Shorter Contributions to 

Paleontology and Stratigraphy 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to 

Paleontology and Stratigraphy 

Edited by WILLIAM j. SANDO 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade. product. or firm names in this publication is for descriptive purposes 

only and does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990 

For sale by the 

Books and Open-File Reports Section, 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging in Publication Data 

Shorter contributions to paleontology and stratigraphy. 

(U.S. Geological Survey bulletin ; 1881) 

Includes bibliographies. 

Supt. of Docs. no.: I 19.3:1881 

1. Paleontology- United States. 2. Geology, Stratigraphic-Cretaceous. 

3. Geology, Stratigraphic-Permian. I. Sando, William Jasper. 

II. Series. 

QE75.B9 no.1881 557.3 s [560'.973] 88-607932 

[QE746] 
CONTENTS 

CHAPTER A 

Leonardian-Wordian (Permian) Deposition in the Northern Del Norte 

Mountains, West Texas 

Bruce R. Wardlaw, Robert A. Davis, David M. Rohr, and Richard E. Grant 

CHAPTER B 

Variation and Ontogeny of Calycoceras (Proeucalycoceras) canitaurinum 

(Haas, 1949) from the Upper Cretaceous (Cenomanian) of the Western 

Interior of the United States 

William A. Cobban and W. james Kennedy 

CHAPTER C 

Observations on the Cenomanian (Upper Cretaceous) Ammonite Calycoceras (Calycoceras) obrieni Young, 1957 from Arizona and New 

Mexico 

William A. Cobban and W. james Kennedy 

CHAPTER D 

Revision of the Nucula percrassa Conrad, 1958 Group in the Upper Cretaceous of the Gulf and Mid-Atlantic Coastal Plains: An Example of Bias 

in the Nomenclature 

G. Lynn Wingard and Norman F. Sohl 

CHAPTER E 

HUM Lithosome: An Example of Regional Stratigraphic Synthesis in the 

Mississippian of the Western Interior of the United States 

William j. Sando 

Contents Ill 

Chapter A 

Leonardian-Wordian 

(Permian) Deposition in the 

Northern Del Norte 

Mountains, West Texas 

By BRUCE R. WARDLAW, ROBERT A. DAVIS, DAVID M. 

ROHR, and RICHARD E. GRANT 

Leonardian and Wordian units in the northern Del Norte 

Mountains represent deposition in a fan delta and distal tidal 

flat complex 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to Paleontology and Stratigraphy 

CONTENTS 

Abstract Al 

Introduction Al 

Stratigraphic units Al 

Cathedral Mountain Formation A2 

Unit 1: Interbedded coarse siltstone, fine sandstone, and carbonates A2 

Unit 2: Fine sandstone, coarse siltstone, and discontinuous carbonate beds 

A3 

Unit 3: Skeletal carbonate A3 

Unit 4: Interbedded very fine to fine sandstone and carbonates A3 

Unit 5: Interbedded mudstone, coarse siltstone, fine sandstone, and carbonates A6 

Unit 6: Sandy conglomerate A6 

Road Canyon Formation A6 

Unit 7: Skeletal carbonate and minor sandstone and shale A6 

Word Formation A6 

First unnamed sandstone member A6 

Unit 8: Pebbly, very fine to coarse sandstone and discontinuous conglomerate beds A6 

Willis Ranch Member A 7 

Unit 9: Cherty sandy carbonate and minor sandy siltstone A 7 

Unit 10: Interbedded siltstone, sandstone, lime mudstone, and discontinuous skeletal carbonate beds A 7 

