnaeus, 1758

Spiny Dogfish Sharks – Squalidae

The spiny dogfish sharks, or spurdogs, are mesotrophic littoral species that are known to move into deeper shelf habitats. 

They have an elongated body and two widely spaced dorsal fins, 

each with a stout spine on the leading edge. Dogfish are active 

sharks feeding on a variety of prey, including teleosts, elasmobranchs, crustaceans, and cephalopods. The maximum size for 

most species is about 1 m (Bigelow and Schroeder, 1948; Compagno, 1984, 1990b; Castro, 2011). 

B

A

C

D

E

FIGURE 2.6. Echinorhinus and Squalus fossils (separate 1 mm scale bars for A–C and D+E). (A) Echinorhinus blakei right anterolateral tooth; 

lingual view (CMM-V-7691; bed 3, Pamunkey River, Virginia). (B) E. blakei right lateral tooth; lingual view (CMM-V-7743; Chesapeake 

Beach, Maryland). (C) Echinorhinus? dermal thorn; apical view (CMM-V-2775; Bayfront Park, Md.). (D) Squalus sp. 1; labial view (CMM-V7724; bed 3B, New Kent County, Va.). (E) Squalus sp. 2; labial view (CMM-V-7725; bed 3B, New Kent County, Va.).
6 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

The cutting teeth of Squalus have a simple, distally angled 

crown and a well-defined apron. They are similar in both jaws, 

except that lower teeth are somewhat larger than the uppers. The 

cutting edges are usually smooth, although some species have 

weakly crenulate or serrate cutting edges. There is a prominent 

distal heel, separated from the distal cutting edge of the crown 

by a distinct notch. The enameloid forming the crown protrudes 

lingually into a short uvula, and an obvious apron in the labial 

face extends below the basal margin of the root. There is mild 

gynandric heterodonty, with male teeth having crowns that are 

somewhat more erect than those of females (Bass et al., 1976; 

Cappetta, 1987; Herman et al., 1989). 

There are two tooth forms of Squalus from Calvert Cliffs, 

which are both very small and easily overlooked. In situ specimens collected by washing and screening are necessary for definitive identification, as beach specimens are almost always 

too badly worn and broken. The roots in particular are highly 

susceptible to damage and are missing even on many screened 

specimens. Fragmentary Squalus have been rarely collected in 

screened material from the northern end of the Calvert Formation but are too worn and incomplete to be easily identifiable. 

The more complete teeth shown in Figure 2.6 were obtained 

from screened samples from bed 3 of the Calvert Formation in 

Virginia and are consistent with those from Calvert Cliffs. 

Purdy et al. (2001), Ward and Bonavia (2001), and Reinecke 

et al. (2011) have all commented on the difficulty of assigning 

isolated Squalus teeth to individual species. The two Squalus

tooth morphologies from the Calvert Formation are listed without specific attribution since it is unclear whether they represent 

two species or positional variants of a single species. 

Squalus sp. 1

FIGURE 2.6D

Description. These small teeth (≤3 mm) are as high as 

they are wide. The mesial cutting edge is weakly sigmoidal, convex basally and becoming weakly concave near the apex. The 

strongly arcuate distal heel is separated from the convex distal 

edge of the crown by a deeply incised notch. The uvula is slender 

and bent mesially. The apron is broad based but tapers quickly 

to a long, narrow basal end with parallel sides that extend below 

the basal root margin. 

Discussion. These teeth are similar to the late Oligocene (Chattian) Squalus aff. cubensis specimens illustrated by 

Reinecke et al. (2005), the early Miocene (Burdigalian) Squalus

sp. of Reinecke et al. (2011), and the middle Miocene (Langhian) 

S. alsaticus of Bor et al. (2012). 

Squalus sp. 2

FIGURE 2.6E

Description. The teeth are small (≤3 mm wide) and are 

generally wider than they are high. The crown is compressed and 

oblique, with smooth cutting edges. The mesial cutting edge is 

broadly convex. The distal cutting edge is weakly convex and 

meets the moderately convex distal heel at an acute angle in a 

moderately deep notch. A short, robust uvula is present, positioned roughly perpendicular to the lingual face of the crown. 

The apron is broad based, tapering to a short, relatively wide 

basal end extending below the basal root margin. 

Discussion. Müller (1999:32; pl. 1, fig.7) reports S. aff. 

acanthias from the Calvert Formation and the St. Marys Formation (Little Cove Point Member). The illustrated specimen in 

Müller (1999) is close to the tooth morphology of Squalus sp. 2 

described here, although details of this specimen are not easily 

observed. These teeth also are generally comparable with the late 

Oligocene (Chattian) S. acanthias (Müller, 1999: pl. 1, figs. 4–6; 

Reinecke et al., 2005: pl. 5), and the late Miocene (Tortonian) S. 

almeidae (Antunes and Jonet, 1970: fig. 7). 

Squalus teeth are exceptionally rare from Calvert Cliffs, at 

present known for eight teeth. Some damaged teeth from the 

Calvert Formation may represent additional species. Unfortunately, the range of variability is so poorly known for both extinct and extant Squalus that at present it is unclear whether 

these represent additional species or simply variants of the two 

morphospecies already identified. 

The fin spines of Squalus are known as fossils (Cappetta, 

1987, 2012) but, as yet, have not been collected from Calvert 

Cliffs. 

Order Squatiniformes Buen, 1926

Family Squatinidae Bonaparte, 1838

Genus Squatina Dumeril, 1806

Angel Sharks – Squatinidae

Angel sharks (Squatina) are demersal sharks occurring from 

the littoral zone to the upper continental slope. They are unusual 

sharks in that they have a depressed body and greatly enlarged 

pectoral fins. In many respects they closely resemble batoids, although the leading edge of Squatina pectoral fins is free, rather 

than fused to the head, as in skates and rays. Angel sharks are 

ambush predators, lying buried in soft sediments to await prey, 

primarily small bony fishes, crustaceans, and mollusks. The 
NUMBER 100 • 6 1

maximum size for most species is about 1.6 m, although at least 

one species reaches 2 m (Bigelow and Schroeder, 1948; Castro, 

1983; Compagno, 1984, 1990b, 2002; Compagno et al., 2005; 

Castro, 2011). 

The clutching teeth of Squatina have a simple, erect crown, 

smooth cutting edges extending onto the shoulders, and a conspicuous apron on the labial face of the root. This tooth morphology is evolutionarily conservative and has been largely 

unchanged since the Late Jurassic. The virtually homodont dentition exhibits only a slight decrease in coronal height toward the 

corners of the jaws (Cappetta, 1987). 

Squatina sp.

FIGURE 2.7A–C

Description. The teeth are small (≤10 mm), with a slender crown and a reduced, platform-like root (Figure 2.7A,B). 

The cutting edges of the crown are smooth and extend out onto 

conspicuous enameloid shoulders. The root is very short and 

protrudes lingually (i.e., perpendicular to the plane of the crown 

and enameloid shoulders) to form a conspicuous shelf. This shelf 

is roughly triangular in basal view and has a weakly concave 

basal surface. The labial face of the crown is convex and medially extends below the basal margin of the root to form a prominent apron. 

Anterior teeth have a relatively tall, erect crown and are 

roughly equal in height and width. Lateral teeth are similar in 

shape, although the crown becomes lower and distally inclined 

and the tooth height becomes smaller than the width. 

Discussion. Eastman (1904) applied the name S. occidentalis to Squatina teeth from Maryland. Kent (1994) listed this 

species as S. subserrata, a species known from the Miocene of 

Europe (Cappetta, 1987; Nolf, 1988), because Maryland teeth 

could not be reliably separated from the European teeth. The 

approximately 16 species of extant angel sharks all have relatively restricted geographic ranges, and none occur on both sides 

of a major ocean basin. These restricted ranges are unsurprising, given the demersal lifestyle of angel sharks on continental 

shelves, so it seems unlikely that S. subserrata would be found 

along both the eastern and western coasts of the North Atlantic. 

Further, David Ward (in Ward and Bonavia, 2001) notes that 

the Mediterranean Sea has three extant Squatina species that 

are readily identifiable on the basis of whole-body morphology 

but are, for practical purposes, indistinguishable on the basis 

of tooth morphology. For these reasons, identifying the Calvert 

Cliffs teeth as Squatina sp., rather than S. occidentalis or S. subserrata, is the most prudent designation. 

Stratigraphic and Geographic Ranges. Squatina sp. teeth are found along the length of Calvert Cliffs, although they are never abundant (Visaggi and Godfrey, 2010), 

and only 15 teeth were examined for this study. These teeth are 

A C B

D

E

FIGURE 2.7. Squatina and Rhincodon fossils (separate 1 mm scale bars for A–C and D+E). (A) Squatina sp. lateral tooth; labial view (CMMV-7732; bed 3B, New Kent County, Virginia). (B) Squatina sp. lateral tooth; basal view (CMM-V-7732; bed 3B, New Kent County, Va.). (C) 

Squatina sp. dermal thorn; apical view (CMM-V-7731; bed 3B, New Kent County, Va.). (D) R. typus tooth; profile view (CMM-V-7692; bed 

3, Pamunkey River, Va.). (E) R. typus tooth; basal view (CMM-V-7693; bed 3, Pamunkey River, Va.). 
6 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

primarily beach specimens, although teeth have been collected 

in situ from beds 3, 4, 8, and 10. The scarcity of these teeth and 

their conservative tooth morphology preclude any determination 

of whether these teeth represent one or more species. 

Neogene Squatina fossils are very widely distributed, including Belgium, the Czech Republic, France, Hungary, Germany, Malta, the Netherlands, Peru, Portugal, Venezuela, and 

the Mid-Atlantic coast of the eastern United States (Antunes and 

Jonet, 1970; Cappetta, 1970, 1987; Itiogawa and Nishimoto, 

1974; Nolf, 1988; Kent, 1994; Antunes et al., 1999a; Müller, 

1999; Aguilera and Rodriguez de Aguilera, 2001; Purdy et al., 

2001; Ward and Bonavia, 2001; Kocsis, 2007; Schultz et al., 

2010; Reinecke et al., 2011; Vialle et al., 2011; Cappetta, 2012; 

Bor et al., 2012; Landini et al., 2017). 

Dermal Thorns. Extant Squatina have enlarged dermal 

thorns scattered among the smaller dermal denticles on the body 

surface (Bigelow and Schroeder, 1948). Cappetta (1970: fig. 10, 

type E) illustrated similar dermal thorns from the Miocene of 

France but did not assign them to a taxon. Case (1980) attributed similar thorns from the early Miocene Trent Formation 

to Squatina subserrata. Van den Bosch (1984: fig. 62a-c, type 

D) tentatively assigned thorns to the cetorhinids on the basis of 

similarities in morphology. Reinecke et al. (2005) and Cicimurri 

and Knight (2009b) concurred and attributed these thorns to 

Cetorhinus. Reinecke et al. (2011) disagreed and assigned them 

to Squatina. Bor et al. (2012) concurred with this interpretation 

and assigned these dermal thorns to Squatina. 

Bigelow and Schroeder (1948: figs. 23, 104) provided anatomical line drawings of the thorns of both Cetorhinus maximus

(fig. 23) and Squatina dumeril (fig. 104). Cetorhinus maximus

dermal thorns have relatively erect, recurved cusps, a medial 

ridge on the face, and a base consisting of numerous radiating 

ridges. The S. dumeril thorns have more recumbent cusps with 

four or more ridges and a rounded base. 

The dermal thorns from Calvert Cliffs have a low, reclined 

cusp (Figure 2.7C). The surface of the cusp has a medial ridge 

flanked on either side by irregular wrinkles and pits. The base is 

flattened, circular, or ovoid in outline and has a weakly convex 

basal surface. In form, these thorns are very similar, but not identical, to those of S. dumeril and are allied here with the Squatina

sp. from Calvert Cliffs. 

These dermal thorns are small and easily overlooked. The 

six specimens examined for this study were all obtained by 

screening Calvert Formation sediments. 

Superorder Galeomorphii Compagno, 1973

Order Orectolobiformes Applegate, 1972

Family Rhincodontidae Müller and Henle, 1838

Genus Rhincodon Smith, 1829

Whale Sharks – Rhincodontidae

The whale sharks are represented by a single extant species 

found worldwide in tropical and warm temperate oceans, except 

for the Mediterranean. They are open-ocean, pelagic sharks, although they are known to also occur in nearshore waters. Whale 

sharks are the largest living elasmobranchs, reaching lengths of 

at least 8 m and perhaps as much as 21 m. They are derived 

littoral-tachypelagic sharks that are exclusively microphagous. 

Unlike the ram-feeding basking sharks, whale sharks are suction feeders and are capable of feeding on a somewhat larger 

size range of planktonic and small nektonic prey, including teleosts, cephalopods, and crustaceans. Consistent with their planktivorous lifestyle, the Rhincodon dentition consists of numerous 

rows of simple, minute teeth (Compagno, 1984, 1990b, 2002; 

Colman, 1997; Compagno et al., 2005; Hazin et al., 2008; Castro, 2011). 

Rhincodon typus Smith, 1829

FIGURE 2.7D,E

1970 Rhincodon typus Smith – Cappetta, p. 40, text-fig. 8, pl. 7:7.

2001 Rhincodon sp. – Purdy et al., p. 100, fig. 15o.

2009b Rhincodon cf. typus Smith – Cicimurri and Knight, p. 630, fig. 3C.

Description. These teeth are small (maximum dimension of about 6 mm) and easily overlooked. In profile (Figure 

2.7D), the acutely pointed crown is short and arched lingually, 

whereas the root is laterally compressed and has a convex basal 

margin. Both the labial and lingual surfaces of the crown are 

smooth and convex. The labial surface of the root is covered 

by an obvious enameloid apron. The cutting edges are smooth 

but inconspicuous and may not reach the basal margin of the 

enameloid. The root has a pronounced lingual protuberance but 

lacks conspicuous lobes. Basally, the root is bisected by a strong 

nutrient groove with a single nutrient foramen (Figure 2.7E). 

There is an obvious margin-lingual foramen on each lateral face 

of the root in a shallow depression basal to the crown. 

Discussion. In both size and morphology Miocene Rhincodon teeth appear to be indistinguishable from those shown by 

Herman et al. (1992) for the extant R. typus. 
NUMBER 100 • 6 3

Stratigraphic and Geographic Ranges. Visaggi 

and Godfrey (2010) report a beach specimen of Rhincodon from 

the northern ends of Calvert Cliffs, but this attribution appears 

unlikely, and this tooth is likely a worn symphyseal carcharhinid 

tooth (see Figure 2.28F,G). In situ specimens of R. typus teeth 

are known from the Fairhaven/Plum Point Members (beds 3–4) 

of the Calvert Formation (Mark Bennett, Marks’ Fossils, Halethorpe, Maryland, personal communication, 2014). Seven teeth 

were examined for this study. 

Rhincodon teeth have been reported from the Miocene of 

Delaware, Maryland, North Carolina, Virginia, and southern 

France (Cappetta, 1970, 1987; Kimmel and Purdy, 1984; Kent, 

1994; Purdy, 1998a; Purdy et al., 2001), as well as the late Miocene/early Pliocene of Costa Rica (Laurito Mora, 1999). Similar 

teeth have also been reported from the late Oligocene of South 

Carolina (Cicimurri and Knight, 2009b). 

Order Lamniformes Berg, 1958

Family Odontaspididae Müller and Henle, 1839

Sand Tiger Sharks – Odontaspididae

The sand tiger sharks of the family Odontaspididae are 

represented by two extant genera, Carcharias and Odontaspis. 

Despite a number of similarities, these two genera have very different lifestyles and long, separate evolutionary histories. Recent 

morphological and molecular research does not support odontaspidid monophyly and raises the possibility of splitting the 

Odontaspididae into two families (Shimada, 2005; Vélez-Zuaro 

and Agnarsson, 2011; Maisey, 2012). 

Carcharias sand tigers are littoral species of tropical and 

temperate coastlines and continental shelves. They have a stocky, 

fusiform body and a tearing-type dentition and reach lengths 

in excess of 3 m. The diet consists of a diverse range of small 

teleosts and elasmobranchs, as well as cephalopods and crustaceans (Compagno, 1984, 1990b, 2002; Compagno et al., 2005; 

Castro, 2011). 

The Odontaspis sand tigers are morphologically similar in 

overall morphology and reach even larger sizes (to 3.6 m). But 

they are also bathic sharks with smaller, more delicate teeth, relatively soft muscles, and poor skeletal mineralization, which are 

associated with the deeper waters of outer continental shelves 

and continental slopes in tropical and warm temperate climates. 

The diet is similar to that of Carcharias but, because of their 

less substantial dentitions, is believed to consist of somewhat 

smaller, less heavily armored prey (Compagno, 1984, 1990b, 

2002; Compagno et al., 2005; Castro, 2011). 

The Calvert Cliffs odontaspidids are represented by three 

species in the genus Carcharias and one species in the extinct 

genus Carcharoides. The latter genus is usually allied with the 

family Lamnidae, but recent research (Reinecke et al., 2011) 

makes a placement in the odontaspidids more plausible. Although sharks in the genus Odontaspis are known from older 

Paleogene formations in Maryland (Kent, 1994), none have been 

found in Calvert Cliffs. 

Genus Carcharias Rafinesque, 1810

Carcharias cuspidatus (Agassiz, 1843)

FIGURE 2.8A–F

1843 Lamna cuspidatus Agassiz – Agassiz, p. 290, pl. 37a, figs. 45–49.

1994 Carcharias cuspidata (Agassiz) – Kent, p. 42, fig. 9.3G.

1999 Carcharias cuspidatus (Agassiz) – Müller, p. 36, tafel [fig.] 2, 

fig. 20–27.

2001 Carcharias cuspidata (Agassiz) – Purdy et al., pp. 102–103, 

figs. 17a,b, 18.

2005 Carcharias cuspidatus (Agassiz) – Reinecke et al., pl. 9, figs. 1–7.

2009b Carcharias cuspidatus (Agassiz) – Cicimurri and Knight, p. 631, 

fig. 4D.

Description. The teeth of this common species differ 

from those of the other Carcharias species from Calvert Cliffs 

by the complete absence of striations on the lingual face of the 

crown. They reach large sizes, with anteriors reaching heights of 

nearly 30 mm. 

Upper anterior teeth have tall, erect, broad upper cusps that 

are erect to slightly inclined distally. The labial coronal face is 

flat, whereas the lingual face is convex. The cutting edges are 

smooth and incomplete, restricted to the apical two-thirds of the 

crown in first and second anteriors and nearly complete in third 

anteriors. The crown is weakly to moderately recurved when 

viewed in profile. Each shoulder has one or two short, curved 

mediolingually directed cusplets. On many teeth, the secondary cusplets are very small and inconspicuous; these secondary 

cusplets are missing on many beach specimens. The lingual protuberance is moderately strong. The nutrient foramen is basal to 

the most elevated portion of the lingual protuberance in a short 

medial groove. The root lobes are thick and moderately long 

and meet at a weakly obtuse angle. Lower anterior teeth have 

less compressed, more recurved crowns, a more elevated lingual 

protuberance, and longer root lobes that form a more acute 

angle. In basal (Figure 2.8F) and profile perspectives, the lobes of 

both upper and lower anteriors taper smoothly from the lingual 

protuberance to the tips.

Lateral teeth (Figure 2.8B–D) have lower, relatively broad 

crowns that are distally inclined in uppers and erect in lowers. The 
6 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

cutting edges are complete or nearly so and smooth, although on 

some lateral teeth the cutting edges are weakly crenulate adjacent 

to cusplets. The cusplets are short and sharp, with two or, rarely, 

three present on each shoulder. The taller, medial cusplet on each 

shoulder is curved mediolingually, whereas more lateral cusplets 

are more erect. On some laterals the cusplets partially fuse 

basally, forming jagged heels (Figure 2.8D). The root lobes are 

robust and meet at a very broad angle. 

Lower first anterior (=symphyseal) teeth (Figure 2.8E) are 

small, with heights typically less than 10 mm. They resemble the 

larger anterior teeth but are narrower, with asymmetrical root 

lobes meeting at a very acute angle. 

Discussion. Upper and lower anteriors of C. cuspidatus have crowns that are somewhat broader than those of C. 

reticulatus and short, curved cusplets (like those of C. taurus), 

although two pairs of cusplets are usually present. Upper and 

A C B D

E

G

H

F I J

K

FIGURE 2.8. Carcharias and Carcharoides teeth (separate 1 cm scale bars for A–D and E–K). (A) Carcharias cuspidatus right lower anterior 

tooth; lingual view (CMM-V-1625; Scientists Cliffs, Maryland). (B) C. cuspidatus lower lateral tooth; lingual view (CMM-V-1625; Scientists 

Cliffs, Md.). (C) C. cuspidatus lower lateral tooth; labial view (CMM-V-1625; Scientists Cliffs, Md.). (D) C. cuspidatus upper lateral tooth; 

lingual view (CMM-V-794; Popes Creek, Md.). (E) C. cuspidatus symphyseal tooth; lingual view (CMM-V-7728; Bayfront Park, Md.). (F) 

C. cuspidatus lower anterior tooth; basal view (UMCP 1041; Clifton, Md.). (G) Carcharias taurus lower anterior tooth; lingual view (UMCP 

1130; Pamunkey River, Virginia). (H) C. taurus lower anterior tooth; basal view (UMCP 1130; Pamunkey River, Va.). (I) Carcharias reticulatus 

lower anterior tooth; lingual view (CMM-V-2736; Randle Cliff, Md.). (J) Carcharoides catticus upper lateral tooth; lingual view (CMM-C-203 

[voucher cast]; bed 3, Pamunkey River, Va.). (K) C. catticus upper lateral tooth; labial view (CMM-C-204 [voucher cast]; bed 3, Pamunkey 

River, Va.). 
NUMBER 100 • 6 5

lower laterals have wider crowns, more robust roots, and shorter, 

more lingually curved cusplets than C. reticulatus. 

Carcharias cuspidatus is an Oligocene species that is closely 

allied with, and likely ancestral to, the Miocene species C. vorax

(De Schutter, 2011), although there is disagreement on whether 

this name should also be applied to early Miocene teeth from 

the northwestern Atlantic. On the basis of the presence of multiple low cusplets on lateral teeth, Reinecke et al. (2011) consider 

the Miocene form of C. cuspidatus to be a junior synonym of 

C. vorax, although they note that there are differences between 

Miocene teeth from the northwestern and northeastern Atlantic. On the other hand, De Schutter (2011) considers C. vorax

to be endemic to the northeastern Atlantic and the more robust 

teeth from the early Miocene of the northwestern Atlantic to be 

closer to the Oligocene C. cuspidatus. He also argues that the 

multiple cusplets on lateral teeth that were used by Reinecke et 

al. (2011:21) to place these teeth in C. vorax are inappropriate since this character also occurs in Oligocene C. cuspidatus. 

Overall, teeth from Calvert Cliffs (and the Pungo River Formation of North Carolina; Purdy et al., 2001) are relatively stout, 

with broader crowns and smaller cusplets than C. vorax from 

Europe and appear to represent relict populations of the Oligocene C. cuspidatus (De Schutter, 2011). The teeth of C. cuspidatus from both Calvert Cliffs and the Pungo River Formation are 

quite large, with a maximum height of more than 40 mm. 

Cappetta (2012:191–192) assigns these teeth to the genus 

Araloselachus Glikman, as A. cuspidata. As such, it represents 

the terminal species of a lineage originating in the late Eocene. 

His arguments are based on several distinctive characters (the 

lack of a sigmoidal coronal profile, simple cusplets on anterior 

teeth, low cusplets on lateral teeth, and a completely smooth lingual coronal face). This generic assignment is plausible, but in 

the absence of a detailed phylogenetic analysis of fossil Carcharias-like odontaspidid teeth the lability of these characters is 

unknown. For the present, these teeth are retained within Carcharias, with the understanding that future research could produce 

justification for a separate genus. 

Stratigraphic and Geographic Ranges. This 

species is by far the most abundant Carcharias shark collected 

from Calvert Cliffs and has previously been reported from this 

area by Kent (1994) and Müller (1999). Teeth of C. cuspidatus are 

most abundant along the northern half of the cliffs, and more than 

100 were examined for this study. This species has been collected 

in situ in beds 3–4, 8, 10, 12, and 17 or 19. Carcharias cuspidatus

teeth have also been collected from river exposures of older beds 1 

and 2 of the Calvert Formation in Maryland and Virginia. 

Many paleontological records of C. cuspidatus are more 

likely attributable to C. vorax (De Schutter, 2011; Reinecke et al., 

2011). There are numerous records for C. cuspidatus from the 

late Oligocene (Chattian) through middle Miocene (Serravallian) 

of the eastern United States (Maryland, North Carolina, South 

Carolina, and Virginia; Leriche, 1942; Kent, 1994; Müller, 1999; 

Purdy et al., 2001; Cicimurri and Knight, 2009b), as well as the 

Oligocene (Rupelian-Chattian) of Europe, northern Africa, Chile, 

Peru, and Japan (Leriche, 1942; Radwański, 1965; Nolf, 1988; 

Kent, 1994; Yabumoto and Uyeno, 1994; Antunes et al., 1999a; 

Müller, 1999; Purdy et al., 2001; Reinecke et al., 2005, 2011; Suarez et al., 2006; Kocsis, 2007; Marsili et al., 2007; Cicimurri and 

Knight, 2009b; Cook et al., 2010; Landini et al., 2017). 

Carcharias taurus Rafinesque, 1810

FIGURE 2.8G,H

Synonymy follows Marsili et al. (2007; as C. acutissima) and Reinecke et al. 

(2011).

Description. Upper anterior teeth have tall, broad upper 

cusps that are erect to slightly inclined distally. The labial coronal face is flat, whereas the lingual face is convex. The cutting 

edges are smooth and incomplete basally to complete. In profile, the crown is lingually inclined with an apex that is straight 

or only weakly recurved. A single short, triangular, mediolingually hooked cusplet is present on each shoulder. On some wellpreserved teeth a low, rounded bump is present in areas where 

secondary cusplets would occur. The lingual protuberance is 

pronounced and forms a distinct mound clearly separated from 

the root lobes. The root lobes are narrow and meet at an acute 

angle. There is a short medial groove with a nutrient foramen 

that is basal to the most elevated portion of the lingual protuberance. Lower anterior teeth have less compressed, more recurved 

crowns, a more elevated lingual protuberance, and longer root 

lobes that form a more acute angle. In both upper and lower anteriors the lingual protuberance forms a distinct mound clearly 

separated from the root lobes in both basal (Figure 2.8H) and 

profile views.

The lateral teeth of C. taurus have narrow crowns that are 

distally inclined in upper teeth and erect in lower teeth. The 

cutting edges are smooth and complete or nearly so. A single 

mediolingually curved cusplet is present on each shoulder but 

is generally shorter than on anterior teeth. Rarely, a secondary, 

more laterally placed cusplet is present. The root lobes are robust 

and meet at an obtuse angle. 

Discussion. Research on extant C. taurus has shown 

that tooth morphology can be quite variable between individuals (Lucifora et al., 2001, 2003), and this variation can complicate the assignment of individual fossil teeth to specific jaw 

positions. Jaw regions (upper anterior, lower lateral, etc.) can be 

determined with more confidence, and with care more definitive 

positional placements are possible for most teeth (Cunningham, 

2000, 2004). 

The teeth of C. taurus can easily be confused with those of 

C. cuspidatus because of similar morphologies and large size (exceeding 25 mm in height). The presence of lingual coronal striations on C. taurus teeth is sufficient to separate the two species, 

although they can be inconspicuous, especially on larger, beachworn specimens. The anterior teeth of C. taurus also typically 
6 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

lack secondary cusplets, whereas they are present, if frequently 

small, in C. cuspidatus. Lateral C. taurus teeth have narrower 

crowns and fewer cusplets than in C. cuspidatus. 

The teeth listed here as C. taurus are typically identified as 

C. acutissima in the paleontological literature on the basis of the 

presence of more extensive striations on the lingual face of the 

crown in the latter species. Reinecke et al. (2011) qualitatively 

evaluated these differences and found that although they did exist, 

there was such broad overlap between the Neogene and Holocene 

forms that they could not be reliably separated into distinct species. Instead, the two appear to represent phyletic evolution of this 

character within a single lineage, although a more thorough quantitative analysis is needed to confirm these observations. 

The striations on the lingual crown face of C. taurus teeth 

from Calvert Cliffs are comparatively sparse and inconspicuous. 

They are most evident on smaller specimens and become progressively less numerous and obvious on larger teeth. This situation differs from that on specimens from the contemporaneous 

Pungo River Formation of North Carolina (Purdy et al., 2001; B. 

W. Kent, personal observations) and the Lower Mica Fine Sand 

Formation in Saxony, Germany (Reinecke et al., 2011), where 

striations are more prevalent, even on larger teeth. Too few 

specimens were available to determine whether they represent a 

separate taurus-like species in Calvert Cliffs or simply regional 

variation in C. taurus. Research on extant populations of C. taurus have demonstrated that there is substantial regional variation 

for both morphological (Lucifora et al., 2003) and molecular 

(Ahonen et al., 2009) characters, providing some support for the 

latter explanation. 

The teeth of C. taurus from Calvert Cliffs are of modest 

size with a maximum height of about 20 mm. This height differs 

from those of C. taurus in the contemporaneous Pungo River 

Formation in North Carolina, where maximum size was more 

than 40 mm (Purdy et al., 2001). As yet, it is not clear if this 

size disparity is due to differences in the paleoenvironments represented by the Calvert Cliffs and Pungo River sediments or is 

a consequence of sampling error. Purdy et al. (2001) examined 

more than 200 C. taurus teeth, whereas only nine teeth of this 

species were available from Calvert Cliffs. 

Stratigraphic and Geographic Ranges. Carcharias taurus is the rarest sand tiger from Calvert Cliffs, as previously observed by Eastman (1904; as Odontaspis elegans), and 

only nine were examined for this study. Teeth have been collected 

primarily from the northern half of Calvert Cliffs, and in situ 

specimens have been recovered from beds 3–4, 8, and 10, as well 

as in river exposures of beds 1 and 2 (Calvert Formation). The 

Neogene form of C. taurus has been widely reported in the North 

Atlantic from the early Oligocene (Rupelian) through middle 

Miocene (Serravallian) of Maryland, North Carolina, and Virginia (Kent, 1994; Müller, 1999; Purdy et al., 2001) and Europe 

(Radwański, 1965; Nolf, 1988; Antunes et al., 1999a; Ward and 

Bonavia, 2001; Kocsis, 2007; Marsili et al., 2007; Marsili, 2008; 

Reinecke et al., 2011; Bor et al., 2012). The species also has been 

reported from Argentina (Cione et al., 2000, 2005), the Azores 

(Ávila et al., 2012), the Lesser Antilles (Portell et al., 2008), Mallorca (Vicens and Rodríguez-Perea, 2003), Australia (Fitzgerald, 

2004), Japan (Yabumoto and Uyeno, 1994), and Peru (Apolín et 

al., 2004; Landini et al., 2017). 

Carcharias reticulatus (Probst, 1879)

FIGURE 2.8I

Synonymy follows Reinecke et al. (2005, 2011).

Description. The upper anterior teeth have crowns that 

are narrow and erect but only moderately tall. The coronal apex 

is acutely pointed, but the crown flares basally in joining the 

shoulders. The cutting edges are typically incomplete. The labial 

face is flat and smooth, whereas the convex lingual face has fine 

basal striations. There is a single cusplet on each shoulder that 

is tall, slender, and erect to weakly divergent; a much smaller, 

secondary cusplet is present on some teeth. In profile, the crown 

is weakly recurved. The root lobes are slender and moderately 

elongated and meet at a weakly obtuse to broadly acute basal 

root angle. There is a single nutrient foramen positioned basal to 

the most elevated portion of the lingual protuberance in a short 

medial groove. 

The lower anterior teeth are similar to upper anteriors 

(Figure 2.8i) but have thicker, more strongly recurved crowns. 

The root lobes are also somewhat longer and meet at a less 

obtuse, or even weakly acute, angle.

The lateral teeth of C. reticulatus have narrow crowns like 

those of C. taurus but differ in cusplet morphology. The cusplets 

are shorter than in anterior teeth but are erect and not mediolingually arched. Also, secondary cusplets are usually present in 

C. reticulatus but only rarely on C. taurus lateral teeth. The cutting edges are smooth and complete. The root is robust with 

widely divergent lobes. 

Discussion. The appropriate specific name for these Miocene Carcharias teeth is not fully resolved. De Schutter (2011) 

considers the middle Miocene form C. reticulatus to be sufficiently 

distinct from the similar Oligocene C. gustrowensis to retain separate names. Conversely, Reinecke et al. (2011) consider the Oligocene and Miocene forms similar enough to warrant only a single 

name, C. gustrowensis. Neither provides convincing evidence, so 

pending a more detailed analysis of their respective morphologies, 

separate names for the Oligocene (C. gustrowensis) and Miocene 

(C. reticulatus) forms are recognized here. 

This Carcharias species is infrequently collected from Calvert Cliffs. The teeth of C. reticulatus are not easily confused 

with those of other Calvert Cliffs Carcharias. The anteriors have 

shorter crowns and taller, more erect cusplets than either C. taurus or C. cuspidatus. Like C. taurus, C. reticulatus teeth typically 

have striations on the lingual face of the crown, although those of 

C. reticulatus are generally somewhat more conspicuous. In overall morphology, C. reticulatus teeth are smaller (maximum height 
NUMBER 100 • 6 7

of about 20 mm) and also more delicate than those of either 

C. cuspidatus or C. taurus. Upper and lower laterals have narrower crowns, two pairs of taller cusplets, and more conspicuous 

striations than those of C. taurus. Upper laterals lack basal crenulations on cutting edges sometimes present in C. cuspidatus.

The delicate teeth of C. reticulatus are known primarily 

from broken, incomplete specimens. The distinctive cusplets are 

particularly vulnerable and rarely intact. The most distinctive 

feature of incomplete C. reticulatus teeth is the narrow crown 

that quickly flares basally, which is most obvious on anterior 

teeth but is also present on laterals. 

Stratigraphic and Geographic Ranges. This 

species was previously reported from Calvert Cliffs as C. reticulata (Probst) in Kent (1994) and has been collected from beds 3, 

4, and 8. This species is never common, and only about 20 teeth 

were available for this study.

Carcharias reticulatus has been widely reported in the North 

Atlantic from the early Oligocene (Rupelian) through at least the 

middle Miocene (Serravallian) and perhaps the early late Miocene (Tortonian). It is a rare species in northwestern Atlantic fossil beds of Maryland, North Carolina, and Virginia (Kent, 1994; 

Müller, 1999; Purdy et al., 2001). Teeth with this morphology 

from North Carolina were listed as Odontaspis cf. O. acutissima (Agassiz) by Purdy et al. (2001), but Reinecke et al. (2011) 

reevaluated these specimens and assigned them to C. gustrowensis (=reticulatus). The species is more common in European 

and Mediterranean fossil beds of Austria, Belgium, Catalonia, 

France, Germany, the Netherlands, Malta, Slovakia, and Switzerland (Leriche, 1926; Menesini, 1974; Nolf, 1988, planche 44, 

figs. 8, 9, as Synodontaspis acutissima; Ward and Bonavia, 2001; 

Reinecke et al., 2011; Bor et al., 2012). 

Genus Carcharoides Ameghino, 1901

The genus Carcharoides is an unusual lamniform that possesses distinctly different anterior and lateral tooth morphologies (Antunes, 1969; Müller, 1999; Ward and Bonavia, 2001; 

Reinecke et al., 2005; Kocsis, 2007). Traditionally, Carcharoides has been assigned to the lamnids, primarily on the basis of 

the presence of lateral teeth with broad crowns and short root 

lobes (Cappetta, 1987, 2006). Recently, Reinecke et al. (2011) 

presented a detailed argument for moving this genus to the family Odontaspididae. Their arguments have two components, the 

overall similarity of the Carcharoides dentition to that of other 

odontaspidids and, more specifically, the structure of the upper 

intermediate tooth. The upper intermediate teeth of odontaspidids and lamnids are not analogous, with those of the former 

developing on the cartilaginous bar between the anterior and 

lateral dental bullae, whereas those of the latter are reduced 

third anteriors that develop within the anterior bulla (Siverson, 

1999; Shimada, 2002). The different developmental origins of 

odontaspidid and lamnid intermediates are reflected in different root morphologies. The intermediate teeth of Carcharoides

have a flat basal root face that compares favorably with that of 

odontaspidids and differs from the larger intermediates of lamnids, which have longer, more obvious root lobes. 

Purdy et al. (2001) dismiss Carcharoides as a valid genus. 

They argue that the anterior teeth of Carcharoides are actually those of the odontaspidid Carcharias, whereas the lateral 

teeth belong to the carcharhiniform Triaenodon. Although there 

is some superficial resemblance of anterior Carcharoides teeth 

to those of Carcharias and lateral Carcharoides teeth to those 

of Triaenodon, these assignments are unlikely. Ward and Bonavia (2001) provide three lines of evidence for the validity of 

Carcharoides:

• The teeth of Carcharoides have the osteodont histological 

morphology found in lamniforms, rather than the orthodont histology typically found in carcharhiniforms. This 

distinction between orders is not absolute (e.g., the extant 

carcharhiniform Hemipristis has pseudo-osteodont teeth, 

whereas the Neogene H. serra has orthodont teeth; Compagno, 1970; Herman et al., 1991), but such exceptions 

are rare.

• Like other lamniforms, the teeth of Carcharoides can be 

separated into distinctive anterior and lateral tooth morphologies. Triaenodon has gradient monognathic heterodonty, without an abrupt transition between anterior 

and lateral teeth. 

• The lower lateral teeth of Triaenodon frequently have a 

pair of cusplets on the mesial shoulder of the tooth. This 

condition has never been observed in Carcharoides, although a secondary cusplet is rarely present on the distal 

shoulder (Reinecke et al., 2011, pl. 27, fig. 6).

Further, Reinecke et al. (2011) were able to examine a sample of approximately 1,100 Carcharoides teeth and construct a 

dentition that combines anteriors and laterals with compatible 

morphologies. 

Carcharoides catticus (Philippi, 1946)

FIGURE 2.8J,K

Synonymy follows Reinecke et al. (2005, 2011).

Description. At present, only the distinctive upper lateral teeth are known from Calvert Cliffs. These teeth have short, 

broad, and distally inclined crowns. The cutting edges are smooth 

and continuous between the crown and cusplets. The cusplets are 

large, triangular, and dissimilar in size; the mesial cusplet is taller 

and more erect than the distally inclined distal cusplet. The root is 

shallow and compressed, with lobes widely divergent. 

Discussion. Reinecke et al. (2011) provide extensive 

documentation for the other tooth positions in the C. catticus

dentition not yet recorded from Calvert Cliffs. The upper anterior teeth have narrow crowns that are erect or weakly inclined 

distally. The labial face is flat and extends onto the lingual face 

of the root a short distance, whereas the lingual face is weakly 
6 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

convex. In profile, the crown is weakly recurved. The cutting 

edges are smooth and may not extend to the cutting edges on the 

cusplets on some anterior teeth. The cusplets are tall (up to about 

25% of the coronal height), slender, and highly compressed, with 

smooth cutting edges. The root lobes are moderately elongated 

and meet at an obtuse basal root angle. There is a single nutrient foramen positioned basal to the most elevated portion of the 

lingual protuberance in a short medial groove. The lower anterior teeth are similar to upper anteriors but have thicker, more 

strongly recurved crowns. The root lobes are also somewhat longer and meet at a less obtuse, or even weakly acute, angle. Some 

lower anterior teeth have cusplets that are lower and rounded. 

Lower lateral teeth are somewhat narrower than upper laterals, 

with erect to slightly inclined crowns. The cusplets are large, triangular, and frequently divergent. 

The teeth of this shark are surprisingly delicate, and intact 

specimens are rare. Even when fragmentary, upper lateral teeth are 

not easily mistaken for other sharks because of the combination 

of highly compressed crowns; tall, triangular cusplets; and short 

roots. Damaged anterior and, to a lesser extent, lower lateral teeth 

are most easily mistaken for those of Carcharias species. 

Stratigraphic and Geographic Ranges. This 

species is rare in Calvert Cliffs, and only four teeth were examined for this study. Calvert Cliffs records are confined to the 

northern half of the cliffs, although specimens of C. catticus have 

been collected in situ from bed 3 of the Calvert Formation in 

Virginia (M. Bennett, pers. comm., 2014).

Carcharoides catticus has been widely reported in the North 

Atlantic from the early Oligocene (Rupelian) through middle 

Miocene (Langhian). It is a rare species in northwestern Atlantic fossil beds of Maryland, North Carolina, and Virginia (Kent, 

1994; Müller, 1999; Purdy et al., 2001, as Triaenodon obesus). 

The species is more common in European and Mediterranean 

fossil beds of Austria, Belgium, Catalonia, France, Germany, 

Hungary, the Netherlands, Malta, Slovakia, and Switzerland 

(Leriche, 1926; Menesini, 1974; Nolf, 1988; Ward and Bonavia, 

2001; Kocsis, 2007; Reinecke et al., 2011; Cappetta, 2012; Bor 

et al., 2012; Everaert, 2014). 

Family Lamnidae Müller and Henle, 1838

Genus Isurus Rafinesque, 1810

Mako Sharks – Lamnidae

Extant mako sharks in the genus Isurus are large, pelagic 

predators. There are two living species, the shortfin mako 

(I. oxyrinchus) and the longfin mako (I. paucus). Much of the 

known biology of makos is based on that of the abundant and 

widely distributed I. oxyrinchus. Like many other pelagic lamniforms, the shortfin mako is a mesotherm that maintains elevated 

temperatures for the aerobic muscles, viscera, brain, and eyes, 

with the greatest elevation occurring in cooler waters at higher 

latitudes or in deeper waters (Carey and Teal, 1969; Carey, 1982; 

Block and Carey, 1985; Bernal et al., 2001b). With these elevated 

temperatures makos can be more active than ectothermic fishes, 

allowing them to pursue prey at higher speeds with aerobic muscles, rather than more quickly fatigued anaerobic muscles (Katz, 

2002). The rarer longfin mako (I. paucus) has many of the same 

morphological adaptations for mesothermy as I. oxyrinchus, although it is unclear whether this species maintains an elevated 

body temperature (Carey, 1982; Compagno, 2002). 

Extant shortfin makos are ichthyo- and teuthyophagous, feeding primarily on a range of small, pelagic fishes and squid and, to a 

lesser extent, on demersal fishes and invertebrates. Larger individuals have proportionally broader teeth and are capable of successfully attacking comparatively large individual fishes, sea turtles, 

and porpoises (Compagno, 1984, 2002; Castro, 2011). The longfin mako is presumed to have a broadly similar diet, although its 

comparative rarity precludes a more definitive assessment. 

Both extant makos are epipelagic and found worldwide in 

tropical and warm temperate marine waters (Compagno, 2002). 

Again, because of its rarity the complete range of I. paucus is 

poorly known. On the basis of fossil tooth abundance in deep-sea 

sediments, makos (especially I. oxyrinchus) were the predominant large epipelagic sharks throughout the Neogene (Belyaev 

and Glikman, 1970). Only within, at most, the past 4,000 years 

have they been supplanted in this ecological role by the abundant and ubiquitous blue shark, Prionace glauca (Litvinov, 1989, 

2007). There are two fossil mako sharks known from Calvert 

Cliffs, the comparatively common I. oxyrinchus and the much 

rarer I. retroflexus. 

Isurus oxyrinchus Rafinesque, 1810

FIGURE 2.9A–F

Synonymy follows Purdy et al. (2001), Marsili et al. (2007), and Reinecke 

et al. (2011). 

Description. Anterior I. oxyrinchus teeth are elongate, 

with slender crowns and divergent root lobes. In upper anteriors 

the crown is distally curved or angled and weakly sigmoidal in 

profile, and when viewed in profile, the coronal apex is bent labially. The mesial cutting edges are nearly complete on both the 

first and second anteriors, whereas the distal cutting edge may be 

either nearly complete or restricted to the apical portion of the 

crown. The extent of the distal cutting edges varies both ontogenetically and by tooth position (first versus second anterior). On 

first anterior teeth the distal cutting edge in smaller individuals 
NUMBER 100 • 6 9

is restricted to the apical half of the crown, becoming nearly 

complete in larger individuals (Figure 2.9A,B). The distal cutting 

edge of the second upper anterior is nearly complete at all sizes 

(Figure 2.9C). The root lobes of anterior teeth are extended and 

generally meet at an obtuse angle. The lobes are also elongate 

and comparatively narrow, with rounded ends. Either a single 

nutrient foramen or a tight cluster of foramina in larger teeth is 

present just basal to the most elevated portion of the moderately 

thick lingual protuberance. A nutrient groove is either lacking or 

broad and indistinct. 

Lower anterior teeth have crowns that are more erect and 

strongly recurved (Figure 2.9D). The distal cutting edge reflects 

the condition present in upper anteriors. Lower first anteriors 

have incomplete distal cutting edges on smaller teeth and nearly 

complete cutting edges on larger teeth. Second lower anteriors 

have nearly complete distal cutting edges. The roots have a more 

A B

C

D

E

G H

F

I

J

K

FIGURE 2.9. Isurus fossils (1 cm scale bar). (A) I. oxyrinchus right first upper anterior tooth; lingual view (CMM-V-445; bed 11, Parkers 

Creek, Maryland). (B) I. oxyrinchus right first upper anterior tooth; labial view (CMM-V-445; bed 11, Parkers Creek, Md.). (C) I. oxyrinchus

left upper lateral tooth; lingual view (CMM-V-1623; Scientists Cliffs, Md.). (D) I. oxyrinchus second upper anterior tooth: labial view (CMMV-437; bed 12, Parkers Creek, Md.). (E) I. oxyrinchus left(?) lower anterior tooth; lingual view (CMM-V-1623; Scientists Cliffs, Md.). (F) I. 

oxyrinchus juvenile right second upper anterior tooth; labial view (UMCP 1003; Matoaka Cottages, Md.). (G) I. retroflexus lower anterior 

tooth; lingual view (CMM-V-7717; beds 3 and 4, New Kent County, Va.). (H) I. retroflexus left upper anterior tooth; lingual view (CMMV-4484; Willows Beach, Md.). (I) I. retroflexus right upper lateral tooth; lingual view (CMM-V-1539; Scientists Cliffs, Md.). (J) I. retroflexus

lower lateral tooth (CMM-V-7028; labial view; bed 12, Scientists Cliffs–Parkers Creek, Md.). (K) Isurus sp. vertebral centrum; dorsal perspective (CMM-V-3610; Scientists Cliffs, Md.). 
7 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

prominent lingual protuberance, bearing a single or several 

loosely clustered nutrient foramina, and root lobes meeting at a 

broadly acute, or weakly obtuse, angle. 

Lateral teeth of I. oxyrinchus have progressively lower 

crowns and shorter root lobes meeting at a broadly obtuse angle. 

The crowns of the upper laterals are angled or distally arched 

and more compressed (Figure 2.9E). Lower laterals have crowns 

that are more erect and less compressed. Lateral teeth typically 

have a single nutrient foramen. 

Small, presumably juvenile, teeth of I. oxyrinchus are typically more slender and gracile than larger teeth and frequently 

have a single small cusplet on each shoulder (Figure 2.9F). 

Discussion. The teeth of I. oxyrinchus resemble those of 

a second narrow-toothed Isurus (I. retroflexus) and the broadercrowned species, Carcharodon hastalis (see below). Differences 

between the three species are most obvious in the first and second anterior teeth. The crowns of these I. oxyrinchus teeth are 

narrower and less bladelike than the other two species, and the 

incomplete distal cutting edge of the I. oxyrinchus first upper 

anterior does not occur on either I. retroflexus or C. hastalis. 

In profile, the coronal apex has marked labial curvature, which 

also occurs in C. hastalis but is absent or only weakly expressed 

in I. retroflexus. Likewise, for lower anterior teeth, the combination of narrower crowns, incomplete distal cutting edges on first 

anteriors, and a strongly recurved profile separates I. oxyrinchus

from I. retroflexus or C. hastalis. Lateral I. oxyrinchus teeth 

have narrower crowns and longer root lobes than those of either 

I. retroflexus or C. hastalis. 

Stratigraphic and Geographic Ranges. The 

teeth of I. oxyrinchus are moderately common along Calvert 

Cliffs, and more than 60 were available for study. This species 

is somewhat more prevalent at the northern end of the cliffs and 

has been collected in place from beds 4, 8, 10, 12, and 14 of 

Calvert Cliffs and from inland exposures of beds 1 and 2 of the 

Calvert Formation. 

This species may have appeared as early as the late Oligocene (Chattian) and has been widely reported from Belgium, 

France, the Netherlands, Hungary, Italy, Malta, Poland, Portugal, Chile, Japan, Costa Rica, Cuba, the Lesser Antilles, Angola, 

Zaire, and the eastern United States (Radwański, 1965; van den 

Bosch et al., 1975; Cappetta, 1987, 2012; Nolf, 1988; Kent, 

1994; Yabumoto and Uyeno, 1994; Iturralde-Vinent et al., 1996; 

Antunes et al., 1999a; Müller, 1999; Purdy et al., 2001; Ward 

and Bonavia, 2001; Suarez et al., 2006; Kocsis, 2007; Marsili 

et al., 2007; Laurito Mora and Valerio-Zamora, 2008; Marsili, 

2008; Portell et al., 2008; Bor et al., 2012; Everaert, 2014). Most 

of these records assign these teeth to I. desori. However, there are 

several problems with the use of the specific name desori, and it 

seems advisable to assign these teeth to the extant species, I. oxyrinchus (Purdy et al., 2001; Marsili, 2007a; Ward and Bonavia, 

2001 Reinecke et al., 2011; Bor et al., 2012). 

Isurus retroflexus (Agassiz, 1843)

FIGURE 2.9G–J

Synonymy follows Reinecke et al. (2011). 

Description. The upper anterior teeth of I. retroflexus

have crowns that are compressed, bladelike, and nearly erect to 

distally inclined (Figure 2.9G). The cutting edges are smooth and 

complete and meet at a relatively broad, spatulate apex. In profile, the crown is erect or only weakly bent lingually and lacks 

a marked labial curvature of the apex. The root is moderately 

thick, with rounded lobes of modest length that diverge at an obtuse angle. A broad shelf is present on the lingual root face below 

the neck and extends and broadens laterally on the shoulders. A 

conspicuous callosity is present on the labial root face, extending 

out onto the apical surface of the root. Laterally, the callosity is 

contiguous with the basal shelf on the lingual face of the root. 

A ridge is frequently present on the shoulders at this junction 

of the callosity with the lingual shelf. The ridge may be covered with enameloid, forming broad, low mesial and distal heels. 

Many, particularly larger, teeth have short, vertical wrinkles on 

the enameloid of the basal portion of the labial face. The root 

is only moderately thick, with rounded lobes of modest length. 

One or more nutrient foramina are located medially, basal to the 

lingual protuberance. 

Lower anterior I. retroflexus teeth are similar to uppers but 

are more symmetrical, with a somewhat thicker, more prominent 

lingual protuberance (Figure 2.9H). In profile, the crown is bent 

lingually and lacks any conspicuous apical recurvature. The root 

lobes can be slightly longer, with more narrowly rounded ends, 

and meet at a smaller angle than in upper anteriors. 

Lateral teeth have lower cusps that are distally inclined (Figure 2.9I,J). In profile, the cusp on upper teeth is erect or weakly 

bent labially, whereas in lowers the cusp is arched lingually. The 

heels may bear one or a few low, rounded cusplets (Figure 2.9J). 

The root lobes meet at a very wide obtuse angle and may have 

a shallow medial concavity. The root lobe ends can range from 

rounded to rectilinear. Smaller teeth have a single median nutrient foramen located basal to the most elevated portion of the 

lingual protuberance. Larger teeth usually have several loosely 

clustered foramina. 

Discussion. Purdy et al. (2001) considered I. retroflexus

a nomen dubium on the basis of uncertainty about Agassiz’s 

original description and figure (Agassiz, 1843) and considered 

this specimen unidentifiable to species. This classification creates a serious difficulty since there are morphologically distinct 

Neogene Isurus teeth assigned to I. retroflexus (Lawley, 1881; 

Leriche, 1926; Cappetta, 1970; Kent, 1994; Ward and Bonavia, 

2001) that are now orphaned. This approach seems overly conservative, as the root morphology of the type specimen is distinctive, and the specific name retroflexus is retained for these teeth 

(Reinecke et al., 2011). 
NUMBER 100 • 7 1

The teeth of I. retroflexus resemble those of both I. oxyrinchus and C. hastalis but differ from these species in crown 

and root morphology. The short, broad, compressed crowns of 

I. retroflexus anteriors are very different from the taller, narrower crowns of I. oxyrinchus but superficially resemble those of 

C. hastalis. But I. retroflexus crowns lack the conspicuous labial 

curvature present in the latter species. At similar tooth sizes, I. 

retroflexus crowns also tend to have broader, more ogival apices. 

The distinctive roots of I. retroflexus have a pronounced lingual 

shelf and labial callosity that are absent from either I. oxyrinchus

or C. hastalis. Lateral teeth of the three species are more easily 

confused, but the length of the root lobes and the idiosyncratic 

shelf and callosities are sufficient to separate I. retroflexus from 

the other species. 

Herman (1979) resurrected the genus Anotodus Le Hon 

and argued that this species (as A. retroflexus) was actually a 

giant alopiid. This attribution has been largely ignored by other 

researchers, although it was recently advocated by Cappetta 

(2012:242) on the basis of similarities in dental morphology between this species and alopiids. Although retroflexus lateral teeth 

can superficially resemble those of alopiids, this is less true of 

anteriors. Further, the resemblance is most marked in the largest teeth; smaller teeth (particularly, the tall, narrow anteriors) 

strongly resemble those of Isurus. An analysis of Neogene Isurus by Bourdon (2005) documents these similarities in detail and 

provides strong support for retaining retroflexus within Isurus

and allying it with the extant longfin mako, I. paucus. 

Stratigraphic and Geographic Ranges. Isurus retroflexus teeth are currently known only from the northern portions of Calvert Cliffs. They have been collected in situ 

from beds 12 and 17 or 19, although they seem more common 

in bed 12 than anywhere else along the cliffs. This species is less 

abundant than I. oxyrinchus in Calvert Cliffs (only 17 available for study) but nonetheless has a wide geographic distribution in the early Miocene (Burdigalian) through early Pliocene 

(Zanclean), including the United States (Maryland, Virginia, and 

North Carolina), Australia, Austria, Belgium, France, Germany, 

Hungary, Italy, Japan, the Netherlands, Malta, Peru, and Switzerland (Hirota, 1979; Cappetta, 1987, 2012; Nolf, 1988; Kent 

1994; Yabumoto and Uyeno, 1994; Ward and Bonavia, 2001; 

Kocsis, 2007; Marsili et al., 2007, as Isurus sp.; Reinecke et al., 

2011; Bor et al., 2012; Landini et al., 2017, as Anotodus cf. A. 

agassizi).

Isurus Vertebral Centra

FIGURE 2.9K

Description. Presumed Isurus centra from Calvert Cliffs 

are short, discoidal, and circular in axial perspective. The dorsal and ventral foramina are ovoid and stop short of the rims. 

In dorsal or ventral perspective, the walls are concave, recurved 

near the rims, and septate. The septa are simple and straight 

medially but undergo complex, reticulating branching near the 

rims. This branching causes the septa to have an intricate, lacy 

appearance. 

Discussion. The morphology of the vertebral centra 

from the extant Isurus has been well documented (Kozuch and 

Fitzgerald, 1989; Kraig, 2008) and is consistent with the centrum shown here (Figure 2.9K). Only three presumed Isurus centra have been studied from Calvert Cliffs. 

Genus Carcharodon Smith, 1838

White Sharks – Carcharodon

White sharks of the genus Carcharodon are the most famous, and one of the most heavily studied, of all living sharks 

(Compagno et al., 1989, 2005; Compagno, 2002; Castro, 2011). 

The extant species, Carcharodon carcharias, is large, powerful, 

and archipelagic, combining a high-speed tachypelagic body with 

robust jaws and a versatile dentition of bladelike cutting teeth 

(Compagno, 1990b). Although primarily inhabitants of continental and insular shelves, white sharks are capable of cruising 

long distances and have one of the most extensive geographic 

ranges of any shark. They occur most commonly in temperate 

waters, although large adults are occasionally reported from the 

tropics. White sharks occupy depths from the surf line down to 

about 1,300 m. Extant white sharks are top predators in marine 

communities, and the combination of large size, efficient locomotion, and large cutting teeth allows them to successfully subdue a broad range of prey, including bony fishes, sharks, skates, 

rays, sea turtles, sea birds, seals, sea lions, porpoises, invertebrates (gastropods, cephalopods, and crustaceans), and carrion. 

Marine mammals are particularly important in the diet of large 

white sharks, either as predation or scavenging. Maximum size 

for extant white sharks appears to be 6 m (Compagno, 1984, 

1990b, 2002; Compagno et al., 1989, 2005; Wroe et al., 2008; 

Castro, 2011; Fallows et al., 2013). 

Carcharodon has a tooth morphology very similar to that 

of sharks typically placed in the extinct genus Cosmopolitodus. 

Both groups have dignathic heterodonty with broad compressed 

crowns on the upper teeth and somewhat narrower, less compressed crowns on the lower teeth. The root lobes are comparatively short. Larger teeth have a cluster of nutrient foramina on 

the labial root face, basal to the most elevated portion of the 

lingual protuberance. In some cases, the foramina are contained 
7 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

within a larger external opening (Kent, 1994:64; Cappetta, 

2012:211). Differences between Carcharodon and Cosmopolitodus are almost entirely based on the condition of the cutting 

edges; the cutting edges are coarsely serrate in Carcharodon and 

smooth or weakly crenulate in Cosmopolitodus. 

In recent years the evolution of Carcharodon from Cosmopolitodus has been extensively documented in the Pacific 

Ocean, with an unserrated ancestor giving rise to increasingly 

more strongly serrated forms (Stewart, 1999, 2000; Yabe, 2000; 

Stewart and Perry, 2002; Ehret et al., 2009a, 2009b, 2012). The 

primary difficulty is in unambiguously distinguishing between 

Cosmopolitodus and Carcharodon. The simplest descriptor is 

the presence or absence of serrated cutting edges on the crown 

(Cappetta, 2006; Mewis, 2008; Ehret et al., 2009a, 2012). This 

delineation parallels the marked changes in the triple-layered 

neoselachian enameloid necessary to produce true serrations 

(Andreev, 2010; BWK, pers. obs.). Smooth and crenulated cutting edges have essentially identical orientations of fibers in the 

parallel enameloid bundles, whereas serrations have pronounced 

bending of these bundles to biomechanically reinforce the 

notches between serrations. The problem with this distinction 

is that it ignores a variety of intermediate forms, including teeth 

with crenulate, partially serrate, and weakly serrate cutting edges 

(Muizon and DeVries, 1985; Kent, 1994; Mewis, 2008; Ehret et 

al., 2009a, 2012). A further difficulty is that by the early Pliocene 

both Cosmopolitodus and Carcharodon also evolved broader, 

more triangular crowns. An unresolved question is whether the 

extant C. carcharias (1) arose from a narrow, fully serrated ancestor and independently evolved the broad tooth form or (2) 

arose from a broad-toothed ancestor with smooth, unserrated 

cutting edges and independently evolved serrated cutting edges. 

Retaining Cosmopolitodus as a separate genus would make it a 

A B

C D E

G

H

F

FIGURE 2.10. Carcharodon teeth (1 cm scale bar). (A) C. hastalis left upper anterior; lingual view (CMM-V-245; Parkers Creek, Maryland). 

(B) C. hastalis left lower anterior; lingual view (CMM-V-245; Parkers Creek, Md.). (C) C. hastalis left upper lateral with cusplets; labial view 

(CMM-V-7569; bed 12, Scientists Cliffs–Parkers Creek, Md.). (D) C. hastalis left upper lateral with basal serrations; labial view (UMCP 12025; 

Matoaka Cottages, Md.). (E) C. hastalis left upper lateral with root spurs; labial view (CMM-V-7716; Scientists Cliffs–Warrior’s Rest, Md.). 

(F) C. subserratus upper anterior; labial view (CMM-V-3876; Flag Ponds, Md.). (G) C. subserratus upper anterior with cusplets; labial view 

(CMM-V-4173; Flag Ponds, Md.). (H) C. subserratus lower lateral with crenulate cusplets; labial view (CMM-V-7802; Windmill Point, Md.).
NUMBER 100 • 7 3

paraphyletic stem group to the genus Carcharodon. The more 

parsimonious solution is to make the whole CosmopolitodusCarcharodon complex a single clade, for which Carcharodon

would have priority, as has been proposed by Mewis (2008), 

Cione et al. (2012), and Ehret et al. (2012). 

Two species of Carcharodon are definitively known from 

Calvert Cliffs, the abundant C. hastalis and the much rarer C. 

subserratus. Those of C. hastalis are actually the most abundant 

large lamnid teeth collected from these beds (reanalyzed data 

from Visaggi and Godfrey, 2010). Teeth attributed to the extant 

C. carcharias have also been rarely reported from the Calvert 

Cliffs beds. 

Carcharodon hastalis (Agassiz, 1843)

FIGURES 2.10A–E, 2.11

Synonymy follows Marsili et al. (2007) and Reinecke et al. (2011).

Description. This is a large lamnid with relatively 

broad, compressed teeth. Like the extant C. carcharias the dentition has dignathic heterodonty. Upper anterior teeth have tall, 

moderately broad, triangular crowns with complete, unserrated 

cutting edges (Figure 2.10A). The mesial margin of the crown 

is weakly convex to nearly straight, whereas the distal margin 

is concave to slightly sigmoidal. In profile, the coronal apex is 

labially recurved. The crown is separated from the root by a narrow neck with roughly parallel sides. The roots have abbreviated 

lobes that meet at an obtuse angle. Large teeth have a cloacal 

cluster of nutrient foramina basal to the inconspicuous lingual 

protuberance. Upper lateral teeth are similar, although the 

crowns become progressively lower and more distally inclined in 

tooth row groups closer to the jaw commissure. The root lobes 

become somewhat longer but meet at increasingly larger obtuse 

angles. 

Lower anterior teeth (Figure 2.10B) are similar to upper anteriors but have somewhat narrower, less compressed crowns, 

a more prominent lingual protuberance, and longer root lobes 

meeting at less obtuse angles. As in the upper jaw, lateral teeth 

have lower crowns, although they have more erect crowns than 

corresponding uppers. Also, the root lobes of lower lateral teeth 

(compared to lower anterior teeth) become shorter and meet at 

a larger angle. 

There is considerable variation in many of these characters. 

As is common with many lamniforms, smaller teeth are more 

delicate, with narrower crowns and slightly longer root lobes, 

than larger teeth. Smaller teeth also have a simple cluster of nutrient foramina or, in the smallest teeth, a single foramen. Some 

teeth, particularly those in lateral files, can have cusplets (Figure 

2.10C), basal serrations (Figure 2.10D), or root spurs (Figure 

2.10E). These serrations are coarse and comparable in size and 

shape to those of C. carcharias but are restricted to the most 

basal portions of the cutting edges. 

Discussion. The larger, broader teeth of C. hastalis resemble those of the later Pliocene species usually identified as C. xiphodon (Agassiz). Ward and Bonavia (2001) considered this species 

name to be a nomen dubium. According to Cione et al. (2012), 

the next available name for these teeth is C. plicatilis (Agassiz), 

although Cappetta (2006) lists plicatilis as a Miocene (rather than 

Pliocene) species. But Cappetta’s stratigraphic placement appears 

to be an error, as the type locality of plicatilis (“du terrain calcaire 

de Castell-Arquato,” i.e., limestones of Castell’Arquato) contains 

predominately Pliocene sediments. Further, the limestones in this 

area are from the middle Pliocene (Piacenzian; Roveri and Taviani, 2003). This is consistent with the early to middle Pliocene 

(Zanclean–Piacenzian) age of this broad-toothed form (listed as 

Isurus xiphodon; Purdy et al., 2001; Ward, 2007; Marsili, 2008). 

As proposed by Cione et al. (2012), C. plicatilis will be used here 

as the name for the Pliocene Carcharodon with broad, triangular 

crowns and smooth cutting edges. 

Ehret et al. (2012) considered C. hastalis and C. plicatilis

(listed as C. xiphodon) to represent different forms of a single 

chronospecies and united them under the senior synonym C. 

hastalis. This approach is overly conservative and ignores the 

stratigraphically relevant differences in morphology between the 

Miocene C. hastalis and the early to middle Pliocene C. plicatilis

(Whitenack and Gottfried, 2010; listed as I. xiphodon). 

An assemblage of 31 large teeth and 18 vertebral centra 

was collected from Calvert Cliffs south of Parkers Creek (CMMV-245; Figure 2.11A) and provides insights into the transition 

between C. hastalis and C. plicatilis. The teeth represent morphologies attributable to a number of tooth row groups, although there are relatively few of the smaller teeth closer to the 

jaw commissure. The largest tooth is a lower second anterior 

from the right side of the jaw with a height of 65.4 mm. The largest upper tooth is a 63.5 mm tall second anterior from the left 

side. Although the first and second anterior teeth in both jaws 

were easily allocated to position, lateral teeth were more difficult 

to assign. The ambiguity in the assignment of lateral teeth was 

due in part to the small number of tooth groups represented in 

the association and to the variability in tooth size and shape in 

known extant Carcharodon. Purdy et al. (2001) examined the 

Calvert Cliffs tooth assemblage (at the time consisting of only 27 

teeth) when constructing their artificial tooth sets of C. plicatilis

from Lee Creek Mine, North Carolina. To evaluate the teeth of 

the assemblage, they were compared to the Purdy et al., (2001) 

artificial tooth sets for C. hastalis (fig. 27) and C. plicatilis (figs. 

29, 30; as I. xiphodon). The tooth morphologies of the Calvert 

Cliffs assemblage were also compared with dentitions reconstructed from tooth assemblages of C. plicatilis (Lawley, 1881: 

pl. 5, based on 140 teeth) and C. subserratus (=escheri; Mewis, 

2008: fig. 14, based on 42 teeth), as well as the associated dentition of C. hubbelli (Ehret et al., 2012: fig. 7, based on 222 teeth). 

The Lawley reconstruction places the largest upper lateral tooth 

in the first lateral tooth position. The largest upper lateral tooth 

is actually in the second position, rather than the first (Shimada, 

2002), and this was corrected before analysis. The relative sizes, 
7 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

height-width ratios, and coronal angles were evaluated in these 

six dentitions to help assign the Calvert Cliffs teeth to positions 

in the jaws. Anterior teeth were most easily assigned to position, 

but lateral teeth exhibit greater variability between individuals 

and species, and the positions of these teeth in Figure 2.11A are 

more provisional. 

An additional thirty-second tooth from the assemblage is 

not included in the reconstructed dentition. This is a narrow, 

moderately sized tooth (height = 36.8 mm) that almost certainly 

represents an upper second anterior of a smaller individual. 

The centra from the association are largely intact, discoidal 

cylinders with straight sidewalls, diameters between 34.3 and 

62.0 mm, and diameter-to-length ratios of 2.22–2.80. They have 

the typical septate condition present in lamniforms, with large 

numbers of closely spaced septa. The septa are relatively straight 

and simple, although they have a tendency for one or two dichotomous branchings at their anterior and posterior ends. They 

are comparable to those of C. carcharias described by Kozuch 

and Fitzgerald (1989) and those of Carcharodon hubbelli (Ehret 

et al., 2009a: fig. 9; 2012: fig. 8). Extant Isurus centra have septa 

with a distinctive pattern of complex reticulated branchings at 

their anterior and posterior ends (Kozuch and Fitzgerald, 1989). 

Small areas on a few of the associated centra (Figure 2.11B) resemble this pattern, but it is unclear whether these represent true 

reticulations or the remnants of an incompletely preserved superficial cartilage. Overall, the morphology of the centra is much 

closer to C. carcharias than to Isurus and provides additional 

evidence for placing these broad-toothed sharks in the genus 

Carcharodon. 

Exceptionally large anteriors of C. hastalis from Calvert 

Cliffs resemble the broad, markedly triangular teeth of C. plicatilis. This tooth morphology is purportedly also present in 

smaller individuals of C. plicatilis (Purdy et al., 2001). Although 

a few large teeth with broader crowns are known (e.g., Figure 

2.10C), there is no persuasive evidence from Calvert Cliffs for 

smaller teeth with the C. plicatilis morphology. Further, in the 

associated set of teeth discussed above (Figure 2.11) the upper 

anteriors have broad, triangular plicatilis-like crowns but retain 

the more rounded root lobes of smaller specimens. The laterals 

and lower anteriors in the tooth assemblage are of typical hastalis morphology. On the basis of the absence of the plicatilis tooth 

morphology in either smaller individuals or the lateral teeth of 

large individuals, all of these teeth from Calvert Cliffs are referred to C. hastalis. 

Stratigraphic and Geographic Ranges. The 

teeth of C. hastalis have been collected along the length of Calvert Cliffs as beach specimens. Teeth have also been collected in 

place from beds 3, 10–14, 17 (or 19), and 24 from Calvert Cliffs 

B

A

FIGURE 2.11. Associated teeth and centra of Carcharodon hastalis (CMM-V-245; Parkers Creek, Maryland). (A) Reconstructed dentition 

(lingual view; 5 cm scale bar on symphysis). (B) Vertebral centrum (three-quarters view; enlarged 1 cm scale bar). 
NUMBER 100 • 7 5

and river exposures of bed 1. This is the most abundant large 

shark from Calvert Cliffs, and more than 200 teeth were available for study. 

Carcharodon hastalis has a very wide geographic distribution, having been found from the late Oligocene (Chattian) 

through late Miocene (Messinian) in Belgium, Chile, Cuba, Fiji, 

Germany, Japan, Malta, the Netherlands, Peru, Poland, Portugal, and Spain, as well as Maryland, North Carolina, and Virginia (Radwański, 1965; Hirota, 1979; Cappetta, 1987, 2012; 

Nolf, 1988; Kent, 1994; Yabumoto and Uyeno, 1994; IturraldeVinent et al., 1996; Antunes et al., 1999a; Müller, 1999; Purdy et 

al., 2001; Ward and Bonavia, 2001; Vicens and Rodríguez-Perea, 

2003; Suarez et al., 2006; Wijnker et al., 2008; Reinecke et al., 

2011; Bor et al., 2012; Everaert, 2014; Landini et al., 2017; 

BWK, pers. obs., USNM 22504). 

Carcharodon subserratus Agassiz, 1843

FIGURE 2.10F–H

1970 Isurus cf. oxyrinchus var. escheri Rafinesque – Antunes and Jonet, 

pp. 140–143, fig. 21. 

1987 Isurus escheri Agassiz – Cappetta, p. 96. 

2006 Carcharodon escheri (Agassiz) – Cappetta, p. 78.

2008 Carcharodon escheri (Agassiz) – Mewis, pp. 23–28, pls. 4, 5.

2009 Isurus escheri (Agassiz) – García et al., p. 681, fig. 5c,d.

2015 Carcharomodus escheri (Agassiz) – Kriwet et al., pp. 862–870, 

figs. 10, 11.

Description. This species has teeth that resemble those 

of similarly sized C. hastalis, except for the presence of fine crenulations on the cutting edges. The teeth are exceptionally rare 

in the cliffs and presently known only from four specimens of 

moderate size. As with C. hastalis teeth of comparable size, the 

crowns are comparatively narrow, and the root lobes are somewhat elongated. The crenulations are small and inconspicuous 

and can be easily overlooked during a casual inspection. Partially 

serrate C. subserratus teeth are also known from the Chesapeake 

Group, some of which also have a simple, triangular cusplet on 

each shoulder (Figure 2.10G). Specimens with crenulations on 

the cusplets are also known (Figure 2.10H). 

Discussion. The teeth identified here as C. subserratus

are more commonly listed in the paleontological literature with 

the specific name of escheri, which has produced confusion as 

to the correct name (Antunes and Jonet, 1970; Cappetta, 1987, 

2006, 2012; Bourdon et al., 2005b; Mewis, 2008). The original 

description of Carcharodon escheri (Agassiz, 1843: tbl. 36, figs. 

16–21) is of a pair of lateral teeth, one an upper and the other a 

lower. Purdy et al. (2001) considered the type specimens of this 

species to represent a crenulated form of Isurus oxyrinchus on 

the basis of the presence of slightly recurved coronal apices that 

do not occur in C. plicatilis. Although this distinction is generally 

true, lateral teeth with recurved apices do occur in the morphologically similar C. hastalis (BWK, pers. obs.), and it seems imprudent to ally the type specimens with I. oxyrinchus. 

A second difficulty with the specific name escheri is that 

Agassiz earlier named another tooth with crenulated cutting 

edges (Agassiz, 1843: tbl. 36, figs. 14, 15) Carcharodon subserratus. This tooth (NHMUK P. 2356) is taller and narrower 

than those shown for Agassiz’s C. escheri and likely represents 

an upper anterior tooth. The tooth has an unusual indentation 

near the base of the distal cutting edge, which is associated with 

a convex distal heel. Further, when viewed in profile, the tooth 

has unusual depressions on both the labial and lingual faces of 

the crown and likely represents a slightly pathological specimen. 

Unfortunately, the locality where this specimen was originally 

collected (London Clay, Sheppey, UK) is suspect, as it would 

put this specimen in the early Eocene (Ypresian), rather than the 

Miocene (Cappetta, 2006, 2012). An Eocene age assignment is 

unlikely, and this tooth was more likely collected from the Miocene beds of Belgium or the Netherlands (David Ward, Natural 

History Museum, London, pers. comm., 2016). Despite this confusion about the locality of subserratus, Woodward (1889:411) 

regarded it as the senior synonym of escheri on the basis of both 

page and figure priority. Consequently, the specific name subserratus is used here for these crenulated North Atlantic teeth. 

The crenulation size of a Calvert Cliffs upper anterior C. 

subserratus (CMM-V-4173; Figure 2.10F) was compared to 

those of similar-sized upper anterior C. subserratus teeth from 

the Berchem Formation of Antwerp, Belgium (UMCP 10055 and 

UMCP 11104). Ten randomly selected crenulations were measured on the distal cutting edge of each tooth. Although the crenulations were slightly smaller on the Calvert Cliffs tooth (mean 

= 0.82 mm) than the Belgian teeth (mean = 1.05 and 0.93), the 

differences were not significant (one-way ANOVA, F2,27 = 2.35, 

P = 0.115), and there was broad overlap in crenulation size between the teeth.

Ehret et al. (2012) considered C. subserratus to be more 

closely related to Isurus than to C. hastalis, primarily on the 

basis of the shape of the root lobes. However, their arguments 

are based on comparisons between the broader, triangular 

crowns and more rectilinear roots of C. plicatilis (Pliocene representatives of their chronospecies C. hastalis). The more appropriate comparison is between contemporaneous middle Miocene 

C. subserratus and C. hastalis. Teeth of these two species have 

similar morphologies and, except for crenulations on the former 

species, can be easily confused. A placement of C. subserratus

in Carcharodon is more plausible than an assignment to Isurus. 

Mewis (2008) reconstructed the dentition of C. subserratus

on the basis of a partially disassociated assemblage of 42 teeth 

and 49 vertebral centra from the Miocene of Germany. Teeth 

within the dentition exhibited substantial variation, including 

cusplets on some teeth and smooth cutting edges on others. Subsequently, this assemblage was used to erect a new genus for this 

species (Kriwet et al., 2015; as Carcharomodus escheri), but there 

seems to be little justification for this new, monotypic genus. 
7 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Stratigraphic and Geographic Ranges. Fossils 

of C. subserratus are apparently restricted to the North Atlantic, 

having been previously documented from the middle Miocene 

through early Pliocene of Belgium, Germany, Portugal, and Spain 

(Antunes and Jonet, 1970; van den Bosch et al., 1975; Moths, 

1998; Andres, 2002; Mewis, 2008; García et al., 2009). In the 

Mid-Atlantic of the eastern United States, C. subserratus is known 

from only four teeth, one from bed 19 of the Choptank Formation (John Nance, Calvert Marine Museum, Solomons, Maryland, 

pers. comm., 2016) and three from localities associated with the 

Choptank and St. Marys Formations (Figure 2.10F–H). 

Crenulated Carcharodon teeth have also been reported 

from the Pacific, but these appear to represent an independent 

acquisition of these modifications to the cutting edges (Nyberg 

et al., 2006; Cappetta, 2012, as “Carcharodon” escheri; Ehret 

et al., 2012). 

Fossil Carcharodon teeth with coarsely serrated cutting 

edges have typically been referred to the extant species, C. carcharias, although a number of other names have been proposed 

that are generally considered junior synonyms (Cappetta, 1987, 

2006). Newton (1997) used relative warp analysis to determine 

that 5-my-old fossil Carcharodon teeth were narrower and had 

larger basal serrations than those of either 3-my-old fossil teeth 

or Holocene C. carcharias teeth, suggesting that a reanalysis of 

older fossils was warranted. Subsequently, Ehret et al. (2012) 

erected the name C. hubbelli for a large, well-preserved set of 

associated teeth and vertebral centra from the late Miocene of 

Peru that have crowns that are narrower and less prominently 

serrated than younger C. carcharias. 

Carcharodon carcharias (Linnaeus, 1758)

FIGURE 2.12A–E

Synonymy follows Marsili (2006) and Adnet et al. (2010).

Description. Great white sharks (C. carcharias) are exceptionally rare from Calvert Cliffs and are represented by only 

three teeth of uncertain origins. The remarkably large specimen 

shown in Figure 2.12A (CMM-V-7031) is an upper anterior 

from an old amateur collection. The exact context of this tooth 

is unknown but is purportedly a beach-collected tooth from the 

northern half of Calvert Cliffs. This tooth has a relatively broad, 

triangular crown with coarsely serrate, nearly straight cutting 

edges. Both faces of the crown are convex, although the labial 

face is only weakly so. There is a narrow neck on the labial face 

of the root. The root is moderately thick with cloacal nutrient 

pores basal to the thickest portion of the root. The root lobes are 

abbreviated, rounded, and joined at a very large obtuse angle. 

The second Calvert Cliffs specimen (Figure 2.12B; CMM-V5806) was beach collected (Visaggi and Godfrey, 2010) from the 

northern end of Calvert Cliffs. It consists of a triangular crown 

of moderate size with coarsely serrated cutting edges. Although 

the crown is intact, the root is missing. The morphology of the 

crown is consistent with that of an upper anterior tooth.

The final specimen (Figure 2.12C; USNM 336204) was collected in situ from the Plum Point Member (bed 10) and has 

previously been illustrated by Purdy (1996: fig. 3D) and Gottfried and Fordyce (2001: fig. 7). The crown is broadly triangular 

and semi-erect, with relatively coarse serrations. The crown is 

moderately compressed, and both the labial and lingual faces are 

weakly convex. The root is partially eroded, and the mesial root 

lobe is incomplete. The distal root lobe is short and rounded, and 

the basal root margin is weakly arcuate to broadly obtuse. 

Discussion. There is some controversy about the earliest 

appearance of coarsely serrate Carcharodon in the fossil record, 

with a number of reports from the early through late Miocene 

(Leriche, 1927; Hatai et al., 1974; Purdy, 1996; Tanaka and 

Mori, 1996; Stewart, 1999, 2000; Yabe, 2000; Gottfried and 

Fordyce, 2001; Stewart and Perry, 2002; Boessenecker, 2011; 

Cione et al., 2012). The specimens from Maryland are some of 

the oldest known representatives, so their identity and context 

must be carefully assessed. The largest of the three is a complete 

upper anterior tooth that is undeniably referable to C. carcharias

and was reported to have been a beach specimen from the northern half of Calvert Cliffs. The enameloid has a dull, matte patina, 

and the tips of most of the serrations are worn, both of which 

are consistent with a beach specimen. But its provenance is suspect because there is no direct documentation of its collection. 

The specimen is also very large, relatively wide, and triangular, 

a shape typically seen in Pliocene specimens (e.g., Purdy et al., 

2001; Ehret et al., 2012). 

The assessment of this tooth is complicated by the documented trade in fossil and Holocene shark teeth by Native Americans. Large teeth of C. carcharias were particularly valued and 

are represented at exceptionally high frequencies in archeological sites from the Chesapeake Bay to Ohio (Colvin, 2011; Lowery et al., 2011). There are a number of Native American sites 

along the western shore of the Chesapeake Bay, so the possibility 

that CMM-V-7031 represents an unmodified Native American 

trade tooth cannot easily be dismissed. Robert Purdy (in Lowery et al., 2011) suggests the Choptank Formation (middle Miocene) in Caroline County, Maryland, on the opposite shore of the 

Chesapeake Bay from Calvert Cliffs as a likely source of these 

teeth. A reevaluation of the four C. carcharias teeth from this 

locality (cataloged as USNM 235 and USNM 407) indicates that 

they are highly variable in color and degree of mineralization 

and are unlikely to have been derived from the same formation. 

The teeth were not collected in situ and may themselves represent 

trade teeth. 

The other two specimens are smaller and less complete, with 

only an isolated crown in CMM-V-5806 and a crown with a 

nearly complete, but poorly preserved, root in USNM 336204. 

The identification of these incomplete teeth is difficult, since 

the Miocene sediments of Calvert Cliffs overlie Paleogene marine sediments. These sediments contain numerous shark teeth 

that can be reworked into the younger Miocene sediments at 
NUMBER 100 • 7 7

the extreme northern end of the cliffs (Bayfront Park to Randle 

Cliff; Shattuck, 1904:lxxii; BWK, pers. obs.). Among the teeth 

potentially present in these older sediments of the Chesapeake 

Bay area are those of the rare species Palaeocarcharodon orientalis (Sinzow). Intact C. carcharias and P. orientalis anterior teeth 

can easily be recognized on the basis of differences in root and 

enameloid shoulder morphology, but these diagnostic areas are 

missing on CMM-V-5806. The gross morphology of this tooth 

is consistent with both Carcharodon and Palaeocarcharodon. 

Serrations of the former genus are perpendicular to the cutting edges, whereas those of the latter have a tendency to angle 

slightly toward the coronal apex. Serrations on CMM-V-5806 

are perpendicular to the cutting edge, but since this orientation 

was also observed in some P. orientalis (BWK, pers. obs.), this 

characteristic is not definitive. 

Serration width on CMM-V-5806 was compared with similarly sized teeth of P. orientalis from Maryland (CMM-V-4336) 

and C. carcharias from Lee Creek Mine, North Carolina (CMMV-864). The basal width of 10 randomly selected serrations from 

both the mesial and distal cutting edges of each tooth were measured and statistically analyzed with a one-way ANOVA. There 

were no significant differences in serration size among the teeth 

(F2,57 = 1.670, P = 0.197). The absence of a root on CMM-V5806 complicates an unambiguous assignment of this tooth to 

Carcharodon. This specimen was collected from the beach and 

has the dull, abraded enameloid and worn serrations typical of 

such specimens. The crown is tall and triangular, consistent with 

an upper anterior of either C. carcharias or P. orientalis. However, the serrations are more prominent than in the late Miocene 

(Messinian) C. hubbelli from Peru, and an assignment of this 

specimen to Palaeocarcharodon is plausible.

B

A

C

D E

FIGURE 2.12. Purported Carcharodon carcharias teeth from the Chesapeake Group (1 cm scale bar). (A) First upper anterior tooth, lingual 

view (CMM-V-7031; indeterminate location, northern Calvert Cliffs, Maryland). (B) Upper anterior tooth fragment, lingual view (CMM-V5806; Dares Beach–Plum Point, Md.). (C) Right upper lateral tooth, lingual view (USNM 336204; bed 10, Camp Kaufmann, Md.). (D) Right 

upper anterior tooth, lingual view (CMM-V-7734; St. Marys/Eastover Formation(?), Southampton County, Virginia). (E) Left lower anterior 

tooth, lingual view (CMM-V-7734; St. Marys/Eastover Formation(?), Southampton County, Va.). 
7 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

The third specimen (USNM 336204) was collected in situ 

(bed 10) with very specific locality data and has glossy enameloid 

and intact serrations, suggesting that it was unlikely to have been 

reworked from older sediments. The broadly triangular semierect crown is comparable to upper lateral teeth of Carcharodon

but very different from the narrower, more oblique crowns of 

upper P. orientalis teeth. Further, the distal shoulder of this tooth 

is nearly intact but has no evidence of the distinctive coarsely serrate cusplet that would be present on a P. orientalis tooth (Cappetta, 1987; Case, 1989, 1993; Kent, 1994; Purdy, 1998c). 

Ehret et al. (2012) reevaluated USNM 336204 and concluded it is actually a small C. megalodon and not C. carcharias. 

They note three unusual features of this tooth: (1) the crown is 

too thick for C. carcharias, (2) the angled basal margin of the 

crown on the lingual face is inconsistent with C. carcharias, and 

(3) the serrations are somewhat coarser than is typical for C. 

megalodon. Although this identification is plausible, it cannot be 

verified on the basis of the anecdotal evidence they provide. In 

particular, the morphology of this tooth has some resemblance to 

larger neonatal teeth of Carcharocles from Calvert Cliffs. Their 

reassignment of this tooth was tested by comparing it to similarly sized neonatal Carcharocles teeth from Calvert Cliffs (Figure 2.14C–F; see the C. megalodon section for a more detailed 

description of these neonatal teeth).

Neonatal teeth of Carcharocles have a crown that is particularly thick, largely because of a convex labial face, producing 

a lenticular cross section on the apical half of the crown. This 

convexity is most pronounced on small anterior teeth (<20 mm) 

and declines as tooth size approaches 50 mm. USNM 336204 

has a convex labial face and lenticular cross section. Although 

this compares favorably with that of neonatal Carcharocles, a 

similar, if somewhat less pronounced, lenticular cross section 

infrequently occurs in C. carcharias (BWK, pers. obs.). The 

coronal thickness of USNM 336204 was compared to that of 

seven upper neonatal Carcharocles teeth of roughly similar size 

(UMCP 12599-12604, USNM 639784). To compensate for 

slight differences in tooth size, thickness was expressed as relative coronal thickness (tooth thickness at mid-crown divided by 

tooth height). Many statistical procedures for comparing a single 

observation with a sample suffer from an elevated type 1 error 

rate, so the data were analyzed with the Crawford and Howell (1998) modification of the special-case t-test proposed by 

Sokal and Rohlf (1995:227–229). The relative coronal thickness 

of USNM 336204 (0.168) was not significantly different from 

those of the seven neonatal Carcharocles teeth examined (mean 

= 0.187; Crawford-Howell modified t-test, t = 0.711, P = 0.504).

The angular basal coronal margin on the lingual face is common in Carcharocles but is also known, if rare, in C. carcharias

(BWK, pers. obs.). The important distinction between the two 

is that the angled margin in Carcharocles is associated with a 

broad, chevron-shaped neck covered with orthodentine, whereas 

in C. carcharias the neck is narrow and relatively inconspicuous. The chevron-shaped neck on Carcharocles neonatal teeth 

is distinct but is also quite delicate and is incomplete to absent 

on many specimens. In some of these specimens, the shape and 

breadth of the neck are still detectable as a smooth area immediately basal to the enameloid. Unfortunately, the root in USNM 

336204 is too poorly preserved to reconstruct the shape of 

the neck, and the basal margin angle is the only available metric. 

The basal coronal angle on the lingual face of USNM 336204 

(=131°) was compared with the same seven upper neonatal 

teeth used to examine coronal thickness (UMCP 12599–12604; 

USNM 639784). There was no significant difference in basal 

angle between the Carcharocles neonatal teeth (mean = 123°) 

and USNM 336204 (Crawford-Howell modified t-test, t = 

0.628, P = 0.553). 

The serrations of USNM 336204 were compared with the 

two upper neonatal Carcharocles teeth most similar in overall size (UMCP 12602 and UMCP 12603). Twenty randomly 

selected serrations from each tooth were measured on photographic enlargements. There was no significant difference in serration size between these three teeth (one-way ANOVA; F2,57 = 

0.510, P = 0.603). Serration size in USNM 336204 is fully comparable with that of neonatal Carcharocles.

In summary, using the three attributes first suggested by 

Ehret et al. (2012), USNM 336204 appears to be more closely 

allied to Carcharocles than to Carcharodon. The crown is statistically indistinguishable in thickness from those of neonatal 

Carcharocles, although it is among the thinner teeth measured. 

Likewise, the angled basal coronal margin on the lingual face 

is not statistically different from those of the neonatal Carcharocles examined. Finally, contrary to Ehret et al. (2012), USNM 

336204 does not have coarser than expected serrations; there 

was no significant difference in serration size between this tooth 

and the two neonatal Carcharocles of similar size. Taken as a 

whole, there is no convincing evidence to retain USNM 336204 

within Carcharodon. Instead, its overall morphology is consistent with a neonatal, or transitional neonatal-juvenile, Carcharocles tooth. 