Unit 11: Stromatolitic lime mudstone A7 

Unit 12: Interbedded sandstone, siltstone, mudstone, and carbonate 

AlO 

Second unnamed sandstone member AlO 

Unit 13: Very fine to medium sandstone AlO 

Altuda Formation AlO 

Unit 14: Interbedded carbonate and mudstone AlO 

Unit 15: Interbedded carbonate and siltstone AlO 

Unit 16: Mudstone and minor discontinuous carbonate beds AlO 

Unit 17: Interbedded carbonate and mudstone AlO 

Unit 18: Interbedded lime mudstone and mudstone AlO 

Conodont biostratigraphy AlO 

Guadalupe Mountains AlO 

Glass Mountains AlO 

Del Norte Mountains All 

Depositional setting Al3 

Cathedral Mountain Formation Al3 

Road Canyon Formation Al3 

Word Formation Al3 

Altuda Formation Al3 

References cited A14 

Contents Ill 
IV Contents 

FIGURES 

1. Map showing location of the northern Del Norte Mountains, the Glass Mountains, 

and important paleogeographic features of the Permian of West Texas A2 

2. Chart showing generalized relationship of stratigraphic units of the northern Del 

Norte Mountains and the Glass Mountains and the stratigraphic distribution of 

important conodonts A3 

3. Geologic map of the east-central portion of the Bird Mountain 7.5-min quadrangle 

showing section locations A4 

4. Lithic representation of measured sections I and II, units 1 through 4 AS 

5, 6. Photographs showing: 

5. Channel deposits in the Cathedral Mountain Formation A6 

6. Channel conglomerates in the Cathedral Mountain Formation and stromatolitic limestone in the Willis Ranch Member A 7 

7-9. Lithic representations of measured sections III and IV: 

7. Units 5 through 7 AS 

8. Units 8 through 12 A9 

9. Units 13 through 18 Al2 

TABLE 

1. Conodont faunas recovered from samples of Permian units from the northern Del 

Norte Mountains of West Texas All 
Leonardian-Wordian (Permian) Deposition in the 

Northern Del Norte Mountains, West Texas 

By Bruce R. Wardlaw,1 Robert A. Davis/ David M. Rohr, 3 and Richard E. Grant4 

Abstract 

The upper part of the Cathedral Mountain Formation, the Road Canyon Formation, and the first sandstone 

member of the Word Formation of West Texas represent 

deposition in a fan delta complex that successively consisted of distal fan delta lobe plain, distal delta front, and 

prodelta, carbonate shelf, and lower delta plain. 

The Willis Ranch Member and the second sandstone 

member of the Word Formation and the Altuda Formation 

represent deposition in a distal tidal flat complex reflecting cutoff, abandonment, and migration of the active fan 

delta. 

Conodont biostratigraphy supports correlation of 

the Altuda Formation with the Appel Ranch Member of the 

Word Formation or younger units in the Glass Mountains. 

INTRODUCTION 

The middle Permian deposits of the northern Del 

Norte Mountains of West Texas represent the southernmost 

and westernmost preserved sedimentary rocks deposited on 

a narrow shelf that includes the Glass Mountain regional 

standard sections for the Wolfcampian, Leonardian, and 

Wordian. The narrow shelf existed between the Marathon 

folded belt to the south and basinal deposits of the Hovey 

channel and Sheffield channel to the west and north, 

respectively (fig. 1). The Marathon folded belt probably 

was an emergent area and a source for the abundant clastic 

rocks within the Permian section (King, 1931). Clastic 

deposition is more prevalent in the Del Norte Mountains 

than it is in the Glass Mountains, where significant carbonate deposits occur within a clastic sequence (fig. 2). The 

deposition of clastic rocks has been variously interpreted as 

basinal (Cys and Mazzullo, 1978; Ross, 1986) or shelfal 

(King, 1931; Flores and others, 1977, 1981). The clastic 

rocks of the northern Del Norte Mountains were deposited 

in shallow marine shelf, tidal flat, and fluvial deltaic 

settings. Periodic marine carbonate incursions, related to 

1 U.S. Geological Survey, Reston, VA 22092. 2 Ensearch Exploration, Dallas, TX 75206. 3 Sul Ross State University, Alpine, TX 79832. 4 Smithsonian Institution, Washington, DC 20560. 

Manuscript approved for publication November 16, 1988. 

local relative rises in sea level, represent southward migration of shelf deposition over deltaic marine and fluvial 

clastic sediments. 

The upper Cathedral Mountain, Road Canyon, Word, 

and Altuda Formations are described, and their distribution 

in the east-central portion of the Bird Mountain 7 .5-min 

quadrangle in Brewster County, Texas, is shown (fig. 3). 

The upper Cathedral Mountain Formation represents 

shallow-water marine deltaic deposition including quietwater fossil plant and high-energy channel conglomeratic 

deposition. The Road Canyon Formation was deposited on 

a shallow-water marine shelf, dominated by carbonates. 

The Word Formation represents shallow-water to supratidal 

deposition of sheet sands marked by sparse channels and 

overflow deposits preserved as pebble beds. Sand deposition was interrupted by very shallow water marine shelf 

deposition of the Willis Ranch Member, which concluded 

with intertidal to supratidal deposition of stromatolitic lime 

mudstones. The Altuda Limestone represents tidal flat and 

marine tidal channel deposition. 

The Road Canyon Formation and the Willis Ranch 

Member of the Word Formation are represented by transgressive marine shelfal facies over shallow water to supratidal sandstone and conglomerate facies. The Altuda Limestone, on the other hand, is not as laterally extensive as the 

Road Canyon or Willis Ranch and appears as a lateral facies 

of carbonate-clastic deposition to the general sandstone and 

siltstone deposition of the upper part of the Word. 

STRATIGRAPHIC UNITS 

The upper Cathedral Mountain, Road Canyon, Word, 

Altuda, and Capitan Formations crop out in the east-central 

part of the Bird Mountain 7. 5-min quadrangle, forming a 

crescent-shaped amphitheater capped by the Capitan Limestone (fig. 3). Four sections (fig. 3) were measured. Lithic 

units ( 1-18) were described and assigned to the various 

formations and members. Measured sections I and II (fig. 4) 

consist of the Cathedral Mountain Formation (units 1--4). 

Measured section IV .·consists of the upper part of the 

Cathedral Mountain, Road Canyon, and Word Formations 

(units 5-13). The Altuda Formation was measured and 

collected for conodonts, but, because it was substantially 

Leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas A1 
0 

32 r-··-·· 

·.,_ 

., .. , 

·.,_ 

.,._ 

NORTHERN 

DEL NORTE 

0 

30 MOUNTAINS 

COUNTY 

50 KM 

I I ., 

50 Ml 

l 

I 

Figure 1. Location of the northern Del Norte Mountains, the Glass Mountains, and important 

paleogeographic features of the Permian of West Texas (modified from Flawn and others, 1961; 

Ross, 1986). 

the same as section III, it was not included in this report. 

Measured section III consists of the uppermost Cathedral 

Mountain, Road Canyon, Word, and Altuda Formations 

(units 5-18). The Capitan Limestone in this area is a 

massive cliff-forming unit composed largely of carbonate 

collapse breccias and virtually devoid of fossils. Its deposition is not dealt with in this text. 

Cathedral Mountain Formation 

Unit 1: Interbedded Coarse Siltstone, Fine Sandstone, and 

Carbonates 

The lower part of the unit (section I, fig. 4), near 

intrusive rocks of Smith Peak, consists of interbedded 

recrystallized carbonates and coarse siltstone to fine sandstone, siliceous cement, and laminar and wavy bedding. 

Most primary features of the carbonates have been 

destroyed; only some fossil molds remain. Epidote is the 

dominant secondary mineral. The carbonates become less 

recrystallized upward where some skeletal grains are identifiable. 

A2 Shorter Contributions to Paleontology and Stratigraphy 

Above the recrystallized part of the unit are two 

clastic sequences that generally coarsen upward and terminate in carbonates. Clastics consist of coarse siltstone and 

siliceous cement grading upward to fine sandstone and of 

scattered discontinuous beds of sandy skeletal wackestone. 

The clastics display laminar and wavy bedding and bioturbation; horizontal burrows are present in the upper part. The 

upper part of the lower sequence is sandstone and calcareous cement and is terminated by a sandy pelletal skeletal 

lime mudstone overlain by an intraclastic pelletal skeletal 

wackestone to packstone that displays discontinuous channeling, lag deposits, graded beds, and trough crossbedding. 

The upper sequence is sandstone and siliceous cement that 

ends in a laterally discontinuous massive bed of sandy 

intraclastic wackestone. 

In section II (fig. 4), the sandstone and carbonate 

intervals are almost entirely sandy intraclastic skeletal 

wackestone to packstone. Discontinuous graded beds and 

local crossbedding occur in the lower sequence. Sandy 

skeletal wackestone to packstone characterized by discontinuous graded beds is in the upper sequence. Siltstone in 

the upper sequence has siliceous cement near the bottom 

and calcareous cement near the top. 
~ 

'CC 

Q: 

Q: 

NORTHERN 

DEL NORTE 

MOUNTAINS 

CAPITAN 

LIMESTONE 

GLASS 

MOUNTAINS 1 

CAPITAN 

LIMESTONE z 

1111( 

-

a. LU ~(/) 

.... 'CC 

AL TUDA FORMATION ~ :;:) 

~ 

LL .... 

1111( 'CC. 