None of the three alleged C. carcharias teeth from Calvert 

Cliffs can be accepted as proof of this species in the late to middle Miocene of the western Atlantic. There is better evidence that 

late Miocene Carcharodon may have been present, if uncommon, 

in the St. Marys Formation (Tortonian) or Eastover Formation 

(Messinian) of Virginia on the basis of 13 teeth from site #PQBH9812 in Southampton County, Virginia. None of the teeth 

were collected in situ, but at this site the St. Marys and Eastover 

Formations are overlain by unfossiliferous Pleistocene/Holocene 

sands. Further, Pliocene beds from which the teeth could have 

been derived are not present at either this site (A. Alford, National Network of Public Health Institutues, Washington, D.C., 

pers. comm., 2015) or nearby USGS core holes (Weems et al., 

2010). Finally, these specimens are unlikely to have been Native American trade teeth, as they all have similar, distinctive 

permineralization that corresponds to that of other St. Marys 

or Eastover vertebrate fossils from this locality. The difficulty 

in interpreting these teeth is that they are relatively broad and 
NUMBER 100 • 7 9

comparable in morphology to those of C. carcharias, rather than 

late Miocene C. hubbelli. However, none of these 13 teeth were 

collected in context, and despite the absence of younger fossiliferous horizons from which they could have been derived, they 

do not provide irrefutable evidence for this species in the late 

Miocene (Tortonian-Messinian). Research is continuing at this 

site, which could help clarify the ultimate source of these teeth.

Stratigraphic and Geographic Ranges. Carcharodon carcharias is not reliably known from Calvert Cliffs, 

although teeth collected from Virginia suggest there is a slight 

possibility they could be present in the St. Marys Formation 

at the southern end of the cliffs. Likewise, Miocene records of 

Carcharodon from other areas are rare and in many cases very 

poorly documented (Andres, 2006), although several reasonably 

reliable reports of this genus are known:

• Iturralde-Vinent et al. (1996) reported the presence of C. 

carcharias from the early to middle Miocene of Cuba (Cojímar Formation), although the teeth were not illustrated. 

• Reis (2005) lists five lower C. carcharias teeth from the 

early Miocene Pirabas Formation of northern Brazil and 

illustrates one specimen (fig. 11). This figure is somewhat 

indistinct, but the morphology seems consistent with that 

of Carcharodon. 

• Walsh and Suárez (2005) report C. carcharias teeth from 

a bone bed in the Bahía Inglesa Formation of Chile. Teeth 

are not illustrated, so the reliability of this identification 

is unclear. But the teeth were collected below an ash layer 

in the lower part of the Lechero Member with a K-Ar 

date of 7.6 ± 1.3 mya and can be no younger than the late 

Miocene (Tortonian) and no older than middle Miocene. 

Walsh and Suárez (2005) also report that C. carcharias

teeth are much more commonly collected above the ash 

layer in early Pliocene portions of the Bahía Inglesa Formation. Unfortunately, they do not discuss the possibility 

that these early Pliocene teeth could have been reworked 

into older horizons by bioturbational burrowing.

• Cione et al. (2012) describe and illustrate teeth of a Carcharodon sp. collected in situ from the late Miocene 

Paraná Formation of Argentina. Although these teeth are 

somewhat worn, they conclude that the serrations are 

larger and more distinct than those of C. subserratus but 

slightly smaller and less well defined than those of Pliocene and extant C. carcharias.

• Ehret et al. (2012) recalibrated the stratigraphy of the 

specimen earlier described as Carcharodon sp. (Ehret et 

al., 2009a), moving it to the late Miocene and naming it 

as a new species, C. hubbelli. This is the single most reliably documented late Miocene Carcharodon and firmly 

establishes fully serrated species of this genus in the eastern Pacific.

Carcharodon (usually as C. carcharias) is far more widely, 

and definitively, known from early Pliocene and younger 

sediments, including both coasts of North and South America, 

Japan, Australia, southern and western Africa, and southern Europe (Cappetta, 1987; Kemp, 1991; Scudder et al., 1995; Stewart, 1999, 2000; Yabe, 2000; Purdy et al., 2001; Stewart and 

Perry, 2002; Walsh and Suárez, 2005; Andres, 2006; Marsili, 

2007a; Adnet et al., 2010; Ehret et al., 2012). 

Evidence of Feeding. Extant Carcharodon are primarily piscivorous as juveniles and shift to marine mammals 

(e.g., seals, sea lions, cetaceans) as adults (Tricas and McCosker, 1984; McCosker, 1985; Long and Jones, 1996; Estrada et 

al., 2006). Living C. carcharias are primarily described as active predators (Compagno, 1990b), but scavenging on marine 

mammal carcasses is known for both juveniles and adults (Carey 

et al., 1982; Dicken, 2008; Fallows et al., 2013). Carey et al. 

(1982) have even argued that meals of energy-rich mammalian 

blubber are necessary for large C. carcharias to undertake longdistance, open ocean migrations. 

Determining whether feeding in extinct Carcharodon species was comparable to that of the extant C. carcharias is difficult, although bite marks on, or shark teeth associated with, 

marine mammal skeletons can provide evidence of predatory attacks or scavenging events. In a few cases the predatory/scavenging habits of fossil C. carcharias have been documented in the 

fossil record, and as with observations on extant C. carcharias, 

attacks are principally on cetaceans (Deméré and Cerutti, 1982; 

Cigala-Fulgosi, 1990; Bianucci et al., 2000; Ehret et al., 2009b). 

To date, there are no studies documenting piscivory by C. carcharias in the fossil record.

The similarity in tooth morphology between serrate and unserrate Carcharodon would suggest at least some similarity in 

diet. Purdy et al. (2001) attribute unserrated bite marks on the 

humerus of a phocid seal to C. plicatilis (listed as I. xiphodon). A 

large upper anterior tooth from the St. Marys Formation (CMMV-3777; height = 71.0 mm, width = 50.1 mm) was associated 

with a shark-tooth-marked cetacean skeleton (Cephalotropis 

coronatus Cope, CMM-V-3277). Bite mark evidence for unserrated Carcharodon utilizing cetaceans as a food source also has 

been reported from Argentina (Noriega et al., 2007) and Italy 

(Bianucci et al., 2010). Collareta et al. (2017b) have described 

a unique juvenile C. hastalis skeleton from Peru with a number 

of pilchard (Sardinops cf. S. sagax) fossils in the abdominal region. These teleost fossils were interpreted as ingested prey and 

indicate the diet of juvenile C. hastalis was comparable to that 

of juvenile extant C. carcharias. As previously discussed, there is 

evidence in the form of a caudal spine embedded in a C. hastalis tooth (Figure 2.2) that this species preyed on myliobatiform 

rays. Curiously, the ubiquitous unserrated Carcharodon species 

were not quickly supplanted by serrated Carcharodon species 

and continued as the most abundant lamnids through the early 

Pliocene. The presence of numerous other large macrophagous 

sharks may have simply maintained populations of different 

Carcharodon species at levels low enough to preclude extensive 

direct competition for resources.
8 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Family Otodontidae Glikman, 1964

Genus Carcharocles Jordan and Hannibal, 1923

Megatooth Sharks – Carcharocles

The extant great white shark (Carcharodon carcharias) has 

cutting teeth that are broad and compressed and have serrated 

cutting edges. These teeth are ideally suited to slicing chunks 

of flesh from large vertebrate prey, such as fishes and marine 

mammals. A number of fossil lamniforms have teeth with similar morphology and are frequently referred to as “fossil white 

sharks.” In this context, there has been a long, ongoing discussion about whether fossil white sharks represent a monophyletic 

clade allied with C. carcharias or a polyphyletic grade united 

by the convergent evolution of a common tooth morphology. 

These discussions are fundamental to understanding how white 

sharks evolved and their relationship to other lamniform groups. 

Most of these discussions have focused on the relationship of the 

large-toothed Carcharocles megalodon and its ancestral forms 

(variously known as megatooth sharks or giant white sharks) to 

the extant great white shark. 

Currently, there are three competing models for the evolution and systematic placement of the megatooth sharks within 

the Lamniformes:

1. In the Carcharodon model, all fossil white sharks represent 

a single monophyletic clade and should be assigned to the 

genus Carcharodon with the extant C. carcharias (Dockery and Manning, 1986; Uyeno et al., 1989; Applegate and 

Espinosa-Arrubarrena, 1996; Gottfried et al., 1996; Purdy, 

1996; Gottfried and Fordyce, 2001; Purdy et al., 2001). In 

this model white sharks are a clade, and all extinct and extant species are assigned to the family Lamnidae. 

2. In the Carcharocles model, the megatooth sharks represent 

a separate lineage from that leading to the extant C. carcharias and should be placed in a separate genus. Several 

genera have been erected for this lineage, including Carcharocles (Jordan and Hannibal, 1923), Procarcharodon

(Casier, 1960), and Megaselachus (Glikman, 1964). The 

genus Carcharocles has priority and has been used in preference to the other generic names (Cappetta, 1987:103; Ward 

and Bonavia, 2001; Bourdon et al., 2005a; Nyberg et al., 

2006; Mewis, 2008; Ehret et al., 2009a). In this model the 

“white shark” tooth form is homoplastic, with the Carcharocles lineage placed in a separate family (Otodontidae) 

from that of the extant Carcharodon (Lamnidae). 

3. The Otodus/Megaselachus model (Zhelezko and Kozlov, 

1999; Cappetta, 2006) describes the evolution of megatooth sharks from the genus Otodus through the progressive acquisition of serrated cutting edges and loss of lateral 

cusplets. This model envisions a linear series of chronospecies arising by phyletic gradualism from the ancestral Otodus obliquus with smooth, unserrated cutting edges and 

cusplets. Zhelezko and Kozlov (1999: figs. 25–27) provide a 

detailed stratigraphic sequence of chronospecies to support 

their model. All cuspletted forms (regardless of the presence 

or absence of serrated cutting edges) are referred to the genus 

Otodus. Only the terminal, serrated, and noncuspletted species is placed in the monotypic genus Megaselachus, as M. 

megalodon. Cappetta (2006) alters this slightly by including 

serrate, but weakly cuspletted, species within Megaselachus. 

Both Otodus and Megaselachus are placed in the family 

Otodontidae, with Carcharodon in the Lamnidae. Cappetta (2012:224) further modified this model by placing all 

species within this lineage in the genus Otodus, containing 

three subgenera, Otodus, Carcharocles and Megaselachus. 

Much of the discussion about megatooth shark evolution 

and systematics has focused on the Carcharodon and Carcharocles models, whereas the Otodus/Megaselachus model has 

received relatively little attention until recently. To some extent 

this lack of discussion of the third model reflects its status as 

simply a variant of the second that provides an alternative generic assignment of megatooth sharks. But at a deeper level, the 

Otodus/Megaselachus model hypothesizes a fundamentally different mechanism for megatooth shark evolution based on anagenesis, or phyletic gradualism. Anagenesis occurs by the slow 

accumulation of mutations over time, producing a linear series 

of progressively different chronospecies that do not overlap in 

time. This process differs from cladogenesis, where speciation 

occurs rapidly by divergent branching events and sister species 

overlap in time. In general, paleontologists prefer cladogenesis 

as an evolutionary model since it more closely matches the common speciation models in evolutionary biology, although both 

anagenesis and cladogenesis have been documented in the fossil 

record (Freeman and Herron, 2004:679–680; Foote and Miller, 

2007:82). 

There are several inherent problems with documenting 

gradual, anagenetic evolution across the large time spans in the 

megatooth shark fossil record. First, the stratigraphic range of a 

species in the fossil record is almost always an underestimate of 

the actual temporal range because of inadequate or biased sampling (Smith, 1994:183–187; Foote and Miller, 2007:171–173). 

So the obvious question is whether the fossil record of the megatooth sharks is sufficiently detailed to demonstrate anagenesis. 

Freeman and Herron (2004:680) propose two criteria for distinguishing anagenesis from cladogenesis: (1) the phylogeny of the 
NUMBER 100 • 8 1

clade is known, and individual species can be identified, and (2) 

individual species survive long enough for ancestral and descendant species to temporally co-occur. Fundamental to this methodology is a fossil record that is simultaneously stratigraphically 

fine grained and geographically broad (Smith, 1994:186; Liow, 

2010). This requirement is difficult to meet for rare species, such 

as the megatooth sharks. Certainly, we have megatooth sharks 

from many horizons and localities, but rarely do we have tightly 

correlated contemporary horizons that adequately represent the 

presumed geographic range of the species present at the time. 

A second, related difficulty concerns the temporal resolution 

implicit in the chronospecies model of anagenesis. Zhelezko and 

Kozlov (1999: figs. 26, 27) designate stratigraphically distinct 

species and subspecies on the basis of serration shape and cusplet 

shape. Unfortunately, they do not discuss the range of variability 

within either chronospecies or chronosubspecies from specific 

horizons. Cusplet shape, in particular, is known to be morphologically disparate because of ontogenetic changes and position within the jaws (Menesini, 1974; Gottfried and Fordyce, 

2001; Purdy et al., 2001) and the stratigraphic precision of the 

chronospecies proposed by Zhelezko and Kozlov is untested. In 

many respects the pattern observed in megatooth sharks closely 

parallels the situation for the dental evolution of rodents, where 

definitive separations are impossible due to wide morphological overlap (R. A. Martin, 1993, 1995). Martin proposed the 

term chronomorph to describe these complex, frequently mosaic, 

evolutionary changes in rodent tooth morphology. The chronomorph concept implicitly acknowledges the problem of individual variation in describing evolutionary change in dental-based 

taxa and provides a more plausible framework for investigating 

evolution in the megatooth sharks than the stratigraphically pristine designation of chronospecies. Operationally, chronomorphs 

can overlap in time, whereas chronospecies cannot, which allows 

these two models of anagenesis to be tested with a sufficiently 

detailed fossil record. 

The final problem with the Otodus/Megaselachus model is 

the designation of genera and chronospecies within the lineage. 

Zhelezko and Kozlov (1999) and Cappetta (2006) use Otodus

for the ancestral portion of the lineage, with Megaselachus for 

the single, terminal species, whereas Cappetta (2012) uses Otodus for the entire lineage. Distinctions within a phyletic lineage 

are, of necessity, based on arbitrary decisions about the degree of 

differences relative to morphological traits (Benton and Pearson, 

2001; Liow, 2010; Aldhebiani, 2017). Further, such distinctions 

are based on tooth morphology and lack information from the 

whole body. In such situations it can be particularly difficult to 

detect anagenetic morphs since the critical differences either are 

not based on morphological differences (Charlesworth, 1990), 

or have not been preserved in the fossils. 

Despite these difficulties of unambiguously identifying 

morphs within the megatooth shark lineage, it does provide 

a useful framework for viewing megatooth shark evolution. 

Ward and Bonavia (2001) acknowledge the utility of this model 

but merge it with the second model by using Carcharocles for 

serrated species within this group. Further, they concur with 

Menesini (1974) that specific names should be based on large, 

adult individuals. In the discussion that follows, this chronospecies perspective of megatooth shark evolution will be considered 

a plausible, if currently untestable, variant of the Carcharocles

model.

The relative merits of the Carcharodon and Carcharocles

models are complex and, in some cases, contentious. Arguments 

about the generic and familial assignment of megatooth sharks 

in these two models revolve around several lines of evidence, 

including dental morphology, vertebral centrum morphology, 

nutrient foramina morphology, heterochronic change, molecular 

divergence times, and stratigraphic ranges and first appearances 

in the fossil record. 

Dental Morphology. Extant Carcharodon and Isurus are both characterized by the presence of two upper anterior 

teeth in each half jaw, rather than the three present in the more 

primitive odontaspids. Applegate and Espinoza-Arrubarrena 

(1996) argued that Carcharodon has a symmetrical first upper 

anterior tooth, whereas Isurus has an asymmetrical first upper 

anterior. From this observation they concluded that the two 

upper anteriors in Carcharodon represented the first and third 

tooth positions in odontaspids, whereas those of Isurus were derived from the second and third ancestral tooth positions. On the 

basis of the nonhomology of the upper anteriors in Carcharodon

and Isurus, the two genera could not be closely related. 

Applegate and Espinoza-Arrubarrena provided no data to 

support this supposed difference in symmetry. In the same volume, Hubbell (1996) published data on coronal angle for upper 

anteriors in Carcharodon. A statistical analysis of Hubbell’s data 

for the two anterior tooth positions demonstrates that they are 

statistically indistinguishable (paired t-test, t = 0.200, P 0.843). 

Shimada (2002) reached the same conclusion with a larger data 

set, although without statistical analysis. More importantly, Shimada evaluated dental homologies among extant lamniforms 

and demonstrated that the upper anteriors in Carcharodon and 

Isurus were homologous. 

Nyberg et al. (2006) tested differences in tooth morphology 

in a more rigorous way and with more tooth positions (upper anteriors, lower anteriors, upper laterals, and lower laterals) using 

the generalized Procrustes method and principal components 

analysis. Both whole-tooth morphology and root morphology 

were analyzed for all four tooth positions and for four species, C. 

megalodon, C. carcharias, C. plicatilis (listed as Isurus hastalis), 

and the “Sacaco species” (a weakly serrated form subsequently 

named Carcharodon hubbelli; Ehret et al., 2012). For all four 

tooth positions for both whole-tooth morphology and root morphology, C. carcharias, C. plicatilis, and C. hubbelli clustered 

together and had little or no overlap with C. megalodon (Nyberg 

et al., 2006: figs. 4, 5). 

The upper intermediate tooth of C. carcharias is large and 

has a crown inclined mesially, rather than distally as in other 

upper teeth (Applegate and Espinoza-Arrubarrena, 1996; Purdy 

et al., 2001). This condition is not diagnostic for any other 
8 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

extant lamniform, and Purdy et al. (2001) propose it as a synapomorphy for the genus Carcharodon and as a justification for 

suppressing Carcharocles as simply a junior synonym of Carcharodon. They provide no cladistic analysis to support this contention, relying instead on the disposition of the upper intermediate 

tooth in artificial tooth sets assembled from C. megalodon teeth. 

No intact Carcharocles dentition has ever been collected. 

The best available evidence is based on disassociated assemblages 

of Carcharocles teeth from a single individual that have not been 

preserved in life position. Reconstructions of dentitions from 

such tooth assemblages (e.g., Uyeno et al., 1989; Gottfried and 

Fordyce, 2001; Purdy et al., 2001) use the extant C. carcharias

dentition (with a reversed upper intermediate) as the model. This 

reconstructed dentition is then used as evidence to support the 

presence of a reversed upper intermediate tooth in Carcharocles. 

But in these reconstructions, assignment of an intermediate tooth 

to the right or left side of the dentition is determined solely by 

assuming a Carcharodon-like dentition with a reversed upper intermediate (Mewis, 2008; Ehret et al., 2009) and circular reasoning used to posit monophyly of Carcharocles and Carcharodon

(Nyberg et al., 2006). 

Extant C. carcharias have exceptionally large upper intermediate teeth when compared to other lamnids, including unserrated Carcharodon (Shimada, 2002; Mewis, 2008:79, fig. 

15). Because of the development of teeth within dental bullae 

in lamniforms, the evolution of a reversed intermediate tooth in 

Carcharodon simply appears to be a developmental constraint of 

producing a large intermediate tooth within the confined space of 

the anterior dental bulla (Shimada, 2002: fig. 14). In this sense, 

a reversed upper intermediate may be an autapomorphy of this 

species. This possibility is supported by the largely intact fossil 

of Carcharodon hubbelli from the late Miocene of Peru with the 

teeth preserved in near-life position (Ehret et al., 2009a, 2012). 

The teeth of this species are unusual in that they are narrower 

and have weaker serrations than in C. carcharias. Further, the 

intermediate tooth is relatively small and has a distally directed 

crown. Overall, this specimen shares characteristics with both C. 

hastalis and C. carcharias. 

Siverson (1989) stated that C. megalodon lacks the obvious dignathic heterodonty present in C. carcharias. Purdy et al. 

(2001:125) disagreed with this contention, arguing that it is present in C. auriculatus (Dockery and Manning, 1986: pls. 2, 3) and 

is “very marked” in juveniles and associated tooth sets (Purdy et 

al., 2001: figs. 34, 35). A visual inspection of the figures in these 

two publications indicates that there are differences in tooth 

shape when viewed from the lingual surface, but these differences are relatively subtle. The morphometric analysis of tooth 

shape by Nyberg et al. (2006) found that although anterior teeth 

could be assigned to the correct jaw on the basis of either wholetooth morphology or root morphology, there was a high degree 

of overlap in both tooth and root morphology for lateral teeth. 

Although there are differences in coronal curvature between 

upper and lower teeth when viewed in profile, these are generalized lamniform symplesiomorphies, rather than synapomorphies 

of Carcharodon (sensu lato). On the basis of the currently available evidence, both Siverson (1989) and Purdy et al. (2001) were 

partially correct. The anterior teeth of C. megalodon can be reliably assigned to upper and lower jaws, although differences are 

not as obvious as in C. carcharias. 

Vertebral Centra. The large discoidal centra of 

C. megalodon are infrequently collected. The most complete 

set consists of about 150 associated specimens from Antwerp, 

Belgium (Leriche, 1926; Gottfried et al., 1996). Although this 

is a large number of centra from a single individual, the entire 

vertebral column is not present. The best estimates for the total 

number of centra in the entire vertebral column range from 190 

to 200 centra (Gottfried et al., 1996; Gottfried and Compagno, 

2006). This large number of centra is roughly comparable to the 

number in C. carcharias, providing some support for allying C. 

megalodon and C. carcharias in a single genus. Unfortunately, 

this argument is comparatively weak on two counts. 

First, C. carcharias is the paradigm used for making these 

estimates. This paradigm implicitly assumes that the two species have similar numbers and proportions of precaudal and 

caudal centra. This assumption fundamentally constrains the 

reconstructed C. megalodon vertebral column to be a derivative 

version of that in C. carcharias. Under these circumstances, a 

similar number of centra would not be particularly surprising. 

Second, claims of similarity in centra counts ignore disparities between C. megalodon and extant lamnids. Gottfried et al. 

(1996) estimate that C. megalodon had 130 precaudal centra. 

Comparable numbers for extant species are consistently lower, 

with 84–91 for Lamna nasus, 108–112 for Isurus spp., and 

103–108 for C. carcharias. Likewise, the estimated total number 

of 190–200 centra is generally higher than those of these same 

extant lamnids: 150–162, 187–197, and 172–187, respectively 

(Springer and Garrick, 1964). By this criterion, C. megalodon

would be more closely related to Isurus than to Carcharodon.

Vertebral centra counts in and of themselves are of limited utility in reconstructing taxonomic relationships since they 

represent a single, somewhat variable character without a clear 

phylogenetic signal. Conversely, details of morphology (Kozuch 

and Fitzgerald, 1989) and mineralization patterns (Gottfried and 

Compagno, 2006) of the centra are far more useful, as there are 

a number of taxonomically relevant characters present. Gottfried 

and Compagno (2006) provided the first qualitative comparison 

of the internal mineralization pattern of the centra and reported 

that they are comparable in C. megalodon and C. carcharias. 

This observation supports the congener status for these two species, although they did not place these conclusions in a phylogenetic context. Kraig (2008) used computerized tomography 

to evaluate internal structures more thoroughly, using cladistic 

techniques to assess the distribution of the external and internal 

structures of centra in lamniforms. In her analysis, C. carcharias

aligned with Isurus, rather than with C. megalodon. This alignment is consistent with separate origins of C. megalodon and 

C. carcharias. Curiously, she also found that C. megalodon and 

the older C. auriculatus formed a clade that was a sister group 
NUMBER 100 • 8 3

to Lamna nasus. This association has not previously been hypothesized for the origins of C. megalodon and is diametrically 

opposed to the simpler vertebral count data shown above. The 

strength of this association is unclear; although a total of 35 

characters were used in the analysis, many are based on ratios or 

covarying morphological features. This interdependence of features would reduce the number of independent characters and 

phylogenetic resolution to an unknown extent. But these results 

do provide new insights into lamniform relationships and merit 

a more extensive study that includes a larger number of species. 

An analysis that incorporated both vertebral characters, such 

as those in Kraig (2008), and dental characters (e.g., Shimada, 

2005; Mewis, 2008) would likely provide even better resolution.

Nutrient Foramina. As discussed in the introduction 

to this chapter, the evolution of large tooth size is under strong 

fractal constraints arising from the need to produce a greatly 

elaborated capillary system within developing teeth. In C. megalodon teeth, the nutrient foramina are dispersed in an arc over 

the lingual face of the root and are added in a straightforward 

and predictable way during development (Kent, 1994). Small 

individuals have teeth with a single, medial nutrient foramen located at the thickest portion of the root. In progressively larger 

teeth, additional foramina are added laterally. If C. carcharias

arose from C. megalodon, the nutrient foramina of C. carcharias

should increase in number by following the same developmental 

pathway, with perhaps a different terminal condition. The smallest teeth in C. carcharias have a single medial pore, although it 

is located closer to the basal margin of the root than in C. megalodon. As tooth size increases, additional pores are added as a 

tight cluster. In the largest teeth, the pore cluster frequently fuses 

to form a single large opening. This cloacal pore condition in the 

largest teeth (Kent, 1994), and the developmental sequence that 

produces it, is very different than the pattern in C. megalodon

but is like that of fossil smooth-edged Carcharodon and, to a 

lesser extent, Isurus. 

Heterochronic Changes. Gottfried and Fordyce 

(2001) and Purdy et al. (2001) argue that the apparent differences between C. megalodon and C. carcharias are simply sizerelated ontogenetic effects and that similarly sized teeth of the 

two species are comparable in shape and serration size. In this 

view, the two species share the same developmental pathway, 

and morphological differences arise by heterochronic mechanisms. Unfortunately, heterochrony can be difficult to evaluate in 

fossils since it reflects a three-way interaction between age, size, 

and shape. With isolated fossil shark teeth age cannot be determined, and heterochronic processes cannot be directly evaluated. 

McKinney and McNamara (1991) proposed the simplifying assumption that if size and age are correlated, then allometric relationships are a reasonable proxy for heterochronic relationships. 

Nyberg et al. (2006) used this assumption and were able to 

test both of these suppositions about heterochronic relationships 

between C. megalodon and C. carcharias. Ontogenetic changes 

in tooth morphology were evaluated for three species, C. megalodon, C. carcharias, and C. plicatilis (listed as I. hastalis). Nyberg 

et al. (2006) used the relationship between two derived variables, 

approximated tooth area (=size metric) and aspect ratio (=shape 

metric), to test for similarities in developmental trajectories. 

They restricted this portion of their study to upper and lower 

anteriors since these tooth positions exhibited less intraspecific 

variation. Data were analyzed with reduced major axis regression. For both upper and lower anteriors, C. carcharias and 

C. plicatilis shared similar slopes and y intercepts and were very 

different in both respects from C. megalodon (Nyberg et al., 

2006: figs. 6, 7).

Serration size was measured in three megatooth species (C. 

auriculatus, C. subauriculatus, and C. megalodon), C. carcharias, 

and a weakly serrated species (subsequently named Carcharodon

hubbelli; Ehret et al., 2012). The serrations of C. carcharias and 

C. hubbelli were wider and more variable than in the three megatooth species. Further, they were triangular in shape and unlike 

the lobed serrations of C. auriculatus, C. subauriculatus, and C. 

megalodon (Nyberg et al., 2006: figs. 8, 9). 

First Appearances in the Fossil Record. 

Muizon and DeVries (1985) argued that weakly serrate teeth 

known from the late Miocene of Peru, rather than C. megalodon, were ancestral to C. carcharias. Purdy (1996), Gottfried 

and Fordyce (2001), and Purdy et al. (2001:121) refute this 

interpretation on the basis of a single, well-documented tooth 

collected in situ (USNM 336204) from the middle Miocene of 

Maryland. If correctly identified, this tooth is older than the purported ancestral partially or weakly serrate teeth known from 

the late Miocene of Peru (Muizon and DeVries, 1985; Ehret et 

al., 2009a, 2012) or the latest Miocene to earliest Pliocene (Yabe, 

2000) and early Pliocene (Kemp, 1991: pl. 19H). Arguments 

based on first appearances in the fossil record are always tenuous, as a single new record can extend the stratigraphic range of 

a species by millions of years. Further, as discussed above (see 

Carcharodon section), USNM 336204 is most likely referable 

to Carcharocles rather than Carcharodon, and the oldest reliably dated serrated Carcharodon (C. hubbelli) is from the late 

Miocene. Finally, because of the vagaries of preservation in different localities, a descendant species can appear earlier in the 

fossil record than the presumed ancestral one (Foote and Miller, 

2007:155–156). Consequently, the argument that C. megalodon

must be placed in the genus Carcharodon (i.e., Carcharodon

model) because it appears in the fossil record before its presumed 

ancestral form among unserrated Carcharodon (Carcharocles

model) is not supported. 

Molecular Divergence Times. A. P. Martin (1995) 

and Martin et al. (2002) used molecular clock data to estimate 

that Isurus and Carcharodon diverged from a common ancestor 

approximately 60 mya. This estimate predates the appearance of 

the oldest known megatooth shark and precludes a hypothesized 

origin of C. carcharias from Isurus tens of millions of years later 

in the Miocene. This date is an apparently strong piece of evidence for the Carcharodon model, but there are two difficulties 

with this interpretation. 
8 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

First, the molecular data were based on extant Isurus and 

Carcharodon. As discussed above, unserrated Carcharodon teeth 

previously placed in the genus Cosmopolitodus are morphologically closest to C. carcharias. Further, a cladistic analysis of tooth 

morphology in large-toothed lamniforms places unserrated Carcharodon and C. carcharias in a clade that is the sister group to 

Isurus (Mewis, 2008). This placement would mean that molecular dates would reflect divergence between Isurus (sensu stricto) 

and unserrated Carcharodon + C. carcharias, not between Isurus

+ unserrated Carcharodon and C. carcharias. In this scenario, a 

more ancient molecular divergence time between extant Isurus

and Carcharodon would be more plausible. 

Second, a reliable, universally accepted molecular clock for 

dating ancient events has proved elusive. Numerous complications can adversely affect the reliability of molecular divergence 

times, with different systems producing widely different estimates (Heads, 2005; Ware and Grimaldi, 2011; White and Last, 

2012). The 60 mya divergence time of Isurus and Carcharodon

must be accepted with an appropriate level of caution, and Bernal et al. (2001a) used a recalibrated molecular clock to obtain a 

43 mya divergence time between these two genera. 

As reviewed here, the best available evidence makes the Carcharodon model of megatooth shark evolution untenable, and 

the Carcharocles and Otodus/Megaselachus models are better 

representations of the evolutionary history of this group. As discussed above, these two models have a number of similarities but 

differ in the generic organization of the lineage. The taxonomy 

of the Carcharocles model follows that of a number of researchers (Casier, 1960; Cappetta, 1987; Nyberg et al., 2006; Mewis, 

2008; Ehret, 2010) who have argued for placement of these species in a separate extinct family (Otodontidae) and genus (Carcharocles). In the Otodus/Megaselachus model, Cappetta (2006) 

advocated the use of Megaselachus for megatoothed sharks, 

although he later (2012:224) used Megaselachus as a subgenus 

of Otodus. In this later scenario, the subgenus Megaselachus is 

separated from the older subgenus Carcharocles not only by the 

presence of teeth with cusplets that are greatly reduced or absent 

but, more importantly, by having smaller, more uniform serrations and parallel basal crown and root margins on the labial 

face of the tooth. Unfortunately, all of these characters are quite 

variable and not as definitive as proposed. For example, Nyberg 

et al. (2006: fig. 9A–C) compiled serration size data for three 

specimens of C. auriculatus, two specimens of C. subauriculatus

(=C. chubutensis; see below), and four specimens of C. megalodon. These data were reanalyzed with a one-way ANOVA of the 

three Carcharocles species (C. auriculatus, mean = 0.676, variance = 0.014; C. chubutensis, mean = 0.696, variance = 0.005; 

C. megalodon, mean = 0.752, variance = 0.013). Significant differences in serration sizes were present (F2,93 = 4.91, P = 0.009), 

although subsequent Tukey HSD pairwise comparisons indicated 

that the significant differences (P < 0.05) were localized between 

C. auriculatus and C. megalodon. But the differences in serration size were in the opposite direction from that predicted by 

Cappetta. Further, the two species had similar variances, which 

is contrary to the expectation of greater uniformity of serration 

size in C. megalodon. The variance is smaller in the teeth of 

C. chubutensis, but this may simply reflect the smaller sample 

size for this species. 

Cappetta’s model of megatooth shark evolution based on 

a single genus (Otodus) and three subgenera (Otodus, Carcharocles, and Megaselachus) explicitly acknowledges the role of 

phyletic evolution in this lineage, but the subgeneric distinctions 

between Carcharocles and Megaselachus are based on variable 

and, in some cases, poorly documented differences (see above; 

see also Bor et al., 2012:38). Further, Cappetta’s assignment of 

all species within the lineage to a single genus requires an expansion of Otodus far beyond its original intent and provides no 

additional clarity on evolutionary relationships. The more common usage of Carcharocles separates this genus from the genus

Otodus (=Cappetta’s Otodus subgenus) by the presence of serrations and combines Cappetta’s Carcharocles and Megaselachus

subgenera into a single genus. The appearance of fully formed 

serrations, as opposed to the crenulate edges of some Otodus, 

is the most reliable character separating the basal and terminal 

species in the megatooth shark lineage. The use of this character is supported by recent research showing that fully functional 

serrations are characterized by fundamental changes in the 

arrangement of fibers in the parallel bundled enameloid layer of 

neoselachian teeth (Andreev, 2010). 

At present, the question of whether the transition from Otodus to Carcharocles is phyletic (as assumed by Cappetta, 2012) 

or arose by cladogenesis is unresolved. The distributional data for

Otodus and Carcharocles currently lack both the stratigraphic 

precision and the geographic breadth to fully address this question, although two recent studies have provided some insights.

• King et al. (2013) examined the evolution of serrations 

in this lineage across a series of strata. Each stratum contained a range of cutting edge morphologies with serrations becoming larger or more pronounced in younger 

horizons. This is the strongest evidence for phyletic evolution within this lineage, although it assumes that each 

stratum represents a time-averaged sample of a local 

breeding population. An alternative scenario is that each 

stratum reflects the convergence of separate populations 

on a common feeding area. 

• Pimiento and Balk (2015) have documented geographically distinct populations of C. megalodon, rather than a 

single global population. Such discrete populations would 

facilitate cladogenesis if they represented different breeding populations, but as yet, it is unclear whether these 

differences have a genetic basis or are ecophenotypic. Furthermore, on the basis of fossils alone, there is no easy 

way to distinguish evolutionary differences from ecophenotypic ones. 

Phyletic evolution, as seems apparent in the megatooth 

shark lineage (Zhelezko and Kozlov, 1999; Ward and Bonavia, 

2001; Cappetta, 2006, 2012; King et al., 2013; Shimada et al., 
NUMBER 100 • 8 5

2016), is typically found in widespread pelagic groups with few 

reproductive barriers (Benton and Pearson, 2001; Hull and Norris, 2009). This pattern is consistent with the widespread distribution of megatooth shark chronomorphs, although the work by 

Pimiento and Balk (2015) suggests that some barriers may have 

been present. 

Unfortunately, there are problems with straightforward interpretations of such trends in phyletic lineages, including (1) 

rates of evolutionary change that are surprisingly slow and (2) 

the difficulty of identifying cryptic species that may be present 

(Hull and Norris, 2009; Geary et al., 2010; Liow, 2010; Saylo et 

al., 2011). One unusual characteristic of the megatooth lineage 

is its longevity of about 60 my (using data in Cappetta, 2012; 

Pimiento and Clements, 2014). Even less dramatic changes, such 

as the loss of vestigial cusplets during the early Miocene, required 

about 4 my (on the basis of specimens collected in situ from the 

Calvert Formation; see below). Such slow directional change 

in a lineage is not easily explained, as it is difficult to envision 

a selective pressure that could act continuously over such long 

time periods. Likewise, research on extant elasmobranchs has 

demonstrated that cryptic species are quite common (Sole-Cava 

and Levy, 1987; Eitner, 1995; Heemstra, 1997; Pank et al., 2001; 

Gardner and Ward, 2002; Sandoval-Castillo et al., 2004; Keeney and Heist, 2006; Quattro et al., 2006; Castilho et al., 2007; 

Corrigan et al., 2008; Boomer et al., 2010). Cryptic species are 

highly likely to exist in fossil sharks because chronomorphs are 

based almost exclusively on teeth, which form a tiny portion of 

the entire body. 

Resolving the unanswered questions about the megatooth 

shark lineage may require a new, more inclusive model to explain 

evolution within this group. A useful analogy for such a model 

can be found in the detailed evaluation of a long-lived (18 my) 

lineage of graptolites (Urbanek et al., 2012). In this species complex a basic lineage evolved phyletically and periodically produced short-lived sister clades that themselves exhibited phyletic 

evolution, as well as convergence with other clades. Although 

the exact mode of evolution described by Urbanek and colleagues may be inappropriate for megatooth sharks, a composite 

evolutionary model combining both anagenesis and cladogenesis 

is both possible and consistent with the findings of King et al. 

(2013; broad overlap of chronomorphs) and Pimiento and Balk 

(2015; geographically distinct intraspecific groups) discussed 

above. Sorting out the details of evolution in the megatooth 

sharks will require extensive research with rigor comparable to 

these two studies. This work will also likely require the application of statistical approaches to distinguish different modes of 

evolution (Hunt, 2006). 

Because of these unresolved issues surrounding the evolution of the megatooth sharks the genus name Carcharocles is 

used here for serrated member of the megatooth lineage. This 

follows the widespread usage of this genus by a number of researchers (Casier, 1960; Cappetta, 1987; Antunes et al., 1999a; 

Müller, 1999; Aguilera and Rodrigues de Aguilera, 2001; Apolín 

et al., 2004; Nyberg et al., 2006; Kocsis, 2007; Mewis, 2008; 

Portell et al., 2008; Cicimurri and Knight, 2009b; García et al., 

2009; Ehret, 2010; Pimiento et al., 2010, 2013a, 2013b; Visaggi 

and Godfrey, 2010; Cione et al., 2011; Pimiento and Clements, 

2014; Pimiento and Balk, 2015; Carrillo-Briceño et al., 2016), 

including researchers such as Ward and Bonavia (2001) who accept that the group evolved phyletically. The use of Otodus and 

Carcharocles for the ancestral and descendant members of the 

lineage, respectively, provides taxonomic stability while additional research is pursued. Conversely, using Otodus for the entire lineage (or Otodus for earlier species and Megaselachus for 

the terminal species) provides no new information and requires 

assumptions that have not been fully tested. 

Two different Carcharocles tooth morphologies occur in 

Calvert Cliffs. Weakly cuspletted Carcharocles teeth are collected from the northern half of Calvert Cliffs, where the species 

co-occurs with the more common C. megalodon. Identification 

of these two tooth forms to species is problematic because of ontogenetic changes in tooth morphology, with cusplets occurring 

more commonly on both lateral teeth and from those of smaller 

individuals (Menesini, 1974; Purdy et al., 2001; Ward and Bonavia, 2001). There are two plausible names for these weakly 

cuspletted teeth. Purdy et al. (2001) argue that the specific name 

subauriculatus (Agassiz, 1839) has priority, partially because 

this name is based on anterior teeth, rather than lateral teeth. 

However, the original illustrated specimens of C. subauriculatus

(Agassiz, 1843: tbl 30a, figs. 11–13) lack cusplets, and only one 

(fig. 12) has a small, inconspicuous notch on the cutting edge to 

separate the cutting edge from a cusplet. In his description Agassiz actually separated C. subauriculatus from C. megalodon on 

the basis of a more triangular crown with nearly straight cutting 

edges and considered the tooth with a faint notch (fig. 12) to 

be closer to C. megalodon than to the definitive C. subauriculatus specimen (figs. 11, 11’). Further, Cappetta (2006:220) notes 

that the original locality data for C. subauriculatus (Tertiary 

of Maastricht, the Netherlands) is dubious and, like Leriche 

(1926), places subauriculatus in synonymy with C. megalodon. 

Leriche (1926) uses the specific name chubutensis (Ameghino, 

1906) for weakly cuspletted teeth, and this name was retained 

as a valid species by Cappetta (2006). The type specimen of 

chubutensis is based on a lateral tooth but is consistent with the 

morphology of the cuspletted teeth from Calvert Cliffs, and that 

name is used here. 

Carcharocles chubutensis (Ameghino, 1906)

FIGURE 2.13

Synonymy follows Purdy et al. (2001; under Carcharodon subauriculatus) 

and Marsili et al. (2007; under Carcharodon subauriculatus), with the 

following additions:

2006mMegaselachus chubutensis (Ameghino, 1906): Cappetta, p. 51.

2010mCarcharocles chubutensis (Ameghino, 1906): Cook et al., p. 80, 

2010mfig. 2B,C.
8 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Description. The cuspletted teeth of C. chubutensis are 

smaller than those of the more famous C. megalodon. The crown 

of upper teeth has a relatively wide, compressed cusp with a 

broadly ogival apex, and weakly sigmoidal, moderately coarsely 

serrate, cutting edges (Figure 2.13A). The lingual face is convex, whereas the labial face is flat to weakly concave. In profile, 

the coronal apex is arched labially. On each shoulder is a low, 

broad, serrated cusplet that is separated from the main cusp by 

a shallow notch. Between the crown and root on the lingual surface is a broad, chevron-shaped neck covered with a thick layer 

of orthodentine (=bourlette of Kent, 1994). The root lobes are 

moderately elongated with shallow concavities on the mesial and 

distal margins. There is a broadly U-shaped basal root margin. 

The nutrient foramina are scattered in a broad arc over the thickest portion of the lingual protuberance. In anterior positions, the 

crown is tall and erect or weakly inclined distally. In lateral tooth 

positions, the crown becomes lower and more distally inclined, 

whereas the root lobes become more widely separated, with an 

obtusely angled basal margin (Figure 2.13B,C,E). 

Lower teeth are similar to upper teeth, although with somewhat narrower cusps and less widely separated root lobes. The 

labial face of the crown is usually weakly convex, with the lingual face more strongly convex. Viewed in profile, the crown is 

straight or slightly bent lingually. The root is somewhat more 

robust but is otherwise similar to those of upper teeth. Lower 

lateral teeth resemble upper lateral teeth in overall morphology 

but retain a slightly more robust root (Figure 2.13D). 

Discussion. Carcharocles chubutensis teeth never reach 

the remarkable sizes of the more famous C. megalodon, but because of its comparative rarity, the maximum size for this species 

from Calvert Cliffs is difficult to determine. Case (1980) reported 

a maximum tooth height of 130 mm for C. chubutensis from 

the Trent Marl in North Carolina, but no teeth of this size are 

known from Calvert Cliffs. Teeth in excess of 100 mm have been 

collected from the cliffs, and the largest measured tooth (USNM 

392158) is an upper anterior from bed 14. The height of this 

tooth is 106.9 mm, although the coronal apex is damaged; the 

reconstructed height of the intact tooth is about 110 mm. A fragment (CMM-V-4459; Figure 2.13E) is the largest lateral tooth 

available and has a width of 86 mm and an incomplete crown. 

Comparisons with intact upper lateral C. megalodon teeth of the 

same size and shape produce estimated heights of 89–92 mm.

The smaller maximum size of C. chubutensis from Calvert 

Cliffs may simply reflect immature individuals, rather than a 

separate species, since cusplets are more commonly present on 

smaller teeth (Menesini, 1974; Purdy et al., 2001; Ward and Bonavia, 2001). The difficulty in assessing this possibility is that 

there is no direct evidence for the maximum sizes of different life 

stages in Carcharocles. Gottfried et al. (1996) assumed similar 

ontogenetic trajectories in C. megalodon and C. carcharias to 

infer total body lengths of 3.6–4.2 m for the neonatal–immature 

adult transition and about 10.5 m for the immature adult–mature adult transition in males and 13.3 m in females. Pimiento 

et al. (2010) used transitions sizes of 4 and 10.5 m, along with 

position-specific regression equations from C. carcharias (Shimada, 2003), to reconstruct the life stages for C. megalodon

teeth and inferred the presence of a nursery area in the Miocene 

of Panama. Applying this same methodology, the largest C. chubutensis tooth examined from Calvert Cliffs (USNM 392158, a 

first or second upper anterior) has a reconstructed coronal height 

of 90 mm, and using the regression equations for the first and 

second upper anteriors of C. carcharias (Shimada, 2003), this 

would represent an individual with a total body length of 10.4–

10.8 m. Other possible methods of reconstructing body lengths 

from anterior teeth using either the midline tooth height (Gottfried et al., 1996) or root width (C. Jeremiah in Renz, 2002) 

produce estimates of 10.3 and 12.2 m, respectively.

Unfortunately, the life stage sizes inferred by Gottfried et al. 

(1996) and Pimiento et al. (2010) largely ignore some serious difficulties. The most obvious is that C. megalodon is dramatically 

larger than C. carcharias. Extrapolations far beyond the available data are always risky because they ignore a number of possible confounding factors (Schmidt-Nielsen, 1984; Glazier, 2005). 

Gottfried et al. (1996: tbl. 1, footnote c) recognized this difficulty, 

and on the basis of a general trend for a reduced relative fetal size 

in larger sharks, proposed that the largest neonates could have 

had smaller total body lengths of 2–3 m in C. megalodon. They 

made no comparable prediction of the juvenile-adult transition, 

but 6–7.5 m would seem plausible. These scaling difficulties also 

are complicated by the presence of mesothermy in C. carcharias

(Block and Finnerty, 1994; Goldman, 1997; Carlson et al., 2004; 

Bruce, 2009). The metabolic condition of C. megalodon is unknown, although Purdy (1996) speculates that on the basis of its 

warm temperate distribution C. megalodon was an endotherm. 

Scaling relationships are known to differ between ectotherms 

and endotherms (McNab, 2002; Suarez et al., 2004; Glazier, 

2009), further complicating any straightforward determination 

of life stage sizes in C. megalodon. Finally, the fundamental assumption of Gottfried et al. (1996) was that C. megalodon and 

C. carcharias had similar developmental trajectories. Nyberg et 

al. (2006: figs. 6, 7) evaluated size-related changes in the upper 

and lower anterior teeth of these two species and found that they 

were very different, casting further doubt on current size estimates for different life stages in C. megalodon.

Despite these complications, extrapolations from C. carcharias scaling of life history stages are, at present, the best 

available estimates for the sizes of neonatal, juvenile, and adult 

Carcharocles. On the basis of these relationships it seems likely 

that the largest C. chubutensis teeth from Calvert Cliffs represent 

mature individuals and a separate chronomorph of C. megalodon that overlaps in time for approximately 4 my (beds 3–14 of 

the Calvert Formation) in Calvert Cliffs. Cuspletted teeth that 

are less than half the dimensions of the largest teeth are relatively 

common but may represent small individuals of either C. chubutensis or C. megalodon (Figure 2.13C,D). 

Stratigraphic and Geographic Ranges. Carcharocles chubutensis teeth appear to be restricted to the northern half of Calvert Cliffs and appear to be most prevalent in the 
NUMBER 100 • 8 7

B

A

C

D

E

FIGURE 2.13. Carcharocles chubutensis teeth (1 cm scale bar). (A) Right upper anterior tooth, lingual view (CMM-C-205 [voucher cast]; bed 

3, Pamunkey River, Virginia). (B) Left upper lateral tooth, lingual view (CMM-C-206 [voucher cast]; bed 3, Pamunkey River, Va.). (C) Juvenile(?) C. megalodon/chubutensis right upper lateral tooth, labial view (CMM-V-818; Popes Creek, Maryland). (D) Juvenile(?) C. megalodon/

chubutensis right lower lateral tooth, lingual view (CMM-V-124; Popes Creek, Md.). (E) Right upper lateral tooth, labial view (CMM-V-4459; 

bed 10, Plum Point, Md.). 
8 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

lower Calvert Formation (bed 4 and below; Purdy et al., 2001; 

BWK, pers. obs.), with in situ specimens known from beds 3, 4, 

10, 12, and 14. In the general Chesapeake Bay area, C. chubutensis teeth have also been collected in situ from bed 1 of the Calvert Formation of Virginia. Carcharocles chubutensis teeth are 

uncommon, and only about 40 were available for study. Most of 

these were small (heights of 4–7 cm), and only three had a vertical height of at least 100 mm. 

Elsewhere, C. chubutensis has been reported from early to 

middle Miocene (Aquitanian to Langhian) beds of Argentina, 

Baja California, Brazil, Egypt, Germany, Florida, Italy, Panama, 

and North Carolina (Ameghino, 1906; Kimmel and Purdy, 1984; 

Dülge and Engelhard, 1988; Müller, 1999; González-Barba and 

Thies, 2000; Hulbert, 2001; Purdy et al., 2001; Marsili et al., 

2007; Costa et al., 2009; Cook et al., 2010; Pimiento et al., 

2013b; Pimiento and Balk, 2015). In younger sediments C. chubutensis is replaced by the larger C. megalodon, possibly because 

of the evolution of larger cetacean prey beginning in the middle 

Miocene (Pyenson and Vermeij, 2016). 

Carcharocles megalodon (Agassiz, 1843)

FIGURE 2.14

Synonymy follows Purdy et al. (2001) and Reinecke et al. (2011).

Description. The enormous teeth of C. megalodon are 

the most avidly pursued fossil from Calvert Cliffs. At heights in 

excess of 150 mm, they are the largest chondrichthyan teeth and, 

except for C. chubutensis, are not easily confused with other 

Calvert Cliffs teeth. In general, the descriptions of teeth from 

the two Carcharocles species are similar, although they differ 

in some details. Specifically, both the upper (Figure 2.14A) and 

lower (Figure 2.14B) teeth of C. megalodon tend to be somewhat broader, with more spatulate coronal tips than those of C. 

chubutensis, although this really becomes obvious only in larger 

specimens. The shoulders lack cusplets, although in some cases 

there is a low, vestigial cusplet that joins the coronal cutting edge 

without an intervening notch. In other respects the two species 

are comparable.

Small, heart-shaped Carcharocles teeth are infrequently collected from Calvert Cliffs (Figure 2.14D,E). These teeth have 

thick crowns with convex labial and lingual surfaces, producing 

a lenticular cross section in the apical half of the crown. Basally, 

the lingual face becomes more weakly convex, whereas the labial 

face is more complex, with convex lateral margins and a medial 

triangular depression. This triangular area is contiguous, with 

a broad shallow depression on the labial root face that extends 

to a broad concavity on the basal margin of the tooth. Both the 

mesial and distal cutting edges are completely serrated and are 

weakly convex to nearly straight. On some specimens, the cutting edges are broadly undulating, with a shallow concavity at 

mid-crown (Figure 2.14G). Presumed upper and lower teeth are 

distinguished by the position of the coronal apex when viewed 

in profile. In upper teeth, the coronal apex is arched labially. 

This curvature is most obvious in teeth > 30 mm in height and 

subtler in smaller teeth. Lower teeth have a crown that is erect 

or bent lingually in profile and varies little across the size range 

examined. Roots are relatively short and separated into lobes by 

a shallow to deep concavity of the basal root margin. Maximum 

size for these teeth is about 50 mm. 

Discussion. The huge size of C. megalodon teeth makes 

them unmistakable, and they have been extensively discussed in 

both the popular and professional literature. Less clear are the 

scaling relationships in tooth morphologies that govern shape 

changes across the enormous size range of these teeth. Of particular interest are the comparatively small, heart-shaped teeth 

(Figure 2.14C–E). These unusual teeth are sometimes referred 

to as “Hubbell teeth” (not to be confused with the late Miocene 

lamnid Carcharodon hubbelli Ehret et al., 2012) and were first 

reported in the literature by Applegate and Espinosa-Arrubarrena (1996:32, fig. 11, nos. 3–5). Teeth with this morphology 

have been described as being either slightly pathological (Purdy 

et al., 2001:134) or from neonatal individuals (Renz, 2002:89; 

Pimiento et al., 2010). Of these two possibilities, a neonatal 

origin of the teeth is the more plausible as the teeth are typically symmetrical and of consistent morphology (unusual for 

pathological teeth) and restricted to smaller sizes. Pimiento et 

al. (2010) argue that there is a progression in morphology from 

the smallest neonatal teeth to the more typical juvenile teeth but 

provide little evidence to support this premise. On the basis of 

scaling relationships (Shimada, 2003) and ontogeny of the modern C. carcharias they separate neonates from juveniles at a total 

length of about 4 m. Upper anterior teeth for sharks of this size 

would have crown heights of 33–35 mm (=total height of about 

50 mm), whereas lower anterior teeth would have crown heights 

of 27–30 mm. Lateral teeth for sharks of 4 m length would have 

smaller teeth with maximum crown heights of about 27–29 mm 

for upper laterals and 21–22 mm for lower teeth. On the basis 

of these criteria, more than 30 neonatal teeth were available for 

study from Calvert Cliffs, and changes in morphology with increasing tooth size can be easily traced across a size range of 

15–50 mm.

The tooth size for the neonatal-juvenile transition is highly 

variable, as previously suggested by Pimiento et al. (2010). Even 

the smallest teeth examined had the distinctive convex labial 

crown face and bilobed roots of neonates, but the changes in 

these two characteristics were decoupled in larger teeth. Some 

teeth (Figure 2.14F) are of comparatively small size but have a 

fully adult morphology for this tooth position. Conversely, some 

teeth (e.g., CMM-V-366; upper lateral tooth fragment, width = 

72.5 mm) have an adult coronal morphology but retain the bilobed neonatal root structure. 

Stratigraphic and Geographic Ranges. The 

teeth of C. megalodon are most commonly collected as beach 

specimens, and although they occur along the length of Calvert 

Cliffs, they are most often found from the middle of Calvert 
NUMBER 100 • 8 9

B

A

C

D E

F G

FIGURE 2.14. Carcharocles megalodon teeth (separate 1 cm scale bars for A–C and D–G). (A) Left upper anterior tooth, lingual view (UMCP 10061; Matoaka Cottages, Maryland). (B) Left lower lateral tooth, lingual 

view (UMCP 10060; Western Shores, Md.). (C) Left upper lateral tooth, labial view (UMCP 11165; Matoaka 

Cottages, Md.). (D) Lower neonatal tooth, lingual view (UMCP 11397; Matoaka Cottages, Md.). (E) Lower 

neonatal tooth, lateral view (UMCP 11397; Matoaka Cottages, Md.). (F) Upper lateral tooth, lingual view 

(UMCP 12599; Bayfront Park, Md.). (G) Upper neonatal/juvenile tooth, lingual view (UMCP 12600; north of 

Calvert Cliffs Nuclear Power Plant, Md.).
9 0 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Cliffs northward. Teeth found in place are known from beds 

3–5, 8, and 10–14. Although large C. megalodon teeth are quite 

rare, smaller specimens are not, and more than 150 teeth were 

examined for this study. 

Carcharocles megalodon is a cosmopolitan species, and 

teeth have been very widely reported from early Miocene (Burdigalian) through late Pliocene (Piacenzian) formations from many 

countries, including Argentina, the Azores, Australia, Austria, 

Belgium, Congo, the Czech Republic, France, Germany, India, 

Italy, Japan, Lesser Antilles, Madagascar, Mallorca, Malta, the 

Netherlands, New Zealand, Panama, Peru, Poland, Portugal, 

Spain, Tunisia, United States, and Venezuela (Radwański, 1965; 

Cappetta, 1970; Keyes, 1972; Hirota, 1979; Cappetta, 1987; 

Nolf, 1988; Kemp, 1991; Yabumoto and Uyeno, 1994; Antunes 

et al., 1999a; Müller, 1999; Aguilera and Rodriguez de Aguilera, 

2001; Purdy et al., 2001; Ward and Bonavia, 2001; Vicens and 

Rodríguez-Perea, 2003; Apolín et al., 2004; Marsili, 2008; Portell et al., 2008; Rögl et al., 2008; Pimiento et al., 2010; Schultz 

et al., 2010; Cione et al., 2011; Reinecke et al., 2011; Ávila et 

al., 2012; Cappetta, 2012; Bor et al., 2012; Andrianavalona et 

al., 2015; Pimiento and Balk, 2015; Reolid and Molina, 2015; 

Landini et al., 2017). By evaluating post-Miocene records for 

C. megalodon, Pimiento and Clements (2014) were able to 

produce a most likely estimate of the C. megalodon extinction 

at ~2.6 mya. 

Carcharocles Vertebral Centra

FIGURE 2.15A–C

Description. Likely Carcharocles centra from Calvert 

Cliffs are round or weakly ovoid in axial view and septate and 

have thickened rims. The septa are simple and straight and may 

bifurcate as they approach the rims. The interseptal spaces are 

ovoid and relatively broad. When viewed from either dorsal or 

ventral perspective, the centra have straight lateral margins, although the distal edges of the septal walls are thin and easily 

damaged, making this character difficult to observe. The rim 

margins are straight or weakly recurved. The dorsal and ventral 

foramina are ovoid and reach almost to the rims. 

Discussion. Although the teeth of C. megalodon are 

widely known, other skeletal elements are infrequently collected and even more rarely described in the literature (Leriche, 

1926:426; Gottfried et al., 1996: fig. 1C; Kraig, 2008:19–21). 

Bartsch and Barwick (1941) erroneously listed vertebrae from 

Calvert Cliffs as those of C. megalodon, although Gottfried et 

al. (1996) reevaluated those centra and identified them as being 

consistent with the centra of Cetorhinus. Centra attributable to 

C. megalodon are quite rare, and only two were examined for 

this study. 

Large Carcharocles vertebrae can be easily mistaken only 

for those of Cetorhinus. However, Cetorhinus centra have much 

more delicate septa that are rarely preserved and an axial foramen 

that is lacking in Carcharocles centra. Carcharocles centra differ 

from those of other large lamniforms, such as Isurus and Carcharodon, in having thicker rims and larger interseptal spaces. 

Carcharocles Morphology and Biology

Carcharocles megalodon was among the largest marine 

predators in the Earth’s history, and numerous attempts have 

been made to reconstruct both its appearance and body size. 

Unfortunately, the absence of intact, well-documented skeletons 

precludes simple, direct interpretations of either body shape or 

size. Instead, C. megalodon reconstructions must rely on the 

application of general principles of functional morphology and 

scaling relationships. 

Reconstructed Morphology. The physical appearance of C. megalodon has generally been reconstructed using 

C. carcharias as a model, with one of the most rigorous of these 

reconstructions (Gottfried et al., 1996) being based on statistical 

extrapolations of C. carcharias morphology. This evidence was 

used for a skeletal reconstruction at the Calvert Marine Museum 

(Figure 2.15) at the southern end of Calvert Cliffs in Solomons, 

Maryland. But if (as discussed above) the preponderance of evidence supports an evolutionary lineage for C. megalodon that 

is separate from that of C. carcharias, how realistic are these 

morphological reconstructions? An assessment requires a twopronged approach: (1) a biomechanical evaluation of the likely 

overall morphology of a very large, axially swimming shark and 

(2) a review of how different specific morphological details map 

onto phylogenetic relationships within the lamniforms. 

Carcharocles was a macrophagous carnivore feeding on 

prey that were likely both widely dispersed and evasive, requiring a body morphology capable of covering long distances efficiently (Webb, 1988; Vermeij, 2016; Ferrón et al., 2017). Large 

axial swimmers (such as Carcharocles) must operate at very high 

Reynolds numbers, which, in turn, places strong physical constraints on plausible body morphologies. These constraints are 

so restrictive that numerous large, axial swimmers (e.g., lamnid 

sharks, tunas, odontocete whales, ichthyosaurs) have all evolved 

biomechanically similar thunniform body morphologies (Webb, 

1988; Weihs, 1989; McGowan, 1991; Motani et al., 1996; 

Wilga and Lauder, 2004). All of these groups are characterized 

by (1) a relatively rigid fusiform body with large anterior depth, 

(2) a lunate, high-aspect-ratio caudal fin with lateral keels on 

the caudal peduncle, (3) reduced second dorsal and anal fins of 

the posterior half of the body, (4) a spacing between the first (or 

only) dorsal fin and caudal fin of about 40% the fork length, 

and (5) long pectoral fins. Many thunniform swimmers are also 

at least partially endothermic, either through mesothermy (e.g., 

tunas, lamnid sharks) or true endothermy (e.g., cetaceans). Because of its enormous size, C. megalodon could also maintain an 

elevated body temperature as a gigantotherm (Paladino et al., 

1990) in conjunction with either an ectothermic or a mesothermic metabolism. 
NUMBER 100 • 9 1

The two large, relatively docile planktivores, the whale shark 

(Rhincodon; Orectolobiformes) and basking shark (Cetorhinus; 

Lamniformes), are the only living sharks comparable in size to C. 

megalodon. Despite operating at comparably low speeds, these 

large sharks also have a thunniform body plan. Motani et al. 

(1996: fig. 2a) found a strong correlation in sharks between the 

fineness ratio of the body (maximum body depth divided by precaudal length) and the caudal fin height-length ratio (analogous 

to caudal fin aspect ratio). Further, they found that Rhincodon

and Cetorhinus clustered with the lamnids at one extreme of the 

shark body and caudal fin morphology spectrum. At such large 

body sizes, even the slow-moving basking and whale sharks apparently need a thunniform body form to maintain high swimming efficiency for long-distance cruising (Wilga and Lauder, 

2004). The fossils of C. megalodon are very widely distributed 

and are known from deep-sea sediments (Séret, 1987; Roux and 

Geistdoerfer, 1988; Purdy, 1996), which would be consistent 

with a coastal to oceanic lifestyle where the ability to efficiently 

move long distances would be critical. Zoogeographical research 

on extant sharks reinforces the inference since broad geographic 

ranges are correlated with large (>3 m) size, pelagic habits, and 

coastal to oceanic habitats (Musick et al., 2004; Stevens, 2010).

A B

C

D

FIGURE 2.15. Carcharocles skeleton (1 cm scale bar for A–C). (A) Vertebral centrum; axial view (CMM-V-4739; Scientists Cliffs(?), Maryland). (B) Vertebral centrum; ventral view (CMM-V-4739; Scientists Cliffs(?), Md.). (C) Vertebral centrum; lateral view (CMM-V-4739; Scientists Cliffs(?), Md.). (D) Skeletal reconstruction of Carcharocles megalodon at the Calvert Marine Museum, Solomons, Md. (courtesy of Calvert 

Marine Museum; drawing by Connie Barut-Rankin).
9 2 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

There is an alternative body morphology for large coastal 

to oceanic sharks that is less efficient but nonetheless possible. 

Carcharhiniform swimming (Thompson and Simanek, 1977; 

Webb, 1988) is a form of carangiform swimming widespread 

in carcharhinid and sphyrnid sharks, although it also occurs in 

lamniforms, such as Carcharias, Odontaspis, and Alopias. Carcharhiniform swimmers are less specialized than thunniform 

swimmers with (1) less body depth, (2) great flexibility, (3) a 

lower-aspect-ratio caudal fin, (4) a thicker caudal peduncle lacking lateral keels, (5) larger second dorsal and anal fins, (6) a more 

flattened head, and (7) a lack of mesothermy. Within this group 

there is a broad range of morphologies, with some carcharhinids 

approaching thunniform swimmers in fineness ratio and caudal 

fin height-length ratio (Motani et al., 1996). Some carcharhinids 

have even independently evolved thunniform features, such as 

the caudal keels of Galeocerdo (Compagno, 1984). The lamniforms within this body morphology are also diverse. Odontaspids have low fineness ratios and caudal fin height-length ratios 

(Motani et al., 1996) and are comparatively sluggish swimmers 

(Compagno, 1984, 1990b). Further, the low caudal fin heightlength ratio in these sharks is due to a low heterocercal angle 

(=elevation of the dorsal lobe relative to the body axis), a feature 

associated with a diet of small prey in lamniforms (Kim, 2009). 

The alopiids are an unusual group with a morphology that is difficult to assign to a single group. The unique, exceptionally long 

dorsal lobe of the caudal fin is used to stun small schooling fish 

and is held at a relatively low angle, like most carcharhiniform 

swimmers. Like this group, alopiids also have flattened heads and 

lack caudal keels. But they have reduced second dorsal fins and 

anal fins and partial endothermy (in A. vulpinus) like thunniform 

swimmers (Compagno, 2002; Sepulveda et al., 2005). Further, 

one species (A. superciliosus) has a shorter dorsal lobe and has 

evolved a caudal fin functionally comparable to the thunniform 

lamnids (Kim, 2009). 

One final possibility is an elongate, anguilliform body plan. 

This morphology occurs in a few large, primarily coastal, amniotes, such as primitive ichthyosaurs and the cetacean Basilosaurus. But the slow swimming speeds associated with this body 

morphology would require that these animals either feed on slow 

or immobile prey or capture prey from ambush (Motani et al., 

1996; Massare, 1998; McHenry, 2009:437; Corrie, 2013:54). 

This lifestyle is inconsistent with the global, coastal to oceanic 

distribution of Carcharocles and is very unlikely to have been 

present in this genus. 

On the basis of the need to move long distances and the 

physical constraints on operating at high Reynolds numbers, 

the most likely body shape of Carcharocles would be that of 

a thunniform swimmer. A specialized form of carcharhiniform 

swimmer with a body morphology approaching that of thunniform swimmers is possible, although none of the sharks with 

these adaptations have ever approached the tremendous size of 

Carcharocles. The physical constraints of such a large body may 

simply require the inherent efficiency of the thunniform body 

plan to be biologically viable. 

Biomechanical constraints on morphology are, to a large extent, independent of evolutionary history. So the caudal fins of a 

lamnid shark and an odontocete whale push the body forward in 

fundamentally similar ways; the caudal fin has a high lift-to-drag 

ratio and generates hydrodynamic lift that pushes the body forward. The same is not true of the internal morphological details 

of how these two caudal fins are constructed. For example, the 

Carcharodon caudal fin contains phylogenetic signals about how 

it evolved, which, in turn, allows an assessment of which characters are plesiomorphic and which are apomorphic. Generalized 

lamniforms synapomorphies, such as plesodic pectoral fins, were 

almost certainly present in Carcharocles. On the other hand, derived characters restricted to the extant lamnids are unlikely to 

be found in an independent Carcharocles lineage. Unfortunately, 

the unsettled phylogeny of extinct lamniforms complicates definitive assessments of some skeletal features. 

A number of skeletal attributes likely differed between Carcharodon and Carcharocles, although many of them would be 

difficult to observe on a skeleton, let alone a soft-tissue reconstruction. For example, lamniforms are characterized by a reduction of the labial cartilages, which are present in Mitsukurina, 

Odontaspis, and Carcharias but lacking in more derived groups 

(Shimada et al., 2009). Because lamniform phylogeny is not fully 

resolved, particularly with respect to extinct genera, labial cartilages may have been present in Carcharocles. Fortunately, their 

presence or absence would have no outward manifestation on 

a whole-body reconstruction. Likewise, Carcharodon and other 

lamnids have the palatoquadrate attached to the chondrocranium by a single palatonasal ligament, whereas less derived macrophagous lamniforms (e.g., Alopias) have both a palatonasal 

ligament and a pair of ethmopalatine ligaments (Wilga, 2005). 

The two forms of jaw suspension have subtle differences in the 

size of the ligament attachment areas of the palatoquadrate and 

chondrocranium that would be difficult to observe on a skeleton. 

These differences could have important consequences for jaw 

movements during prey capture but would have no discernible 

effect on a static reconstruction. Likewise, any number of other 

skeletal details (e.g., the number of fin rays in the pectoral fins, 

the curvature of the palatoquadrate, and Meckel’s cartilages) 

either are difficult to assess without better information from 

extant species or would produce minimal changes in reconstructions. Overall, only two morphological features of the skeletal 

reconstruction shown in Figure 2.15D (i.e., the rostrum and the 

caudal fin) reflect derived features unlikely to have been present in Carcharocles and distinctive enough to affect whole-body 

reconstructions. 

The rostrum in the Gottfried et al. (1996) reconstruction 

is a straightforward extrapolation of rostral morphology in C. 

carcharias. The rostrum of C. carcharias is shorter than in other 

lamniforms and appears to be an autapomorphy (Compagno, 

1990a; Mollen, 2010). When the C. carcharias rostrum is extrapolated to a much larger body size, it becomes shorter and 

more robust, producing the distinctive pug-nosed head profile of this reconstruction. The majority of lamniforms have a 
NUMBER 100 • 9 3

somewhat longer rostrum, which seems to be a more likely condition for Carcharocles. 

The caudal fin of C. carcharias (and as reflected in the skeletal reconstruction of C. megalodon in Figure 2.15D) has both 

a high heterocercal angle (=the angular elevation of the dorsal 

lobe of the tail relative to the body axis) and a high hypochordal 

angle (=the angle of the hypochordal cartilages of the tail relative to the vertebral column in the caudal fin). This combination 

is a synapomorphy of the family Lamnidae and is not known in 

any other lamniforms. The only lamniform with roughly comparable caudal fin morphology is the basking shark (Cetorhinus 

maximus). The semilunate caudal fin of this species also has a 

high heterocercal angle but has a lower hypochordal angle and 

a correspondingly smaller ventral lobe (Kim, 2009). Despite the 

difference in morphology, the Cetorhinus caudal fin nonetheless 

has an elevated height-length ratio comparable to that of extant 

lamnids (Motani et al., 1996: fig. 2). Further, the orectolobiform 

whale shark, Rhincodon typus, has independently evolved a 

semilunate caudal fin with a high height-length ratio fully comparable to that of cetorhinids and lamnids (Motani et al., 1996: 

fig. 2). As discussed above, a thunniform body morphology, including a high-aspect-ratio caudal fin, appears to be a prerequisite for a very large axial swimmer. Either a lunate caudal fin 

(as in lamnids) or a semilunate caudal fin (as in Cetorhinus and 

Rhincodon) is a plausible morphology, although the structural 

details in Carcharocles may differ from these extant species. 

In particular, the lunate caudal fin of lamnids uses a uniquely 

elevated hypochordal angle to support the longer ventral lobe. 

Carcharocles would need to either independently evolve a high 

angle on the hypochordal cartilages or support an elongated ventral lobe using other mechanisms. An independently derived high 

hypochordal angle is certainly plausible. The bigeye thresher 

(A. superciliosus) has a relatively elongated dorsal lobe but has 

evolved a high hypochordal angle and a caudal fin functionally 

analogous to that of the lamnids (Kim, 2009). Other morphological modifications, such as a fusion or heavier mineralization of 

fin rays, an increase in the density of connective tissues, or an increase in the aspect ratio of the lobe (Weihs, 1989; Sfakiotakis et 

al., 1999; Lingham-Soliar, 2005a–c), have been shown to stiffen 

caudal fin lobes in thunniform swimmers. In lieu of steeply angled hypochordal cartilages, one or more of these mechanisms 

could have been present in Carcharocles to support an elongated 

ventral lobe. A semilunate caudal fin, like that of Cetorhinus and 

Rhincodon, would have required less extreme structural modifications and may be even more likely as a caudal fin morphology 

for Carcharocles. In Cetorhinus the caudal vertebral skeleton is 

relatively weakly mineralized, commensurate with the less active 

lifestyle of this planktivore. Such a condition would be unlikely 

for a presumably more active macrophage, like Carcharocles, 

where more extensive mineralization would have been necessary. 

All extant lamniforms with a low heterocercal angle (e.g., 

Carcharias, Odontaspis, and most Alopias) feed on comparatively small prey (Kim, 2009). These sharks also have low fineness ratios and caudal fin height-length ratios (Motani et al., 

1996). Lamniforms with high heterocercal angles are all coastal 

to oceanic cruising forms but can have two different lifestyles, 

either as predators of comparatively large prey (Carcharodon, 

Isurus, Lamna) or as microphagous filter feeders (Cetorhinus). 

All of these sharks also have large fineness ratios and caudal fin 

height-length ratios (Motani et al., 1996).

Estimated Body Size. There have been a number of 

attempts to determine the maximum body length for C. megalodon. The most reliable means of determining length is an intact skeleton, but none is yet available. In the absence of intact 

skeletons, estimates must be based on tooth parameters, such as 

enameloid height of the first upper anterior tooth (=13 m; Randall, 1973), anterior tooth height measured along the midline of 

the tooth (=15.9 m; Gottfried et al., 1996), length of the mesial 

cutting edge (=15.1 m, Shimada, 2003; 16.8 m, Pimiento et al., 

2010; ~18 m, Pimiento and Balk, 2015), and tooth width (=15.5 

m; C. Jeremiah in Renz, 2002). These estimates are based on the 

largest specimens available at the time and may not reflect the 

largest individuals. Other, less rigorous estimates push the maximum length to at least 24 m (Papson, 1992). 

Length estimates produced as extrapolations far beyond the 

size range of extant analogs all implicitly assume that size relationships are linear at all scales and that there are no ceiling 

effects due to biomechanical or physiological constraints. There 

is some evidence that the extant whale shark (Rhincodon typus) 

may reach 20 m (Chen et al., 1997; Compagno, 2002), so neoselachians are under no apparent biomechanical constraints on 

building a cartilaginous skeleton of a size comparable with some 

of the larger estimates for C. megalodon. But physiological constraints, such as on the cardiovascular system, could be a very 

different matter. Rhincodon is a slow-moving filter feeder and 

would make comparatively low demands on its cardiovascular 

system. Yet there are strong selective pressures for filter-feeding 

sharks to be as large as possible since swimming speed and efficiency both increase with body size (Vogel, 1988:310–312; 

McMahon and Bonner, 1993:187–191; Alexander, 1998). So a 

slow-moving 20 m whale shark is probably at the maximum size 

for a shark of this lifestyle. 

The higher-speed locomotion of a macrophagous shark of 

comparable size would put far higher demands on the cardiovascular system. Sharks have a comparatively simple, single-circuit 

cardiovascular system in which blood must pass through both 

the gill capillaries and body capillaries before returning to the 

heart (Muñoz-Chápuli, 1999). Large, active sharks have evolved 

adaptations to improve blood flow during high-speed locomotion, including more efficient cardiac pumping, venous pumps, 

and larger gills (Emery et al., 1985; Emery and Szczepanski, 

1986; Lai et al., 1997, 2004; Satchell, 1999). Although these 

allow for higher activity levels in extant lamnids, such as the 

shortfin mako (I. oxyrinchus) and great white shark (C. carcharias), which reach maximum sizes of about 6 m, it is unclear 

whether they would be adequate for a truly gigantic, fast-swimming shark of about 20 m. 
9 4 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A C. megalodon of 20 m or more could face additional, unexpected difficulties in capturing prey. As already noted, swimming speed increases with body length. But swimming speed is 

also inversely related to maneuverability, and a predator that 

becomes substantially larger than its prey loses the ability to 

capture elusive prey (Alexander, 1998; McKenzie et al., 2007; 

Lucifora et al., 2009). Gigantic filter feeders, such as Rhincodon, 

are under no such constraint since they feed on prey with such 

limited powers of locomotion that they are essentially immobile. 

Smaller C. megalodon would certainly be capable of pursuing 

and capturing a broad range of prey species, but at larger sizes 

scavenging may have become a more energetically viable foraging strategy. If C. megalodon ever reached the length of 20 m 

or more, as sometimes proposed, they may have been relatively 

slow moving, obligate scavengers that used their sheer size to 

intimidate smaller scavengers. This interpretation is supported 

by a recently published model on the evolution of giant marine 

predators (Ferrón et al., 2017) that found that even with a mesothermic thermal strategy large C. megalodon would be at the 

lowest activity levels possible for a macrophagous predator. This 

low activity level would interfere with the ability of C. megalodon to pursue actively swimming prey but would have less impact on scavenging. 

Evidence of Feeding. As a top carnivore, C. megalodon undoubtedly preyed on a broad range of prey. The best 

available evidence is the presence of large bite marks in marine 

mammal bones (Purdy, 1996; Renz, 2002; Godfrey and Altman, 

2005; Aguilera et al., 2008; Kallal et al., 2010; Collareta et al., 

2017a). In most cases, the marks are large, deep gashes, although 

in exceptional cases, fine parallel grooving produced by the serrated cutting edges is visible (Figure 2.16A). As with most bite 

mark data, it is not always clear whether these bite marks reflect 

predation, failed predation, or scavenging by C. megalodon. The 

distribution of large (≥4 mm wide) bite marks on a cetotherid 

whale from Calvert Cliffs (Newell, 1998; Figure 2.16B) appears 

to be evidence of an attack on a live whale. The bite marks are 

concentrated in the thoracic region, rather than on the flanks, 

where the large swimming muscles are present. Using biomechanical principles, predatory strikes on prey should be directed 

at the center of mass, as it is the most predictable target on the 

prey’s body. For piscoid prey the center of mass corresponds to 

the deepest portion of the body, about one-third of the body 

length from the anterior end (Webb and Skadsen, 1980; Webb, 

1984). This position matches the highest concentration of bite 

marks on the whale skeleton and is consistent with this predicted 

attack strategy. This region contains numerous visceral organs, 

such as the heart and lungs, and a bite in this area would quickly 

subdue the prey. But the thoracic viscera are also protected by 

numerous rib and forelimb bones that could deter attacks and 

protect vital organs. The teeth of C. megalodon are particularly 

robust and appear adapted for surviving impacts against bones 

(Farlow et al., 1991; Kent, unpubl. data). 

This apparent attack strategy by C. megalodon is very different from the placement of attacks by the extant C. carcharias, 

which avoids this area in cetaceans and instead attacks other 

body areas, including the abdomen and caudal peduncle. These 

areas have major blood vessels and swimming muscles, and 

damage to these areas would quickly disable the prey (Long and 

Jones, 1996). This is a very efficient attack strategy, but the caudal area of cetaceans, in particular, would be a less predictable 

target than the center of mass and would require more rapid 

neuronal processing in the brain to be successful. Lamnids are 

known to maintain elevated brain temperatures, which would 

facilitate their ability to track the complex movements of the 

caudal area during an attack (Bernal et al., 2012). Further, although a caudal attack is plausible for C. carcharias feeding on 

smaller, porpoise-sized cetaceans, such an attack on much larger 

whales by C. megalodon would expose the shark to possible 

damage from the powerful caudal fluke (Collareta et al., 2017a). 

Genus Parotodus Cappetta, 1980

The higher taxonomic classification of the genus Parotodus

is, at present, not fully resolved (Bourdon, 2008; Shimada et al., 

2016). There is little doubt that Parotodus is a lamniform, but 

several possible familial alignments have been proposed in the 

literature. None of these proposals is supported by strong evidence, although the reason is primarily the lack of any information from nondental sources.

• For Lamnidae (e.g., Purdy et al., 2001), the assignment 

allies Parotodus with extinct and extant members of Carcharodon, Isurus, and Lamna. This approach is a conservative one that forces extinct species into morphologically 

less diverse extant taxa. This assignment is possible but 

ignores consistent morphological details that separate 

Parotodus from extant lamnids.

• For Cardabiodontidae (Siverson, 1999), the assignment 

places Parotodus with the Late Cretaceous genus Cardabiodon. Because there are tens of millions of years between the latest Cardabiodon in the Cenomanian and the 

earliest Parotodus in the Oligocene, the cardabiodontids 

would be a Lazarus taxon (Jablonski, 1986) that reappears after an extended absence from the fossil record. 

This does not preclude the alliance of Parotodus with 

Cardabiodon since new discoveries could bridge this gap. 

But when combined with differences in tooth morphology, this disjunct distribution makes this assignment possible but unlikely. In later research, Siverson discussed 

morphological differences between these two genera and 

the problems with the assignment of Parotodus to the 

Cardabiodontidae (Siverson and Lindgren, 2005). 

• For Alopiidae (Herman, 1979; Purdy et al., 2001), the 

assignment is based on the superficial similarity between 

the teeth of Parotodus and those of some extant thresher 

sharks, including the absence of marked size differences 

between anterior and lateral teeth. Such similarities must 

be viewed with caution because of the huge size differences 
NUMBER 100 • 9 5

B

A

FIGURE 2.16. Cetacean bone damage attributable to Carcharocles. (A) Close-up of a bite mark with distinctive 

serration striations on a cetothere mandible from Calvert Cliffs (CMM-V-3095; Little Cove Point/Driftwood 

Beach, Maryland; 1 cm scale bar). (B) Distribution of large bite marks on a Pelocetus calvertensis skeleton from 

Calvert Cliffs (USNM 11976; Newell, 1998). 
9 6 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

between extant Alopias teeth and Parotodus teeth. Allometric (i.e., size-related) changes in shape due to scaling phenomena are widely known in animals, including 

sharks (Huber et al., 2006; Nyberg et al., 2006). Two 

giant Alopias are known from the Miocene, but although 

their teeth approach those of Parotodus in size, they have 

fundamentally different patterns of tooth vascularization. 

• For Otodontidae (Glikman, 1964; Cappetta, 1987, 

2006), the assignment is based on relatively generalized 

dental characters, such as large size, a robust crown and 

root, and a wide neck that allies Parotodus with Otodus

and Carcharocles. These characters are not unique and 

occur in varying degrees in other large lamniform teeth, 

such as those of Cardabiodon, Cretolamna, and Cretoxyrhina. The one character that allies Parotodus with other 

otodontids is the presence of nutrient foramina in a broad 

mesiodistal arc over the thickest portion of the root (i.e., 

dispersed pores of Kent, 1994). This differs from the mesiobasal cluster of foramina in other large lamniforms. 

Mewis (2008) performed a phylogenetic analysis of tooth 

morphology in fossil lamniforms to evaluate the relationships 

among unserrated Carcharodon, C. carcharias, and Carcharocles. The consensus tree from this study had Parotodus as the 

sister group of a clade containing the Otodontidae and the Lamnidae. Unfortunately, it is difficult to assess the reliability of this 

study with respect to the status of Parotodus since (as Mewis acknowledges) the alopiids were not included in the analysis, and 

many character states for P. benedenii were listed as undefined. 

Consequently, this study does little to resolve ambiguities over 

the familial placement of Parotodus. 

At the present time, the rather meager available evidence 

supports the retention of Parotodus within the Otodontidae. The 

similarities in gross tooth morphology, along with the distinctive 

vascularization in these three genera, are consistent with their 

confamilial status. A thorough evaluation of tooth morphology in Parotodus, including a more comprehensive phylogenetic 

analysis of dental morphology comparable to that of Mewis 

(2008), is clearly needed. 

Parotodus benedenii (Le Hon, 1871)

FIGURE 2.17

Synonymy follows Purdy et al. (2001), Marsili et al. (2007), and Reinecke 

et al. (2011).

Description. The teeth of this species can be large and 

remarkably robust. The crown is thick and triangular and either curved distally in upper teeth or distally curved to erect in 

lower teeth (Figure 2.17A). In profile, the crowns of upper teeth 

are curved labially, whereas those of lower teeth are erect or inclined lingually. The cutting edges are smooth and unserrated. 

The crown is separated from the root on the lingual face by a 

broad neck that retains a comparatively consistent width out 

B

A

C

D

FIGURE 2.17. Parotodus benedenii teeth (1 cm scale bar). (A) Lower anterior tooth; lingual view (CMM-V-1633; Scientists Cliffs, Maryland). 

(B) Upper lateral tooth; lingual view (CMM-V-7803; Plum Point, Md.). (C) Upper lateral tooth; labial view (CMM-V-7803; Plum Point, Md.). 

(D) Lateral tooth; labial view (CMM-V-18; Bayfront Park, Md.).
NUMBER 100 • 9 7

onto the mesial and distal shoulders of the tooth. The root is very 

thick, and lower teeth have a particularly massive root because 

of a large lingual protuberance. The basal margin of the root 

is broadly concave, and the root lobes are elongated and have 

rounded ends. Small teeth have a single nutrient foramen on the 

most elevated portion of the lingual protuberance. In progressively larger teeth, additional foramina appear laterally. In large 

teeth the nutrient foramina are disposed in a broad mesiodistal 

arc over the thickest portion of the root, although these foramina 

are typically small and can be difficult to observe. 

Lateral teeth of both the upper and lower jaws have somewhat lower crowns. The height and width of lateral teeth are 

similar (Figure 2.17B,C) but otherwise resemble the taller anteriors. Crowns in both jaws become distally curved and, in profile, 

become more erect. Roots of lower teeth lose the prominent lingual protuberance, although they are still thicker than those of 

comparable upper teeth. Some lateral teeth near the commissure 

may bear low, broad cusplets, particularly on the distal shoulder 

(Figure 2.17D). 

Discussion. Kent and Powell (1999) reconstructed the 

dentition of P. benedenii on the basis of an assemblage of 114 

teeth as having 14 upper and 13 lower tooth positions (USNM 

489114). Position assignments were based on patterns of changes 

to crown and root morphology derived from extant lamnid and 

alopiid dentitions. The most speculative position assignment was 

for a moderately sized coronal fragment that was more compressed than anterior teeth and more erect than lateral teeth. 

Two possible assignments for this fragment were proposed, either a tooth from another individual or an upper intermediate 

(=third anterior) tooth. The general rarity of P. benedenii would 

make a second individual unlikely. Further, in bivariate plots of a 

variety of coronal parameters (corrected to minimize the effect of 

size as a confounding factor) the fragment consistently graphed 

as an outlier from both anterior and lateral teeth. Using these 

observations, it was designated as an upper intermediate tooth. 

Ward and Bonavia (2001) proposed a third alternative, that 

the coronal fragment represented a symphyseal tooth. This interpretation is unlikely, as the morphology of this fragment is unlike 

the symphyseals in an associated set of about 30 P. benedenii

teeth from the early Miocene Batesford Limestone of Victoria, 

Australia (Kemp, 1991: pl. 32). Kemp tentatively identifies one 

of these teeth (pl. 32D) as a lower symphyseal and a second (pl. 

32E) as an upper symphyseal. Purdy et al. (2001) agree with the 

assignment of these two teeth on the basis of the relative compression of the crowns. The morphology of these two teeth is 

consistent with symphyseals reported from associated dentitions 

of other large lamniform sharks (Shimada, 2002, 2007; Siverson, 

1999) and very different from the coronal fragment identified as 

an upper intermediate tooth in USNM 489114. 

One final, more speculative interpretation of this tooth is 

that it actually represents the upper first anterior, and the two 

anterior files reported by Kent and Powell represent the second 

and third files, respectively. 

Stratigraphic and Geographic Ranges. The 

teeth of P. benedenii are very rare along Calvert Cliffs (six specimens), having been collected primarily on beaches associated 

with the Calvert and Choptank Formations. In situ specimens 

are known only from beds 3 and 10. At inland sites in the MidAtlantic area, specimens are also known in situ from bed 1 of the 

Calvert Formation, as well as from the Eastover Formation (indeterminate horizon; late Miocene). Parotodus benedenii has been 

widely reported from early Oligocene through early Pliocene fossil beds of Europe (Belgium, Germany, Hungary, Italy, Malta, 

the Netherlands, Portugal, Slovakia, and Switzerland), Africa 

(Angola and South Africa), the Azores, and the United States 

(Maryland, North Carolina, and Virginia), along with Australia, 

Japan, and New Zealand in the western Pacific (Davies, 1964; 

van den Bosch et al., 1975; Osawa et al., 1978; Kuga, 1985; 

Cappetta, 1987, 2012; Nolf, 1988; Kemp, 1991; Yabumoto and 

Uyeno, 1994; Kent and Powell, 1999; Purdy et al., 2001; Ward 

and Bonavia, 2001; Reinecke et al., 2005, 2011; Kocsis, 2007; 

Marsili et al., 2007; Marsili, 2008; Ávila et al., 2012; Bor et al., 

2012; Cappetta, 2012; Everaert, 2014). In addition to published 

records of P. benedenii, specimens are also known from California, South Carolina, and Peru (BWK, pers. obs.). 

Miocene specimens of P. benedenii, such as those from Calvert Cliffs, are typically smaller and slightly more gracile than the 

massive specimens recovered from the early Pliocene (Cappetta, 

1987, 2012). 

Family Alopiidae Bonaparte, 1838

Genus Alopias Rafinesque, 1810

Thresher Sharks – Alopiidae

The thresher sharks belong to the macroceanic ecomorphotype (Compagno, 1990b), large, active, neritic to epipelagic 

sharks found in tropical and temperate oceans worldwide. They 

are easily recognized because of their distinctive body profile 

with a stout, fusiform body; a relatively short, broad head; a 

small mouth; and an elongated, scythe-like dorsal lobe of the 

caudal fin. Living threshers reach a length of at least 5.7 m (and 

perhaps up to 6.5 m), although because the dorsal lobe of the 

caudal fin is approximately as long as the body itself, maximum 

weights are considerably less than would be expected on the 

basis of total length. Extant threshers are specialized predators 

of small schooling squid and fishes (e.g., sardines, herring, anchovies, mackerels, and bluefishes) and also benthic fishes (e.g., 
9 8 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

flounder and hake) and pelagic crustaceans. They swim around 

schools of prey in circles of decreasing size, herding them into 

compact masses, and then use the dorsal lobe of the tail to stun 

and cripple prey. Threshers then turn and consume the disabled 

prey (Compagno, 1984, 2002; Aalbers et al., 2010; Castro, 

2011). 

The dentition is unusual for a macrophagous lamniform 

in that there are no greatly enlarged anterior teeth. Instead, the 

dentition of comparatively small teeth has weak gradient homodonty, with anterior teeth only slightly larger than the lateral 

teeth. Because threshers ingest crippled prey that have limited 

ability to escape, their teeth are relatively small and numerous. 

Two extant species, the pelagic thresher (A. pelagicus) and the 

common thresher (A. vulpinus), have an elevated and variable 

number of tooth row groups, ranging from 41–45 in the upper 

jaw and 37–38 in the lower jaw in A. pelagicus to 32–52 in the 

upper jaw and 25–50 in the lower jaw of A. vulpinus. The third 

extant species, the bigeye thresher (A. superciliosus) has larger 

teeth and a lower tooth count of 22–27 in the upper jaw and 

20–24 in the lower jaw. The larger teeth of A. superciliosus allow 

it to prey on larger prey, such as lancet fishes and small billfishes. 

The exceptionally large eyes of A. supercilious also allow this 

species to forage in deeper water such as the outer continental 

shelves and upper continental slopes (Compagno, 2002). 

Four species of Alopias are known from Calvert Cliffs, two 

small-toothed species (maximum tooth height about 15 mm) and 

two giant-toothed species (maximum tooth height > 40 mm). The 

small-toothed species have teeth that are similar in size and overall morphology and are allied with extant thresher shark species. 

Alopias cf. A. vulpinus (Bonnaterre, 1788)

FIGURE 2.18A–C

Synonymy follows Purdy et al. (2001) and Reinecke et al. (2011).

Description. The most common Alopias from Calvert 

Cliffs is A. cf. A. vulpinus. The teeth are small, reaching a maximum size of about 15 mm in either height or width. The crown 

is broad, triangular, and erect in anterior files (Figure 2.18A,B). 

The cutting edges are smooth and complete. The crowns are 

compressed and erect in profile. The root has an arched basal 

margin and extended root lobes with rounded ends. The lingual 

face of the root has a modest lingual protuberance bearing a 

single nutrient foramen. The labial face of the crown is flat and 

overhands the labial root face and the proximal portions of the 

root lobes in the form of distinctive callosities. The callosities 

are generally smooth, although a few fine, vertical plicae may be 

present. The basal root margin is widely concave, and the root 

lobes are rounded. In anteriors, the tooth height and width are 

roughly equal. 

Lateral teeth resemble anteriors but have a crown that 

is curved distally (Figure 2.18C). The crown is lower than in 

anterior teeth, and overall, the tooth height is somewhat less 

than the tooth width. 

Discussion. Miocene teeth of this morphology are frequently listed as A. latidens (Cappetta, 1987; Kent, 1994; Müller, 1999) on the basis of the presence of very broad crowns, 

although Purdy et al. (2001) note that coronal width in extant 

A. vulpinus teeth can be quite variable. No extant A. vulpinus

dentition of comparable size was available for study, but differences in relative coronal width (=coronal width measured at the 

inflection point on the distal cutting edge divided by the total 

tooth width) were compared using 12 A. cf. A. vulpinus teeth 

from Calvert Cliffs and 14 teeth from comparable tooth positions from the illustrated dentition of an extant 4 m [13 ft] A. 

vulpinus (Bourdon, 2008–2009, photographically enlarged). 

There was no significant difference in relative coronal width between A. cf. A. vulpinus (mean = 0.37) and A. vulpinus (mean = 

0.39; t = 1.61, P = 0.12). Purdy et al. (2001) note that the labial 

callosity is rounded and plicate in A. cf. A. vulpinus from the 

Pungo River and Yorktown Formations. This condition is less 

pronounced in the teeth from Calvert Cliffs, where the callosity 

is typically thinner and fine, inconspicuous plications are only 

infrequently present. 

Stratigraphic and Geographic Ranges. The 

teeth of A. cf. A. vulpinus are infrequently collected from Calvert Cliffs, although they represent the most abundant thresher 

shark species. This species is known from the Calvert, Choptank, 

and St. Marys Formations, although it is more common on the 

northern and middle portions of the cliffs (Visaggi and Godfrey, 

2010). The only specimens found in situ were from beds 10, 12, 

and 17. More than 20 teeth were examined for this study. 

This species (sometimes listed as A. latidens) has previously 

been reported from the Miocene of Belgium, France, Italy, and 

Maryland (Cappetta, 1987; Kent, 1994; Bourdon, 2006–2009). 

It has also been reported from the late Oligocene (Chattian; 

Steurbaut and Herman, 1978; Nolf, 1988; Baut and Génault, 

1999; Reinecke et al., 2005), but it is unclear whether these teeth 

are conspecific or a separate species, A. latidens. 

The extant common thresher (A. vulpinus) is a circumglobal, 

temperate to occasionally tropical species that occurs primarily 

in oceanic waters. Alopias vulpinus is largely piscivorous but 

also consumes pelagic cephalopods and crustaceans (Gubanov, 

1972; Compagno, 1984, 2002; Compagno et al., 2005; Castro, 

2011). 

Alopias cf. A. superciliosus (Lowe, 1840)

FIGURE 2.18D

Synonymy follows Reinecke et al. (2011; as A. exigua).

Description. The second species of small-toothed 

thresher known from Calvert Cliffs is much less common than 

A. cf. A. vulpinus. The teeth of this species are similar in size to 
NUMBER 100 • 9 9

those of A. cf. A. vulpinus but are much more gracile (Figure 

2.18D). The crown is narrow to only moderately broad and distally inclined, with smooth cutting edges. The cutting edges are 

somewhat variable, ranging from incomplete (restricted to the 

apical half of the crown) to complete. Incomplete cutting edges 

occur primarily on the narrow, relatively erect anterior teeth, 

with complete cutting edges that extend out onto the enameloid 

shoulders becoming more prevalent on lateral teeth. In profile 

the crowns are bent lingually, or slightly reflexed. The labial face 

of the crown overhangs the root to form long, narrow callosities. The root is more delicate than in A. latidens, with a concave basal margin and elongate root lobes with rounded ends. 

The mesial root lobe is frequently longer than the distal lobe 

and roughly aligned with the mesial edge of the crown. The lingual protuberance has one (or sometimes two) nutrient foramina 

within a deeply incised nutrient groove. 

A C B D

E

G

H

F

I

J

K

FIGURE 2.18. Alopias teeth (separate 1 cm scale bars for A–D and E–K). (A) Alopias cf. A. vulpinus anterior tooth; lingual view (CMM-V823; bed 10, Plum Point, Maryland). (B) A. cf. A. vulpinus anterior tooth; labial view (CMM-V-823; bed 10, Plum Point, Md.). (C) A. cf. A. 

vulpinus lateral tooth; lingual view (CMM-V-767; bed 10, Willows, Md.). (D) A. cf. A. superciliosus lateral tooth; lingual view (CMM-V-7694; 

bed 3, Pamunkey River, Virginia). (E) A. grandis partially crenulate upper anterior tooth; labial view (CMM-V-7804; Randle Cliff, Md.). (F) 

A. grandis left lower lateral tooth; lingual view (CMM-V-1335; Chesapeake Beach, Md.). (G) A. grandis left lower lateral tooth; labial view 

(CMM-V-1335; Chesapeake Beach, Md.). (H) Serrated Alopias sp. right upper anterior tooth; lingual view (CMM-V-385; bed 12, Parkers 

Creek, Md.). (I) Serrated Alopias sp. right upper anterior tooth; labial view (CMM-V-385; bed 12, Parkers Creek, Md.). (J) Serrated Alopias

sp. right upper lateral tooth; lingual view (CMM-V-3981; Parkers Creek, Md.). (K) Serrated Alopias sp. right upper lateral tooth; labial view 

(CMM-V-3981; Parkers Creek, Md.).
100 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Discussion. There is some controversy over the exact 

designation for these teeth. The name A. exigua has been widely 

used for narrow-crowned Neogene Alopias, but Purdy et al. 

(2001) and Ward and Bonavia (2001) rejected it on the grounds 

that the type specimens represent a mixture of different species. 

Instead, they allied these teeth (as A. cf. A. superciliosus) with 

the extant bigeye thresher (A. superciliosus). Reinecke et al. 

(2011) reevaluated the type specimens of A. exigua and compared them with a comparatively large sample of teeth from 

the Miocene of Germany. They concluded that A. exigua was a 

valid species and applied this name to Miocene teeth with narrow crowns. Further, they separate A. exigua from A. superciliosus by the absence of the distinct distal heels and shallower 

roots that characterize the latter species. But these characters are 

quite variable in extant A. superciliosus, and it is unclear if they 

are actually adequate for separating the two species. Finally, the 

teeth of A. superciliosus are sexually dimorphic, with anterior 

teeth of females having comparatively broader, more bladelike 

crowns than the narrower, more flexuous crowns of male anteriors (Gruber and Compagno, 1981). This difference is never 

noted by Reinecke et al. (2011), although it does appear to be 

present in their illustrated specimens (e.g., pl. 44, fig. 2). Bor et 

al. (2012) recognize two different tooth morphologies from the 

Miste Beds (Langhian) of the Netherlands, listing them as separate, co-occurring species, A. exigua and A. superciliosus. But 

like Reinecke et al. (2011), they do not consider the possibility 

of sexual dimorphism. 

Unfortunately, the range of variability has never been fully 

documented in either A. exigua or A. superciliosus. Coupled with 

the small number of specimens from Calvert Cliffs, a definitive 

assessment of these teeth is difficult. Pending a more extensive, 

quantitative analysis, the small, narrow-toothed threshers from 

the Calvert Cliffs beds will be allied with A. superciliosus (the 

senior synonym), as A. cf. A. superciliosus. 

Stratigraphic and Geographic Ranges. Teeth 

of A. cf. A. superciliosus are quite rare from Calvert Cliffs, and 

only five were available for study. Fossil teeth of this morphology 

have also been reported from Barbados, Belgium, France, Germany, Italy, Japan, Malta, the Netherlands, Portugal, Venezuela, 

Maryland, Virginia, and North Carolina (Cigala-Fulgosi, 1983, 

1988; Cappetta, 1987, 2012; Nolf, 1988; Kent, 1994; Yabumoto 

and Uyeno, 1994; Antunes et al., 1999; Aguilera and Rodrigues 

de Aguilera, 2001; Purdy et al., 2001; Ward and Bonavia, 2001; 

Bourdon, 2006–2009; Reinecke et al., 2011; Bor et al., 2012).

Living bigeye threshers (A. superciliosus) are a coastal to 

oceanic, tropical and temperate shark that ranges from shallow, 

nearshore waters to depths of more than 700 m. The diet consists of pelagic teleost fishes and cephalopods (Compagno, 1984, 

2002; Compagno et al., 2005; Castro, 2011).

The giant-toothed Alopias not only have teeth that are considerably larger than those of A. cf. A. vulpinus and A. cf. A. 

superciliosus but also have crowns that are broader and taller 

(Figure 2.3B). The root is highly compressed, with much shorter 

root lobes, and in many respects more closely resembles the roots 

of similarly sized lateral teeth of Isurus and Carcharodon. The 

roots of large Alopias differ from these latter genera in having a 

typically arched basal root margin and a single nutrient foramen. 

In Isurus the basal root margin is relatively straight with a medial indentation, whereas in Carcharodon the basal root margin 

is obtusely angled to nearly straight. Both of these genera usually 

have two or three clustered nutrient foramina. 

Kozlov (2001) transferred the giant-toothed Alopias to the 

genus Trigonotodus. Members of this genus, including T. alteri from the late Oligocene, have short, relatively narrow, erect 

crowns; elongated root lobes; obvious callosities on the labial 

root face; and a conspicuous cusplet on each shoulder. The gianttoothed threshers do not easily fit into the Trigonotodus tooth 

morphology, and both Cappetta (2006) and Maisey (2012) doubt 

that Trigonotodus is actually an alopiid. The teeth of Trigonotodus

are more consistent with those of the littoral habitus of Compagno 

(1990b: 54–55) and rather different from the conspicuously taller 

and broader crowns of giant Alopias teeth. Further, the root lobes 

of giant Alopias teeth are more abbreviated and compressed and 

lack prominent cusplets. A few specimens may have weak vestigial 

cusplets or long, low distal heels, but since these are also known 

from small-toothed Alopias (e.g., A. cf. A. vulpinus and A. cf. A. 

superciliosus; BWK, pers. obs.), their presence is unremarkable. 

Overall, the similarity in morphology to the ubiquitous smalltoothed Alopias makes the assignment of the Calvert Cliffs giant 

threshers to this genus highly likely. 

Alopias grandis (Leriche, 1942)

FIGURE 2.18E–G

1942 Alopecias grandis Leriche: Leriche, p. 73, pl. 5, figs. 21–22.

2001 Trigonotodus grandis (Leriche), Kozlov, pp. 89–91, figs. 2, 3.

Description. The large teeth of A. grandis have broad, 

smooth-edged, distally curved crowns. The crown is relatively 

tall with an ogival apex. The mesial cutting edge is moderately 

to strongly convex, although in some teeth the cutting edge is 

weakly sigmoidal. The distal cutting edge is broadly concave. 

Both coronal faces are smooth; the lingual face is flat, whereas 

the labial face is convex. In profile, the crowns are erect or nearly 

so. The root is compressed, with root lobes that are short. On 

the labial face of the root the enameloid does not extend out 

onto the root lobes, although there may be an indistinct layer 

of orthodentine forming a thin callosity in this area. A single 

nutrient foramen is located on the midline of the tooth and on 

or just basal to the weakly developed lingual protuberance. The 

basal margin of the root is typically arched, although it becomes 

obtusely angled in some specimens. 

Anterior teeth (Figure 2.18E) have taller, hooked crowns 

and narrower roots than lateral teeth. Lateral teeth are quite 

variable in coronal width, ranging from moderately wide (Figure 

2.18F,G) to nearly triangular. 
NUMBER 100 • 101

Discussion. The teeth of A. grandis resemble those of A. 

cf. A. vulpinus but are larger (≥40 versus ≤15 mm) in both height 

and width. The crown is proportionally larger and more ogival 

than in A. cf. A. vulpinus, with a mesial cutting edge that is more 

strongly convex than the curved, triangular crown of A. cf. A. 

vulpinus. The root of A. grandis is more compressed, with root 

lobes that are shorter and somewhat deeper. 

Cappetta (1970, 2006, 2012) and Kent (1994) incorrectly 

interpreted these teeth as either intermediate or lateral teeth of 

Isurus or unserrated Carcharodon. With larger sample sizes of 

well-preserved teeth the differences between A. grandis and these 

lamnid laterals are readily apparent. The confusion arises in part 

because a few specimens may have a basal root margin that tends 

toward broadly angled, rather than arched. In this respect, the 

root superficially resembles those of Carcharodon and some Isurus upper laterals, although in these two genera the angle of the 

basal root margin is generally greater than in A. grandis. Further, 

the broader, spade-like apex and strongly convex mesial margin 

of the crown of A. grandis is distinctive. 

Although monognathic heterodonty is present, there are no 

clear indications of either dignathic or gynandric heterodonty. 

Some teeth have slightly broader crowns that may be erect when 

viewed in profile, whereas other teeth have somewhat narrower 

crowns that are erect to weakly inclined lingually. But there is 

also substantial overlap in these characters, and their significance 

is unknown. 

A few A. grandis specimens are known that have weak, irregular crenulations on the cutting edges (Figure 2.18E). These 

crenulations are difficult to detect in a cursory examination and 

may occupy the entire cutting edges or only portions of the edges. 

Stratigraphic and Geographic Ranges. Because of their rarity, A. grandis teeth are almost unknown in 

the paleontological literature but have been documented by amateur collectors from the late Oligocene through middle Miocene. 

Alopias grandis teeth are rare along Calvert Cliffs, with only 10 

available for study. They have been collected on beaches associated with the Calvert and Choptank Formations and in situ from 

beds 3, 10, and 12. 

Teeth of A. grandis have been collected from the eastern 

United States in Miocene sediments on the Potomac River and its 

tributaries in Maryland and Virginia (Leriche, 1942; Cappetta, 

1970; Kent, 1994; M. Bennett, pers. comm., 2011, 2015), Hertford and Beaufort Counties in North Carolina (Gary Greaser, 

Buried Treasure Fossils, Richmond, Texas, pers. comm., 2011; 

M. Bennett, pers. comm., 2016). Alopias grandis teeth are also 

known from the late Oligocene (Chattian) Ashley and Chandler Bridge Formations in Charleston, Dorchester, and northern 

Beaufort Counties in South Carolina (Weems and Lewis, 2002: 

fig. 9; Steven Alter, Steve’s Fossil Shark Teeth, Inc., White Bird, 

Idaho, pers. comm., 2015). 

In Europe, A. grandis have been reworked into the early 

Pliocene Kattendijk Formation (early Zanclean) in Belgium 

from older early to earliest middle Miocene sediments (late 

Aquitanian, Burdigalian, or early Langhian; Pieter De Schutter, 

National Institute of Criminalistics and Criminology, Brussels, 

Belgium, pers. comm., 2012; Everaert, 2014). They have also 

been found in the Middle Globigerina beds (Burdigalian; Ward 

and Bonavia, 2001) of Malta (D. Ward, pers. comm. 2015). 

Alopias grandis has also been reported from Barbados 

(Casier, 1966) and Peru (M. Bennett, pers. comm., 2016) and 

from deep-sea sediments of the central Pacific Ocean (Belyaev 

and Glikman, 1970). 

Serrated Alopias species

FIGURE 2.18H–K

Description. See Kent and Ward (this chapter’s Addendum) for the complete description of this new species. 

Discussion. The second giant-toothed Alopias from 

Calvert Cliffs (Figure 2.18H–K) resembles A. grandis but has 

coarsely serrated cutting edges. These serrations are substantially 

larger and more distinctive than those of the weakly crenulate 

specimens of A. grandis (Figure 2.18E) discussed above. 

Stratigraphic and Geographic Ranges. See 

Kent and Ward (this chapter’s Addendum).

Alopias grandis and the related serrated species are particularly rare, and there are no known sets of associated teeth from 

these species. Without such evidence it is impossible to reconstruct the dentition of these species or even speculate on how 

tooth row counts may have differed from those of extant Alopias. Their lifestyle was probably unlike that of extant, smalltoothed thresher sharks on the basis of differences in tooth 

morphology. The tall, compressed, smooth-edged or serrated 

crowns (Figure 2.3B) and compressed roots with reduced root 

lobes likely would produce biomechanical properties more like 

those of Carcharodon upper laterals than small-toothed Alopias. 

How these differences in tooth morphology would have been 

reflected in overall body morphology is unknown, although the 

bladelike cutting teeth of the giant-toothed Alopias may have 

obviated the need for the greatly elaborated sickle-like tail of 

living threshers. 

Extant small-toothed Alopias are primarily open-ocean, epipelagic species, and a similar distributional pattern apparently 

occurs with the giant threshers as well. Along Calvert Cliffs, the 

distributions of both A. grandis and the serrated species parallel 

that of the common small-toothed thresher (A. cf. A. vulpinus, 

77 of 79 teeth; data from Visaggi and Godfrey, 2010, listed as A. 

latidens) and reflect primarily open shelf marine environments 

(Kidwell, 1989: fig. 2). Likewise, the distribution of A. grandis

and serrated Alopias teeth along the Potomac River in Virginia, 

as well as in North and South Carolina, also reflects open marine 

shelf habitats (Miller, 1982; Idris and Henry, 1995; Powars et 

al., 2005).

Conversely, the younger St. Marys Formation (beds 22 and 

23, early to middle Tortonian) at the southern end of Calvert 

Cliffs represents marginal marine environments that would be 

unlikely habitats for primarily epipelagic sharks such as Alopias. 
102 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Family Cetorhinidae Gill, 1862

Genus Cetorhinus Blainville, 1816

Basking Sharks – Cetorhinidae

The sole extant basking shark, Cetorhinus maximus (Gunner), is a derived tachypelagic, ram-feeding planktivore that consumes planktonic crustaceans, such as shrimp and copepods, and 

teleost fish eggs by filtering them on long, numerous gill rakers. 

Cetorhinus maximus occurs in cold temperate to boreal waters 

and is found in nearshore waters to well offshore. The basking 

shark is the second largest living elasmobranch, reaching lengths 

of at least 11 m and perhaps in excess of 15 m. Their biology 

is poorly understood, although they have been found to direct 

their movements to track plankton-rich patches and to shed their 

gill rakers before overwintering in deeper waters (Matthews and 

Parker, 1950; Compagno, 1984, 1990b, 2002; Sims and Merrett, 

1997; Sims and Quayle, 1998; Compagno et al., 2005; Castro, 

2011). 

The teeth of Cetorhinus are small and superficially resemble 

those of other large filter-feeding sharks, the lamniform megamouth shark (Megachasma), and the orectolobiform whale 

shark (Rhincodon) in having short, recurved crowns and shortened root lobes (Cappetta, 1987; Compagno, 1990a).

Cetorhinus sp.

FIGURE 2.19A

Description. Cetorhinus is presently known from Calvert Cliffs exclusively in the form of vertebral centra. The centra are large and are ovoid when viewed axially. The maximum 

diameter for these centra is more than 9 cm. The articular faces 

consist of deep conical surfaces with concentric growth lines on 

the articular surfaces of the cones. The anterior and posterior 

cones of each centrum typically join apically at an ovoid axial 

perforation. The radial, cartilaginous septa that form the body 

of the centra are thin and fragile. 

Discussion. The septa on Cetorhinus centra are rarely 

preserved, and these centra are typical represented by isolated 

articular cones (Gottfried, 1995), although a partial skeleton of 

a juvenile with well-preserved centra is known (Hovestadt and 

Hovestadt-Euler, 2012). 

The Cetorhinus centra from Calvert Cliffs cannot be reliably assigned to a species since the two named species, C. parvus Leriche (middle Eocene to middle Miocene) and C. maximus

(Gunnerus) (middle Miocene to Holocene), both occur during 

this time (Leriche, 1926; Herman, 1979; Cione and Reguero, 

1998; Hovestadt and Hovestadt-Euler, 2012). 

The absence of either Cetorhinus teeth or gill rakers from 

Calvert Cliffs is troubling since these are far more common as 

fossils than the centra (Leriche, 1908; Jordan and Hannibal, 

1923; Jonet, 1947; Uyeno and Matsushima, 1974; Herman, 

1975, 1979; Schultz, 1978; Bendix-Almgreen, 1983; van den 

Bosch, 1984; Nakagawa and Yasuno, 1985; Cappetta, 1987; 

Bellwood and Schultz, 1991; Baut, 1993; Génault, 1993; Long, 

1993; Yabumoto and Uyeno, 1994; Cione and Reguero, 1998; 

Purdy et al., 2001; Hovestadt and Hovestadt-Euler, 2012). The 

lack of either teeth or gill rakers of Cetorhinus from Calvert 

Cliffs is likely the result of collecting bias rather than a true 

absence. Teeth are relatively nondescript and small (maximum 

height about 7 mm). They have a stout, arched crown with weak 

cutting edges, with short, thick root lobes (van den Bosch, 1984; 

Cappetta, 1987; Reinecke et al., 2011). Cetorhinus gill rakers 

are much larger than the teeth (up to 60 mm for C. parvus and 

200 mm for C. maximus) but very elongated and easily damaged. The gill rakers have a compressed, fan- to comma-shaped 

proximal body attached to a slender, prolonged distal rod. The 

distal rod and adjacent portions of the proximal body are covered with smooth enameloid. The enameloid-free portion of the 

proximal body consists of osteodentin (Herman, 1979; van den 

Bosch, 1984; Cione and Reguero, 1998; Cappetta, 1987; Hovestadt and Hovestadt-Euler, 2012). Cetorhinus gill rakers are 

likely present in Calvert Cliffs, although the largely unconsolidated sediments of these formations would make their collection 

unlikely without careful excavation. 

Dermal thorns are also known from Cetorhinus (van den 

Bosch, 1984; Cione and Reguero, 1998; Hovestadt and Hovestadt-Euler, 2012). Thorns from the Calvert Formation compare favorably with those from the late Oligocene Chandler 

Bridge Formation assigned by Cicimurri and Knight (2008) to 

Cetorhinus, although, as noted previously, these are more plausibly assigned to Squatina (which see). 

Stratigraphic and Geographic Ranges. Cetorhinus centra have been reliably collected as beach specimens 

from the northern portion of Calvert Cliffs and likely derived 

from the Calvert and Choptank Formations. Vertebrae collected 

in situ have come from beds 10–13. 

Fossil Cetorhinus are widely distributed, although rarely 

collected, in Eocene through Pleistocene sediments of Antarctica, 

Japan, Chile, California, North Carolina, Virginia, Maryland, 

Austria, Belgium, Romania, Denmark, France, Germany, Italy, 

the Netherlands, and Switzerland (Leriche, 1908; Jordan and 

Hannibal, 1923; Jonet, 1947; Uyeno and Matsushima, 1974; 

Herman, 1975, 1979; Schultz, 1978; Bendix-Almgreen, 1983; 

van den Bosch, 1984; Nakagawa and Yasuno, 1985; Cappetta, 

1987, 2012; Nolf, 1988; Bellwood and Schultz, 1991; Baut, 
NUMBER 100 • 103

1993; Génault, 1993; Long, 1993; Yabumoto and Uyeno, 1994; 

Gottfried, 1995; Cione and Reguero, 1998; Purdy et al., 2001). 

Order Carcharhiniformes Compagno, 1977

Family Scyliorhinidae Gill, 1862

Cat Sharks – Scyliorhinidae

The Scyliorhinidae (or cat sharks) is the largest family of 

benthic sharks, with at least 17 extant genera and 160 species. 

The cat sharks are generally small sharks; most species are less 

than 80 cm in length, and the largest is about twice as long. They 

have distinctive catlike eyes and a slender, elongated body. Their 

teeth are small and relatively delicate, with a slender crown and, 

in many cases, lateral cusplets. Their biology is poorly known, 

but they are generally believed to prey on small fishes and invertebrates (Bass et al., 1975; Compagno, 1984, 1988, 2002; 

Musick et al., 2004; Compagno et al., 2005; Castro, 2011). 

Recent molecular studies evaluating relationships in the 

Carcharhiniformes have produced evidence that the Scyliorhinidae as presently defined is paraphyletic (Human et al., 2006). 

The family Scyliorhinidae (sensu stricto) is restricted to the genera Scyliorhinus and Cephaloscyllium, whereas other genera are 

more closely allied with other carcharhiniforms (Iglesias et al., 

2005). This discovery greatly complicates the familial assignment 

to extinct “scyliorhinid” genera since tooth morphology is very 

conservative among these sharks. In addition to slender crowns 

and cusplets, scyliorhinid-like teeth typically have a callosity on 

A C B

D E

FIGURE 2.19. Cetorhinus, Scyliorhinid, and Mustelus fossils (1 cm scale bar for A; 1 mm scale bar for B–E). (A) Cetorhinus vertebral centrum; 

axial view (CMM-V-1683; bed 12, Parkers Creek, Maryland). (B) Scyliorhinid sp. anterior tooth; labial view (CMM-V-7719; bed 3B, New 

Kent County, Virginia). (C) Scyliorhinid sp. anterolateral tooth; labial view (CMM-V-7719; bed 3B, New Kent County, Va.). (D) Mustelus sp. 

tooth; lingual view (CMM-V-7741; bed 3B, New Kent County, Va.). (E) Mustelus sp. tooth; labiobasal view (CMM-V-7741; bed 3B, New 

Kent County, Va.).
104 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

the labial face and longitudinal ridges on the basal portions of 

the crown and cusplets (Bass et al., 1975; Herman et al., 1990; 

Soldo et al., 2000). Given the currently unsettled state of scyliorhinid systematics and the high morphological overlap of teeth 

in this group, the specimens from Calvert Cliffs are assigned only 

to familial status. 

Scyliorhinid sp.

FIGURE 2.19B,C

Description. These teeth are minute, with the largest 

≤1.5 mm in height. Anterior teeth (Figure 2.19B) have an erect, 

narrow crown that is weakly inclined lingually. The coronal cutting edges are weakly developed and complete or nearly so. The 

shoulders bear weakly convex heels or low cusplets. The labial 

coronal face is slightly to moderately convex, whereas the lingual face is more strongly convex. The labial face of the crown 

extends basally over the surface of the root as a pronounced callosity. Short, distinct ridges are present along the basal portion 

of the labial face of the cusp and laterally on the lingual face. 

Lateral teeth (Figure 2.19C) are similar but have more widely 

angled root lobes and a tall, sharp cusplet on each shoulder. 

The roots are poorly preserved on the available specimens 

and cannot be adequately described. 

Discussion. Several scyliorhinid teeth have been reported 

from the Miocene, including specimens from Scyliorhinus joleaudi 

Cappetta, Pachyscyllium dachiardii (Lawley), and Premontreia 

distans (Probst) (Marsili, 2007c; Reinecke et al., 2011; Vialle et 

al., 2011; Bor et al., 2012; Underwood and Schlogl, 2013), but 

those from Calvert Cliffs cannot be unambiguously assigned to 

any of these species. The teeth from Calvert Cliffs have some resemblance to those of the extant genus Apristurus in having slender cusps and cusplets with basal ridges (Herman et al., 1990; 

Marsili, 2007c). But the absence of cusplets on the anterior teeth 

of the scyliorhinid teeth from Calvert Cliffs, along with the absence of typically bathyal shark species (e.g., Marsili, 2007c; Vialle 

et al., 2011; Underwood and Schlogl, 2013) in Calvert Cliffs sediments, would make such a generic assignation unlikely. 

There is also some resemblance to the teeth of Scyliorhinus 

canicula (Herman et al., 1990: pls. 31, 32), although too few 

specimens are available for a definitive identification. 

Purdy et al. (2001: fig. 44a–h) report a scyliorhinid from 

the Pungo River Formation in North Carolina. These teeth, 

like those of most other Neogene scyliorhinids, are considerably larger than the specimens from Calvert Cliff. Further, the 

cusplets on the Pungo River teeth are arched medially, which is 

not observed in the specimens from the Calvert Formation.

The assignment of these teeth to the scyliorhinids is based 

on the carcharhiniform tooth morphologies defined by Compagno (1988:35). The scyliorhinid tooth type is characterized 

by strong, longitudinal ridges on the crown; a pronounced labial callosity with a medially indented basal margin; cusplets 

typically present; serrations lacking; and a deep, often trilobate, 

root. The teeth from the Calvert Formation are consistent with 

these characteristics, although the root characteristics cannot be 

fully assessed. 

The available specimens are all of very small size, and at present, it is unclear whether they represent juvenile or adult teeth. 

Stratigraphic and Geographic Ranges. Teeth 

of the morphology shown in Figure 2.19B,C are known only 

from a few poor-quality beach specimens from the extreme 

northern end of Calvert Cliffs and from nine specimens collected 

in bed 3 of the Calvert Formation at inland sites in the MidAtlantic region.

Family Triakidae Gray, 1851

Genus Mustelus Linck, 1790

Smooth Hounds: Triakidae

The smooth hounds are a modestly diverse group of about 

two dozen extant species. They are small sharks with a maximum length of about 1.5 m. They are littoral, cancritrophic 

(=crustacean-feeding) sharks that use their crushing dentitions 

of low, rounded teeth to feed on crustaceans and occasionally 

other benthic invertebrates and small bony fishes (Compagno, 

1984, 1988, 1990b, 2002; Castro, 2011). The teeth are unusual 

for a shark in having a domed crown with a transverse ridge, a 

pronounced labial lip with vertical plicae, and an obvious uvula. 

This tooth morphology is convergent with some batoids, such as 

Pristis, Rhynchobatus, and Rhinobatos (Cappetta, 1987). Despite having an unusual dentition for a shark, recent molecular 

evidence suggests that the genus Mustelus is actually paraphyletic (López et al., 2006).

Extant Mustelus are very difficult to identify to species 

and can require the use of both morphological and molecular 

techniques (Boomer et al., 2012; Giresi et al., 2013; Pérez‐Jiménez et al., 2013). Identification of teeth to species is even more 

problematic because of a scarcity of definitive characters. Compagno (1984:398–399; 1988:220) describes three different tooth 

morphologies in Mustelus: (1) crown has short, erect cusp and 

cusplets, (2) crown has low, blunt cusp, and (3) crown is broad, 

rounded, and lacking a cusp. Unfortunately, the range of intraand interspecific variation in tooth morphology of extant Mustelus is very poorly documented, which greatly complicates the 

identification of isolated teeth to species. 
NUMBER 100 • 105

Mustelus sp.

FIGURE 2.19D,E

Description. The teeth are broad (<1.5 mm) and low 

crowned. The crown is elliptical in occlusal view and has the lingual and labial faces separated by a transverse ridge. The labial 

face of the crown overhangs the root, forming a prominent lip. 

The lip and basal portions of the labial face are ornamented with 

closely spaced, irregular plicae. The lingual face has a conspicuous uvula and plicae similar to those of the labial face. The root 

has an obvious lingual protuberance basal to the uvula, a flat 

basal face, and wide nutrient groove. 

Discussion. Müller (1999: fig. 17/1–4, pl. 5, figs. 3–6) 

recorded an unnamed Mustelus species (Mustelus sp. 2) from the 

St. Marys Formation of Maryland, the Eastover Formation of 

Virginia, and the Yorktown Formation of North Carolina. Purdy 

et al. (2001) reported Mustelus teeth from the Pungo River Formation of North Carolina. These specimens are very close to 

those from the Calvert Formation, and they plausibly represent 

the same species, although the range of variation within Neogene 

species is currently undocumented. 

Stratigraphic and Geographic Ranges. Mustelus teeth are rarely reported as fossils because of their very small 

size and nondescript shape. Along Calvert Cliffs they are known 

with certainty only from the Little Cove Member (beds 22/23) 

of the St. Marys Formation. They are also known from bed 3 of 

the Calvert Formation and bed 24 of the St. Marys Formation 

at river and inland sites of the Mid-Atlantic region. Neogene records of Mustelus from other areas are uncommon but include 

the late Miocene (Messinian) of Portugal (Balbino, 1995), late 

Miocene–early Pliocene of Costa Rica (Laurito Mora, 1999), 

and the early Pliocene (Zanclean) of France (Cappetta, 1987) 

and Italy (Cappetta and Cavallo, 2006; Marsili, 2008). 

Family Hemigaleidae Haase, 1979

Genus Hemipristis Agassiz, 1843

Snaggletooth Sharks – Hemigaleidae

There is a single extant species in this genus, H. elongatus

(Klunzinger, 1871), a nearshore shark occurring in a broad arc 

from the east coast of Africa, the Red Sea, Persian Gulf, India, the 

Philippines, and northern Australia. The teeth of H. elongatus

are relatively large compared to those of other carcharhiniforms 

of similar body lengths and have a distinctive cutting-clutching 

dentition of dignathic heterodonty, with triangular upper teeth 

and awl-like lower teeth. Hemipristis elongatus is piscivorous, 

feeding on a range of bony and cartilaginous fishes. Maximum 

size for this species is about 2.4 m (Compagno, 1984). The teeth 

of H. elongatus are unusual in that the orthodont tooth condition that typifies carcharhiniform teeth has been modified by a 

unique secondary infilling of osteodentin (i.e., the pseudo-osteodont condition of Herman et al., 1991). 

The snaggletooth sharks (Hemipristis spp.) first appear 

in the Eocene, and although widespread, the genus was never 

particularly diverse. The earliest species, H. curvatus, is known 

from Egypt, western Africa, Peru, and the eastern United States 

(White, 1956; Cappetta, 1987; Ward and Wiest, 1990; Kent, 

1994). 

There is a single snaggletooth shark species, H. serra, known 

from all along Calvert Cliffs. The teeth of this species are both 

abundant and the largest carcharhiniform in the Chesapeake 

Group. 

Hemipristis serra Agassiz, 1843

FIGURE 2.20

Synonymy follows Purdy et al. (2001), Marsili et al. (2007), and Reinecke 

et al. (2011). 

Description. Upper anterior teeth are relatively narrow 

and erect (Figure 2.20A). Both cutting edges are coarsely serrated, except for a distinctive smooth apical tip. The serrations 

are unusual in two respects; they are obliquely angled with respect to the coronal margin and are somewhat larger on the distal edges of the crown. The mesial cutting edge is weakly convex 

to nearly straight, whereas the distal cutting edge is straight to 

weakly sigmoidal. The lingual surface of the root is high, with 

a protuberance of modest size, and has a broad, but shallow, 

nutrient groove with one or more nutrient foramina. The basal 

margin of the root is strongly arched, whereas root lobes are 

comparatively short and rounded. 

Lower H. serra teeth are very different in morphology, with 

a thick, narrow crown and a thicker, more robust root (Figure 

2.20B). Unlike the serrated cutting edges of upper teeth, those of 

the lowers are unserrated and limited to roughly the apical third 

of the crown. One or more large, slender serrations occur on the 

mesial and distal shoulders. 

Upper lateral teeth are broader and more triangular than 

anterior teeth (Figure 2.20C). Like upper anterior teeth, both 

cutting edges are coarsely serrated, except for the smooth apex. 

The mesial heel is weakly convex and transitions smoothly into 

a convex, serrated mesial cutting edge. The distal cutting edge 

is strongly concave and serrate. The distal serrations are particularly large, with the largest adjacent to the smooth tip and 
106 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

decreasing in size basally. The lingual face of the root has a moderately large protuberance with a wide, shallow nutrient groove. 

The basal margin of the root is straight, except for a shallow 

medial concavity. The mesial root lobe is extended and pointed, 

whereas the distal lobe is short and rounded or rectilinear. Near 

the jaw commissure, the crowns of upper teeth become lower 

and broader (Figure 2.20D). 

Lower lateral teeth have crowns that are lower and more 

distally inclined than lower anteriors, with the serrations expanding apically onto the basal half of the crown. 

Hemipristis serra vertebral centra are short, cylindrical, and 

aseptate, with thick rims and straight to weakly concave sides 

(Figure 2.20E,F). The dorsal and ventral foramina are rectilinear 

to ovoid, and each is bisected by prominent diagonal lamella 

extending to the surface of the centrum. Pores of moderate to 

large size are common, with some following the outlines of the 

foramina and rims and others scattered over the surface between 

these structures. In axial perspective the central are circular to 

ovoid, with a width greater than the height. 

Discussion. Chandler et al. (2006) document both ontogenetic and phyletic changes in tooth morphology in H. serra. 

Immature teeth are small in size and have smooth or very weakly 

serrated mesial cutting edges and a few, large serrations of the 

distal cutting edges. Immature specimens were comparatively 

rare in the samples examined in this study, but this is not unexpected given the strong preservational bias against immature 

individuals in the fossil record (Raup, 1977; Smith, 1994:108–

117). Adult teeth are more strongly serrated, with the unserrated 

tip of the crown becoming proportionally smaller as tooth size 

increases. 

Hemipristis serra vertebral centra were first described on 

the basis of centra collected in association with teeth from the 

Calvert Formation (USNM 467531; Purdy et al., 2001: fig. 48a). 

Burris (2004: fig. 10) used radiography to investigate the internal 

morphology of H. serra centra as part of a cladistic analysis of 

carcharhiniform vertebral centra. 

Recently, a partial skeleton of H. serra has been collected 

from the Calvert Formation. This skeleton is in a private collection and consists of a large number of vertebrae and teeth, along 

B

A

C

D

E

F

FIGURE 2.20. Hemipristis serra fossils (1 cm scale bar). (A) Upper anterior tooth; lingual view (CMM-V-704; Parkers Creek, Maryland). (B) 

Lower anterior tooth; lingual view (CMM-V-699; Parkers Creek, Md.). (C) Upper lateral tooth; lingual view (CMM-V-699; Parkers Creek, 

Md.). (D) Upper posterolateral tooth; labial view (UMCP 2171; Matoaka Cottages, Md.). (E) Vertebral centrum; ventral view (CMM-V-3618; 

Flag Ponds, Md.). (F) Vertebral centrum; axial view (CMM-V-3618; Flag Ponds, Md.).
NUMBER 100 • 107

with fragments of cartilage (Stephen Godfrey, Calvert Marine 

Museum, Solomons, Maryland, pers. comm.). 

Stratigraphic and Geographic Ranges. Hemipristis serra teeth are widely distributed as beach specimens in 

the Calvert, Choptank, and St. Marys Formations. Teeth have 

been collected in place from beds 3–5, 8, 10–14, and 17–19 of 

Calvert Cliffs, as well as from local inland exposures of beds 1 

and 2. More than 150 teeth were examined for this study. 

The species is very widely distributed in warmer-water 

formations worldwide from the late Oligocene (Chattian) 

through Pleistocene formations of the Atlantic Ocean, Caribbean Sea, Mediterranean Sea, Indian Ocean, and Pacific Ocean 

(Radwański, 1965; Longbottom, 1979; Gillette, 1984; Cappetta, 

1987; Kent, 1994; Yabumoto and Uyeno, 1994; Scudder et al., 

1995; Iturralde-Vinent et al., 1996; Antunes et al., 1999b; Müller, 1999; Sánchez-Villagra et al., 2000; Aguilera and Rodriguez 

de Aguilera, 2001; Purdy et al., 2001; Ward and Bonavia, 2001; 

Vicens and Rodríguez-Perea, 2003; Kocsis, 2007; Marsili et al., 

2007; Portell et al., 2008; Cicimurri and Knight, 2009b; Laurito 

Mora and Valerio-Zamora, 2008; Schultz et al., 2010; Costa et 

al., 2009; Cione et al., 2011; Bor et al., 2012; Cappetta, 2012; 

Pimiento et al., 2013a, 2013b; Andrianavalona et al., 2015). 

Most records for H. serra are from the Miocene, and this species 

appears to have been particularly abundant during that epoch. 

The extant H. elongatus is a much smaller shark than H. 

serra and is restricted to the tropical Indo-West Pacific. This species is primarily piscivorous, although it will take a broader range 

on prey when available. Little has been inferred about the diet 

of H. serra, although a diet comparable to that of H. elongatus

but including larger prey is likely. Large H. serra teeth have been 

found in association with a Squalodon skeleton (USNM 183055), 

although it is unclear whether this represents scavenging or predation on other scavengers attracted to the whale carcass. 

Family Carcharhinidae Jordan and Evermann, 1896

Genus Galeocerdo Müller and Henle, 1837

Tiger Sharks – Galeocerdo

Tiger sharks in the genus Galeocerdo are represented by a 

single extant species, G. cuvier. This is a large, cosmopolitan 

species in tropical to warm temperate oceans. Tiger sharks are 

found primarily on continental shelves, and although they have 

been observed farther offshore around islands, they are not truly 

pelagic sharks. Galeocerdo cuvier is remarkably eurytrophic and 

has been known to consume an astonishing range of prey, including a variety of invertebrates (e.g., scyphozoans, gastropods, 

cephalopods, and decapod crustaceans), numerous species of 

bony fishes, sharks, skates and rays, marine reptiles (sea turtles, 

sea snakes, and marine iguanas), marine birds, marine mammals 

(seals, sea lions, and small cetaceans), and carrion. Large individuals purportedly reach a length of 9.1 m, although this has 

not been reliably established. The largest confirmed lengths are 

about 5.5 m (Compagno, 1984, 2002; Compagno and Niem, 

1998; Castro, 2011). Tiger sharks can be so abundant, and the 

risk of tiger shark predation so high, that some prey, such as 

bottlenose dolphins (Tursiops aduncus), are known to alter their 

foraging behavior to avoid habitats where tiger sharks are more 

common (Heithaus and Gill, 2002). 

The teeth of G. cuvier are distinctive and not easily confused 

with those of other sharks. The crown is compressed and distally 

directed with compound serrations on the cutting edges and a 

strongly arcuate mesial margin. There are large compound serrations of graded size on the distal heel and a prominent notch 

between the distal cutting edge and heel. The root is compressed 

with short, rounded root lobes and a low lingual protuberance 

with a weak nutrient groove. This tooth shape is adapted for 

slicing tissues in both mesial and distal directions, although by 

different mechanisms. As the tooth is pushed mesially, prey tissues are forced along the arched mesial cutting edge toward the 

coronal apex. As the tooth is pulled distally, tissues are forced 

into the notch between the crown and the distal heel. The notch 

has a thin, sharp edge and seems particularly well adapted for 

cutting tough, fibrous tissues. This dual-action slicing mechanism may be partially responsible for the ability of G. cuvier

to feed on an exceptionally broad range of prey (Motta, 2004). 

Unlike many other carcharhiniforms, the dentition of G. cuvier

lacks dignathic and gynandric heterodonty, having only weak 

gradient heterodonty (Compagno, 1984; Cappetta, 1987). 

Galeocerdo has traditionally been placed in the family Carcharhinidae (Compagno, 1984, 2002; Cappetta, 1987; 

Compagno and Niem, 1998). An analysis of carcharhiniform 

relationships by López et al. (2006) provided some evidence for 

placing Galeocerdo either as a basal member of the Hemigaleidae or as the sister group to the hemigaleid-carcharhinid clade. 

Using these results, Maisey (2012) opted to ally Galeocerdo with 

the hemigaleids. Herman et al. (1991) also note that the root vascularization of G. cuvier is atypical for a carcharhinid but make 

no further comment on the familial assignment of tiger sharks. 

With only a single study supporting a familial realignment of 

Galeocerdo, additional evidence is needed to more fully assess 

this possibility. Pending such studies, Galeocerdo is retained here 

as a carcharhinid. 

The earliest Galeocerdo are recorded from the early Eocene of Morocco (Arambourg, 1952; Cappetta, 1987; Sepkoski, 

2002), commensurate with the comparatively basal position of 

this genus within the carcharhinids (Naylor, 1992). The genus 
108 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

is never particularly specious, with typically one or at most two 

contemporaneous species. 

Traditionally, two species, G. aduncus and G. contortus, 

have been reported from the Miocene, frequently co-occurring in 

the same formations (Cappetta, 1987; Kent, 1994; Purdy, 1998a; 

Purdy et al., 2001; Kocsis, 2007; Marsili et al., 2007; Visaggi 

and Godfrey, 2010). Ward and Bonavia (2001) noted that the 

two species typically occur together and remarked on the similarities of the two tooth morphologies to the heterodont dentitions of the extinct carcharhinid genus Physogaleus. From these 

observations they concluded that both tooth forms belonged to a 

single species, P. aduncus (which has priority). In this interpretation the broader aduncus morph is derived from females, whereas 

the narrower contortus morph is referable to males. There are 

some advantages to this classification, principally since the contortus tooth morphology was never entirely consistent with placement in Galeocerdo. But there are also a number of problems 

raised by this assignment. In particular, there are a number of 

localities where only one of these two morphologies is present (Radwański, 1965; Hirota, 1979; Kemp, 1991; IturraldeVinent et al., 1996; Antunes et al., 1999a, 1999b; Vicens and 

Rodríguez-Perea, 2003; Apolín et al., 2004; Rögl et al., 2008; 

Cicimurri and Knight, 2009b; Vialle et al., 2011). The reliability 

of some of these records is unknown and may simply reflect the 

unavailability of large numbers of specimens for studies. Others 

are based on large sample sizes (e.g., Kemp, 1991) and are more 

likely to reflect the actual absence of a second species. 

The problem with interpreting aduncus and contortus teeth 

is compounded by the presence of three tooth morphologies in 

Miocene sediments, such as those of Calvert Cliffs. One is the 

typical aduncus morphology (Figure 2.21A,B): a broad, compressed, and distally directed crown with simple serrations on 

the cutting edges, large compound serrations of graded size on 

the distal heel, a prominent notch between the distal cutting edge 

and heel, and a low lingual protuberance with a weak nutrient 

groove. The contortus morphology (Figure 2.21E,F) differs in 

several important respects: the crown is slender, lingually twisted, 

and distally directed with simple serrations on the cutting edges, 

and there are moderately sized simple serrations on the distal 

heel, an arched or weakly notched junction between the distal 

cutting edge and heel, and a prominent lingual protuberance 

with a weak to moderate nutrient groove. The third tooth morphology (Figure 2.21C,D) is intermediate in form between the 

two: the crown is slender, lingually twisted, and distally directed 

with simple serrations on the cutting edges, large compound 

serrations of graded size on the distal heel, a prominent notch 

between the distal cutting edge and heel, and a low lingual protuberance with a weak nutrient groove. All three tooth morphologies co-occur along the length of Calvert Cliffs in the expected 

range of graded sizes and shapes for anterior through posterior 

tooth positions. Although all three are frequently collected, the 

contortus tooth form is typically the least common at localities 

along the cliffs (reevaluation of samples from Visaggi and Godfrey, 2010). 

The most plausible interpretation is that two of these tooth 

forms (Figure 2.21A,B and 21C,D) represent a single species (G. 

aduncus), whereas the third tooth form (Figure 2.21E,F) is from 

a second species (Physogaleus contortus; see below). This interpretation is consistent with previous research in which adequate 

sample sizes are present; for example, Kemp (1991) illustrates 

a large number of G. aduncus teeth (both broad and narrow 

forms) from the Miocene of Australia but none of the P. contortus morphology. Applegate (1978, 1992) has advocated the presence of dignathic heterodonty in G. aduncus with broad teeth in 

the upper jaw and narrow teeth in the lower jaw. Further, Applegate (1992) argues that heterodonty in Galeocerdo is traceable 

as far back as the early Eocene and is widely distributed among 

other carcharhinids. In this interpretation of the Galeocerdo fossil record, the nearly homodont dentition of G. cuvier is a relatively recent derivation. 

A second plausible interpretation of the two tooth morphologies in G. aduncus is that they represent gynandric heterodonty 

(Cicimurri and Knight, 2009b). A number of other carcharhiniforms are known to have sexual dimorphisms in tooth morphology, for example, Carcharhinus (Bass et al., 1973), Iago

(Compagno and Springer, 1971), Physogaleus (Cappetta, 1980), 

and Prionace (Litvinov and Laptikhovsky, 2005), so such an interpretation is conceivable. In this model of the G. aduncus dentition, broad teeth would be the female tooth form, whereas narrow 

teeth would have been from males (D. Ward, pers. comm.). 

Unfortunately, there are no intact dentitions of G. aduncus

on hand to test these two competing hypotheses. The most intact 

specimen available is a Galeocerdo jaw fragment with six teeth 

of the narrow morphology from Calvert Cliffs (Figure 2.21G). 

This specimen could be interpreted as a portion of the Meckel’s 

cartilage or part of either the palatoquadrate or Meckel’s cartilage of a male individual (Gottfried, 1993). Only more complete 

specimens can resolve this matter.

Galeocerdo aduncus Agassiz, 1943

FIGURE 2.21A–D,G

Synonymy follows Ward and Bonavia (2001; as Physogaleus aduncus, in 

part), Marsili et al. (2007), and Reinecke et al. (2011). 

Description. The teeth of this species exist in two morphologies (i.e., broad and narrow), although it is unclear whether 

this represents dignathic or gynandric heterodonty. The broad 

tooth morphology (Figure 2.21A,B) has a relatively wide, compressed crown that is angled distally. The crown has simple serrations on the arched mesial and angled distal cutting edges. The 

distal margin of the crown is divided by a deep, prominent notch 

that separates the distal margin of the crown from the distal heel. 

The distal heel bears large compound serrations that progressively 

decrease in size away from the notch. The root is compressed, with 

short, rounded root lobes and an arched basal margin and a low 

lingual protuberance with a weak nutrient groove.
NUMBER 100 • 109

The narrow tooth morphology (Figure 2.21C,D) resembles 

the broad tooth morphology in overall form, particularly in the 

structure of the root. The principal difference is in the structure 

of the crown, which in the narrow form is more gracile. The mesial cutting edge is less strongly arched than in the broad tooth 

form and is deflected lingually. Like the broad tooth form of G. 

aduncus, the narrow form has simple serrations on the coronal 

cutting edges and large compound serrations of graded size on 

the distal heel that are separated from the distal cutting edge 

by a deep prominent notch. The root is compressed with short, 

rounded root lobes, an arched basal margin, and a low lingual 

protuberance with a weak nutrient groove.

Discussion. Purdy et al. (2001) place this species in synonymy with the extant G. cuvier on the basis of similarities in 

morphology. Marsili et al. (2007) dismiss this assignment because of the presence of simple, rather than complex, serrations 

A C B D

E G

H

F

I J

K L

FIGURE 2.21. Galeocerdo and Physogaleus fossils (separate 1 cm scale bars for A–G and H–L). (A) Galeocerdo aduncus anterolateral tooth, 

broad form; lingual view (UMCP 1169; Matoaka Cottages, Maryland). (B) G. aduncus anterolateral tooth, broad form; labial view (UMCP 

1169; Matoaka Cottages, Md.). (C) G. aduncus anterolateral tooth, narrow form; lingual view (UMCP 1188; Matoaka Cottages, Md.). (D) G. 

aduncus anterolateral tooth, narrow form; labial view (UMCP 1188; Matoaka Cottages, Md.). (E) Physogaleus contortus anterolateral tooth; 

lingual view (UMCP 999; Matoaka Cottages, Md.). (F) P. contortus anterolateral tooth; labial view (UMCP 999; Matoaka Cottages, Md.). (G) 

G. aduncus jaw fragment (CMM-V-21; Scientists Cliffs, Md.). (H) P. contortus anterior tooth; lingual view (CMM-V-7742; Bayfront Park, 

Md.). (I) Physogaleus hemmooriensis anterior tooth; lingual view (CMM-V-7729; Bayfront Park, Md.). (J) P. hemmooriensis anterior tooth; 

labial view (CMM-V-7729; Bayfront Park, Md.). (K) P. hemmooriensis anterolateral tooth; lingual view (CMM-V-7729; Bayfront Park, Md.). 

(L) P. hemmooriensis anterolateral tooth; labial view (CMM-V-7729; Bayfront Park, Md.). 
110 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

on the mesial and distal cutting edges of the crown and the distal 

heel. Costa et al. (2009) report teeth with compound serrations 

on the medial and basal portions of the crown, although it is impossible to determine from their illustrated tooth whether compound serrations occur on both the mesial cutting edge and the 

cutting edges of the distal heel. In extant G. cuvier, compound 

serrations are present on all cutting edges on the tooth. In G. 

aduncus from Calvert Cliffs, compound serrations are restricted 

to the distal heel. The serrations on both the mesial and distal 

edges of the crown are somewhat irregular and variable in size 

but are simple in structure. Further, unlike G. cuvier, G. aduncus

has a heterodont dentition, although the exact nature of the heterodonty is unclear. 

Stratigraphic and Geographic Ranges. Galeocerdo aduncus is a common species in Calvert Cliffs, with more 

than 200 specimens examined for this study. Teeth of this species 

have been collected in all three Calvert Cliffs formations, with 

in situ specimens from beds 3–5, 8, 10–14, and 17. Specimens 

are also known from beds 1 and 2 in inland sites in the MidAtlantic region. This species is present from the early Oligocene 

(Rupelian) through late Miocene (Messinian) worldwide, including Europe, the Mediterranean, Zaire, the eastern and western 

coasts of the United States, the Caribbean, Ecuador, Peru, Baja 

California, Australia, India, and Japan (Dartevelle and Casier, 

1959; Mehrotra et al., 1973; Applegate, 1978; Itiogawa et al., 

1985; Cappetta, 1987; Nolf, 1988; Kemp, 1991; Yabumoto and 

Uyeno, 1994; Iturralde-Vinent et al., 1996; Müller, 1999; Schultz 

et al., 2010; Aguilera and Rodriguez de Aguilera, 2001; Purdy et 

al., 2001; Ward and Bonavia, 2001; Vicens and Rodríguez-Perea, 

2003; Apolín et al., 2004; Kocsis, 2007; Marsili et al., 2007; 

Cicimurri and Knight, 2009b; Reinecke et al., 2011; Vialle et al., 

2011; Bor et al., 2012; Cappetta, 2012; Landini et al., 2017). 

Genus Physogaleus Cappetta, 1980

Sharks in the extinct genus Physogaleus are known from 

the late Paleocene through middle Miocene. The teeth of this 

genus are characterized by a distally inclined crown that slightly 

overhangs the labial face of the root and may have a few basal 

serrations on the mesial cutting edge. The distal heel typically 

has one or more large serrations that decrease in size distally 

and is separated from the distal cutting edge of the crown by a 

distinct notch. The root is robust, with a prominent lingual protuberance bearing a deep nutrient groove that forms a conspicuous notch on the relatively straight basal root margin (Cappetta, 

1980; Reinecke et al., 2005; Reinecke and Hoedemakers, 2006). 

The dentition of this genus is generally believed to exhibit gynandric heterodonty in the lower anterior files, where male lower 

anterior teeth have slender, sigmoidal crowns, whereas those of 

females have somewhat broader, more compressed crowns (Cappetta, 1987). There is some disagreement on whether this heterodonty is actually due to a sexual dimorphism (Reinecke and 

Hoedemakers, 2006). 

Physogaleus contortus (Gibbes, 1849)

FIGURE 2.21E,F,H

Synonymy follows Ward and Bonavia (2001; as Physogaleus aduncus, in 

part), Marsili et al. (2007; as Galeocerdo contortus), and Reinecke et 

al. (2011). 

Description. The teeth of P. contortus are small to moderate in size and have a distinctive morphology that is generally 

similar in both jaws. The crown is slender and distally angled, 

with a sigmoidal apex. Viewed apically, the crown is twisted with 

the mesial cutting edge displaced lingually. The cutting edges on 

the crown and distal heel are serrate, with slightly larger serrations on the latter. The junction between the distal cutting 

edge and the distal heel can be arcuate or weakly notched. The 

root has moderately elongated root lobes, with an arched basal 

margin, and a weak nutrient groove on an elevated lingual protuberance. Weak gradient monognathic heterodonty is present. 

Anterior teeth have more erect crowns and shorter root lobes. 

Some anteriors also have crowns that are nearly as thick as they 

are broad at the base, but it is unclear whether these represent 

male lower teeth or are found in both genders. Toward the jaw 

articulation the teeth become progressively lower, with more 

acutely angled crowns and a less elevated lingual protuberance.

Discussion. Physogaleus contortus was originally assigned to the genus Galeocerdo, although this assignation was 

never entirely plausible. A number of characters in this species 

are at variance with most other Galeocerdo species: (1) a slender, 

finely serrate crown, (2) the absence of large, compound serrations 

on the distal heel, (3) the absence of a distinct notch separating 

the distal cutting edge from the distal heel, and (4) a thicker, more 

prominent lingual protuberance. As already discussed (see above), 

the crown resembles the narrow tooth form of G. aduncus, but the 

other three characters are sufficient to separate the two. 

This species has been assigned to Physogaleus, in agreement 

with a number of other researchers (Reinecke et al., 2005: textfig. 13, pl. 36; Reinecke and Hoedemakers, 2006; D. Ward, pers. 

comm.). As a derived Physogaleus, P. contortus has evolved a 

tooth morphology somewhat different from that of more typical 

members of this genus. The addition of serrations on the cutting 

edges, the modification of the root shape, and the suppression of 

heterodonty are all consistent with observable trends in Physogaleus during the Eocene and Oligocene (Reinecke et al., 2005; 

Reinecke and Hoedemakers, 2006). Physogaleus contortus is the 

largest member of the genus (Reinecke et al., 2005). Although of 

only modest size compared to many other sharks in Calvert Cliffs, 

P. contortus reflects the evolution of gigantism in Physogaleus. 

The paleobiology of P. contortus is largely unknown, although the slender twisted crown is consistent with a largely 

piscivorous diet. The skeleton of an unnamed sperm whale 

from the lower Calvert Formation of Popes Creek, Maryland 

(Popes Creek Sand bed; USNM 489195) has 37 associated 
NUMBER 100 • 111

P. contortus teeth. Although the teeth are exceptionally large, 

these sharks were far too small to have attacked and killed such 

a substantial prey. Typically, such an association of teeth would 

be attributed to scavenging, although this is difficult to confirm. 

On the basis of the tooth morphology of P. contortus, it seems 

equally plausible that this tooth concentration represents Physogaleus preying on small scavenging fishes that had been attracted 

to the carcass. 

Stratigraphic and Geographic Ranges. The 

teeth of P. contortus are common along the cliffs, and about 180 

teeth have been studied. Physogaleus contortus teeth have been 

found in situ in a number of beds, including 3–5, 8, 10–15, and 

17, and river teeth have also been collected from bed 1. The 

worldwide distribution of this species is more difficult to document since the narrow tooth form of G. aduncus is frequently 

listed as G. contortus. Teeth are known from the early and middle Miocene (Burdigalian-Langhian or perhaps Serravallian) of 

the eastern Unites States (Maryland, North Carolina, and Virginia), Cuba, Panama, Peru, Germany, and Hungary (Gillette, 

1984; Iturralde-Vinent et al., 1996; Müller, 1999; Purdy et al., 

2001; Kocsis, 2007; Marsili et al., 2007; Reinecke et al., 2011; 

Pimiento et al., 2013a; Landini et al., 2017). Reinecke et al. 

(2011) also list P. contortus from the late Oligocene (Chattian) 

of South Carolina on the basis of Cicimurri and Knight (2009b). 

The only narrow tooth form illustrated by Cicimurri and 

Knight (fig. 5F) appears to have compound serrations of graded 

sizes on the distal heel; this morphology is more consistent with 

G. aduncus than with P. contortus. 

Physogaleus hemmooriensis Reinecke and 

Hoedemakers, 2006

FIGURE 2.21I–L

Synonymy follows Reinecke et al. (2011). 

Description. Anterior teeth have tall, sinuous crowns 

and narrow roots with reduced lobes (Figure 2.21I,J). The mesial 

margin is sinuous to weakly concave, whereas the distal margin 

is convex. The cutting edges are smooth and extend onto the 

mesial and distal heels. The distal shoulder may have a long, 

low cusplet or broad blade. The root is thick, with a prominent 

medial nutrient groove and one or more foramina. 

In anterolateral teeth the crown is slender and oblique, with 

a long, sinuous to noticeably concave mesial margin (Figure 

2.21K,L). A slightly convex, irregularly crenulated mesial heel is 

present. The distal cutting edge of the cusp is convex and meets 

the distal heel at a conspicuous notch. The distal heel is short and 

bears two to four large serrations that decrease in size distally. 

The root lacks a marked lingual protuberance and is relatively 

thin. A deep nutrient groove and a basal notch are present. The 

basal margin of the root is weakly sinuous, concave medially, 

and convex on the root lobes. 

Discussion. These teeth have been assigned to P. hemmooriensis on the basis of comparing descriptions of teeth of this 

genus with those of the generally similar teeth in the genera Chaenogaleus, Galeorhinus, and Paragaleus (Cappetta, 1987; Reinecke 

and Hoedemakers, 2006; Reinecke et al., 2011). The anterolateral 

teeth of all three of these genera have shorter cusps and a larger 

number of cusplets on the distal heel. Galeorhinus teeth also have 

a pronounced labial callosity. This thickening of the basal edge of 

the enameloid can occur in some Chaenogaleus and Paragaleus as 

well. These latter two genera occasionally have distinct serration 

on the mesial heel, which is lacking in P. hemmooriensis.

The medial teeth of P. hemmooriensis have not been collected from Calvert Cliffs. Reinecke and Hoedemakers (2006) describe these teeth as having nearly symmetrical crowns with one 

to rarely three serrations on each shoulder. In this respect, medial 

teeth differ from anterior and anterolateral P. hemmooriensis

teeth, which never have mesial serrations. Reinecke and Hoedemakers (2006) differentiate upper and lower anterolateral teeth 

on the basis of the shape of the mesial coronal margin; in upper 

teeth the margin is undulating, whereas in lower teeth it is clearly 

concave and produces a vertically directed coronal apex.

Stratigraphic and Geographic Ranges. This 

species is rarely collected from Calvert Cliffs, although the rarity 

may be confounded by the small size and comparative delicacy 

of the teeth. The largest tooth is 5.1 mm high and 7.7 mm wide, 

which is near the maximum size for this species (Reinecke and 

Hoedemakers, 2006; Reinecke et al., 2011). Physogaleus hemmooriensis teeth have been collected only as two beach specimens from the extreme northern end of Calvert Cliffs and are 

presumably derived from the Calvert Formation. This species is 

reliably known from the early to middle Miocene of Belgium, 

Germany, and the Netherlands and possibly from the Calvert 

Formation of Delaware and Pungo River Formation of North 

Carolina (Reinecke and Hoedemakers, 2006; Reinecke et al., 

2011; Bor et al., 2012; Everaert, 2014). 

Genus Carcharhinus Blainville, 1816

Gray Sharks – Carcharhinus

The gray sharks of the genus Carcharhinus are spectacularly successful in Holocene faunas, occupying a broad range of 

lifestyles. Most species (e.g., C. brachyurus, C. perezii, and C. 

plumbeus) are littoral and mesotrophic active coastal sharks that 
112 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

are generalized predators of moderate-sized fishes and lightly armored invertebrates. Others, such as C. leucas, are larger sharks of 

littoral habitats that are more eurytrophic, capable of consuming 

larger prey than the mesotrophic sharks. The gray sharks have 

also diversified into pelagic habitats, including the macroceanic C. 

falciformis and C. longimanus (Compagno, 1984, 1988, 1990b, 

2002; Compagno and Niem, 1998). Most Carcharhinus species 

have a cutting-clutching-type dentition based on dignathic heterodonty with compressed, triangular cutting teeth in the upper jaw 

and slender clutching teeth in the lower jaw (Cappetta, 1987). 

The explosive expansion of the carcharhiniforms during the late Oligocene and Miocene created a number of taxonomic difficulties, and these problems are particularly evident 

when identifying species of Carcharhinus. Extant Carcharhinus

are characterized by exceptionally high diversity and a high degree of structural similarity (Garrick, 1982; Compagno, 1984; 

Chiaramonte, 1998; Compagno and Niem, 1998). This is readily apparent in the teeth of extant species, which can be reliably 

identified to species only with the use of morphometric and cladistic techniques (Naylor and Marcus, 1994). At present, our 

understanding of how this remarkable genus diversified during 

the Neogene to produce such a successful group is particularly 

meager. The earliest Carcharhinus are found in the middle to 

late Eocene of Antarctica (Kriwet, 2005). Eocene and Oligocene 

Carcharhinus are comparatively homogeneous, with upper teeth 

having unserrated or weakly serrated crowns that are separated 

from the enameloid shoulders by a distinct notch, although a 

few teeth with a more modern morphology are known (Adnet 

et al., 2007; Underwood et al., 2011: fig. 4N). On the basis of 

molecular data, the genus underwent extensive diversification 

between the late Oligocene and late Miocene, 23–9 mya (A. P. 

Martin, 1995), including the elaboration of serrated coronal cutting edges on many species (Adnet et al., 2007). During the Miocene diversification, teeth of this genus have broadly overlapping 

morphologies and can be difficult to assign to individual species. 

Sarao (2005) used the Procrustes method with principle component analysis to evaluate 500 Neogene Carcharhinus teeth. Despite the utility of this technique for identifying individual species 

on the basis of their teeth (e.g., Nyberg et al., 2006; Whitenack 

and Gottfried, 2010), Sarao was unable to unequivocally identify separate species in this genus because of high morphological 

overlap and phyletic evolution. In studies with negative evidence 

there is always the possibility that the most relevant characters 

were not identified and a larger suite of characters might produce more resolution (Naylor and Marcus, 1994). This does not 

appear to be the case in Sarao’s study, in which 10 lingual and 

9 labial characters were employed. However, serrations are a 

critical factor for identifying Holocene Carcharhinus teeth, so 

an analytical approach capable of quantifying serration size and 

disposition (e.g., Chandler et al., 2006) might provide additional 

clarity. This possibility has yet to be demonstrated for Carcharhinus teeth, so for the present, some Miocene teeth can be reliably 

assigned to a species but many cannot. This problem is particularly true for lower teeth, which appear to be morphologically 

more conservative than upper teeth (Purdy et al., 2001). With 

the exception of the distinctive lower teeth of C. leucas, the 

assignment of Carcharhinus lower teeth from Calvert Cliffs is 

more provisional than assignments of the upper teeth and must 

be viewed with appropriate caution. 

By the Pliocene, fossil teeth closely resembling those of extant Carcharhinus species are present (Purdy et al., 2001; Marsili, 2007b), although their antecedents in the Miocene are still 

somewhat murky and contentious. 

Traditionally, Neogene (especially Miocene) Carcharhinus

have been assigned to two rather broadly defined species, C. 

egertoni and C. priscus (Gillette, 1984; Muizon and DeVries, 

1985; Cappetta, 1987; Kent, 1994; Yabumoto and Uyeno, 1994; 

Laurito Mora and Valerio-Zamora, 2008). Purdy et al. (2001) 

made the first serious attempt to sort out Neogene Carcharhinus species in the Pungo River and Yorktown Formations of Lee 

Creek Mine, North Carolina, by comparing them with extant 

species. Bourdon (2009) followed this basic framework but 

provided a more comprehensive review of Lee Creek Mine Carcharhinus. Marsili (2007b) largely followed Purdy et al. in classifying Pliocene Carcharhinus from Italy. These three publications 

represent a substantial improvement over older studies, although 

they do not resolve all taxonomic issues. Unfortunately, Miocene Carcharhinus from Calvert Cliffs reside within the 23–9 

mya interval of rapid diversification of this genus (A. P. Martin, 

1995) and, as suggested by Sarao (2005), reflect a complex, lowrelief morphospace of rapidly evolving species. Such an adaptive 

radiation would likely be composed of many relatively localized 

species with many overlapping and few unique characters. The 

more recognizable Pliocene and subsequent Holocene species almost certainly arose from this swarm of Miocene Carcharhinus

by a winnowing of some species and phyletic evolution in others.

The Miocene Carcharhinus teeth from Calvert Cliffs are 

surprisingly diverse and undoubtedly represent multiple species, 

although the exact number is unclear. Seven tooth forms can be assigned to identifiable species with a reasonable degree of certainty, 

although many teeth are of intermediate morphologies and combine characters of different tooth forms. Species assignments have 

been based on comparisons with extant dentitions and published 

figures and descriptions (Garrick, 1982; Compagno and Niem, 

1998; Bourdon, 2009; Voigt and Weber, 2011).

Carcharhinus cf. C. altimus (Springer, 1950)

FIGURE 2.22A,B

1950 Eulamia altima Springer – Springer, pp. 9–10. 

Description. These uncommon teeth are typically small, 

with a height of about 10 mm, although an exceptionally large 

specimen (Figure 2.22A,B) with a height of 13 mm is known. 

Upper teeth have moderately narrow, tapered crowns. The mesial and distal heels are weakly to moderately convex, and the 
NUMBER 100 • 113

A C B D E

F H G I J

K L

M

N

O

P

Q R S T

FIGURE 2.22. Carcharhinus fossils (1 cm scale bar for A–H, K–T; 1 mm scale bar for I, J). (A) Carcharhinus cf. C. altimus upper lateral tooth; 

lingual view (CMM-V-3348; Windmill Point, Maryland). (B) Carcharhinus cf. C. altimus upper lateral tooth; labial view (CMM-V-3348; 

Windmill Point, Md.). (C) Carcharhinus falciformis upper lateral tooth; lingual view (CMM-V-587; bed 12, Parkers Creek, Md.). (D) C. falciformis upper lateral tooth; labial view (CMM-V-587; bed 12, Parkers Creek, Md.). (E) C. falciformis lower lateral tooth; labial view (UMCP 

980; Matoaka Cottages, Md.). (F) Carcharhinus leucas upper lateral tooth; lingual view (CMM-V-2106; Governor Run, Md.). (G) C. leucas

upper lateral tooth; labial view (CMM-V-2106; Governor Run, Md.). (H) C. leucas lower lateral tooth; labial view (UMCP 985; Matoaka Cottages, Md.). (I) Carcharhinus macloti upper lateral tooth; lingual view (CMM-V-2945; Bayfront Park, Md.). (J) C. macloti upper lateral tooth; 

labial view (CMM-V-2945; Bayfront Park, Md.). (K) Carcharhinus perezii upper lateral tooth; lingual view (CMM-V-659; bed 10, Plum Point, 

Md.). (L) C. perezii upper lateral tooth; labial view (CMM-V-659; bed 10, Plum Point, Md.). (M) C. perezii lower lateral tooth; labial view 

(UMCP 987; Matoaka Cottages, Md.). (N) Carcharhinus priscus upper lateral tooth; lingual view (UMCP 981; Matoaka Cottages, Md.). (O) 

C. priscus upper lateral tooth; labial view (UMCP 981; Matoaka Cottages, Md.). (P) C. priscus lower lateral tooth; labial view (UMCP 2186; 

Matoaka Cottages, Md.). (Q) Carcharhinus plumbeus upper lateral tooth; lingual view (CMM-V-2951; Flag Ponds, Md.). (R) C. plumbeus

upper lateral tooth; labial view (CMM-V-2951; Flag Ponds, Md.). (S) Pathological C. leucas upper lateral tooth; labial view (CMM-V-2095; 

bed 12, Scientists Cliff–Parkers Creek, Md.). (T) C. leucas? vertebral centrum; dorsal perspective (CMM-V-1652; Parkers Creek, Md.).
114 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

distal heel may be separated from distal cutting edge by a notch. 

The cutting edges have fine serrations that are slightly larger near 

the junctions between the crown and heels and may become obsolete near the coronal apex. The labial face of the crown is flat, 

whereas that of the lingual face is weakly convex. A distinct neck 

is present. There is a moderate to deep nutrient groove on the 

lingual face of the root, and a basal notch may be present on the 

weakly arched basal margin of the root. Lower teeth of C. cf. 

C. altimus have not been reliably identified from Calvert Cliffs. 

Discussion. These teeth have been allied with the extant 

bignose shark (C. altimus) on the basis of a similarities of the fossil specimens with the extant species. In his original description, 

Springer noted that the teeth of C. altimus have heights about 

150% of the width. The tallest teeth of C. cf. altimus had heights 

only about 115% of the tooth width. Unfortunately, published 

dentitions of C. altimus (Heim, 2000; Voigt and Weber, 2011: pl. 

3) are from large adults, rather than juveniles of a size comparable to the typically small teeth from Calvert Cliffs. So although 

a relationship with C. altimus seems likely, the upper teeth of the 

two species do show some consistent differences, and other associations are possible. 

The teeth most closely resemble those of the C. remotus

(Duméril) specimen illustrated by Bigelow and Schroeder (1948: 

fig. 76). However, this name is considered invalid and has been 

placed in synonymy with the blacknose shark, C. acronotus

(Poey) (Garrick, 1982; Compagno, 1984; Voigt and Weber, 

2011). The teeth of C. cf. C. altimus do share some similarities 

with those of C. acronotus. Both have upper teeth with narrow, 

tapered, finely serrated cusps and weakly convex, finely serrated 

heels (Compagno, 1984, 2002; Compagno and Niem, 1998; 

Voight and Weber, 2011). But although the teeth of C. acronotus

have a distinctly angular notch between the distal cutting edge 

and heel, this notch is much less pronounced and more obtuse in 

C. cf. C. altimus. 

The teeth of C. cf. C. altimus also have some similarity to 

those of the extant sandbar shark, C. plumbeus (Nardo). Heim 

and Bourdon (1998–2009b: fig. 8) make the strongest case for 

placing the teeth identified here as C. cf. C. altimus in synonymy 

with C. plumbeus by reconstructing an artificial tooth set and 

comparing it with the dentition of an extant female C. plumbeus

with an estimated body length of 1.8 m. Their reconstructed dentition does bear a strong resemblance to the extant C. plumbeus

dentition, but there are two difficulties with this interpretation. 

First, the extant dentition has crowns that appear to be somewhat narrower than many other C. plumbeus dentitions (Bigelow and Schroeder, 1948; Garrick, 1982; Heim, 2001). Second, 

the reconstructed dentition represents a nonrandom subset of the 

teeth available for reconstructing the dentition and likely underestimates the total variability within the fossil tooth sample. To 

test the validity of this assertion, four samples of upper teeth 

were analyzed. The first sample consists of 11 C. cf. C. altimus

from Calvert Cliffs. The second sample is of five teeth from 

Calvert Cliffs identified as C. plumbeus (see below). The third 

sample is of the anteriormost eight teeth (excluding symphyseals) 

of the extant C. plumbeus dentition illustrated by Heim and 

Bourdon (1998–2009b: fig. 8, photographically enlarged), and 

the fourth sample is the same eight tooth positions of a somewhat broader, more typical dentition from a 1.78 m male (Voigt 

and Weber, 2011: pl. 25, photographically enlarged). The first 

eight tooth positions were chosen in the two extant dentitions 

because they were consistent with the range of tooth morphologies present in the fossil teeth of the first two samples. Differences in coronal width between the four samples were quantified 

by comparing relative coronal widths (i.e., the width of the cusp 

at the junction with the shoulders divided by the total width of 

the tooth) with one-way and subsequent pairwise Tukey HSD 

tests. Highly significant differences were present (F3,27 = 23.58, 

P < 0.0001), although they were confined to pairwise differences 

between C. cf. C. altimus (mean = 0.42; HSD P < 0.01) and each 

of the three C. plumbeus samples (means = 0.54, 0.54, and 0.57, 

respectively). None of the pairwise differences between the C. 

plumbeus samples were significant (HSD P > 0.05). The teeth 

identified here as C. cf. C. altimus have crowns that are significantly narrower than those of C. plumbeus. 

In some respects these teeth also resemble those of C. ackermannii Silva Santos and Travassos, 1960 from the early Miocene 

Pirabas Formation of Brazil (Santos and Travassos, 1960). Reis 

(2005) refers these teeth to the extant species C. sorrah (Valenciennes, in Müller and Henle, 1841), although this assignment 

seems inappropriate, as C. ackermannii teeth lack the obliquely 

inclined crown, deep distal notch, and large, simple serrations 

of graded sizes that characterize C. sorrah (Compagno, 1984, 

1988, 1990b, 2002; Compagno and Niem, 1998; Voigt and 

Weber, 2011). Like the teeth from Calvert Cliffs, the teeth of 

C. ackermannii have a tapered, finely serrate crown and convex, serrated mesial and distal heels. The teeth of C. ackermannii

differ from the teeth identified as C. cf. C. altimus in having a 

broader cusp with more strongly convex cutting edges. Too few 

specimens of either C. ackermannii or C. cf. C. altimus are available to determine if they are conspecific. 

Stratigraphic and Geographic Ranges. Carcharhinus cf. C. altimus teeth are infrequently collected from 

Calvert Cliffs, with fewer than 20 known specimens. Teeth are 

known from all three formations in the cliffs but, as yet, have 

been collected in situ only from beds 8 and 14. Carcharhinus

cf. C. altimus has previously been reported in the fossil state 

from the early to middle Miocene (Burdigalian to Serravallian) 

of Maryland (Kent, 1994; as Carcharhinus sp. A) and the late 

Miocene to early Pliocene of Baja California (Applegate, 1978: 

tbl. 1; González-Barba and Thies, 2000). 

Extant C. altimus is an offshore, littoral shark of tropical and 

warm temperate oceans. It is principally piscivorous, feeding on 

a variety of teleosts, sharks, and rays, and has been known to eat 

cuttlefishes. Adults are found primarily in outer shelf habitats at 

depths of 90 to 500 m, although they are known to make nocturnal migrations into somewhat shallower water. Juvenile individuals are found in water as shallow 25 m (Compagno, 1984, 

2002; Anderson and Stevens, 1996; Compagno and Niem, 1998; 
NUMBER 100 • 115

Compagno et al., 2005; Castro, 2011; Voight and Weber, 2011). 

This habitat segregation between adults and juveniles may explain 

the overwhelming prevalence of smaller teeth in Calvert Cliffs. 

Carcharhinus falciformis (Bibron in Müller 

and Henle, 1839)

FIGURE 2.22C–E

Synonymy follows Purdy et al. (2001) and Marsili (2007b). 

Description. The upper teeth (Figure 2.22C,D) have 

moderately broad, triangular, distally inclined crowns with serrated cutting edges. At roughly the midpoint of both margins 

the coronal edges are separated from the heels by a notch or gap 

between serrations. These notches are most easily observed on 

the labial face, with lighting at a low angle of incidence. Apical 

to these notches the cutting edges have moderately fine serrations. Basal to the notches the mesial and distal heels have more 

coarsely serrate edges. The mesial edge is straight or very nearly 

so, whereas the distal cutting edge is roughly perpendicular to 

the basal root margin. The labial face of the crown is flat, and 

the lingual face is clearly convex. There is an indistinct neck between the crown and high root. The nutrient groove is moderately deep, usually forming a shallow notch in the middle of the 

weakly arched basal margin. 

The lower teeth (Figure 2.22E) have very narrow, erect to 

weakly inclined crowns. Both the mesial and distal edges are convex apically, producing a narrow, spade-like tip, and flare basally 

onto a steeply angled shoulder. The cutting edges are smooth or 

weakly serrated, primarily on the coronal apex. There is a concave transition between the cusp and shoulders, and transverse 

roots with a moderately deep nutrient groove are present. 

Discussion. Teeth of the silky shark are comparatively 

large, with a maximum height of about 15 mm. The upper teeth 

of C. falciformis are distinctive in having moderately broad 

crowns separated from the mesial and distal shoulders by a distinct notch or gape in the serrations. The condition of the cutting 

edges on lower teeth is variable and may represent differences 

between populations (S. Kato, pers. comm. in Applegate, 1967). 

Some authors describe the cutting edges as smooth (Garrick, 

1982; Bass et al., 1973; Compagno, 1984), and some describe 

them as finely serrate (Compagno and Niem, 1998; Heim and 

Bourdon, 1998–2009a) and occasionally as smooth or finely serrate (Voigt and Weber, 2011). The length of the cutting edges on 

lower teeth also vary by position, being restricted to the apical 

portion of the crown in more anterior teeth and becoming complete on teeth nearer the jaw commissure (Heim and Bourdon, 

1998–2009a). 

Stratigraphic and Geographic Ranges. The 

teeth of C. falciformis are found all along Calvert Cliffs, but although they are common in the Calvert and Choptank Formations, they are rarer in the St. Marys Formation. They have been 

collected in situ from beds 3–5, 8, 10–12, 14, and 17 or 19 in 

Calvert Cliffs and bed 2 in inland sites. Nearly 90 teeth of this 

species were examined for this study. 

Fossils of C. falciformis (frequently listed as C. egertoni) 

have previously been reported from the Miocene of North 

America (Maryland and North Carolina), Lesser Antilles, Italy, 

Malta, and Panama (Leriche, 1942; Menesini, 1974; Kent, 1994, 

as Carcharhinus sp. A; Purdy et al., 2001; Portell et al., 2008, as 

C. obscurus; Pimiento et al., 2013a). As discussed below, one of 

the syntypes of C. similis (Probst, 1878: text-fig. 21d–f) from the 

Miocene of southern Germany is likely attributable to C. falciformis. Teeth from C. falciformis have also been reported from 

the Pliocene of California, South Carolina, and Italy (Applegate, 

1978; Marsili, 2007b; Cicimurri and Knight, 2009a). 

The silky shark is a macropelagic, tropical species that 

reaches maximum lengths of 3.3–3.5 m. Young individuals are 

chiefly found over continental shelves, whereas adults venture 

well out into the open ocean. The species is primarily piscivorous 

but is also known to feed on squid and crustaceans (Compagno, 

1984, 1988, 1990b, 2002; Compagno and Niem, 1998; Castro, 

2011; Voigt and Weber, 2011). The teeth of C. falciformis have 

been found in association with a Squalodon skeleton (USNM 

183055), although it is unclear whether these sharks were scavenging the carcass itself or feeding on smaller fishes attracted to 

the carcass.

Carcharhinus leucas (Valenciennes in Müller 

and Henle, 1839)

FIGURE 2.22F–H,S

Synonymy follows Purdy et al. (2001) and Marsili (2007b). 

Description. The upper teeth (Figure 2.22F,G) of the 

bull shark are large (up to about 18 mm high), broad, and triangular, with a distally inclined cusp. The edges are coarsely serrated, with the serrations becoming somewhat finer near the tip 

of the crown. The distal heel is separated from the crown by a 

very shallow notch on some teeth. The mesial edge is relatively 

straight and sometimes weakly convex near the tip, whereas the 

distal edge is concave. The labial face of the crown is flat, and 

the lingual face is weakly convex. There are an obvious neck 

and a high root. There is a short, weak nutrient groove with the 

nutrient foramen displaced basally. The basal margin of the root 

is arched or angled (Garrick, 1982; Purdy et al., 2001; Marsili, 

2007b).

The distinctive lower teeth (Figure 2.22H) have a relatively 

broad, erect cusp with serrated edges and shoulders. The margins of the apical portion of the crown are ogival, becoming parallel on the basal portion before merging with the steeply angled 

shoulders. The root has a moderately deep nutrient groove and a 

noticeably arched or angled basal margin. 
116 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Discussion. Reinecke et al. (2011: text-fig. 21) illustrated the syntypes of C. similis (Probst, 1878), a Miocene species with broad, triangular crowns and serrated cutting edges, 

noting its resemblance to the extant species C. leucas and C. amboinensis (Müller and Henle, 1839). The lower teeth (Reinecke 

et al., 2011: text-fig. 21k–p) do resemble those of C. leucas, but 

other teeth are probably more properly allied to other species, 

including C. falciformis (text-fig. 21d–f) and C. plumbeus (textfig. 21a–c,g–i). The smaller teeth in Probst’s syntypes could be C. 

leucas, one an upper in the posterior half of the jaw (Reinecke et 

al., 2011: text-fig. 21q,r) and the other a lower (text-fig. 21s,t), 

but cannot be assigned with certainty. 

A few C. leucas upper teeth have a peculiar, presumably 

pathological, condition where the apical portion of the mesial 

cutting edge is weakly concave and separated from the basal portion by a distinct angularity (Figure 2.22S). This condition is not 

unique to C. leucas and has also been found less commonly in 

Calvert Cliffs specimens of C. falciformis and C. perezii, as well 

as in the angel shark, Squatina sp., and the thresher, A. cf. A. 

superciliosus (BWK, pers. obs.). 

The C. leucas teeth from Calvert Cliffs reach a maximum 

height of about 18 mm. This size is comparable to those of the 

contemporaneous Pungo River Formation of North Carolina 

(Purdy et al., 2001). This size is considerably smaller than either 

Pliocene teeth (Purdy et al., 2001) or those of extant individuals, 

which reach a height of about 27 mm (BWK, pers. obs.). 

Stratigraphic and Geographic Ranges. Carcharhinus leucas teeth are common fossils, and more than 70 

were examined. This species occurs in all three Calvert Cliffs formations and has been collected in place from beds 4, 8, 10–12, 

14, and 17 and at inland sites from bed 1. Other locality data, 

as with C. falciformis, can be difficult to interpret, as the fossil 

teeth of C. leucas are frequently listed as C. egertoni. Miocene 

records of C. leucas include Maryland, North Carolina, Ecuador, Germany (discussed above), Malta, and Portugal (Agassiz, 

1843; Leriche, 1942; Menesini, 1974; Longbottom, 1979; Antunes et al., 1999a; Purdy et al., 2001; Antunes and Balbino, 

2004). Other records include those from the late Miocene/early 

Pliocene of the Azores (Ávila et al., 2012); the Pliocene of California, North Carolina, South Carolina, Angola, Italy, Panama, 

and Peru (Antunes, 1963; Applegate, 1978; Purdy et al., 2001; 

Marsili, 2007b; Cicimurri and Knight, 2009a, as C. longimanus; 

Pimiento et al., 2013a; Landini et al., 2017); and the early Pleistocene of Florida (Scudder et al., 1995). 

Bull sharks are large (up to 3.5 m) eurytrophic littoral 

sharks found in nearshore tropical to warm temperate habitats. 

They also occur in estuaries and are one of the few sharks to 

penetrate into freshwater rivers. The large, robust teeth of C. 

leucas are suitable for an exceptionally broad range of prey, including numerous species of teleosts and elasmobranchs, as well 

as sea turtles, dolphins, terrestrial mammals, sea birds, crustaceans, mollusks, and echinoderms (Compagno, 1984, 1988, 

1990b, 2002; Compagno and Niem, 1998; Castro, 2011; Voigt 

and Weber, 2011). 

Carcharhinus macloti (Müller and Henle, 1838)

FIGURE 2.22I,J

Synonymy follows Purdy et al. (2001). 

Description. The upper teeth (Figure 2.22I,J) have narrow, tapered crowns with smooth cutting edges that are slightly 

oblique anteriorly and increasingly inclined toward the commissure. The mesial margin of the cusp is straight to weakly convex, whereas the distal margin is straight to somewhat concave. 

The shoulders bear enlarged, cusplet-like serrations, particularly 

on the distal shoulder, which is separated from the distal cutting edge by a notch. Serrations on the mesial shoulder are less 

prominent and may be absent on some teeth. The root lobes are 

rounded and meet at a broadly obtuse angle. On the lingual face 

is a narrow nutrient groove that ends basally at a notch. 