Q::C: LL ----------......-------1 

c Q a: 1111( Q: 

LU 

(/)(/) 

WILLIS RANCH 0 :;:) ;: " Cii:Z: 

~ 

CANYON FM ROAD CANYON FM. 

0 

~ 

'CC 

9 

c: I 

NEOGONDOLELLA 

SPECIES RANGES 

CATHEDRAL 

MOUNTAIN 

FORMATION 

CATHEDRAL 

MOUNTAIN 

FORMATION 

z 

1111( 

Q -

A: 

1111( 

z 

0 

w 

.... 

1 MODIFIED FROM COOPER AND GRANT (1972) 

2 MEMBER OF THE WORD FORMATION <CARBONATE) 

Figure 2: Generalized relationship of stratigraphic units of the northern Del Norte 

Mountams and the Glass Mountams and the stratigraphic distribution of important 

conodonts. 

Unit 2: Fine Sandstone, Coarse Siltstone, and Discontinuous 

Carbonate Beds 

Section I is represented by very fine to fine, immature, hematitic sandstone, siliceous cement, and quartz and 

chert grains. All sandstones but the lowest bed contain 

fossil leaves and horizontal burrows along bedding planes. 

The lowest sandstone bed contains large horizontal burrows 

filled with lime mud and exhibits low-angle crossbedding. 

Section II is represented by coarse siltstone and siliceous 

and calcareous cement, composed mostly of quartz but 

containing some chert grains and sedimentary rock fragments. Wavy bedding is common, and horizontal burrows 

are present in the upper parts of some beds. The carbonates 

are discontinuous beds of two general types in both sections: (1) thin to medium beds of sandy, intraclastic, 

skeletal lime mudstone containing pelletal intraclasts and 

(2) medium to massive beds of sandy, skeletal wackestone 

to packstone that display graded bedding in thicker beds and 

are laterally discontinuous. Sand grains are quartz and 

chert; some beds contain pelletal intraclasts. 

Unit 3: Skeletal Carbonate 

Unit 3 is generally massive-bedded, sandy, intraclastic, skeletal wackestone to packstone and minor pelletal 

grainstone. Intraclasts are indeterminate sedimentary rock 

fragments and pelletal lime mudstone. Sand grains are 

predominantly quartz, but some are chert and feldspar. The 

beds contain abundant fusulinids and display some graded 

bedding, low-angle crossbedding, and channels that cut into 

one another (fig. 5A). This unit is fairly continuous over the 

map area but shows considerable local pinching and swelling (fig. 5B). 

Unit 4: Interbedded Very Fine to Fine Sandstone and 

Carbonates 

Sandstones are immature and hematitic and contain 

siliceous and calcareous cement and mostly quartz and chert 

grains. Some beds show increasing sedimentary rock fragments in the upper part of the unit. Beds display both 

parallel and wavy bedding planes. The bases of some beds 

contain rip-up clasts and pebbles of novaculite and silicified 

wood. Carbonates are discontinuous in the lower part but 

fairly continuous in the upper part; they are generally 

massive and consist of sandy, intraclastic, skeletal wackestone to grainstone and minor skeletal lime mudstone. Beds 

commonly display graded bedding and crossbedding. Intraclasts are common and include clastic rocks and pelletal 

lime mudstone. Sand grains are mostly quartz. Packstones 

and grainstones contain abundant fusulinids. Chert replacement of fossils is common. 

Leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas A3 
1 0 3° 3 1, 8 5 I 0 

EJ 

[] 

~ 

0 

QUATERNARY ALLUVIUM 

1 KM 

TERTIARY SYENITE AND TRACHYTE 

CRETACEOUS EDWARDS LIMESTONE 

PERMIAN 

CAPITAN LIMESTONE 

1 

a o0 1 9. eo' 

30° 1 7 .82' 

MILE 1 o 3° 3 o. o o g 

\ SECTION LINE 

-\.. CONTACT 

~/ 

//<;) FAULT 

a 

[§] AL TUDA FORMATION CONTOUR INTERVAL 

200 FT 

D 

1m 

D 

rn 

SANDSTONE MEMBERS, WORD FORMATION 

WILLIS RANCH MEMBER, WORD FORMATION 

ROAD CANYON FORMATION 

CATHEDRAL MOUNTAIN FORMATION 

Figure 3. East-central portion of the Bird Mountain 7.5-min quadrangle showing section locations (mapping by 

R.A. Davis, compilation by B.R. Wardlaw). 

A4 Shorter Contributions to Paleontology and Stratigraphy 
200 FT 

100 

0 

SECTION 

~~ o USGS 29397-PC 

SECTION II 

CATHEDRAL 

MOUNTAIN 

FORMATION 

-- -E:au€N"cE 

----toWERS 

~~r-:usGS 29396-PC 

UNIT 1 ~~r----

- AEdRvsTAIOzEb-- --+-.,.....,;ro-..,.... 

o USGS 29395-PC 

~ LIMESTONE OR LIMEY 

[] SANDSTONE OR SANDY 

LE) SILTSTONE OR SILTY 

~ STROMATOLITIC 

0 LEAF FOSSILS 

(;:;] RECRYSTALLIZED 

MUDSTONE AND SHALE OR MUDDY 

CONGLOMERATE OR CONGLOMERA TIC 

TRACHYTE SILL 

Figure 4. Measured sections I and II, units 1 through 4, and explanation of lithic symbols. 

leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas AS 
A 

B 

Figure 5. Channel deposits in the Cathedral Mountain 

Formation. A, Multiple sets of opposite-dipping, truncated, channel crossbedded wackestone and packstone 

interpreted as tidal channels. Bioturbation is uncommon 

in these beds. Cathedral Mountain Formation, section II, 

unit 3. B, Tidal channel deposit of crossbedded packstones cutting into siltstone. Abundant abraded marine 

bioclasts are present. Cathedral Mountain Formation, section II, unit 3. 

Unit 5: Interbedded Mudstone, Coarse Siltstone, Fine 

Sandstone, and Carbonates 

Unit 5 is generally poorly exposed. Sandstones and 

siltstones are similar to those in units below. Mudstones are 

common and generally sandy and commonly display contorted laminations. Carbonates are similar to those in units 

below but also include sandy and rare pebbly grainstone, 

sandy lime mudstone, wackestone, and packstone (not 

skeletal). One bed displays tabular cross bedded granular 

mudstone channeling into sandy packstone. The bed immediately above consists of a highly burrowed, very fine, 

immature, subarkosic sandstone and siliceous cement. The 

burrows are large Skolithos-type vertical burrows. The 

upper part of this unit is finely laminated, immature, sandy 

siltstones and shales and siliceous and calcareous cement. 

A6 Shorter Contributions to Paleontology and Stratigraphy 

Abundant leaf impressions are found near the top (Mamay 

and others, 1984). These beds contain layers of black 

organic shale and abundant calcispheres and are interbedded 

with lime mudstone containing a sparse gastropod fauna and 

common conodonts. 

Unit 6: Sandy Conglomerate 

Unit 6 is sandy conglomerate interbedded with fine 

sandstone lenses (fig. 6A). Conglomerate is composed 

mostly of chert grains, pebbles, and cobbles; carbonate 

clasts containing silicified fossils are present, as are uncommon logs of silicified wood and rare clasts of other rock 

fragments. Sandstone is very fine to fine and submature and 

contains calcareous and siliceous cement. Grains are mostly 

quartz and chert and include some sedimentary rock fragments. Beds commonly display graded bedding, reverse 

graded bedding, and rare slump structures that display 

recumbent folding. 

Road Canyon Formation 

Unit 7: Skeletal Carbonate and Minor Sandstone and Shale 

The Road Canyon Formation thins dramatically from 

east to west in the map area (200-20 ft). Section III (fig. 7) 

contains a thin ledge of limestone composed of sandy 

grainstone at its base and grades upward to skeletal packstone and silty skeletal wackestone. Quartz and skeletal 

grains commonly show slight imbrication in the grainstones. Skeletal elements in the packstone and wackestone 

are commonly large. Section IV (fig. 7) contains a poorly 

exposed, thick sequence of sandy, skeletal packstone at its 

base. In the upper part of the sequence are sandy skeletal 

packstone and wackestone interbedded with limey medium 

sandstone containing quartz and lithic grains. Carbonates 

are predominantly packstone in the lower part and wackestone in the upper part. Lime mudstone is common at the 

base of the skeletal wackestone beds. Packstone contains 

rip-up clasts. The uppermost part of the formation is a 

poorly sorted, fine, immature calcareous sandstone grading 

to shale and overlain by a thick ledge of carbonate composed of lime mudstone grading to skeletal wackestone. 