Discussion. The upper teeth of C. macloti are rare from 

Calvert Cliffs, and only seven specimens were available for study. 

They are consistent with teeth of similar morphology that were 

identified as belonging to juvenile or subadult C. priscus by 

Reinecke et al. (2011:66, pl. 77, figs. 6–10). 

Lower teeth have not been unambiguously identified from 

Calvert Cliffs. In extant C. macloti the lower teeth have narrow, 

erect to slightly inclined crowns with smooth cutting edges and 

smooth, unserrated shoulders. The cutting edges and shoulders 

meet at a slightly obtuse angle, although the junction is narrowly 

rounded, rather than notched. The roots are transverse or very 

widely angled. The nutrient groove resembles that on upper teeth 

and ends in a deep basal notch (Garrick, 1985; Compagno and 

Niem, 1998; Voigt and Weber, 2011). 

Stratigraphic and Geographic Ranges. Carcharhinus macloti teeth are rarely reported as fossils, probably 

because of their small size and delicate construction, and only 

nine were available for study. From Calvert Cliffs they are reliably known only from the Calvert Formation and have been 

collected directly from beds 3, 8, and possibly 14. They have previously been identified from the early Miocene of Brazil (Costa 

et al., 2009), the Miocene of Maryland (Kent, 1994), the Miocene and possibly early Pliocene of North Carolina (Purdy et al., 

2001). 

The living hardnose shark is a small, slender shark (maximum length of about 1 m) of tropical inshore habitats in the 

Indo-West Pacific region. The dentition exhibits gradient monognathic and dignathic heterodonty and is technically of the 

cutting-clutching type (Cappetta, 1987). However, the crowns of 

the upper teeth are so narrow that they probably function with 

the lower teeth as clutching dentition for grasping and restraining small prey. Carcharhinus macloti is believed to be primarily piscivorous, feeding chiefly on small teleosts, although it is 

known to also consume cephalopods and lightly armored crustaceans (Compagno, 1984, 1988, 1990b, 2002; Compagno and 

Niem, 1998; Voigt and Weber, 2011). 
NUMBER 100 • 117

Carcharhinus perezii (Poey, 1876)

FIGURE 2.22K–M

Synonymy follows Purdy et al. (2001) and Marsili (2007b); as C. perezi. 

Description. The upper teeth (Figure 2.22K,L) have 

moderately narrow, distally inclined crowns. Both the mesial and 

distal edges have moderately fine serrations that become slightly 

coarser on the mesial and distal heels. The transition between the 

cusp and heels is generally gradual, although the distal heel may 

be separated from the distal cutting edge by an inconspicuous 

notch. The mesial edge can be convex or nearly straight and in 

some teeth appears truncated. The distal cutting edge is vertical or concave. There are a flat labial crown face and a convex 

lingual face. A distinct neck is present. The root of the lingual 

face is high, with a moderately wide, sometimes shallow, nutrient 

groove. The basal margin is arched or obtusely angled. 

The lower teeth (Figure 2.22M) have erect to semierect, 

moderately narrow, and smoothly tapered crowns, with fine serrations. In some teeth the crown is separated from the shoulders 

by an angular transition. The roots are transverse or may have a 

gently arched basal margin. 

Discussion. The Caribbean reef shark has teeth that can 

be confused with those of C. falciformis and, in smaller sizes, C. 

priscus. The teeth of C. falciformis differ from those of C. perezii

in having slightly broader crowns and notches separating both 

the mesial and distal coronal cutting edges from the shoulders. 

Carcharhinus priscus teeth typically have more angular junctions 

between the cutting edges than those of C. perezii and a tendency 

for the serrations to become obsolete apically. Carcharhinus perezii uppers are among the largest Carcharhinus teeth from Calvert Cliffs and can reach maximum heights of about 18 mm and 

widths of 22 mm.

Lower C. perezii teeth resemble those of C. falciformis, except that the crowns tend to be more uniformly tapered than 

the ogival coronal apex of the latter species. Although lower C. 

perezii teeth are usually described as completely serrated (Compagno, 1984; Compagno and Niem, 1998; Voigt and Weber, 

2011), Bourdon and Heim (2008–2009) report serrations are 

restricted to the apical portion of the crown on anterior teeth. 

Stratigraphic and Geographic Ranges. More 

than 60 teeth of C. perezii were examined in this study. They 

are commonly found in the Calvert, Choptank, and St. Marys 

Formations of Calvert Cliffs. In situ specimens have been collected from beds 3, 4, 8, 10, 12, 14, and 17 or 19, as well as 

beds 1 and 2 at inland sites. Fossil teeth of C. perezii have been 

documented from the Miocene of Delaware (Purdy, 1998a), 

Maryland (Kent, 1994; as Carcharhinus sp. B), North Carolina 

(Purdy et al., 2001), Panama (Pimiento et al., 2013a), Portugal 

(Antunes et al., 1999a; Sánchez-Villagra et al., 2000; Antunes 

and Balbino, 2004), along with the Pliocene of North Carolina 

and Italy (Purdy et al., 2001; Marsili, 2007b). 

The Caribbean reef shark is a large (3 m long) mesotrophic 

littoral species and is the most common shark associated with 

coral reefs in the Caribbean and southern Brazil. It is primarily 

piscivorous (Compagno, 1984, 1988, 1990b, 2002; Compagno 

and Niem, 1998; Castro, 2011; Voigt and Weber, 2011).

Carcharhinus priscus (Agassiz, 1843)

FIGURE 2.22N–P

Synonymy follows Reinecke et al. (2011). 

Description. These teeth are small and relatively delicate 

(Figure 2.22N,O), with a maximum height of about 10 mm. The 

upper teeth have a narrow, distally inclined crown. The cutting 

edges are finely serrated, becoming apically obsolete on some 

teeth. The mesial edge is weakly convex and is separated from 

the mesial heel by a weak notch. The distal cutting edge is almost 

vertical and is separated from the slightly coarser serrations of the 

distal heel by a notch. The labial face is flat or weakly convex, 

whereas the lingual face is more strongly convex. There is a distinct neck between the crown and a low root. A moderately deep 

nutrient groove and a weakly arched basal margin are present. 

The lower teeth (Figure 2.22P) are similar to uppers but 

have narrower, semierect cusps with finely serrated edges, although in some anterior teeth these may be limited to the coronal apex. They have a moderately deep nutrient groove, a basal 

notch, and transverse roots.

Discussion. Purdy et al. (2001) and Marsili (2007b) 

placed C. priscus as a junior synonym of C. brachyurus (Günther). Garrick (1982) was the first to note that on upper C. 

brachyurus teeth the apical portion of the mesial cutting edge 

is markedly arched and angled distally. This “truncated” crown 

morphology was used by both Purdy et al. (2001) and Marsili 

(2007b) in assigning these teeth to C. brachyurus. 

Reinecke et al. (2011) reexamined the type specimens of C. 

priscus, noting that synonymy with C. brachyurus was based on 

a morphologically constrained subset of these teeth that most 

closely resembled the extant species. Further, they found that all 

of the tooth morphologies in the type specimens were present 

in a large sample of teeth from the Lower Mica Fine Sand Formation (early Miocene) of Germany. This sample included teeth 

with morphologies that are similar to, but not entirely consistent 

with, those of the extant species C. brachyurus, C. limbatus, and 

C. perezii. Reinecke et al. (2011) concluded that these teeth were 

morphologically distinct and represented a separate species, C. 

priscus. Teeth from Calvert Cliffs are fully comparable with the 

illustrated specimens of C. priscus in Reinecke et al. (2011: pls. 

71–77, figs. 6–13). The coronal margins on their early Miocene 

specimens are somewhat variable, ranging from weakly crenulate to finely and regularly serrate. Teeth from Calvert Cliffs are 

more typically serrate, although teeth where the serrations disappear apically are still found with some regularity. Further, the 

truncated crowns used to ally these teeth with C. brachyurus are 

comparatively uncommon. 
118 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Of the three extant species Reinecke et al. (2011) found to 

be similar to C. priscus, only one (C. brachyurus) has gynandric heterodonty; mature males have teeth with narrower, more 

oblique crowns with finer serrations (Garrick, 1982). Reinecke 

et al. (2011) do not discuss gynandric heterodonty, but there are 

C. priscus upper teeth from Calvert Cliffs that have somewhat 

finer serrations. The crown morphology of these teeth is no more 

oblique than those of other teeth, so it is unclear whether this 

represents an incipient heterodonty or simply natural variation 

in a species with comparatively variable tooth morphology. 

The biology of this extinct species is unknown, although the 

similarities of its teeth to those of C. brachyurus, C. limbatus, 

and small C. perezii would suggest a piscivorous diet. Carcharhinus priscus teeth were found in association with a Squalodon

skeleton (USNM 183055), although it is unclear whether these 

sharks were actively scavenging or opportunistically feeding on 

smaller fishes attracted to the carcass. 

Stratigraphic and Geographic Ranges. Carcharhinus priscus is abundant and widely distributed along the 

full length of Calvert Cliffs, although specimens in place are 

known only from beds 3–5, 8, 10, and 12. Teeth have also been 

collected at inland sites from beds 1 and 2 of the Calvert Formation. More than 150 teeth were evaluated for this study. 

The geographic range of C. priscus is difficult to determine 

since the name has been applied to a range of tooth morphologies. 

Carcharhinus plumbeus Nardo, 1827 

FIGURE 2.22Q,R

Synonymy follows Purdy et al. (2001) and Marsili (2007b). 

Description. The upper teeth (Figure 2.22Q,R) have a 

triangular, highly compressed crown. The mesial coronal margin 

is weakly sigmoidal, with a steeply angled shoulder. The distal 

margin is concave and continues out onto the angled shoulder. 

The cutting edges are finely serrate, becoming slightly coarser on 

the shoulders. On a few teeth the serrations on the crown and 

shoulders are separated from the finer serrations near the coronal tip by a gap at roughly the midpoint of both the mesial and 

distal cutting edges. The labial face of the crown is flat, and the 

lingual face is very weakly convex. There are a distinct neck and 

a high root, with a straight or slightly arched basal margin. The 

nutrient groove is weak and forms a shallow basal notch. 

Discussion. Some upper teeth have coarser shoulder 

serrations separated from the finer serrations of the cusp by a 

falciformis-like gap, and the apex is labially arched. These teeth 

are thin and compressed and have similarities to those of C. albimarginata. Unlike the teeth of this species, the transition between fine and coarse serrations is more apically displaced. Too 

few teeth of this morphology are available for detailed study 

and are listed here as a form of C. plumbeus. Similar teeth are 

also known from Lee Creek Mine in North Carolina (USNM 

476293; Purdy et al., 2001: fig. 56e). As yet, the lower teeth of C. 

plumbeus have not been reported from Calvert Cliffs. 

Stratigraphic and Geographic Ranges. Carcharhinus plumbeus teeth are relatively uncommon along Calvert 

Cliffs (eight known specimens) but occur in all three formations. 

Teeth collected in context have been obtained only from beds 12 

and 14. The teeth of C. plumbeus have also been found in the fossil state in the Miocene of North Carolina, Libya, Panama, and 

Portugal (D’Erasmo, 1951; Antunes et al., 1999a; Purdy et al., 

2001; Antunes and Balbino, 2007; Pimiento et al., 2013a); the 

Pliocene of North Carolina, South Carolina, and Italy (Purdy et 

al., 2001; Marsili, 2007a, 2007b; Cicimurri and Knight, 2009a); 

and the Pleistocene of Florida (Scudder et al., 1995). 

The sandbar shark is a large (3 m long) coastal to pelagic 

shark of temperate and tropical oceans between the shoreline 

and depths of 280 m. The diverse diet consists of many species of 

teleosts, sharks, skates, rays, bivalves, gastropods, cephalopods, 

and crustaceans (Compagno, 1984, 1988, 1990b, 2002; Compagno and Niem, 1998; Castro, 2011; Voigt and Weber, 2011).

Carcharhinus Vertebral Centra

FIGURE 2.22T

Vertebral centra attributable to Carcharhinus are collected 

with some regularity along Calvert Cliffs. Carcharhinus vertebral centra are short, aseptate, and cylindrical. The walls are 

straight to slightly convex. Foramina are rectilinear to ovate. Diagonal lamellae are present deep within the foramina. Pores tend 

to be tiny and inconspicuous and can be scattered over the surface or can outline the foramina and rims. Unfortunately, these 

characters are fairly conservative and vary by region along the 

vertebral column, making the identification of isolated centra to 

species particularly difficult (Kozuch and Fitzgerald, 1989; Burris, 2004).

CMM-V-1652 is a set of 11 associated centra (10 complete 

and 1 partial) from bed 14 with diameters of 35.5–36.1 mm and 

lengths of 14.0–14.9 mm (Figure 2.22T). Associated with the 

centra was an upper lateral C. leucas tooth with a height of 13.4 

mm and a width of 16.4 mm. 

With seven identified Carcharhinus tooth morphologies 

from Calvert Cliffs, the diversity of this genus is comparable to 

that of the contemporaneous Pungo River Formation of North 

Carolina (six species; Purdy et al., 2001) but considerably larger 

than the Lower Mica Fine Sand Formation of Germany (two species; Reinecke et al., 2011). 

Genus Negaprion Whitley, 1940

Lemon sharks in the genus Negaprion are mesotrophic littoral sharks of tropical and temperate coastal waters. They are 

primarily found in shallow waters, to depths of at least 90 m, 

and are known to occur in estuarine and lower river habitats. 
NUMBER 100 • 119

Lemon sharks are of moderately large size, reaching maximum 

lengths of more than 3 m. Although relatively sluggish, lemon 

sharks are capable of capturing a variety of teleosts and elasmobranchs, along with seabirds, mollusks, and crustaceans (Compagno, 1984, 2002; Compagno et al., 2005; Castro, 2011). 

The dentition is characterized by gradient monognathic heterodonty, and there is little differentiation between upper and 

lower teeth (Compagno, 1987). 

Negaprion eurybathrodon (Blake, 1862)

FIGURE 2.23A–D

Synonymy follows Purdy et al. (2001), Marsili et al. (2007), and Reinecke 

et al. (2011). 

Description. The largest carcharhinid teeth from Calvert Cliffs are from this uncommon species, reaching maximum 

heights of at least 20 mm. The upper teeth (Figure 2.23A,B) have 

a narrow, slightly distally inclined crown with smooth cutting 

edges. The mesial edge is weakly sigmoidal to convex, whereas 

the distal edge is weakly sigmoidal to nearly straight, collectively 

producing a smoothly tapered cusp with a mildly ogival apex. 

The crown is compressed, with a flat labial face and weakly 

convex lingual face. The elongate enameloid shoulders are 

weakly serrate. The root is modestly compressed, with a poorly 

defined nutrient groove. The root lobes are relatively narrow, 

meeting at a broadly obtuse angle. Upper anterior teeth are taller 

than wide, whereas the larger lateral teeth have more elongate 

root lobes and teeth are wider than they are tall. 

The lower teeth have narrower, less compressed, and more 

erect crowns (Figure 2.23C,D). The cutting edges are smooth 

and may be waisted on the basal half of the cusp of lower anterior teeth (Figure 2.23C). The mesial and distal coronal margins are convex apically, producing an abruptly pointed coronal 

apex. The shoulders are usually smooth, although they can be 

very weakly serrate in some specimens. The root is somewhat 

thicker than on upper teeth, and the lobes are transverse. Root 

lobes become more elongate on lateral teeth, so that these teeth 

are broader than they are high. 

Discussion. Eastman (1904) reported these kinds of teeth 

from the Maryland Miocene as two different species, Carcharias

magna and C. collata. White (1955) later placed both of these 

tooth forms in a single species, with the former as the upper teeth 

and the latter as the lowers. 

Purdy et al. (2001) consider N. eurybathrodon the senior 

synonym of the extant N. brevirostris. The largest teeth from 

Calvert Cliffs (>20 mm) are similar to those examined by Purdy 

A B

C D

E

F

G H

I J

FIGURE 2.23. Negaprion, Rhizoprionodon, and Sphyrna teeth (1 cm scale bar for A–D and G–J; 5 mm scale bar for E, F). (A) Negaprion eurybathrodon upper lateral tooth; lingual view (UMCP 11335; Matoaka Cottages, Maryland). (B) N. eurybathrodon upper lateral tooth; labial 

view (UMCP 11335; Matoaka Cottages, Md.). (C) N. eurybathrodon lower anterior tooth; labial view (CMM-V-2104; Governor Run/Parkers 

Creek, Md.). (D) N. eurybathrodon lower lateral tooth; labial view (CMM-V-643; Parkers Creek, Md.). (E) Rhizoprionodon sp. lateral tooth; 

lingual view (CMM-V-2946; Bayfront Park, Md.). (F) Rhizoprionodon sp. lateral tooth; labial view (CMM-V-2946; Bayfront Park, Md.). (G) 

Sphyrna laevissima upper lateral tooth; lingual view (CMM-V-2947; Bayfront Park, Md.). (H) S. laevissima upper lateral tooth; labial view 

(CMM-V-2947; Bayfront Park, Md.). (I) S. laevissima lower lateral tooth; lingual view (CMM-V-2947; Bayfront Park, Md.). (J) S. laevissima

lower lateral tooth; labial view (CMM-V-2947; Bayfront Park, Md.).
120 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

et al. and, on the basis of their comparisons with extant N. brevirostris, indicate a maximum body length of about 3 m. This size 

is identical to that of N. brevirostris but less than the reported 

maximum body length of 3.8 m for the Indo-Pacific species N. 

acutidens (Fischer et al., 1990). 

Stratigraphic and Geographic Ranges. More 

than 30 teeth of this species from Calvert Cliffs were available 

for study. Beach specimens of N. eurybathrodon are known from 

the Calvert, Choptank, and St. Marys Formations. Teeth collected in situ have been found in beds 3, 4, 8, 10, 12–14, 17, and 

19, as well as in bed 1 of inland sites in the Mid-Atlantic region. 

Negaprion eurybathrodon teeth have also been reported from 

the early Miocene through early Pleistocene of the eastern United 

States (Maryland, Florida, North Carolina), Australia, Cuba, 

Ecuador, France, Italy, Malta, Panama, Peru, Poland, and Venezuela (Radwański, 1965; Antunes and Jonet, 1970; Cappetta, 

1970; Longbottom, 1979; Cappetta, 1987; Kent, 1994; Scudder 

et al., 1995; Iturralde-Vinent et al., 1996; Müller, 1999; Aguilera 

and Rodriguez de Aguilera, 2001; Purdy et al., 2001; Ward and 

Bonavia, 2001; Apolín et al., 2004; Marsili et al., 2007; Pimiento 

et al., 2013a, 2013b; Landini et al., 2017). If Purdy et al. (2001) 

are correct in considering N. eurybathrodon the senior synonym 

of the extant N. brevirostris, the stratigraphic range of this species would extend to the present. 

Genus Rhizoprionodon Whitley, 1929

The sharpnose sharks (Rhizoprionodon) are represented 

by seven extant species found in tropical and temperate oceans. 

Although primarily coastal, they have been reported to depths 

of 500 m on continental slopes. They are small in size, with a 

maximum length of 1.8 m, a slender body, and a long snout. 

They are primarily piscivorous, although they are also known 

to feed on a wide range of primarily benthic invertebrates, such 

as cephalopods, decapods, crustaceans, polychaetes, and gastropods (Compagno, 1984, 2002; Gallo et al., 2010; Castro, 2011). 

The dentition of Rhizoprionodon is sexually dimorphic 

(Springer, 1964; Cappetta, 1987). Females have relatively broad, 

compressed teeth in both jaws, with smooth cutting edges and a 

convex distal heel. Male upper teeth are similar to female teeth. 

Male lower teeth are more distinctive, with a slender, more erect 

cusp and a more robust root with a prominent lingual protuberance (Cappetta, 1987). 

The identification of isolated Rhizoprionodon teeth is exceptionally difficult. Garry (2003, 2004) examined the teeth 

of extant species of Rhizoprionodon and Sphyrna using morphometric analysis. Although she was able to unambiguously 

separate the two genera, she was unable to distinguish between 

individual Rhizoprionodon species. Further, Rhizoprionodon

teeth are regarded by many researchers as virtually impossible to 

distinguish from those of the extant genera Loxodon and Scoliodon (Springer, 1964; Cappetta, 1987; Purdy et al., 2001, Ward 

and Bonavia, 2001). Reinecke et al. (2011) reviewed the tooth 

morphology in these genera and noted some general differences, 

although they have yet to be quantitatively evaluated. Because of 

these difficulties, assignment of the teeth from Calvert Cliffs to 

Rhizoprionodon must be considered provisional. 

Rhizoprionodon has a long fossil record, with the earliest species (R. ganntourensis) present in the early through late 

Eocene of Morocco and France (Cappetta and Nolf, 1981; 

Noubhani and Cappetta, 1997). A number of specific names, 

including those of several extant species, have been applied to 

fossil teeth from formations dating as far back as the Eocene 

(Leriche, 1927; Antunes and Jonet, 1970; Case, 1980, 1981; 

Applegate, 1986; Bhalla and Dev, 1988; Cappetta, 1987; Naylor 

and Marcus, 1994; Mustafa and Zalmout, 2000; Wallet, 2006). 

Species-level identifications are particularly difficult since Rhizoprionodon teeth have few diagnostic characters and are morphologically very conservative. The situation is further complicated 

because Rhizoprionodon teeth are also similar in form to those 

of a number of other sharks, such as Loxodon, Scoliodon, and 

Sphyrna (Springer, 1964; Cappetta, 1987; Purdy et al., 2001; 

Ward and Bonavia, 2001; Garry, 2003, 2004; Adnet et al., 2011). 

Rhizoprionodon sp.

FIGURE 2.23E,F

Description. The teeth from Calvert Cliffs assigned 

to Rhizoprionodon are small (maximum dimension of about 6 

mm), with an oblique crown, a long, weakly to moderately concave mesial margin, and a convex distal heel (Figure 23E,F). The 

root has a marked lingual protuberance, bearing a deep nutrient 

groove and a basal notch on the relatively flat basal root edge. 

Discussion. Kent (1994) assigned Calvert Cliffs specimens to the European species, R. ficheuri. But given the difficulties of assigning isolated teeth of this complex to a specific taxon 

and the relatively restricted geographic ranges of extant members 

of this genus (Gallo et al., 2010), it seems prudent to use Rhizoprionodon sp., as advocated by Purdy et al. (2001). Unlike 

the teeth described from Lee Creek Mine, where some teeth are 

weakly serrate, all of the specimens examined from Calvert Cliffs 

have entirely smooth cutting edges. 

Among Calvert Cliffs fossils, the teeth of Rhizoprionodon

sp. most closely resemble those of the hammerhead shark, 

Sphyrna laevissima. The teeth of the former are generally smaller, 

with a maximum dimension of about 6 mm, compared to 18 mm 

for the latter. Further, the mesial cutting edge of the crown in 

Rhizoprionodon sp. is concave, whereas that of S. laevissima is 

convex or weakly sigmoidal. Some lower S. laevissima teeth can 

also have weakly serrate mesial cutting edges but are nonetheless 

distinct from Rhizoprionodon sp. Compared to lower teeth of S. 

laevissima, the teeth of Rhizoprionodon sp. have a more strongly 

hooked (i.e., mesially directed) coronal apex and a much longer 

mesial cutting edge extending out onto a noticeably prolonged 

mesial root lobe. 

Stratigraphic and Geographic Ranges. Rhizoprionodon teeth are widely distributed in all three formations 
NUMBER 100 • 121

from Calvert Cliffs, but they are infrequently collected because 

of their small size, and only about 30 were examined. In situ 

specimens have been collected from beds 4, 8–10, and 12 in the 

cliffs and in beds 1 and 2 at inland sites.

Rhizoprionodon teeth have been widely reported in Miocene 

formations of Austria, France, Germany, Italy, Malta, Portugal, 

and Switzerland in Europe (Antunes and Jonet, 1970; Cappetta, 

1970; Bolliger et al., 1995; Hiden, 1995; Antunes et al., 1999a; 

Ward and Bonavia, 2001; Antunes and Balbino, 2004; Cappetta 

and Cavallo, 2006; Reinecke et al., 2011; Vialle et al., 2011) and 

in the eastern United States (Kent, 1994; Purdy, 1998a; Müller, 

1999; Purdy et al., 2001).

Family Sphyrnidae Gill, 1872

Genus Sphyrna Rafinesque, 1810

Hammerhead Sharks – Sphyrnidae

The hammerhead sharks are characterized by a broad, flattened cephalofoil, forming the distinctive hammer-shaped head 

that gives the group its name. There are eight Holocene species 

of hammerheads, and they are widely distributed in tropical to 

warm temperate coastal waters. They are primarily benthopelagic, although at least one species, S. lewini, seasonally ranges 

farther offshore. Although most species have relatively localized 

distributions, the three largest species, S. lewini, S. mokarran, 

and S. zygaena, occur circumglobally (Compagno, 1984, 1988, 

1990b, 2002; Castro, 2011). 

A number of functions have been hypothesized for the 

iconic hammerhead cephalofoil, including improved prey localization with vision, olfaction, or electroreception; hydrodynamic 

lift; and enhanced maneuverability (Springer and Gold, 1989; A. 

P. Martin, 1993). Experimental studies on possible cephalofoil 

functions have demonstrated that at the very least, this structure 

broadens the sensory field of hammerheads, allowing them to 

search more efficiently. Other functions, such as improved sensory localization and hydrodynamic proficiency have either not 

been conclusively demonstrated or remain untested (Kajiura, 

2001; Kajiura and Holland, 2002; Kajiura et al., 2003, 2005). 

Sphyrnids have teeth of moderate size that are organized 

into dentitions that exhibit dignathic and gradient monognathic 

heterodonty. Upper teeth typically have broad, distally inclined 

crowns and a weak to strong distal heel. The lower teeth are similar, except that the crown is somewhat narrower and more erect. 

The cutting edges can be smooth to finely serrate (Cappetta, 

1987; Purdy et al., 2001). Hammerheads are primarily piscivorous, feeding on a variety of teleosts and elasmobranchs, although some smaller species, such as the bonnethead (S. tiburo), 

are typically durophagous, consuming primarily crustaceans and 

mollusks (Compagno, 1984, 1988, 2002; Castro, 2011). 

Extant sphyrnids are represented by two genera, Sphyrna

(seven species) and Eusphyra (one species). The taxonomy of living sphyrnids has yet to be fully determined since studies have 

produced markedly different phylogenies (Gilbert, 1967; Compagno, 1988; Lavery, 1992; Naylor, 1992; A. P. Martin, 1993). 

A recent supertree analysis of these earlier studies settles some 

of these issues while leaving others (e.g., whether Eusphyra is 

embedded within a paraphyletic Sphyrna) incompletely resolved 

(Cavalcanti, 2007). 

Undoubted sphyrnids are known from the early Miocene 

and may be derived from a Rhizoprionodon-like ancestral form 

(Compagno, 1988; Naylor, 1992; Musick et al., 2004). An earlier origin in the Oligocene is plausible (Dutheil, 1991; Génault, 

1993; Adnet et al., 2007; Cicimurri and Knight, 2009b), and 

an even earlier origin in the late Eocene is possible (Adnet et 

al., 2011). The fundamental difficulty is that early Sphyrna and 

Rhizoprionodon teeth both have short, distally angled crowns, a 

conspicuous distal heel, and a root with a deep nutrient groove 

and horizontal lobes. Further, purported late Eocene and early 

Oligocene Sphyrna teeth are typically comparable in size to the 

small teeth of Rhizoprionodon, making definitive identifications 

difficult. Finally, early teeth of the two genera appear to grade 

into each other (Underwood et al., 2011; Adnet et al., 2011), 

and small sample sizes prevent quantitative assessments of the 

degree of overlap. Garry (2003, 2004) has shown it is possible to 

separate teeth of these two genera with morphometric analysis, 

but these techniques have not been employed on fossil Sphyrna

older than the Miocene. 

Sphyrna laevissima (Cope, 1867)

FIGURE 2.23G–J

Synonymy follows Reinecke et al. (2011).

Description. The upper teeth of S. laevissima have 

broad, distally inclined crowns and a weakly convex to straight 

distal heel separated from the distal cutting edge by a distinct 

notch (Figure 2.23G,H). The mesial margin of the crown is 

arched, although in some anterolateral teeth there may be a very 

shallow indentation separating the weak mesial shoulder from 

the mesial cutting edge. The cutting edges are smooth, although 

a few teeth have weak, irregular crenulations on the distal 

heel. The crowns become lower and more distally inclined in 

posterior-lateral teeth. The root lobes are moderately elongated 

and bear a deep medial nutrient groove ending in a conspicuous 

basal notch. 
122 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Lower teeth (Figure 2.23I,J) are similar, although the 

crowns are narrower and generally more erect. As with upper 

teeth, the crowns become shorter and more inclined near the jaw 

commissure.

Discussion. Purdy et al. (2001) regarded S. laevissima as 

a junior synonym of S. zygaena on the basis of similarities in tooth 

morphology. Although similarities do exist, the teeth of the two 

species are morphologically distinct. A morphometric analysis of 

the teeth of these two species (Reinecke et al., 2011) found several 

consistent differences. In particular, the upper teeth of S. laevissima have broader crowns that are more erect and have a shorter 

distal cutting edge, whereas the lower teeth have shorter, more 

triangular crowns. Reinecke et al. (2011) also note that a morphological gradient in late Miocene to early Pliocene teeth suggests 

that S. zygaena may have been derived from S. laevissima. 

Stratigraphic and Geographic Ranges. Along 

Calvert Cliffs, S. laevissima has been associated as beach specimens with the Calvert and Choptank Formations (Kent, 1994; 

Müller, 1999) and has been collected from beds 3–5, 8, 10–13, 

and 19. This species is only infrequently collected, and only 22 

teeth were examined. 

Teeth attributable to S. laevissima are known from the late 

Oligocene through the middle (or perhaps late) Miocene of the 

eastern United States (Maryland, Virginia, North Carolina, and 

South Carolina), as well as Barbados, France, Germany, Hungary, the Netherlands, Peru, Poland, Portugal, and Switzerland 

(Casier, 1958; Antunes and Jonet, 1970; Cappetta, 1970; Antunes et al., 1981; Kent, 1994; Müller, 1999; Purdy et al., 2001; 

Kocsis, 2007; Cicimurri and Knight, 2009b; Reinecke et al., 

2011; Bor et al., 2012; Landini et al., 2017). 

Superorder Batomorphii Cappetta, 1980

Order Pristiformes Compagno, 1973 

Family Pristidae Bonaparte, 1838

Genus Pristis Linck, 1790

Sawfishes – Pristidae

The sawfishes of the genus Pristis are elongated rays with 

a long, dorsoventrally compressed rostrum bearing large, laterally directed rostral teeth. The rostral teeth are unusual in that 

they grow continuously and are embedded within alveoli along 

the lateral margins of the rostrum. On the basis of their mode of 

development, they may not actually represent true teeth (Miller, 

1974). The rostral teeth can be quite large, reaching maximum 

lengths of at least 80 mm (Kent, 1999b; pers. obs.). The number of 

rostral teeth is variable (16–32 pairs in extant species) and is sexually dimorphic (Thorson, 1973). Oral teeth in Pristis (like those 

of other elasmobranchs) have terminal growth and are attached 

to the surface of the jaws by proteinaceous fibers. These teeth are 

quite small (<3 mm) and rarely collected (Cappetta, 1987). 

Sawfishes have a surprisingly sharklike body, although they 

can be readily distinguished from the similar saw sharks (Pristiophorus) by the presence of dorsally positioned eyes, ventral 

gill slits, and pectoral fins with proximal margins that are attached to the head. They use the toothed rostrum to probe soft 

sediments for buried prey and to stun free-swimming prey. The 

diet consists primarily of small benthic invertebrates and teleosts, although sawfishes are also capable of consuming smaller 

nektonic fishes. Extant Pristis spp. occur primarily in marine and 

estuarine habitats, although they can infrequently occur in freshwater (Bigelow and Schroeder, 1953; Whitehead et al., 1984; 

Smith and Heemstra, 1986; Lythgoe and Lythgoe, 1992). 

Pristis sp.

FIGURE 2.24A,B

Description. The rostral teeth are large, elongate, 

and dorsoventrally compressed, with the crowns covered with 

smooth enameloid. The mesial margin of the crown is broadly 

convex, whereas the distal margin is nearly straight to weakly 

convex near the apex. The mesial cutting edge of the crown is 

rounded, whereas the distal is flat or weakly concave because of 

the presence of a longitudinal groove running along the distal 

margin of the crown. The tooth base is wider than the crown, 

is not covered with enameloid, and has similar, if somewhat less 

pronounced, mesial and distal profiles. The small oral teeth of 

this species have not been reported from Calvert Cliffs.

Discussion. Ontogenetic changes may also complicate 

identifications; extant Pristis adult teeth have a grooved distal 

margin, whereas this characteristic is absent in juvenile teeth 

(Purdy et al., 2001). Both of the Pristis teeth from Calvert Cliffs 

are of similar size (lengths of 37.0 and 35.3 mm) and are intermediate in size between the smaller, ungrooved teeth (lengths of 

23.5–25.5 mm) and larger tooth (length of 52.7 mm) described 

by Purdy et al. (2001). The larger of the two Calvert Cliffs 

Pristis teeth has a flat distal margin, and the smaller has a very 

shallow, incipient groove. 

Stratigraphic and Geographic Ranges. Only 

two Pristis rostral teeth were available for study, CMM-V-1297 

and CMM-V-2113. They were collected in situ from beds 3 and 

14, respectively. 

A number of Pristis spp. have been named from the Miocene of the North Atlantic, including P. aquitanicus Delfortrie, 

P. atlanticus Zbyszewsky, and P. caheni Dartevelle and Casier 

(Cappetta, 1987, 2006). Little research has examined the range 

of variability in these species to assess their validity or even if 

they are morphologically distinct from extant species. 
NUMBER 100 • 123

FIGURE 2.24. Pristis, Rhynchobatus, Raja, and Dasyatis fossils (separate 1 cm scale bars for A+B and O+P; separate 1 mm scale bars for 

C+D and E–N). (A) Pristis sp. rostral tooth; dorsal view (CMM-V-2113; bed 14, Governor Run–Parkers Creek, Maryland). (B) Pristis sp. 

rostral tooth; distal view (CMM-V-2113; bed 14, Governor Run–Parkers Creek, Md.). (C) Rhynchobatus sp. tooth; occlusal view (CMMV-7737; Bayfront Park, Md.). (D) Raja sp. female tooth, occlusal view (CMM-V-7723; bed 3B, New Kent County, Virginia). (E) Raja sp. 

male tooth; lateral view (CMM-V-7730; bed 3B, New Kent County, Va.). (F) Raja dorsal thorn; apicolateral view (CMM-V-7695; bed 

3, Pamunkey River, Va.). (G) Raja alar(?) thorn; lateral view (CMM-V-3775; bed 24, Windmill Point, Md.). (H) Dasyatis rugosa female 

tooth; lingual view (CMM-V-7727; bed 3B, New Kent County, Va.). (I) D. rugosa female tooth; occlusal view (CMM-V-7727; bed 3B, 

New Kent Co., Va.). (J) D. rugosa male tooth; lateral view (CMM-V-7726; bed 3B, New Kent Co., Va.). (K) D. rugosa male tooth; labial 

view (CMM-V-7726; bed 3B, New Kent Co., Va.). (L) D. probsti female tooth; lingual view (CMM-V-7733; bed 3B, New Kent Co., Va.). 

(M) D. probsti female tooth; occlusal view (CMM-V-7733; bed 3B, New Kent Co., Va.). (N) D. probsti male tooth; labial view (CMMV-7733; bed 3B, New Kent Co., Va.). (O) Dasyatis dermal thorn; dorsal view (CMM-V-4572; Bayfront Park, Md.). (P) Dasyatis dermal 

thorn; dorsal view (CMM-V-4542; Plum Point, Md.). 
124 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Order Rajiformes Berg, 1940

Family Rhynchobatidae Garman, 1913

Genus Rhynchobatus Müller and Henle, 1837

Wedgefishes – Rhynchobatidae

The wedgefishes of the genus Rhynchobatus are the sole 

representatives of the family Rhynchobatidae. The biology of 

Holocene Rhynchobatus is poorly known, at least in part because of the current rarity of many species due to human activities. They occur in nearshore slope habitats (from the surf zone 

down to about 70 m) in tropical and subtropical oceans, principally in the Indo-Pacific. Wedgefishes belong to the rhinobenthic 

ecomorphotype and have a sharklike body with a dorsoventrally 

compressed head that is contiguous with a triangular snout and 

the pectoral fins. They reach lengths of about 3.1 m, have a comparatively small mouth and teeth, and feed on benthic prey, such 

as crustaceans, mollusks, and teleosts (Grant, 1978; van der Elst 

1993; Compagno et al., 1989; Compagno, 1990b; Compagno 

and Last, 1999; Cavanagh et al., 2003). 

Rhynchobatus sp.

FIGURE 2.24C

Description. These teeth are small and inconspicuous 

(≤2 mm) and have rarely been collected (six specimens) from the 

northern end of Calvert Cliffs. The crown is low and globular, 

is covered with faintly sculptured enameloid, and has a weakly 

differentiated transverse crest. The most conspicuous feature is 

a short, moderately broad uvula extending over the medial portion of the lingual root surface. Unlike the similar teeth of Rhinobatos, no secondary uvulas extend from the lateral margins of 

the crown. Instead, the coronal margins angle from the lateral 

surfaces to the base of the uvula. 

Discussion. Teeth from Calvert Cliffs are typically worn 

and usually lack intact roots. Generalized features include roots 

that are narrower than the crown, displaced lingually, and separated into two lobes by a broad, deep groove bearing one or two 

nutrient foramina (Cappetta, 1987; Antunes and Balbino, 2007). 

Stratigraphic and Geographic Ranges. Neogene Rhynchobatus teeth, usually listed as R. pristinus, have 

been widely reported from Europe (Cappetta, 1970; Ward and 

Bonavia, 2001; Antunes and Balbino, 2007; Reinecke et al., 

2011) and somewhat less frequently from Florida and North 

Carolina (Stoutamire, 1975; Case, 1980; Purdy et al., 2001, as 

Rhinobatos sp.). Unfortunately, there are relatively few speciesspecific diagnostic characters on Rhynchobatus teeth, and they 

can be easily obliterated by either feeding activities or postmortem wear. As a result, it is unclear whether all of these records 

represent a single relatively ubiquitous Atlantic species or multiple species. There is some evidence that cryptic species are present in Holocene Rhynchobatus; for example, R. djiddensis may 

represent at least four separate species (Compagno, in Cavanagh 

et al., 2003). Although it is certainly possible that more than one 

Rhynchobatus species existed during the Neogene of the North 

Atlantic, the possibility is difficult to demonstrate on the basis of 

the meager evidence currently available. 

Family Rajidae Bonaparte, 1831

Skates – Rajidae

The skates of the family Rajidae (=suborder Rajoidei) are 

an exceptionally diverse component of Holocene faunas, with 27 

genera, 245 named species, and perhaps 50–100 unnamed species. Despite their diversity, skates are a very conservative group 

largely restricted to soft-substrate bottoms in cold antitropical 

and deepwater environments (McEachran and Miyake, 1990; 

Ebert and Compagno, 2007; Ebert et al., 2008). The major portion of the disklike body is dorsoventrally compressed, with large 

triangular pectoral fins fused to the head that produce a roughly 

rhomboidal body shape. The distal ends of these enlarged pectoral fins produce a metachronal wave that provides the propulsive force for swimming. Unlike the superficially similar dasyatid 

stingrays, there is no venomous sting on the elongated caudal 

portion of the body. The mouth and gill slits are ventrally positioned, and they frequently have enlarged thorny denticles on 

the dorsal surface. They are benthic durophages (rajobenthic 

ecomorphotype) that feed on crustaceans, mollusks, and small 

fishes (Feduccia and Slaughter, 1973; Compagno, 1990b; Smale 

and Cowley, 1992; Orlov, 1998; Scenna et al., 2006). The dentitions of many extant rajids exhibit both gynandric and gradient 
NUMBER 100 • 125

monognathic heterodonty. Female teeth are low and globular, 

roughly comparable to those of other rajiforms, such as Rhinobatos and Rhynchobatus, whereas male teeth have a tall to 

very tall, lingually angled crown (Cappetta, 1987). This sexual 

dimorphism is presumed to allow diet partitioning, although the 

elevated male teeth may be more critical for reproductive behavior (Feduccia and Slaughter, 1973; Smale and Cowley, 1992; 

Orlov, 1998; Scenna et al., 2006). There is fossil evidence that 

rajids also use their teeth to scavenge cetacean carcasses (van 

Netten and Reumer, 2009). 

The earliest Raja-like fossils are known from the Late Cretaceous, and their teeth are widely distributed in fossil beds 

during the Cenozoic (Cappetta, 1987; Prasad and Cappetta, 

1993). There are numerous fossil species assigned to this genus, 

although in most cases these species are based on isolated teeth. 

Identification of rajids on the basis of individual teeth is particularly difficult. Tooth morphology is conservative (Herman et 

al., 1995), and distantly related genera can have nearly indistinguishable teeth (e.g., Raja and Bathyraja; Long, 1994). Further, a 

substantial number of individuals can have dental anomalies that 

can complicate identifications (Delpiani et al., 2012). 

Genus Raja Linnaeus, 1758

Raja sp. 

FIGURE 2.24D,E

Description. Female teeth (Figure 2.24D) have a low, 

lingually directed crown. The labial face of the crown is convex 

and lacks a labial cutting edge. Labial and distal cutting edges 

are present. In occlusal view, the coronal base is cordate to rhomboidal, with shallow depression between the crown, the cutting 

edges, and the labiolateral margins of the crown base. The root 

is small and does not extend beyond the lateral margins of the 

crown base. In profile, the root is weakly displaced lingually. The 

flat basal surface of the root is bisected by a conspicuous nutrient groove. 

Male teeth (Figure 2.24E) are similar but have a taller, more 

lingually displaced crown. In profile, the labial margin is convex between the coronal apex and a thick, rounded labial hood, 

whereas the lingual margin is concave.

Discussion. As is true of most fossil rajid teeth, the specimens from Calvert Cliffs are assigned to the nominate genus, 

Raja. But with numerous rajid genera having conservative dentitions, this generic assignment is, at best, provisional. 

Müller (1999) lists six species of fossil Raja from the eastern 

United States. Only one of them is listed from the Calvert and 

St. Marys Formations of Maryland (Raja sp. 2; Müller, 1999:57, 

text-fig. 18/14–17; pl. 12, figs. 4–5; tbl. 4), and the teeth are 

comparable to those described above. Curiously, Müller (1999) 

also lists two additional species (Raja sp. 3 and Raja sp. 4) from 

the Little Cove Point Member of the St. Marys Formation in the 

legends to plate 12 (figs. 7, 9–11) and plate 13 (figs. 3–5). Neither 

of these species is listed from this formation in the text (p. 57), 

instead being listed as occurring in the Rushmere Member of the 

early Pliocene Yorktown Formation of North Carolina. The reason for this discrepancy is unclear, and no specimens matching 

these specimens are currently known from Calvert Cliffs. Additional species could certainly be present, and ongoing research at 

the University of Maryland is investigating this possibility. 

These teeth resemble R. ceciliae (Steurbaut and Herman) 

in having a small root and mesial and distal cutting edges but 

lack the distinctive labial cutting edge present on that species 

(Reinecke et al., 2011). The teeth of R. gentili have smooth 

crowns lacking cutting edges (Cappetta, 1970; Ward and Bonavia, 2001).

Stratigraphic and Geographic Ranges. Raja

teeth are rarely reported from the Calvert Cliffs, and only 14 

specimens are presently known. The teeth of fossil rajids (usually 

as the nominate genus Raja) are widely reported during the Neogene, occurring in virtually all temperate paleofaunas in which 

microteeth have been examined (Radwański, 1965; Cappetta, 

1970, 1987, 2012; Long, 1994; Antunes et al., 1999a; Müller, 

1999; Aguilera and Rodriguez de Aguilera, 2001; Purdy et al., 

2001; Ward and Bonavia, 2001; Valsecchi et al., 2005; Antunes, 

2007; Antunes and Balbino, 2007; Marsili, 2008; Reinecke et 

al., 2008, 2011; Wijnker et al., 2008; Schultz et al., 2010; Boessenecker, 2011; Vialle et al., 2011; Bor et al., 2012). 

Raja Dermal Thorns

FIGURE 2.24F,G

Rajids have dermal denticles enlarged into three different 

types of dermal thorns: (1) generalized thorns along the dorsal 

midline, (2) alar thorns on the distal surfaces of the pectoral fins 

of males, and (3) malar thorns lateral to the orbits and spiracles 

of males (McEachran and Konstantinou, 1996). Thorn morphology is quite variable and has not been rigorously studied in fossil 

rajids. 

Dorsal thorns are relatively large and robust, with stellate bases (Figure 2.24F). Alar and malar thorns are somewhat 

smaller and more delicate than dorsal thorns and are rarely collected. Alar thorns generally have simple, linear bases, whereas 

malar thorns can have linear bases like alar thorns or delicate, 

stellate bases similar to that of dorsal thorns. The thorn shown in 

Figure 2.24G has a narrow, elongate base and a slender, sigmoidal spine that is covered by enameloid and closely resembles one 

of the fossil alar thorns illustrated by Bor et al. (2012: pl. 54, fig. 

3a–c). This spine morphology is comparable to that of the alar 

spines belonging to the extant species Bathyraja kincaidii and R. 

eglanteria in McEachran and Konstantinou (1996: figs. 10a,11b, 

respectively). 
126 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Order Myliobatiformes Compagno, 1973

Family Dasyatidae Jordon, 1888

Dasyatis Rafinesque, 1810

Whiptail Stingrays – Dasyatidae

The widely distributed whiptail stingrays (Dasyatidae) have 

a dorsoventrally compressed, ovate to rhomboidal body, lacking both dorsal and caudal fins and possessing a long whiplike 

tail, usually armed with one or more venomous spines. Dasyatids 

are well adapted for a benthic lifestyle, with dorsal-placed eyes, 

ventral gill slits, and large winglike pectoral fins. They are found 

primarily in warm temperate to tropical inshore marine habitats, 

where they prey on small benthic animals (Bigelow and Schroeder, 1953; Whitehead et al., 1984; Smith and Heemstra, 1986; 

Lythgoe and Lythgoe, 1992). 

The taxonomy of fossil Dasyatis is currently in a state of 

flux. A number of names have been applied to Neogene Dasyatis

fossils, including extinct species (Cappetta, 1970, 1987; Schultz, 

1977; Reinecke et al., 2011), as well as Holocene species (Purdy 

et al., 2001; Cappetta and Cavallo, 2006). Further, there is evidence that the dasyatids are not a monophyletic group (Carvalho 

et al., 2004; Claeson et al., 2010; Maisey, 2012). 

Like the rajids, Dasyatis teeth exist is both cuspidate and 

molariform morphologies. In the extant Atlantic stingray, D. sabina (Lesueur, 1824), Kajiura and Tricas (1996) found that these 

two tooth forms were not due to a simple sexual dimorphism. 

Immature individuals and mature females had molariform teeth. 

The teeth of mature males varied seasonally, with taller cuspidate teeth during the breeding season and molariform teeth the 

remainder of the year. Such seasonal gynandric heterodonty was 

likely also present in Calvert Cliffs Dasyatis, given the comparative rarity of cuspidate teeth. 

Two species are presently recognized from Calvert Cliffs, 

which may underestimate the number of species actually present. Sculpturing on the occlusal surface of the teeth is critical 

for correctly identifying species, yet these structures are rapidly degraded by the durophagous lifestyle of dasyatids. A high 

proportion of fossil dasyatid teeth from Calvert Cliffs have polished occlusal surfaces from use and cannot be reliably identified to species. This high incidence of tooth wear complicates the 

recognition of rarer species without access to large numbers of 

specimens. 

Dasyatis rugosa (Probst, 1877)

FIGURE 2.24H–K

Synonymy follows Cappetta (1970) and Reinecke et al. (2011).

Description. The molariform teeth (Figure 2.24H,I) 

have a crown that is moderately high and stout and labial and 

lingual surfaces that are similar in size. The labial face is moderately to strongly convex, with densely packed ridges and 

grooves. The lingual face is smooth or ornamented with a few 

pits and strongly to weakly concave in profile. In occlusal view 

the labial visor is angular in anterior and lateral teeth, although 

it may become progressively rounded in posterior teeth. The lingual visor is parabolic or a truncated parabola in occlusal view. 

The transverse ridge separating the labial and lingual faces is 

rounded, arched lingually, and irregularly ornamented with 

ridges and grooves. The root is lingually displaced and has two 

lobes separated by a deep nutrient groove. 

Cuspidate teeth (Figure 2.24J,K) are generally similar to the 

more common molariform teeth, but the crowns are taller and 

narrower. They are acutely pointed and triangular in anterior 

files, becoming lower, less pointed, and asymmetrical in lateral 

files. The crown base is pentagonal or hexagonal in occlusal view. 

Discussion. Müller (1999) lists two Dasyatis species 

from Calvert Cliffs: D. cavernosa from the Choptank Formation 

(p. 60; taf. 14, figs. 1–10; abbildungs 19/5–6) and Dasyatis sp. 1 

from all three Calvert Cliffs Formations (pp. 60–61; taf. 13, figs. 

6–8, 10–11). The illustrated specimens appear to be primarily 

D. rugosa, although some (e.g., abb. 19/6) are referable to D. 

probsti. 

The teeth of D. delfortrieri Cappetta are generally similar to 

those of D. rugosa in having a completely wrinkled lingual surface. Despite a superficial resemblance, the teeth of the former 

species differ from those of the latter in having a more regular, 

honeycomb-like pattern of ridges and pits (Reinecke et al., 2005, 

2008). There is also some evidence that D. delfortrieri was extinct 

by the latter part of the early Miocene (Reinecke et al., 2011). 

Stratigraphic and Geographic Ranges. This 

species is known from all three formations along Calvert Cliffs, 

and teeth have been collected in situ from bed 3 of the Calvert 

Formation in Virginia. Because of their globular shape and small 

size they are rarely collected, and only 18 specimens were available for study. 

Dasyatis rugosa has previously been found from the late 

Oligocene through the early late Miocene of Austria, Belgium, 

northern and southern Germany, the Netherlands, Portugal, 
NUMBER 100 • 127

Switzerland, and North Carolina in the United States (Barthelt et 

al., 1991; Daxner-Höck et al., 2004; Balbino and Antunes, 2006; 

Haye et al., 2008; Reinecke and Wienrich, 2009; Reinecke et al., 

2011; Bor et al., 2012). 

Dasyatis probsti Cappetta, 1970

FIGURE 2.24L–N

Synonymy follows Reinecke et al. (2011).

Description. The molariform teeth of this species (Figure 2.24L,M) have moderately high and comparatively stout 

crowns. The labial face has two distinct regions. Apically, there is 

an ovoid concavity that is smooth or has only a few weak ridges. 

Between this depression and the labial visor the enameloid is ornamented with irregular grooves and ridges. The transverse ridge 

is strongly arched lingually, sharp, and irregularly ornamented 

with ridges and pits. The lingual face of the crown is smooth and 

strongly concave in profile. In occlusal view, the labial visor is 

angular, whereas the lingual visor is in the form of a parabola or 

a truncated parabola. The root is small and lingually displaced. 

Two lobes are present, separated by a deep nutrient groove. 

The cuspidate male teeth (Figure 2.24N) resemble the molariform teeth, except that they have a tall, lingually directed 

crown. The crown is acute and triangular in anterior files, becoming lower and asymmetrical in lateral files; the labial face 

has a deep depression covered with fine, vertical ridges, whereas 

the lingual face is smooth. In occlusal aspect, the crown base is 

hexagonal in shape.

Discussion. The teeth of D. probsti are similar in some 

respects to those of Taeniura cavernosa (Probst). Both species 

have an apical concave depression on the labial coronal face, although it is subcircular in the former species and more triangular 

in the latter species. The ornamentation on the labial face of T. 

cavernosa consists of closely packed pits (rather than wrinkles), 

and the edge of the visor is smooth and unornamented. In occlusal view, the labial visor of T. cavernosa is arched, whereas that 

of D. probsti is angular (Reinecke et al., 2011).

Stratigraphic and Geographic Ranges. The 

distribution of D. probsti along Calvert Cliffs is poorly documented because of the small size and worn occlusal surfaces of 

the teeth. Beach specimens occur primarily on the northern half 

of Calvert Cliffs and are probably associated with the Calvert 

and Choptank Formations. Teeth of this species are also known 

from bed 3 of the Calvert Formation at inland sites in the Chesapeake Bay area. Only seven Calvert Cliffs specimens were identifiable to this species. 

Dasyatis probsti teeth have been previously reported from 

the middle Miocene of Europe, including Austria, Belgium, 

southern France, Germany, and the Netherlands (Cappetta, 

1970; Schultz, 1977; Bolliger et al., 1995; Reinecke et al., 2011; 

Bor et al., 2012). 

Dasyatis Dermal Thorns

FIGURE 2.24O,P

Large dorsal thorns are commonly collected from Calvert 

Cliffs and can be quite variable in form. These thorns have a 

roughly circular to ovoid (sometimes quite elongate) outline. The 

most elevated portion of each thorn has one to several raised 

points, each associated with a lobed or lanceolate enameloid cap. 

The enameloid-free portion of the thorn surface can be striated 

(Figure 2.24O) or smooth (Figure 242.P). Thorns with striated 

surfaces are associated with the caudal region, whereas those 

with smooth surfaces occur on the trunk portion of the body 

(Bigelow and Schroeder, 1953; Purdy et al., 2001).

Family Myliobatidae Bonaparte, 1838

Eagle Rays – Myliobatidae

The myliobatid, or eagle, rays are large, aquilopelagic species. They are powerful swimmers using tapered, high-aspectratio pectoral fins for lift-based underwater flight. Eagle rays are 

durophagous predators of benthic crustacean and mollusks, with 

strong jaws bearing a dentition of broad, interlocking teeth modified into grinding plates (Bigelow and Schroeder, 1953; Cappetta, 1987; Compagno, 1990b; Herman et al., 2000). 

Two genera of myliobatids are known from Calvert Cliffs. 

The most abundant myliobatid teeth from the Maryland Miocene have traditionally been placed in the genus Myliobatis Cuvier, 1817, with Eastman (1904) assigning these teeth to three 

different species, M. frangans Eastman, M. pachyodon Cope, 

and M. gigas Cope. Purdy et al. (2001), in discussing comparable 

Miocene teeth from the Pungo River Formation of North Carolina, argued that they should be more appropriately placed in the 

genus Pteromylaeus. Myliobatis teeth can be differentiated from 

those of Pteromylaeus by the lateral elongation of the crown; 

the width to depth ratio in Myliobatis teeth tends to be 4–5:1, 

whereas in Pteromylaeus it is closer to 7–8:1. In addition, Pteromylaeus roots tend to be more lingually extended (Herman et al., 

2000; Bourdon, 2000–2007; Reinecke et al., 2011). The teeth 
128 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

from Calvert Cliffs are consistent with those of Pteromylaeus

and, following Purdy et al. (2001), are transferred to this genus. 

The less common myliobatid teeth from Calvert Cliffs are very 

distinctive and can be reliably assigned to the genus Aetobatus.

Genus Pteromylaeus Garman, 1913

The bull rays of the genus Pteromylaeus are widely distributed in warm temperate and tropical nearshore and brackish 

habitats. The body is broadly rhombohedral, with the enlarged, 

alate pectoral fins used for locomotion. The head is broad and 

rounded, whereas the tail is long and slender. Bull rays feed on a 

variety of invertebrates, such as crustaceans, and mollusks. Large 

individuals commonly reach lengths of 1.5 m. There are two extant species, one from the Mediterranean, southeastern Europe, 

and western to southeastern Africa and the other from Ecuador 

and the Pacific coast of Panama (Compagno et al., 1989; Compagno, 1990b; Schneider, 1990; Brito, 1991; McEachran and 

Notarbartolo di Sciara, 1995; Seck et al., 2002). 

The Pteromylaeus tooth plate contains one medial row 

group and one to three lateral row groups, which may be either 

labiolingually or laterally elongated on each side (Compagno et 

al., 1989; Herman et al., 2000; Reinecke et al., 2011).

Pteromylaeus sp.

FIGURE 2.25

Description. Medial teeth are elongated hexagons with 

acutely angled ends. The occlusal surface is flat to weakly convex 

and weakly arched, with the ends bent lingually (Figure 2.25A). 

The basal surface of the root has numerous, parallel, labiolingually directed laminae (Figure 2.25B). The labial and lingual 

crown faces are ornamented basally with vertical wrinkles that 

interdigitate between adjacent teeth (Figure 2.25C). A narrow 

basal ledge on the lingual face supports the basal edge of the 

crown on the next tooth in the file. In either labial or lingual 

view there is a weak to moderately strong notch separating the 

crown from the root at the lateral margins. The roots are slightly 

thickened medially and in profile are lingually displaced. Foramina run along the labial face above the laminae; the occlusal face 

shows foramina near the juncture of the laminae, and the lingual 

face generally bears foramina between the laminae just below 

the crown.

Lateral teeth are smaller and rhomboidal but otherwise 

have a structure similar to that of the medial teeth. 

Discussion. The medial teeth of Pteromylaeus can easily 

be confused with those of either Myliobatis or Aetomylaeus. Pteromylaeus and Myliobatis medial teeth are very similar but differ in 

shape in occlusal view, being arched in Pteromylaeus and relatively 

straight in Myliobatis (Cappetta, 2012:453). Aetomylaeus medial 

teeth differ from both of these genera in having crowns that are 

noticeably thicker medially than laterally (Cappetta, 2012:446). 

The range of variability in extant Pteromylaeus teeth is 

poorly documented. Herman et al. (2000) examined five specimens from P. bovinus and found that both ontogenetic and 

gynandric heterodonty were present but were unable to examine dentitions of the second species, P. asperrimus. A number 

of names have been applied to Neogene species, apart from the 

three Maryland species listed in Eastman (1904), including P. 

apenninus (Costa), P. crassus (Gervais,), P. gemmellaroi (Salinas), and P. meridionalis (Gervais). Most of these species are 

based on fragmentary material, and their validity and possible 

relationships with extant species are unknown. At present, it is 

unclear whether one or more Pteromylaeus species are present in 

the Maryland Miocene or which name(s) should be used. Purdy 

et al. (2001) and Bourdon (2000–2007) proposed listing the 

Miocene teeth from North Carolina as Pteromylaeus sp. pending 

more detailed analyses. That practical approach is followed here. 

Stratigraphic and Geographic Ranges. Teeth 

attributable to Pteromylaeus are very commonly collected along 

Calvert Cliffs, and more than 120 specimens (mostly as fragments) were used in this study. They have been found in place in 

beds 3–5, 9–12, 14, 17, 19, and 21–23. The geographic range of 

Miocene Pteromylaeus is difficult to determine because of confusion of this genus with Myliobatis and possibly Aetomylaeus and 

the fragmentary nature of many specimens. The Pteromylaeus

illustrated by Cappetta (1970) from southern France and those 

shown by Purdy et al. (2001) from North Carolina are similar to 

those from Calvert Cliffs. 

Genus Aetobatus Blainville, 1816

Spotted eagle rays are nearshore, neritic batoids that are 

known to occur in lagoonal, estuarine, and coral reef habitats. 

They have a grinding dentition and are durophagous predators 

of a variety of benthic species, including polychaetes, mollusks, 

crustaceans, and teleost fishes (Michael, 1993; Homma and Ishihara, 1994; Compagno and Last, 1999; McEachran and de Carvalho, 2002; Schluessel et al., 2010). 

The dentition of Aetobatus is unusual among myliobatids 

in that the teeth are not hexagonal in the occlusal perspective. 

The lateral margins are convexly arched and lingually directed. 

Further, there are no lateral tooth rows, and the medial teeth are 

greatly elongated laterally. The upper and lower teeth are morphologically distinct and easily distinguished. The upper teeth 

are broadly arched, whereas the lowers are in the form of an 

acute to weakly obtuse chevron. 

Aetobatus arcuatus Agassiz, 1843

FIGURE 2.26

Synonymy follows Reinecke et al. (2011).
NUMBER 100 • 129

Description. The crescent-shaped upper teeth have flat 

occlusal surfaces and rounded ends (Figure 2.26A,B). The labial 

and lingual faces of the crown are vertical and have numerous 

irregular ridges and grooves that interlock with adjoining teeth. 

A narrow ridge along the lingual crown face fits into a groove 

that runs the length of the labial crown face of the next tooth. 

The roots are very strongly displaced lingually when viewed in 

profile. As with Pteromylaeus teeth, the basal surface of the root 

A B

C

FIGURE 2.25. Pteromylaeus sp. fossils (1 cm scale bar). (A) Dental plate; occlusal view (CMM-V-2284; Parkers Creek, Maryland). (B) Dental 

plate; basal view (CMM-V-2284; Parkers Creek, Md.). (C) Medial tooth; lingual view (CMM-V-1219; bed 14, Governor Run, Md.). 
130 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

has numerous parallel laminae. Because of this strong displacement, the laminae on the lingual surface of the root are readily 

apparent in occlusal view. 

The lower teeth are similar in structure to the uppers, except 

for the angular, chevron-like shape of the crown and root in occlusal and basal views (Figure 2.26C,D). 

Discussion. Two different names have been used for 

Maryland Miocene Aetobatus (Hay, 1902:321), A. arcuatus Agassiz and A. profundus (Cope). The differences between these two 

has not been critically evaluated, and Cappetta (2006) considers 

profundus to be a junior synonym of arcuatus. Even this attribution is, at best, somewhat tentative, as the range of variation 

in extinct and extant Aetobatus is poorly known. Claeson et al. 

(2010) compared A. arcuatus teeth with the similarly shaped teeth 

of the extant A. narinari and found that they differed in coronal 

thickness. In A. narinari the crown is uniformly thick, whereas in 

A. arcuatus the crown is thicker medially because of a basal expansion of the crown onto the root face. But this character has not 

been examined in other extant Aetobatus, and its usefulness for 

unambiguously identifying A. arcuatus teeth is untested. For the 

present, A. arcuatus is retained as a valid species name. 

Stratigraphic and Geographic Ranges. Beach 

specimens of A. arcuatus teeth are known from the entire length of 

Calvert Cliffs and have been reported in situ from beds 4, 5, 10–15, 

17, and 19. The species is also known from bed 1 of the Calvert 

Formation and bed 24 of the St. Marys Formation in river and inland sites of the Mid-Atlantic region. Teeth are somewhat less abundant than those of Pteromylaeus, and almost 90 were examined. 

Aetobatus arcuatus has previously been reported from early 

to late Miocene formations of Europe (Leriche, 1926, 1927; 

Radwa ski, 1965; Cappetta, 1970; van den Bosch et al., 1975; 

Holec et al., 1995; Reinecke et al., 2011; Bor et al., 2012), 

Costa Rica (Mora, 2004), Panama (Gillett, 1984), Saudi Arabia 

(Thomas et al., 1982), and the eastern United States (Leriche, 

1942; Müller, 1999; Purdy et al., 2001). 

Family Rhinopteridae Jordan and Evermann, 1896

Cow-Nosed Rays – Rhinopteridae

The cow-nosed rays, like the related eagle rays, are large, 

aquilopelagic durophages. They are globally distributed in warm 

temperate and tropical nearshore and brackish habitats. The 

body has large triangular pectoral fins used for locomotion, a 

weakly bilobed head, and a long, flexible tail. Cow-nosed rays 

have strong jaws and a grinding dentition comparable to that of 

the myliobatids and have a similar diet of a variety of mollusks 

and crustaceans. The dental plates typically consist of a medial 

row of broader teeth, flanked on each side by three or four lateral rows of narrower teeth. Large individuals reach a width of 

about 200 cm (Bigelow and Schroeder, 1953; Cappetta, 1987; 

Compagno, 1990b; Herman et al., 2000). 

Genus Rhinoptera van Hasselt, 1824

Rhinoptera cf. R. studeri (Agassiz, 1843)

FIGURE 2.27A–C

Synonymy follows Cappetta (1970), with the following additions:

1999 R. aff. brasiliensis Müller – Müller, pp. 64–65, taf. 15, figs. 4, 5.

1999 R. aff. bonasus (Mitchell) – Müller, p. 65, taf. 15, fig. 7.

2009b Rhinoptera cf. R. studeri (Agassiz) – Cicimurri and Knight, 

p. 641, fig. 6G.

Description. Medial teeth are moderately broad hexagons with acutely angled ends. The occlusal surface is flat and 

symmetrical, with crowns of uniform thickness. The labial and 

lingual crown faces are only weakly ornamented with fine wrinkles. A weak basal ledge on the lingual face of the crown supports 

the rounded basal edge of the labial crown face of the adjacent 

tooth in the file. In profile, the roots are lingually displaced, so 

that the lingual surface projects slightly beyond the crown. The 

basal surface of the root has numerous, parallel, labiolingually 

directed laminae. 

The lateral teeth in the files on either side of the medial file 

are hexagonal and slightly narrower than those of the medial file. 

They are slightly asymmetrical and have crowns that become thinner distally. Teeth in the marginal files are also hexagonal or pentagonal but have length and breadth that are more nearly equal. 

Discussion. The assignment of Miocene Rhinoptera to 

species suffers from many of the same difficulties as myliobatids, 

such as Pteromylaeus. Tooth morphology of extant species is 

highly variable, and because of the weak interconnection between 

teeth, fossil species are known almost entirely from isolated teeth. 

The teeth from Calvert Cliffs most strongly resemble those of R. 

studeri, although without intact dentitions, it is difficult to discern 

their identity with absolute certainty. Teeth from the medial and 

adjacent files of R. cf. R. studeri can most often be confused with 

the medial teeth of Pteromylaeus sp. Teeth of R. cf. R. studeri have 

a lower breadth-to-length ratio (about 7:1) compared to that of 

Pteromylaeus sp. (about 12:1). Lateral teeth are more difficult to 

separate, although the relatively fine ornamentation on the labial 
NUMBER 100 • 131

and lingual coronal faces is recognizably different from the coarse 

ornamentation of Pteromylaeus sp. Finally, the root in R. cf. R. 

studeri is less strongly displaced lingually than in Pteromylaeus sp. 

and so is less conspicuous in occlusal view. 

Müller (1999:64–65) listed four species of Rhinoptera

from Calvert Cliffs, R. aff. brasiliensis (taf. 15, figs. 4, 5), R. aff. 

bonasus (taf. 15, fig. 7), Rhinoptera sp. 1, and Rhinoptera sp. 2. 

Although four species could have co-occurred, a more likely interpretation is that these represent positional variants of a single 

species (Cicimurri and Knight, 2009b). 

Stratigraphic and Geographic Ranges. Along 

Calvert Cliffs, Rhinoptera teeth are typically collected as beach 

specimens along the northern two-thirds of the cliffs associated 

with the Calvert and Choptank Formations. Teeth have been collected in situ from beds 2, 3, 10, 12, 14, 17, and 19. This species 

is less common than either Pteromylaeus or Aetobatus, and only 

14 teeth were studied. 

Teeth resembling R. studeri have previously been reported 

from the late Oligocene (Chattian) to middle Miocene (Serravallian) 

of Europe and eastern North America (Leriche, 1927; Cappetta, 

1970, 1987, 2012; Müller, 1999; Cicimurri and Knight, 2009b). 

Family Mobulidae Gill, 1893

Devil Rays – Mobulidae

B

A

C D

FIGURE 2.26. Aetobatus arcuatus teeth (1 cm scale bar). (A) Upper tooth; occlusal view (CMM-V-1264; Western Shores Estates, Maryland). 

(B) Upper teeth; basal view (CMM-V-1264; Western Shores Estates, Md.). (C) Lower teeth; occlusal view (CMM-V-1703; bed 14, Parkers 

Creek, Md.). (D) Lower teeth; basal view (CMM-V-1703; bed 14, Parkers Creek, Md.).
132 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A B

C

D

E F

H

G

I J K

L M

FIGURE 2.27. Rhinoptera, Plinthicus, and Mobula fossils (separate 1 cm scale bars for A–E and L–M; 1 mm scale bar for F–K). (A) Rhinoptera 

cf. studeri medial tooth; occlusal view (CMM-V-2780; bed 24, Windmill Point, Maryland). (B) R. cf. studeri medial tooth; basal view (CMM-V2780; bed 24, Windmill Point, Md.). (C) R. cf. studeri medial tooth; lingual view (CMM-V-2780; bed 24, Windmill Point, Md.). (D) Plinthicus 

stenodon medial tooth; labial view (CMM-V-1188; bed 12, Parkers Creek, Md.). (E) P. stenodon medial tooth; lingual view (CMM-V-1188; 

bed 12, Parkers Creek, Md.). (F) Mobula loupianensis female tooth; occlusal view (CMM-V-7736; bed 3B, New Kent County, Virginia). (G) M. 

loupianensis male tooth; labial view (CMM-V-7736; bed 3B, New Kent Co., Va.). (H) M. pectinata female tooth; occlusal view (CMM-V-7740; 

Bayfront Park, Md.). (I) M. pectinata female tooth; basal view (CMM-V-7740; Bayfront Park, Md.). (J) M. fragilis tooth; labial view (CMM-V7739; Bayfront Park, Md.). (K) M. fragilis tooth; lingual view (CMM-V-7739; Bayfront Park, Md.). (L) Mobulid caudal spine base; lateral view 

(CMM-V-4263; Warrior’s Rest, Md.). (M) Mobulid caudal spine base; dorsal view (CMM-V-4263; Warrior’s Rest, Md.). 
NUMBER 100 • 133

The devil rays of the family Mobulidae are epipelagic and 

planktivorous, with an aquilopelagic body morphology. The 

body in the dorsal or ventral perspective is rhomboidal because 

of the presence of enlarged triangular, winglike pectoral fins. The 

pectoral fins flap like wings to generate hydrodynamic lift for 

propulsion. The preorbital portions of the pectoral fins are modified into paired cephalic lobes. They are unique in being the only 

microphagous batoids; zooplankton is directed into the mouth 

by expanded cephalic lobes, where it is captured on specialized 

surfaces of the internal gill openings. Devil rays reach very large 

sizes, with a span across the pectoral fins of up to 5.2 m and a 

mass of perhaps 1 ton. Only the Manta rays, also in the Mobulidae, attain larger sizes at 7.6 m and 2.4 tons (Notarbartolo-diSciara, 1988; Compagno, 1990b; Dean et al., 2007; Sampson et 

al., 2010).

Mobulids appear to have evolved from ancestral durophagous myliobatiforms with a grinding dentition. The evolution 

of planktivory in mobulids was accompanied by the loss of the 

more robust tooth morphologies necessary for crushing armored 

invertebrate prey and an overall reduction in tooth size. This 

reduction has been most extensive in Mobula and Manta and 

less so in the older Plinthicus (Cappetta, 1987; Adnet et al., 

2012). Mobulid rays are continuous ram-feeders (Sanderson and 

Wassersug, 1993). At least some extant species are specialized 

euphausid feeders (Sampson et al., 2010).

Genus Plinthicus Cope, 1869

The teeth of Plinthicus are less derived than those of Manta

and Mobula and in morphology more closely resemble the grinding dentition of durophagous myliobatiforms, such as Rhinoptera. The dentition consists of multiple files, broadest in medial 

positions and narrowing laterally. The teeth show few signs of 

wear, indicative of a diet of soft-bodied prey, prompting Cappetta (1987) to place this genus in the Mobulidae. Manning 

(2004: fig. 21.6) speculates on a likely evolutionary scenario for 

the evolution of Plinthicus. Manning envisions the origins of 

Plinthicus from the early to middle Eocene Burnhamia daviesi

(Woodward, 1889), a mobulid with Rhinoptera-like teeth. Unlike those of Rhinoptera, the teeth of Burnhamia have a conspicuous transverse groove on the occlusal surface of the crown 

and exhibit little premortem wear. In Burnhamia, the crown 

is relatively low and positioned almost directly over the root. 

The intermediate stage is represented by an unnamed Plinthicus sp. from the late Eocene–early Oligocene Byram Formation 

of Mississippi. Bor (1990) named a new Plinthicus species (P. 

kruibekensis) from the early Oligocene Boom Clay Formation 

of Belgium, but it is unclear if it is conspecific with this contemporaneous unnamed Plinthicus sp. from Mississippi. Both have 

crowns that are taller and thinner, with a reduced root. But P. 

kruibekensis have a smooth occlusal face, whereas the Mississippi Plinthicus has a transverse occlusal groove. The terminal 

species, the middle Miocene P. stenodon, has a crown that is 

taller and strongly angled lingually. 

Plinthicus stenodon Cope, 1869

FIGURE 2.27D,E

1869 Plinthicus stenodon Cope – Cope, p. 316. 

2001 Plinthicus stenodon Cope – Purdy et al., pp. 95–96, fig. 12f–j. 

2011 Plinthicus stenodon Cope – Reinecke et al., pl. 99, fig. 4. 

Description. The teeth are distinctive but fragile and 

rarely collected intact. The crown is very high, labiolingually 

compressed, and inclined lingually. The occlusal surface is typically flat and may have a few low, flat ridges oriented perpendicular to the long axis of the tooth. Some teeth also have a 

narrow groove running across the occlusal surface immediately 

adjacent to the lingual edge. The labial face of the crown is high 

and concave in profile. The surface is covered by shallow, vertical 

grooves. The lingual face of the crown is convex in profile and 

has many narrow, subparallel ridges running from the occlusal 

surface toward the root. The root is short and narrower than the 

occlusal surface. The basal surface of the root consists of alternating laminae and deep, foramina-bearing grooves. 

Discussion. Purdy et al. (2001) reconstructed the 

P. stenodon dentition as having seven rows, a broad medial 

row, flanked on each side by somewhat narrower lateral rows, 

and a pair of much narrower lateral rows along each margin of 

the dental plate. In the medial and immediately adjacent lateral 

rows the crown is symmetrical and has a constant coronal height 

along the width of the tooth. 

Stratigraphic and Geographic Ranges. Plinthicus stenodon teeth have been collected as beach specimens 

from the Calvert and Choptank Formations and in situ from 

beds 3–5, 8, 10, and 12. Specimens are usually badly broken, 

and largely intact teeth are rare. During this study six large fragments and more than 30 small pieces were examined. 

This species has previously been reported from the late 

Oligocene (Chattian) of South Carolina (Cicimurri and Knight, 

2009b) and the early to middle Miocene (Aquitanian–Serravallian) of Maryland, New Jersey, North Carolina, France, Panama, 

and Venezuela (Leriche, 1942; Cappetta, 1979, 1987; Tedford and 

Hunter, 1984; Müller, 1999; Purdy et al., 2001; Aguilera and Rodriguez de Aguilera, 2004). Plinthicus teeth from the early Miocene of Germany (Reinecke et al., 2011) and Panama (Pimiento et 

al., 2013b) are not identified to species but have a tall, lingually 

angled coronal morphology that is consistent with P. stenodon. 

Genus Mobula Rafinesque, 1810

Mobula teeth are much smaller (≤3.5 mm) and morphologically more derived than those of Plinthicus. Fossil Mobula are 

known only from isolated teeth and first appear in the early Oligocene (Rupelian; Adnet et al., 2012; Cappetta, 2012). By the Miocene, Cappetta (1970) recognized three Mobula species from the 

south of France, M. loupianensis, M. pectinata, and M. fragilis. 
134 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

However, the teeth of Mobula are highly variable within individual 

species, exhibiting ontogenetic, gynandric, monognathic, and dignathic heterodonty (Notarbartolo-di-Sciara, 1987), and it is difficult to determine whether the first two represent distinct species 

or not. Cicimurri and Knight (2009b) in assessing late Oligocene 

(Chattian) Mobula from the Chandler Bridge Formation of South 

Carolina placed M. loupianensis and M. pectinata in synonymy, 

with the specific name M. loupianensis having priority. Adnet et al. 

(2012) performed a more extensive analysis of mobulids and concluded that M. loupianensis and M. pectinata represented separate 

species. They noted that differences were most obvious in female 

teeth; M. loupianensis female teeth were characterized by an indistinctly cuspletted transverse ridge, whereas those of M. pectinata

had more conspicuous cusplets on the transverse ridge. Mobula

fragilis teeth have a very different morphology and are not easily 

confused with those of M. loupianensis and M. pectinata. 

Mobula teeth are very rarely collected from Calvert Cliffs, 

although Purdy et al. (2001) note that Mobula teeth were common throughout the Pungo River Formation. It is unclear if the 

comparative rarity of Mobula from Maryland is due to the somewhat cooler waters of this area or a collecting bias arising from 

the small size and irregular shape of these teeth. Despite the rarity of Mobula teeth from Calvert Cliffs, all three of Cappetta’s 

species appear to be present. 

Mobula loupianensis Cappetta, 1970

FIGURE 2.27F,G

1970 Mobula loupianensis Cappetta – Cappetta, pp. 108–110, fig. 20, 

pl. 26, figs. 1–6.

1976 Mobula loupianensis Cappetta – Jonet, pp. 54–56, figs. 1–13.

2001 Mobula sp. – Purdy et al., pp. 96, fig. 15a–i,m–o.

Description. These rare teeth are small and delicate, 

with two distinctive morphologies. Female teeth (Figure 2.27F) 

have relatively broad, ovoid to rectilinear, lingually inclined 

crowns that have indistinctly cuspidate transverse ridges. The 

labial and lingual faces of the crown have undulating surfaces 

of low, vertical folds that end apically in low, inconspicuous 

cusplets. The roots are low and in width are equal to or slightly 

narrower than the crown. The basal surface of the root is divided 

by one or more shallow grooves, forming two or more lobes. In 

profile, the root is lingually displaced. 

Unicuspidate male teeth (Figure 2.27G) have a prominent 

central cusp typically flanked by multiple small, but distinct, lateral cusplets on each shoulder. The labial surface of the crown 

has a broad medial concavity that is most pronounced basally 

and fades apically. The root is similar to that of female teeth but 

is noticeably narrower than the crown. 

Discussion. The tooth morphology of M. loupianensis

superficially resembles that of the extant M. hypostoma, although 

M. loupianensis teeth consistently have smoother crowns than the 

sculptured occlusal surfaces of the extant species (Adnet et al., 

2012). 

The male tooth shown here is tentatively allied with M. 

loupianensis as this is the only Mobula species currently known 

from the horizon where this tooth was collected. 

Stratigraphic and Geographic Ranges. 

Mobula loupianensis teeth are rarely collected in this area, having been reported only from four beach specimens from the extreme northern ends of Calvert Cliffs and in situ from bed 3 of 

the Calvert Formation in Virginia. 

Mobula loupianensis has previously been reported from the 

middle Miocene (Langhian–Serravallian) of France (Cappetta, 

1970), Portugal (Jonet, 1976), and North Carolina (Purdy et al. 

(2001). 

Mobula pectinata Cappetta, 1970

FIGURE 2.27H,I

1970 Mobula pectinata Cappetta – Cappetta, pp. 111–112, fig. 21, pl. 26, 

figs. 7–9.

1976 Mobula pectinata Cappetta – Jonet, pp. 57–58, figs. 14–16.

2001 Mobula sp. – Purdy et al., pp. 96–97, fig. 14a–p.

Description. This rare species is known from a single, 

well-preserved female tooth. This tooth is small and delicate. The 

crown is relatively broad, rectilinear, and lingually inclined, with 

two distinct cusps of different sizes and a smaller, low cusp on 

the transverse ridge. The labial face of the crown has numerous 

irregular wrinkles that extend out onto the cusps. The roots are 

low and slightly narrower than the crown. The basal surface of 

the root is divided by a single shallow nutrient groove, forming 

two lobes of unequal sizes. 

Discussion. The tooth morphology of M. pectinata

is similar to that of the extant species M. thurstoni. Despite 

these similarities to the extant form, both Cicimurri and Knight 

(2009b) and Adnet et al. (2012) found that M. pectinata teeth 

have smoother crowns than the heavily wrinkled occlusal surfaces of M. thurstoni. 

Stratigraphic and Geographic Ranges. Mobula

pectinata is exceptionally rare and is presently known on the basis 

of only a single beach specimen from Bayfront Park, Maryland.

Mobula pectinata has previously been reported from the 

middle Miocene (Langhian) of France (Cappetta, 1970) and Serravallian of Portugal (Jonet, 1976). 

Mobula fragilis (Cappetta, 1970)

FIGURE 2.27J,K

1970 Manta fragilis Cappetta – Cappetta, p. 112, pl. 26, figs. 10, 11.

1976 Mobula fragilis Cappetta – Jonet, pp. 57–58, figs. 14–16.

1976 Mobula cappettai Jonet – Jonet, pp. 57–58, figs. 14–16.

1981 Paramobula fragilis (Cappetta) – Pfeil, p. 366.

2001 Mobula sp. – Purdy et al., p. 96, fig. 14j–l.

2102 Mobula fragilis (Cappetta) – Bor et al., pp. 84–85, pl. 52, figs. 5–8. 
NUMBER 100 • 135

Description. These teeth are very rare and at present 

are known only from fragments. The teeth are compressed and 

mesiodistally broader than those of either M. loupianensis or M. 

pectinata. The crown is tall, very broad, and lingually inclined. 

The labial face is concave and thrown into large, vertical ridges 

and grooves that end as an undulating transverse crest. The roots 

are low and narrower than the crown. The basal surface of the 

root is divided by numerous shallow labiolingual grooves, dividing the root into parallel lamellae. 

Discussion. The teeth of M. fragilis are noticeably larger 

and of a different morphology than those of M. loupianensis and 

M. pectinata. On the basis of this distinctive morphology, Pfeil 

(1981) erected the genus Paramobula for these teeth. But these 

teeth are within the rather wide range of variation known for 

extant Mobula, and they should be assigned to this genus (Adnet 

et al., 2012; Cappetta, 2012). 

Stratigraphic and Geographic Ranges. 

Mobula fragilis teeth are rarely collected in this area, having been 

reported only as five beach specimens from the extreme northern end of Calvert Cliffs. Mobula fragilis has previously been reported from the late Oligocene of South Carolina (Cicimurri and 

Knight, 2009b), the middle Miocene (Langhian–Serravallian) of 

France (Cappetta, 1970), the Netherlands (Bor et al., 2012), Portugal (Jonet, 1976), and the eastern United States (Müller, 1999; 

Purdy et al., 2001). 

Other Elasmobranch Fossils

A number of elasmobranch fossils from Calvert Cliffs cannot be attributed to a specific genus or, in many cases, family. 

There are also a number of intrusive elasmobranch fossils that 

have been reworked from underlying Paleogene beds that can be 

encountered while collecting along the cliffs but do not represent 

species resident during the Miocene. 

Skeletal Fragments

FIGURE 2.28A,B

Elasmobranch skeletal fragments other than vertebral centra 

are rarely collected from Calvert Cliffs. Elasmobranchs are characterized by the presence of tesserate mineralization of the cartilaginous endoskeleton (Grogan and Lund, 2004; Maisey, 2012). 

Individual tesserae are prisms of hydroxyapatite-mineralized cartilage and are visible on the surface of skeletal elements as tightly 

packed, roughly hexagonal plates (Kemp and Westrin, 1979). 

Description. Well-preserved skeletal fragments are easily recognized by the presence of a uniformly pebbled surface 

composed of closely spaced tesserae (Figure 2.28A). Individual 

tesserae are typically less than 2 mm across and hexagonal in end 

view. When intact, tesserae have a low, weakly domed outer cap, 

collectively producing the characteristically textured surface of 

elasmobranch cartilage. The outer caps of tesserae are frequently 

lost, exposing the narrow walls and homogeneous interior of the 

prisms and giving the cartilage a distinctive alveolation, or honeycombed, appearance (Figure 2.28B). 

Discussion. The outer tesserate layer of elasmobranch 

cartilage is frequently badly degraded on beach specimens, revealing the inner core of hyaline cartilage. Such specimens are difficult 

to distinguish from worn fragments of teleost skeletal elements 

because the few remaining tesserae can be easily overlooked. 

Coprolites

FIGURE 2.28C–E 

Coprolites represent permineralized fecal masses of animals. 

In many cases, coprolites from marine habitats have a whorled 

or coiled appearance, and they have frequently been attributed to 

sharks (e.g., Milàn, 2010). But such identifications, particularly 

in older Paleozoic and Mesozoic sediments, are conjectural as 

such fecal morphologies are known from other groups (Northwood, 2005; Hunt et al., 2007; Dentzien-Dias et al., 2012). By 

the Cenozoic, most of the other groups producing such coprolites were extinct or exceptionally rare, so attribution to elasmobranchs is more plausible. 

Description. The best-preserved specimens have a cylindrical to ellipsoidal, heteropolar morphology with overlapping 

whorls restricted to one end. The outer surface is smooth, pitted 

(Figure 2.28C) or weakly pebbled (Figure 2.28D). The material 

is generally uniform in composition and in cross section consists 

of a layer several millimeters thick wrapped over earlier whorls. 

In many specimens, the ends are damaged or eroded and can be 

recognized as a coprolite by the outer layer broadly overlapping 

the core (Figure 2.28E). In other specimens, the coprolite has 

been fractured, revealing the internal whorls (Figure 2.28D). 

Discussion. Spirally coiled coprolites occur in two broad 

morphologies; amphipolar coprolites have external coiling visible as a spiral groove extending evenly over the entire surface, 

and heteropolar coprolites have external coiling restricted to 

a portion of the surface. Amphipolar coprolites are attributed 

to primitive fishes with simple intestinal valve morphologies, 

whereas heteropolar coprolites are believed to have been produced by the more complex intestinal valves of elasmobranchs 

(Northwood, 2005; Hunt et al., 2007; Dentzien-Dias et al., 

2012). Elasmobranch heteropolar coprolites can be classified 

on the basis of the distribution of the external spiral groove on 

the surface; macrospiral coprolites (=spiral coprolites of Kent, 

1994) have a groove over a substantial portion of the surface, 

whereas microspiral coprolites (=scroll coprolites of Kent, 1994) 

have the groove restricted to a small area at one end (Hunt et al., 

2007). In older Cenozoic sediments, both morphologies are commonly present (Kent, 1999a, pers. obs.; King, 2011), but in Calvert Cliffs the majority are of the microspiral scroll morphology. 

The classification of elasmobranch coprolites to more specific 

taxa (e.g., orders, families, or genera) is generally accepted as being 

impossible because of broad similarities between elasmobranch taxa 

and high variability within individual species (McAllister, 1985). 
136 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Carcharhinid Symphyseal Teeth

FIGURE 2.28F,G

Description. These teeth are small, with a crown that 

is very strongly inclined lingually. The cutting edges are smooth, 

unserrated to weakly serrate. A low, broad ridge may be present 

on each shoulder of the tooth. The root has short to moderately 

long lobes and a prominent lingual protuberance that together 

form a rectilinear or triangular base. A weak nutrient groove is 

present on the lingual protuberance of some teeth. 

Discussion. These teeth are relatively common along 

the cliffs, although they are easily overlooked because of their 

small size (typically, <7 mm) and globular shape. There are three 

similar forms of teeth with this general morphology: (1) one like 

those in Figure 2.28F,G, with a short crown, very weak cutting 

edges, broad, rounded shoulders, and a weakly bilobed root with 

a flat lingual face, (2) similar teeth, but typically with weakly serrate cutting edges and a flat, rectilinear lingual root face, and (3) 

teeth with slightly taller, weakly distally inclined crowns almost 

always with serrate edges and a weakly bilobed, less flattened 

root. The last form has a morphology that grades into that of 

symphyseal P. contortus teeth (Figure 2.21H). All three tooth 

morphologies could reasonably be interpreted as positional variants of carcharhinid symphyseal teeth, although they cannot be 

easily assigned to particular species or genera.

A C B D

E F

H

G

I

J

K

FIGURE 2.28. Other elasmobranch fossils (1 cm scale bar for A–E, H, I; 1 mm scale bar for F, G; 1 cm scale bar for J, K). (A) Elasmobranch 

tesserate cartilage (CMM-V-7722, Bayfront Park, Maryland). (B) Elasmobranch tesserate cartilage (CMM-V-7453, Scientists Cliffs, Md.). 

Photo by Stephen Godfrey. (C) Microspiral coprolite; pitted upper surface (UMCP 11475; Matoaka Cottages, Md.). (D) Microspiral coprolite; fractured lower surface revealing whorled interior (UMCP 11475; Matoaka Cottages, Md.). (E) Microspiral coprolite with overlapping 

outer whorl; lateral view (UMCP 11474; Matoaka Cottages, Md.). (F) Carcharhinid symphyseal tooth; lingual view (CMM-V-7720; 

Chesapeake Beach, Md.). (G) Carcharhinid symphyseal tooth; labial view (CMM-V-7720; Chesapeake Beach, Md.). (H) Squalicorax kaupi

tooth; labial view (CMM-V-7738; Bayfront Park, Md.). (I) Cretolamna appendiculata tooth; labial view (CMM-V-7721; Bayfront Park, Md.). 