Word Formation 

First Unnamed Sandstone Member 

Unit 8: Pebbly, Very Fine to Coarse Sandstone and 

Discontinuous Conglomerate Beds 

Section III (fig. 8) is fine to medium sandstone that 

can be divided into two parts. The lower part is submature 

and contains siliceous cement at the base and calcareous 

cement at the top; the sandstone is hematitic and limey and 
A 

B 

Figure 6. Channel conglomerates in the Cathedral Mountain Formation and stromatolitic limestone in the Willis 

Ranch Member. A, Graded discontinuous channel conglomerates of unit 6 of the Cathedral Mountain Formation 

in section IV. Clasts include sandstone, chert, novaculite, 

and uncommon silicified wood. 8, Stromatolitic limestone 

containing microscopic algal filaments from the Willis 

Ranch Member of the Word Formation in unit 11 of 

section IV. This bed is continuous across the map area. 

characterized by bimodal grain distribution. The upper 

(larger) part is immature, contains siliceous cement, and 

fines upward; discontinuous layers of chert pebbles are 

present throughout. The unit is dominated by angular quartz 

grains, some chert, and very sparse mica and sedimentary 

rock fragments. Scattered low-angle crossbedding is found 

in float. Section IV (fig. 8) is represented from base to top 

by (1) very fine, silty, immature sandstone and siliceous 

cement, (2) fine, immature sandstone and calcareous 

cement, (3) fine, submature sandstone and siliceous 

cement, and (4) very fine, immature sandstone and calcareous cement. Silicified wood is common as cobbles at the 

base. A lenticular-shaped channel deposit of submature 

sandy conglomerate, containing calcareous and siderite 

cement, and chert pebbles and cobbles is near the base. 

Relatively clean quartz sands are in the middle of the unit, 

and a coarse fining-upward sequence near the top displays 

scattered discontinuous pebble beds and low-angle crossbedding. 

Willis Ranch Member 

Unit 9: Cherty Sandy Carbonate and Minor Sandy Siltstone 

Section III (fig. 8) is represented by sandy skeletal 

packstone and sandy, pelletal, skeletal grainstone. Crossbedding and graded bedding occur sporadically throughout 

this unit. Abundant fusulinids and sparse rip-up clasts of 

sedimentary rock occur in the middle of the unit as a 

channel deposit of silty fusulinid packstone in silty, cherty 

lime mudstone. Chert is abundant in some layers along 

bedding planes. Section IV is represented by sandy skeletal 

wackestone and one bed of sandy siltstone near the middle 

of the unit. Wackestone has common chert stringers and 

faint crossbedding throughout the unit. Fusulinids are abundant in the middle of the unit. 

Unit 10: Interbedded Siltstone, Sandstone, Lime Mudstone, 

and Discontinuous Skeletal Carbonate Beds 

In unit 10, sections III and IV are similar, both 

consisting of interbedded sandy siltstone, siltstone, and 

sandy mudstone. Section III exhibits a few beds of limey, 

pelletal, fine sandstone in siltstone and a thick discontinuous bed of fusulinid packstone to wackestone containing 

common cobble-sized lithoclasts near the base (channel lag 

deposit) overlain by lime mudstone. In section IV, two 

relatively thin, discontinuous beds of fusulinid wackestone 

to lime mudstone occur. The uppermost bed is overlain by 

laminated siltstone and contains abundant clasts and intraclasts of pelletal lime mudstone in a heavily dolomitized 

matrix. 

Unit 11: Stromatolitic Lime Mudstone 

The thin-bedded lime mudstone that comprises unit 

11 exhibits microscopic algal filaments (fig. 6B) and 

irregular algal laminations. 

Leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas A7 
SECTION IV 

ROAD CANYON 

FORMATION 

SECTION Ill 

200 FT 

100 

0 

o USGS 29808-PC 

UNIT 6 

UNIT 5 

o USGS 29404-PC o USGS 29403-PC 

o USGS 29402-PC 

CATHEDRAL 

MOUNTAIN 

FORMATION 

o USGS 2940 1-PC 

g;j LIMESTONE OR LIMEY 

D SANDSTONE OR SANDY 

(B SILTSTONE OR SILTY 

g STROMATOLITIC 

0 LEAF FOSSILS 

(;] RECRYSTALLIZED 

~ MUDSTONE AND SHALE OR MUDDY 

~ CONGLOMERATE OR CONGLOMERATIC 

~ TRACHYTE SILL 

Figure 7. Measured sections Ill and IV, units 5 through 7, and explanation of lithic symbols. 

A8 Shorter Contributions to Paleontology and Stratigraphy 
SECTION IV 

WILLIS RANCH 

MEMBER, 

WORD 

o USGS 29406-PC 

o USGS 29405-PC 

200 FT 

FORMATION 

100 

0 

UNIT 8 

~ LIMESTONE OR LIMEY 

D SANDSTONE OR SANDY 

(B SILTSTONE OR SILTY 

·····'· 

·, ·.· .. · .. · 

..... ... ~· .' ... 

FIRST 

SANDSTONE 

MEMBER, 

WORD 

FORMATION 

~ STROMATOLITIC 

0 LEAF FOSSILS 

(;:;] RECRYSTALLIZED 

~ MUDSTONE AND SHALE OR MUDDY 

~ CONGLOMERATE OR CONGLOMERATIC 

~ TRACHYTE SILL 

Figure 8. Measured sections Ill and IV, units 8 through 12, and explanation of lithic symbols. 

Leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas A9 
Unit 12: Interbedded Sandstone, Siltstone, Mudstone, and 

Carbonate 

Unit 12 in section III is composed of siltstone and 

siliceous cement, overlain by a skeletal lime mudstone 

containing abundant brachiopod spines; fine to medium, 

submature sandstone and calcareous cement; and siltstone 

and siliceous cement, overlain by silty skeletal lime mudstone containing lithoclasts of lime mudstone. There is 

abundant calcite veining in the unit. Section IV is represented by siliceous siltstone overlain by skeletal coarse 

sandstone containing calcareous cement, abundant brachiopod spines, and some chert. 

Second Unnamed Sandstone Member 

Unit 13: Very Fine to Medium Sandstone 

Section III (fig. 9) contains a thin interval of fine to 

medium sandstone, which is immature and hematitic and 

contains siliceous cement. In section IV (fig. 9), the unit is 

considerably thicker and consists of medium, submature 

sandstone and siliceous cement; very fine, immature sandstone and calcareous cement; and fine and medium, mature 

sandstone and siliceous cement. The dominant grains in 

both sections are quartz; some chert and rare feldspar are 

also present. Ripples displaying mud drapes are common 

near the top of both sections, and clasts containing scattered 

low-angle crossbedding are found in float. Tertiary trachyte 

sills cut through this unit in both sections. 

Altuda Formation 

Unit 14: Interbedded Carbonate and Mudstone 

Unit 14 is silty, intraclastic. pelletal, skeletal wackestone to lime mudstone containing intraclasts of pelletal 

lime mudstone. Some micritic envelopes are present around 

sparite-filled rounded voids. The unit becomes more skeletal and the wackestone more coarse toward the top. 

Unit 15: Interbedded Carbonate and Siltstone 

Skeletal, pelletal wackestone to packstone, some with 

intraclasts of pelletal lime mudstone and other lithic fragments, are interbedded with pelletallimey siltstone and silty 

lime mudstone, which are commonly composed of pellets, 

some of which display micritic envelopes, as in unit 14. A 

trachyte sill cuts the top of this unit in section III (fig. 9). 

Unit 16: Mudstone and Minor Discontinuous Carbonate 

Beds 

Poorly exposed mudstone contains small ledges of 

discontinuous carbonate beds near the top. The carbonate is 

pelletal lime mudstone and sparse skeletal, intraclastic 

A 1 0 Shorter Contributions to Paleontology and Stratigraphy 

pelletal packstone contammg intraclasts of pelletal lime 

mudstone and other lithic fragments. 

Unit 17: Interbedded Carbonate and Mudstone 

Unit 17 is gradational with unit 16 and represents an 

increase in the number and thickness of carbonate beds. The 

carbonates in this unit are the same lithology as those in unit 

16. 

Unit 18: Interbedded Lime Mudstone and Mudstone 

Finely laminated silty lime mudstone having indistinct grains exhibits scattered ripple marks. Limey mudstone is generally not laminated. 

CONODONT BIOSTRATIGRAPHY 

Behnken (1975) and Clark and Behnken (1979) have 

developed a loosely defined biostratigraphic zonation for 

Leonardian and Guadalupian rocks based on the succession 

of Neogondolella species in the Permian sequence of the 

Guadalupe Mountains of West Texas. 