(J) Myliobatiform caudal spine; dorsal view (CMM-V-2326; Flag Ponds, Md.). (K) Myliobatiform caudal spine; ventral view (CMM-V-2326; 

Flag Ponds, Md.). 
NUMBER 100 • 137

 Reworked Paleogene Teeth

FIGURE 2.28H,I

At the extreme northern end of Calvert Cliffs the Calvert 

Formation unconformably overlies older Paleogene sediments 

(Shattuck, 1904). Although these older horizons are below beach 

level, teeth from these horizons can be reworked into the lower 

Calvert Formation. Two Paleogene species occasionally collected 

from the northern end of Calvert Cliffs are Cretolamna appendiculata (Figure 2.28i) and Squalicorax kaupi (Figure 2.28H). 

Identification of the former species is complicated by the description of a new lamniform species with large, cuspletted teeth from 

the early Miocene (Megalolamna paradoxodon; Shimada et al., 

2016). Since M. paradoxodon has been reported from the Miocene of North Carolina, this species could be present in Calvert 

Cliffs as well. As noted above (see Carcharodon), Palaeocarcharodon orientalis may also be present as reworked specimens. 

Reworked Paleogene Carcharias teeth are a more complex 

issue, as they can be difficult to definitively separate from those 

of Miocene species. The identification of Carcharias species is 

based largely on the size, shape, and number of cusplets and 

on the extent of the striations on the lingual face of the crown. 

Unfortunately, all of these characters are quickly degraded on 

beach-worn specimens, making them essentially unidentifiable to 

individual species. The large, durable teeth of Paleogene myliobatids and rhinopterids are almost certainly reworked as well, 

but as yet, none have been definitively identified from Calvert 

Cliffs. 

Myliobatiform Caudal Spines

FIGURE 2.28J,K

Description. These spines are elongate and tapered and 

have a roughly ovoid cross section and coarsely serrated margins. 

The spine is composed primarily of dentine, although the dorsal 

surface and ventrolateral margins are covered with enameloid. 

The enameloid on the dorsal surface of the spine is covered with 

reticulated longitudinal ridges that are strongest basally and tend 

to become obsolete distally. The distal portion of the spine is 

typically more flattened than the base and has a broad, shallow 

longitudinal groove of variable length. The marginal enameloid 

serrations are numerous and triangular, with the apices directed 

basally. There is an elongate to globular base of variable size that 

anchors the spine in the soft tissues of the body, although it is 

missing in many specimens. 

Discussion. The myliobatiforms are characterized by the 

presence of one or more caudal spines at the base of the tail. 

But despite being a distinctive synapomorphy of this order, morphological differences in caudal spines have been largely ignored 

until relatively recently. 

Schwartz (2005, 2007, 2008a,b) documented morphological variation in extant species on the basis of spine length, the 

number and distribution of serrations, the relative size of the 

exposed portion of the spine, and the relative length of the dorsal 

groove. Individual extant species were generally discernible by 

suites of these characters, and spine morphology was correlated 

with habitat or lifestyle. Unfortunately, intraspecific variation 

was also exceptionally high, and there was broad morphological overlap between species, genera, and families in these characters (Schwartz, 2008a:48–49, tbl. 1; 2008b:29–33, tbl. 1). 

Further, correlations between spine morphology and habitat or 

lifestyle may not be as definitive as originally proposed (Cuny 

and Piyapong, 2007). Consequently, isolated spines and spine 

fragments of fossil myliobatiforms cannot be reliably assigned 

to specific ray taxa or ecomorphotypes (Marmi et al., 2010). 

The one apparent exception is the large, distinctive spine base in 

the mobulids (Figure 2.27L,M), which can be easily identified at 

least to family. 

THE CALVERT CLIFFS CHONDRICHTHYAN FAUNA

Completeness of the Calvert Cliffs Fauna

Calvert Cliffs provides a unique window into the changes 

occurring in chondrichthyans during the early and middle stages 

of the Neogene. These changes were based on new groups that 

arose in the Paleocene or Eocene and then underwent extensive 

diversification during the late Oligocene and Miocene. Calvert 

Cliffs captures a detailed record of these changes for an approximately 10 my interval from the late early Miocene (late Burdigalian) through the early late Miocene (early Tortonian). This 

fossil record of sharks and rays is extensive (Foote and Sepkoski, 

1999; Cappetta, 2012; Maisey, 2012) but unfortunately biased. 

The primary problem is that the fossil record of these groups is 

represented almost entirely by teeth, which is not unexpected 

since teeth are the hardest and most durable tissues produced 

by cartilaginous fishes (Garrick, 1982). But the completeness of 

the skeleton has been shown to be correlated with estimates of 

diversity of fossil groups (Benton et al., 2013; Brocklehurst and 

Fröbisch, 2014), and the identification of sharks and rays based 

almost entirely on isolated teeth complicates any comparisons of 

shark and ray diversity for fossil and Holocene faunas. Additionally, a number of other factors can further confound estimates 

of fossil diversity and produce unexpected biases (Cooper et al., 

2006; Benton et al., 2013; Brocklehurst and Fröbisch, 2014; 

Huang et al., 2015). 

There have been relatively few studies that have examined 

diversity patterns in fossil elasmobranchs (Foote and Sepkoski, 

1999; Kriwet and Benton, 2004; Underwood, 2006; Guinot 

et al., 2012; Sorenson et al., 2014). Although not all of these 

studies are directly related to diversity in the Neogene, they all 
138 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

provide an evolutionary context for the appearance of modern 

shark faunas. The earliest of these studies (Foote and Sepkoski, 

1999) found that 95% of extant elasmobranch genera were represented in the fossil record. Further, it found that the probability 

of an elasmobranch genus being detected within a 5 my time 

interval was 10%–15% for Paleozoic genera and 25%–40% for 

Mesozoic genera. The authors attribute the difference between 

the Paleozoic and Mesozoic to differences in the available fossil 

material; Paleozoic forms are known mainly from whole-body 

fossils, whereas Mesozoic forms are identified primarily from 

isolated teeth from unconsolidated sediments (see also Cappetta, 

2012:30–31; Maisey, 2012). They provide no data for Cenozoic 

forms but argue that it should be comparable to those from the 

Mesozoic since both are based on teeth. This supposition is plausible and is consistent with other data on the relative completeness of the fossil record in the Mesozoic and Cenozoic (Benton 

et al., 2000). 

More recently, Guinot et al. (2012) provided a rigorous 

reevaluation of elasmobranch diversity over the past 300 my. 

They found that elasmobranch diversity was essentially constant 

for orders, families, and genera during the late Cenozoic and 

that virtually all Holocene elasmobranch taxa above the species level are represented as fossils during the Neogene (Guinot 

et al., 2012: fig. 3A). These estimates are roughly comparable 

to those of Foote and Sepkoski (1999) indicating that 95% of 

extant chondrichthyan genera were represented in the fossil 

record. But the estimates from both of these studies are global 

and are not directly applicable to a temporally and regionally 

restricted locality, such as Calvert Cliffs. Further, these studies do not address the problem of species-level diversity within 

elasmobranchs. 

In overall diversity, the Calvert Cliffs elasmobranch fauna, 

with 51 species in 32 genera, is roughly comparable to the Holocene fauna from the Mid-Atlantic region of the eastern United 

States (the Chesapeake Bay and the continental shelves of Delaware, Maryland, and Virginia), with 46 species in 29 genera 

(Tables 2.1, 2.2). Not included in these tables are the three chimaera species in three separate genera, which raises the totals 

for the Calvert Cliffs chondrichthyan faunas to 54 species in 

35 genera. Of the 29 Holocene genera along the Mid-Atlantic 

coast, 19 (66%) are present in Calvert Cliffs. Eight additional 

genera found in Calvert Cliffs (i.e., Chimaera, Hexanchus, Notorynchus, Hemipristis, Negaprion, Rhynchobatus, Aetobatus, 

and Pteromylaeus) are extant but not currently resident in MidAtlantic waters. Taken as a whole, this number suggests that the 

Calvert Cliffs fossil beds contain a relatively complete assemblage 

of chondrichthyans, although studies on other groups (Cooper et 

al., 2006; Benton et al., 2013; Brocklehurst and Fröbisch, 2014; 

Huang et al., 2015) have suggested additional, as yet undetected, 

taxa were very likely present. 

Although direct comparisons between the Calvert Cliffs and 

Holocene faunas are easily interpreted, their validity is difficult 

to assess. The Calvert Cliffs data are time averaged and represent a range of habitats over a span of approximately 10 my. 

Conversely, the Holocene data are cross sectional and represent 

a geologically brief snapshot in time. Further, taxa missing from 

the described Calvert Cliffs fauna of fossil cartilaginous fishes 

will not be randomly distributed among the taxa originally present. The missing taxa will be dominated by forms that are small 

and rare and have poorly mineralized hard parts. This bias will 

be exacerbated by collecting techniques typically used along the 

cliffs that favor larger, more conspicuous teeth over smaller specimens (Raup, 1977; Smith, 1994:108–117; Cooper et al., 2006; 

Benton et al., 2013; Brocklehurst and Fröbisch, 2014; Huang et 

al., 2015). 

Unfortunately, more precise estimates of the number of species of chondrichthyans in Calvert Cliffs are more difficult to 

obtain. Extant species of chondrichthyans are described using 

whole-body morphology and would seem to be well-documented 

for most groups. But as conservation researchers on extant elasmobranchs have discovered, molecular techniques used to identify body parts have produced ample evidence for cryptic species 

that were difficult, or even impossible, to separate solely on the 

basis of morphological criteria. A broad range of chondrichthyans, including cow sharks (Hexanchus; Daly-Engel et al., 2018), 

angel sharks (Squatina; Sole-Cava and Levy, 1987), thresher 

sharks (Alopias; Eitner, 1995; see Trejo, 2004, for an opposing view), hound sharks (Mustelus; Heemstra, 1997; Gardner 

and Ward, 2002), guitarfishes (Rhinobatos; Sandoval-Castillo 

et al., 2004), requiem sharks (Carcharhinus; Barnstetter, 1982; 

Pank et al., 2001; Keeney and Heist, 2006; Boomer et al., 2010), 

hammerhead sharks (Sphyrna; Quattro et al., 2006), cat sharks 

(Galeus; Castilho et al., 2007), and wobbegong sharks (Orectolobus; Corrigan et al., 2008), all have cryptic sibling species. 

There is every reason to believe that extinct species based only 

on tooth morphology would be even more likely to underestimate the number of species present within a genus. This issue 

is already a concern for some genera (e.g., Squatina, Ward and 

Bonavia, 2001; Rhizoprionodon, Garry, 2003, 2004; Carcharhinus, Sarao, 2005) in which species cannot be reliably separated 

by dental characters alone. The validity of these concerns is unclear and remains to be resolved with more detailed morphometric analyses. 

Disparity of Calvert Cliffs Chondrichthyans

Although the total number of species and genera is similar 

between Calvert Cliffs and Holocene elasmobranch faunas, the 

prevalence of different higher taxa can vary widely (Table 2.1). 

The Calvert Cliffs selachian fauna of 39 species is dominated 

by two orders, the lamniforms (16 species) and the carcharhiniforms (16 species), which collectively account for 82% of the 

shark species (Table 2.1). The Holocene fauna retains a broad 

range of carcharhiniforms (16 species) but has a dramatically 

reduced number of lamniforms (7 species), or a total of 82% of 

selachians. 

What is particularly striking in the selachian fauna is the 

incidence of gigantism (i.e., largest species in a genus); 10 such 
NUMBER 100 • 139

TABLE 2.1. Number of species per genus of sharks in Calvert Cliffs and the Holocene epoch 

of the Mid-Atlantic states of Delaware, Maryland, and Virginia. The number of giant shark 

species with teeth greater than 3 cm in maximum height or width are shown in parentheses; 

a dash (–) indicates none are present. Extinct genera are indicated with a dagger (†). Four 

additional extant species (Echinorhinus brucus, Ginglymostoma cirratum, Lamna nasus, 

and Negaprion brevirostris) may rarely occur as stray individuals. Holocene distributions are 

based on Bigelow and Schroeder (1948), Compagno (1984, 2002), Whitehead et al. (1984), 

Smith and Heemstra (1986), Lythgoe and Lythgoe (1992), Michael (1993), Schwartz (2003), 

Compagno et al. (2005), and Murdy et al. (2013).

Sharks Calvert Cliffs Holocene Mid-Atlantic

Order Hexanchiformes 

Notorynchus 1 (1) –

Hexanchus 1 (1) –

Order Echinorhiniformes 

Echinorhinus 1 (–) –

Order Squaliformes 

Centroscyllium – 1 (–)

Etmopterus – 1 (–)

Squalus 2 (–) 1 (–)

Order Squatiniformes 

Squatina 1 (–) 1 (–)

Order Orectolobiformes

Rhincodon 1 (–) 1 (–)

Order Lamniformes 

Carcharias 3 (1) 1 (1)

Carcharoides† 1 (–) –

Isurus 2 (2) 2 (2)

Carcharodon 2 (2) 1 (1)

Carcharocles† 2 (2) –

Parotodus† 1 (1) –

Alopias 4 (2) 2 (–)

Cetorhinus 1 (–) 1 (–)

Order Carcharhiniformes 

Scyliorhinid sp. 1 (–) 1 (–)

Mustelus 1 (–) 1 (–)

Hemipristis 1 (1) –

Galeocerdo 1 (–) 1 (1)

Physogaleus† 2 (–) –

Carcharhinus 7 (–) 8 (–)

Prionace – 1 (–)

Negaprion 1 (–) –

Rhizoprionodon 1 (–) 1 (–)

Sphyrna 1 (–) 3 (–)

Total 39 (13) 28 (5)
140 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

species are present in Calvert Cliffs in the genera Notorynchus, 

Hexanchus, Carcharias, Isurus, Carcharodon, Carcharocles, 

Parotodus, Alopias, Hemipristis, and Physogaleus, but only 6 

occur in the Holocene fauna of the Middle Atlantic states (Carcharias, Isurus, Carcharodon, Galeocerdo, Carcharhinus, and 

Sphyrna). This discrepancy in the number of giant species is 

even more pronounced because of the puzzling co-occurrence of 

pairs of species of very similar size within a genus. A reexamination of the Calvert Cliffs shark fauna revealed indications that 

this pairing is particularly true for larger macrophagous species 

with teeth of at least 3 cm in maximum dimension (Table 2.1). 

Two such genera (Isurus and Alopias) have a pair of species 

of essentially identical size, making it impossible to determine 

whether one species is actually larger than its congener (e.g., Figure 2.3A). Two other genera (Carcharodon and Carcharocles) 

each have two giant species with the second-largest species only 

slightly smaller than the largest species. Finally, the genus Carcharias is represented by only a single giant species (C. cuspidatus) 

in Calvert Cliffs, although a second giant species is a possibility. 

Carcharias taurus is known to have teeth comparable in size to 

C. cuspidatus (Purdy et al., 2001) but is known from only nine 

teeth in Calvert Cliffs. Whether larger Calvert Cliffs C. taurus

teeth are present, making it yet another giant species, will require 

additional research. In contrast, reevaluating the Holocene fauna 

for species with teeth more than 3 cm in any dimension adds 

only a single giant species, a second species in Isurus. Taking into 

account all large macrophagous sharks, there are 13, or possibly 

14, species in Calvert Cliffs compared to 5 in the Holocene fauna 

(Table 2.1).

The Calvert Cliffs batoid fauna (Table 2.2) has a very different diversity pattern from that of the selachians, with twothirds the number of species (12) of the Holocene fauna (18). 

TABLE 2.2. Number of species per genus of batoids in Calvert Cliffs and the Holocene epoch 

of the Mid-Atlantic states of Delaware, Maryland, and Virginia. Extinct genera are indicated 

with a dagger (†); a dash (–) indicates none are present. Three additional species (Aetobatus 

narinari, Manta birostris, and Rhinobatos lentiginosus) may rarely occur as stray individuals. 

Holocene distributions are based on Bigelow and Schroeder (1953), Whitehead et al. (1984), 

Smith and Heemstra (1986), Lythgoe and Lythgoe (1992), Michael (1993), Schwartz (2003), 

and Murdy et al. (2013).

Sharks Calvert Cliffs Holocene Mid-Atlantic

Order Pristiformes

Pristis 1 1

Order Rajiformes

Amblyraja – 1

Breviraja – 1

Dipturus – 1

Leucoraja – 3

Raja 1 1

Rhynchobatus 1 –

Order Torpediniformes 

Torpedo – 1

Order Myliobatiformes 

Dasyatis 2 4

Gymnura – 2

Aetobatus 1 –

Myliobatis – 1

Pteromylaeus 1 –

Rhinoptera 1 1

Mobula 3 1

Plinthicus† 1 –

Total 12 18
NUMBER 100 • 141

The discrepancy is greatest for three families, the Rajidae (1 Calvert Cliffs species versus 6 Holocene species), the Gymnuridae (0 

versus 2 species), and the Dasyatidae (2 versus 5 species). These 

three families account for 72% of Holocene batoids but only 

25% of those from Calvert Cliffs. 

Differences in Calvert Cliffs and Holocene faunas are even 

more striking when species are sorted by their ecological roles 

within the elasmobranch community. Figure 2.29 depicts the 

frequency of the five most common elasmobranch ecomorphotypes for Calvert Cliffs compared with the Holocene Mid-Atlantic shark fauna (Compagno, 1990b, with some modifications). 

Three selachian ecomorphotypes are listed. Eurytrophic sharks 

are large, active sharks capable of feeding on a broad range of 

large prey. The littoral piscivorous ecomorphotype is a generalized group of sharks that feed primarily on a variety of fishes. It 

includes Compagno’s littoral and sphyrnid ecomorphotypes but 

excludes sharks with more specialized diets of the teuthitrophic 

(=squid-feeding) and cancritrophic (crustacean-feeding) ecomorphotypes. Three of Compagno’s ecomorphotypes, archipelagic, 

macroceanic, and tachypelagic, are difficult to unambiguously 

distinguish in fossil sharks on the basis of teeth and are combined in Figure 2.29 as a composite macropelagic ecomorphotype. The macropelagic sharks are strongly overrepresented in 

Calvert Cliffs, almost entirely because of the presence of the 

giant sharks (e.g., Carcharodon, Carcharocles, Parotodus, and 

Alopias). So the loss of the giant sharks was not simply a loss of 

lamniforms but more broadly the decimation of sharks with a 

specific lifestyle.

Two batoid ecomorphotypes are listed in Figure 2.29. Aquilopelagic batoids are large myliobatiform rays adapted for 

FIGURE 2.29. Comparison of common ecomorphotypes in Calvert Cliffs and the Holocene fauna of the Mid-Atlantic states of the eastern 

United States. See text for descriptions of ecomorphotypes. 
142 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

underwater flight using large, triangular pectoral fins. This ecomorphotype is moderately overrepresented in Calvert Cliffs because of the presence of four mobulids (one Plinthicus and three 

Mobula species), along with two myliobatids (Pteromylaeus and 

Aetobatus) not present in Holocene faunas of the Middle Atlantic region. The rajobenthic ecomorphotype (i.e., rajids, gymnurids, and dasyatids; Compagno, 1990b) is the most diverse 

group of living batoids but is seriously underrepresented in the 

Calvert Cliffs fauna. Three factors could plausibly contribute to 

the paucity of Calvert Cliffs rajobenthic species. First, rajobenthic batoids generally have very small teeth sizes of 3 mm or 

less. In addition, the teeth have a nondescript, generally globular 

shape and, taking into account their small size, are easily overlooked during collecting. Second, these batoids use their teeth 

to crush benthic prey. Such feeding quickly abrades the occlusal 

surface of the crown, obliterating many of the diagnostic characters used for identifying individual species. Finally, these groups 

may have been undergoing evolutionary diversification during 

the Neogene and were not as diverse in the middle Miocene as 

in Holocene faunas. Good molecular data indicate that this was 

occurring in the rajids, which had rapid speciation from the 

late Miocene to Pleistocene (Valsecchi et al., 2005; Pasolini et 

al., 2011). What is unclear is whether this speciation dramatically increased rajid diversity or reflected species turnover while 

maintaining relatively constant species richness. In the former, 

few species of rajids would be present in the middle Miocene, 

whereas if the latter condition occurred, a number of rajid species are yet to be identified from Calvert Cliffs. Comparable molecular data are not available for gymnurids or dasyatids, so the 

impact of comparatively recent speciation events is unknown. 

Future Research on Calvert Cliffs Chondrichthyans

Despite the extensive history of research on the chondrichthyans of Calvert Cliffs, a number of questions are currently unresolved. The most basic concerns the total number of species 

actually present along the cliffs. The diversity of the Calvert Cliffs 

chondrichthyan fauna is certainly comparable to two other wellstudied and roughly contemporaneous faunas from the North 

Atlantic; the Pungo River Formation of Lee Creek Mine, North 

Carolina (Purdy et al., 2001: tbl. 1), has 46 species in 33 genera, and the Lower Mica Fine Sand Formation in Werder-Uesen, 

Lower Saxony, Germany (Reinecke et al., 2011), contains 49 species in 38 genera. But these comparisons also suggest that although 

the known Calvert Cliffs fauna is extensive, it is almost certainly 

incomplete. Several genera (e.g., Ginglymostoma, Isistius, Megachasma, Megalolamna, Paragaleus, Pseudocarcharias, Gymnura) 

are not presently reported from Calvert Cliffs, although their presence would not be unexpected. The diversity of a number of other 

genera, such as the rajobenthic Raja and Dasyatis, are probably 

underestimated. Neogene representatives of all of these genera 

have been relatively extensively studied, and new additions to the 

Calvert Cliffs fauna will probably represent range extensions of 

known species, rather than new, unnamed species. 

At finer levels of resolution, the distribution of species 

among different horizons is known only at the most basic level, 

that of presence-absence data. Each horizon represents a specific 

environment, and along Calvert Cliffs these environments range 

from open ocean to marginal marine habitats (Visaggi and Godfrey, 2010). Understanding the organization of elasmobranch 

communities in different habitats requires not only a list of the 

species present but also the relative abundance of different species and ecomorphotypes. 

There is accumulating evidence that tooth morphology in 

many lineages arises by phyletic evolution. Although this may 

not reflect the actual evolutionary mechanism producing individual species, documenting stratum-specific changes in morphology will facilitate our understanding of how tooth morphology 

within a lineage changes over time. For example, Carcharhinus 

priscus has cutting edges with variable morphology (Reinecke 

et al., 2011). Late Oligocene (Chattian) specimens have cutting edges that can be weakly crenulate to finely serrate. Carcharhinus priscus occurs along the length of Calvert Cliffs, and 

although the teeth are commonly finely serrate, on many specimens the serrations become obsolete apically. What is less clear is 

whether there are any stratigraphic trends in the condition of the 

serrations or if they are simply characteristic of a variable morphospecies. Resolving these issues will require both the use of 

increasingly sophisticated research technologies to provide new 

types of information and increased participation by the public in 

the research process. 

Since the last major reviews of Calvert Cliffs chondrichthyans (Kent, 1994; Müller, 1999), research on fossil sharks, rays, 

and chimeras has relied increasingly on statistical methodologies 

for quantifying and evaluating teeth (Naylor and Marcus, 1994; 

Adnet, 2006; Chandler et al., 2006; Nyberg et al., 2006; Shin, 

2010; Whitenack and Gottfried, 2010). These techniques can 

provide rigorous assessments of morphology but rely on large 

samples of carefully collected, well-documented teeth to be of 

value. For common species, obtaining adequate sample sizes is 

not particularly difficult, but with species that either are rare 

or preserve poorly, it requires far more effort. Fortunately, research on fossil chondrichthyans has long benefitted from the 

active participation by the public. Many individuals are amateur 

or recreational collectors, although some are so knowledgeable 

that they are more appropriately considered avocational or independent paleontologists (Cozart, 1997). The importance of all of 

these individuals cannot be overestimated; numerous individuals 

routinely make their private collections available for study, and 

this generosity is reflecteded by the high proportion of museum 

specimens that were obtained from nonprofessionals. 

As already discussed, the only ecomorphological group seriously underrepresented in the Calvert Cliffs beds is the rajobenthic ecomorphotype (Figure 2.29). Further complicating the 

detection and identification of batoids in these three families is 

that they all have similar tooth morphologies, with most of the 

diagnostic characters being the occlusal surface of the crown. 
NUMBER 100 • 143

Unfortunately, rajobenthic batoids use their teeth to crush benthic invertebrates, effectively obliterating the diagnostic characters before the teeth are shed and replaced. Even in large samples 

of these teeth, most cannot be reliably identified to species, and 

many cannot be identified to genus. This sampling deficiency 

is currently being addressed with a very large scale citizen science project in cooperation with the Paleo Quest, in which high 

school students sort screened sediment samples and extract microteeth for more detailed analysis by the Fossil Shark Research 

Group at the University of Maryland, College Park. The project 

has the capacity to process large volumes of screened material 

in order to find and identify overlooked species of batoids and 

selachians. Preliminary results from this synergistic relationship 

include evidence for additional scyliorhinid, hemigaleid, and 

rajid species, as well as the first ginglymostomatid and parascylliid species from Calvert Formation sediments. As yet, none of 

these species have been fully documented and are the subject of 

ongoing research. 

 ACKNOWLEDGMENTS

Numerous people have generously helped with the preparation of this chapter, including providing helpful insights and 

discussions: Aaron Alford, Steve Alter, Mark Bennett, David Bohaska, Pieter De Schutter, Mike Ellwood, John Fitz Jr., Stephen 

Godfrey, Gary Greaser, Henry Hays, Walt Johns, Hans Lemke, 

Judi McKay, John Nance, Jason Osborne, Peter Picard, Robert Purdy, and David Ward. I particularly thank the following 

for donating specimens to the Calvert Marine Museum for this 

research: Aaron Alford, Mark Bennett, Mike Ellwood, Henry 

Hays, Walt Johns, Hans Lemke, Jason Osborne, Karen TeichZabroski, and David Ward. I would also thank students from the 

University of Maryland Fossil Sharks Research Group (Max Ambrosino, Jessica Howard, Javier Morales, Lauren Rose, Christopher Smith, and Emily Wagner) for their tireless hours spent 

working with elasmobranch microteeth, Steven Wolniak and 

Carl Zeiss Microscopy for assistance with microphotography, 

and Tim Scheirer for his whole-body drawings. Connie Barut 

Rankin drafted the skeleton of C. megalodon illustrated in Figure 2.15D. Nicholas D. Pyenson and David J. Bohaska very helpfully reviewed the manuscript. Finally, I extend special thanks to 

my wife, Karen Nelson Kent, for photographing countless fossils 

and tolerating the long hours my mind spent lost in the Miocene. 

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ADDENDUM: A NEW SPECIES OF GIANT 

THRESHER SHARK (FAMILY ALOPIIDAE) 

WITH SERRATED TEETH

Bretton W. Kent and David J. Ward1

The Neogene has a remarkably complex array of large macrophagous sharks (BWK, this chapter) that is well represented 

along the eastern United States. Despite extensive research on 

fossil elasmobranchs in this area, one species of large thresher 

shark (family Alopiidae) with distinctively serrated teeth has not 

been previously named. 

Systematic Paleontology

Subclass Elasmobranchii Bonaparte, 1838

Superorder Selachimorpha Nelson, 1984

Order Lamniformes Berg, 1958

Family Alopiidae Bonaparte, 1838

 Genus Alopias Rafinesque, 1810

Alopias palatasi, new species

FIGURE 2.A1

Holotype. An anterior tooth at the Calvert Marine 

Museum (CMM-V-385).

Type Locality. Parkers Creek, Maryland.

Horizon. Calvert Formation (bed 12). 

1 Department of Earth Sciences, Natural History Museum, Cromwell Road, 

London SW7 5BD, UK.
158 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Paratypes. Calvert Marine Museum: CMM-V-3876 

(beach-collected tooth, Flag Ponds, Maryland), CMM-V-3981 

(beach-collected tooth, Parkers Creek, Maryland), CMM-V4242 (beach-collected tooth, Calvert County, Maryland), and 

CMM-V-5823 (river-collected tooth, south end of Buck Island, 

Calibogue Sound downstream of the mouth of the May River, 

South Carolina). U.S. National Museum of Natural History: 

USNM 411148 (bed 12, Calvert Formation, Parkers Creek, 

Maryland) and USNM 639783 (beach-collected tooth, Parkers 

Creek, Maryland). 

Additional Material. Kent’s reference collection, 

University of Maryland, College Park: UMCP 12147 (beachcollected tooth, Chesapeake Beach, Maryland), UMCP 12155 

(river-collected tooth, Morgan River, South Carolina), UMCP 

12158 (river-collected tooth, Westmoreland/Stratford Hall, Virginia), and UMCP 12166 (beach-collected tooth, northern Calvert Cliffs, Maryland). Mike Elwood collection: two teeth (bed 

12, Calvert Formation, north of Scientists Cliffs, Maryland). 

Harriet Ertman collection: one river-collected tooth (Stratford 

Hall, Virginia). Walt Johns collection: one beach-collected tooth 

(Governor Run, Maryland), one beach-collected tooth (Plum 

Point, Maryland), and three beach-collected teeth (one whole 

tooth and two tooth fragments; Stratford Hall, Virginia). Jason 

Osborne collection: scuba-collected tooth (Newport News unit, 

Calvert Formation, New Kent County, Virginia). 

Etymology. Named for Mark Palatas, who provided 

one of the original specimens (CMM-V-5823; Figure 2.A1G,H) 

for study. 

Diagnosis. The holotype (CMM-V-385; Figure 2.A1A,B) 

is an upper anterior (A3?) tooth. The crown is broad and compressed, with cutting edges that are coarsely serrated. The serrations are irregular in size on the basal portions of the crown, 

becoming somewhat finer and more regular apically. The mesial 

cutting edge is convex, whereas the distal edge is markedly concave. The lingual coronal face is relatively flat, whereas the labial 

face is weakly convex. The root is compressed with substantially 

shortened and relatively deep root lobes that do not extend beyond the lateral shoulders of the crown. The basal root margin 

is strongly arched. 

Anterior teeth closer to the jaw symphysis (Figure 2.A1C,D) 

are less strongly arched distally than the holotype and have 

somewhat broader crowns. The root lobes on these teeth may 

extend slightly beyond the lateral margins of the crown. 

Upper lateral teeth (Figure 2.A1E,F) are more triangular, 

with the height and width being nearly identical. The mesial cutting edge is less convex than in anterior teeth and may become 

weakly sigmoidal in some specimens. The distal edge is only 

weakly concave. The root is compressed, with a broadly arched 

to slightly obtuse basal margin. The root is typically slightly 

broader than the base of the crown. 

Lower lateral teeth (Figure 2.A1G,H) have crowns weakly 

inclined distally and a strongly arched basal root margin. The 

root is slightly thicker than in upper lateral teeth, although this 

character is somewhat variable. 

Lateral teeth located nearer the commissure have crowns 

that become lower and more distally arched. In some cases the 

coronal apex is positioned distal to the distal margin of the root. 

The distal cutting edge becomes progressively more strongly concave, and the basal root margin becomes more weakly arched. 

Remarks. Alopias palatasi resembles the more widely 

known A. grandis but has coarsely serrated cutting edges. These 

serrations are substantially larger and more distinctive than 

those of the weakly crenulated specimens of A. grandis (Kent, 

this chapter). The teeth of A. palatasi can also be quite large, 

with the largest specimens more than 40 mm in height (P. Picard, 

Germany, personal communication, 2015). 

The teeth of A. grandis and A. palatasi are similar in a number of respects, including large teeth with tall, broad, compressed 

crowns and shortened root lobes. In addition to coarsely serrate 

cutting edges A. palatasi also differs from the unserrated species 

in having more extensive monognathic heterodonty; the broadly 

triangular lateral teeth of A. palatasi are only occasionally present in A. grandis. 

A number of embayments occur along the Neogene paleocoastline of the eastern United States (Ward and Powars, 2004: 

fig. 1), and teeth of A. palatasi have been found in three of these, 

the Salisbury Embayment (Maryland and Virginia), the Albemarle Embayment (North Carolina), and the Charleston Embayment (South Carolina). From north to south localities where A. 

palatasi teeth have been found include the following.

Maryland. The distribution of A. palatasi along Calvert Cliffs is restricted to the northern portion of the cliffs (Flag 

Ponds to Chesapeake Beach), a region of the cliffs associated 

with the Calvert and Choptank Formations (Ward and Andrews, 

2008: fig. 5; Visaggi and Godfrey, 2010: fig. 3). The Calvert Formation within this region of the cliffs includes a small exposure 

of the Fairhaven Member (bed 3B, middle Burdigalian) and a 

much more extensive exposure of the Plum Point Member (beds 

4–16A, late Burdigalian to late Langhian). The entire sequence 

of Choptank Formation sediments (beds 17–20, Serravallian) is 

present in this region. 

Virginia. Alopias palatasi teeth have been found as beach 

specimens along the Potomac River at Wakefield, Horseshoe 

Cliffs, Stratford Cliffs, and Nomini Cliffs. The stratigraphy 

along this portion of the Potomac River is moderately complex 

(Ward and Andrews, 2008: fig. 7); the principal horizons in 

these localities are extensive exposures of the Calvert Formation 

(Plum Point Member, beds 14, 15; late Langhian) and the Eastover Formation (Claremont Manor Member [late Tortonian] and 

Cobham Bay Member [Messinian]). Between the Calvert and 

Eastover sediments are smaller, more variable exposures of the 

Choptank Formation (Boston Cliffs Member, bed 19; middle Serravallian) and the St. Marys Formation (late Serravallian). The 

St. Marys sediments have been reliably assigned to a specific horizon (Ward and Andrews, 2008:49, fig. 7); possible assignments 

include the Little Cove Point Member (beds 21–23, Tortonian) 

and the Windmill Point Member (bed 24). The cliffs in this area 

are capped with a layer of sediments questionably assigned to 
NUMBER 100 • 159

the middle Pliocene Yorktown Formation (late Zanclean to early 

Piacenzian). A single specimen has also been collected in situ 

from the Pamunkey River, New Kent County (J. Osborne, Paleo 

Quest, pers. comm., 2015), in the Newport News unit (basal 

Calvert Formation, early Burdigalian; Edwards et al., 2005). 

North Carolina. Alopias palatasi is poorly documented from North Carolina. This species is not listed in the 

extensive review of sharks and rays from Lee Creek Mine, North 

Carolina (Purdy et al., 2001). Teeth have been collected as river 

specimens from the Meherrin River, Hertford County, North 

Carolina (M. Palatas, Sharks Underground, pers. comm., 2014; 

S. Alter, pers. comm., 2015). The fossil beds in this area represent the early to middle Miocene Pungo River Formation (Burdigalian to Langhian), late Miocene Eastover Formation (Cobham 

Bay Member, Messinian), and the Middle Pliocene Yorktown 

Formation (Sunken Meadow, Rushmere and Morgarts Beach 

Members, late Zanclean to early Piacenzian; Miller, 1982; Gibson, 1983; Geisler et al., 2012). Although the Pungo River Formation is generally accepted as being of Burdigalian to Langhian 

age (Gibson, 1987; Purdy et al., 2001), the beds in this area may 

extend into the early Serravallian (Gibson, 1983). 

South Carolina. Teeth of A. palatasi are occasionally collected as river or scuba specimens from the coastal area 

of southwestern South Carolina in southern Beaufort County, 

including the Broad and May River areas (M. Palatas, pers. 

comm., 2014; S. Alter, pers. comm., 2015). The stratigraphy of 

Beaufort County consists largely of undifferentiated early Miocene (Aquitanian and Burdigalian) sediments typically overlain 

with Quaternary marine terraces (Doar and Clendenin, 2002). 

Alopias palatasi specimens from this area are almost certainly 

derived from these early Miocene sediments. Seaward a thin stratum of the younger Coosawhatchie Formation intrudes between 

the undifferentiated Miocene formations and the cap of marine terraces (Doar and Clendenin, 2002). The Coosawhatchie 

Formation is middle Miocene in age (Langhian to Serravallian; 

Popenoe, 1990), and A. palatasi teeth collected in tidal portions 

of the South Carolina coastline (such as the Mark Palatas specimen; CMM-V-5823) could be from this formation rather than 

the underlying early Miocene beds. 

A B C D

E

G H

F

FIGURE 2.A1. Alopias palatasi (new species) teeth. Scale bar = 1 cm. (A) Right upper anterior tooth (holotype; CMM-V-385; lingual view). 

(B) Right upper anterior tooth (holotype; CMM-V-385; labial view). (C) Right upper anterior tooth (CMM-V-7735; lingual view). (D) Right 

upper anterior tooth (CMM-V-7735; labial view). (E) Right upper lateral tooth (paratype; CMM-V-3981; lingual view). (F) Right upper lateral 

tooth (paratype; CMM-V-3981; labial view). (G) Left lower lateral tooth (paratype; CMM-V-5823; labial view). (H) Left lower lateral tooth 

(paratype; CMM-V-5823; lingual view). 
160 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Outside of the eastern United States, partially and fully serrated teeth of A. palatasi are occasionally found in the Upper 

Globigerina Limestone above the C2 phosphorite on the Mediterranean island of Malta (middle Miocene, Langhian; Ward and 

Bonavia, 2001), indicating that it had a wider distribution than 

the western Atlantic (D. Ward, personal observation). As yet 

there is no evidence of A. palatasi in mainland Europe. Recent 

monographs on the elasmobranchs of Germany (Reinecke et al., 

2011) and the Netherlands (Bor et al., 2012) include no teeth attributable to A. palatasi. The sister species, A. grandis, is known 

from Belgium, but no A. palatasi have been found to date (Pieter 

De Schutter, pers. comm., 2012; Everaert, 2014).

The rarity of A. palatasi precludes a definitive assessment of 

its stratigraphic range, although across all three Neogene embayments A. palatasi is, with one possible exception, always found 

in localities with Burdigalian or Langhian fossil beds. Certainly, 

both older and younger sedimentary horizons occur in all of the 

localities, so a broader stratigraphic range is possible, but the 

Burdigalian-Langhian interval appears to be the primary distribution. Further, in all three embayments A. palatasi teeth are 

typically found comingled with the teeth of the giant otodontid 

Carcharocles chubutensis, a species well represented in the Burdigalian to Langhian and possibly into the Serravallian (BWK, 

this chapter). The distribution of A. palatasi teeth in the Langhian of Malta is consistent with Burdigalian-Langhian distribution observed in the western North Atlantic. 

The one exception to this general Burdigalian-Langhian pattern of distribution is a single A. palatasi tooth from Flag Ponds 

(CMM-V-3876). This is a heavily worn beach specimen, so it is 

unclear whether it was derived from the Choptank Formation 

(Serravallian) or the upper Plum Point Member (late Langhian) 

located slightly more than 2 km upstream of Flag Ponds at Calvert Beach. This distance is likely too far for water transport of 

the tooth given the weak alongshore currents in this area, but it 

could have been rafted downstream attached to beach ice during 

the spring thaw. 

The three known in situ specimens of A. palatasi provide 

a somewhat clearer estimate of stratigraphic range. The oldest 

specimen was collected from the Newport News beds, an informal basal unit of the Calvert Formation on the Pamunkey River, 

Virginia. There is some controversy about the exact age of this 

bed, ranging from late Aquitanian (on the basis of the age of bed 

1; Vogt et al., this volume) to earliest Burdigalian (Edwards et 

al., 2005). The other two A. palatasi specimens were both collected from bed 12 of the Plum Pont Member (Calvert Formation, middle Langhian).

ACKNOWLEDGMENTS

We thank both Mark Palatas (Sharks Underground, Louisville, Kentucky) and Jason Osborne (Paleo Quest, Midland, 

Texas) for providing specimens and donating them to the Calvert Marine Museum. Mark Havenstein (Lowcountry Geologic, 

Charleston, South Carolina) and Steve Alter (Steve’s Fossil Shark 

Teeth, Inc., White Bird, Idaho) provided further material and 

stratigraphic information. Carmel Galea Bonavia (University of 

Malta) and Richard Curmi (Malta) shared their knowledge of 

Maltese records, and Peter Picard (Germany) provided a number 

of useful images of U.S. specimens for study. Karen Nelson Kent 

(Silver Spring, Maryland) photographed additional teeth used in 

this species description. 

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Geological Survey Professional Paper, 1688:H1–H71.

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Churchilldok en Leopolddok (Antwerpse haven, rechteroever): een stratigrafsche interpretatie. Afzettingen WTKG, 35(1):20–27. 

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Late Miocene Inioid (Cetacea, Odontoceti) from the Meherrin River, North 

Carolina, U.S.A. Journal of Vertebrate Paleontology, 32(1):198–211. https://

doi.org/10.1080/02724634.2012.629016.

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of the United States Central Atlantic Coastal Plain.” In Geology and Paleontology of the Lee Creek Mine, North Carolina, I, ed. C. E. Ray, pp. 35–80. 

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Mine and Adjacent Areas.” In Geology and Paleontology of the Lee Creek 

Mine, North Carolina, II, ed. C. E. Ray, pp. 31–112. Smithsonian Contributions to Paleobiology 61. Washington, D.C.: Smithsonian Institution Press.

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River Formation of North Carolina. North Carolina Geological Survey Bulletin 87. Raleigh: North Carolina Department of Natural Resources and Community Development.

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Southeastern United States.” In Phosphate Deposits of the World, ed. W. C. 

Burnett and S. R. Riggs, pp. 352–380. New York: Cambridge University Press. 

Purdy, R., V. Schneider, S. Applegate, J. McLellan, R. Meyer, and R. Slaughter. 

2001. “The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, 

Aurora, North Carolina.” In Geology and Paleontology of the Lee Creek 

Mine, North Carolina, III, ed. C. E. Ray and D. J. Bohaska, pp. 71–202. 

Smithsonian Contributions to Paleobiology 90. Washington, D.C.: Smithsonian Institution Press. 

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Fauna of the Late Burdigalian, Miocene, at Werder-Uesen, Lower Saxony, 

Germany, and Its Relationships with Early Miocene Faunas in the North Atlantic, Central Paratethys and Mediterranean. Palaeontos, 20. 

Visaggi, C. C., and S. J. Godfrey. 2010. Variation in Composition and Abundance 

of Miocene Shark Teeth from Calvert Cliffs, Maryland. Journal of Vertebrate 

Paleontology, 30(1):26–35. https://doi.org/10.1080/02724630903409063.

Ward, D. J., and C. G. Bonavia. 2001. Additions to, and a Review of, the Miocene 

Shark and Ray Fauna of Malta. Central Mediterranean Naturalist, 3(3):131–

146.

Ward, L. W., and G. W. Andrews. 2008. Stratigraphy of the Calvert, Choptank, 

and St. Marys Formations (Miocene) in the Chesapeake Bay Area, Maryland 

and Virginia. Virginia Museum of Natural History Memoir 9. Martinsville: 

Virginia Museum of Natural History.

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ABSTRACT. Bony fishes are relatively common in the Miocene deposits of the Chesapeake Group. In the past three decades, intensive collecting has resulted in the accumulation of a large number of bony fish remains. Thirty-eight actinopterygian taxa, based on 

fossil bones, are now known from the Chesapeake Group. A diverse otolith assemblage 

of at least 55 taxa has also been reported. The reduced size of many of the otoliths is 

probably related to their juvenile nature. Such an abundance of juveniles suggests that 

the Salisbury Embayment represented a nursery ground for most of the Miocene. The fish 

taxa recognized in the deposits of the Chesapeake Group show a clear general affinity for 

well-oxygenated muddy and sandy substrates. The assemblages are dominated primarily by shallow-water fishes characteristic of the inner shelf and secondarily by epipelagic 

taxa. Benthopelagic fishes characteristic of the outer shelf and upper slope are nearly absent in the Calvert Formation (exceptions are Brotula sp. and Lopholatilus ereborensis). 

The common occurrence of open-ocean taxa (billfishes, tunas, wahoos) in the Calvert, 

Choptank, and Eastover Formations suggests that deposition took place in the distal 

portions of the inner shelf. Overall, the ichthyofaunal composition is consistent with the 

sedimentary and paleontological record, which evidences a general regressive trend from 

the Calvert to the St. Marys Formations, representing a gradual shallowing within the 

Salisbury Embayment. The fish assemblages of the Chesapeake Group exhibit a modern 

aspect, with most of the taxa belonging to genera or higher categories that currently 

occur in the northwestern Atlantic, including along the coasts of Maryland and Virginia. 

3 Miocene Bony Fishes of the 

Calvert, Choptank, St. Marys, 

and Eastover Formations, 

Chesapeake Group, Maryland 

and Virginia

Giorgio Carnevale1* and 

Stephen J. Godfrey2

1 Professor, Dipartimento di Scienze della Terra, 

Università degli Studi di Torino, Via Valperga Caluso 35, I-10125 Torino, Italy.

2 Curator of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, Maryland 20688, 

USA. Also, Research Associate, National Museum of Natural History, Smithsonian Institution, 

Washington, D.C., USA.

* Correspondence: 

giorgio.carnevale@unito.it

Received 1 May 2015; accepted 25 August 2017.
162 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

INTRODUCTION

Miocene deposits of the Middle Atlantic Coastal Plain include a series of remarkably fossiliferous interbedded siliciclastic 

deposits that extensively crop out with spectacular exposures 

in the Chesapeake Bay area in Maryland and Virginia. These 

richly fossiliferous deposits have attracted the attention of North 

American paleontologists since the nineteenth century (e.g., Conrad, 1830, 1842; Darton, 1891; Harris, 1893), providing the 

basis for stratigraphic subdivision and correlation of the Neogene Chesapeake Group (see Shattuck, 1904). Multiple systems 

of stratigraphic subdivision have been used to define the sedimentary units of the Miocene deposits of the Chesapeake Group, 

including the zones (Harris, 1893; Shattuck, 1904), members 

(Gernant, 1970), depositional sequences (e.g., Kidwell, 1984, 

1988, 1989, 1997), depositional events (e.g., Ward, 1992), and 

beds (Ward and Andrews, 2008). Kidwell (1988) pointed out 

that the Miocene siliciclastic deposits of the Chesapeake Group 

provide rare, direct evidence for coastal sediment sinks during 

marine transgression. Stratigraphic and taphonomic evidence 

suggests that fossil concentrations in these Miocene units can be 

interpreted as stratigraphically condensed records of a suite of 

transgressive shallow marine to paralic environments (Kidwell, 

1989). In the Maryland-Virginia area, the Neogene deposits 

of the Chesapeake Group directly overlie Paleogene units. The 

Miocene sedimentary units of the Chesapeake Group include 

the Calvert, Choptank, St. Marys, and Eastover Formations 

separated from each other by relatively short temporal gaps, 

spanning the Aquitanian, Burdigalian, Langhian, Serravallian, 

and Tortonian stages (see Vogt et al., this volume). Overall, the 

Miocene deposits of the Chesapeake Group record the gradual 

shallowing within the Salisbury Embayment, a landward extension of the Baltimore Canyon Trough bounded by the Norfolk 

High on the south and by the South Jersey High on the north 

(Poag, 1979). Within the Salisbury Embayment, maximum water 

depth and fully marine inner to middle shelf conditions occurred 

during deposition of the Calvert, Choptank, and Eastover Formations, whereas deposition of the St. Marys Formation took 

place during the transition from open marine shelf conditions to 

tidally influenced low-salinity muddy coastal environments (e.g., 

Ward and Blackwelder, 1980; Kidwell, 1989). 

Bony fishes are relatively abundant in the Miocene deposits of the Chesapeake Group. However, these remains have not 

been properly investigated, resulting in a largely incomplete and 

underestimated diversity (see Kimmel and Purdy, 1984). Fossil 

bony fish remains were first documented from the deposits of 

the Chesapeake Group by Cope (1867), who cursorily reported 

the presence of isolated sphyraenid teeth in the Maryland Miocene. Two years later, he described (Cope, 1869) the sciaenid 

Pogonias multidentatus on the basis of a single upper pharyngeal 

plate from the Miocene deposits of Nomini Cliffs, Westmoreland 

County, Virginia. Subsequently, Leidy (1873a,b,c) described the 

sturgeon Acipenser ornatus and the wrasse Protautoga conidens

from the Miocene of Virginia. Eastman (1904) produced the first 

systematic account of the fish remains of the Miocene of Maryland, describing teeth of the barracuda Sphyraena speciosa from 

the Calvert Formation, as well as of gadid and sciaenid saccular 

otoliths from the St. Marys Formation. Hussakof (1908) discussed and illustrated the type specimen of Pogonias multidentatus in his catalog of types and illustrated fossil fishes housed in the 

American Museum of Natural History. Smith (1909) presented 

new material of this species from the Miocene of Maryland, providing additional morphological evidence to support its separate 

specific status. In 1917, Berry described the sailfish Istiophorus 

calvertensis on the basis of an incomplete rostrum collected from 

Tar Bay, Virginia, in the argillaceous beds assigned to the Calvert 

Formation and more recently referred to the Eastover Formation 

(Kimmel and Purdy, 1984; Fierstine, 1998). Berry (1932) documented the presence of isolated teeth belonging to the sparid 

genus Lagodon from the St. Marys Formation, and Lynn and 

Melland (1939) presented a well-preserved neurocranium with 

associated otolith from the Calvert Formation that they assigned 

to Felichthys stauroforus. Blake (1940) described the albuloid 

Paralbula dorisiae on the basis of an eroded dental plate collected at Plum Point from deposits of the Calvert Formation. In 

his monographic review of the Tertiary fish faunas of the eastern 

and central United States, Leriche (1942) listed seven taxa from 

the Miocene deposits of the Chesapeake Group (Acipenser ornatus, Arius sp., Sphyraena speciosa, Pogonias multidentatus, Protautoga conidens, Gadidae indet., and Sciaenidae indet.). Dante 

(1953) reviewed the sciaenid otolith previously illustrated by 

Eastman (1904), together with additional material from the Calvert Formation, and described Sciaenops eastmani. Kimmel and 

Purdy (1984) provided a brief overview of the fish faunas of the 

Calvert and Eastover Formations, listing at least 12 taxa. Weems 

(1985) analyzed the ocean sunfish genera Mola and Ranzania

from the Calvert and Choptank Formations. More recently, Müller (1999) presented a broad analysis of the otolith assemblages 

of the whole Chesapeake Group. Moreover, a number of new 

species were described from the St. Marys Formation, including the stargazer Astroscopus countermani by Carnevale et al. 

(2011), the channel catfish Ictalurus countermani by Lundberg 

and Luckenbill (2012), and the needlefish Belone countermani

by de Sant’Anna et al. (2013). Finally, Carnevale and Godfrey 

(2014) described the skeletal remains and possible trace fossils of 

the tilefish Lopholatilus ereborensis from the Calvert Formation.

Extensive geological and paleontological explorations of 

the Miocene deposits of the Chesapeake Group in the last three 

decades have resulted in the accumulation of a vast collection of 

bony fish remains primarily housed in the Calvert Marine Museum (CMM), Solomons, Maryland, and the Department of Paleobiology of the National Museum of Natural History (USNM), 

Smithsonian Institution, Washington, D.C. This chapter briefly 

describes and illustrates the diversity of Miocene bony fishes of 

the marine and paralic siliciclastic deposits of the Chesapeake 

Group and discusses their paleoenvironmental significance. The 

taxonomic classification and nomenclature used, unless otherwise 
NUMBER 100 • 163

noted, follow Nelson (2006). Many of the taxa described herein 

would benefit from a more detailed examination. Furthermore, it 

is our hope that this chapter will prompt collectors to show their 

fish finds to qualified researchers and that this will stimulate additional research into this remarkable ichthyofauna.

SYSTEMATIC DESCRIPTIONS

Class Osteichthyes Huxley, 1880

Subclass Actinopterygii Cope, 1887 

Series Chondrostei Müller, 1844

Order Acipenseriformes Berg, 1940

Family Acipenseridae Bonaparte, 1831

Gen. et sp. indet.

FIGURE 3.1A,B

Sturgeon – Acipenseridae

Referred Material. CMM-V-98, partially complete lateral scute; CMM-V-99, partially complete right posttemporal and fragments of skull roofing bones; CMM-V-100, 

dorsal dermal bony scute (Figure 3.1A); CMM-V-265, partially 

complete lateral scute; CMM-V-279, fragments of skull roofing 

bones; CMM-V-289, lateral scute; CMM-V-1417 (Figure 3.1B), 

lateral scute; CMM-V-1907, dorsal scute; CMM-V-1997, partially complete left cleithrum and two isolated lateral scutes and 

fragments of dermal scutes; CMM-V-2068, partially complete 

dermal scute; CMM-V-2140, partially complete dermal scute; 

CMM-V-2439, partially complete dermal scute; CMM-V-2577, 

partially complete dermal scute; CMM-V-2597, partially complete dermal scute; CMM-V-2612, partially complete ventral 

scute; CMM-V-2767, partially complete lateral scute; CMMV-2913, extensively fragmented skull roofing bones; CMM-V3785, eight isolated dermal scutes; CMM-V-3938, two isolated 

partially preserved dermal scutes; CMM-V-3953, partially complete dermal scute; CMM-V-3985, partially complete lateral 

scute; CMM-V-4104, partially complete left supracleithrum; 

CMM-V-4126, two isolated partially complete dermal scutes; 

CMM-V-4234, partially complete dermal scute; CMM-V-4250, 

partially complete left clavicle and three isolated dermal scutes; 

CMM-V-4299, partially complete right opercle; CMM-V-4312, 

four isolated dermal scutes; CMM-V-4423, dorsal scute; CMMV-4530, partially complete dermal scute; USNM 25880, fragments of dermal bones; USNM 438665, partially complete 

lateral scute; USNM uncataloged, fragmentary skull roofing 

bones and two isolated dermal scutes and five isolated partially 

complete lateral scutes.

Horizon. Calvert, Choptank, St. Marys, and Eastover 

Formations.

Remarks. The material consists of isolated, thick, and 

often fragmented dermal bones, including skull roofing and pectoral girdle elements and, more frequently, dermal bony scutes 

(Figure 3.1A,B). These dermal bones exhibit a strongly ornamented outer surface and a nearly smooth inner surface.

Overall, the available Miocene acipenserid material from 

the Chesapeake Group has not revealed any genus- or specieslevel diagnostic feature, thereby precluding a detailed taxonomic 

identification. Leidy (1873b) described the species Acipenser ornatus on the basis of a lateral scute from the Calvert Formation, 

Virginia (see also Leriche, 1942); the type specimen described 

and illustrated by Leidy is now considered lost (Purdy et al., 

2001). In a recent revision of the North American fossil record 

of the Acipenseridae, Hilton and Grande (2006) demonstrated 

that there are no diagnostic characters that differentiate the type 

material of this fossil species from other acipenserids, thereby 

rendering Acipenser ornatus a nomen dubium. 

Sturgeons are anadromous and occur in the shallow waters 

of the continental shelf, commonly near the mouth of rivers. 

They are bottom feeders, mostly on benthic invertebrates and 

small fishes.

Series Neopterygii Regan, 1923 

Division Ginglymodi Cope, 1872 

Order Lepisosteiformes Hay, 1929 

Family Lepisosteidae Cuvier, 1825

Genus Lepisosteus Linnaeus, 1758

Lepisosteus sp.

FIGURE 3.1C–E

Gar – Lepisosteus sp.
164 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Referred Material. CMM-V-3137, partially complete right frontal (Figure 3.1C); isolated scales CMM-V-97, 

CMM-V-362, CMM-V-3079, CMM-V-3135, CMM-V-3278, 

CMM-V-3575, CMM-V-3992 (Figure 3.1D), CMM-V-4625, 

partial left dentary (Figure 3.1E); USNM uncataloged, isolated 

scales.

Horizon. St. Marys Formation. 

Remarks. An incomplete, narrow (measurable frontal 

width to length ratio = 0.24), and finely sculptured right frontal (Figure 3.1C), an incomplete extremely slender right dentary 

(Figure 3.1E), and 10 isolated rhomboid ganoid scales (Figure 

3.1D) possibly belonging to a single individual are referred to 

the family Lepisosteidae. Within Lepisosteidae, the genus Lepisosteus is characterized by the lowest values of the ratio between 

frontal width to length (0.21–0.28; Grande, 2010); because of 

the incompleteness of the available frontal, it is reasonable to hypothesize that the calculated value was certainly originally lower 

than 0.24, thereby suggesting that the fossil remains from the 

St. Marys Formation pertain to the genus Lepisosteus. 

Gars are freshwater and estuarine ambush predators that 

feed primarily on smaller fishes.

Division Halecostomi Regan, 1923

Subdivision Halecomorphi Cope, 1872 

Order Amiiformes Hay, 1929

Family Amiidae Bonaparte, 1838

A B

C

D

E

FIGURE 3.1. (A) CMM-V-100, Acipenseridae gen. et sp. indet., dorsal dermal bony scute in dorsal view. (B) CMM-V-1417, Acipenseridae 

gen. et sp. indet., right lateral dermal bony scute in lateral view. Anterior to right. (C) CMM-V-3137, Lepisosteus sp., right frontal in dorsal 

view. Anterior to left. (D) CMM-V-3992, Lepisosteus sp., ganoid scale, external view. Anterior to left. (E) CMM-V-4625, Lepisosteus sp., right 

dentary in medial view. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm. 
NUMBER 100 • 165

Genus Amia Linnaeus, 1766

Amia cf. calva Linnaeus, 1766

FIGURE 3.2

Bowfin – Amia cf. calva

Referred Material. CMM-V-3134 (Figure 3.2), wellpreserved isolated bones from a single individual, including left 

and right frontals, right parietal, right dermosphenotic, right dermopterotic, right extrascapular, right posttemporal, left lachrymal, left antorbital, left nasal, a single left postinfraorbital (io4), 

two right postinfraorbitals (io4 + io5), right subinfraorbital, left 

preopercle, right opercle, right hyomandibula, right metapterygoid, left branchiopercle, left branchiostegal ray, left and right 

supracleithra, partially complete left cleithrum, a single abdominal centrum, and a single scale.

Horizon. St. Marys Formation. 

Remarks. The available material consists of 25 bones 

belonging to a single individual (Figure 3.2). Most of the bones 

are extensively sculptured on their outer surfaces and are nearly 

identical to the corresponding ones of the extant bowfin Amia 

FIGURE 3.2. CMM-V-3134, Amia cf. calva disarticulated partial skull (flattened into the dorsoventral plane; elements variously 

shown in dorsal or lateral view). Anterior to left. Not all cranial bones preserved are included here. Specimen lightly coated with 

sublimed ammonium chloride. Scale bar equals 10 mm.
166 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

B

C D A

E

F G

H I J
NUMBER 100 • 167

calva. Unfortunately, because the skull is not complete, we could 

not confirm generic-level diagnostic characters (i.e., pointed teeth 

on coronoids and vomers, parasphenoid tooth patch being long 

and narrow, and possession of 75–82 preural centra; Grande 

and Bemis, 1998). Nevertheless, the great similarity of the fossil 

bones illustrated herein to those of the bowfin suggests a similar 

generic assignment. As far as the attribution at the species level 

is concerned, considering that the material from the St. Marys 

Formation includes two right postinfraorbital bones, of which 

the upper is evidently larger than the lower, which is in accordance with the species diagnosis provided by Grande and Bemis 

(1998), it is possible to tentatively refer CMM-V-3134 to the 

living species of bowfin.

Bowfins inhabit swampy, vegetated lakes and rivers of eastern North America. They are voracious and opportunist feeders 

subsisting on insects, crustaceans, fishes, and amphibians.

Subdivision Teleostei Müller, 1846

Order Clupeiformes Bleeker, 1859

Family Clupeidae Cuvier, 1817

Genus Alosa Linck, 1790

Alosa sp.

FIGURE 3.3A,B

Shad – Alosa sp.

Referred Material. CMM-V-3070 (Figure 3.3A,B), 

partially complete neurocranium; CMM-V-3405, partially complete neurocranium.

Horizon. St. Marys Formation.

Remarks. The available material consists of two incomplete neurocrania lacking most of the orbital and ethmoid 

portions (Figure 3.3A,B). The general external outline of the 

neurocrania, particularly the relative development and mutual 

position of the epioccipitals; the broad and perpendicularly oriented transverse processes of the sphenotics; ornamentation of 

the frontals; and the morphology of pterotics, prootics, and intercalars are consistent with those of certain species of the clupeid 

genus Alosa (see Svetovidov, 1964). Despite a close similarity to 

the extant Alosa sapidissima, the fragmentary nature of the material does not allow for a more detailed taxonomic attribution.

Shad of the genus Alosa are anadromous planktivores that 

feed primarily on small arthropods, fish eggs, and algae. They 

are very common in nearshore waters but also occur in depths of 

more than 200 m.

Order Siluriformes Cuvier, 1817

Family Ictaluridae Gill, 1861

Genus Ictalurus Rafinesque, 1820

Ictalurus countermani Lundberg & Luckenbill, 2012

FIGURE 3.3C–G

Catfish – Ictalurus countermani

FIGURE 3.3. (Facing page) (A, B) CMM-V-3070, Alosa sp., partial neurocranium in dorsal and ventral views, respectively. Anterior to top of 

page. (C) CMM-V-3282, Ictalurus countermani, holotype, nearly complete neurocranium in dorsal view. Anterior to top of page. (D) CMMV-3318, Ictalurus countermani, paratype, partial mesethmoid. Anterior to top of page. (E) CMM-V-3282, Ictalurus countermani, holotype, left 

cleithrum and coracoid bones in lateral view. (F, G) CMM-V-3207, Ictalurus countermani, paratype, left cleithrum in lateral and medial views, 

respectively. (H–J) USNM 15746, Ariopsis stauroforus, holotype, neurocranium in dorsal, ventral, and left lateral views, respectively. Anterior 

to top of page. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
168 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Holotype. CMM-V-3282, nearly complete neurocranium with articulated Weberian complex (Figure 3.3C), left 

supracleithrum, left pectoral girdle (Figure 3.3E), pectoral-fin 

spine, and two abdominal vertebrae.

Paratypes. CMM-V-3207, left cleithrum (Figure 

3.3F,G); CMM-V-3316, right premaxilla; CMM-V-3318, mesethmoid (Figure 3.3D).

Referred Material. CMM-V-3319, dorsal-fin spine.

Horizon. St. Marys Formation.

Remarks. A few isolated bones and a nearly complete 

neurocranium belonging to a single individual are assigned to 

the extant genus Ictalurus. Placement within the family Ictaluridae is justified by the presence of three of the four putative synapomorphies of this family as proposed by Lundberg (1970) and 

subsequently discussed by Grande and Lundberg (1988). The synapomorphies include (1) the possession of a large and smooth 

temporal fossa bounded by the adductor muscle scar that develops 

from the lateral edge of the frontal to the occipital region involving the sphenotic, pterotic, supraoccipital, and posttemporo-supracleithrum; (2) a posttemporo-supracleithrum with an anterior 

process (=subpterotic process of Lundberg, 1970, 1982) that articulates with the ventral surface of the outer pterotic wing; (3) 

the position of the exit of the infraorbital canal from the frontal 

located well anterior to the frontal-sphenotic joint; and (4) the 

lack of vomerine teeth. The outline of the neurocranial bones, 

cleithrum, and pectoral-fin spine cannot be distinguished in the 

fossil and extant species of the genus Ictalurus (see Lundberg, 

1970, 1975). More particularly, the available material shows at 

least some of the synapomorphies of the genus Ictalurus defined 

by Lundberg (1982): a superficial part of the supraoccipital ornamented with longitudinal grooves and ridges, the absence of the 

spine located along the lateral margin of the sphenotic, lateral ethmoid wings curved downward, an enlarged optic foramen, and 

a ventral keel of the coracoid that is elongated, nearly reaching 

the coracoid symphysis. According to Lundberg and Luckenbill 

(2012), Ictalurus countermani exhibits four synapomorphies of 

the I. punctatus group (channel catfish): the transverse crest of the 

supraoccipital being tilted obliquely backward and expanded onto 

the base of the supraoccipital process; the parasagittal crest of the 

supraoccipital being narrow and rounded; the horizontal shelves 

of the orbitosphenoid being reduced in width; and the posterior 

process of the cleithrum being strongly ornamented with at least 

moderately coarse tubercles.

Ictalurus countermani is unique within the I. punctatus

group in having a low, obtusely angular sphenotic process developed at midlength along the sphenotic margin; a posterior 

cleithral process deep at its base, with an exceptionally coarse 

tuberculate ornamentation; and a pectoral-fin spine shaft that is 

broad, dorsoventrally depressed, and lenticular in cross section 

with ridged and dentate anterior and posterior margins, anterior 

dentations that are evenly spaced and relatively large, and posterior dentations that are relatively small in size (see Lundberg and 

Luckenbill, 2012). 

Catfishes of the genus Ictalurus inhabit streams, rivers, 

creeks, ponds, and lakes and rarely enter brackish waters. They 

feed on a wide variety of prey items, including worms, mollusks, 

insects, crustaceans, fishes, and small mammals.

Family Ariidae Bleeker, 1862

Genus Ariopsis Gill, 1861

Remarks. In a recent phylogenetic study of the family Ariidae, Kailola (2004) considered the genus Ariopsis as valid, characterized by two distinct geographic components, one American 

and the other typical of Australia and New Guinea. Marceniuk 

and Menezes (2007) included the species of this genus within the 

limits of the genus Sciades. Ferraris (2007) interpreted the two 

geographic components hypothesized by Kailola (2004) as separate genera, with the American species included in Ariopsis and 

those of the Australia–New Guinea region placed in Neoarius. 

Ariopsis stauroforus (Lynn & Melland, 1939)

FIGURE 3.3H–J

Catfish – Ariopsis stauroforus

1939 Felichthys stauroforus Lynn & Melland, pp. 14–20, figs. 1–3.

1975 Arius stauroforus (Lynn & Melland) – Lundberg, p. 3.

1984 Arius felichthys – Kimmel & Purdy, pl. 1, fig. 5.

1999 Arius stauroforus (Lynn & Melland) – Muller, p. 77, fig. 27.

2001 Bagre stauroforus (Lynn & Melland) – Purdy, Schneider, Applegate, 

McLellan, Meyer, & Slaughter, p. 165.

2007 Felichthys stauroforus Lynn & Melland – Ferraris, p. 32.

2012 cf. Ariopsis felis – Lundberg & Luckenbill, p. 8, fig. 23.

Holotype. USNM 15746, a partially complete neurocranium and a left lapillus (utricular otolith; Figure 3.3H–J).

Referred Material. CMM-V-3317, complete 

dorsal-fin spine (see Lundberg and Luckenbill, 2012); USNM 

336490, partial neurocranium; USNM 336491, partial pectoralfin spine; USNM 542405, partial neurocranium lacking the anterior portion of the orbital and ethmoid regions.

Horizon. Calvert Formation.
NUMBER 100 • 169

Remarks. Lynn and Melland (1939) presented a detailed description of the type specimen that was interpreted to 

be closely related to the extant hardhead catfish Ariopsis felis. 

Subsequently, Kimmel and Purdy (1984) presented a partial neurocranium that they referred to the sea catfish genus Arius. 

The analysis of the type and other material has evidenced 

several diagnostic features of the family Ariidae (see Acero and 

Betancur, 2007), including an extremely developed lapillus, relatively swollen otic capsules, a well-developed ventral process 

of the basioccipital, and a well-developed foramen (=temporal 

fossa of Acero and Betancur, 2007) between the posttemporo-supracleithrum, extrascapula, and pterotic. The well-defined aortic 

canal on the basioccipital and the absence of the anterior nuchal 

plate clearly support its inclusion within the subfamily Ariinae 

(see Acero and Betancur, 2007). Among the new-world genera 

of the subfamily Ariinae, the overall physiognomy of the fossils 

is consistent with that of certain species of the genus Ariopsis. 

More specifically, the neurocranium exhibits a close similarity to 

those characteristics of the extant Ariopsis felis, from which they 

differ in having a larger parasphenoid, a wider medial groove of 

the neurocranium that originates from the center of the supraoccipital, and enlarged anterior and posterior cranial fontanels.

Extant sea catfishes of the genus Ariopsis inhabit coastal marine and brackish environments and, to a lesser degree, large and 

medium rivers, where they are found in turbid waters over muddy 

bottoms. They feed mainly on invertebrates and small fishes.

Genus Bagre Cloquet, 1816

Bagre sp.

FIGURE 3.4A,B

Catfish – Bagre

Referred Material. USNM 542406, articulated 

skeleton consisting of an incomplete neurocranium lacking the 

ethmoid and most of the orbital regions, and part of the left pectoral girdle (including the pectoral-fin spine), the median nuchal 

plate, and the dorsal-fin spine (Figure 3.4A,B).

Horizon. Calvert Formation.

Remarks. The outer surface of the cranial bones and 

cleithrum is extensively sculptured. The morphology of the 

skull roofing bones, the overall outline of the neurocranium and 

cleithrum, the relative development of the postcleithral process 

of the cleithrum, the presence of transverse ridges with one or 

two peaks along the anterior margin of the dorsal-fin spine (see 

Purdy et al., 2001), the subrectangular morphology of the supraoccipital bone, the overall morphology of the median nuchal 

plate, and the size and shape of the foramen (=temporal fossa 

of Acero and Betancur, 2007) between the posttemporo-supracleithrum, extrascapula, and pterotic are extremely similar to 

those of the species of the catfish genus Bagre, to which the material documented herein is tentatively referred.

Sea catfishes of the genus Bagre mainly inhabit marine habitats around the mouths of rivers but also inhabit brackish estuaries with high salinities. They prefer muddy bottoms and feed 

primarily on benthic invertebrates and small fishes.

Order Gadiformes Goodrich, 1909

Family Merlucciidae Gill, 1884

Genus Merluccius Rafinesque, 1810

Merluccius sp.

FIGURE 3.4C–F

Hake – Merluccius sp.

Referred Material. CMM-V-3488, nearly complete left mandible (Figure 3.4E,F); CMM-V-4492, partially 

complete right premaxilla (Figure 3.4C,D); USNM uncataloged, 

partially complete right dentary.

Horizon. St. Marys Formation.

Remarks. The premaxilla has a short, nearly vertical ascending process and a robust articular process with a rounded 

dorsal profile (Figure 3.4C). The alveolar process is long and 

straight, with two rows of large teeth. The dentary is greatly 

elongate and bears two rows of conical pointed teeth with lingually recurved tips; the teeth of the labial row are more firmly 

attached to the dentary than those of the lingual row, which are 

not preserved in the specimen; a deep groove extends for most 

of the length of the dentary along its ventrolateral surface. The 

anguloarticular is laminar, with a short and narrow coronoid 

process (Figure 3.4E,F). 

The morphology of the premaxilla and mandibular bones 

is consistent with that of the genus Merluccius. In particular, 
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the arrangement of the premaxillary teeth in two rows is typical of that genus (see Inada, 1981; Howes, 1991). Within the 

genus Merluccius, the identification at the species level is based 

primarily on the morphology of selected osteological structures 

(hyomandibula, sagitta, urohyal) that are not observable in the 

available material.

Hakes are marine demersal fishes recorded at depths of 1 to 

400 m. They are often abundant on sandy grounds. Hakes are 

voracious predators of fishes and crustaceans.

Order Ophidiiformes Berg, 1937

Family Ophidiidae Rafinesque, 1810

Genus Brotula Cuvier, 1829

Brotula sp.

FIGURE 3.4G–H

Brotulas – Brotula sp.

Referred Material. CMM-V-4637, partially complete articulated skeleton (Figure 3.4G,H).

Horizon. Calvert Formation.

Remarks. The single available specimen consists of a 

partially complete, articulated skeleton represented by a wellpreserved neurocranium and fragmentary skull bones, 11 abdominal vertebrae, and fragments of what appear to be pleural 

ribs and epineural bones.

The neurocranium is elongate and tubular, its length approximately three times its maximum depth (Figure 3.4G). The ethmoid 

region is very short. The orbit is oblong. The skull roof is smooth 

except for a low crest developed in the temporal region of the 

frontal. The vomer prominently projects ventrally. The mesethmoid consists of a stout, nearly vertical and laterally compressed 

bony lamina. The lateral ethmoid bears a laterally directed flange. 

The frontals are the largest bones of the skull roof. The parietal 

is subtriangular in outline. The supraoccipital extends posteriorly 

into a very low, laterally compressed crest. The parasphenoid and 

basioccipital are very robust and thickened. 

The vertebral centra are massive and subquadrangular, 

bearing large bladelike parapophyses (Figure 3.4H). The bases 

of the neural arches are greatly expanded. The lateral surfaces 

of the centra, neural arches, and parapophyses are extensively 

ornamented with small deep pits and delicate ridges. 

The morphological features of the neurocranium (general 

proportions and the structure of the frontals, supraoccipital 

crest, parasphenoid, and vomer) and the architecture and ornamentation of the abdominal vertebrae are extremely similar to 

those of the bearded brotula Brotula barbata (e.g., Patterson and 

Rosen, 1989: fig. 8). The specimen is referred herein to an indeterminate species of the genus Brotula; because of its incompleteness, it is preferable to use the open nomenclature until more 

complete articulated skeletons become available.

Brotulas are benthopelagic, inhabiting marine waters to 

depths of more than 600 m, but are common on the continental 

shelf on muddy and sandy bottoms. Brotulas feed primarily on 

fishes and crustaceans, mainly crabs.

Order Batrachoidiformes Goodrich, 1909

Family Batrachoididae Jordan & Evermann, 1898

Genus Opsanus Rafinesque, 1818

Opsanus sp.

FIGURE 3.4I

Toadfish – Opsanus sp.

FIGURE 3.4. (Facing page) (A, B) USNM 542406, Bagre sp., partial articulated skeleton in dorsal and ventral views, respectively. (A) Anterior to 

right. (B) Anterior to left. (C, D) CMM-V-4492, Merluccius sp., right premaxilla in lateral and ventral views, respectively. (E, F) CMM-V-3488, 

Merluccius sp., left mandible in medial and lateral views, respectively. (G) CMM-V-4637, Brotula sp., neurocranium in right lateral view. Anterior 

to right. (H) CMM-V-4637, Brotula sp., abdominal vertebrae in left lateral view. (I) CMM-V-2509, Opsanus sp., partial left mandible, medial 

view. (J) CMM-V-839, Lophius sp., partial right premaxilla in medial view. (K) USNM 24865, Lophius sp., palatine in lateral view. (L) CMMV-4628, Lophius sp., partial left dentary in lateral view. Anterior to left. Specimens lightly coated with sublimed ammonium chloride. Scale bars 

equal 10 mm.
172 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

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NUMBER 100 • 173

Referred Material. CMM-V-2509, partially complete left mandible (Figure 3.4i).

Horizon. Choptank Formation.

Remarks. A single left mandible documents the presence 

of the toadfish genus Opsanus in the Miocene deposits of the Chesapeake Group. The dentary is elongate and slender, with a single 

row of rounded sockets that extends for most of its length. In the 

symphyseal region, some supernumerary teeth are irregularly arranged in an additional row. The anguloarticular is characterized 

by a thick ridge along its lateral side and a well-developed, obliquely 

oriented coronoid process. The dorsal margin of the joint between 

the dentary and the coronoid process of the anguloarticular is characterized by a rounded profile (see Greenfield et al., 2008).

The mandible cannot be distinguished from those of the extant oyster toadfish Opsanus tau. However, additional comparative information is necessary for a more detailed identification of 

the material.

Toadfishes of the genus Opsanus occur primarily inshore at 

depths up to 50 m on rocky bottoms and close to reefs. According to Thomson et al. (1978), some species of this genus migrate 

offshore during cold weather. Toadfishes are voracious predators 

that feed primarily on worms, crustaceans, and fishes.

Order Lophiiformes Garman, 1899

Family Lophiidae Rafinesque, 1810

Genus Lophius Linnaeus, 1758

Lophius sp.

FIGURE 3.4J–L

Lophiid Anglerfish – Lophius sp.

Referred Material. CMM-V-839, partially complete right premaxilla (Figure 3.4J); CMM-V-1363, partially 

complete right premaxilla and right dentary associated with a 

vertebral column of Thunnus sp.; CMM-V-2777, isolated teeth; 

CMM-V-4624, partially complete right premaxilla; CMM-V4628, partially complete left dentary (Figure 3.4L); CMM-V4629, partially complete left dentary; USNM 24865, left and 

right dentaries and a right palatine (Figure 3.4K); USNM uncataloged, partially complete right premaxilla.

Horizon Calvert, St. Marys, and Eastover Formations.

Remarks. All the available bones are incomplete and 

only moderately well preserved. The large and robust caniniform 

teeth with shallow vertical grooves at their bases, as well as the 

posterior triangular teeth of the outer row of the dentary, exhibit 

the attachment structure (ankylosis and fibrous hinge) typical of 

the genus Lophius (see Kerebel et al., 1979). The bifid anterior 

head of the palatine also supports the assignment to the genus 

Lophius (see Carnevale and Pietsch, 2012).

Lophiid anglerfishes of the genus Lophius are benthic and inhabit different substrates at depths ranging from the shoreline to 

greater than 600 m, where they feed on fishes and invertebrates.

Order Beloniformes Berg, 1937

Family Belonidae Bonaparte, 1837

Genus Belone Cuvier, 1816

Belone countermani de Sant’Anna, Collette, 

& Godfrey, 2013

FIGURE 3.5A,B

Needlefish – Belone countermani

Holotype. CMM-V-3695, articulated partially complete premaxillae and dentaries belonging to a single individual 

(Figure 3.5A,B).

FIGURE 3.5. (Facing page) (A, B) CMM-V-3695, Belone countermani, holotype, articulated partial premaxillae and dentaries, respectively, in 

occlusal views. Anterior to right. (C, D) CMM-V-2006, Prionotus sp., partial neurocranium in dorsal and ventral views, respectively. Anterior 

to left. (E, F) CMM-V-2195, Prionotus sp., partial neurocranium in dorsal and ventral views, respectively. Anterior to left. (G) CMM-V-4631, 

Prionotus sp., left infraorbitals and preopercle and opercle. Anterior to left. (H) CMM-V-4535, Agonidae gen. et sp. indet.; nearly complete 

articulated skeleton in ventral view. Anterior to left. (I) USNM 542411, Morone sp., partial head skeleton in left lateral view. Anterior to left. 

Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
174 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Horizon. St. Marys Formation.

Remarks. De Sant’Anna et al. (2013) provided a detailed description of this specimen, the only fossil belonid known 

from the Maryland Miocene. The premaxillae are delicate and 

elongate (Figure 3.5A). There are two series of premaxillary 

teeth; the teeth of the inner series are arranged into a single row 

of relatively large conical elements, whereas those of the outer 

series consist of a dense band of very small accessory teeth that 

reach the lateral margin of the bone. The dentaries are slender 

and elongate, characterized by a thickened symphyseal portion 

and a moderately thin rostral end. The contralateral dentaries articulate through strong symphyseal interdigitation (Figure 3.5B; 

de Sant’Anna et al., 2013: fig. 6); however, this interdigitation 

does not extend up to the anterior tip of the mandible. Sockets 

document the presence of a single row of teeth of varying sizes in 

the rostral region; these teeth are associated with a dense series 

of numerous tiny accessory villiform elements posteriorly and a 

single outer series of accessory teeth in the symphyseal region (de 

Sant’Anna et al., 2013: figs. 4, 5). 

The dentition of Belone countermani most closely resembles 

that of B. belone, an extant needlefish that inhabits the Mediterranean Sea and eastern North Atlantic Ocean (Collette and 

Parin, 1970; de Sant’Anna et al., 2013). Although they are similar, morphological differences warrant placement in separate 

species. With so little fossil material known of B. countermani, 

there is a high probability that additional finds will add significantly to our understanding of its morphology. 

The garfish B. belone inhabits the brackish, shallow marine 

and oceanic biotopes of the eastern North Atlantic and Mediterranean, where it feeds on small fishes, mostly clupeoids.

Order Scorpaeniformes Garman, 1899

Family Triglidae Risso, 1926

Genus Prionotus Lacépède, 1801

Prionotus sp.

FIGURE 3.5C–G

Sea Robin – Prionotus sp.

Referred Material. CMM-V-2006, partially complete neurocranium (Figure 3.5C,D); CMM-V-2195 (Figure 

3.5E,F), partially complete neurocranium; CMM-V-3408, partially complete lachrymal; CMM-V-4337, partially complete 

neurocranium; CMM-V-4338, partially complete neurocranium; 

CMM-V-4631, left infraorbitals and preopercle and opercle (Figure 3.5G).

Horizon. Calvert and St. Marys Formations.

Remarks. The available material consists exclusively of 

cranial remains (Figure 3.5C–G). The outer sides of the bones exhibit the elaborate sculpturing pattern characteristic of the members of the family Triglidae (e.g., Allis, 1909; Carnevale, 2008). 

The neurocrania are always represented by the orbital-ethmoid 

region, which includes the median mesethmoid, paired nasals, 

lateral ethmoids, and the anterior part of the frontals (Figure 

3.5C–F). The neurocranial architecture and the morphological 

structure of the opercular bones (Figure 3.5G), as well as the 

external ornamentation pattern of the bones, fit very well with 

those of the sea robins of the genus Prionotus. A more detailed 

taxonomic identification is not possible without additional and 

more complete specimens. 

Sea robins of the genus Prionotus are marine demersal inhabitants of the continental shelf down to about 200 m, where 

they feed primarily on worms, mollusks, and crustaceans. Prionotus species often enter brackish waters.

Family Agonidae Swainson, 1839

Gen. et sp. indet.

FIGURE 3.5H

Poacher – Agonidae

Referred Material. CMM-V-4535, nearly complete articulated skeleton partially embedded in sediment (Figure 

3.5H).

Horizon. St. Marys Formation.

Remarks. A recently discovered nearly complete articulated skeleton documents the presence of the family Agonidae in 

the deposits of the Little Cove Point Member of the St. Marys 

Formation (Figure 3.5H). The fossil is still partially embedded 

in sediment, and its detailed anatomical and systematic analysis is currently in progress using computer tomography. The 

general morphology of the fossil, with a slender body tapering to the caudal peduncle and covered with thick bony plates 

bearing a strong blunt retrorse spine arising from the center, 
NUMBER 100 • 175

unambiguously supports its assignment within the family Agonidae (see Kanayama, 1991). 

Agonids inhabit the sandy and rocky bottoms of the shallow 

marine biotopes of the northern Pacific, North Atlantic, North 

Sea, and the Patagonian region, where they feed on crustaceans 

and other benthic invertebrates. 

Order Perciformes Bleeker, 1859

Family Moronidae Fowler, 1907

Genus Morone Mitchill, 1814

Morone sp.

FIGURE 3.5I

Bass – Morone sp.

Referred Material. USNM 542410, partially complete head skeleton; USNM 542411, partial head skeleton (Figure 3.5i).

Horizon. Calvert Formation.

Remarks. The available material includes two partial 

skulls collected from the Calvert Formation. The excellent preservation of these specimens allows for the observation of a number of anatomical features that clearly evidence their affinity with 

the extant species of the genus Morone. In particular, the general 

outline of the neurocranium, the irregular configuration of the 

transverse lateral process of the sphenotic, the delicate subtriangular anterior process arising from the anterodorsal margin 

of the mesethmoid, the morphology of the jaw and suspensorial 

bones, the large bands of small premaxillary and dentary teeth, 

and the posterior enlarged laminar flange at the angle formed by 

the convergence of the horizontal and vertical arms of the preopercle are extremely similar to those of the extant striped bass 

Morone saxatilis (see Woolcott, 1957). However, the complete 

absence of characters of the axial skeleton, as well as of any 

morphometric or meristic features, does not allow for an unambiguous taxonomic interpretation at the specific level.

Basses of the genus Morone are anadromous and extremely 

common in shallow coastal waters and brackish biotopes. They 

enter rivers to spawn mostly during the spring. Fishes of the 

genus Morone are voracious and opportunistic predators that 

feed on a variety of fishes and invertebrates.

Family Serranidae Swainson, 1839

Gen. et sp. indet.

FIGURE 3.6

Referred Material. CMM-V-4622, partially complete articulated skeleton preserved inside joined valves of a 

Chesapecten (Figure 3.6).

Horizon. Choptank Formation.

Remarks. Although a large part of the skeleton is still 

embedded in the sediment, it is possible to observe the skull 

roof, both lower jaws, the right suspensorium, and the opercular complex (Figure 3.6). The preopercle is ornamented 

FIGURE 3.6. CMM-V-4622, Serranidae, gen. et sp. indet. (A) Partial articulated skeleton preserved inside joined valves of a Miocene 

scallop shell, Chesapecten nefrens. (B) Enlarged view of skull in right 

lateral view. Anterior to right. Scale bars equal 10 mm.
176 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

with fine serrations along the posterior margin of the vertical 

arm and by short, strong spines along the ventral margin of 

the horizontal arm and at the corner formed by the confluence 

of the two arms (Figure 3.6B). The opercle has three spines 

along its posterior margin, of which the central spine represents 

the distal end of the median horizontal ridge that originates 

from the articular surface for the opercular process of the 

hyomandibula. 

The serrated posterior and ventral margins of the preopercle 

and the presence of three spines along the posterior margin of 

the opercle are clearly indicative of the family Serranidae (see 

Johnson, 1983). A more detailed identification of the fossil is not 

possible because of its inadequate preservation.

The family Serranidae includes more than 470 species of 

marine predatory fishes common in tropical and temperate areas 

of the world.

Family Malacanthidae Günther, 1861

Genus Lopholatilus Goode & Bean, 1880

Lopholatilus ereborensis Carnevale & Godfrey, 2014

FIGURE 3.7

Tilefish – Lopholatilus ereborensis

1984 Lopholatilus sp. – Kimmel and Purdy, p. 208, fig. 20, pl. 2, figs. 1–2.

Holotype. USNM 467782, nearly complete well-preserved head skeleton and partial axial skeleton (Figure 3.7).

Paratypes. CMM-V-4635, partially complete head skeleton; CMM-V-4636, partially complete head skeleton; CMM-V4638, partially complete head skeleton; CMM-V-4821, partially 

complete head skeleton plus six articulated abdominal vertebrae; 

USNM 467776, partially complete head skeleton.

Referred Material. CMM-V-4639, partially complete head skeleton; USNM 467777, partially complete head 

skeleton; USNM 467779, partially complete head skeleton; 

USNM 467781, partially complete head skeleton.

Horizon. Calvert Formation.

Remarks. All the available material consists of relatively well preserved articulated cranial remains from beds 11 

to 14 of the Calvert Formation. USNM 467782 also includes 10 

abdominal centra, two caudal centra, some scattered dorsal-fin 

elements, and large parts of the appendicular girdles. 

The head is massive, rather wide, and moderately deep, with 

its maximum depth contained slightly less than two times in head 

length. The snout is very short (contained more than four times 

in head length) and the orbit is moderately large (Figure 3.7). 

Because of the reduced length of the snout, the anterior profile of 

the head appears very steep.

The neurocranium is very high and bears a robust, moderately high supraoccipital crest that apparently reaches the anterior margin of the orbit and a less developed temporal crest; two 

prominent thick anteroventrally directed processes with a nearly 

ovoid anterior profile arise from the anterodorsal margin of the 

mesethmoid. The occipital region gently slopes in an oblique 

direction. The high lachrymal is thickened and extensively ornamented along its lateral surface.

B

A

C

FIGURE 3.7. (A–C) USNM 467782, Lopholatilus ereborensis, holotype, nearly complete well-preserved skull and partial axial skeleton in dorsal, left lateral, and ventral views, respectively. Specimen 

is lightly coated with sublimed ammonium chloride. Scale bars equal 

10 mm.
NUMBER 100 • 177

The upper jaw is protrusible and slightly oblique, approximately reaching the posterior margin of the orbit. The premaxilla bears a very short and distally pointed ascending process 

(length of the ascending process 34–36.5% of the length of the 

alveolar process) and a laminar articular process with rounded 

dorsal profile. The alveolar process bears a single outer row of 

strong conical teeth and an inner dense band of villiform teeth. 

The dentary bears a single outer row of strong conical teeth similar to those of the premaxilla and villiform teeth restricted to the 

symphyseal region. A very short, pointed, and vertically directed 

symphyseal process arises from its anteroventral corner. 

The suspensorial bones are relatively well exposed in most 

of the specimens. 

The preopercle has a finely serrated posterior margin; the 

angle between the vertical and horizontal arms measures about 

120°. The vertical arm of the preopercle is considerably shortened, with the horizontal arm measuring between 52.8% and 

66.4% of the length of the vertical arm. The opercle is laminar, 

very thin, and characterized by a strongly thickened anterior 

margin; a thickened horizontal ridge extends posteriorly from 

the articular condyle for the hyomandibular process and possibly 

terminates posteriorly into a spine.

The hyoid bar is very compact, with a medially exposed 

dorsal hypohyal. There are six saber-like branchiostegal rays. 

Except for the atlas and second abdominal vertebra, the vertebral centra are subrectangular, longer than high, with a deep 

fossa along their lateral sides. Vertebrae 3 through 10 bear relatively large bladelike parapophyses. 

The overall morphology of the neurocranium, upper and 

lower jaws, suspensorial bones, and opercular apparatus is 

very similar to that of the great northern tilefish Lopholatilus 

chamaeleonticeps. In particular, the specimens examined show 

some features that are clearly diagnostic of Lopholatilus, including the paired prominent curved and anteroventrally directed 

processes arising from the anterodorsal margin of the mesethmoid, the large thick and extensively sculptured lachrymal, and 

the oral jaw dentition pattern. Despite their incompleteness, the 

fossils show a few evident characters that clearly separate them 

from the extant species of the genus Lopholatilus (Carnevale and 

Godfrey, 2014). Compared to those of extant congenerics, the 

head of Lopholatilus ereborensis is moderately developed vertically; its depth is contained slightly less than two times in head 

length (~52% versus 72%–100% of head length). As a result 

of the strong shortening of the ethmoid region of the neurocranium, the snout of Lopholatilus ereborensis is broadly shortened 

relative to that characteristic of both extant species (snout length 

~22% versus 27%–51% of head length). The ascending process 

of the premaxilla is notably reduced in size compared to those 

of extant species, its length being 34%–36.5% of that of the alveolar process (versus 49%–52% in Lopholatilus chamaeleonticeps). The vertical arm of the preopercle is remarkably shortened 

compared with that of extant members of the genus Lopholatilus (the length of the horizontal arm of the preopercle measures 

between 52.8% and 66.4% of that of the vertical arm versus 

~42% in Lopholatilus chamaeleonticeps). Finally, the vertical 

and horizontal arms of the preopercle form an angle (~120°) 

broader than that of the extant species (105°–110°; see Dooley, 

1978). All of these characters appear to be unique to the 

Miocene fossils, representing a reasonable basis for the creation 

of a new species. Purdy et al. (2001) described the species Lopholatilus rayus on the basis of material from the Pliocene Yorktown 

Formation, North Carolina. On the basis of their diagnosis, 

the separate status of that extinct species was supported by a 

single character, the possession of an inner row of villiform 

teeth on the dentary that extends backward from the symphyseal region up to the coronoid process. As discussed above, this 

character is absent in the fossil Lopholatilus from the Calvert 

Formation. 

North Atlantic tilefishes of the genus Lopholatilus generally occur along the continental slope and the upper reaches of 

the canyons at depths ranging between 120 and 200 m (Dooley, 

1978). Lopholatilus has been recorded at depths of more than 

500 m. Grimes et al. (1986) recognized two critical habitat requirements for Lopholatilus, a temperature range between 9°C 

and 14°C and shelter; they are known to excavate large vertical 

and oblique burrows. Carnevale and Godfrey (2014) proposed 

that certain large (10–25 cm in diameter) cylindrical-shaped trace 

fossils (dwelling burrows, i.e., domichnia) penetrating the finegrained sands of the middle part of the Calvert Formation were 

produced by Lopholatilus ereborensis, representing the product 

of their burrowing activity. Tilefishes of the genus Lopholatilus

prey on fishes and a variety of invertebrates.

Family Pomatomidae Gill, 1865

Genus Pomatomus Lacépède, 1802

Pomatomus sp.

FIGURE 3.8A

Bluefish – Pomatomus sp.

Referred Material. CMM-V-1933, partially complete right dentary (Figure 3.8A); CMM-V-3237, isolated tooth.

Horizon. Calvert and St. Marys Formations.
178 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

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NUMBER 100 • 179

Remarks. The dentary is relatively large, slightly curved, 

and bears a single row of labiolingually compressed, subtriangular, and deeply socketed teeth along its dorsal margin (Figure 

3.8A; Johnson, 1986; Bemis et al., 2005). The symphyseal margin of this bone is strongly thickened and nearly vertical, with a 

medially curving dorsal portion. A single isolated tooth is also 

present in the collection of the CMM; it is subtriangular in shape 

and laterally compressed, identical to those of the extant bluefish 

Pomatomus saltatrix.

The fragmentary nature of the material does not allow for 

a more detailed taxonomic interpretation, for which much more 

comparative information would be necessary.

Bluefishes occur in coastal and oceanic tropical and subtropical waters with a circumglobal distribution. Adults often 

enter estuaries and other brackish-water biotopes. Bluefishes are 

voracious and aggressive predators that feed on cephalopods, 

crustaceans, and other fishes.

Family Rachycentridae Gill, 1895

Genus Rachycentron Kaup, 1826

Rachycentron sp.

FIGURE 3.8B–H

Cobia – Rachycentron sp.

Referred Material. CMM-V-3694, several partially articulated bones belonging to a single individual: articulated sclerotic ring, nearly complete right premaxilla (Figure 

3.8E,F), nearly complete left maxilla (Figure 3.8G), partially 

complete left suspensorium, partially complete left preopercle 

(Figure 3.8B,C), right second pharyngobranchial (Figure 3.8H), 

nearly complete right posttemporal, and three caudal vertebrae 

(Figure 3.8D).

Horizon. Calvert Formation.

Remarks. The available material consists of a largely 

incomplete individual collected from bed 11 of the Calvert 

Formation.

The premaxilla is long and curved, with massive and articular processes; the dentigerous area is extremely expanded, 

with a large number of tiny alveoli for the insertion of villiform 

teeth (Figure 3.8E,F). The maxilla is strongly curved and gradually expands posteriorly; the articular head is massive, separated 

through a deep sulcus from the lateral process; the latter bears 

a prominent dorsally thickened apophysis anteroventrally connected with the articular head; the posterior margin of the maxilla is nearly vertical, notably expanded, and characterized by a 

crenulated margin (Figure 3.8G). The suspensorium consists 

of several bony fragments, among which the anterior palatine 

articular head for the maxillary facet can be easily recognized. 

The preopercle is crescent-shaped, with a thickened anterior 

ridge preceded by a bony shelf (Figure 3.8B,C). What appears to 

be the second pharyngobranchial is a thick, rodlike bone with a 

broad anterior articular head and an elongate dentigerous area 

along its ventral margin (Figure 3.8H). The posttemporal is laterally flattened, elliptical, and elongate, with two anterior processes 

for neurocranial articulation. The dorsal process is extremely 

elongate and terminates anteriorly as a dorsoventrally flattened 

bony lamina; the ventral process is short and round in cross 

section; a bony lamina is placed between these two processes. The 

vertebral centra are subrectangular with well-developed dorsolateral fossa and strong ventral prezygapophyses (Figure 3.8D).

None of the available bony elements can be distinguished 

from those of the extant cobia Rachycentron canadum. However, despite this great similarity, the incompleteness of the specimen does not allow for an unambiguous identification at the 

species level. 

Cobias are marine and occur worldwide in a variety of tropical and subtropical habitats and occasionally enter estuaries and 

other brackish biotopes, feeding on crustaceans, cephalopods, 

and other fishes.

Family Sparidae Bonaparte, 1832

Genus Lagodon Holbrook, 1855

FIGURE 3.8. (Facing page) (A) CMM-V-1933, Pomatomus sp., partial right dentary in medial view. Anterior to left. (B, C) CMM-V-3694, 

Rachycentron sp., left preopercle in lateral and medial views, respectively. (D) CMM-V-3694, Rachycentron sp., caudal vertebra in lateral 

view. (E, F) CMM-V-3694, Rachycentron sp., premaxilla in ventral view and an enlargement, respectively. Anterior to top. (G) CMM-V3694, Rachycentron sp., left maxilla in medial view. Anterior to right. (H) CMM-V-3694, Rachycentron sp., right second pharyngobranchial 

in ventral view. (I) CMM-V-2023, Lagodon sp., isolated tooth. (J, K) CMM-V-3209, Stenotomus sp., partial right premaxilla in ventral and 

dorsal views, respectively. Specimens (except I) are lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm, except for that 

of (I), the Lagodon sp. tooth, which is 1 mm.
180 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Lagodon sp.

FIGURE 3.8I

Pinfish – Lagodon sp.

Referred Material. CMM-V-2023, isolated tooth 

(Figure 3.8i); CMM-V-2715, isolated tooth; CMM-V-2778, isolated tooth.

Horizon. Calvert and St. Marys Formations.

Remarks. The available material consists solely of isolated 

incisiform teeth with bilobate tips and a base that is rounded in 

cross section (Figure 3.8i). These teeth are identical to those characteristic of the extant pinfish Lagodon rhomboides. Isolated teeth 

belonging to the genus Lagodon were described from the deposits 

of the St. Marys Formation by Berry (1932).

The pinfish is a shallow marine sparid commonly found to 

depths of about 70 m on vegetated or rocky bottoms. It commonly enters brackish and freshwater environments. Pinfishes 

feed primarily on crustaceans and other invertebrates.

Genus Stenotomus Gill, 1865

Stenotomus sp.

FIGURE 3.8J,K

Scup – Stenotomus

Referred Material. CMM-V-3209, partially complete right premaxilla (Figure 3.8J,K); USNM 559398, partially 

complete right premaxilla.

Horizon. St. Marys Formation.

Remarks. Both available specimens are represented by 

right premaxillae characterized by largely incomplete ascending 

processes. The alveolar process is distally spatulate and bears 

sockets of rounded, possibly molariform teeth that become gradually larger distally. 

Despite their incompleteness, the overall morphology of the 

premaxillae and the gradual distal enlargement of the teeth are 

very similar to those found exclusively within the extant Atlantic 

scup Stenotomus chrysops.

Scups of the genus Stenotomus are shallow marine demersal 

fishes that often enter brackish waters. They feed on a variety of 

invertebrates, including worms, crustaceans, cephalopods, and 

echinoderms.

Family Sciaenidae Cuvier, 1829

Genus Micropogonias Bonaparte, 1831

Micropogonias sp.

FIGURE 3.9A

Croaker – Micropogonias sp.

Referred Material. CMM-V-1688, partially complete left preopercle (Figure 3.9A).

Horizon. Calvert Formation.

Remarks. The available material consists of an incomplete left preopercle. The preopercle is crescent shaped, with a 

strong thickening along its anterior margin. The posterior margin is serrated, with three short spines and a strong robust spine 

located at the level of the angle formed by the convergence of 

the horizontal and vertical arms. A broad shallow laterosensory 

canal is overlaid by narrow struts that run longitudinally behind 

the anterior thickening of the bone. 
NUMBER 100 • 181

A B

C

D

E

F G

H I J K

FIGURE 3.9. (A) CMM-V-1688, Micropogonias sp., partial left preopercle in lateral view. (B–D) CMM-V-3982, Pogonias sp., premaxilla in occlusal, medial, and lateral views, respectively. (E–G) CMM-V-4627, Pogonias sp., left dentary in occlusal, lateral, and medial 

views, respectively. (H, I) CMM-V-2341, Pogonias sp., third pharyngobranchial in occlusal and dorsal views, respectively. (J, K) USNM 

336494, Pogonias sp., partial fifth ceratobranchial in right lateral and occlusal views, respectively. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
182 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

The general morphology of the bone and, in particular, the 

relative development and position of the spines along its posterior 

margin are extremely similar to those of the preopercle of the extant species of the genus Micropogonias, more specifically to those 

of the preopercle of the Atlantic croaker Micropogonias undulatus.

Croakers of the genus Micropogonias are demersal and usually occur in coastal marine or brackish waters over soft bottoms, where they feed on worms, crustaceans, and fishes.

Genus Pogonias Lacépède, 1801

Pogonias sp.

FIGURES 3.9B–K, 10

Black Drum – Pogonias sp.

Referred Material. CMM-V-173, isolated pharyngeal tooth; CMM-V-201, isolated pharyngeal tooth; 

CMM-V-272, 23 isolated pharyngeal teeth and partial maxilla; CMM-V-280, nearly complete dentary; CMM-V-328, two 

isolated pharyngeal teeth; CMM-V-951, partial third pharyngobranchial; CMM-V-1045, isolated pharyngeal tooth; CMMV-1067, two isolated pharyngeal teeth; CMM-V-1093, isolated 

pharyngeal tooth; CMM-V-1168, isolated pharyngeal tooth; 

CMM-V-1375, isolated pharyngeal tooth; CMM-V-1394, isolated pharyngeal tooth; CMM-V-1778, isolated pharyngeal 

tooth; CMM-V-2142, isolated pharyngeal teeth; CMM-V2258, isolated pharyngeal tooth; CMM-V-2341, four partial 

third pharyngobranchials (Figure 3.9H,I) and a single partial 

fifth ceratobranchial; CMM-V-2372, isolated pharyngeal tooth; 

CMM-V-2377, six isolated pharyngeal teeth; CMM-V-2584, 

two isolated pharyngeal teeth; CMM-V-2655, isolated pharyngeal teeth; CMM-V-2779, nine isolated pharyngeal teeth; 

CMM-V-2793, two isolated pharyngeal teeth; CMM-V-3071, 

partial third pharyngobranchial; CMM-V-3382, partial third 

pharyngobranchial; CMM-V-3392, third pharyngobranchial; 

CMM-V-3566, two complete premaxillae; CMM-V-3794, two 

third pharyngobranchials; CMM-V-3962, partially complete 

third pharyngobranchial; CMM-V-3982, premaxilla (Figure 

3.9B–D); CMM-V-3999, premaxilla; CMM-V-4100, partially 

complete third pharyngobranchial; CMM-V-4203, four isolated 

pharyngeal teeth; CMM-V-4226, partially complete third pharyngobranchial; CMM-V-4254, two isolated pharyngeal teeth; 

CMM-V-4314, two third pharyngobranchials; CMM-V-4532, 

two partially complete third pharyngobranchials; CMM-V-4627, 

dentary (Figure 3.9E–G); USNM 13904, third pharyngobranchial; USNM 16362, partially complete fifth ceratobranchial; 

USNM 336494, partially complete fifth ceratobranchial (Figure 

3.9J,K); USNM 542408, poorly preserved posterior portion of 

the neurocranium (Figure 3.10A,B); USNM 542409, poorly preserved posterior portion of the neurocranium; USNM uncataloged, extensively fragmented neurocranial remains and a single 

premaxilla and nine partial third pharyngobranchials.

Horizon. Calvert, Choptank, St. Marys, and Eastover 

Formations.

Remarks. The available material consists primarily of 

cranial and branchial bones, dominated by the massive and robust 

pharyngeal plates (third pharyngobranchials and fifth ceratobranchials), which, presumably because they are so robust, seem predisposed to becoming fossilized. The neurocranial remains, even 

if scarcely preserved, exhibit the characteristic parasphenoid with 

a flat semicircular facet encircled by a thin crest-like rim (Figure 

3.10A,B), which is functionally associated with the upper pharyngeal jaws (e.g., Stiassny and Jensen, 1987; Sasaki, 1989). 

The premaxilla bears an anteroposteriorly flattened elongate 

ascending process that gradually tapers dorsally and an oblong, 

well-developed articular process (Figure 3.9B–D). The alveolar 

process is relatively short, with numerous sockets of varying 

sizes, of which the anterior ones and those of the labial row are 

more developed. The dentary is relatively short and subtriangular in outline and tapers conspicuously anteriorly; the symphyseal surface is flattened and obliquely oriented; in dorsal view, 

the alveolar surface has an elongate teardrop shape, with many 

small circular alveoli (Figure 3.9E–G). A wide furrow through 

which the mandibular laterosensory canal passes is clearly exposed along the lateral surface of this bone (Figure 3.9F). 

The upper pharyngeal jaw (third pharyngobranchial) is massive, elongate, and roughly ovoid in outline (Figure 3.9H,I); its 

dorsal surface is characterized by a thick ridge along the medial 

margin. At about the midpoint in the length of this ridge, a strong 

rounded process for the articulation of the second epibranchial 

originates and passes posterolaterally toward the center of the 

bone. Most of the occlusal surface is occupied by 28 to 45 thick, 

rounded to polygonal molariform crushing teeth of varying sizes. 

The lateral portion of the occlusal surface exhibits several alveoli 

for small conical teeth. The lower pharyngeal jaw is very large and 

massive and consists of the fully coalesced fifth ceratobranchials 

forming a single unit characterized by an interdigitating suture between the elements (Figure 3.9J,K; see Chao, 1978; Sasaki, 1989; 

Grubich, 2003), a unique condition of the genus Pogonias. The 

occlusal surface of the lower pharyngeal jaw bears a varying number of rounded to polygonal molariform crushing teeth.
NUMBER 100 • 183

The overall morphology of the upper pharyngeal jaws is 

extremely similar to that of the extant black drum Pogonias 

cromis; moreover, the number of crushing teeth of each upper 

pharyngeal element is also within the range of this species. Cope 

(1869) described the fossil species Pogonias multidentatus on the 

basis of a single upper pharyngeal bone from the Calvert Formation of Westmoreland County, Virginia, characterizing it as 

having a higher number of molariform teeth on its occlusal surface compared to the extant black drum. Just like the specimen 

reported by Cope (1869; but see also Smith, 1909; Purdy et al., 

2001), some of the upper pharyngeal jaws available to us have 

45 molariform teeth, which is more than in the extant species. A 

cursory comparative analysis of the extant Pogonias pharyngeal 

apparatus reveals broad variability in the number of molariform 

teeth (22–43) in the occlusal surface of the upper pharyngeal 

jaws of the black drum, thereby suggesting that the number of 

molariform teeth in the upper pharyngeal jaw does not represent 

a valid diagnostic character for the discrimination of the species 

within the genus Pogonias. As a consequence, Pogonias multidentatus should be regarded as a nomen dubium.

Black drums occur in brackish and shallow water and are 

very common over muddy and sandy bottoms, especially in areas 

with large river runoffs. They feed mostly on mollusks, crustaceans, and fishes.

Genus Sciaenops Gill, 1863

Sciaenops sp.

FIGURES 3.11–13

Red Drum – Sciaenops sp.

Referred Material. CMM-V-132, opercle (Figure 

3.12G); CMM-V-139, opercle and a single vertebral centrum 

and several pleural ribs; CMM-V-144, opercle; CMM-V-157, 

premaxilla; CMM-V-166, premaxilla (Figure 3.11A–C); CMMV-162, two dentaries; CMM-V-167, premaxilla; CMM-V-271, 

first abdominal vertebra; CMM-V-276, premaxilla; CMMV-319, 13 vertebrae belonging to a single individual (Figure 

A B

FIGURE 3.10. (A, B) USNM 542408, Pogonias sp., poorly preserved posterior portion of the neurocranium in posterior and ventral views, 

respectively. Specimen is lightly coated with sublimed ammonium chloride. Scale bar equals 10 mm.
184 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A B

C

D

E

F

G

H

I J
NUMBER 100 • 185

3.13A–F); CMM-V-836, premaxilla; CMM-V-896, maxilla; 

CMM-V-954, lachrymal and opercle; CMM-V-977, dentary 

(Figure 3.11D–F); CMM-V-1259, premaxilla; CMM-V-1436, 

articular (Figure 3.12A,B); CMM-V-1600, premaxilla; CMMV-1604, posttemporal (Figure 3.11G); CMM-V-1721, isolated 

scale; CMM-V-1781, isolated scale; CMM-V-1868, vomer; 

CMM-V-1912, premaxilla; CMM-V-2134, premaxilla; CMMV-2185, premaxilla; CMM-V-2340, premaxilla; CMM-V-2341, 

three third pharyngobranchials; CMM-V-2356, partial anguloarticular with associated retroarticular (Figure 3.12C,D); 

CMM-V-2357, dentary; CMM-V-2423, premaxilla; CMMV-2457, premaxilla; CMM-V-2503, third pharyngobranchial; 

CMM-V-2786, premaxilla; CMM-V-2954, four premaxillae 

and two dentaries; CMM-V-2964, first abdominal vertebra; 

CMM-V-3026, maxilla; CMM-V-3038, opercle; CMM-V-3074, 

isolated scale; CMM-V-3116, preopercle (Figure 3.12F); CMMV-3205, quadrate (Figure 3.11 I,J); CMM-V-3234, vomer (Figure 3.11H); CMM-V-3242, palatine; CMM-V-3243, isolated 

scales; CMM-V-3254, dentary; CMM-V-3395, maxilla; CMMV-3398, single scale; CMM-V-3460, premaxilla; CMM-V-3462, 

several scales; CMM-V-3476, palatine; CMM-V-3517, vertebral 

centrum; CMM-V-3566, three premaxillae and six maxillae, five 

dentaries, and a single hyomandibula (Figure 3.12E); CMM-V3567, several vertebral centra; CMM-V-3719, isolated scales 

and lepidotrichia (Figure 3.13G); CMM-V-3725, two maxillae 

and four dorsal spines; CMM-V-3735, premaxilla; CMM-V3798, eight premaxillae and a single dentary; CMM-V-3928, 

premaxilla; CMM-V-3954, premaxilla; CMM-V-3969, two premaxillae; CMM-V-3974, vomer; CMM-V-4039, opercle; CMMV-4098, partially complete preopercle; CMM-V-4119, nine 

opercles and several dorsal-fin spines; CMM-V-4135, opercle; 

CMM-V-4169, third pharyngobranchial; CMM-V-4249, four 

opercles; CMM-V-4280, opercle; CMM-V-4294, third pharyngobranchial; CMM-V-4311, 10 premaxillae and two maxillae, 

a single quadrate, and several isolated vertebrae and dorsal-fin 

spines; CMM-V-4313, third pharyngobranchial; CMM-V-4493, 

nearly complete hyoid bar (Figure 3.12I); CMM-V-4529, two 

maxillae; CMM-V-4554, three opercles and three hypobranchials; CMM-V-4626, third pharyngobranchial (Figure 3.12H); 

CMM-V-4628, two partial opercles and a single hyoid bar; 

USNM 387748, premaxilla; USNM uncataloged, four premaxillae, four dentaries, a single anguloarticular with an articulated 

retroarticular, and a single opercle.

Horizon. Calvert, Choptank, St. Marys, and Eastover 

Formations. 

Remarks. The material referred to the genus Sciaenops 

consists mostly of isolated cranial bones collected throughout 

the Chesapeake Group. 

The vomer is diamond shaped and toothless, with a cavernous ventral surface characterized by thick irregular struts (Figure 3.11H); the vomerine lateral process has broad and flat to 

slightly convex facets. 

The posttemporal is laminar and approximately triangular 

in outline (Figure 3.11G). It possesses an elongate and dorsoventrally flattened dorsal arm that tapers anteriorly into a blunt 

spine; the posterior portion of the bone consists of a laterally 

compressed and flat bony lamina marked by a trough for the 

laterosensory canal. The infraorbital branch of the laterosensory 

canal occupies most of the ventral portion of this bone, with 

two external large fenestrae separated from each other by a large 

laminar strut. 

The premaxilla has a large and anteroposteriorly flattened 

ascending process nearly perpendicular to the alveolar process 

and an articular process with a thickened and gently rounded 

posterior margin and relatively low postmaxillary process (Figure 

3.11A–C). The alveolar process is elongate, with an outer row of 

large conical teeth that increase in size toward the symphysis and 

a dense inner band of villiform teeth that also increase in size 

anteriorly, reaching remarkable size in the lingual row (Figure 

3.11C). The proximal portion of the maxilla is characterized by 

a large articular head with slightly concave anterior facets of irregular shapes; the articular head is continuous posteriorly with 

a laterally compressed shank from which it is separated through 

a marked notch for the articulation of the palatine. All available 

dentaries are incomplete; the alveolar surface is occupied by a 

dense series of closely spaced sockets for strongly pointed teeth 

(Figure 3.11D–F). The thick symphyseal margin is nearly vertical, and there is a deep notch along the anteroventral margin. A 

relatively deep furrow that held the mandibular laterosensory 

canal is clearly visible along the lateral surface of the dentary. 

The anguloarticular is massive, with a large articular condyle for 

the quadrate (Figure 3.12C,D); along the lateral surface of the 

anguloarticular there is a deep trough for the mandibular laterosensory canal, which is partially arched by a relatively narrow, 

flat laminar strut. The thick retroarticular caps the posteroventral corner of the mandible. 

The quadrate is flat and rectangularly shaped, with a nearly 

vertical anterior edge, an extremely large and thickened transverse articular head, and a large medial recess to accommodate 

the symplectic (Figure 3.11 I,J). The transverse development of 

FIGURE 3.11. (Facing page) (A–C) CMM-V-166, Sciaenops sp., left premaxilla in lateral, medial, and occlusal views, respectively. (D–F) 

CMM-V-977, Sciaenops sp., left dentary in occlusal, lateral, and medial views, respectively. (G) CMM-V-1604, Sciaenops sp., posttemporal in 

lateral view. (H) CMM-V-3234, Sciaenops sp., vomer in ventral view. (I, J) CMM-V-3205, Sciaenops sp., right quadrate in lateral and medial 

views, respectively. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
186 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

H

I

A B

C D

E F G
NUMBER 100 • 187

the articular head extends to the whole posterior of the bone. 

The palatine is a toothless bone with a robust thickened anterior ethmoid process. Both the rostropalatine (anterior) and ethmopalatine (posterior) facets for the connection with the lateral 

ethmoid are well developed. Only a partial left hyomandibula 

is available for comparative analysis (Figure 3.12E); it bears an 

anterior articular head and an anterodorsal lens-shaped condyle 

for articulation with the prootic and sphenotic. A well-developed 

lateral crest can be observed along the main shaft of the bone; 

both lateral and medial surfaces are ornamented by a complex 

cavernous system of irregular ridges, furrows, and pits. 

The preopercle is crescent-shaped (Figure 3.12F), with a 

strongly thickened anterior margin and a finely serrated posterior 

margin; the configuration of the canal for the laterosensory system 

is clarified by five external fenestrae separated from each other 

by relatively large laminar horizontal struts that overlie the canal 

itself. The opercle is large, massive, and apparently quadrangular 

in shape (Figure 3.12G), with a convex dorsal margin and a finely 

sculptured outer surface characterized by delicate and irregular 

elongate ridges. Its anterior margin is conspicuously thickened, 

but it terminates at the anterodorsal corner of the bone with a 

rounded articular facet for the opercular process of the hyomandibula. A shallow furrow that passes vertically parallel to the anterior thickening of the bone represents the trough for the opercular 

branch of the facial nerve. Additionally, a strong ridge originates 

from the anterodorsal corner and terminates posteriorly as a blunt 

spine with a rounded profile; another spine is located ventral to 

the major one, separated from it by a shallow concavity.

The hyoid bar is relatively large and robust (Figure 3.12I). 

The dorsal hypohyal is extremely thick and irregular in shape, 

with a slightly concave recess for the basibranchial articulation 

along its medial surface. The ventral hypohyal is conical, with a 

robust anteroventral process. The anterior ceratohyal is the largest bone of the hyoid bar; it is laterally compressed and hourglass 

shaped, with a low laminar median process emerging along its 

ventral margin. The posterior ceratohyal is triangular and laterally compressed. 

The upper pharyngeal plate (third pharyngobranchial) appears to be approximately quadrangular in outline. The occlusal 

surface is flattened to gently convex and completely covered with 

large and thick conical teeth, in many cases represented by their 

sockets. The third hypobranchial is short and clavate, with a flattened dorsal surface.

The atlas (first abdominal vertebra) has a very short diskshaped centrum with an autogenous neural spine, two large 

anterodorsal condylar surfaces, and posteriorly directed lateral 

apophyses (Figure 3.13A,B). The second abdominal vertebra is 

short and disk-shaped, with well-developed dorsal prezygapophyses, posteriorly directed lateral apophyses, and a deep fossa for 

epineural insertion on the laterodorsal surface of the centrum at 

the base of the neural arch (Figure 3.13C,D). The third vertebra 

has a short centrum with well-developed dorsal prezygapophyses, reduced lateral apophyses, and dorsolaterally large fossa for 

the insertion of pleural ribs (Figure 3.13E). The other abdominal vertebrae are subrectangular (longer than high), with short 

postzygapophyses, parapophyses, and deep and large lateral fossae (Figure 3.13F; mesonephros pits sensu Topp and Cole, 1968). 

Some abdominal centra possess a thin osseous bridge across the 

contralateral parapophyses. The caudal vertebrae are rectangular, longer than high, and morphologically uniform, with two 

deeply ornamented lateral fossae separated from each other by a 

strengthening ridge.

The scales are large, feebly ctenoid, and subrectangular to 

ovoid, with a gently rounded posterior margin (Figure 3.13G).

The classification of the taxa of the family Sciaenidae is 

based primarily on characters that are not observable (otolith, 

swim bladder, etc.) in the preserved fossils (e.g., Chao, 1978). 

However, a comparative osteological analysis of the fossils documented herein has revealed a close similarity to the extant red 

drum Sciaenops ocellata. In particular, the dentition pattern and 

the morphology of the premaxilla, articular head of the maxilla, 

opercle, and third pharyngobranchial are clearly diagnostic of 

the genus Sciaenops (Sasaki, 1989; Grubich, 2003). The fossil 

material cannot be confidently accommodated within the variability of Sciaenops ocellata because there are some remarkable 

differences that might support a separate specific status, including the extremely variable size of the dentary teeth of the inner 

band, most notably the enlarged ones in the symphyseal area, 

the presence of an osseous bridge across the parapophyses of the 

posterior abdominal vertebrae, and the disk-shaped morphology 

and reduced size of the two anteriormost vertebral centra.

The red drum is demersal and typically is found in coastal 

marine and brackish waters from Massachusetts to northern 

Mexico. It feeds primarily on mollusks, crustaceans, and fishes.

FIGURE 3.12. (Facing page) (A, B) CMM-V-1436, Sciaenops sp., anguloarticular. (C, D) CMM-V-2356, Sciaenops sp., left partial anguloarticular with associated retroarticular in medial and lateral views, respectively. (E) CMM-V-3566, Sciaenops sp., hyomandibula in lateral 

view. (F) CMM-V-3116, Sciaenops sp., preopercle in lateral view. (G) CMM-V-132, Sciaenops sp., opercle in lateral view. (H) CMM-V-4626, 

Sciaenops sp., third pharyngobranchial in occlusal view. (I) CMM-V-4493, Sciaenops sp., nearly complete hyoid bar. Specimens lightly coated 

with sublimed ammonium chloride. Scale bars equal 10 mm.
188 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A B

C D E

F G
NUMBER 100 • 189

Family Labridae Cuvier, 1817

Genus Tautoga Mitchill, 1814

Tautoga sp.

FIGURE 3.14A

Tautog – Tautoga sp.

1873 Protautoga conidens Leidy – (Leidy, 1873c)

1902 Tautoga conidens (Leidy, 1873c) – Hay, p. 401.

Referred Material. CMM-V-327, partially complete right premaxilla; CMM-V-4138, left upper third pharyngobranchial; CMM-V-4160, premaxillary tooth; CMM-V-4395, 

partially complete right premaxilla and three isolated teeth; 

CMM-V-4632, partially complete left premaxilla (Figure 3.14A); 

USNM uncataloged, fragmentary pharyngeal jaw. 

Horizon. Calvert, St. Marys, and Eastover Formations. 

Remarks. The available premaxillae are incomplete, 

lacking the ascending (and fused articular) process (Figure 

3.14A). The anteriormost tooth of each premaxilla is the largest 

and is characterized by an elongate pedicel that sustains a massive thick crown of variable morphology, from blunt and rounded 

to incisiform and paddle shaped to approximately pointed. The 

teeth are arranged in two rows, the outer characterized by widely 

separated large elements, whereas the inner consists of small incompletely erupted elements. The upper pharyngeal jaws (third 

pharyngobranchials) are subtriangular in shape, with teeth characterized by blunt rounded crowns of varying sizes. 

The morphology of the premaxillae, pharyngeal jaws, and 

teeth are very similar to those of the extant tautog Tautoga 

onitis. The fossils are therefore referred to the genus Tautoga; 

however, because of the fragmentary nature of the available material, it is not possible to extend the taxonomic identification 

to the species level. According to Purdy et al. (2001), the fossil 

species Protautoga conidens established by Leidy (1873a) on the 

basis of an incomplete premaxilla from the Miocene of Virginia 

(see also Leriche, 1942) must be considered a junior synonym of 

Tautoga onitis. 

The tautog is a western north Atlantic demersal species typical of hard-bottom habitats at depths up to 75 m. It occasionally enters brackish waters. The tautog diet consists primarily of 

worms, mollusks, and crustaceans.

Family Uranoscopidae Bleeker, 1859

Genus Astroscopus Brevoort in Gill, 1860

Astroscopus countermani Carnevale, Godfrey, & 

Pietsch, 2011

FIGURE 3.14B–E

Stargazer – Astroscopus countermani

Type Material. CMM-V-4231 (Figure 3.14B–E), holotype, nearly complete neurocranium and a nearly complete right 

hyomandibula; CMM-V-2022, paratype, partially complete 

neurocranium.

Horizon. St. Marys Formation.

Remarks. The available material was described in detail 

and illustrated by Carnevale et al. (2011). According to these 

FIGURE 3.13. (Facing page) (A, B) CMM-V-319, Sciaenops sp., atlas vertebra in left lateral and anterior views, respectively. (C, D) CMMV-319, Sciaenops sp., second abdominal vertebra in left lateral and anterior views, respectively. (E) CMM-V-319, Sciaenops sp., third vertebra 

in left lateral view. (F) CMM-V-319, Sciaenops sp., posterior abdominal vertebra in left lateral view. (G) CMM-V-3719, Sciaenops sp., isolated 

scales and lepidotrichia. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
190 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

authors, the fossils exhibit a number of features that strongly support their placement as a new species of the stargazer genus Astroscopus. The neurocranium is short, broad, and dorsoventrally 

depressed, with a rugose or strongly sculptured outer surface 

(Figure 3.14B–E). The postorbital portion of the neurocranium 

is longer than the orbital portion and is laterally expanded, with 

the distance between the lateral tips of the lateral ethmoids representing less than 60% of the measurement taken between the 

outermost margins of the sphenotics. The neurocranial length 

represents more than 90% of its width. The interorbital anterolateral processes of the frontals are broad, not constricted 

at their bases, with the width of the interorbital region representing 27% of the neurocranial width. The posterior region of 

the frontal has a large anterolateral expansion that results in the 

nearly complete exclusion of the sphenotic from the cranial roof. 

The large parietals are rectangular. The anterolateral corner of 

the sphenotic is prominent and forms a short posterolateral border of the orbit. The hyomandibula is characterized by having a 

prominent tuberosity arising from its dorsolateral surface, large 

and elongate articular heads, and a well-developed anteriorly directed spur.

Carnevale et al. (2011) hypothesized that Astroscopus 

countermani was a predatory fish that inhabited the subtropical 

and warm temperate Atlantic coasts of North America during 

the Miocene, living in shallow marine and paralic waters nearly 

totally buried in muddy or sandy substrates.

Family Sphyraenidae Rafinesque, 1815

Genus Sphyraena Klein, 1778

Sphyraena sp.

FIGURE 3.14F

Barracuda – Sphyraena sp.

Referred Material. CMM-V-1063, CMM-V-1098, 

CMM-V-2376, CMM-V-2776, CMM-V-3198, CMM-V-3335, 

CMM-V-3580, isolated tooth (Figure 3.14F); USNM uncataloged, 21 isolated teeth.

Horizon. Calvert, St. Marys, and Eastover Formations.

Remarks. The presence of barracudas in the Miocene deposits of the Chesapeake Group is evidenced exclusively by isolated teeth (Figure 3.14F). The teeth are lanceolate, 

labiolingually compressed, in some cases with a slightly sigmoid 

cutting edge, and ornamented with short and discontinuous vertical striae. Premaxillary teeth appear to be characterized by a 

postapical barb (Nishimoto and Ohe, 1982), as seen in Figure 

3.14F.

Sphyraenid teeth do not show diagnostic characters to differentiate one species from another. Leidy (1873a) described a 

sphyraenid, Sphyraena speciosa on the basis of isolated teeth 

from the Calvert Formation, Virginia; this species was also reported from the Miocene of Maryland by Cope (1867). On the 

basis of his description, it is not possible to detect any diagnostic feature to distinguish such a species from other sphyraenids, 

thereby suggesting that S. speciosa should be considered a nomen 

dubium. 

Barracudas occupy a wide range of marine and brackish 

habitats, where they live predominantly near the surface. They 

are voracious predators that feed primarily on fishes and cephalopods and occasionally on crustaceans.

Family Scombridae Rafinesque, 1815

Remarks. Kimmel and Purdy (1984) illustrated some 

scombrid bones that they referred to an indeterminate species of 

the genus Katsuwonus. A morphological analysis of that material has not revealed any diagnostic character of Katsuwonus,

and it is therefore interpreted as belonging to an indeterminate 

scombrid taxon. Indeterminate scombrid remains from the Calvert Formation were previously reported by Leriche (1942).

Genus Acanthocybium Gill, 1862

Acanthocybium cf. solandri (Cuvier, 1832 in Cuvier 

& Valenciennes, 1831)

FIGURE 3.15

Wahoo – Acanthocybium cf. solandri

Referred Material. CMM-V-137, hypural complex; CMM-V-158, dentary fragment; CMM-V-159, partial 

right dentary; CMM-V-160, left premaxilla (Figure 3.15A,B); 

CMM-V-284, partially complete left dentary; CMM-V-322, 

dentary fragment; CMM-V-357, premaxillary fragment; CMMV-1598, partially complete right dentary; CMM-V-1812, partially complete right dentary (Figure 3.15C,D); CMM-V-2010, 

dentary fragment; CMM-V-2332, partially complete left dentary 
NUMBER 100 • 191

(Figure 3.15E,F); CMM-V-2629, partially complete right dentary; CMM-V-3710, dentary fragment; CMM-V-4426, dentary 

fragment; CMM-V-4432, complete hypural complex (Figure 

3.15G); USNM 559394, dentary fragment; USNM 20108, complete right premaxilla; USNM 20109, partially complete left dentary; USNM 135183, premaxillary fragment; USNM 135184, 

dentary fragment; USNM 135186, dentary fragment; USNM 

204217, partially complete left dentary; USNM 214428, partially complete right dentary; USNM 265236, dentary fragment; 

USNM uncataloged, partially complete left premaxilla, right 

premaxilla, left dentary, and dentary fragment.

Horizon. Calvert and Choptank Formations.

Remarks. The premaxilla is long, curved, and anteriorly 

pointed (Figure 3.15A,B). The ascending process is long and very 

A F

B C

D E

FIGURE 3.14. (A) CMM-V-4632, Tautoga sp., partial left premaxilla in medial view. (B–E) CMM-V-4231, Astroscopus countermani, holotype, nearly complete neurocranium in dorsal, ventral, posterior, and right lateral views, respectively. (F) CMM-V-3580, Sphyraena sp., isolated 

tooth. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
192 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

robust. The anterior and ventral margins form an angle of about 

37°. The alveolar process bears a single row of large, tightly 

packed, and labiolingually compressed subtriangular teeth. The 

dentary is thick, massive, and laterally compressed, with a nearly 

straight anteroventral margin, a prominent notch along the anterior margin (see Collette and Russo, 1984), and a dense series of 

large, closely spaced, and labiolingually compressed subtriangular teeth (Figure 3.15C,F).

The hypural complex is rhomboid in outline, with a median 

notch along its posterior margin (Figure 3.15G). The complex is 

characterized by the complete fusion of the parhypural and bears 

a well-developed laterally emerging parhypurapophysis. A deep 

fossa is usually developed just behind the fused hemicentrum.

The fossils from the Calvert and Choptank Formations are 

tentatively referred (see Conrad, 1938; Collette and Russo, 1984) 

to Acanthocybium solandri because of the following characteristics unique to the wahoo. The premaxilla has an arrow-shaped 

outline, with a relatively low angle between its anterior and ventral margins. The morphology of the dentary is characterized by 

a prominent notch along its anterior margin. Finally, the structure of the hypural complex has a median posterior indentation, 

the complete fusion of the parhypural, and the presence of a deep 

fossa behind the fused hemicentrum. 

The wahoo is an oceanic epipelagic piscivorous species distributed worldwide in tropical to warm temperate waters.

Genus Sarda Cuvier, 1829

Sarda sp.

FIGURE 3.16A,B

Bonito – Sarda sp.

Referred Material. USNM 559305, nearly complete left premaxilla (Figure 3.16A,B).

Horizon. Calvert Formation.

Remarks. The premaxilla is moderately curved, with a 

stout arrow-shaped anterior portion and a single row of welldeveloped conical teeth. The angle between the anterior and ventral margins measures 50°. The ascending process has a sharp 

anterodorsal end. The general outline of the bone, more specifically the anterodorsal end of the ascending process, is clearly 

diagnostic of the genus Sarda (see Collette and Chao, 1975).

This premaxilla does not present sufficient anatomical information to differentiate or ally it with any extant species within 

the genus Sarda.

Bonitos of the genus Sarda are coastal epipelagic fishes that 

often enter estuaries. They prey on cephalopods and a variety of 

other fishes.

Genus Thunnus South, 1845

Thunnus sp.

FIGURE 3.16C–H

Tuna – Thunnus sp.

Referred Material. CMM-V-137, hypural (Figure 

3.16F); CMM-V-161, partially complete right dentary (Figure 

3.16C,D); CMM-V-932, nearly complete abdominal vertebra; 

CMM-V-947, partially complete caudal peduncle vertebra; 

CMM-V-950, partially complete caudal peduncle vertebra; 

CMM-V-964, three associated nearly complete caudal peduncle vertebrae (Figure 3.16G,H); CMM-V-1363, partially complete articulated vertebral column associated with jaw bones of 

Lophius sp.; CMM-V-1640, partially complete right dentary; 

CMM-V-2052, numerous partially complete caudal and caudal 

peduncle vertebrae; CMM-V-4178, nearly complete caudal peduncle vertebra; CMM-V-4388, four partially complete caudal 

vertebrae and a single nearly complete caudal peduncle vertebra (Figure 3.16E); USNM 24899, extensively fragmented skull 

bones (premaxillae, dentaries, fragments of opercular bones) and 

partially complete articulated vertebral column (31 vertebrae); 

USNM 387790, partially complete abdominal vertebra; USNM, 

uncataloged specimen consisting of four partially complete isolated caudal vertebrae.

Horizon. Calvert and Choptank Formations.

Remarks. The premaxilla is stout and curved, with a 

single row of small, widely spaced conical teeth. The dentary is 

rather thick and characterized medially by a strong crest with 

a rounded profile that originates from the symphyseal region 
NUMBER 100 • 193

B

A

C D

E

F

G

FIGURE 3.15. (A, B) CMM-V-160, Acanthocybium cf. solandri, left premaxilla in lateral and medial views, respectively. (C, D) CMM-V-1812, 

Acanthocybium cf. solandri, partial right dentary in lateral and medial views, respectively. (E, F) CMM-V-2332, Acanthocybium cf. solandri, 

partial left dentary in lateral and medial views, respectively. (G) CMM-V-4432, Acanthocybium cf. solandri, hypural in left lateral view. Specimens lightly coated with sublimed ammonium chloride. Scale bars equal 10 mm.
194 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

(Figure 3.16C,D). The anterior margin of this bone is subvertical, with a shallow concave notch developed labially in the 

middle of its length. Another well-developed notch is located anteroventrally just behind the symphysis. Small and widely spaced 

conical teeth arranged in a single row occupy the dorsal margin 

of the dentary. The opercle and subopercle are approximately 

polygonal in outline.

The abdominal centra are approximately square (Figure 

3.16E), whereas the caudal centra are subrectangular and longer 

than high (Figure 3.16G,H). The centra are characterized by two 

deep fossae separated by a strong median ridge along the lateral 

sides, and an approximately triangular articular surface for ligament attachment is located anteriorly on the median strengthening ridge. The vertebrae of the caudal peduncle are remarkably 

compressed dorsoventrally and possess a thin, broad keel arising 

laterally from the median ridge on both sides and flattened, stout 

neural and haemal spines.

The hypural is rhomboid in outline, with a deep fossa developed just behind the fused hemicentrum and immediately above 

the small hypurapophyses (Figure 3.16F).

The premaxillae, dentaries, and vertebrae have several morphological features that are clearly diagnostic of the genus Thunnus (De Sylva, 1955; Gibbs and Collette, 1967; Collette and Chao, 

1975). In particular, the outline of the dentaries, the tooth size and 

arrangement, and the vertebrae with deep fossae separated by a 

median horizontal strengthening ridge with an anterior articular 

surface for the insertion of the epineurals, strongly support this generic attribution. Unfortunately, classification at the specific level is 

not possible because of the fragmentary nature of the available material. Moreover, as reported by Gibbs and Collette (1967), morphological variability is so great in some skeletal elements of the 

genus Thunnus that it is not possible to distinguish between extant 

species on the basis of these highly variable bones. Some skeletal 

characters are useful for the positive identification of species, but 

these are not preserved in the material available to us.

Tunas are oceanic and migrate seasonally close to shore, often 

entering brackish-water habitats. Usual prey includes schooling 

fishes, but they also feed on crustaceans and cephalopods.

Family Istiophoridae Lütken, 1875

Remarks. Billfish remains are usually found in the Miocene deposits of the Chesapeake Group as isolated fragmented 

bones (Berry, 1917; Kimmel and Purdy, 1984). The identification 

of billfish remains to genus or species is extremely problematic, 

the results of which are usually broadly subjective. In an attempt 

to reduce ambiguity in the taxonomic analysis of isolated billfish 

remains, Fierstine and Voigt (1996) and Fierstine (1998, 2001) 

examined the range of variation in extant skeletal elements and 

developed a morphometric technique of identification that could 

be applied to disarticulated bones, whether fossil or extant. 

This method has been used to analyze billfish remains from the 

Miocene deposits of the Chesapeake Group of Maryland and Virginia, leading to the recognition of at least two taxa, Istiophorus cf. platypterus and Makaira cf. nigricans. According to the 

method elaborated by Fierstine (1998, 2001), an identification can 

be made by converting measurements of individual fossil bones 

into ratios and comparing them to those obtained for extant billfishes (see Carnevale et al., 2002). Some of the fossil ratios are 

outside the ranges observed for extant material; for this reason, 

specimens identified at the species level are only tentatively assigned to an extant taxon. In many cases the preservation of the 

material is inadequate to allow for the morphometric survey and, 

as a consequence, for a reasonable taxonomic interpretation.

Genus Istiophorus Lacépède, 1801

Istiophorus cf. platypterus (Shaw & Nodder, 1792)

FIGURE 3.17A–D

Sailfish – Istiophorus cf. platypterus

1917 Istiophorus calvertensis Berry, pp. 461–463, figs. 1–2.

1984 Istiophorus calvertensis (Berry) – Kimmel and Purdy, p. 208, pl. 1, 

fig. 7.

1987 Pseudohistiophorus calvertensis (Berry) – Schultz, p. 171.

1998 Istiophorus cf. platypterus (Shaw & Nodder, 1792) – Fierstine, 

pp. 40–41, figs. 8B, 9.

2001 Istiophorus cf. platypterus (Shaw & Nodder, 1792) – Fierstine, 

pp. 36–37.

Referred Material. CMM-V-270, complete atlas 

(first abdominal vertebra), (Figure 3.17B,C); CMM-V-1766, articulated partially complete dentaries; USNM 9344, partially complete rostrum (Figure 3.17A); USNM 186813, partially complete 

rostrum; USNM 542404, hypural complex (Figure 3.17D).

Horizon. Calvert, Choptank, and Eastover Formations.

Remarks. The material consists of two partially preserved rostra (Figure 3.17A), a single isolated first abdominal 

vertebra (Figure 3.17B,C), and a complete hypural complex 

(Figure 3.17D). One of the rostra, USNM 9344, constitutes the 

holotype specimen of Istiophorus calvertensis described by Berry 

(1917) from the deposits of the Eastover Formation cropping 
NUMBER 100 • 195

FIGURE 3.16. (A, B) USNM 559305, Sarda sp., nearly complete left premaxilla in lateral and medial views, respectively. (C, D) CMM-V-161, 

Thunnus sp., partial right dentary in lateral and medial views, respectively. (E) CMM-V-4388, Thunnus sp., abdominal vertebra. (F) CMM-V137, Thunnus sp., hypural in right lateral view. (G, H) CMM-V-964, Thunnus sp., three associated caudal peduncle vertebrae. (I, J) CMM-V2490, “Paralbula” dorisiae, tooth plate in occlusal and lateral views, respectively. Specimens lightly coated with sublimed ammonium chloride. 

Scale bars equal 10 mm.
196 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

B

A

C

D

H

E F

G
NUMBER 100 • 197

out at Tar Bay, James River, Virginia. Fierstine (1998, 2001) 

redescribed the specimen in detail and provided morphometric 

evidence of its affinities with the extant sailfish I. platypterus. 

The ratios of the rostrum formerly referred to I. calvertensis, as 

well as the other material referred herein to I. cf. platypterus, are 

presented in Table 3.1.

The sailfish is an oceanic, epipelagic species usually inhabiting the waters above the thermocline. Sailfishes are distributed 

close to the coasts, where they feed on fishes, cephalopods, and 

crustaceans.

Genus Makaira Lacépède, 1802

Makaira cf. nigricans Lacépède, 1802

FIGURE 3.17E–G

Blue Marlin – Makaira cf. nigricans

1998 Makaira cf. nigricans Lacépède – Fierstine, pp. 30–40, figs. 4–8A.

2001 Makaira cf. nigricans Lacépède – Fierstine, p. 37.

Referred Material. CMM-V-128 and CMM-V129, partially complete rostra; USNM 375733, partially complete neurocranium, basisphenoid, vomer, rostrum, right lateral 

ethmoid, right ectopterygoid, right metapterygoid, right anguloarticular, right maxilla, right palatine, left prenasal, left dentary, 

predentary, and right lachrymal; USNM 542403, predentary and 

left quadrate (Figure 3.17E–G); USNM uncataloged, complete 

hypural complex.

Horizon. Calvert and Eastover Formations.

Remarks. Fierstine (1998) presented a detailed description of a partially articulated neurocranium, a rostrum, a jaw, 

and suspensorial bones. The ratios of selected bones described by 

Fierstine (1998), as well as the other material referred herein to 

Makaira cf. nigricans, are presented in Table 3.2.

The blue marlin is an oceanic species that primarily inhabits 

blue waters down to 200 m, where it feeds mostly on fishes but 

also on cephalopods.

Family Istiophoridae, gen. et sp. indet.

Referred Material. CMM-V-183, partially complete rostrum; CMM-V-184, partially complete rostrum; CMMV-220, complete abdominal vertebra; CMM-V-321, partially 

complete rostrum; CMM-V-337, complete abdominal vertebra; 

CMM-V-1839, partially complete predentary; CMM-V-1908, 

partially complete predentary; CMM-V-1915, two partially 

complete hypural complexes; CMM-V-1998, complete caudal vertebra; CMM-V-1999, partially complete right scapula; 

CMM-V-2239, partially complete rostrum; CMM-V-2511, partially complete abdominal vertebra; CMM-V-2684, partially 

complete rostrum; CMM-V-2983, partially complete rostrum; 

CMM-V-3835, partially complete rostrum; CMM-V-3956, partially complete rostrum; CMM-V-4148, two complete caudal 

vertebrae; CMM-V-4576, partially complete rostrum; CMMV-4827, partially complete neurocranium; USNM 186808, partially complete rostrum; USNM 186809, two vertebrae (one 

abdominal and one caudal); USNM 186810, five abdominal vertebrae and right cleithrum, right coracoid, right postcleithrum, 

and caudal-fin rays; USNM 186812, partially complete caudal 

vertebra; USNM 241559, hypural complex and five isolated dorsal-fin spines; USNM 639712, predentary and partial abdominal 

vertebra; USNM 415609, partially complete rostrum; USNM 

559395, partially complete rostrum; USNM 559393, partially 

complete rostrum; USNM uncataloged, partially complete 

rostrum and two partially complete caudal vertebrae, a single 

abdominal vertebra, and a single hypural complex.

Horizon. Calvert, Choptank, St. Marys, and Eastover 

Formations.

Order Pleuronectiformes Bleeker, 1859

Family Paralichthyidae Regan, 1910

Genus Paralichthys Girard, 1858

FIGURE 3.17. (Facing page) (A) USNM 9344, Istiophorus cf. platypterus (holotype of I. calvertensis), partial rostrum. (B, C) CMM-V-270, 

Istiophorus cf. platypterus, complete atlas in anterior and left lateral views, respectively. (D) USNM 542404, Istiophorus cf. platypterus, hypural 

complex in left lateral view. (E, F) USNM 542403, Makaira cf. nigricans, predentary in occlusal and right lateral views, respectively. (G) USNM 

542403, Makaira cf. nigricans, left quadrate in lateral view. (H) USNM 542407, Paralichthys sp., left dentary in lateral view. Specimens lightly 

coated with sublimed ammonium chloride. Scale bars equal 10 mm.
198 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Paralichthys sp.

FIGURE 3.17H

Lefteye Flounder – Paralichthys sp.

Referred Material. USNM 542407, left and right 

dentaries belonging to a single individual (Figure 3.17H).

Horizon. Eastover Formation.

Remarks. The dentaries are high and very thick, with a 

single row of strong caniniform teeth (Figure 3.17H). The anterior margin is nearly straight and obliquely oriented. There is a 

shallow notch along the anteroventral margin. Two parallel and 

relatively deep grooves run ventrally from the symphyseal region 

along the lateral surface. A flat bony flange with a linear dorsal 

profile is located along the dorsal margin behind the tooth row.

The dentaries from the Eastover Formation documented 

herein cannot be distinguished from those of the extant flounder 

Paralichthys dentatus.

Lefteye flounders of the genus Paralichthys are benthic species that occur primarily on sandy or muddy substrates from the 

TABLE 3.1. The ratios of the rostrum formerly referred to I. calvertensis, as well of the other material referred herein to I. cf. platypterus. Abbreviations follow Fierstine and Voigt (1996) and Fierstine (1998, 2001); a dash (–) indicates data are unavailable.

Ratios USNM 9344 USNM 186813 USNM 542404 CMM-V-270 CMM-V-1766

Rostrum

D1/W1 0.72 – – – –

H1/D1 0.27 – – – –

DD1/D1 0.43 – – – –

D2/W2 0.69 0.57 – – –

H2/D2 0.27 0.27 – – –

DZ/P 0.34 – – – –

Dentary 

DAD/DJL – – – – 0.43

22nd vertebra 

ASW/VAD – – – 0.70 –

VAD/CL – – – 0.83 –

VPD/CL – – – 0.83 –

LAD/LPD – – – 0.86 –

NW/CL – – – 0.57 –

NW/LPD – – – 0.70 –

ASW/CL – – – 0.74 –

VAD/LAD – – – 1.17 –

VPD/LPD – – – 1.01 –

VAD/VPD – – – 1.00 –

LAD/CL – – – 0.70 –

LPD/CL – – – 0.81 –

Hypural 

HDD/HL – – 0.56 – –

HDD/HH – – 0.29 – –

HDD/HW – – 0.50 – –

HL/HH – – 0.52 – –

HW/HL – – 0.98 – –

HW/HH – – 0.51 – –

HNL/HL – – 0.30 – –
NUMBER 100 • 199

shore to a depth of 200 m. They often enter brackish waters and 

feed primarily on fishes and crustaceans.

Order Tetraodontiformes Regan, 1929

Family Diodontidae Bibron, 1855

Genus Chilomycterus Bibron, 1846

Chilomycterus sp. 

FIGURE 3.18K,L

Burrfish – Chilomycterus sp.

Referred Material. CMM-V-172, fused dentaries; 

CMM-V-361, fused premaxillae; CMM-V-890, fused premaxillae; CMM-V-891, fused premaxillae; CMM-V-3338, fused 

dentaries (Figure 3.18K); CMM-V-3770, fused dentaries; CMMV-4624, isolated dermal spine (Figure 3.18L).

Horizon. Calvert and Eastover Formations.

Remarks. Mouth plates are represented by both upper 

and lower jaws, which in origin consisted of the teeth of the biting 

edge fused with the dentaries and premaxillae into a solid crushing beak. The trituration teeth internal to the biting edge of both 

upper and lower jaws form a large plate divided into right and left 

halves, each formed by a series of large, flattened triturating tooth 

plates (Tyler, 1980; Figure 3.18K). The number of individual plates 

in the single series to each side of the midline usually increases 

with increasing specimen size. Unfortunately, all the jaw specimens 

are strongly eroded, represented only by fused contralateral tooth 

plates. Lower jaws can be distinguished from the upper jaws because of their rounded rather than pointed profile when observed 

in occlusal view (Figure 3.18K). Mouth plates, however, are not 

taxonomically useful because they are nearly indistinguishable in 

the genera Diodon and Chilomycterus. However, these two genera 

can be easily separated on the morphology of their dermal spines 

(see Tyler, 1980). CMM-V-4624 (Figure 3.18L) consists of a nonerectile, short, thick, and pointed spine arising from a large triradiate basal plate clearly belonging to the genus Chilomycterus (see 

Tyler, 1980; Leis, 2006). Because spines of Diodon have not yet 

been found, we tentatively suggest that all the diodontid skeletal 

remains found in the Miocene deposits of the Chesapeake Group 

should be assigned to Chilomycterus. The fragmentary nature of 

the material does not allow for species-level attribution. 

Burrfishes occur primarily in seagrass beds in bays and 

coastal lagoons, where they feed on crustaceans.

Family Molidae Ranzani, 1837

Genus Mola Koelreuter, 1770

Mola pileata (Van Beneden, 1881)

FIGURE 3.18A–C

Ocean sunfish – Mola pileata

Holotype. USNM 186983, premaxillary beak (Figure 

3.18A–C). 

Horizon. Choptank Formation.

Remarks. Weems (1985) referred a toothless premaxillary beak lacking a palatal tooth brace from bed 19 of the 

Choptank Formation to the molid species Mola chelonopsis

(Figure 3.18A–C). However, Gregorova et al. (2009) concluded 

that this same specimen likely belongs to Mola pileata or perhaps 

to a new undescribed species of Mola.

Ocean sunfishes of the genus Mola are pelagic, with a 

worldwide distribution in tropical to temperate waters; they feed 

mainly on jellyfishes and other pelagic soft-bodied invertebrates 

and fish larvae.
200 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 3.2. The ratios of selected bones described by Fierstine (1998), as well as of the other material referred herein to Makaira cf. 

nigricans. Abbreviations follow Fierstine and Voigt (1996) and Fierstine (1998, 2001); a dash (–) indicates data are unavailable.

Ratios USNM 375733 USNM 542403 USNM uncataloged CMM-V-128+129

Neurocranium 

TD/MBO 0.50 – – –

NWB/TD 0.70 – – –

PAD/PAFW 0.53 – – –

PAW/PAFW 0.70 – – –

PAD/PAW 0.76 – – –

Predentary 

PW/PL 0.74 0.65 – –

PD/PL 0.52 0.41 – –

PD/PW 0.70 0.63 – –

Rostrum 

D2/W2 0.70 – – 0.54

H2/D2 0.18 – – 0.30

DD2/D2 0.47 – – 0.27

Maxilla 

ML/MOL 0.17 – – –

MW/MOL 0.14 – – –

MW/ML 0.79 – – –

MH/ML 0.64 – – –

MVW/MVH 1.3 – – –

MVW/ML 0.37 – – –

MVW/MW 0.46 – – –

MVW/MH 0.57 – – –

Articular 

AL/ASM 0.79 – – –

AW/AL 0.77 – – –

AAL/AL 0.59 – – –

ATW/AL 1.2 – – –

AW/ATW 0.66 – – –

Quadrate 

QAW/QH – 0.23 – –

QMW/QAW – 1.10 – –

QAW/QHS – 0.30 – –

QMW/QHS – 0.34 – –

QMW/QHL – 0.96 – –

Hypural 

HDD/HL – – 0.41 –

HDD/HH – – 0.15 –

HL/HH – – 0.37 –

HNL/HL – – 0.17 –
NUMBER 100 • 201

Genus Ranzania Nardo, 1840

Remarks. The genus Ranzania includes a single extant 

species, Ranzania laevis, and at least four fossil species (see Carnevale and Santini, 2007), two of which are known exclusively 

from the Miocene and Pliocene deposits of the Middle Atlantic 

Coastal Plain (see Weems, 1985). Ranzania laevis is an oceanic 

pelagic species that occurs worldwide in warm and temperate 

waters, where it feeds primarily on planktonic crustaceans. On 

the basis of functional considerations, however, Weems (1985) 

suggested that the fossil species Ranzania grahami was characterized by feeding habits similar to those of Mola. 

Ranzania grahami Weems, 1985

FIGURE 3.18D–I

Ocean sunfish – Ranzania grahami

Holotype. USNM 186986, premaxillary and dentary 

beaks (Figure 3.18D,E) and jugular and nasal dermal plates (not 

illustrated) and a partially complete articulated dorsal dermal 

shield (Figure 3.18H,I).

Paratypes. USNM 16364, premaxillary beak; USNM 

16668, premaxillary beak; USNM 16743, premaxillary beak; 

USNM 186982, premaxillary beak; USNM 265391, partial 

premaxillary beak; USNM 265394, premaxillary beak; USNM 

265395, premaxillary beak; USNM 265651, nasal dermal plate; 

USNM 265653, jugular dermal plate (Figure 3.18F,G). 

Referred Material. CMM-V-140, nasal dermal 

plate; CMM-V-150, dentary beak; CMM-V-186, premaxillary beak; CMM-V-187, premaxillary beak; CMM-V-191, nasal 

dermal plate; CMM-V-217, premaxillary beak; CMM-V-232, 

jugular dermal plate; CMM-V-230, nasal dermal plate; CMMV-233, nasal dermal plate; CMM-V-285, premaxillary beak; 

CMM-V-286, premaxillary beak; CMM-V-315, dentary beak; 

CMM-V-888, premaxillary beak; CMM-V-892, a single nasal and 

two jugular dermal plates; CMM-V-1004, dentary beak; CMMV-1005, dermal plate; CMM-V-1641, two premaxillary beaks; 

CMM-V-1719, nasal dermal plate; CMM-V-1854, premaxillary 

beak; CMM-V-1883, dentary beak; CMM-V-1891, three premaxillary beaks and five jugular and five nasal dermal plates; CMMV-1984, jugular dermal plate; CMM-V-2044, premaxillary beak; 

CMM-V-2064, a single dentary and four premaxillary beaks and 

one jugular and one nasal dermal plates; CMM-V-2137, three premaxillary beaks; CMM-V-2138, three nasal dermal plates; CMMV-2139, two dermal plates; CMM-V-2143, two jugular plates; 

CMM-V-2246, jugular dermal plate; CMM-V-2434, premaxillary 

beak; CMM-V-2501, dentary beak; CMM-V-2508, jugular dermal 

plate; CMM-V-2510, nasal dermal plate; CMM-V-2553, jugular 

dermal plate; CMM-V-2561, a single jugular and two nasal dermal plates; CMM-V-2579, jugular dermal plate; CMM-V-2685, 

premaxillary beak and nasal dermal plate; CMM-V-2788, dermal 

plates; CMM-V-3029, three nasal plates; CMM-V-3076, jugular 

dermal plate; CMM-V-3078, jugular dermal plate; CMM-V-3328, 

premaxillary beak; CMM-V-3800, two premaxillary beaks and six 

jugular and two nasal dermal plates; CMM-V-4004, premaxillary 

beak; CMM-V-4092, premaxillary beak; CMM-V-4211, premaxillary beak; CMM-V-4227, jugular dermal plate; CMM-V-4255, 

premaxillary beak and three nasal dermal plates; CMM-V-4277, 

nasal dermal plate; CMM-V-4292, nasal dermal plate; CMM-V4308, jugular dermal plate; CMM-V-4340, nasal dermal plate; 

CMM-V-4413, two premaxillary beaks; CMM-V-4420, premaxillary beak and nasal dermal plate; CMM-V-4424, dermal plate; 

CMM-V-4547, jugular dermal plate; CMM-V-4558, jugular 

dermal plate; CMM-V-4565, nasal dermal plate; CMM-V-4577, 

nasal dermal plate; CMM-V-4596, jugular dermal plate; USNM 

135737, jugular dermal plate; USNM 265649, premaxillary beak; 

USNM 265652, partial jugular dermal plate; USNM 391878, 

premaxillary beak; USNM 410274, jugular dermal plate; USNM 

639711, premaxillary beak; USNM 2015682, dentary beak. 

Horizon. Calvert Formation.

Remarks. Abundant jaw and dermal skeleton remains 

are referred herein to the species Ranzania grahami on the basis 

of the diagnostic features described by Weems (1985).

The premaxillary beak is massive and does not have a bony 

shelf on the palatal bracing; it is usually toothless and only rarely 

has small and irregularly disposed teeth (Figure 3.18D). The dentary beak, with a robust biting edge, is similar to that of the 

extant Ranzania laevis; the teeth appear to be absent or, at least, 

remarkably reduced (Figure 3.18E). 

The massive carapace consists of irregular and extremely 

thickened plates (Figure 3.18H,I). Of the whole dermal covering, the nasal and jugular plates can be distinguished from the 

other elements. The nasal plate is approximately ovoid in outline, whereas the jugular plate is greatly elongate, with a rounded 

external surface and a flat to slightly concave median surface 

characterized by a thick median ridge (Figure 3.18F,G).
202 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A B

C

D

E

F G

H

I

K

J

L
NUMBER 100 • 203

Ranzania tenneyorum Weems, 1985

FIGURE 3.18J

Ocean sunfish – Ranzania tenneyorum

Holotype. USNM 265392, premaxillary beak (Figure 

3.18J).

Referred Material. Six premaxillary beaks: CMMV-185, CMM-V-931, CMM-V-2137, CMM-V-2441, CMM-V4464, USNM 336431. 

Horizon. Calvert Formation.

Remarks. The available material consists solely of 

isolated premaxillary beaks. The beaks are characterized by 

three well-developed pairs of tooth rows located on a bony shelf 

separated by a vertical sill from the main level of the palatal 

bracing bone; a notch is clearly exposed behind the tooth rows 

(Figure 3.18J).

Comments on “Paralbula” dorisiae Blake, 1940

FIGURE 3.16 I,J

A few thick tooth plates with phyllodont teeth (see Estes, 

1969) from the Calvert and St. Marys Formations are present 

in the collections of the CMM (CMM-V-325, CMM-V-1024, 

CMM-V-2154, CMM-V-2215, CMM-V-2490; Figure 3.16 I,J) 

and USNM (USNM 16134, holotype; USNM 559397; USNM 

uncataloged). The teeth are irregularly arranged, nearly globular 

or subspherical in outline, and slightly depressed apically (Figure 3.16 I,J). Blake (1940) interpreted these tooth plates as being 

related to those of the Eocene albuloid Paralbula marylandica

and created the new species Paralbula dorisiae to accommodate 

them. In a comprehensive study on the evolution and diversity of 

phyllodont fishes, Estes (1969) excluded the possibility that the 

Miocene tooth plates from the Chesapeake Group could belong 

to the genus Paralbula and, more generally, to the albuloid family Phyllodontidae. According to Estes (1969), the Miocene phyllodont tooth plates from the Chesapeake Group actually belong 

to the percomorph Crommyodus irregularis, a species created 

by Cope (1869) on the basis of material from the Miocene of 

New Jersey. Within percomorphs, phyllodont teeth are known to 

occur in the Carangidae, Diodontidae, and Labridae (hypsigenines, odacines, scarines) and, possibly, in certain extinct members 

of the family Sciaenidae (Estes, 1969). However, the fragmentary 

nature of the available material, as well as the lack of useful 

characters to interpret its possible affinities within percomorphs, 

defies taxonomic identification at this time.

Remarks on Otolith Assemblages

FIGURE 3.19

Otoliths, together with isolated teeth, were the first reported actinopterygian remains from the Miocene deposits of 

the Chesapeake Group (Eastman, 1904; Hay, 1928). In the first 

synoptic work on the Miocene fishes from Maryland, Eastman 

(1904) briefly discussed the otolith record of the Chesapeake 

Group and illustrated gadid and sciaenid sagittas from the St. 

Marys Formation without any indication of their taxonomic 

affinities. About half a century later, Dante (1953) described a 

new species, Sciaenops eastmani, on the basis of the material 

previously illustrated by Eastman (1904) and additional specimens from the Calvert Formation; his diagnosis was based on 

juvenile features, and for this reason Fitch and Lavenberg (1983) 

considered it to be a synonym of the extant Sciaenops ocellata. 

Nevertheless, Schwarzhans (1993) included Sciaenops eastmani

FIGURE 3.18. (Facing page) (A–C) USNM 186983, Mola pileata, premaxillary beak in right lateral, ventral (occlusal), and dorsal views, respectively. Anterior to top of page. (D) USNM 186986, Ranzania grahami, holotype, premaxillary beak in ventral (occlusal view). Anterior to top of 

page. (E) USNM 186986, Ranzania grahami, holotype, dentary beak in dorsal (occlusal view). Anterior to top of page. (F, G) USNM 265653,

Ranzania grahami, jugular dermal plate in external and internal views, respectively. (H, I) USNM 186986, Ranzania grahami, holotype, partial 

articulated dorsal dermal shield, internal view (H shows an enlarged view of the anterior margin of I). (J) USNM 265392, Ranzania tenneyorum, holotype, premaxillary beak in ventral (occlusal view). Anterior to top of page. (K) CMM-V-3338, Chilomycterus sp., fused dentaries, 

occlusal view. Anterior to top of page. (L) CMM-V-4624, Chilomycterus sp., isolated dermal spine. Specimens lightly coated with sublimed 

ammonium chloride. Scale bars equal 10 mm.
204 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

within the fossil genus Trewasciaena together with material from 

the Miocene of Germany. A comprehensive study of the Miocene otoliths of Maryland was being prepared by John E. Fitch 

(n.d.), but unfortunately, his untimely death precluded full revision of the material. More recently, Müller (1999) made an 

extensive study of Tertiary ichthyofaunas of the Atlantic Coastal 

Plain, including the Calvert, Choptank, St. Marys, and Eastover Formations. About 64 taxa were described and illustrated 

from the Miocene of the Chesapeake Group, and several new 

otolith-based taxa were created. Many of his generic identifications, however, are not consistent with the analysis of skeletal 

remains presented herein. Since a complete review of the Miocene otolith assemblages of the Chesapeake Group is beyond the 

scope of our study, we investigated the relatively large otolith 

collection housed in the CMM in light of the results of the study 

of skeletal remains. Therefore, our taxonomic interpretations 

may appear rather conservative and with a broad use of open 

nomenclature. The most commonly found taxa are compiled in 

Figure 3.19. Throughout the Miocene, members of the families 

Gadidae (Gadiculus cf. argenteus, Micromesistius cognatus, 

Trisopterus sculptus) and Sciaenidae (Cynoscion sp., Genyonemus sp., Leiostomus sp., Menticirrhus sp., Pachyurus sp., Pogonias sp., Sciaenops sp.) are by far the dominant components 

of the assemblages, which also include a subordinate contingent 

of taxa of the families Ophidiidae (Lepophidium aff. cervinum, 

Otophidium sp.), Merlucciidae (Merluccius sp.), Ammodytidae 

(Ammodytes sp.), Triglidae (Prionotus sp.), Uranoscopidae (Astroscopus sp.), and Paralichthyidae (Citharichthys sp.). Representatives of other families are relatively rare (see Müller, 1999, 

for a detailed account). In some cases, the otolith and skeletal 

records are strongly consistent, including relative abundances as, 

for example, in the case of the red drum Sciaenops, which is 

extremely abundant in both records.

DISCUSSION

The analysis of the bony fish remains from the marine and 

paralic siliciclastic deposits of the Chesapeake Group presented 

herein provides a substantial improvement of our knowledge 

about the evolution of the structure and composition of the Miocene fish communities of the Salisbury Embayment and, more 

generally, of the middle sector of the eastern Atlantic coast of 

the North American continent. The investigation carried out on 

the paleoichthyological material housed in the collections of the 

CMM and the Department of Paleobiology of the USNM resulted in the identification of at least 38 taxa on the basis of 

fossil bones collected over more than a century from the Calvert, 

Choptank, St. Marys, and Eastover Formations. This represents 

a remarkable increase in the number of recognized taxa with 

respect to the previous reviews of the paleoichthyological record 

(e.g., Leriche, 1942; Kimmel and Purdy, 1984), which recognized 

less than a dozen taxa. An evaluation of the Miocene bony fish 

diversity from the deposits of the Chesapeake Group, however, 

should also include the diverse otolith assemblages described 

by Fitch (n.d.) and more recently by Müller (1999), who recognized at least 55 taxa in the Chesapeake Group. Therefore, a 

combined census of both the skeletal remains and otoliths of the 

Chesapeake Group results in the identification of at least 87 fish 

taxa, of which only a few (e.g., Ariopsis stauroforus, Brotula sp., 

Merluccius sp., Pogonias sp., Prionotus sp., Sciaenops sp.) are 

common to both records (Tables 3.3, 3.4).

As previously mentioned, this paleoichthyofaunal survey is 

based on the study of museum material fortuitously collected 

over more than a century from the deposits of the Chesapeake 

Group cropping out in Maryland and Virginia. The complete 

absence of a quantitative approach in the collection of these fossils makes it very difficult to provide a detailed paleoecological 

analysis of the fish assemblages. Nevertheless, some general paleoecological considerations can be provided on the basis of the 

biological and environmental affinities of the recognized taxa. 

Within the sedimentary successions of the Chesapeake 

Group, skeletal remains are much more abundant and diverse 

in the Calvert and St. Marys Formations, with 26 and 20 taxa 

respectively, possibly reflecting depositional contexts wherein 

fossilization was favored. The otolith record shows a similar 

trend, with highly diverse assemblages in the Calvert and St. 

Marys Formations and only a few taxa recognized from both the 

Choptank and Eastover Formations (see Müller, 1999). 

The fish assemblages of the Calvert, Choptank, St. Marys, 

and Eastover Formations exhibit a modern aspect. Although the 

ichthyofaunal compositions of the various formations are characterized by broad differences, it is interesting to note a persistent 

abundance of sturgeons (Acipenseridae gen. et sp. indet.), drums 

(Pogonias sp., Sciaenops sp.), and billfishes (Istiophoridae gen. et 

sp. indet.) throughout the sedimentary successions of the Chesapeake Group. The faunistic differences existing between the four 

formations clearly reflect the physiographic and environmental 

evolution of the Salisbury Embayment during the Miocene (e.g., 

Ward and Andrews, 2008; Petuch and Drolshagen, 2010). 

The reduced size of many of the otoliths (ammodytids, cynoglossids, gadids, merlucciids, ophidiids, paralichthyids, and sciaenids) from the deposits of the Chesapeake Group is probably 

related to their juvenile nature. Such an abundance of juveniles 

suggests that the Salisbury Embayment represented a nursery 

ground for most of the Miocene.

The Calvert ichthyofauna is dominated by sturgeons 

(Acipenseridae gen. et sp. indet.), tilefishes (Lopholatilus ereborensis), drums (Pogonias sp., Sciaenops sp.), scombrids (Acanthocybium cf. solandri, Thunnus sp.), billfishes (Istiophorus

cf. platypterus, Makaira cf. nigricans, Istiophoridae gen. et sp. 

indet.), burrfishes (Chilomycterus sp.), and ocean sunfishes 

(Ranzania grahami). The presence of tunas, billfishes, and other 

schooling predatory fishes, together with the abundance of 

large sharks and marine tetrapods, suggests that the Salisbury 

Embayment was a highly productive feeding ground during the 

deposition of the Calvert Formation. Overall, the Calvert ichthyofauna consists of a mixture of tropical, subtropical, and 
NUMBER 100 • 205

warm temperate taxa, with a few taxa of cold temperate affinity 

(Lopholatilus ereborensis). The tropical-subtropical contingent 

includes the sea catfish Ariopsis stauroforus, the wahoo Acanthocybium cf. solandri, the billfishes Istiophorus cf. platypterus and 

Makaira cf. nigricans, and the barracuda Sphyraena sp., which 

are indicative of temperatures of 27°C or higher (see Purdy et 

al., 2001). According to Müller (1999), the abundance of gadid 

otoliths in the deposits of the Calvert Formation is indicative of 

the presence of cool waters; however, the recognized gadid taxa 

belong to the thermophilous genera Gadiculus, Micromesistius, 

Phycis, and Trisopterus, which commonly occur in warm temperate waters (see Carnevale et al., 2012). 

The Calvert ichthyofauna shares some taxa (Bagre, Chilomycterus, Lagodon, Pogonias, Sarda, Sphyraena, and Thunnus) with the partially coeval Burdigalian assemblage of the 

Pungo River Formation, North Carolina (see Purdy et al., 2001). 

However, the Pungo River ichthyofauna is characterized by a 

lower number of taxa, some of which (Aluterus sp., Auxis sp., 

Micromesistius cognatus

Genyonemus sp.

Prionotus sp.

Astroscopus sp.

Cynoscion sp.

Pogonias sp.

Lepophidium aff. cervinum

Menticirrhus sp.

Otophidium sp.

Gadiculus cf. argenteus Trisopterus sculptus Merluccius sp.

Sciaenops sp. Citharichthys sp.

Leiostomus sp. Pachyurus sp.

A C B D

E F G H

I J K L

M N O P

FIGURE 3.19. Otoliths from the Chesapeake Group. (A) Micromesistius cognatus. (B) Gadiculus cf. argenteus. (C) Trisopterus sculptus. (D) 

Merluccius sp. (E) Lepophidium aff. cervinum. (F) Otophidium sp. (G) Prionotus sp. (H) Cynoscion sp. (I) Genyonemus sp. (J) Menticirrhus sp. 

(K) Leiostomus sp. (L) Pachyurus sp. (M) Pogonias sp. (N) Sciaenops sp. (O) Astroscopus sp. (P) Citharichthys sp. Not to scale.
206 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Hemirhabdorhynchus sp., Megalops cf. atlanticus) have not 

been recorded in the Calvert Formation or, more generally, in the 

whole Chesapeake Group. 

Fish remains are relatively uncommon in the Choptank 

Formation. The Choptank ichthyofauna, however, is similar to 

that of the Calvert Formation, being dominated by sturgeons 

(Acipenseridae gen. et sp. indet.), drums (Pogonias sp., Sciaenops sp.), scombrids (Acanthocybium cf. solandri, Thunnus sp.), 

and billfishes (Istiophorus cf. platypterus, Istiophoridae gen. et 

sp. indet.).

The fish assemblage of the St. Marys Formation seems to 

document a general cooling, as evidenced by the absence of thermophilous sea catfishes and wahoos and, more specifically, by 

the presence of Merluccius sp. and a member of the family Agonidae, a clade currently exclusive to cold temperate and polar 

waters of the North Pacific, Arctic Sea, northern North Atlantic, 

and North Sea and off the Patagonian region of the Southern 

Hemisphere (Kanayama, 1991). The remarkable cooling trend 

that occurred during deposition of the St. Marys Formation is 

also well documented in the otolith record. According to Müller 

(1999), the presence of otoliths belonging to the larger gadines 

Gadus and Melanogrammus in the St. Marys Formation resulted 

from a transatlantic migration of taxa typical of the North Sea 

Basin facilitated by a general drop in the temperatures in the 

North Atlantic. However, despite the abundance of cool-water 

taxa, remains of a certain number of subtropical and tropical 

fishes, including barracudas (Sphyraena sp.) and billfishes (Istiophoridae gen. et sp. indet.), are relatively common in the St. 

Marys Formation.

The Eastover ichthyofauna is scarcely diversified and is characterized by rare remains, among which drums (Pogonias sp., 

Sciaenops sp.) and billfishes (Istiophorus cf. platypterus, Makaira cf. nigricans, Istiophoridae gen. et sp. indet.) are dominant.

In summary, the mixture of thermophilous fishes with taxa 

of cold temperate and northern affinities characteristic of the assemblages of the Calvert, Choptank, St. Marys, and Eastover 

Formations could be indicative of the persistent presence of a 

well-defined climatic latitudinal zonation but also of wide seasonal temperature changes in a general condition similar to that 

characterizing the Chesapeake Bay area today (see Murdy et al., 

1997). 

The fish taxa recognized in the deposits of the Chesapeake 

Group show a clear general affinity for well-oxygenated muddy 

and sandy substrates. The assemblages are dominated primarily by shallow-water fishes characteristic of the inner shelf and 

secondarily by epipelagic taxa. Benthopelagic fishes characteristic of the outer shelf and upper slope are nearly absent in the 

Calvert Formation (exceptions are Brotula sp., Lopholatilus

ereborensis). The common occurrence of open-ocean taxa (billfishes, tunas, wahoos) in the Calvert, Choptank, and Eastover 

Formations suggests that the deposition took place in the distal 

portions of the inner shelf. Overall, the ichthyofaunal composition is consistent with the sedimentary and paleontological record, which evidences a general regressive trend from the Calvert 

to the St. Marys Formation, representing a gradual shallowing 

within the Salisbury Embayment (e.g., Gernant et al., 1971; 

Kidwell, 1984, 1988, 1989, 1997; Ward, 1992; Shideler, 1994; 

Ward and Andrews, 2008). 

The depth of deposition of the Calvert Formation is highly 

variable, with bed 11 having originated in the basinward parts 

of the shelf, recording the maximum depositional depth of the 

formation (Kidwell, 1989). Fish remains were collected in large 

part from beds 11, 12, and 14 of the Plum Point Member. These 

beds include tilefish remains belonging to the genus Lopholatilus, which can provide some indication of the minimum depth 

of the Calvert depositional environment. Extant species of the 

genus Lopholatilus range in depth between 80 and 540 m but 

usually occur at depths between 100 and 300 m near the 15°C 

isotherm (Dooley, 1978; Grimes et al., 1980, 1986); this range 

suggests that it is unlikely that the depositional depths of beds 

11, 12, and 14 were shallower than 80 m, as suggested by micropaleontological studies (Gibson, 1983).

There are no fish taxa that would suggest a precise estimate 

of the minimum depositional depth for the Choptank Formation. However, toadfishes of the genus Opsanus usually occur 

at depths less than 50 m (Manooch, 1984). Gernant (1970) suggested that depositional environments were less than 60 m deep 

for the formation as a whole and that the ocean was less than 

25 m deep for some beds. On the basis of foraminiferal assemblages, Gibson (1983) suggested that deposition of the Choptank 

Formation took place in open, shallow marine waters up to 30 

m deep.

The presence of brackish and freshwater (e.g., Amia cf. 

calva, Lepisosteus sp., Ictalurus countermani) taxa in the St. 

Marys Formation and the concurrent abundance of marine euryhaline and stenohaline species could be related to wide seasonal oscillations of salinity that possibly occurred within the 

Salisbury Embayment because of episodic increase of the freshwater supply, as well as to habitat heterogeneity. Because of the 

variety of the recognized ecological categories, the evaluation of 

the depositional depth of the St. Marys Formation is rather problematic; in any case, taking into consideration the presence of the 

benthopelagic genus Merluccius and of indeterminate remains 

belonging to the billfish family Istiophoridae, it seems reasonable 

to conclude that the average depositional depth for the St. Marys 

Formation would have been a few dozen meters. 

As far as the Eastover Formation is concerned, sedimentary 

features and macrobenthic assemblages (see Ward and Blackwelder, 1980) appear to be consistent with the ichthyofaunal 

composition and are indicative of marine depositional environments located in the inner shelf. 

As discussed above, the fish assemblages of the Chesapeake 

Group exhibit a modern aspect, with most of the taxa belonging 

to genera or higher categories that currently occur in the northwestern Atlantic, including the coasts of Maryland and Virginia. 

Two of the taxa recorded in the St. Marys Formation, however, 

are very interesting from a biogeographic point of view since 

today they are absent or have been artificially introduced in 
NUMBER 100 • 207

TABLE 3.3. Skeletal taxonomy of bony fishes from the Chesapeake Group. An X indicates a taxon is present in a particular formation 

or habitat; a question mark (?) indicates a taxon may be present; a dash (–) indicates taxon is not present.

Taxonomy Formation Habitat

 St. Shallow Open

Family Taxon Calvert Choptank Marys Eastover Freshwater Brackish marine marine

Acipenseridae Acipenseridae gen. et sp. indet. X X X X X X X –

Lepisosteidae Lepisosteus sp. – – X – X X – –

Amiidae Amia cf. A. calva – – X – X – – –

Clupeidae Alosa sp. – – X – X X X X

Ictaluridae Ictalurus sp. – – X – X X – –

Ariidae Ariopsis stauroforus X – – – X X X –

 Bagre sp. X – – – – X X –

Merlucciidae Merluccius sp. – – X – – – X X

Ophidiidae Brotula sp. X – – – – – X X

Batrachoididae Opsanus sp. – X – – – – X –

Lophiidae Lophius sp. X – – – – – X X

Belonidae Belone sp. – – X – – X X X

Triglidae Prionotus sp. X – X – – X X –

Agonidae Agonidae gen. et sp. indet. – – X – – X X –

Perciformes indet. “Paralbula” dorisiae X – X – ? ? ? ?

Moronidae Morone sp. X – – – X X X –

Serranidae Serranidae gen. et sp. indet. – X – – – X X X

Malacanthidae Lopholatilus ereborensis X – – – – – X X

Pomatomidae Pomatomus sp. X – X – – X X X

Rachycentridae Rachycentron sp. X – – – – X X X

Sparidae Lagodon sp. X – X – – X X –

 Stenotomus sp. – – X – – X X –

Sciaenidae Micropogonias sp. X – – – – X X –

 Pogonias sp. X X X X – X X –

 Sciaenops sp. X X X X – X X –

Labridae Tautoga sp. X – X X – X X –

Uranoscopidae Astroscopus countermani – – X – – X X –

Sphyraenidae Sphyraena sp. X – X X – X X X

Scombridae Acanthocybium cf. solandri X X – – – – X X

 Sarda sp. X – – – – X X X

 Thunnus sp. X X – – – X X X

Istiophoridae Istiophorus cf. platypterus X X – X – – X X

 Makaira cf. nigricans X – – X – – X X

 Istiophoridae gen. et sp. indet. X X X X – – X X

Paralichthyidae Paralichthys sp. – – – X – X X –

Diodontidae Chilomycterus sp. X – – X – – X –

Molidae Mola pileata – X – – – – X X

 Ranzania grahami X – – – – – X X

 Ranzania tenneyorum X – – – – – X X
208 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

TABLE 3.4. Otolith taxonomy of bony fishes from the Chesapeake Group, based primarily on Müller (1999), except for Sciaenops, 

which is based on Fitch (n.d.). An X indicates a taxon was present in a particular formation; a dash (–) means taxon was not present.

Taxonomy Formation

Family Taxon Calvert Choptank St. Marys Eastover

Congridae Conger sp. X – – –

Brevoortia aff. B. tyrannus (Latrobe, 1802) – – X –

Ariidae Ariopsis aff. A. felis (Linnaeus, 1758) – X – –

 Ariopsis stauroforus (Lynn & Melland, 1939) X – – –

Argentinidae Argentina sp. – – X –

Myctophidae Diaphus sp. X – – –

Gadidae Phycis spp. X – – –

 Urophycis aff. U. tenuis (Mitchill, 1815) – – X –

 “gen. aff. Urophycis” sp. – – X –

 Gadiculus argenteus (Guichenot, 1850) – – X –

 Gadiculus labiatus (Schubert, 1905) X – X –

 Gadiculus aff. benedeni (Leriche, 1926) – – – X

 Trisopterus sculptus (Koken, 1884) X X X –

 Gadus marylandicus Müller, 1999 – – X –

 Melanogrammus antecedens Müller, 1999 – – X –

 Micromesistius cognatus (Koken, 1891) X X X –

Merlucciidae Merluccius albidus (Mitchill, 1817) X – X –

 Merluccius sp. X – – –

Ophidiidae Brotula sp. X – – –

 Lepophidium aff. cervinum (Goode & Bean, 1885) – – – X

 Lepophidium elongatum Müller, 1999 – – X –

 Chilara aff. C. taylori (Girard, 1858) – – – X

 Otophidium nolfi Müller, 1999 – – X –

Triglidae Prionotus spp. X X X –

 “genus Triglidarum” sp. X – – –

Chandidae “genus Chandidarum” sp. – – X –

Serranidae “genus Serranidarum” spp. – – X X

 Epinephelus sp. – – X –

 “gen. aff. Epinephelus” sp. X – – –

Haemulidae “genus Pomadasyidarum” sp. – – – X

Carangidae “genus Carangidarum” sp. – – X –

Sparidae Archosargus sp. – – X –

 Lagodon aff. L. rhomboides (Linnaeus, 1766) X – X –

 “genus Sparidarum” sp. – – X –

Sciaenidae Umbrina sp. – – X –

 Pogonias sp. – – X –

 Sciaenops sp. X – X –

 Leiostomus compressus Müller, 1999 X – – –

 Leiostomus crassior Müller, 1999 – – X –
NUMBER 100 • 209

the northwestern Atlantic waters. One of these is the needlefish 

Belone that is today restricted to the eastern Atlantic and the 

Mediterranean Sea; the occurrence of Belone in the St. Marys 

Formation might be in some ways related to the same transatlantic migration that resulted in the arrival of the gadine Gadus and 

Melanogrammus in the northwestern Atlantic waters. 

Lundberg and Luckenbill (2012) discussed the biogeographic significance of the peculiar distribution of the Miocene 

catfish Ictalurus countermani, which is extralimital to the known 

range of fossil and extant channel catfish species (I. punctatus

group) and, more generally, the entire genus Ictalurus; the current presence of at least two Ictalurus species along the Atlantic 

coasts of the United States is the result of transplantation that 

started in the last decades of nineteenth century (Lundberg and 

Luckenbill, 2012).

ACKNOWLEDGMENTS

This review chapter would not have been possible without 

the efforts of many professional and avocational collectors. They 

include Aaron A. Alford, Jullie Allinson, E. Andres, Betty Ashby, 

Cooper Ashby, Wallace L. Ashby, L. Bivens, Sidney F. Blake, 

Warren C. Blow, David J. Bohaska, Paula Bohaska, Cynthia 

Bonora, Francis P. Buehler, David Cammack, Russell Channell, 

Karl Coch, R. Lee Collins, Joseph Coscia, William Counterman, 

B. Daugherty, a Mr. Drew, William F. Douglas, Ralph E. Eshelman, C. Faust, Helen B. Fink, George C. Fonger, William F. Foshag, Richard Frye, Stephen J. Godfrey, Michael D. Gottfried, 

Frederick Von H. Grady, Fredda Granada, Jim Gscheidle, Stephen Hale, Don Hanson, Robert M. Hazen, Gloria Hicks, Hammond Hobbs, William Holliman, Jean Hooper, Roger Horman, 

Becky Hyne, Walt Johns, James A. Kaltenbach, Joyce Kauffman, 

Remington Kellogg, Peter G. Kimmel, William Kirwan, LeiLani 

Kubik, Nick Kubik, Suzanne B. Lepple, Arnold E. Lewis, William G. Lynn, Terri Mackabee, Peter McCrery, Joe Miller, Paul 

R. Murdoch, John R. Nance, Scott Nieman, F. O’Neil, H. O’Neil, 

Jeff O’Neil, Edward Otte, Billy Palmer, J. Patton, Catherine A. 

Phalen, Pam Platt, David Rhea, Norman L. Riker, Betty “Sandy” 

Roberts, H. Scarupa, Robert Schmidt, Lois M. Schoonover, 

Leonard P. Schultz, John Seyfried, Walter Simonson, Margaret 

C. Smith, the Smithsonian Research Expedition Group, Andrea 

A. Stamper, William C. Strobell, Gladwyn “Tut” Sullivan, Jane 

Thayer, Frederick W. True, Titus Ulke, Paula Wagner, Lauck 

W. Ward, Robert E. Weems, Michael Welzenbach, Scott Werts, 

James Westgate, Frank C. Whitmore Jr., Kristina W. Wibbenmeyer, Gayle A. Wichers, and Earl Windsor. Our hope is that this 

publication will encourage future generations of collectors and 

those who publish on their finds.

We thank James C. Tyler (USNM) and Walter Landini (Dipartimento di Scienze della Terra, Università di Pisa, Pisa) for 

useful suggestions and a critical review of an early draft of the 

 Genyonemus calvertensis Müller, 1999 X – – –

 “gen. aff. Genyonemus” pertenuis Müller, 1999 X – – –

 Menticirrhus aff. M. litoralis (Holbrook, 1855) – – X –

 Menticirrhus sp. – – X –

 “gen. aff. Pachyurus” atavus Müller, 1999 X – – –

 “gen. aff. Pachyurus” breviformus Müller, 1999 – – X –

 Cynoscion senior Müller, 1999 X – X X

Uranoscopidae Astroscopus sp. – – X X

Ammodytidae Ammodytes aff. hexapterus Pallas, 1814 – – X X

 Ammodytes sp. – – X –

 “genus Percoideorum” subcircularis Müller, 1999 X – – –

 “genus Percoideorum” sp. – – X –

Pleuronectidae “genus Pleuronectidarum” sp. – – X –

Paralichthyidae Citharichthys spp. X – X X

Cynoglossidae Symphurus sp. X – – –

 “genus Pleuronectiformorum” spp. – – X –

TABLE 3.4. (Continued)

Taxonomy Formation

Family Taxon Calvert Choptank St. Marys Eastover
210 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

text and Federica Giudice (Torino) for technical help. The drawings of the extant fishes were superbly rendered by Tim Scheirer 

(CMM). We thank John Nance (CMM), David J. Bohaska, Jeff 

Clayton, and G. David Johnson (USNM) for access to fossil and 

extant specimens in their care. The late John Pojeta (USNM) 

welcomed us to use his lab to whiten most of the fossils illustrated herein. Jason Osborne (Howard Hughes Medical Institute, Janelia Research Campus) generously provided access to a 

microscope that was used to photograph the otoliths in Figure 

3.19. David J. Bohaska and Nicholas D. Pyenson are thanked for 

constructive advice on improving the manuscript.

Research by SJG was made possible with funding from the 

citizens of Calvert County, the Calvert County Board of County 

Commissioners, and the Clarissa and Lincoln Dryden Endowment for Paleontology at the Calvert Marine Museum. Visits to 

Solomons and Washington by GC in 2011 and 2012 were supported by the Clarissa and Lincoln Dryden Endowment for Paleontology and a Smithsonian Short-term Fellowship. Research 

by GC was supported by grants (ex-60% 2015–2017) from the 

Università degli Studi di Torino.

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Clark, G. B. Shattuck, and W. D. Hall, pp. xxxii–cxxxvii. Baltimore: Johns 

Hopkins Press.

Shideler, G. L. 1994. Sedimentological Indicators of Paleoenvironments and Siliciclastic Stratigraphic Sequences in Some Miocene Deposits of the Calvert 

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Smith, B. 1909. Note on the Miocene Drum Fish – Pogonias multidentatus Cope. 

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ABSTRACT. Crocodilian remains from the Calvert Cliffs are referable to the tomistomine genus Thecachampsa. The closest living relative is Tomistoma schlegelii, the false 

gharial of Southeast Asia. Two species are present: Thecachampsa sericodon Cope and 

Thecachampsa antiquus (Leidy). The type specimen of the Florida tomistomine Gavialosuchus americanus is referable to T. sericodon, and some other specimens previously 

referred to G. americanus belong to T. antiquus. These tomistomine species are found 

in shallow marine coastal deposits, indicating that they habitually inhabited coastal marine waters as do the modern saltwater crocodile (Crocodylus porosus) and American 

crocodile (C. acutus). Tomistomine remains are fairly common in the Miocene coastal 

marine deposits of North America, South America, Europe, Africa, and southern Asia. 

By the Pliocene, however, tomistomines had become restricted to Southeast Asia. Today, 

Tomistoma schlegelii, the sole surviving tomistomine species, is found only in freshwater. 

A few crocodilian osteoderms from the Calvert Formation in Delaware do not pertain to 

Thecachampsa. They may pertain to Alligator olseni White and indicate that a strictly 

freshwater crocodilian was also present during Calvert time. Its remains should eventually be found along the Calvert Cliffs.

INTRODUCTION AND TAXONOMIC HISTORY

Joseph Leidy (1851a, 1852) described the first Miocene crocodilian from the Atlantic Coastal Plain and named it “Crocodilus antiquus.” It was based upon two teeth, 

two vertebrae, a rib fragment, and an ungual phalanx collected from bluffs along the 

Potomac River at Stratford Hall Plantation, the ancestral home of the Lee family of 

Virginia (Figure 4.1). These bluffs expose vertebrate-bearing Miocene strata referable to 

4 Crocodilians of the 

Calvert Cliffs

Robert E. Weems

Research Associate, Department of Paleontology, 

Calvert Marine Museum, Solomons, Maryland 

20688, USA.

Correspondence: rweems4@gmail.com

Received 1 May 2015; accepted 25 August 2017.
214 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Ν

Calve

rt

Clis

Chesapeake

Beach

Chesapeake

Ranch Estates

Governors Run

Dares Beach

Wakeeld

Stratford

Popes Creek

Thomas

Residence

N38 ̊ 30’

W77 ̊

1

2

3

4

W E S T M O R E L A N D

K I N G

G E O R G E

FIGURE 4.1. Map of a portion of northeastern Virginia and adjacent Maryland, showing locations where the skulls and postcranial remains of Miocene tomistomine crocodilians described herein were mostly found. (1) Stratford Hall and Wakefield (George Washington 

Birthplace National Monument), located in Westmoreland County, Virginia, along the south bank of the Potomac River. The holotype of 

“Crocodilus” antiquus is from near Stratford Hall. (2) The Popes Creek bluffs, located in Charles County, Maryland, along the east bank 

of the Potomac River. (3) The Thomas residence, located in Charles County, Maryland, near the west bank of the Patuxent River. (4) The 

Calvert Cliffs along the western shore of the Chesapeake Bay in Calvert County, Maryland.
NUMBER 100 • 215

four formations: the upper part of the Calvert Formation and the 

Choptank Formation (middle Miocene) and also the St. Marys 

and Eastover Formations (upper Miocene; Figure 4.2A). Leidy 

did not specify a specific horizon from which his specimen came, 

but he did state that it was found in association with “Pecten 

jeffersonius.” This name cannot represent a valid modern identification because today that species name is affixed to a Pliocene 

species (Chesapecten jeffersonius) that does not occur in any of 

the Miocene and Pleistocene units exposed at Stratford. However, it does serve to associate Leidy’s crocodile remains with 

some other species of Chesapecten, shells of which are abundant in the Stratford area in the Choptank Formation but not 

in the Calvert, St. Marys, or Eastover Formations. Therefore, 

the type specimen almost certainly was found in the Choptank 

Formation.

In 1867, Edward Drinker Cope described two additional 

species of Miocene crocodilians from the Maryland Coastal Plain 

and assigned them to a new genus, Thecachampsa. He based 

one species, T. contusor, on a single, short, conical tooth (Figure 

4.2B) from southern Maryland. The other species, T. sericodon, 

he based upon elongate, curved teeth of cylindrical form with 

long, delicate cutting edges (Figure 4.2E) that came from Maryland and also New Jersey (Cope, 1869b). Cope (1869a,b) also 

described a third species that he named Thecachampsa sicaria

(Figure 4.2D). 

This last species, also from the Miocene of Maryland, was 

based on a posterior maxillary fragment with teeth that had 

greatly compressed crowns and very long crenulated cutting 

edges. In the same year, Othniel C. Marsh (1869) introduced a 

name for a fourth new species of Thecachampsa, T. squankensis, 

on the basis of teeth that came from either the Eocene (Cope, 

1882) or the Miocene (Steel, 1973) of New Jersey. 

In addition to these Miocene species, Cope also named 

or assigned several Eocene species to Thecachampsa. In 1869, 

he referred “Crocodilus” fastigiatus (Leidy, 1851b) to Thecachampsa, and in 1871 he also referred “Crocodilus” rugosus

(Emmons, 1858) to Thecachampsa. In 1872, he described Thecachampsa serratus from the Eocene of New Jersey, possibly the 

Shark River Formation (Hay, 1930:154). All of these species are 

of very doubtful validity (i.e., they are nomena dubia), and none 

of them has any direct bearing on the Miocene species assigned 

to Thecachampsa. 

Of the five nominal Miocene species placed within the genus 

Thecachampsa prior to 1870, three proved to be invalid. Several years after he described T. contusor, Cope (1871a:64) concluded that the distinctive surface texture characteristics of the 

type specimen tooth for this species came from “attrition and 

partial destruction of the enamel.” He therefore synonymized 

this species with “Crocodilus” antiquus, with which it agreed in 

all other characteristics, as a new combination, Thecachampsa 

antiqua. This made Thecachampsa contusor a junior synonym 

of “Crocodilus” antiquus, and later authors have concurred 

with this designation (for example, Steel, 1973). In the case of 

Thecachampsa squankensis, Marsh published this name in anticipation of describing it as a new species. He never illustrated, described, or designated type material for this species, however, so 

T. squankensis is a name without any type specimen or description and thus is a nomen vanum. Two species of Thecachampsa

(T. sericodon and T. sicaria) were considered to be different until 

Myrick (2001) noted that the two different tooth morphologies 

characterizing these putative species were present in teeth found 

in close association with a single skull (USNM 25243). The 

obvious conclusion was that these two types of teeth represent 

only one species of heterodont crocodilian, for which the name 

Thecachampsa sericodon has priority. Myrick, however, also 

TABLE 4.1. Differences and similarities among species of Thecachampsa.

Character Thecachampsa carolinensis Thecachampsa antiquus Thecachampsa sericodon

Snout proportions Relatively wide Narrow Very narrow

Premaxillaries Short Elongate Elongate

Nasals Narrow Very narrow Very narrow

Dentition Homodont Homodont Heterodont

Carinas on teeth Weak to absent Weak to absent Usually prominent

Tooth function Crushing Crushing Piercing (anterior), shearing 

 (posterior)

Tooth spacing Close Wide Wide

Premaxillaries indent 

 maxillaries ventrally Slightly Deeply Deeply

Number of teeth in dentary 16 17 18

Femur Moderately robust Robust Moderately robust

Ilium Iliac blade long Iliac blade long Iliac blade short
216 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

2 cm

B

A

C D E

PERIOD EPOCH AGE STRATIGRAPHIC UNIT

Eastover Formation

St. Marys Formation

Choptank Formation

Calvert Formation

20 Ma

15 Ma

10 Ma

Windmill 

Point Member

Little Cove

Point Member

Plum Point

 Member

Fairhaven

 Member

NEOGENE

(part)

Miocene

upper middle lower

A

A

A

B

B

B

C

C

D

D

+

+

+

+ *

*

*

*

*

A

B

A

B

Thecachampsa

antiquus

Thecachampsa

sericodon
NUMBER 100 • 217

concluded that T. antiquus was synonymous with T. sericodon

and T. sicaria because he noticed that some of the teeth in the 

middle region of the tooth row in T. sericodon were quite similar 

to anterior teeth of T. antiquus. This observation is true, but in 

the larger sample available here for study, it is a problem only 

when trying to identify individual teeth, which may be identifiable to Thecachampsa sp. only if they come from the middle region of the tooth row. For anterior and posterior teeth, especially 

for fairly complete individual dentitions, there is no ambiguity in 

separating these two taxa. The heterodont dentition of T. sericodon, with long and recurved anterior teeth (Figure 4.2E) and 

bladelike posterior teeth (Figure 4.2D), is distinctive and quite 

different from the homodont dentition of T. antiquus, which 

consists of shorter and blunter teeth (Figure 4.2B,C). Although 

the type material of both species is sparse, their differences are 

distinctive and diagnostic. Unfortunately, the teeth of the type 

specimen of T. antiquus are missing (Spamer et al., 1995:111) 

and probably lost, but the two most complete holotype teeth 

were illustrated by Leidy (1852) and later by Case (1904). The 

holotype tooth of the junior synonym of T. antiquus, T. contusor, has also been illustrated (Case, 1904), so much of the range 

of tooth morphology of T. antiquus is documented (Figure 4.2). 

These two Miocene species of Thecachampsa clearly had different dietary preferences and feeding strategies (Massare, 1987), 

T. sericodon being adapted to snagging and slicing food (probably fish) and T. antiquus being adapted to crushing food (perhaps turtles). 

The material described here provides a large number of 

additional characteristics that further serve to distinguish these 

two species and also serve to much better characterize the genus 

Thecachampsa relative to other tomistomine crocodilians (Table 

4.1). The type material of these two species would not be considered sufficient to erect a new species today, but both species were 

described long before modern standards became established, 

both species have been in the literature for more than 140 years, 

and the genus Thecachampsa was validly established by Cope, 

as discussed below. For all of these reasons, especially with the 

addition of much more complete material discussed and illustrated here, a meaningfully complete diagnosis is now possible 

both for the genus Thecachampsa and for its two constituent 

Miocene species.

The proper taxonomic placement of the genus Thecachampsa among the Crocodylia long remained enigmatic because the type material was so fragmentary. The type material 

included distinctive teeth, but a meaningful diagnosis of the 

genus Thecachampsa and its placement among the Crocodylia 

could not be made from such sparse remains. In 1870, Cope 

considered Thecachampsa to be a gavial and noted that species of Thecachampsa had been found in Europe. Yet despite 

this prescient analysis, Cope later (1882) synonymized Thecachampsa with “Crocodilus” (i.e., Crocodylus). This synonymy 

of Thecachampsa with Crocodylus has been accepted by some 

subsequent workers (Hay, 1902, 1930; Steel, 1973) and rejected 

by others (Toula and Kail, 1885; Case, 1904). More recently, 

Myrick (2001) chose to revive the name Thecachampsa and correctly associated it with the tomistomine crocodilians.

When Cope (1867) proposed the name Thecachampsa, he 

described two species to go in it (T. contusor and T. sericodon) 

but neglected to designate either of these species as the type species of the genus. Cope (1882:984) later corrected this by noting 

parenthetically that the type of Thecachampsa was T. sericodon. 

Much later, Hay (1902:512) designated T. contusor as the type 

species of Thecachampsa without explanation, perhaps on the 

basis of page priority, which is not supported by the International 

Code of Zoological Nomenclature’s Principle of the First Reviser 

(International Commission on Zoological Nomenclature, 1999: 

article 24). The International Code of Zoological Nomenclature 

(article 69.1) explicitly states, 

If an author established a nominal genus or subgenus 

but did not fix its type species, the first author who 

subsequently designates one of the originally included 

nominal species validly designates the type species 

of that nominal genus or subgenus (type by subsequent designation), and no later designation is valid. 

Thus, Cope’s designation of T. sericodon as the type species 

of Thecachampsa has priority and is binding.

Although Cope suppressed the name Thecachampsa in 1882, 

synonymizing it with Crocodylus, the fact that he bothered at the 

same time to designate T. sericodon as the type species suggests 

that perhaps he held out hope that the genus eventually would 

prove to be valid. The skull discussed by Myrick (2001) fulfilled 

that hope by showing that “sericodon” teeth are distinctive and 

can be uniquely associated with a species of Calvert crocodilian 

FIGURE 4.2. (Facing page) (A) Miocene stratigraphic units present in the coastal plain of Virginia and Maryland. Specimens of Thecachampsa 

sericodon (crosses) have come from the upper Plum Point Member of the Calvert Formation and the lower part of the Choptank Formation. 

Specimens of Thecachampsa antiquus (asterisks) have come from the Calvert, Choptank, and St. Marys Formations. Nearly all of these units 

were deposited in shallow to mid-shelf marine environments. These units range in age from about 19 to 8 mya. (B) Holotype posterior tooth of 

Thecachampsa contusor (junior synonym of Thecachampsa antiquus), adapted from Case (1904). (C) Holotype anterior teeth of Thecachampsa 

antiquus, adapted from Case (1904). (D) Holotype posterior tooth of Thecachampsa sicarius (junior synonym of Thecachampsa sericodon), 

adapted from Cope (1871b). (E) Holotype anterior tooth of Thecachampsa sericodon, adapted from Cope (1871b).
218 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

that clearly does not belong to Crocodylus. Because of this, Thecachampsa again became a valid genus with a valid type species.

Myrick (2001) synonymized “Crocodilus” antiquus with 

Thecachampsa sericodon, but a number of specimens discussed 

here, not considered in his analysis, do not support this conclusion. During the 160 years since Leidy described “Crocodilus” antiquus, far more complete remains of both that species 

and Thecachampsa sericodon have been collected in Virginia 

and Maryland and donated to the collections of the National 

Museum of Natural History and the Calvert Marine Museum. 

Another important specimen, discussed and illustrated here, belongs to Stratford Hall Plantation and is kept there. This material 

shows that although “Crocodilus” antiquus is similar and rather 

closely related to Thecachampsa sericodon, it is not identical to 

that species and therefore represents a distinct second species 

within the genus Thecachampsa.

The specimens on which the present analysis is based come 

from a number of famous vertebrate fossil localities. They are (1) 

the cliffs along the south shore of the Potomac River estuary in 

Westmoreland County, from near Wakefield (George Washington 

Birthplace National Monument) to Stratford Hall Plantation; (2) 

the Popes Creek bluffs along the Potomac River estuary in Charles 

County, Maryland; (3) bluffs along and marl pits near the Patuxent River estuary in Charles County, Maryland; and (4) the Calvert 

Cliffs along the western shore of the Chesapeake Bay in Calvert 

County, Maryland (Figure 4.1). This area encompasses the geographic region and geologic strata from which the type material of 

both Thecachampsa sericodon and “Crocodilus” antiquus came.

Museum Abbreviations

AMNH American Museum of Natural History, fossil amFARB phibian, reptile, and bird collection, New York, New 

York, USA 

ANSP Academy of Natural Sciences of Drexel University, 

Philadelphia, Pennsylvania, USA

CMM Calvert Marine Museum, Solomons, Maryland, USA 

MCZ Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA 

STHA Stratford Hall paleontological collection, Stratford, 

Virginia, USA 

UF University of Florida, Florida Museum of Natural 

History, Gainesville, Florida, USA

USNM National Museum of Natural History (formerly U.S. 

National Museum), Smithsonian Institution, Washington, D.C., USA

 SYSTEMATIC PALEONTOLOGY

Reptilia Laurent, 1768

Archosauria Cope, 1869a

Crocodylia Gmelin, 1789

Gavialidae Adams, Baikie, and Barron, 1854

Tomistominae KÄlin, 1955

Thecachampsa Cope, 1867

Type Species. Thecachampsa sericodon.

Crocodile – Thecachampsa – Gavialidae

Thecachampsa sericodon Cope, 1867

Thecachampsa sericodon Cope, 1867:143 (original description).

Thecachampsa sicaria Cope, 1869b:8 (original description).

Thecachampsa sicaria Cope, 1869a:63, pl. v, fig. 6.

Thecachampsa sericodon Cope, 1867: Cope, 1869a:64–65, pl. v, figs. 7, 8.

Thecachampsa sericodon Cope, 1867: Cope, 1870:90–91.

Thecachampsa sicaria Cope, 1869: Cope, 1870:90–91.

Crocodylus sericodon (Cope, 1869): Cope, 1882:984.

Crocodylus sicaria (Cope, 1869): Cope, 1882:984. 

Crocodylus sericodon (Cope, 1869): Hay, 1902:513.

Crocodylus sicarius (Cope, 1869): Hay, 1902:513.

Tomistoma americana Sellards, 1915:135–138, figs. 1–2.

Crocodylus sericodon (Cope, 1869): Steel, 1973:65.

Crocodylus sicarius (Cope, 1869): Steel, 1973:65.

Megalodelphis magnidens Kellogg, 1944 (holotype only):445, pl. 2, fig. 2; 

pl. 3, fig. 2.

Gavialosuchus americanus (Sellards, 1915): Morgan, 1986:414–415, fig. 1.

Thecachampsa antiqua (Leidy, 1852) (partem): Myrick, 2001:224, fig. 5.

Holotype. Three anterior teeth, ANSP 9443-9445, possibly (but not certainly) from a single individual (Spamer et al., 

1995:150). 

Diagnosis. Medium-sized crocodilian with elongate, 

curved teeth of cylindrical form that bear long, delicate cutting 

edges (carinas).

Type Locality and Horizon. Found near the residence of James T. Thomas, near the Patuxent River, Charles 

County, Maryland, USA, in sediments of the upper Plum Point 

Member (Plum Point D) of the Calvert Formation (middle Miocene; Weems and Edwards, 2007).
NUMBER 100 • 219

Previously Referred Material. (1) AMNH 1321 

(now AMNH FARB 1321), tooth and right maxillary fragment, 

holotype of Thecachampsa sicarius, from Patuxent River, Maryland (Cope, 1869b; a cast of the maxillary fragment is at the 

USNM, USNM 26186). (2) USNM 25243, nearly complete skull 

with associated scattered teeth, bones, and armor collected by 

Albert Myrick in 1968 along bluffs near Wakefield Plantation, 

Westmoreland County, Virginia. Plum Point Member (Plum 

100 mm

4 inches

FIGURE 4.3. Photograph (left) and restoration (right) of the Wakefield skull of Thecachampsa sericodon Cope (USNM 25243) in dorsal view.
220 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Point B), Calvert Formation (middle Miocene). Skull discussed 

and dorsal view illustrated in Myrick (2001).

Newly Referred Material. (1) STHA1, a large 

portion of anterior skull including premaxillae, maxillae, nasals, 

frontals, prefrontals, lacrimals, and portions of the parietals, 

postorbitals, and right quadrate; lower jaws, including most of 

the dentaries, portions of the splenials, surangulars, angulars, 

and the right articular; 22 isolated teeth plus 1 in place in the 

right dentary and 3 in the maxillaries; 22 presacral vertebrae, 

both sacral vertebrae, and 3 caudal vertebrae; both ilia, both ischia, both pubes, 1 complete and 1 partial femur, both tibiae and 

fibulae, left astragalus, left calcaneum; numerous rib fragments; 

100 mm

4 inches

FIGURE 4.4. Photograph (left) and restoration (right) of the Wakefield skull of Thecachampsa sericodon Cope (USNM 25243) in ventral view.
NUMBER 100 • 221

100 mm

4 inches

FIGURE 4.5. The skull of the Stratford Hall Plantation specimen of Thecachampsa sericodon Cope (STHA1). (A) Skull in 

dorsal view, (B) skull in ventral view, and (C) lower jaws in dorsal view.
222 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

numerous whole and fragmentary pieces of dermal armor. Collected by Jon Bachman, Dianne Bachman, Su Weems, and Robert 

Weems in 1997 along bluffs at Stratford Hall Plantation, Westmoreland County, Virginia. Upper Plum Point Member (Plum 

Point D), Calvert Formation (middle Miocene). (2) USNM 8816, 

anterior rostrum, type specimen of Tomistoma americana, collected by Anton Schneider, Polk County, Florida, Bone Valley 

Member of Peace River Formation (middle or upper Miocene). 

(3) MCZ 17883, partial rostrum and portions of right and left 

mandibles, including symphysis, type specimen of Megalodelphis 

magnidens, Mulberry, Polk County Florida, Bone Valley Member of Peace River Formation (middle or upper Miocene). (4) 

CMM-V-2074, posterior tooth, found between Scientists Cliffs 

and Parkers Creek, Calvert County, Calvert Formation, Plum 

Point Member (Plum Point C, Shattuck zone 12) (Shattuck, 

1904). (5) CMM-V-0004, anterior tooth, Harpers’ Cliffs just 

north of Matoaka near St. Leonard, Calvert County, Choptank 

Formation (Choptank A, Shattuck zone 17). (6) CMM-V-1701, 

anterior tooth, south of Parkers Creek, Calvert Formation, Plum 

Point Member (Plum Point D, Shattuck zone 14). (7) CMM-V3548, anterior tooth, western shore of Chesapeake Bay, Calvert 

County, Calvert Formation, Plum Point Member (Plum Point D, 

Shattuck zone 14).

Expanded Diagnosis. Medium-size crocodilian, about 

4 m [13 ft] in total adult body length (assuming body proportions similar to those of Tomistoma schlegelii). Adult skull length 

approximately 70 cm [2 ft]. Rostrum elongate, narrow anteriorly. Nasals widely separated from the narial opening in external 

view by the inward and backward extension of the premaxillaries; outer borders of maxillaries extend much farther forward on 

snout than nasals. Extent of the premaxillaries forward of the 

maxillaries relatively greater than in other well-known tomistomine species, except for “Tomistoma” calaritanus. Prefrontals 

much larger than in “T.” calaritanus. Dentition heterodont; anterior teeth elongate, conical, recurved, and pointed; posterior 

teeth low crowned, laterally compressed, upright, and bladelike. 

Dentaries and splenials fused along an elongate symphysis over 

a distance of about 40% of the length of the lower jaws. Five 

premaxillary teeth, 14 maxillary teeth, and 18 dentary teeth, 

all with prominent carinas. Premaxillary and maxillary teeth 

are separated both by a distinct diastema and by a pronounced 

lateral crocodyloid notch. First premaxillary teeth robust and 

directed forward. Fifth maxillary teeth enlarged and maxilla 

swollen around its socket. In ventral view, premaxillaries deeply 

indent maxillaries along the midline of the mouth back to the 

level of the front of the third maxillary teeth. Pterygoid flanges 

knob-like and flared strongly outward laterally. Dermal armor 

mostly unkeeled but some with low, elongate rounded keels.

Horizon, Age, and Depositional Setting. The 

type specimen of T. sericodon came from the Calvert Formation, 

and the type specimen of T. sicarius probably also came from 

the same unit. The two fairly complete specimens discussed here 

were recovered from the middle Miocene Plum Point Member 

(Plum Point B and D) of the Calvert Formation (Figure 4.2A). 

The Calvert Formation, like most of the other Neogene stratigraphic units in the Virginia and Maryland Coastal Plain, was 

deposited in a low-energy, shallow to mid-shelf marine environment (Mixon et al., 1989). In the cliffs at and between Wakefield 

and Stratford Hall, the Plum Point Member of the Calvert Formation has yielded numerous fossil specimens of whales, porpoises, sea turtles, sharks, rays, and marine bony fishes, as well 

as occasional remains of sea birds, dugongs, and seals (mostly 

deposited at the USNM and the CMM). Remains of land mammals are very rare, but fossil wood and seeds of cherry, walnut, 

and pine, belonging to species described by Berry (1934, 1936), 

are moderately common in these strata. The plant remains indicate either that land was not far to the west at the time these 

strata were deposited or else that a strong river current then was 

spreading plant remains far out onto the Atlantic continental 

shelf.

Discussion. The nearly complete Wakefield skull allows 

a full characterization of the external cranial elements of T. sericodon (Figures 4.3, 4.4). The Stratford specimen (Figure 4.5) 

preserves the anterior part of the skull and most of the lower 

jaws (Figures 4.6, 4.7). The distal end of the right quadrate is 

the only remnant of the posterior cranium of the Stratford specimen that was recovered (Figure 4.6). The portions of the skull 

preserved in both specimens are very similar, and the few teeth 

remaining in the jaws (as well as the numerous teeth found lying 

loose among the bones of both skeletons) demonstrate that this 

animal was markedly heterodont, with piercing teeth in the anterior part of the jaws and cutting teeth in the posterior part (Massare, 1987). The mid-jaw and anterior teeth (Figure 4.8D2,D3) 

are conical, recurved, and elongate; these kinds of teeth constitute the type material of Thecachampsa sericodon. In contrast, 

the posterior teeth (Figure 4.8D1) are low crowned, laterally 

compressed, and possess a long shearing blade; these kinds of 

teeth constitute the type material of Thecachampsa sicaria. Although such heterodonty is unusual among crocodilians, it is not 

unique. For example, the only tooth-bearing skull of the living 

tomistomine species Tomistoma schlegelii in the USNM collections (USNM 52972) shows a similar, although less strongly developed, heterodonty.

The most striking features of these two skulls are their elongate, narrow snouts and the elongate premaxillaries that have 

carried the narial opening far forward beyond the anterior end 

of the nasals as seen in dorsal view (Figure 4.3). These characteristics are also typical of Gavialosuchus eggenburgensis (Toula 

and Kail, 1885) and two tomistomine crocodilians previously 

assigned to Tomistoma (Capellini, 1890; Telles Antunes, 1961). 

In ventral view (Figure 4.4), the snout contains five premaxillary teeth and 14 maxillary teeth on each side. A distinct diastema developed between the premaxillary and maxillary teeth, 

and the snout is perceptibly constricted in this same region. 

The fifth maxillary teeth are enlarged in comparison to nearby 

teeth. The lower jaws are fused along a symphysis that extends 

40% of the length of each jaw (Figures 4.5, 4.7) and includes 

the first 11 teeth; each jaw ramus contains 18 teeth. Figure 4.7 
NUMBER 100 • 223

shows the relative contributions of the dentary, angular, and 

surangular in lateral view.

No elements certainly referable to the shoulder girdle or front 

limbs are known, but many of the rear limb elements have been 

recovered. The right ilium (Figure 4.8B) was nearly complete and 

can be compared to the same element in Thecachampsa carolinensis, Crocodylus, and Alligator (Figure 4.9). It is not especially 

close in conformation to any of these forms. In the size of its acetabulum, it is closer to Alligator and Crocodylus; in the shape 

of its posterior border, it is closer to Thecachampsa carolinensis

and Crocodylus; in the shape of its anterior border, it is closer 

to Thecachampsa carolinensis and Alligator. The femur is rather 

slender but normally proportioned (Figure 4.8C). The numerous 

osteoderms recovered with both specimens indicate that it had an 

100 mm

4 inches

FIGURE 4.6. Restoration of the skull of the Stratford Hall Plantation specimen of Thecachampsa sericodon Cope (STHA1) in dorsal 

(left) and ventral (right) views.
224 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

100 mm

4 inches

FIGURE 4.7. Restoration of the lower jaws of the Stratford Hall Plantation specimen of Thecachampsa sericodon Cope (STHA1) in 

dorsal view (left) and external posterolateral view (right).
NUMBER 100 • 225

extensive subdermal armor, with some osteoderms suturally interconnected and others smooth-bordered and floating free within 

the integument. Most osteoderms are unkeeled (Figure 4.8E1), but 

a few bear low, broad, rounded keels ranging from well developed 

to barely discernable (Figure 4.8E2).

Thecachampsa antiquus (Leidy, 1851)

Crocodilus antiquus, Leidy 1851a:307 (original unillustrated reference).

Crocodilus antiquus Leidy, 1852:135–138, pl. xvi (original description).

Thecachampsa contusor Cope, 1867:143.

Thecachampsa antiqua (Leidy, 1852): Cope, 1869a:64 (synonymized with 

T. contusor).

Crocodylus antiquus Leidy, 1852: Cope, 1882:983, 986.

Crocodylus antiquus Leidy, 1852: Hay, 1902:512.

Gavialosuchus americanus (Sellards, 1915): Mook, 1921a:33–41, pls. V–VII.

Gavialosuchus americanus (Sellards, 1915): Auffenberg, 1954:185–209, fig. 2.

Crocodylus antiquus Leidy, 1852: Steel, 1973:65.

Crocodylus contusor Cope, 1867: Steel, 1973:65.

Thecachampsa antiqua (Leidy, 1852) (partem): Myrick, 2001:221, fig. 2.

Etymology of Name. Although Thecachampsa ends 

in the letter a, “champsa” is not derived from a feminine first 

declension Latin word. Rather, champsa is derived from an 

Egyptian word for crocodile by way of Greek and is a masculine 

noun. Therefore, the Latin species name antiquus should be masculine to conform to the gender of the generic name. The name 

antiquus also has priority.

Holotype. Originally two teeth, two vertebrae, a rib 

fragment, and an ungual phalanx (in part illustrated in Leidy, 

1852: pl. 16, figs. 1–5), collected by Robert H. Nash. According 

to Spamer et al. (1995:111), only the two vertebrae can be found 

at present (ANSP 9188, which is fig. 4 on pl. 16 in Leidy, 1852, 

and ANSP 9189, which is fig. 5).

Original Diagnosis. Medium-sized crocodilian, with 

blunt to moderately elongate conical teeth either lacking a cutting edge (carina) or with a very poorly developed carina.

Type Locality. Bluffs at Stratford Hall Plantation, 

Westmoreland County, Virginia, USA.

Horizon. The horizon is not indicated, but the type material is almost certainly from the Choptank Formation (upper 

middle Miocene) on the basis of the presence of mollusk shell 

material associated with the holotype. The Calvert and St. Marys 

Formations in the Stratford bluffs are not shelly.

Previously Referred Material. Type tooth of 

Thecachampsa contusor (Cope 1867), ANSP 9152, found near 

the residence of James T. Thomas near the Patuxent River, 

Charles County, Maryland, in the Calvert Formation (Plum 

Point D, middle Miocene).

Newly Referred Material. (1) CMM-V-3774, 1 

tooth and numerous postcranial elements, including 9 presacral 

vertebrae, 2 sacral vertebrae, 10 caudal vertebrae, both ilia, 1 ischium, 1 pubis, left femur, anterior end of right femur, both tibia, 

1 fibula, 6 metatarsals, and 4 tarsals, collected by Stephen Roger 

Horman, Robert Weems, Sankar Chatterjee, and Vincent LaPiana, 1976, from bluffs south of Popes Creek, Charles County, 

Maryland, Fairhaven Member (Fairhaven C) of the Calvert Formation (lower Miocene). (2) CMM-V-4668, fused frontals and 

fragments of surrounding bones, collected by Ron Ison from the 

bank of the Pamunkey River, New Kent or King William County, 

Virginia, Fairhaven Member (Fairhaven C) of the Calvert Formation (lower Miocene). (3) Very large mandibular tooth, in 

collection of Robert D. Bowes, from Pollack Farm Fossil Site, 

Kent County, Delaware, Fairhaven Member (Fairhaven C) of 

the Calvert Formation (lower Miocene; described but not illustrated in Holman, 1998). (4) USNM 25243, posterior fragment 

of right maxilla with 3 teeth, collector unlisted, from Lee Creek 

Mine, Beaufort County, North Carolina, Pungo River Formation 

(Myrick, 2001: fig. 2). (5) USNM 299913, cranium, collected by 

Vanscoy and Vanscoy, 1981, at Stratford Hall Plantation, Westmoreland County, Virginia, Choptank Formation (middle Miocene; currently on exhibit at the CMM, Solomons, Maryland). 

(6) CMM-V-2392, anterior tooth, south of Parkers Creek, Calvert County, Maryland, Calvert Formation, Plum Point Member 

(Plum Point D, Shattuck zone 14; middle Miocene). (7) USNM 

25098, anterior portion of lower jaws with teeth, collected by 

W. L. Ashby, 1968, at Parkers Creek, Calvert County, Maryland, 

Choptank Formation (Choptank A, Shattuck zone 17; middle 

Miocene). (8) USNM 24938, posterior portion of a cranium, 

collected by Carla Sanchez in 1966 at Chesapeake Ranch Estates south of Little Cove Point, Calvert County, Maryland, St. 

Marys Formation (upper Miocene). (9) USNM 24939, anterior 

portion of a cranium, fragment of the right prefrontal region, 

and portions of mandibles, collected by Carla Sanchez in 1967 

at Chesapeake Ranch Estates south of Little Cove Point, Calvert 

County, Maryland, St. Marys Formation (upper Miocene). (10) 

CMM-V-1764, mid-caudal vertebra, collected by Gary Wendt, 

Little Cove Point, Calvert County, Maryland, Little Cove Point 

Member, St. Marys Formation (upper Miocene). (11) CMM-V3227, tooth, Windmill Point, St. Marys County, Maryland, St. 

Marys Formation, possibly but not certainly from the Windmill 

Point Member (upper Miocene). (12) AMNH 5663, largely complete skull, donated by Anton Schneider, Polk County, Florida, 

Bone Valley Member of Peace River Formation (middle or upper 

Miocene); AMNH 5662, anterior portion of skull, donated by 

Anton Schneider, Polk County, Florida, Bone Valley Member of 

Peace River Formation (middle or upper Miocene); UF 6225, 

largely complete skull, collector unacknowledged, Alachua 

County, Florida, Bone Valley Member of Peace River Formation 

(middle or upper Miocene).

Expanded Diagnosis. Same as for T. sericodon with 

the following exceptions: Maximum total adult body length 

larger, about 5 m [16 ft]. Maximum skull length approximately 

80 cm [2 ft, 4 inches]. Snout of skull elongate and narrow anteriorly but less narrow than in T. sericodon. Dentition homodont, 

with stout conical crushing teeth that often lack carinas or have 

only weakly developed carinas; first premaxillary tooth relatively 

smaller than in T. sericodon and directed downward rather than 
226 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

B A1

C

D1

E1

A2

A3

D2 D3

E2

50 mm

1 cm 2 inches

1 cm

50 mm

2 inches
NUMBER 100 • 227

FIGURE 4.8. (Facing page) (A1, A2) Dermal armor with a low, faintly visible, vertically oriented longitudinal keel, possibly referable to Alligator olseni (USNM 540749 and USNM 540750, respectively). (A3) Dermal armor of Alligator olseni (UF 171554) with strongly developed 

longitudinal keel. (B–F) Postcranial elements from the Stratford Hall Plantation specimen of Thecachampsa sericodon Cope (STHA1). (B) Right 

ilium. (C) Left femur. (D1, D2, D3) Posterior, mid-range, and anterior teeth, respectively. (E1) Unkeeled armor. (E2) Keeled armor. Scale bars 

refer to all numbered specimens within a lettered grouping.

FIGURE 4.9. The left ilia of (A) Thecachampsa sericodon Cope, (B) Thecachampsa antiquus (Leidy), and (C) 

Thecachampsa carolinensis (Erickson and Sawyer) in comparison with the left ilia of (D) Alligator mississippiensis (Daudin) and (E) Crocodylus acutus Cuvier. Alligator from Gregory (1951), Crocodylus from Mook 

(1921a), and T. carolinensis from Erickson and Sawyer (1996).
228 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

100 mm

4 inches

FIGURE 4.10. Photograph (left) and restoration (right) of the St. Marys Formation skull fragments of Thecachampsa antiquus (Leidy) 

(USNM 24938 and USNM 24939) in dorsal view.
NUMBER 100 • 229

forward. Posterior blade of ilium more elongated than in T. sericodon; fourth trochanter on femur larger and more robust than 

in T. sericodon; ventral internal border of femur straighter than 

in T. sericodon.

Horizon, Age, and Depositional Setting. Although the locality of the type material is known, the stratigraphic 

horizon from which it came was not indicated. The type material was associated with pectinid shells, so it came from above 

the Calvert Formation, which has no preserved pectinid shells 

at this locality. It was likely found in the overlying Choptank 

Formation (Choptank A). The type material of Thecachampsa 

contusor is recorded simply as being from the Calvert Formation, but the locality suggests an upper (Plum Point) Calvert horizon. The specimens described herein come from a much wider 

stratigraphic range than the specimens of T. sericodon, having 

been found as low as the Fairhaven Member (Fairhaven C) of 

the Calvert Formation and with certainty as high as the Little 

Cove Point Member of the St. Marys Formation. One specimen 

of this species, found on the beach at Windmill Point, may have 

come from the Windmill Point Member of the St. Marys Formation (Figure 4.1). This horizon cannot be said with certainty, 

however, because the specimen also could have come from the 

top of the Little Cove Point Member, which is exposed at beach 

level. The depositional setting of all of these deposits was coastal 

shallow marine to offshore mid-shelf.

Discussion. The two specimens from Chesapeake Ranch 

Estates were found at different times but at the same locality by 

the same collector. They are from animals of comparable size, 

but the snout of USNM 24939 was found in association with 

a large but detached fragment of its right prefrontal region that 

is identical in conformation to the comparable region recovered 

with USNM 24938. Therefore, even though these two specimens 

are comparable in size, they must have come from two different 

individuals. Between these two specimens, most features of the 

dorsal and ventral skull can be determined (Figures 4.10, 4.11). 

Although generally similar to T. sericodon, T. antiquus grew to 

a somewhat larger size and had a slightly more robust rostrum 

that held relatively larger, stout, conical teeth that were much the 

same in conformation from the front of the mouth to the back. 

These differences are consistent among the Calvert and St. Marys 

specimens (Figures 4.10–4.13) wherever each character state is 

preserved, and they all contrast with the two fairly complete skulls 

of T. sericodon described above.Similarly, the ilium and femur of 

T. antiquus are quite different in conformation from the same elements in T. sericodon (Figures 4.8, 4.9, 4.14), probably because T. 

antiquus had stronger rear limbs that were well suited for walking. 

These consistent differences, as well as the difference in the 

overall stratigraphic range of the two species, demonstrate that 

this material represents two different but closely related species.

THE STATUS OF GAVIALOSUCHUS AMERICANUS

Sellards (1915) described a species of tomistomine crocodile (“Tomistoma” americana) from the anterior snout of a 

skull found in the Bone Valley Member of the Peace River Formation in Polk County, Florida. At that time, the Bone Valley 

Member was considered to be late Miocene or early Pliocene, 

but more recent work places the age of the tomistomine-bearing 

beds as middle to late Miocene (Hulbert, 2001:150). By 1915, 

the poorly known Maryland and Virginia Miocene crocodilian 

material had been assigned to Crocodylus. The snout described 

by Sellards was clearly a tomistomine, so there seemed no reason at that time to closely compare the Virginia-Maryland material to the Florida specimen. A few years later, Mook (1921a) 

described a much more complete tomistomine skull and other 

material (Mook, 1921b) from the same Florida area, referring 

all of this material to the species that Sellards had described. 

However, Mook recognized that the Florida material, although 

tomistomine, was closer to the genus Gavialosuchus than it 

was to Tomistoma and so redesignated the species as Gavialosuchus americanus. Much later, Auffenberg (1954) described 

more tomistomine material, this time from Alachua County, 

and again assigned it to Gavialosuchus americanus. Myrick 

(2001) synonymized all of this material with the Maryland and 

Virginia material and called it Thecachampsa antiqua.

The type of G. americanus is only a snout, so only this 

part of the Virginia and Maryland specimens can be compared 

with the type Florida specimen; the other two published Florida specimens can be far more fully compared. In dorsal view 

(Figure 4.15) the more complete specimens are separable into 

broader-snouted and narrower-snouted morphotypes.The type 

snout of G. americanus shows no obvious distinguishing characteristics in this view. However, in ventral view (Figure 4.16) 

a distinctive trait can be discerned. When the length of the 

portion of the snout that lies anterior to the center of the fifth 

maxillary tooth sockets is divided by the width of the snout 

at the level of the center of the fifth maxillary tooth sockets, 

the type specimen of G. americanus clearly has snout proportions identical to T. sericodon (Figure 4.17). In contrast, the 

two specimens later discussed by Mook and Auffenberg have 

snout proportions identical to T. antiquus. Thus, the type specimen of G. americanus is a junior synonym of Thecachampsa 

sericodon, but the other two illustrated and largely complete 

skulls are examples of T. antiquus. These conclusions are in 

accord with the conclusions of both Piras et al. (2007) and 

Brochu and Storrs (2012) that Myrick was correct in moving 

the Florida material from Gavialosuchus to Thecachampsa. 

The holotype mandible of Megalodelphis magnidens Kellogg, 

1944, which was later referred to Gavialosuchus americanus by 

Morgan (1986), has posterior teeth that are low crowned and 

laterally compressed. This characteristic makes this specimen referable to T. sericodon rather than to T. antiquus. The specimen 

discussed by Auffenberg (1954) is unique in that the frontal 

does not make contact with the premaxillaries at their proximal 

ends; in all of the other specimens the frontal separates the prefrontals and also distinctly indents the premaxillaries (Figure 

4.15). For now, this difference is assumed to be either a developmental abnormality or an interpretive drafting error, but if 
230 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

100 mm

4 inches

FIGURE 4.11. Photograph (left) and restoration (right) of the St. Marys Formation skull fragments of Thecachampsa antiquus (Leidy) 

(USNM 24938 and USNM 24939) in ventral view.
NUMBER 100 • 231

100 mm

4 inches

FIGURE 4.12. Photograph (left) and restoration (right) of the Calvert Formation Stratford Hall skull of Thecachampsa antiquus (Leidy) 

(USNM 299913) in dorsal view.
232 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

100 mm

4 inches

FIGURE 4.13. (A) Photograph and (B) restoration of the Stratford Hall snout of Thecachampsa antiquus (Leidy) (USNM 299913) 

in ventral view. (C) Tooth in this skull (USNM 299913). (D) Coprolite of Thecachampsa (CMM-V-7573) from the Plum Point 

Member of the Calvert Formation in lateral view. The length of animal that produced this coprolite was about 4.1 m on the basis 

of the ratio established by Milàn (2012). This is the size of an adult T. sericodon (about 4 m) or a subadult T. antiquus (about 

5 m). (E) Caudal vertebra of Thecachampsa antiquus (Leidy) (CMM-V-1764) from the Little Cove Point Member of the St. Marys 

Formation in left lateral view.
NUMBER 100 • 233

B

A

C

D

E

50 mm

2 inches

1 cm

FIGURE 4.14. Postcranial elements of Thecachampsa antiquus (Leidy) (CMM-V-3774) from Popes Creek, Maryland. (A) Left femur in 

anterior view. (B) Right ilium in external lateral view. (C) Left tibia in internal view. (D) Mid-jaw or posterior tooth. (E) Ungual phalanx.
234 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

future collecting consistently turns up more specimens like this, 

then this trait may be a diagnostic characteristic for an as yet 

unrecognized species of Thecachampsa.

COPROLITES OF THECACHAMPSA

Large coprolites (Figure 4.13D) occasionally are found in 

the same beds as skeletal remains of Thecachampsa. Many of 

these, and perhaps all, can be attributed to Thecachampsa for 

several reasons. First, these coprolites are large and thus pertain 

to a large animal. Large sharks such as Carcharocles could produce coprolites of this size, but they would have a strongly spiral shaped, superficially pupa-like morphology quite unlike the 

coprolites discussed here (see Schwimmer, 2002: fig. 8.2C,D for 

examples). Although possible external morphologies are rather 

varied, most crocodilian coprolites are elongate and cylindrical to tapering in shape and have rounded terminations (Milàn, 

2012). Second, the coprolites discussed here have a faintly layered but internally massive internal texture that attests to thorough digestion of any bony material that was ingested. Study 

of modern crocodilian scat has shown that although hair and 

feathers may be present, bony remains are not (Milàn, 2012). 

The reason is mostly because hydrochloric acid concentrations 

are 50 times stronger in crocodilian digestive tracts than in the 

digestive tracts of mammalian carnivores (Coulson et al., 1989). 

Although freshly defecated feces of modern crocodilians can retain “ghosts” of bones and teeth made of organic fibrous materials, they become unrecognizable within a day or two of being 

produced (Fisher, 1981). Third, crocodilian feces are quite cohesive, unlike the feces of bony fishes, sea turtles, and marine mammals, and thus are much more likely to be preserved in aquatic 

environments. For all of these reasons, Thecachampsa is the only 

likely source of these Miocene marine coprolites. 

A strong relationship exists between the diameter of crocodilian scat and the size of the animal that produced it. This relationship is expressed by the formula DS = 0.012(TL) + 1.10, where DS 

is the diameter of the scat and TL is the total length of the animal 

that produced it (Milàn, 2012). A coprolitic mass 6 cm in diameter 

with feather impressions, reported by Wetmore (1943) from Shattuck’s zone 12 of the Calvert Formation near Parkers Creek, could 

belong to Thecachampsa because the animal that produced it was 

about 4 m in length and because feathers and hair are much more 

resistant to crocodilian digestion than bone. It should be noted, 

however, that hair and feather remains are found more commonly 

in regurgitated crocodilian stomach contents analogous to hairballs than in scat (Fisher, 1981). 

It cannot be determined if coprolites of T. antiquus are 

morphologically distinguishable from coprolites of T. sericodon

because crocodilian coprolites and skeletal remains are not yet 

associated in finds from the Chesapeake Group. Even if coprolites associated with skeletons are eventually found, there still is 

Thecachampsa

sericodon

Gavialosuchus

americanus

(sensu Mook)

Thecachampsa

antiquus

Thecachampsa

antiquus

T.

sericodon

Gavialosuchus

americanus

(sensu Auenberg)

Gavialosuchus

americanus

(holotype)

FIGURE 4.15. One nearly complete and one partial skull of Thecachampsa sericodon (far left), one nearly complete and one partial skull of T. 

antiquus (far right), and three partial to nearly complete skulls described as Gavialosuchus americanus between them. All are diagrammatically 

drawn in dorsal view to the same length to emphasize relative proportions.
NUMBER 100 • 235

no guarantee that there will be any consistent differences that 

will distinguish which species produced them. On the basis of 

the estimated size of adults, T. sericodon (4 m) would have produced coprolites up to 6 cm in diameter, and T. antiquus (5 m) 

would have produced coprolites up to 7 cm in diameter. This 

calculation indicates that coprolites larger than 6 cm in diameter 

probably can be attributed to T. antiquus. In the St. Marys Formation, all crocodilian coprolites probably can be assigned to T. 

antiquus by default because T. sericodon apparently was extinct 

by the time of the St. Marys. Otherwise, for now large crocodilian coprolites less than 6 cm in diameter can be identified only 

as Thecachampsa sp.

DISCUSSION AND TAXONOMIC ANALYSIS

Morphological taxonomists generally have included Tomistoma and related extinct genera within a subfamily Tomistominae (nested within the family Crocodylidae) and placed Gavialis

and its extinct relatives in its own family, Gavialidae (basal to all 

other extant crocodilians; Brochu, 1997, 2003, 2006, 2007). In 

contrast, molecular data set studies consistently have supported 

a sister group relationship between Gavialis and Tomistoma (for 

example, Densmore, 1983; Janke et al., 2005; Willis et al., 2007; 

Zhang et al., 2011). These same molecular studies strongly and 

consistently support a fundamental division of Crocodylia into 

two groups, one being Crocodylidae + (Gavialis + Tomistoma) 

and the other being Alligatoridae. In one variation of this phylogeny (for example, Janke et al., 2005; Zhang et al., 2011), 

although Tomistoma and Gavialis are both included within Crocodylidae, together they are basal to all other extant species and 

thus comprise either one or two separate subfamilies. A single 

subfamily for Tomistoma and Gavialis makes sense when only 

considering living forms, but because there are so many fossil 

relatives of both Gavialis and Tomistoma and because the separation of Gavialis and Tomistoma from the rest of Crocodylidae 

is so fundamental, for fossil species it makes sense to retain a 

threefold division of Crocodylia into the families Alligatoridae, 

Gavialidae, and Crocodylidae, with the clear understanding that 

Gavialidae and Crocodylidae are more closely related to each 

other than either is to Alligatoridae. This taxonomic arrangement, advocated by Poe (1996) and Willis et al. (2007), is adopted here. As Gavialis and Tomistoma are the sole surviving 

remnants of two quite distinct, formerly diverse and abundant 

clades within Gavialidae, Gavialis and extinct relatives are considered to comprise the subfamily Gavialinae, and Tomistoma

and extinct relatives are considered to comprise the subfamily 

Tomistominae. 

Thecachampsa

sericodon

Gavialosuchus

americanus

(sensu Mook)

Thecachampsa

antiquus

Thecachampsa

antiquus

T.

sericodon

Gavialosuchus

americanus

(sensu Auenberg)

Gavialosuchus

americanus

(holotype)

FIGURE 4.16. One nearly complete and one partial skull of Thecachampsa sericodon (far left), one nearly complete and one partial skull of T. 

antiquus (far right), and three partial to nearly complete skulls described as Gavialosuchus americanus between them. All are diagrammatically 

drawn in ventral view to the same length to emphasize relative proportions.
236 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

FIGURE 4.17. Bar graph showing relative snout proportions for the skulls shown in Figure 4.16. The vertical axis portrays the 

ratio between the length of the snout from the tip of the nose to the middle of the fifth maxillary teeth, divided by the width of 

the snout at the middle of the fifth maxillary teeth. Specimens from Maryland and Virginia are shown by white bars, and specimens from Florida are shown by gray bars. The Maryland and Virginia specimens contain rows of species-diagnostic teeth. 

One of the Florida specimens previously assigned to Gavialosuchus americanus (USNM 8816, the holotype) has proportions 

that fall in the range of Thecachampsa sericodon, but other published specimens have proportions typical of T. antiquus. Only 

AMNH 5663 has well-illustrated posterior teeth that independently also associate it with T. antiquus.
NUMBER 100 • 237

The subfamily Tomistominae currently includes 13 genera: 

Charactosuchus, Dollosuchoides, Ferganosuchus, Gavialosuchus, 

Kentisuchus, Maroccosuchus, Megadontosuchus, Paratomistoma, 

Penghusuchus, Rhamphosuchus, Thecachampsa, Tomistoma, and 

Toyotamaphimeia (Kobayashi et al., 2005; Brochu, 2007; Piras 

et al., 2007; Shan et al., 2009). The oldest well-known members 

are the early Eocene genera Dollosuchoides, Kentisuchus, and Maroccosuchus. Five genera have been reported from the Miocene: 

Gavialosuchus, Penghusuchus, Rhamphosuchus, Thecachampsa, 

and, allegedly, Tomistoma. Penghusuchus and Rhamphosuchus

are distinctive genera readily separable from Gavialosuchus, Tomistoma, and Thecachampsa because they both have the seventh 

maxillary tooth enlarged rather than the fifth. 

Thecachampsa, Miocene Tomistoma?, and Gavialosuchus

currently are accepted as valid groups of taxa distinctly different from each other (Brochu and Gingrich, 2000; Brochu, 2003, 

2007; Piras et al., 2007).

Erickson and Sawyer (1996) named a new species of tomistomine crocodilian from the mid-Oligocene of South Carolina. 

They assigned their new species to the genus Gavialosuchus

and named it Gavialosuchus carolinensis, but this generic assignment now seems unlikely because all other reported occurrences of Gavialosuchus in North America have proven to be 

Thecachampsa. Gavialosuchus eggenburgensis bears a striking 

superficial similarity to Thecachampsa sericodon (Figure 4.18), 

but the interorbital and postorbital areas of its skull table are 

strikingly different from the same area in the three North American species of Thecachampsa. In Gavialosuchus the frontals and 

postorbitals are greatly shortened anteroposteriorly, whereas in 

Thecachampsa these bones are no more shortened than in the 

living genus Tomistoma. These differences indicate that the Oligocene tomistomid from South Carolina should be classified as 

Thecachampsa carolinensis. This conclusion is in accord with 

the conclusions of both Piras et al. (2007) and Brochu and Storrs 

(2012) that G. carolinensis should be transferred to the genus 

Thecachampsa. It is distinguished from the two Miocene species 

of Thecachampsa by a number of characters (Table 4.1).

Laurito and Valerio (2008) described new tomistomine material from the late Miocene or early Pliocene of Costa Rica and 

assigned it to Gavialosuchus americanus. As discussed above, 

material formerly assigned to G. americanus is here considered 

to be in part T. sericodon and in part T. antiquus. The Costa 

Rican material is too fragmentary to allow species identification 

but clearly does pertain to Thecachampsa and provides a significant southward range extension for this genus.

PALEOECOLOGY

The co-occurrence of T. sericodon and T. antiquus in the 

same beds during the middle Miocene clearly indicates that these 

two species were not direct competitors in the Miocene coastal 

Thecachampsa

carolinensis

Gavialosuchus

eggenburgensis

Tomistoma

schlegelii

Thecachampsa

antiquus

Thecachampsa

sericodon

FIGURE 4.18. Comparison in dorsal view of the skulls of Thecachampsa carolinensis, T. antiquus, T. sericodon, Gavialosuchus eggenburgensis, 

and Tomistoma schlegelii. Thecachampsa carolinensis after Erickson and Sawyer (1996), with the left side corrected for distortion from compaction; G. eggenburgensis after Toula and Kail (1885); T. schlegelii after Mook (1921c).
238 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

environment of the eastern United States. This conclusion is 

supported by the contrasting snout, dental, pelvic, and femoral 

features seen in these two otherwise closely related species. The 

very elongate and narrow snout of T. sericodon, with its elongate 

stabbing anterior teeth and laterally compressed slicing posterior 

teeth, is well suited for catching fish or possibly squid. The somewhat broader snout of T. antiquus, with its blunt, conical, alligator-like teeth, is well suited for catching turtles and crushing their 

shells. These two feeding styles would have minimized competition between these two species and permitted them to coexist in 

the same general environmental setting. Similarly, in Europe the 

very narrow snouts of “Tomistoma” calaritanus and Gavialosuchus eggenburgensis suggest piscivorous diets for those species, whereas the more robust snout of “T.” lusitanica suggests at 

least a tendency toward a chelonian diet in that species. The even 

broader snout of Thecachampsa carolinensis, with its enlarged 

sixth maxillary teeth, suggests that it was better adapted than 

even T. antiquus for crushing turtle shells.

In the Oligocene and Miocene deposits of the Atlantic 

Coastal Plain, remains of Thecachampsa have been found consistently, and sometimes abundantly, in shallow marine to midshelf deposits (Cope, 1867, 1869a; Marsh, 1869; Sellards, 1915; 

Mook, 1921c; Auffenberg, 1954; Webb and Tessman, 1968; 

Morgan, 1986; Erickson and Sawyer, 1996). Their occurrence in 

this depositional setting suggests that these animals regularly visited or normally inhabited the shallow marine waters of what is 

now the southeastern United States continental shelf. This observation is inherently biased by the fact that nearly all Oligocene 

and Miocene deposits in the Atlantic Coastal Plain are of marine 

origin. However, in view of the facts that (1) clearly fluvial crocodilian remains are unknown in the Oligocene and extremely rare 

in the Miocene and (2) remains of any other kinds of fluvial or 

terrestrial vertebrates of any sort are also rare in both the Oligocene and Miocene of this region, the observed abundance of 

remains of Thecachampsa far exceeds what would be expected 

had they been strictly freshwater animals. The general scarcity of 

their remains, when compared to those of whales and sea turtles, 

suggests that they were not extremely common in open marine 

environments. However, considering their large size and high 

position in the Miocene food chain, they should not have been 

extremely common. Erickson and Sawyer (1996) have suggested 

that Thecachampsa carolinensis normally nested and lived in 

beach to lagoonal and estuarine environments, and this seems a 

likely habitat preference. The Miocene species of Thecachampsa

probably nested in this same environmental setting.

In this regard, it is interesting to note that the species Gavialosuchus eggenburgensis, from the Miocene of Europe, also 

occurs in association with remains of marine animals (Telles 

Antunes, 1961; Erickson and Sawyer, 1996). In Portugal, G. 

eggenburgensis not only occurs in marine environments but also 

is found in association with the remains of a smaller species of 

tomistomine crocodilian, “Tomistoma” calaritanus (Telles Antunes, 1961). The co-occurrence of a larger and smaller species 

of tomistomine in the Miocene coastal waters of both Portugal 

and the eastern United States represents a striking parallelism 

in niche partitioning in this group on both sides of the Atlantic.

THE DECLINE OF THE TOMISTOMINAE

During most of the Miocene, tomistomines were abundant 

and diverse in Europe, Asia, Africa, and the Americas (Piras et 

al., 2007). Although Thecachampsa was the only tomistomine 

present in the southeastern United States, it was moderately 

abundant there and during the middle Miocene included two 

species. By the early late Miocene, however, T. sericodon apparently had become extinct, and only T. antiquus persisted. 

The latest Miocene (Messinian) Eastover Formation has yielded 

no remains of tomistomines, so by then they apparently were 

extinct in the southeastern United States. Although there have 

been reports of Thecachampsa from the Pliocene of Florida, they 

probably represent nothing more than reworking of Miocene 

fossils into basal Pliocene deposits (Hulbert, 2001:150). By the 

Pliocene, all well-documented occurrences of tomistomines are 

from Southeast Asia. Two marine species persisted there into the 

Quaternary (“Tomistoma” taiwanicus in Taiwan and Toyotamaphimeia machikanensis in Japan). Today, only the freshwater 

species Tomistoma schlegelii survives.

It is remarkable that the Tomistominae have been reduced 

to a single species, considering that throughout most of the Paleogene and Neogene this was a diverse and successful group 

capable of dispersing across entire ocean basins. Probably, the 

main factor in the decline of this family was the global climatic 

deterioration in the late Neogene that led to Quaternary glaciation across much of the globe (Wolfe, 1994; Zachos et al., 2001; 

Böhme, 2003). It probably is not coincidental that the one area 

where a tomistomine still survives, Southeast Asia, is fully tropical and within 15° of the equator. A second possible factor in 

the decline of the Tomistominae may be that saltwater-tolerant 

species of living crocodiles (particularly Crocodylus porosus in 

the tropical Eastern Hemisphere and Crocodylus acutus in the 

tropical Western Hemisphere) now fill the coastal marine niche 

in tropical regions that the tomistomines once inhabited (Minton 

and Minton, 1973). It is not clear whether the modern crocodiles 

that occupy these niches do so because the tomistomines became 

extinct in those habitats and left them vacant or whether the 

modern species actively moved into those habitats while tomistomines still occupied them and drove them to extinction. In 

the southeastern United States, however, competitive exclusion 

seems unlikely because Crocodylus acutus today occupies only 

the southernmost tip of Florida. Farther north in the southeastern United States, Alligator mississippiensis is abundant, but it 

occupies only freshwater areas that lie inland of the former habitat of Thecachampsa. The failure of either of these two living 

species to occupy a major part of the former habitat of Thecachampsa strongly suggests that late Neogene climatic deterioration and not competition was the main factor that caused the 

disappearance of tomistomines in eastern North America.
NUMBER 100 • 239

AN ENIGMATIC CROCODILIAN FROM 

THE CALVERT FORMATION

Two small crocodilian osteoderms (USNM 540749, USNM 

540750) and part of a third one, all found at the Pollack Farm 

fossil site in Delaware, are different from osteoderms associated 

with either species of Thecachampsa (Figure 4.8E1,E2). These 

osteoderms, from the Fairhaven Member (Fairhaven C) of the 

Calvert Formation (Figure 4.8A1,A2), are not referable to Thecachampsa because they have a low and narrow keel running 

down their longitudinal axis, they are rhomboidal to rectangular 

in outline, and they have smaller and more closely spaced pits on 

their external surfaces. This type of osteoderm does not pertain 

to Thecachampsa, although to what other kind of crocodilian it 

does pertain is uncertain. The only other crocodilian recognized 

so far from the early Miocene of the eastern United States is Alligator olseni. It was first recognized at the Raeford Thomas Farm 

site in Florida (White, 1942), which is close or identical in age to 

the Pollack Farm site in Delaware (Emry and Eshelman, 1998). 

Osteoderms of A. olseni, however, often have a much more pronounced keel than the ones from Pollack Farm and also are often 

larger (Figure 4.8A3), so reference of the Pollack Farm material 

to A. olseni is plausible but not certain. Crocodilian osteoderms 

of the Pollack Farm morphology occur in the midline region of 

modern Crocodylus, Alligator, and Caiman, so this type of dermal armor is not generically distinctive. What is certain, however, is that these osteoderms represent a third kind of small 

crocodilian that is not referable to Thecachampsa. This third 

species of crocodilian presumably was an inhabitant of freshwater environments because many freshwater and terrestrial taxa 

have been found at the Pollack Farm site that are extremely rare 

in the shallow marine environments represented by nearly all of 

the Calvert and Choptank Formation outcrops found elsewhere. 

Although this taxon has not yet been found along the Calvert 

Cliffs, its eventual discovery there should be expected.

ACKNOWLEDGMENTS

I thank David J. Bohaska of the National Museum of Natural History and Ned Gilmore of the Academy of Natural Sciences 

of Drexel University for their help in locating the type specimens 

of Thecachampsa from Maryland and Virginia. I also thank 

Richard C. Hulbert Jr. of the Florida State Museum for making available to me a typical variety of osteoderms from Alligator olseni and Stephen Godfrey and John Nance of the Calvert 

Marine Museum for their assistance throughout the creation of 

this chapter. The coprolite illustrated in Figure 4.13D was found 

by Ethan Matteson and donated to CMM by Peter Vogt. Very 

helpful reviews by David J. Bohaska, James Clark, Austin Platt, 

and Nicholas D. Pyenson are also very gratefully acknowledged. 

Last but not least, I thank the many volunteer collectors whose 

diligence in searching out the material described here has made 

this chapter possible.

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ABSTRACT. The extensive Miocene vertebrate fauna collected from the Chesapeake 

Group in New Jersey, Delaware, Maryland, Virginia, and North Carolina includes relatively rare sirenians of the family Dugongidae. They are most abundant in the early to 

middle Miocene Calvert and equivalent formations and in the Calvert Cliffs and nearby 

exposures in southern Maryland, as well as in the Lee Creek phosphate mine in North 

Carolina. These Calvert-correlative deposits have yielded evidence of at least three sirenian taxa: the halitheriine dugongid Metaxytherium crataegense (=M. calvertense), the 

dugongine dugongid Nanosiren sp., and another dugongine, aff. Corystosiren sp. A possible fourth unidentified form may also be a dugongine. The stratigraphically higher St. 

Marys Formation contains remains that (in view of their late Miocene age) may be referable to Metaxytherium floridanum, but those so far collected are too fragmentary to be 

distinguished morphologically from M. crataegense.

INTRODUCTION

Sirenians, or sea cows (manatees and dugongs), are the only completely herbivorous, 

completely aquatic mammals living today. They are dolphin-sized, thick-skinned, slowswimming animals with flipper-like front limbs, a horizontal tail fin that provides their 

main propulsion, and no hind limbs or dorsal fin. Dense, swollen ribs and other bones (a 

condition known as pachyosteosclerosis) provide ballast, helping them maintain neutral 

buoyancy while they feed on submerged or floating aquatic plants in warm, shallow, salt 

or fresh waters. Their cosmopolitan fossil record spans almost 50 million years (middle 

Eocene to Holocene), mostly in latitudes that are now or were formerly tropical to warm 

temperate.

5 Fossil Sirenia (Mammalia) 

of the Miocene Chesapeake 

Group, Eastern United States

Daryl P. Domning

Professor of Anatomy, Laboratory of Evolutionary 

Biology, Department of Anatomy, Howard 

University, Washington, D.C. 20059, USA.

Correspondence: ddomning@howard.edu

Received 1 May 2015; accepted 25 August 2017.
242 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Fossil sirenians have been collected from the Calvert Cliffs 

of Maryland for more than 100 years but are rare compared 

to Calvert cetaceans (possibly because the cliff exposures represent a deeper-water environment than the sirenians inhabited) 

and are still incompletely known. At least three different species 

of the sirenian family Dugongidae have so far been identified 

from the Miocene deposits of the Chesapeake Group (Calvert, 

Choptank, and St. Marys Formations and their equivalents) that 

crop out on the western side of the Chesapeake Bay, extending 

south into Virginia and North Carolina and north into Delaware 

and New Jersey (Domning, 1984a, 2006). The most important 

study of fossil sea cows from this region, by Remington Kellogg (1966), now requires significant updating. That three (or 

even more) species of dugongs might have lived together in the 

Chesapeake region is no longer surprising since multispecies paleofaunas of sirenians have now been discovered throughout the 

west Atlantic–Caribbean zoogeographic province as well as in 

other parts of the world (Domning, 2001; Bajpai et al., 2010; 

Vélez-Juarbe et al., 2012).

Besides these dugongid fossils, a radius–ulna (USNM 9346 

[see Figure 5.8D and Table 5.4]) of another sirenian was reported from Fairhaven, Anne Arundel County, Maryland, by 

Case (1904). Although Kellogg (1966) also attributed it to the 

Calvert dugongid he described, it is, in fact, one of only two 

Maryland fossil records of the living West Indian manatee (Trichechus manatus), which today is an occasional summertime 

visitor to these waters. This bone presumably came not from any 

part of the Chesapeake Group (which has yielded no manatee 

remains) but from some overlying Pleistocene deposit (Domning, 

2005:689). (The second manatee record is USNM 457373, an 

isolated molar from Randle Cliff, Calvert County, collected from 

float by William D. “Pat” Gotsis in 1990.) The remainder of this 

chapter will address only the Miocene dugongids. 

Since sirenian remains identifiable to genus or species are 

uncommon in the Calvert Cliffs and in the Chesapeake Group as 

a whole, it is necessary to include the entire Chesapeake Group 

in this chapter in order to obtain anything like a clear picture of 

the regional sirenian fauna represented in the Calvert Cliffs. Even 

now, most of these sirenian taxa remain inadequately known, 

which was even more true when the final volume (comprising 

the mammals) of the Lee Creek Mine series was being prepared 

for publication (Ray et al., 2008). This lack of information explains why that otherwise comprehensive work has no chapter 

on the sirenians—an omission that I have tried to remedy with 

this chapter.

Abbreviations

AMNH American Museum of Natural History, New York, 

New York, USA

AMNH-VP AMNH, Department of Vertebrate Paleontology

ChM Charleston Museum, Charleston, South Carolina, USA 

CMM Calvert Marine Museum, Solomons, Maryland, USA

coll. collector(s)

DPUH paleontological collection, Museo de Historia Natural 

Felipe Poey, Universidad de La Habana, Havana, Cuba

MYA million years ago

SCSM South Carolina State Museum, Columbia, South 

Carolina, USA 

USGS U.S. Geological Survey, Reston, Virginia, USA

USNM Department of Paleobiology, National Museum of 

Natural History (formerly U.S. National Museum), 

Smithsonian Institution, Washington, D.C., USA

YPM Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA

FOSSIL DUGONGIDAE IN THE 

MID-ATLANTIC REGION

Metaxytherium calvertense was the name given to the Calvert dugongs by Remington Kellogg (1966), distinguishing it 

from other fossil sirenians such as Felsinotherium ossivallense 

Simpson, 1932 (=Metaxytherium floridanum Hay, 1922) and 

Hesperosiren crataegensis Simpson, 1932, both of which George 

Gaylord Simpson had previously described from Florida—the 

former on the basis of teeth from the Bone Valley phosphate 

mines in Polk County and the latter on the basis of a skull and 

other remains from a fuller’s earth mine in Gadsden County. Unfortunately, this latter skull (AMNH 26838) is badly crushed and 

distorted, leading Simpson to misinterpret some of its features, 

such as the degree of downturning of its snout and the presence 

or absence of tusks. Kellogg’s Calvert skull (USNM 16757), in 

contrast, is undistorted but also lacks the tip of the snout, leaving 

the presence of tusks uncertain. As a result, Kellogg (who probably never compared the two skulls directly) did not perceive what 

I consider to be their basic similarity. Furthermore, they scarcely 

differ in their geochronological ages, which are respectively estimated as late Hemingfordian–early Barstovian for the Florida 

skull and late early Barstovian for the Calvert specimen; that is, 

both lived somewhere within the interval of roughly 15–17 mya. 

For these reasons I concluded that a species distinction (let alone 

a generic distinction) between them could not be defended, so I 

synonymized them (in Aranda-Manteca et al., 1994) under the 

new combination Metaxytherium crataegense (Simpson). 

In the Mid-Atlantic region, M. crataegense (Figures 5.1, 5.2) 

is best known from the Calvert Formation of Maryland and Virginia. A few specimens apparently representing Metaxytherium 

sp. have also been recovered from the overlying St. Marys and 

possibly the Choptank Formations in those states. Other remains 

referable to M. crataegense (as well as other dugongids) have also 

been found at the Lee Creek phosphate mine, North Carolina, 

evidently in the Calvert-correlative Pungo River Formation and 

possibly also in the Calvert Formation of Delaware and the Kirkwood Formation of New Jersey, as described below.
NUMBER 100 • 243

Maryland

The early to middle Miocene Calvert Formation of Maryland and Virginia was divided by Shattuck (1904) into 15 lithologic beds or “zones,” of which zones 1–3 corresponded to the 

Fairhaven Member and 4–15 correspond to the Plum Point 

Member. (These zones are hereinafter called beds, as they are 

lithologic rather than biostratigraphic units.) Gibson (1983a:43, 

fig. 9) restricted the Fairhaven to bed 3 and assigned beds 1 and 

2 to the Popes Creek Sand Member. Kidwell et al. (2015) likewise follow Shattuck’s scheme but do not recognize the Popes 

Creek Sand Member. Robert Weems (Calvert Marine Museum, 

personal communication) states that the age of the Popes Creek 

Sand falls between beds 3A and 3B on the basis of dinoflagellate 

ranges and that it is a bed within the Fairhaven Member that is 

missing in the Maryland section north of Popes Creek. In Kidwell 

et al.’s stratigraphic column (2015: fig. 2) it is represented by an 

unnamed sand unit between beds 3A and 3B that is correlated 

with dinocyst zone DN2b,c. In this chapter it is referred to as the 

“Popes Creek Sand bed.”

Sirenian fossils have been recovered from both the Popes 

Creek Sand bed and the Plum Point Member. The Popes Creek 

Sand bed on Popes Creek, Charles County, Maryland, has 

yielded two partial skeletons (USNM 241562 and CMM-V-244), 

of which at least the former is possibly referable to the dugongid subfamily Dugonginae (see below). In contrast, most of the 

other Calvert Formation sirenian material represents Metaxytherium (in the subfamily Halitheriinae) and is from the Plum Point 

Member, which is extensively exposed in the Calvert Cliffs along 

the western shore of the Chesapeake Bay in Calvert County. 

Kellogg (1966) erected the species Metaxytherium calvertense to include all the Calvert sirenian fossils known to 

him, all of which (except the manatee radius-ulna noted above) 

came from the Plum Point Member, specifically (insofar as their 

stratigraphic provenance was known) from beds 10–12. Some 

of these specimens, however, are now considered to represent a 

much smaller animal, the dugongine Nanosiren (Domning and 

Aguilera, 2008), whereas Kellogg’s species is synonymized with

M. crataegense (Simpson), as explained above. 

The holotype of “M. calvertense” (USNM 16757) was said 

by Kellogg (1966:71) to have been collected by W. E. Salter, A. C. 

Murray, and C. W. Gilmore on 4 August 1943 and to have come 

from “one-half mile south of Plum Point Road end, Calvert Co., 

Md. In compact blue clay at base of zone 11 (below shell band) 

and at tide level at base of cliff.” A holograph note by Gilmore 

himself clarifies that it was found by Salter on 4 August and collected by Salter, Murray, and Gilmore on 5 and 6 August. He also 

states that the locality was “11⁄2 mi. S of Plum Point” and that the 

skeleton “came from layer immediately above heavy shell layer” 

(USNM Registrar’s office, microfilm reel 624, accession number 

165846). As “one-half mile south of Plum Point Road end” arguably refers to the same area as “11⁄2 mi. S of Plum Point” itself, 

FIGURE 5.1. Metaxytherium crataegense, life-size 

body reconstruction created at the Calvert Marine 

Museum; anterior view.
244 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A

B

C

Supraoccipital 

Frontal

Maxilla

nares (mesorostral fossa)

mental foramen

Premaxilla

Parietal

coronoid process

Nasal Squamosal

occipital condyle

Jugal

Parietal Frontal

Squamosal

Lacrimal Jugal

Premaxilla

pterygoid process

Squamosal

condyle

mandibular angle

tusk

exoccipital

Maxilla

50 mm

2 inches

FIGURE 5.2. Metaxytherium crataegense, skull restoration (modified from Kellogg, 1966; based on USNM 

16757, holotype of M. calvertense). (A) Dorsal view. (B) Right lateral view. (C) Lower jaw, right lateral view. 

Anterior to the right.
NUMBER 100 • 245

these two sources are not in contradiction on this. However, according to David Bohaska (USNM, personal communication), 

Kellogg’s specification “below shell band” suggests that the skeleton was actually in bed 9 since the “shell band” was presumably 

bed 10; but more likely, Kellogg’s “below shell band” was an error 

for “above shell band,” as Gilmore said (hence bed 11). 

Gibson (1983b:362) stated that “the probable age for bed 

10 of the Calvert Formation is [planktonic foraminiferal] zone 

N8, and that for the overlying beds 11 and 12 is probably of 

lower zone N9.” The lower part of zone N9, and therefore the 

presumed type horizon of “M. calvertense,” is correlated with 

the late early Barstovian land mammal age, ca. 15 mya (Tedford 

et al., 1987: fig. 6.2). This age is consistent with the correlation, 

based on fossil peccaries found at several horizons in this section, 

by Wright and Eshelman (1987), who correlated Shattuck’s zone 

10 with the late Hemingfordian or early Barstovian and zone 14 

with the early late Barstovian. All of Kellogg’s (1966) specimens 

of M. crataegense therefore appear to be of early Barstovian age. 

Calvert County has also produced remains referable to 

Metaxytherium from the late Miocene St. Marys Formation 

(=beds 21–23) in the area of Little Cove Point and Chesapeake 

Ranch Estates. As discussed below, these specimens likely represent M. floridanum.

Virginia

Some other material also possibly referable to M. floridanum (listed below) has come from the south bank of the Potomac River in Westmoreland County, in the area from Stratford 

Hall past Westmoreland State Park and upriver to the George 

Washington Birthplace National Monument. The section here 

exposes beds 14–15 (Calvert Formation), 19 (Choptank Formation, Boston Cliffs Member), 21–24(?) (St. Marys Formation – east of Stratford only), plus the overlying, latest Miocene 

Eastover Formation (Ward and Andrews, 2008: fig. 7, sections 

PO-11, PO-12; R. Weems, pers. comm.).

The Carmel Church Quarry in Caroline County exposes 

beds 14–16 (here considered equivalent to the uppermost Plum 

Point Member of the Calvert Formation) at the edge of the 

Chesapeake Group depositional basin. It has produced a varied 

fauna, including fragments of “Metaxytherium?” (Dooley et al., 

2004:454), but so far no diagnostic sirenian specimens.

A partial skeleton (USNM 377441-2, 377446-7, 377449) 

from a site on the Pamunkey River in King William County 

(Domning, 1984b) came from a pebble bed about 0.6 m [2 ft] 

above the unconformable contact of the Calvert Formation with 

the Eocene Piney Point Formation. On the basis of mollusks, 

the pebble bed and overlying deposits were correlated with Calvert beds 12–13, hence with the Plum Point Member, by Ward 

(in Ward and Krafft, 1984:272–273). However, using more recent data from dinoflagellates, Weems (pers. comm.) considers 

this horizon to represent the Popes Creek Sand bed. Domning 

(1984b) noted differences between this specimen and Metaxytherium but resemblances to a Calvert sirenian from Popes Creek 

(USNM 241562). Both the Pamunkey River and Popes Creek 

specimens now seem to be dugongines (see below).

Another rib fragment (USNM 377448, coll. Kurt M. Savoie 

and James W. Westgate) from the Pamunkey River was apparently reworked from the Calvert into the overlying, late Miocene 

Eastover Formation (Domning, 1984b). Also of unclear significance is a fragment of the shaft of a humerus from the Pamunkey 

River (AMNH 108643; cast: USNM 307603), collected by E. D. 

Cope in 1895. It may be a Miocene sirenian or possibly a primitive cetacean derived from the Eocene Piney Point Formation.

Dugongid rib and vertebra fragments (USNM 186898) were 

also collected near Weedonville, King George County, questionably from the late middle Miocene Choptank Formation. 

North Carolina

The rich marine vertebrate fauna from the Lee Creek phosphate mine near Aurora, Beaufort County, North Carolina, includes an assortment of sirenian remains, all fragmentary and 

many abraded. They are all thought to be derived from the upper 

part of the Calvert-correlative Pungo River Formation, which is 

exposed in the base of the mine and is of earliest middle Miocene 

age (planktonic foraminiferal zone N8; early Barstovian, ca. 16 

mya; Gibson, 1983b:360; Tedford et al., 1987: fig. 6.2). Many, if 

not all, of them were probably reworked into the overlying early 

Pliocene Yorktown Formation (C. E. Ray, USNM, pers. comm.). 

Compared with bones from the Yorktown Formation, “Pungo 

River fossils generally are darker and more heavily mineralized, 

more polished in appearance, and more worn ... though such 

characters are not infallible” (Eshelman and Whitmore, 2008:18). 

These specimens appear to fall into three groups corresponding 

to three species found in the Calvert Formation: Metaxytherium

crataegense, Nanosiren sp., and aff. Corystosiren sp. This faunal 

resemblance is consistent with the correlation of both units with 

the same planktonic foraminiferal zones, N8 and N9.

Delaware

Bohaska (1998) reported dugongid rib fragments from the 

Cheswold sands of the Calvert Formation at the Pollack Farm Site 

in Kent County. These sands were considered by Bohaska to be 

equivalent in age to bed 3A of the Fairhaven Member and possibly 

of the same age as the Popes Creek Sand bed of the Calvert Formation in Maryland. The sirenian rib fragments (USNM 487268, 

488608, plus another seen by Bohaska in a private collection) are 

not diagnostic; judging from their size (diameters of USNM 487268 

= 38 × 16 mm; smaller diameter of USNM 488608 = 30 mm), they 

could represent either Metaxytherium or some dugongine.
246 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

New Jersey

The early Miocene Asbury Park Member of the lower Kirkwood Formation in Monmouth County, coastal New Jersey, 

contains a fauna (the Farmingdale local fauna) considered by 

Tedford and Hunter (1984) to be of early Hemingfordian age 

(18–20 mya) and correlated by Hunter and Huddlestun (1982) 

with Shattuck’s zones 1–3 of the Calvert Formation in Maryland 

(see below). However, Lucas et al. (1998) consider a late Arikareean age for this fauna to be more likely on the basis of the presence of the rhinoceros Diceratherium and the strontium isotope 

age estimates of 19.2–22.6 ± 0.5 mya obtained by Sugarman et 

al. (1993). Reworked Eocene material is also present.

The Farmingdale local fauna has produced a single, extremely waterworn shaft of a left humerus lacking both ends 

(USNM 243565). The shaft is mediolaterally compressed; a 

sharp anterior ridge extends from the area of the deltoid crest, 

parallel to the long axis of the shaft, and ends distally in a thickening for the insertion of the pectoralis major. In the form of 

this ridge as well as in the bone’s overall size and shape, it most 

closely resembles a dugongid humerus (ChM PV2860) from the 

late Oligocene Chandler Bridge Formation of South Carolina; 

with due allowance for abrasion, it also resembles various Miocene specimens of Metaxytherium. I assign it to Dugongidae, cf. 

Metaxytherium. 

Another worn left humerus (YPM uncataloged), fully resembling M. crataegense in size and shape, bears a label stating that 

it was “found in drawer marked Squankum, New Jersey” and 

that it was collected by O. B. Kinne in 1869. The Squankum 

area, near Farmingdale, contains outcrops of the Asbury Park 

Member, which are the probable source of this specimen (R. W. 

Purdy, USNM, pers. comm.).

Leidy (1856:165) based the name Manatus antiquus (a 

nomen dubium) partly “on fragments of ribs found in the miocene [sic] deposits of New Jersey.” I do not know the present 

whereabouts of these specimens, but together with the humeri 

described above and a Pleistocene(?) radius-ulna of Trichechus

sp. dredged from off New Jersey (Gallagher et al., 1989), they 

represent the northernmost fossil records of sirenians on the Atlantic coast of the Americas. 

SYSTEMATIC PALEONTOLOGY

Class Mammalia Linnaeus, 1758

Order Sirenia Illiger, 1811

Family Dugongidae Gray, 1821

Subfamily Halitheriinae (Carus, 1868) Abel, 1913

Genus Metaxytherium Christol, 1840

Metaxytherium crataegense (Simpson, 1932) 

Aranda-Manteca, Domning, and Barnes, 1994

FIGURES 5.1–5.9; TABLES 5.1–5.4

Dugong: Metaxytherium – Dugongidae, Halitheriinae

Hesperosiren crataegensis Simpson, 1932:426 (original description).

Metaxytherium calvertense Kellogg, 1966:71 (junior synonym). (Holotype: 

USNM 16757, skull and partial skeleton of immature individual. Type 

locality: near Plum Point, Calvert County, Maryland; bed 11, Plum 

Point Member, Calvert Formation [see discussion above]; earliest middle Miocene [Langhian, early Barstovian; lower part of planktonic foraminiferal zone N9].) 

Metaxytherium riveroi Varona, 1972:6 (junior synonym). (Holotype: DPUH 

1255, partial skull and skeletal fragments of juvenile. Type locality: San 

Antonio de Cabezas, Matanzas, Cuba; Güines Formation.)

Metaxytherium crataegense (Simpson) Aranda-Manteca, Domning, and 

Barnes, 1994:192 (new combination).

Holotype. AMNH 26838, skull, vertebrae, and ribs 

of adult. 

Type Locality. Florida, Gadsden County, Floridin Company mine, north of Quincy.

Formation. Hawthorn Group, Torreya Formation, Dogtown Member.

Age. Early to middle Miocene (late Hemingfordian or early 

Barstovian; Bryant, 1991). 

Referred Specimens. 

Maryland (Calvert, Prince Georges, and Anne Arundel 

Counties; Calvert Formation, Plum Point Member): Partial 

skeletons: USNM 12596 (coll. Norman H. Boss and Remington 

Kellogg), USNM 16757 (holotype of Metaxytherium calvertense; 

coll. William E. Salter, A. C. Murray, and C. W. Gilmore; Figures 

5.4A,B, 5.5A, 5.6E, 5.9A,B,C,F), USNM 23213 (coll. R. Lee Collins; Figure 5.8B), CMM-V-242 (coll. David Bohaska, Norman 

Riker, Wallace L. Ashby, August Selckmann, George C. Fonger, 

and Sandy Roberts; Figures 5.5E, 5.6B–D, 5.7J–N). Partial 

braincase: CMM-V-2202 (coll. Ralph Long). Parietal–supraoccipital skullcaps: USNM 16649 (coll. W. S. Cramer), USNM 23503 

(coll. Albert C. Myrick Jr. and Richard Lund; Figure 5.3A,B), 

USNM 241563 (coll. Norman Riker; Figure 5.3C,D). Squamosal: USNM 244539 (coll. Wallace L. Ashby). Maxilla with teeth: 

USNM 244422 (cast; coll. Bruce Rydell; Figure 5.4F). Cheek 

teeth: USNM 23271 (coll. A. Shaftsbury; Figure 5.4H), USNM 

23281 (coll. T. E. Ruhoff), USNM 23409 (coll. R. Lee Collins), 

USNM 437483 (cast; coll. R. S. Gladhill; Figure 5.4G), USNM 

452988 (coll. Sandy Roberts). Humeri: USNM 5360 (coll. F. 
NUMBER 100 • 247

emissary

foramina

Supraoccipital

Parietal

Frontoparietal

sutures

A B

C D

E

50 mm

2 inches

FIGURE 5.3. Metaxytherium crataegense, parietal-supraoccipital skullcaps. (A, B) USNM 23503 in dorsal and 

ventral (internal) views, respectively. (C, D) USNM 241563 in dorsal and ventral views, respectively. The numerous 

large and small emissary foramina in USNM 241563 are atypical and unique to this individual. (E) Line drawing of 

skull in dorsal view, anterior to top of page, showing in white the position of the skullcap. Specimens lightly coated 

with sublimed ammonium chloride.
248 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

mandibular symphysis

condyle

coronoid process

mental foramen

mental foramen

coronoid process

mandibular angle

condyle

mandibular foramen

coronoid canal

B

A

C

D

E

G H

F

50 mm

2 inches
NUMBER 100 • 249

FIGURE 5.4. (Facing page) Mandibles and teeth of Chesapeake Group dugongids. (A, B) Metaxytherium crataegense, USNM 16757 (holotype 

of M. calvertense), right half of mandible in lateral and medial views, respectively. (C, D) Nanosiren sp., USNM 16630, nearly complete mandible in dorsal and left lateral views, respectively. (E) Dugonginae gen. et sp. indet., Pamunkey River, Virginia, USNM 377446, left dentary in 

medial view. Teeth of Metaxytherium crataegense from Maryland, occlusal views: (F) USNM 244422, cast of left maxilla with second and third 

upper molars (M2–3) and alveoli of M1. (G) USNM 437483, cast, right third lower molar (m3) tooth. (H) USNM 23271, left m2. Specimens 

lightly coated with sublimed ammonium chloride. Scale bars for F–H equal 10 mm.

TABLE 5.1. Measurements (mm) of two specimens of skulls of Metaxytherium crataegense from the Chesapeake Group. Letters in 

parentheses denote abbreviation used by Domning (1978, 1988) for the given dimension. Other abbreviations: e = estimated; e? = 

identification of landmark(s) uncertain. A dash (–) indicates measurement could not be taken on specimen. Specimen USNM 16757 is

the holotype of M. calvertense.

Dimension USNM 16757 CMM-V-2202

Height of jugal below orbit (ab) 42 –

Rear of occipital condyles to anterior end of interfrontal suture (BI) 220 –

Zygomatic breadth (CC’) 217 –

Breadth across exoccipitals (cc’) 132e 152e

Top of supraoccipital to ventral sides of occipital condyles (de) 113 –

Length of frontals, level of tips of supraorbital processes to frontoparietal suture (F) 140e –

Length of frontals in midline (LFr) 84 90e?

Breadth across supraorbital processes (FF’) 131 –

Breadth across occipital condyles (ff’) 88e 98e

Breadth of cranium at frontoparietal suture (GG’) 68 64

Width of foramen magnum (gg’) 44e 53

Height of foramen magnum (hi) 56 –

Width of mesorostral fossa (JJ’) 56 –

Length of zygomatic process of squamosal (OP) 131 –

Anterior tip of zygomatic process to rear edge of squamosal below mastoid foramen (OT) 163e –

Length of parietals, frontoparietal suture to rear of external occipital protuberance (P) 97 85e?

Anteroposterior length of root of zygomatic process of squamosal (QR) 51 –

Width of supraoccipital (WSo) 94 92

Height of supraoccipital (HSo) 55 –

Minimum width of parietal roof between squamosal notches 70 78

Maximum width of braincase at level of middle part of parietal-squamosal suture 84e 77

Length of cranial portion of squamosal (ST) 93 –

Breadth across sigmoid ridges of squamosals (ss’) 186 –

Dorsoventral thickness of zygomatic-orbital bridge (T’) 10 –

Height of posterior part of cranial portion of squamosal (UV) 94 –

Dorsoventral breadth of zygomatic process (WX) 47 41

Length of jugal (YZ) 162 –

Deflection of masticating surface of rostrum from occlusal plane (RD; in degrees) 56°e –
250 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

W. True; True, 1906: pl. 76, fig. 4), USNM 186899 (coll. William 

Palmer), USNM 476415 (coll. David Bohaska and William F. 

Douglass Jr.). Ulna: USNM 186896 (coll. Allan Smith). Vertebrae: USNM 23348 (coll. William Thomas Palmer Sr.), USNM 

23367 (not 23667; axis; coll. R. Lee Collins), USNM 23666 

(coll. Adolph Schultz), USNM 360706 (coll. S. F. Blake), USNM 

559307 (coll. William E. Salter). Ribs: USNM 214431 (coll. 

Wallace L. Ashby); numerous uncataloged USNM specimens.

Virginia (Westmoreland County; Calvert Formation): Partial skeleton: USNM 542440 (coll. Peter McCrery, David Bohaska, Daryl Domning, Nardos Fessaha, James McDonald, and 

David and James Laist).

North Carolina (Beaufort County; Pungo River Formation(?), Lee Creek Mine) Exoccipitals: USNM 244182 (coll. 

Peter Harmatuk), USNM 476404 (coll. Becky and Frank 

Hyne). Squamosal: USNM 391875 (coll. Pam and Tom 

Burns). Humeri: USNM 476405 (coll. Peter Harmatuk), USNM 

476406-8 (coll. Becky and Frank Hyne), USNM 476410 (coll. 

F. L. Pearce), USNM 559311 (coll. Clyde Swindell; donated by 

Judy Stiles). Vertebra and rib fragments: USNM 306481 (coll. 

Vincent Schneider); numerous uncataloged USNM specimens.

Range. Late early to early middle Miocene; from the 

Chesapeake Bay region, USA, to the coasts of Brazil(?) and Peru.

Emended Diagnosis. Species of Metaxytherium with 

medium body length (2–3 m; shared with M. serresii and with M. 

albifontanum Vélez-Juarbe and Domning, 2014). Differs from 

M. albifontanum by the more anterior position of the ventral 

extremity of its jugal (character state 85[2] of Domning and Aguilera, 2008). Differs by its smaller tusk from M. serresii and M. 

subapenninum. Differs by its lesser rostral deflection (50°–60°) 

from M. arctodites (80°), M. floridanum (67°–81°), and M. subapenninum (57°–63°). Metaxytherium crataegense and the other 

Metaxytherium species also have an anteroposteriorly elongate 

zygomatic-orbital bridge of the maxilla (state 14[0] of Domning and Aguilera, 2008), whereas the bridge is shortened (state 

14[1]) in some individuals of M. floridanum.

Comments. Metaxytherium of the same general (early to 

middle Miocene) age and not demonstrably different from those 

of the Chesapeake region have also been found in Cuba (Varona, 

1972), Brazil (Toledo and Domning, 1991), and Peru (Muizon 

and Domning, 1985). All are likely to represent the same species, which appears to differ slightly (in smaller size, slenderer 

mandible, and lesser rostral deflection) from the later species M. 

floridanum of Florida (Domning, 1988). However, M. crataegense is poorly sampled relative to M. floridanum, and its distinction from the latter has yet to be clearly demonstrated. For 

example, direct comparison of the immature dentary of USNM 

16757 (Figure 5.4A,B) with immature Bone Valley dentaries of 

comparable growth stage (USNM 356683, 356688) shows essentially no difference in either size, depth of horizontal ramus, 

or rostral deflection. The depth of the ramus is greater in adult 

M. floridanum, but we still lack good, fully adult specimens of 

the Calvert species to compare with the Florida specimens. 

An adult humerus from the Lee Creek Mine in North Carolina (USNM 559311) is, like most other remains from this mine, of 

uncertain stratigraphic provenance. Its proportions fall within the 

range of variation of M. floridanum: the ratio of its distal breadth 

(dimension EF, further defined in Table 5.3) to a measure of its 

overall length (QR, further defined in Table 5.3) is 0.41, compared 

with an average of 0.45 (observed range = 0.40–0.51; N = 12) in 

Florida specimens of M. floridanum. European species have similarly broad ranges of variation: for M. krahuletzi (early Miocene), 

0.36–0.44 (N = 14), for M. medium (middle Miocene), 0.39–

0.48 (N = 8), and for M. serresii (late Miocene–early Pliocene), 

0.37–0.51 (N = 7). However, Metaxytherium is not recorded in 

the western Atlantic later than late Miocene (early Hemphillian) 

time (Domning, 1988), whereas the Yorktown Formation in the 

Lee Creek Mine is considerably later (early Pliocene, N19, Hazel, 

1983; latest(?) Hemphillian, Eshelman and Whitmore, 2008). 

Therefore, the other, lower unit exposed in the mine—the Calvertcorrelative Pungo River Formation—is more likely than the Yorktown Formation to be the source of this specimen.

Reinhart (1976:220–228) referred to M. calvertense several 

specimens from the Bone Valley Formation of Florida; these have 

since been placed in M. floridanum by Domning (1988). 

One additional report of “Metaxytherium, cf. M. calvertense” 

is evidently also erroneous. MacPhee and Wyss (1990) described 

under this name a mandible (AMNH-VP 125780) and a set of 

vertebrae and ribs (AMNH-VP 125781) from the early Miocene 

Miranda Sand Member of the Cibao Formation in Puerto Rico. 

However, features of the mandible suggest that these specimens 

more likely represent a dugongine (Vélez-Juarbe, 2012).

Going back further in time, new fossils from Florida and 

South Carolina (Metaxytherium albifontanum Vélez-Juarbe and 

Domning, 2014) now trace the genus Metaxytherium as far back 

as the late Oligocene in the New World, significantly earlier than 

in Europe, where it is currently recognized only from the early 

Miocene onward. 

Metaxytherium floridanum Hay, 1922

Type Locality. Florida, Polk County, near Mulberry; 

Lower Bone Valley Formation, probably early Clarendonian 

(late middle Miocene).

Range. Metaxytherium floridanum has previously been 

recorded only from the middle and late Miocene (Clarendonian 

and possibly late Barstovian and early Hemphillian) of Florida 

(Domning, 1988).

Metaxytherium cf. M. floridanum Hay, 1922

FIGURES 5.5B, 5.7O–S; 

TABLE 5.2

Localities, Formations, and Ages of Included Specimens. 

Maryland (Calvert County, near Little Cove Point and Chesapeake Ranch Estates): The exposures here all seem to correlate 
NUMBER 100 • 251

to the late Miocene St. Marys Formation (beds 21–23) and higher 

units (Ward and Andrews, 2008: fig. 5, sections C-16, C-17). At 

least the squamosal (USNM 542432) was collected in situ from 

the Little Cove Point Member of the St. Marys Formation.

Virginia (Westmoreland County, South Bank of the Potomac 

River between Stratford Hall and Westmoreland State Park): As 

noted above, the section here exposes parts of the Calvert, 

Choptank, and Eastover Formations (Ward and Andrews, 2008: 

fig. 7, sections PO-11, PO-12). The source of the sirenian remains 

is thus uncertain but is higher than the Plum Point Member of the 

Calvert Formation, which has produced M. crataegense, and thus 

is in either the Choptank or the Eastover Formation.

Included Specimens.

Maryland: CMM-V-4074 (exoccipital; coll. John 

Nance), USNM 542432 (squamosal; coll. Jeff O’Neil), USNM 

452480 (periotic; coll. Elizabeth M. Cridlin), USNM 241546 (immature scapula; coll. Jeff O’Neil; Figure 5.5B), USNM 451030 

(scapula fragment; coll. Elizabeth M. Cridlin), USNM 542433 

(cast of humerus; coll. Oliver Goldsmith), USNM 542434 (anterior 

rib; coll. David Bohaska), CMM-V-4748 (rib; coll. John Nance), 

CMM uncataloged (miscellaneous rib and vertebra fragments).

Virginia: USNM 542436 (large adult humerus; coll. David 

Blondin; Figure 5.7O–S), USNM 542437-38, 542440-41 (clusters of vertebrae and ribs), USNM 377443-5 (other vertebra 

fragments and a rib). 

Comments. The specimens from the St. Marys Formation are significantly later chronostratigraphically than those from 

the Calvert Formation and are roughly contemporaneous with M. 

floridanum from Florida; I tentatively assign them to the latter 

species on that chronostratigraphic basis. As noted above, these 

Florida animals may have been slightly larger than M. crataegense, 

with deeper mandibles and greater rostral deflections. The squamosal (USNM 542432) closely resembles some M. floridanum, 

such as USNM 323127 (Domning, 1988). The large humerus 

from Virginia (USNM 542436; Figure 5.7O–S, Table 5.2) is at or 

above the maximum recorded size of M. floridanum (Domning, 

1988: tbl. 10). It could have come from the upper part of the Calvert Formation, which is exposed along with the Choptank and 

Eastover Formations in the area where it was collected; however, 

its size seems more consistent with the age of the higher units, so 

it and the other remains from the same site are likewise tentatively 

assigned to M. floridanum in order to call attention to this species’ 

possible occurrence in the Chesapeake Group. However, until M. 

crataegense and M. floridanum are more adequately distinguished 

and Chesapeake Group specimens clearly showing diagnostic 

features of M. floridanum are found, the latter name cannot be 

applied in this region without qualification.

Subfamily Dugonginae (Gray, 1821) Simpson, 1932

Genus Nanosiren Domning in Domning and 

Aguilera, 2008

Type Species. Nanosiren garciae Domning in Domning 

and Aguilera, 2008.

Type Locality. Florida, Manatee County, Four Corners 

Mine; Upper Bone Valley Formation, latest Hemphillian (early 

Pliocene), ca. 5.3–4.9 mya.

Range. The genus Nanosiren is believed to have lived from 

the early Miocene through the early Pliocene and inhabited the 

eastern and southeastern United States, the Caribbean region, 

and northern South America, as well as the Pacific coast of South 

America (Domning and Aguilera, 2008). Its late Miocene representative, N. sanchezi Domning and Aguilera, 2008, known 

from Venezuela is the only other named species of the genus.

Nanosiren sp.

FIGURES 5.4C,D, 5.5C, 5.7A–D, 5.8C, 5.9E; 

TABLES 5.1–5.4

Metaxytherium calvertense Kellogg, 1966:71 (in part: USNM 16630, 16715).

Nanosiren sp., Domning and Aguilera, 2008:486, 496.

Localities, Formations, and Ages of Included Specimens. 

Maryland (Calvert County): Calvert Formation, Plum Point 

Member, beds 11–12; early middle Miocene, probably in the 

lower part of planktonic foraminiferal zone N9, late early Barstovian North American Land Mammal Age, ca. 15 mya (Gibson, 1983b:362; Tedford et al., 1987: fig. 6.2).

Virginia (Westmoreland County, Wakefield): Calvert Formation, bed 10 or 11 (R. Weems, pers. comm.); middle Miocene.

North Carolina (Beaufort County, Lee Creek Mine): Pungo 

River Formation(?), upper part; latest early Miocene, planktonic 

foraminiferal zone N8, early Barstovian, ca. 16 mya (Gibson, 

1983b:360; Tedford et al., 1987: fig. 6.2).

Included Specimens. 

Maryland: USNM 16630 (subadult partial skeleton; coll. 

George E. Marsh; Figures 5.4C,D, 5.9E), USNM 16715 (scapula; 

coll. William E. Salter; Figure 5.5C), USNM 23246 (humerus; 

coll. W. H. Boss and Remington Kellogg), USNM 25902 (radiusulna; coll. unknown; Figure 5.8C), USNM 186897 (thoracic 

vertebra; coll. R. Lee Collins), USNM 215078 (humerus; coll. 

MacKenzie L. Kelly; Figure 5.7A–D), USNM 546149 (humerus; 

coll. Russell Sennett, donated by George Klein), USNM 559306 

(2 partial ribs; coll. William E. Salter; may be part of the same 

individual as USNM 16630), USNM 559310 (7 complete or partial ribs; coll. Paul Moffett), CMM-V-2690 (juvenile humerus; 

coll. William F. Douglass Jr.). 

Virginia: USNM 542439 (right rib; coll. Frank C. Whitmore 

Jr. and James Kaltenbach).

North Carolina: USNM 546113 (symphyseal portion of left 

dentary; coll. Peter Harmatuk and sons), USNM 205472 (adult 

humerus; coll. William Bennett), USNM 321923 (immature humerus; coll. Peter Harmatuk), USNM 460119 (thoracic vertebra; 

coll. Anne Leightner Kienlen). 
252 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A B

C

D

E

100 mm

4 inches

FIGURE 5.5. Scapulae of Chesapeake Group dugongids, lateral views. (A) Metaxytherium crataegense, USNM 

16757 (holotype of M. calvertense), right scapula reversed. (B) Metaxytherium cf. M. floridanum, USNM 241546, 

left scapula (immature). (C) Nanosiren sp., USNM 16715, left scapula. (D) Dugonginae, gen. et sp. indet., Pamunkey River, Virginia, USNM 377449, right scapula reversed. (E) Metaxytherium crataegense, CMM-V-242, partial 

right scapula reversed (eroded by unknown cause). See also the cranial elements of this specimen in Figure 5.6B–D 

and the humerus of this specimen in Figure 5.7J–N.
NUMBER 100 • 253

Comments. Kellogg (1966) included in his concept of 

Metaxytherium calvertense some remains of small sirenians, 

which he regarded as juveniles of the larger M. calvertense. Principal among these was the partial skeleton USNM 16630, which 

included the mandible (Figure 5.4C,D). However, Kellogg misinterpreted its dentition as showing it to be much less mature than 

USNM 16757, the holotype of M. calvertense, which is itself immature. In fact, both specimens are of roughly the same life stage, 

with unerupted third molars (Domning and Aguilera, 2008), 

which shows that they represent different species of markedly 

different sizes. “Metaxytherium calvertense” is likely to have 

been close to 3 m in body length, whereas the early Pliocene 

species Nanosiren garciae is estimated to have been only about 

2 m long (Domning and Aguilera, 2008; Sarko et al., 2010), although the Calvert Nanosiren was slightly larger. The specimens 

from the Lee Creek Mine, North Carolina, are here deemed to 

come from the Pungo River Formation and to represent the same 

unnamed species as the Calvert Formation specimens; however, 

given their fragmentary nature, derivation from the overlying, 

early Pliocene Yorktown Formation cannot be excluded on the 

basis of their morphology, in which case they would presumably 

represent N. garciae.

There is further confusion regarding USNM 16630. Kellogg 

(1966:71) reported this skeleton as including the right scapula and 

as having been collected by “G[eorge]. E[verett]. Marsh, Dec. 24, 

1939; 646 yards south of mouth of Parker Creek, Calvert Co., 

TABLE 5.2. Measurements (mm) of scapulae of sirenians from the Chesapeake Group. Letters in parentheses denote abbreviation used 

by Domning (1978, 1988) for the given measurement. Other abbreviations: d = lacking distal epiphysis; e = estimated; + = broken. A 

dash (–) indicates measurement could not be taken on the specimen. Specimen USNM 16757 is the holotype of M. calvertense.

Halitheriinae Dugonginae

Metaxytherium M. cf. Dugonginae

crataegense floridanum Nanosiren sp. gen. et sp. indet.

USNM USNM USNM USNM USNM USNM USNM

16757 23213 241546 16630 16715 241562 377449

(subadult, (adult, (immature, (subadult, (subadult, (adult, (adult,

 Dimension right) right) left) right) left) right) right)

Maximum length, vertebral border 281 – 224d 199 200 – 292

to border of glenoid fossa (AB)

Mediolateral width of glenoid 47e 41 30d 25 24 47 42e

fossa (BI)

Lateral border of glenoid fossa to 49 – – 26e 25 – 46

to inside of concave distal end of 

spine (BJ)

Maximum breadth of blade 208 – 137 133 132 – 219e

dorsally (CD)

Minimum anteroposterior 44 42 32 29 29 – 49

breadth of neck (EF)

Maximum anteroposterior breadth 74 77 52d 47 46 95 74

of distal end (GH)

Summit of spine to medial side 57 – 40 – 38 – 47

of blade, measured parallel to 

plane tangent to posterior edges 

of spine and neck (KL)

Anteroposterior length of glenoid 50 51 – 35 33 58 52

fossa (MN)

Length of teres major origin from 73 – 51 44 44 – 60+

teres protuberance to posterior 

corner of blade (TMO)
254 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY TABLE 5.3. Measurements (mm) of humeri of sirenians from the Chesapeake Group. Letters in parentheses denote abbreviation used by Domning (1978, 1988) for the given measurement. Other abbreviations: e = estimated; p = lacks proximal epiphysis; * = measurement taken on right humerus. A dash (—) indicates measurement could not be taken on the specimen. Specimen USNM 16757 is the holotype of M. calvertense. Halitheriinae Dugonginae Metaxytherium crataegense M. cf. floridanum Nanosiren sp. Dugonginae gen. et sp. indet. USNM USNM USNM USNM USNM USNM USNM USNM USNM USNM USNM USNM 16757 476415 559311 542436 542433 23246 215078 546149 241562 241562 377442 437570 (immature, (adult, (adult, (adult, (adult, (adult, (immature, (immature, (adult, (adult, (adult, (adult, Dimension left) left) right) left) left) right) left) right) left) right) right) left) Maximum length, 

—

— 233 252

—

— 110p

— 191 191

—

—

greater tubercle to distal end (AB)Maximum breadth, 76 103 107 118

—

— 45 39 93 91 77 85

greater to lesser tubercle (CD) Maximum breadth, 68*

— 82 101 75 43 42

— 89

—

—

—

ectepicondyle to entepicondyle (EF)Maximum thickness, 

— 98 110 112e 88

—

—

— 98 99 65

—

posterior side of head to anterior side of greater tubercle (GH) Maximum thickness, 

—

— 33 34e 34 18 19

— 31 30

—

—

posterior to anterior ends of medial rim of trochlea (IJ)Proximolateral- 53 56 67 72 42e

—

—

— 62 56 51 63

mediodistal breadth of head (KL)Proximomedial- 46 57 65 71 41

—

—

— 53 53 45 59

distolateral breadth of head (MN) Breadth of anterior 

—

— 57 72e 56e 24 27

— 54

—

—

—

side of trochlea (OP) Length, saddle 

—

— 199 213e 166

—

—

— 171 165

—

—

between head and greater tubercle to saddle of trochlea (QR)Maximum mediolateral 25 36 34 51 40 14 15 13 30 30 26

—

diameter perpendicular to lateral surface, midshaft (MLD)
NUMBER 100 • 255

Md., in bluish sandy clay, zone 12, Calvert Formation.” A label 

with the specimen adds that it was found “at base of cliff, found 

within a space 6′ × 6′.” Kellogg (1966:71) next reported USNM 

16715, a left scapula (Figure 5.5C) collected by “William E. Salter, 

July 11, 1942; 1,400 feet south of mouth of Parker Creek (in second cliff), Calvert Co., Md., in blue clay of zone 11, about 3 feet 

below top of zone, Calvert formation.” However, Kellogg (1966: 

pl. 43, fig. 2) then illustrated this left scapula but misidentified it 

in the caption as part of “USNM 16630”—the skeleton that did 

not include a left scapula. This mistaken citation of the number 

is understandable: direct comparison of the left and right scapulae reveals that they are of identical size (Table 5.2), morphology, osteological maturity (with fully fused distal epiphyses), and 

preservation, so they surely represent parts of the same individual, 

collected 2.5 years apart by two different people. The discrepancies in the reported localities and horizons are harder to explain. 

The difference between “646 yards” (=1,938 ft or ~591 m) and 

“1,400 feet” (~427 m) might be ascribed to inaccurate estimation 

of the distance or to different definitions of the “mouth of Parker 

Creek,” or the mouth may even have shifted because of storms, as 

sometimes happens (D. Bohaska, USNM, and S. Godfrey, CMM, 

pers. comm.). The identification of bed 12 as the source of USNM 

16630 may also be wrong since “bluish sandy clay” is more typical of bed 11 (Bohaska and Godfrey, pers. comm.). But any or all 

of these errors seem more likely than two scapulae being so similar 

in size and shape yet from different strata and different individuals 

of a species rare in these deposits. 

Finally, two Nanosiren ribs (USNM 559306) and a Metaxytherium vertebra (USNM 559307) were collected by William E. 

Salter on 8 August 1943 “in the water at the bog iron N. of 

Scientists Cliff,” a location arguably close or identical to those 

of the two finds described above. One rib is the right second rib; 

the other is the distal part of a left mid-thoracic rib. Both could 

pertain, without duplication, to the partial ribcage (12 ribs) 

of USNM 16630, which they match in size and preservation. 

It is easy to envision USNM 16630 as a tight cluster of bones 

comprising most of the skeleton, excavated in 1939, the scapula 

USNM 16715 becoming exposed close by in 1942, and the ribs 

USNM 559306 having been washed out of the cliff by 1943. I 

believe that all of these most likely represent the same individual.

 Genus Corystosiren Domning, 1990

Type Species. Corystosiren varguezi Domning, 1990.

Type Locality. Mexico, state of Yucatán, between 

Tizimín and Colonia Yucatán; Carrillo Puerto Formation, early 

Pliocene.

Range. Early Pliocene; Yucatán and Florida. An undescribed primitive species occurs in the South Carolina phosphate 

deposits, whose fauna includes early and middle Miocene elements (Domning, 1989, 1990, 2001).

Aff. Corystosiren sp. 

FIGURES 5.6A, 5.8E

Locality, Formation, and Age of Included Specimen 1. Maryland, Prince Georges County, Potomac Knolls, SW 

side of North Star Drive just W of Old Lantern Court, 38°43′46.0′′N, 

76°58′56.2′′W: green clay with small shark teeth and phosphate 

pebbles; lower Calvert Formation, just above its contact with the 

Eocene Nanjemoy Formation. Outcrops approximately 2.5 km S of 

this locality are assigned by Glaser (1986:64–65) to the “basal Calvert Formation,” which there consists of “3 to 4 feet of dense, clayey 

olive-green to olive-brown sand” overlying the Nanjemoy Formation. 

Early Miocene.

Included Specimen 1. USNM 542442 (tusk fragment; 

coll. George C. Fonger; Figure 5.8E). 

Description. A triangular fragment of a large, flattened 

tusk, 73 × 48 × 10 mm thick, black, partly covered on the outer 

surface with paper-thin gray enamel. The slightly convex outer 

surface exhibits shallow longitudinal grooves 8–12 mm wide; the 

enamel has faint growth lines perpendicular to these grooves.

Comments. This fragment is too broad and flat to represent a form like Dioplotherium, but it compares well with the 

medial surfaces of tusks of large dugongines such as Corystosiren (cf. Domning, 1990: fig. 4B). Indeed, the overall convexity and the spacing of the grooves exactly match those of such 

a tusk (SCSM 2013.33.1) collected by Vance McCollum from 

the Wando Shipping Terminal spoils near Charleston, South 

Carolina. Since an unnamed species of Corystosiren is otherwise 

known to be present in the South Carolina phosphate deposits 

(as noted above), it would not be surprising to encounter it in the 

Calvert Formation or its equivalents.

Locality, Formation, and Age of Included 

Specimens 2 and 3. North Carolina, Beaufort County, Lee 

Creek Mine: specimen 2’s white or light gray indurated limy silt matrix, firmly attached to the bone, contains phosphatic sand grains 

and abundant molds of shells. According to D. Bohaska and R. 

Purdy (pers. comm.), this lithology almost certainly represents the 

indurated unit 4 or 5 of the Pungo River Formation, the matrix of 

which “tends to be firmly attached to the specimens derived from” 

that bed (Kazár and Bohaska, 2008:271). Late early Miocene.

Included Specimen 2. USNM 498744 (skullcap; coll. 

Gaye Williams; Figure 5.6A). 

Included Specimen 3. USNM 476409 (skullcap fragment; coll. Robert W. Purdy et al.).

Description. USNM 498744, the skullcap of a juvenile 

animal (Figure 5.6A), consists of the parietals fused to the broken 

supraoccipital; they were joined to the frontals by a broad, deep, 

interdigitated sutural surface, which has a 1 cm long anterior protuberance at its center. The temporal crests are widely (6.5 cm) 

separated anteriorly and converge posteriorly; they are low (~4 

mm high), distinct, located on the overhanging edges of the flat 

or slightly convex parietal roof, and separated by ~2.5 cm where 

they are closest together (~2 cm in front of the nuchal ridge, which 
256 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
NUMBER 100 • 257

intersects them). The crests are sharp posteriorly and as narrow 

there as they are anteriorly. The parietal roof is convex anteroposteriorly. The external occipital protuberance is large. Endocranially, the posteriorly sharp bony falx cerebri is flattened at the 

frontoparietal suture, which is more or less straight. The internal 

occipital protuberance is distinct but blunt. The skullcap is 36 mm 

thick in the anterior midline and 70 mm wide across its divergent, 

broken anterior extremities. The maximum width of the parietals 

below the level of the roof (measurement GG′ [defined in Table 

5.1]) is about 75 mm; the midline length from the frontoparietal 

suture to the rear of the external occipital protuberance (measurement P [see Table 5.1]) is about 100 mm.

USNM 476409 is a similar but less complete fragment, preserving only the anterior part of the parietals with their anteriorly diverging, overhanging temporal crests, and is 31 mm thick 

in the anterior midline. The parietal roof is flat, with a slight 

median ridge.

Comments. USNM 498744 resembles adult skullcaps 

of Corystosiren varguezi (Domning, 1990) in its overall length, 

but its width and thickness are much smaller, and it lacks their 

strong sculpture on the posterior part of the roof. This difference 

may be due to its immaturity, and/or it may represent a different, 

more primitive species.

Subfamily Dugonginae, gen. et sp. indet.

FIGURES 5.6F, 5.7E–I, 5.8A, 5.9D; 

TABLES 5.1–5.4

Locality, Formation, and Age of Included 

Specimens 1 and 2. Maryland, Charles County, Popes Creek: 

Popes Creek Sand bed of the Calvert Formation. Early Miocene.

Included Specimen 1. USNM 241562 (right scapula, 

right and left humeri [Figure 5.7E–I], left radius, ulna [Figure 

5.8A], and unciform(?); 12 ribs and 14 fragments; coll. Norman 

Riker and Ralph Eshelman).

Included Specimen 2. CMM-V-244 (approximately 6 

fragments of vertebrae and 26 of ribs; coll. Norman Riker and 

Calvin Taylor; not part of same specimen as USNM 241562; 

taxonomic referral provisional; see below).

Locality, Formation, and Age of Included 

Specimen 3. Virginia, King William County, Pamunkey 

River between Piping Tree Ferry and Grimes Landing: pebble 

bed about 0.6 m [2 ft] above the unconformable contact of 

the Calvert Formation with the Eocene Piney Point Formation 

(Domning, 1984b). The pebble bed and overlying deposits are 

here considered part of the Popes Creek Sand bed of the Calvert 

Formation (early Miocene).

Included Specimen 3. USNM 377441-2, 377446-7, 

377449 (left dentary, atlas, axis, 3 other cervical and 4 anterior thoracic vertebrae, about a dozen ribs [Figure 5.9D], right 

scapula, proximal part of right humerus, and miscellaneous 

bone fragments; recovered over several years by David Bohaska, 

Lauck Ward, Robert Weems, Norman Riker, Ralph Eshelman, 

Bruce Alsopp, and Daryl Domning, 1973–1983, but almost certainly representing the same individual; Domning, 1984b).

Locality, Formation, and Age of Included 

Specimen 4. North Carolina, Beaufort County, Lee Creek 

Mine: Pungo River Formation(?) (latest early Miocene).

Included Specimen 4. USNM 437570 (proximal end 

of left humerus; coll. Peter Harmatuk; Figure 5.6F). 

Locality, Formation, and Age of Included 

Specimen 5. Maryland, Calvert County, beach at Kaufmann 

Camp, S of Plum Point: Calvert Formation(?) (early middle 

Miocene(?)).

Included Specimen 5. USNM 363456 (distal end of 

left humerus; coll. George C. Fonger). 

Comments. In the absence of cranial material, the best 

evidence for the dugongine identity of these specimens comes 

from the humerus. Surprisingly, humeri of only three fossil dugongines are known: a complete one belonging to the holotype 

of Crenatosiren olseni (latest Oligocene, Florida; Domning, 

1997: fig. 6B), the proximal half of one associated with an unpublished skull of Dioplotherium cf. D. allisoni (USNM 521235; 

middle Miocene, California), and several humeri of Nanosiren 

spp. (Miocene–Pliocene, southeastern USA; Domning and Aguilera, 2008: fig. 6A). Although differing in other respects, all 

of these (as well as the living Dugong dugon; Sukhanov et al., 

FIGURE 5.6. (Facing page) (A) Parietal-supraoccipital skullcap of aff. Corystosiren sp., Lee Creek Mine, North Carolina, USNM 498744 

(juvenile), with some adhering matrix, dorsal view. (B–D) Metaxytherium crataegense, Maryland (CMM-V-242), parts of associated adult skull 

eroded by unknown cause: (B) Left premaxilla with attached supraorbital process of frontal, lateral view. (C, D) Fragment of left dentary (base 

of ascending ramus and part of alveolar process, showing coronoid canal at left and labial sides of m2–3 alveoli at right), dorsal view and medial 

views, respectively. Note the knife-sharp eroded edges and thinness of bone labial to alveoli. See also the scapula of this specimen in Figure 5.5E 

and the humerus of this specimen in Figure 5.7J–N. (E–J) Humeri of Chesapeake Group dugongids: (E) Metaxytherium crataegense, USNM 

16757 (holotype of M. calvertense), Maryland, left humerus with unfused epiphysis, posterior view. (F) Dugonginae, gen. et sp. indet., Lee Creek 

Mine, North Carolina, USNM 437570, head of left humerus in posteroproximal view. (G–J) Dugonginae, gen. et sp. indet., Pamunkey River, 

Virginia, USNM 377442, right humerus in medial, anterior, lateral, and posterior views, respectively. The 100 mm scale applies to images E–J.
258 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A C B D E

F H G I

J

K L M N

O

P Q R S

100 mm

4 inches
NUMBER 100 • 259

1986: fig. 54) share the unusual trait of a humeral head that is 

transversely expanded in its proximal portion, giving it a more 

or less triangular shape overall (Figures 5.6F,J, 5.7i). This trait 

contrasts with the condition both in halitheriine dugongids (such 

as Metaxytherium; e.g., Domning, 1988: fig. 11B) and in hydrodamalines (Domning, 1978: pl. 13g,h), where the head is more 

or less elliptical and oriented obliquely to the shaft (Figure 5.7S). 

I hypothesize that a roughly triangular, transversely expanded 

humeral head characterizes the Dugonginae, and on this basis I 

refer the specimens listed above to that subfamily.

Included specimens 1, 3, and 4—the humeri from Popes 

Creek (USNM 241562; Figure 5.7E–I), the Pamunkey River 

FIGURE 5.7. (Facing page) Humeri of Chesapeake Group dugongids. (A–D) Nanosiren sp., USNM 215078, left humerus in posterolateral, 

anterior, medial, and posterior views, respectively. (E–I) Dugonginae, gen. et sp. indet., Popes Creek, Maryland, USNM 241562, left humerus in 

proximal, lateral, anterior, medial, and posterior views, respectively. (J–N) Metaxytherium crataegense, CMM-V-242, right humerus showing 

extensive postmortem erosion by unknown cause, in proximal, posterior, lateral, anterior, and medial views, respectively. See also the scapula 

of this specimen in Figure 5.5E and the cranial elements of this specimen in Figure 5.6B–D. (O–S) Metaxytherium cf. M. floridanum, Stratford 

Hall, Virginia, USNM 542436, left humerus in proximal, lateral, anterior, medial, and posterior views, respectively. Specimens lightly coated 

with sublimed ammonium chloride.

TABLE 5.4. Measurements (mm) of radii and ulnae of sirenians from the Chesapeake Group and (for Trichechus) overlying Pleistocene(?) 

deposits. Letters in parentheses denote abbreviation used by Domning (1978, 1988) for the given measurement. Other abbreviations: d 

= lacking distal epiphysis; e = estimated; + = broken. A dash (–) indicates measurement could not be taken on the specimen. 

Dugonginae gen. Trichechus

Metaxytherium crataegense Nanosiren sp. et sp. indet. manatus

USNM 23213 USNM 186896 USNM 25902 USNM 241562 USNM 9346

Dimension (adult, right) (adult, right) (adult, right) (adult, right) (adult, left)

Total length of ulna (AB) – – 103d 193d 157+

Total length of radius, anterior 139d – 83d 160d 117+

lip of semilunar notch to distal 

end (CD)

Height of semilunar notch, 30 – 20 32 39

anterior tip of olecranon to

anterior radial lip of notch (EC)

Thickness of olecranon, anterior 36 37 21 40 27

tip to posterior side (EF)

Distal thickness, anterior side – – 38 83 60

of radius to posterior side of 

ulna (GH) 

Maximum mediolateral breadth, 44 – 23 53 39

radial portion of semilunar 

notch (IJ) 

Maximum mediolateral breadth, 22 45 – 58 –

ulnar portion of semilunar 

notch (KL)

Minimum mediolateral breadth, 22 21 14 26e 27

of semilunar notch at its 

midsection (MN)

Minimum thickness of 27 27 15 26 24

olecranon, posterior side to 

semilunar notch (OP)
260 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

A C B

D

E

F

50 mm

2 inches

50 mm

2 inches
(USNM 377442; Figure 5.6G–J; Domning, 1984b: figs. 3–4), 

and the Lee Creek Mine (USNM 437570; Figure 5.6F), respectively—have several traits in common. All share a subtriangular 

head with the lateral corner extended markedly laterad, an irregular cavity bordering the medial edge of the head, and a very distinct insertion scar for the infraspinatus muscle. They also share 

a prominent, strongly recurved deltoid crest that extends farther 

laterad from the shaft than in most dugongids; indeed, the distance is almost equal to the diameter of the shaft itself (Figure 

5.7G,I). USNM 377442 (Figure 5.6G–J) is slightly smaller than 

the others, but all are mature, with fully fused epiphyses. The 

Californian specimen (USNM 521235) differs from these in that 

its head is less triangular, the medial cavity and muscle scar are 

less distinct, the deltoid crest does not extend so far laterad, and 

the bicipital groove is much narrower. Therefore, I surmise that 

the Chesapeake Group specimens do not represent Dioplotherium. They may possibly pertain to the aff. Corystosiren reported above.

The Pamunkey River scapula (USNM 377449; Figure 5.5D) 

lacks the proportionately narrower neck and broadly concave 

anterior outline consistently seen in species of Metaxytherium

(Figure 5.5A,B) or Nanosiren (Figure 5.5C). Preliminary data 

suggest that this condition may be characteristic of some, though 

not all, dugongines.

Included specimen 5 (USNM 363456), an eroded humerus, 

resembles the humerus of USNM 241562 in that the ridge 

leading down to the ectepicondyle curves outward more than 

in Metaxytherium; this gives the complete bone a more strikingly dumbbell-like shape. Its dimension measurements are 

EF = 67 mm, IJ = 24e mm, and OP = 46e mm (see Table 5.3 for 

definitions).

The dentary of included specimen 3, the Pamunkey River 

specimen (USNM 377446; Figure 5.4E; Domning, 1984b: fig. 

1), is incomplete anteriorly and less distinctive than the humeri, 

but it appears to have been more downturned anteriorly than 

Metaxytherium and perhaps more like USNM 521235. This 

might further support a referral to the Dugonginae. 

Since included specimen 2 lacks a humerus or other parts 

diagnostic of the Dugonginae, it is listed here on the conjectural 

basis that a unique feature of its ribs may exclude it from the 

Halitheriinae. In CMM-V-244, unlike other dugongids, the rib 

capitula are abruptly constricted and much narrower anteroposteriorly (<1.5 cm) than the width of the rib at the level of the tuberculum and are deeper dorsoventrally (1.5–2.0 cm) than they 

are wide.

A TAPHONOMIC MYSTERY

A peculiarity of some sirenian fossils, observed in several 

parts of the world and at different geological periods, is that 

the individual bones or parts of them have been worn away as 

though they had been sandblasted (Van Orden and Godfrey, 

2008). The normally robust ribs, for example, may be smoothly 

sharpened to a point at one end, as if they were sculpted out of 

ice that partly melted, preserving the bone’s shape in “emaciated” form. They are found in this condition when excavated, 

so it is not the result of postburial erosion. Rather, we seem to 

be dealing here with a phenomenon in the realm of taphonomy 

(the study of how fossils get buried and preserved from death to 

fossilization). It happens that perhaps the most dramatic and revealing example of this unexplained phenomenon is a specimen 

from the Calvert Formation in Maryland. (Other Chesapeake 

Group examples are known from Virginia [USNM 542440] and 

from the Lee Creek Mine.)

Almost nothing has been written on this subject; the only 

detailed discussions I have seen are found in papers in German 

by Erich Thenius (1952:33–36) and Otto Sickenberg (1934:128, 

215–218, pl. 6, figs. 3–4). Thenius concluded that the attrition 

of the bones is due to just what it looks like: wind erosion. However, it seems questionable whether sirenian bones would be exposed very often to subaerial sandblasting before burial, which 

would require long exposure to strong winds in a sandy environment, and under such dynamic conditions on a beach, small 

bones would be unlikely to remain associated (see below). Other 

possibilities come to mind: underwater sandblasting by strong 

bottom currents, for example, or slow erosion by weak currents 

(as favored by Sickenberg), chemical dissolution by acids, or 

even the action of living organisms. 

NUMBER 100 • 261

FIGURE 5.8. (Facing page) (A–D) Radii and ulnae of Chesapeake Group sirenians, lateral views: (A) Dugonginae, gen. et sp. indet., Popes 

Creek, Maryland, USNM 241562, right radius-ulna. (B) Metaxytherium crataegense, Maryland, USNM 23213, right radius and partial ulna. 

(C) Nanosiren sp., Maryland, USNM 25902, right radius-ulna. (D) Trichechus manatus, Fairhaven, Maryland, USNM 9346, right radius-ulna. 

Note the short olecranon process and the proximally curved radius that distinguish the Pleistocene manatee (D) from the Miocene dugongids 

(A–C). (E, F) Tusks of dugongine dugongids: (E) Right tusk fragment of aff. Corystosiren sp., Potomac Knolls, Maryland, USNM 542442, 

anterior to left; medial surface showing enamel with growth lines and longitudinal fluting. (F) For comparison, left partial premaxilla and 

complete tusk (cast, reversed) of cf. Rytiodus from Brazil, MPEG 206-V (Toledo and Domning, 1991), in medial view. The entire medial surface 

of each tusk was covered with paper-thin enamel, producing a self-sharpening posteroventral edge. Specimens lightly coated with sublimed 

ammonium chloride.
262 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

B

A C

D

E

F

100 mm

4 inches

FIGURE 5.9. (A–C) Metaxytherium crataegense, USNM 16757 (holotype of M. calvertense): (A) Mid-thoracic 

vertebra in anterior view. (B) First left thoracic rib in anterior view. (C) Left mid-thoracic rib in anterior view. 

(D) Dugonginae, gen. et sp. indet., USNM 377449, first right thoracic rib in posterior view. (E) Nanosiren sp., 

USNM 16630, left mid-thoracic rib in anterior view. (F) Representation of mid-thoracic section of rib cage of 

Metaxytherium crataegense, based on (A) and (C). Scale bar for F equals 100 mm.
NUMBER 100 • 263

Some of these possibilities, however, can be ruled out by 

simple observations of the bones. They show no signs of tooth 

marks or attachment or encrustation by marine life that could 

account for the attrition and sharpening of their extremities. 

Their eroded surfaces are not pitted but are as smooth as the unaltered parts of the same or other bones. Underwater transport 

and tumbling by waves might account for the wear on isolated 

bones, as is commonly the case with other fossils, but this process would not account for the fact that many of these bones 

(such as ribs) are eroded on only one end, with the remainder of 

the bone pristine. Neither would it explain various examples of 

this erosion seen in still-associated skeletons that plainly did not 

undergo transport and scattering before burial. 

Of these specimens, the most impressive example known to 

me is CMM-V-242 (Figures 5.5E, 5.6B–D, 5.7J–N), a subadult 

partial skeleton of Metaxytherium crataegense from the gray 

clay of bed 13 (3.2 m [10.5 ft] above the top of bed 12) near 

Parkers Creek, found by Joseph Turner and collected by David 

Bohaska, Norman Riker, Wallace Ashby, August Selckmann, 

George Fonger, and Sandy Roberts in 1983. It comprises parts 

of the left premaxilla attached to the supraorbital process of the 

frontal, a maxilla, the left dentary, a heavily worn upper molar, 

both scapulae, the right humerus with the proximal epiphysis attached, about 5 vertebrae, and 27 ribs, with other bone 

fragments. Kidwell (2006:19) stated that “Zones 11–13 reflect 

the deepest water and most offshore conditions — specifically, 

water depths >~40–50 m”—of the Calvert Cliffs stratigraphic 

sequence.

Besides the ribs of this specimen, several of which are sharpened at one end or on one surface, some other bones are eroded 

on all sides, even to the extent of becoming barely recognizable. 

They include several parts of the skull and mandible that have 

largely wasted away: the premaxilla plus frontal (Figure 5.6B), 

weighing only 57.5 g; the dentary (Figure 5.6C,D), weighing 

30.9 g; and the maxilla, weighing 16.9 g. The small size of these 

fragments tells us that the agent of erosion probably did not have 

a lot of energy: strong waves or currents would easily have carried away such small, light, delicate objects if they lay loose on 

the bottom, yet they were found still associated with each other 

and with the heavy ribs. The clay sediment itself indicates a lowenergy environment. Either the bones were stuck on or in the 

sediment so that they were hard to move, or else the erosion was 

caused by very gentle “sandblasting” or by chemical dissolution. 

Van Orden and Godfrey (2008:156A) suggest that “either 

the bones were winnowed mechanically through the activity of 

organisms (akin to bone-eating worm action on whale bones 

in whale-fall communities) or they were dissolved chemically.” 

If the latter occurred, they were unable to determine “if it was 

biologically mediated or happened in the absence of a biological 

agent (i.e. abiotic chemical winnowing) either before or after the 

skeletons were entombed in sediment.”

Questions remain. Why has this kind of attrition been observed only on sirenian bones and not on those of other marine 

vertebrates like whales? Are only sirenians exposed to the corrosional agent (unlikely), or is the reason simply because sirenians 

have thick, dense bones that are relatively homogeneous throughout—and thus suitable material for “sculpture”—whereas other 

vertebrate bones are typically spongy on the inside and so would 

not stand up to such corrosion and preserve its effects? 

A very promising possibility is that some sort of bacterial 

film covered the partly exposed bones embedded in the seafloor 

and secreted corrosive substances that dissolved them. Studies of 

deep-sea whale falls have called attention to the role of microbial 

mats in the destruction of bones. Such mats are “largely absent” 

from buried bones; “no evidence of bacterial mats was observed 

on bone surfaces originally lying below the sediment-water interface” (Bennett et al., 1994:212). Moreover, “there is evidence to 

suggest that microbial bioerosion is negatively correlated to the 

oil content of the bone” (Higgs et al., 2011:14). If this destructive mechanism works in shallow water as it does in the deep 

sea, it could explain why dense bones of sirenians, with their low 

lipid content, may be more prone to this kind of erosion than the 

spongier and oilier bones of other marine mammals.

 We still do not have the complete solution to this minor 

mystery of science, which presents an opportunity and a challenge for clever investigators.

DISCUSSION

The sirenians of the Chesapeake Group are significant in 

that they are the northernmost Tertiary sirenians in the entire 

geological record of the western Atlantic bioprovince. As such, 

we might expect them to represent a depauperate sample of the 

Miocene sirenian diversity encountered at lower latitudes. This 

depauperate condition remains a possibility since only three distinct dugongid lineages (Metaxytherium, Nanosiren, and at least 

one other dugongine, probably Corystosiren) have so far been 

identified in the Chesapeake region, compared with at least four 

lineages (including the dugongines Dioplotherium and Corystosiren), and probably more, in the overall west Atlantic and Caribbean during the early and middle Miocene (Domning, 2001). It 

will be interesting to learn whether any (and which) of the larger 

dugongines were indeed absent from the Mid-Atlantic coast and 

what this implies about paleoenvironmental conditions there. 

Large-tusked dugongines like Dioplotherium and Corystosiren seem to have specialized on uprooting and eating the tough, 

fibrous rhizomes of the larger species of seagrasses (Domning 

and Beatty, 2007). These are “climax” species that tend to dominate seagrass communities if left undisturbed. Sirenians that 

disturbed them by disrupting and removing their rhizome mats 

would have acted as “keystone species,” pushing the seagrass 

communities to earlier, more diverse, and more productive successional stages. Earlier successional stages in turn would have 

provided ecological niches for additional, more delicate species 

of seagrasses and for species of sirenians less able to feed on 
264 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

the large rhizomes (Domning, 2001; Vélez-Juarbe et al., 2012). 

If one or more of the known west Atlantic large-tusked 

keystone sirenians were absent from the Mid-Atlantic region, 

this absence might reflect an absence of their favored seagrasses 

or some other undesirable characteristic of the environment. 

Sensitivity to cool temperatures at Mid-Atlantic latitudes, 

however, seems unlikely to have been a problem, given global 

temperatures in the early to middle Miocene that were higher 

than today’s (Zachos et al., 2001).

Besides the three Chesapeake Group sirenian lineages indicated so far, however, it would not be surprising to find additional 

ones. At any rate, more complete specimens of both Calvert and 

Choptank/St. Marys Metaxytherium spp., and especially the 

dugongines, are eagerly awaited. The Chesapeake Group Nanosiren and aff. Corystosiren are evidently undescribed species. 

Properly identifying and naming these and any other new ones 

will require reasonably complete skulls at a minimum, so there is 

certainly important work for the collector to do.

Once we have a better idea of what these animals looked like, 

we can say with more confidence what they ate and how they 

divided up the available food resources. Analyses of the stable isotopes in their tooth enamel may also shed light on their diets. At 

present, such analyses (e.g., Clementz and Sewall, 2011) have been 

able to confirm only that all these sirenians fed on seagrasses, but 

in the future, more detailed distinctions may be possible.

ACKNOWLEDGMENTS

I am indebted to the host of collectors who have assembled, over many years, the sirenian material discussed above. I 

particularly thank Ralph Eshelman, Stephen Godfrey (CMM), 

Clayton Ray, Frank Whitmore Jr., and above all David J. Bohaska (USNM) for many forms of assistance, especially for sharing their unmatched knowledge concerning the deposits of the 

Chesapeake Group and their fossils. I thank Miranda ArmourChelu (Howard University) for useful discussions and references 

on marine taphonomy and Tom Jorstad (USNM) for help with 

weighing several bones. Stephen Godfrey expertly prepared the 

illustrations, and the late John Pojeta (USNM) graciously provided access to his lab, where most of the fossils illustrated herein 

were whitened with sublimed ammonium chloride. Nicholas D. 

Pyenson, David J. Bohaska, and Jorge Vélez-Juarbe helpfully reviewed the manuscript. 

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An “f” following a page number indicates a figure; a “t” following a page number 

indicates a table.

Acanthocybium, 190–192

A. cf. A. solandri, 190–192, 193f, 204, 205, 206

A. solandri, 192

Acipenseridae, 163, 164f

Acipenseridae gen. et sp. indet., 163f, 204, 206

Acipenseriformes, 163

Acipenser ornatus, 162, 163

Aetobatus, 14, 128–130, 142

A. arcuatus, 128–130, 131f

A. narinari, 130

A. profundis, 130

Agonidae, 174–175, 206

Agonidae gen. et sp. indet., 172f–173f, 174–175

agriculture/farming at Calvert Cliffs, 19, 32, 37

Alexander, J. H., 38

Alligator, 223

A. mississippiensis, 227f

A. olseni, 226f–227f, 239

Alligatoridae, 235

along-strike profiles, 17–18, 18f, 19f, 36–37

Alopias, 47, 97–101, 140, 141

A. cf. A. supercilious, 92, 93, 98–100

A. cf. A. vulpinus, 51–52, 52f, 92, 98–99, 99f, 100, 101

A. exigua, 100

A. grandis, 52, 99f, 100–101, 158

A. latidens, 98, 99

A. palatasi, 101, 157–160, 159f

A. pelagicus, 98

A. sp., 99f

A. supercilious, 99f, 100

A. vulpinas, 98

Alopiidae, 97–101

classification of Parotodus, 94, 96

new species, 101, 157–160, 159f

tooth morphology, 51–52f

See also Alopias

Index
268 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Alosa, 167

A. sapidissima, 167

A. sp., 166f–167f, 167

Alsopp, B., 257

Amia, 165, 167

A. calva, 165, 167

A. cf. A. calva, 165, 165f, 167, 206

Amiidae, 164–167

Amiiformes, 164–167

Ammodytes sp., 204

Ammodytidae, 204

amphibia taxa, 8–9

anagenesis vs. cladogenesis, 80–81

anguilliform body plan, 92

Anotodus, 71

A. cf. A. agassizi, 71

Antarctic ice sheet volume, 18

Apristurus, 104

Araloselachus, 65

A. cuspidata, 65

Archosauria, 218–234

Ariidae, 168–169

Ariopsis, 168–169

A. felis, 169

A. stauroforus, 166f–167f, 168–169, 

204, 205

Arius sp., 162

Astroscopus, 189–190

A. countermani, 162, 189–190, 191f

A. sp., 204, 205f

axial swimmers, 90, 93

Bagre, 169, 205

B. sp., 169, 170f–171f

baleen whales, 11, 58, 79

Baltimore Gas and Electric Company, 

20

Banister, John, 14f

barnacles, 8, 9f, 39

Basilosaurus, 92

Bathyraja, 125

B. kincaidii, 125

batoids, 104, 128, 133, 141–143

species per genus, 140t

Batomorphii, 122–137

Batrachoididae, 171, 173

Batrachoidiformes, 171, 173

Bayfront Park (formerly Brownie’s 

Beach), 19

location of beds, 6f–7f

preservation, 21

Bechtel Corporation, 20

Belone, 173–174, 209

B. belone, 174

B. countermani, 162, 172f–173f, 

173–174

Belonidae, 173–174

biocenosis, 8

bioerosion, 31–32, 263

birds, 11

bite marks, 8, 49, 50, 79, 94, 95f

“bloat and float” taphonomy, 11

bony fishes, 8, 204–209. See also individual genus and species

borehole sediment record, N.J., 18

Boss, Norman H., 17f

Boston Cliffs Member

ages/stratigraphic correlation chart 

for, 7f

along-strike profile, 19f

erosion, 25

Brotula

B. barbata, 171

B. sp., 161, 170f–171f, 206

bulkheads, 29, 32, 40

Caiman, 239

Callorhynchidae, 54–55

Calvert Beach Member

cliff retreat rates, 35

preservation, 21

Calvert Cliffs

ages/stratigraphic correlation chart, 7f

along-strike profiles, 17–18, 18f, 19f, 

36–37

batoids, species per genus, 140t

birds, 11

bony fish, 8

chondrichthyan fauna, 137–143

commercial development, 18–19

comparison of common ecomorphotypes, 141f

deposition, 48

Ducatel’s map, 16f

as dynamic landscape, 38

earliest illustrated fossil, 14, 14f

erosion (see erosion at Calvert Cliffs)

evolution of topography and sea level, 

12f–13f

first detailed geographic description, 

14–15

first formal scientific description, 15

future, 40–41

generalized profile, 23f

historical era interpretation, 14–15, 

16f

humans and, 11, 13–15

industrial development, 20

land animals, 11

lithologic and grain size distributions 

inland, 26f–27f

lithostratigraphic/biostratigraphic 

interpretation, modern, 15, 17–18

location, 4f

marine mammals, 11

military development, 20

mollusks, 8

Native Americans, 11, 13

overview, 4f, 5, 6f–7f

plant remains, 5, 8

preservation efforts, 20–21

as regionally significant coastal plain 

landmark, 37–38

in relation to later Pleistocene and 

Holocene geomorphology, 10f–11f

residential development, 19–20

sand particles in beach sand, 37f

shark teeth, 8

sharks, species per genus, 139t

skates and rays, 8

tectonic influence, 36–37

vertebrate remains, 15

Calvert Cliffs Nuclear Power Plant, 20

cliff erosion preventative measures, 32

Calvert Cliffs Stabilization Committee, 

33

Calvert Cliffs State Park, 20–21

cliff retreat rates, 35

freeze-thaw cycle, 29

lithologic and grain size distributions, 

27f

Calvert County Cliff Policy Task Force, 

32

Calvert Formation

along-strike profile, 19f

deposition, 22

erosion, 29, 30f–31f, 35

ichthyofauna, 204–206

nonmarine turtles, 11

stratigraphic units, 216f–217f

Calvert Marine Museum (CMM), 20

Camp Roosevelt, 4f, 19–20, 19f

Carangidae, 203

carangiform swimming, 92

Carcharhinidae, 107–121

Carcharhiniformes, 103–122

dentition, 47

evolution, 47–48

gigantism, 47–48

species per genus of sharks, 139t

See also individual genus and species

carcharhiniform swimming, 92

Carcharhinus, 53, 108, 111–118, 138, 

140

C. ackermannii, 114

C. acronotus, 114

C. albimarginata, 118

C. amboinensis, 116

C. brachyurus, 117, 118

C. cf. C. altimus, 112–115, 113f

C. egertoni, 112

C. falciformis, 112, 113f, 115, 117

C. leucas, 113f, 115–116, 118

C. limbatus, 117, 118

C. longimanus, 112, 116

C. macloti, 113f, 116

C. perezii, 113f, 117
NUMBER 100 • 269

C. plumbeus, 113f, 114, 116, 118

C. priscus, 112, 113f, 116, 117–118

C. similis, 116

C. sorrah, 114

vertebral centra, 118

Carcharias, 63–68, 140

body morphology, 63, 92, 93

C. acutissimia, 66

C. bastal, 49

C. collata, 119

C. cuspidatus, 63–65, 64f, 66, 67, 140

C. gustrowensis, 66, 67

C. magna, 119

C. reticulatus, 64f, 66–67

C. sulcidens, 49

C. taurus, 64f, 65–66, 67, 140

C. vorax, 65

Carcharocles, 47, 78, 80–94, 140, 141

Carcharocles model, 80, 81, 84, 85

Carcharodon model, 80, 81, 83–84

C. auriculatus, 82–83, 84

C. chubutensis, 8, 84, 85–88, 87f, 160

C. megalodon, 8, 9f, 47, 49, 78, 81, 

82–83, 84, 85, 86, 87f, 88–90, 89f, 

90, 91, 93, 94

coprolites, 234

C. subauriculatus, 83, 84, 85

estimated body size, 93

evidence of feeding, 94

evolution and systemic placement, 

80–81

first appearances in fossil record, 83

heterochronic changes, 83

molecular divergence times, 83–85

morphology, dental, 81–82

morphology, reconstructed, 90–93, 

91f

neonatal teeth, 78

nutrient foramina, 83

Otodus/Megaselachus model, 80–81, 

84, 85

skeletal attributes of, vs. Carcharodon, 92

vertebral centra, 82–83, 90, 91f

Carcharodon, 8, 47, 71–79, 80, 140, 

141

C. carcharias, 8, 48, 49, 71, 72, 74, 

76–79, 77f, 81–82, 83, 84, 86, 

92–93, 94

C. escheri, 75, 76

C. hastalis, 9f, 49–50, 50f, 70, 71, 

72f, 73–75, 74f, 79

C. hubbelli, 73, 74, 76, 77, 79, 81, 

82, 83

C. plicatilis, 73, 74, 75, 79, 81, 83

C. subserratus, 72f, 73, 75–76

C. xiphodon, 73

dental morphology, 71–72, 81–82

divergence with Isurus, 83–84

skeletal attributes of, vs. Carcharocles, 

92

Carcharoides, 67–68

C. catticus, 67–68

Cardabiodon, 47

Cardabiodontidae, and classification of 

Parotodus, 94

Caribbean reef shark, 117

Cephaloscyllium, 103

Cephalotropis coronatus, 58, 79

Cetorhinidae, 102–103

Cetorhinus, 62, 90, 91, 93, 102–103, 

103f

C. maximus, 62, 102

C. sp., 102–103

cetotherid whales, 94

Cheasapeake Group

composite section of Miocene strata, 

24f

otoliths from, 205f

otolith taxonomy of bony fishes from, 

208t–209t

skeletal taxonomy of bony fishes 

from, 207t

cheloniid sea turtles, 11

chemical precipitates, 25

Chesapeake Beach Amusement Park, 19

Chesapeake Beach Railway, 19

Chesapeake Group, ages/stratigraphic 

correlation chart for, 7f

Chesapeake Ranch Estates, 19

cliff retreat rates, 35

erosion, 32, 33

lithologic and grain size distributions, 

27f

slope angles, 22

Chesapecten, 215

C. jeffersonius, 14f, 215

Chilomycterus, 199

C. sp., 199

Chimaera, 55

C. sp., 55, 55f

chimaeras, evolution during Neogene, 

46–48

Chimaeridae, 55

Chimaeriformes, 54–55

chondrichthyan fauna, 137–143

completeness of, 137–138

disparity of, 138, 140–142

future research, 142–143

Chondrostei, 163

Choptank Formation

ages/stratigraphic correlation chart, 7f

along-strike profile, 19f

cliff toe erosion, 25

erosion, 29, 33

ichthyofauna, 206

pollen assemblages, 5

stratigraphic units, 216f–217f

tectonic influence, 36

Cincindela

C. dorsalis dorsalis, 39, 40

C. puritana, 9f, 39–40

Citharichthys sp., 204, 205f

cladogenesis, 84

vs. anagenesis, 80–81

cliff toe erosion, 21, 25, 29

Clilomycterus, 199

C. sp., 199, 202f–203f, 204

Clupeidae, 167

Clupeiformes, 167

colluvium, 29

Columbia Gas System, 20

commercial fishing, 39

Conoy Landing, 37

ages/stratigraphic correlation chart, 7f

Conrad, Timothy A., 14, 15

Cope, Edward D., 15

coprolites, 135, 136f

of Thecachampsa, 234–235

Corystosiren, 255–257

Aff. C. sp., 255, 257

C. sp., 245, 256f–257f

C. varguezi, 257

feeding, 263–264

Cosmopolitodus, 71, 72–73, 84

Cove Point

commercial development, 19

erosion, 35

flora, 39

industrial development, 20

location, 10f

preservation, 20, 21

sand accumulations, 36

Crenatosiren olseni, 257, 259

Cretolamna, 47

C. appendiculata, 136f, 137

Cretoxyrhina, 47, 50, 51

C. mantelli, 51

Crocodiles

coprolites, 234–235

decline of Tomistominae, 238

paleoecology, 238–239

skull/postcranial remains, map, 214f

status of Gavialosuchus americanus, 

229, 234

systematic paleontology, 218–234

taxonomic analysis, 235, 237

taxonomic history, 213–218

See also Thecachampsa; Tomistoma

crocodilians

enigmatic, from Calvert Formation, 

239

saltwater crocodiles, 11, 213, 238

“Crocodilus,” 217

“C.” antiquus, 213, 214f, 218

“C.” fastigiatus, 215

“C.” rugosus, 215
270 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Crocodylia, 217, 218–234, 235

Crocodylidae, 235

Crocodylus, 223, 229

C. acutus, 227f, 238

C. porosus, 238

Crommyodus irregularis, 203

cryptic species, 85

Cynorca, 15

Cynoscion sp., 204, 205f

Dares Beach–Wind Cliffs, erosion 

prevention, 32

Dasyatidae, 126–128, 141

Dasyatis, 126–127

D. delfortrieri, 126

D. probsti, 123f, 127

D. rugosa, 123f, 126–127

D. sabina, 126

Delphinidae, 48

Delphinus calvertensis, 15

dental sexual dimorphism, 51, 108, 110, 

122, 125, 126

desiccation, 22, 31

diatoms, 5, 17

Diceratherium, 246

dinoflagellates, 5, 17, 245

Diodon, 199

Diodontidae, 199, 203

Dioplotherium, 263

D. cf. D. allisoni, 257, 259

feeding, 263–264

Driftwood Beach, location of beds, 

6f–7f

driftwood dropstones, 8

droughts, 31

Drumcliff

ages/stratigraphic correlation chart, 7f

along-strike profile, 19f

location, 4f

Drum Point

development, 19

location, 4f, 10f

Ducatel, J. T., 14–15, 16f, 19, 38

Dugon dugon, 257, 259

Dugongidae, 246–261

D. cf. Metaxytherium, 246

fossils in mid-Atlantic region, 

242–246

humeri measurements, 254t

scapula measurements, 253t

See also sirenians

Dugongidae gen. et sp. indet., 248f–

249f, 252f, 256f–257f, 257–261, 

259f, 260f–261f, 262f

dugongs. See Dugongidae; sirenians

Eastover Formation

ages/stratigraphic correlation chart, 7f

ichthyofauna, 206

stratigraphic units, 216f–217f

Echinorhinidae, 58–59

Echinorhiniformes, 58–59

species per genus of sharks, 139t

Echinorhinus, 58–59

E. blakei, 58–59, 59f

E. brucus, 58, 59

E. cookei, 58

E. richiardii, 59

ecotone, 5, 38

Ecphora, 8, 14

E. gardnerae, 9f

E. sp., 14f

ectothermic sharks, 48, 68, 86, 90

Edaphodon, 54

E. antwerpiensis, 54

E. cf. E. sweeti, 54, 55f

E. mirabilis, 54

E. pliocenicus, 54

Edestus, 47

edge habitat, 38–39

Elasmobranchii, 55–135

carcharhinid symphyseal teeth, 136, 

136f

chondrichthyan fauna, 137–143

coprolites, 135, 136f

dentition changes, Late Cretaceous 

through Recent, 46–47, 46f

evolution of, 46–48

evolution of gigantism, 48–49

new species, 157–160

reworked Paleogene teeth, 137

skeletal fragments, 135, 136f

See also rays; sharks

endothermic sharks, 86, 90, 92

erosion at Calvert Cliffs, 21–36

agriculture, 32, 37

beach/no-beach state, 29

bioerosion, 31–32

bulkhead effect, 29

chemical precipitates, 25

cliff-edge housing, 32, 33

cliff toe erosion, 21, 25, 29

desiccation, 22, 31

erosion processes, 22, 25, 29, 30f–31f, 

31–32

freeze–thaw cycles, 22, 29, 31, 34–36

groundwater, 21, 22, 25, 29, 31f

human activity, 32–34

liquefaction, 31, 33

measurement of erosion and recession, 

34–36

offshore sand bars, 36

prevention measures, 32–33, 40

relative sea level (RSL), 21–22, 40

rotational slumps, 31

slides, 22, 29, 30f–31f, 31, 33–34

slope measurements, 22, 25

slope types, 28f

vegetation effects, 22, 25, 28f, 29, 31

wave erosion, 5, 20, 25, 29, 35–36, 

40

eugeneodontid “sharks,” 47

exfoliation joints, 29

Fairhaven Cliffs

ages/stratigraphic correlation chart, 7f

location, 4f, 10f

location of beds, 6f–7f

stratigraphic units, 216f–217f

farming/agriculture at Calvert Cliffs, 19, 

32, 37

Felichthys stauroforus, 162. See also

Ariopsis

Felsinotherium ossivallense, 242

filter-feeding sharks, 93, 94, 102

Finch, John, 14

fishing, 10, 39

Flag Harbor marina, erosion control, 

32–33

Flag Ponds Nature Park

cliff stabilization, 21, 25

erosion, 33, 35

flora, 39

location, 10f

sand accumulations, 36

tiger beetle, 39–40

foraminifera, 8, 17

Ford Foundation, 20

fracking (hydraulic fracturing), 20

freeze–thaw cycles, 22, 29, 31, 34–36

gabions, 32, 33

Gadiculus, 205

G. cf. G. argenteus, 204, 205f

Gadidae, 204, 208t

Gadidae indet., 162

Gadiformes, 169, 171

Gadus, 206, 209

Galeocerdo, 47, 107–110, 140

G. aduncus, 49, 108–110, 109f, 111

G. contortus, 108, 111

G. cuvier, 49, 107

Galeomorphii, 62–122

Gavialidae, 218–234, 235

Gavialis, 235

Gavialosuchus, 229, 237

G. americanus, 229, 234, 235f, 236f, 

237

G. carolinensis, 237

G. eggenburgensis, 222, 237, 237f, 

238

Genyonemus sp., 204, 205f

gigantism, 47–49

Ginglymodi, 163–164

glacial isostatic adjustment, 21

Goldstein, Louis, 20
NUMBER 100 • 271

Governor Run, 19f

age of, 18

ages/stratigraphic correlation chart, 

19f

commercial development, 18–19

lack of preservation, 38

lithology/geotechnical properties, 22

Governor Run sand, 22, 29, 36

graptolites, 85

Great Bluff, 19

groins, 32–33, 39, 40

groundwater, 21, 22, 25, 29, 31f

Gymnuridae, 141

Gyrolithes sp., 8

Halecomorphi, 164–167

Halecostomi, 164–203

Halitheriinae, 246–251

Harlan, Richard, 15

Helicoprion, 47

Hemigaleidae, 105–107

Hemipristis, 105–107, 140

H. curvatus, 105

H. elongatus, 105, 107

H. serra, 105–107, 106f

Hesperosiren cratagensis, 242

heterochrony, 83

Hexanchidae, 55–58, 138

Hexanchiformes, 55–58

species per genus of sharks, 139t

Hexanchus, 47, 57–58, 140

H. gigas, 57–58, 57f

H. griseus, 57–58

Holocene

erosion during, 38

fauna from, 141f

species per genus of batoids, 140t

species per genus of sharks, 139t

Holocephali, 54–55

housing subdivisions, 19–20, 32, 33

“Hubbell” teeth, 88

Hurricane Isabel, 25, 33, 34, 36

hydraulic fracturing (fracking), 20

hydraulic plucking (toilet plunger effect), 29

ichthyosaurs, 90, 92

Ictaluridae, 167–168

Ictalurus, 167–168, 209

I. countermani, 162, 166f–167f, 206

I. punctatus, 168, 206

iron cementation, 25

Ischyodus, 54–55

I. dolloi, 55

I. mortoni, 55

I. sp., 54–55, 55f

Istiophoridae, 194, 196–197

Istiophoridae gen. et sp. indet., 197, 

204, 206

Istiophorus, 194, 197

I. calvertensis, 162, 196f–197f, 198t

I. cf. I. platypterus, 194, 196f–197f, 

197, 198t, 204, 205, 206

Isurus, 68–71, 140

dental morphology, 81

divergence with Carcharodon, 83–84

I. desori, 70

I. oxyrinchus, 47, 48, 49, 68–70, 69f, 

71, 75, 93

I. paucus, 68

I. retroflexus, 69f, 70–71

I. sp., 71

I. spp., 82

I. xiphodon, 73, 79

Jaekelotodus, 47

Jones, Hugh, 14

Katsuwonus, 190

Kenwood Beach

along-strike profile, 19f

erosion, 29, 33, 39

tiger beetle, 39–40

killer whales, 48

Kings Creek, erosion control, 33

Labridae, 203

Lagodon, 162, 179–180

L. rhomboides

L. sp., 178f–179f

Lamna nasus, 82, 83

Lamnidae, 68–79

and classification of Parotodus, 94

Lamniformes, 47, 63–122

new species, 157–160

species per genus of sharks, 139t

See also individual genus and species

land mammals, 15, 116, 222, 245

leatherback turtle, 11

Leiostomus sp., 204, 205f

Lepisosteidae, 163–164

Lepisosteiformes, 163–164

Lepisosteus, 163–164

L. sp., 163–164, 164f, 206

Lepophidium aff. cervinum, 204, 205f

Leptostyrax, 47

Libinia amplissimus, 8

liquefaction, 31, 33

Little Cove Point Member

ages/stratigraphic correlation chart, 7f

pollen assemblages, 5, 8

stratigraphic units, 216f–217f

Lophiiformes, 173

Lophiidae, 173

Lophius, 173

L. sp., 170f–171f, 173

Lopholatilus, 176–177, 206

L. chamaeleonticeps, 177

L. ereborensis, 161, 162, 176–177, 

176f, 204, 206

L. rayus, 177

Loxodon, 120

Lyell, Charles, 15

macropelagic sharks, 48

macrophagous sharks, 47, 79, 90, 92, 

93, 94, 98, 140

Macrorhizodus, 47

Makaira, 197

M. cf. M. nigricans, 196f–197f, 200t, 

204, 205, 206

Malacanthidae, 176–177

Mammalia, 246–261

Manatus antiquus, 246. See also sirenians

Markoe, F., Jr., 15

Maryland Academy of Sciences, 20

Maryland Conservation Council, 20

Maryland Critical Area, 20, 40

Maryland Department of Natural Resources (DNR), 35, 36

Maryland Geological Survey, 35, 45–46

Megalodelphis magnidens, 222, 229

Megalolamna, 47

Megaselachus, 80

M. megalodon, 80

Otodus/Megaselachus model, 80–81, 

84, 85

Melanogrammus, 206, 209

Menticirrhus sp., 204, 205f

Merlucciidae, 169, 171, 204

Merluccius, 169, 171, 206

M. sp., 169, 170f–171f, 171, 204, 

205f, 206

mesothermic sharks, 48, 68, 86, 90, 92, 

94

Metaxytherium, 246–251

M. albifontanum, 250

M. calvertense, 242, 243–245, 244f, 

250, 253

“M. cf. M. calvertense,” 250

M. cf. M. floridanum, 250–251, 252f, 

258f–259f

M. crataegense, 242, 243f, 245, 246, 

247f, 248f–249f, 249t, 251, 252f, 

256f–257f, 259t, 260f–261f, 262f, 

263

M. floridanum, 242, 245, 250, 251

M. serresii, 250

M. sp., 242

M. spp., 264

M. subapenninum, 250

Micromesistius, 205

M. cognatus, 204, 205f

Micropogonias, 180, 182

M. sp., 180, 181f, 182

M. undulates. 182
272 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Middle Miocene Climatic Optimum, 18

Milankovitch cyclicity, 18

Miocene, stratigraphic units, 216f–217f

Miocene Chesapeake Group, 4–5

Miocene toe, 25, 29, 34, 36

Mitchell, Samuel L., 14

Mitsukurina, body morphology, 92

Mobula, 133–135, 142

M. fragilis, 132f, 134–135

M. loupianensis, 132f, 134, 135

M. pectinata, 132f, 134, 135

M. thurstoni, 134

Mobulidae, 131–135

Mola, 162, 199

M. pileata, 199, 202f–203f

Molidae, 199, 201–203

Moran Landing Fault, 36–37

Morone, 175

M. saxatilus, 175

M. sp., 172f–173f, 175

Moronidae, 175

Mustelus, 53, 104–105, 138

M. sp., 103f, 105

Myliobatis

M. frangans, 127

M. gigas, 127

M. pachyodon, 127

Myliobatidae, 127–130

Myliobatiformes, 126–137

caudal spines, 136f, 137

species per genus of batoids, 140t

Nanosiren, 251, 253–255

N. garciae, 253

N. sanchezi, 251

N. sp., 245, 248f–249f, 251, 252f, 

253, 255, 259t, 260f–261f

National Geographic Society, 20

National Museum of Natural History 

(NMNH), 2, 20

National Research Council, 40

National Science Foundation, 20

Native Americans, 8f, 11, 13, 15, 30, 76

Natural History Museum, London, 14

Nature Conservancy, 21

Naval Research Laboratory, 20

cliff erosion prevention, 22, 25, 29, 32

lithologic and grain size distributions, 

26f

slope angles near, 22

Negaprion, 53, 118–120, 119f

N. brevirostris, 119–120

N. eurybathrodon, 119–120, 119f

Neoarius, 168

Neogene

evolution of chondrichthyans 46–48

evolution of gigantism, 48–49

species recognition and identification, 

51–53

stratigraphic units, 216f–217f

trophic interactions in large shark species, 49–50

Neopterygii, 163–203

nonmarine turtles, 11

Notorynchus, 56, 57f, 140

N. cepedianus, 56

N. primigenius, 56, 57f

Odontaspididae, 63–68

Odontaspis

body morphology, 63, 92, 93

O. cf. O. acutissima, 67

O. elegans, 66

odontocete whales, 90, 92

Ophidiidae, 171, 204

Ophidiiformes, 171

Opsanus, 171, 173, 206

O. sp., 170f–171f, 171, 173

O. tau, 173

Orcinus, 48

orectolobids, 53

Orectolobiformes, 62–63

species per genus of sharks, 139t

Orectolobiformes, 8, 91

Orectolobus, 138

Osteichthyes, 163–204

ostracods, 8

Otodontidae, 80–97

and classification of Parotodus, 96

Otodus, 47

O. obliquus, 80

Otodus/Megaselachus model, 80–81, 

84, 85

Otophidium sp., 204, 205f

pachyosteosclerosis, 241

Pachyscyllium dachiardii, 104

Pachyurus sp., 204, 205f

Palaeocarcharodon, 47

P. orientalis, 77, 78, 137

Palmer, Arminia, 17f

Palmer, William, 17f

palynofloras, 5, 8

Parahelicoprion, 47

Paralbula, 203

P. dorisiase, 162, 195f, 203

P. marylandica, 203

Paralichthyidae, 197, 199, 204

Paralichthys, 197, 199

P. dentatus, 198

P. sp., 196f–197f, 198–199

Park Chesapeake, cliff retreat rates, 35

Parkers Creek

along-strike profile, 19f

flora, 39

location, 4f, 10f

location of beds, 6f–7f

relative sea level (RSL), 22, 40

slope angles, 22

tectonic influence, 36

Parkers Creek Bone Bed

age of, 18

bone fragmemts, 8

erosion, 26

relative sea level (RSL), 40

Parkers Creek Preserve, erosion, 29

Parotodus, 47, 94, 96–97, 140

classification, 94, 96

P. benedenii, 8, 53, 96–97, 96f

“Pecten jeffersonius,” 215

Pelagornis, 11

perched water table, 29

Perciformes, 175–197

Phycis, 205

phyletic evolution, 84–85

Physogaleus, 110–111, 140

P. aduncus, 108

P. contortus, 108, 109f, 110–111

P. hemmooriensis, 109f, 111

pleromin, 54

Pleuronectiformes, 197, 199

Plinthicus, 133, 142

P. kruibekensis, 133

P. stenodon, 132f, 133

Plum Point Member

ages/stratigraphic correlation chart, 7f

erosion, 25, 29, 35

ichthyofauna, 206

location, 10f

pollen assemblages, 5

preservation, 21

stratigraphic units, 216f–217f

tectonic influence, 36

Pogonias, 182–183, 205

P. cromis, 183

P. multidentatus, 162, 183

Pogonias sp., 181f, 182–183, 183f, 

204, 205f, 206

pollen assemblages, 5, 8

Pomatomidae, 177, 179

Pomatomus, 177, 179

P. saltatrix, 179

P. sp., 177, 178f–179f, 179

Potamotrygon, 53

Potomac Electric Power Company 

(PEPCO), 20

Premontreia distans, 104

preservation

at Bayfront Park, 20–21

at Calvert Cliffs, 20–21

lack of, at Governor Run, 38

See also erosion at Calvert Cliffs

Prionace glauca, 47, 68

Prionotus, 174

P. sp., 172f–173f, 174, 204, 205f

Pristidae, 122–123f
NUMBER 100 • 273

Pristiformes, 122–125

species per genus of batoids, 140t

Pristis, 122–123f

P. aquitanicus, 122

P. atlanticus, 122

P. caheni, 122

P. sp., 122–123f

Procarcharodon, 80

Protautoga conidens, 162, 189

Pteromylaeus, 127–128, 142

P. apenninus, 128

P. asperrimus, 128

P. bovinus, 128

P. crassus, 128

P. gemmellaroi, 128

P. meridionalis, 128

P. sp., 128, 129f

Pungo River Formation, ichthyofauna, 

205–206

Rachycentridae, 179

Rachycentron, 179

R. canadum, 179

R. sp., 178f–179f, 179

Raja, 125, 127

R. ceciliae, 125

R. eglanteria, 125

R. gentili, 125

R. sp., 123f, 125

R. sp. 3, 125

R. sp. 4, 125

Rajidae, 124–126, 141

Rajiformes, 124–125

species per genus of batoids, 140t

Randall Cliffs

cliff erosion prevention, 32

military research, 20

shoreline retreat, 34

slope angles, 22

Ranzania, 162, 201–203

R. grahami, 201, 202f–203f, 204

R. laevis, 201

R. tenneyorum, 202f–203f, 203

rays

evolution during Neogene, 46–48

whole-body reconstructions of, 51

See also Elasmobranchii; individual 

genus and species

reef balls, 33, 40

relative sea level (RSL), 21–22, 40

Reptilia, 218–229

requiem sharks. See Carcharhinidae

resident/transient sharks, 48

revetment, 33, 40

Rhincodon, 8, 62–63, 91

R. typus, 61f, 62–63, 93

Rhincodontidae, 62–63

Rhinobatos, 138

Rhinoptera, 130–131

R. aff. R. bonasus, 131

R. cf. R. studeri, 130–131, 132f

R. sp. 1, 131

R. sp. 2, 131

Rhinopteridae, 130–131

Rhizoprionodon, 119f, 120–121

R. ficheuri, 120

R. ganntourensis, 120

R. sp., 119f, 120–121

Rhynchobatidae, 124

Rhynchobatus, 124

R. djiddensis, 124

R. pristinus, 124

R. sp., 123f, 124

riprap revetment, 33

Rocky Point

erosion, 25, 33

location of beds, 6f–7f

slope angle, 22

rotational slumps, 31

Sacaco species, 81

Salisbury Embayment

abundance of juveniles, 204

gradual shallowing of, 162, 206

saltwater crocodiles, 11, 213, 238

sand bars, 32, 36, 38

sapping (seepage erosion), 29

Sarda, 192, 205

S. sp., 192, 195f

Say, Thomas, 14

Sciades, 168

Sciaenidae, 180–189, 203, 204

Sciaenidae indet, 162

Sciaenops, 183–189

S. eastmani, 162, 203–204

S. ocellata, 187, 203

S. sp., 183–189, 184f–185f, 186f–

187f, 188f–189f, 204, 205f, 206

Scientists Cliffs

chimaeroid tooth plates, 55f

cliff retreat rates, 34–36

erosion, 29, 30f–31f, 31, 32, 33–34, 

39

housing, 40

lithologic and grain size distributions, 

26f

relative sea level (RSL), 40

sand particles in beach sand, 37f

slope angles, 22

Scientists’ Cliffs History Book 

Committee, 40

Scoliodon, 120

Scombridae, 190–194

Scorpaeniformes, 174–175

Scyliorhinidae, 103–104, 138

Scyliorhinus

S. canicula, 104

S. joleaudi, 104

S. sp., 103f, 104

sea cows. See sirenians

seals, 11

sea turtles, 11

seepage erosion (sapping), 29

selachian fauna, 48, 138–139, 140, 141, 

143

Selachimorpha, 55–62

Serranidae, 175–176

Serranidae gen. et sp. indet., 175–176, 

175f

sexual dimorphism, dental, 51, 108, 

110, 122, 125, 126

sharks

ectothermic, 48, 68, 86, 90

endothermic, 86, 90, 92

filter-feeding, 93, 94, 102

macrophagous, 47, 79, 90, 92, 93, 94, 

98, 140

mesothermic, 48, 68, 86, 90, 92, 94

species per genus at Calvert Cliffs, 

139t

whole-body reconstructions of, 51

See also Elasmobranchii; individual 

genus and species

Sierra Club, 20

Sirenia, 246–261

sirenians, 242–246

humeri measurements, 254t

introduction, 241–242

radii and ulnae measurements, 259t

scapula measurements, 253t

systematic paleontology, 246–261

taphonomic mystery (bone erosion), 

261, 263

See also Dugongidae; Nanosiren

skates

evolution during Neogene, 46–48

See also individual genus and species

slides, 29, 33–34

translational, 22, 31

wet rug, 30f–31f

slopes

measurements, 22, 25

types, 28f

Smith, J., 13, 20, 38

snails, 8, 9f, 14, 14f

Solomons

military research, 20

relative sea level (RSL), 22

Somniosus, 47–48

S. microcephalus, 47–48

Sparidae, 179–180

sperm whales, 11, 110–111

Sphyraena, 190, 205

S. sp., 190, 191f, 205

S. speciosa, 162, 190

Sphyraenidae, 190
274 • SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY

Sphyrna, 120, 121–122, 140

S. laevissima, 119f, 120, 121–122

S. lewini, 121

S. mokarran, 121

S. zygaena, 122

Sphyrnidae, 121–122, 138

Squalicorax, 47, 50

S. kaupi, 136f

Squalidae, 59–60

Squaliformes, 59–60

species per genus of sharks, 139t

Squalus, 59–60, 59f

S. acanthias, 60

S. almeidae, 60

S. cubensis, 60

S. sp. 1, 60

S. sp. 2, 60

Squatina, 60–61

S. dumeril, 62

S. occidentalis, 61

S. sp., 61–62, 61f

S. subserrata, 61

Squatinidae, 53, 60–62, 138

Squatiniformes, 60–62

species per genus of sharks, 139t

Stenotomus, 180

S. chrysops, 180

S. sp., 178f–179f, 180

St. Leonard, ages/stratigraphic 

correlation chart, 7f

St. Marys Formation

ages/stratigraphic correlation chart, 7f

along-strike profile, 19f

deposition, 162

erosion, 29, 31

ichthyofauna, 206, 209

nonmarine turtles, 11

stratigraphic units, 216f–217f

Stratford Hall skull, 214f, 221f, 222–

223, 223f, 224f, 225, 226f–227f

Taeniura cavernosa, 127

Tautoga, 189

T. onitis, 189

T. sp., 189, 191f

Teleostei, 167–203

terrestrial mammals. See land mammals

Tetraodontiformes, 199, 201–203

Thecachampsa, 215, 217–229

coprolites, 232f, 234–235

differences/similarities among species, 

215t

Miocene strategic units, 216f–217f

paleoecology, 238–239

St. Marys skull fragments, 228f, 230f

Stratford Hall skull, 214f, 221f, 

222–223, 223f, 224f, 225, 226f–

227f, 231f

T. antiquus, 215, 216f–217f, 217, 

225, 227f, 228f, 229, 230f, 231f, 

232f, 233f, 234–235, 235f, 236f, 

237f, 238–239

T. carolinensis, 223, 227f, 237, 237f, 

238

T. contusor, 215, 217, 229

T. sericodon, 215, 216f–217f, 217–

225, 219f, 220f, 221f, 225, 229, 

234–235, 236f, 237f, 238–239

T. serratus, 215

T. sicarius, 215, 219, 222

T. sp., 217

T. squankensis, 215

Wakefield skull, 214f, 219f, 220f, 

222–223

See also Crocodiles

thunniform body plan, 90, 91, 93

Thunnus, 192, 194, 205

T. sp., 173, 192, 194, 195f, 204, 206

Tomistoma, 222–223, 235

“T.” americana, 222, 229

“T.” calaritanus, 222, 238

“T.” lusitanica, 238

T. schlegelii, 213, 222, 237f, 238

Tomistominae, 218–234, 235

decline of, 238

genera of, 237

See also individual genus and species

toothed whales, 11

Torpediniformes, species per genus of 

batoids, 140t

tourism at Calvert Cliffs, 19–20

transient/resident sharks, 48

translational slides, 22, 31

Trewasciaena, 204

Triaenodon, 67

T. obesus, 68

Triakide, 104–105

Trichechus manatus, 242, 259t

Triglidae, 174, 204

Trigonotodus, 100

T. alteri, 100

Trisopterus, 205

T. sculptus, 204

true seals, 11

Tursiops aduncus, 107

turtles, 11

Uranoscopidae, 189–190

U.S. Army Corps of Engineers, 40

vegetation, effect on erosion, 22, 25, 

28f, 29, 31

Wakefield skull, 214f, 219f, 220f, 

222–223

Warrior’s Rest Sanctuary, erosion, 29

Western Shores, location of beds, 6f–7f

Westmoreland Cliffs

dating of, 18

palynofloras, 5, 8

wet rug slide, 30f, 31f

whale falls, 263

whales

baleen, 11, 58, 79

cetotherid, 94

killer, 48

odontocete, 90, 92

sperm, 11, 110–111

toothed, 11

whole-body fossils, 138

whole-body reconstructions, 51, 92

wildlife, 38, 39

Windmill Point Member

ages/stratigraphic correlation chart, 7f

stratigraphic units, 216f–217f
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