Guadalupe Mountains 

Neogondolella idahoensis occurs in the Bone Spring 

Formation. The range of N. serrata begins at the base of the 

Cutoff Shale and continues through the Brushy Canyon 

Formation of the Delaware Mountain Group into the lower 

part of the Getaway Limestone Member of the Cherry 

Canyon Formation (Delaware Mountain Group). The range 

of N. aserrata begins in the uppermost bed of the Getaway 

Member of the Cherry Canyon Formation (B.R. Wardlaw, 

unpublished data, 1988) and continues into the South Wells 

and Manzanita Limestone Members of the Cherry Canyon 

Formation and the Hegler Limestone Member of the Bell 

Canyon Fom1ation (Delaware Mountain Group). N. postsen·ata (and various morphotypes not recognized in this 

paper, including N. denticulata, N. babcocki, and N. 

rosenkrantzi of Clark and Behnken, 1979) occurs in the 

upper part of the Hegler, Pinery, Rader, McCombs, and 

Lamar Limestone Members of the Bell Canyon Formation. 

Class Mountains 

Neogondolella idahoensis occurs in the Skinner 

Ranch and Cathedral Mountain Formations. The changeover of N. idahoensis to N. sen·ata is sharp and occurs in the 

lower third of the Road Canyon Formation (Grant and 

Wardlaw, 1984). N. sen·ata is found in the upper part of the 

Road Canyon Formation and the China Tank and Willis 

Ranch Members of the Word Formation. N. aserrata first 
occurs in the limestone lens between the Willis Ranch and 

Appel Ranch Members of the Word Formation and persists 

in the Appel Ranch Member. Conodont faunas become very 

sparse in the Vidrio Limestone Member of the Word 

Formation but appear to contain N. aserrata. Conodont 

faunas have not been recovered from the Capitan Limestone 

in the eastern Glass Mountains. 

Del Norte Mountains 

Neogondolella idahoensis occurs in the Cathedral 

Mountain Formation and the lowermost beds of the Road 

Canyon Formation. N. idahoensis and N. serrata overlap 

ranges for a few feet in the basal beds of the Road Canyon. 

N. serrata is found throughout the remainder of the Road 

Canyon and most beds of the Willis Ranch Member of the 

Word Formation. The uppermost stromatolitic lime mudstone and the brachiopod spine bed of the Willis Ranch 

Member are devoid of conodonts. The sandstones of the 

upper part of the Word Formation are also devoid of 

conodonts and other marine fossils. N. aserrata first occurs 

in the lowest beds of the Altuda Formation and persists 

throughout that unit. The overlying upper massive member 

of the Capitan Limestone, represented mostly by collapse 

breccias, is nearly devoid of all fossils. 

The occurrence of the faunal changeover of N. 

idahoensis to N. serrata within the lower part of the Road 

Canyon Formation in both the Glass and the Del Norte 

Mountains (fig. 2) strongly correlates that unit. The faunal 

changeover of N. serrata to N. aserrata occurs within the 

Word Formation between the Willis Ranch Member and the 

Appel Ranch Members in the Glass Mountains. In the 

northern Del Norte Mountains, this faunal changeover 

occurs within the Word Formation between the Willis 

Ranch Member and the overlying Altuda Formation, which 

correlates the Altuda Formation in the Del Norte Mountains 

with the Appel Ranch Member of the Word Formation or 

younger units in the Glass Mountains (see Rudine and 

others, 1988). 

Wardlaw and Collinson ( 1984) have developed a 

model for Permian conodont biofacies (a series of nearshore 

to offshore biofacies) within the Phosphoria Formation and 

related rocks in the northern Rocky Mountains. Although 

conodont faunas from the Permian of the Del Norte Mountains (table 1) are not exactly the same, the model may still 

be applicable. Limestone samples from the Cathedral 

Mountain Formation all contain a rich fauna dominated by 

Neostreptognathodus; Neogondolella and scattered occurrences of Hindeodus and Sweetina are also present. These 

faunas are diagnostic of intermediate facies. Conodont 

faunas from limestones sampled in the Road Canyon 

Formation and the Willis Ranch Member of the Word 

Formation contain a rich fauna dominated by Neogondolella; Xaniognathus and commonly Hindeodus and scatTable 1. Conodont faunas recovered from samples of 

Permian units from the northern Del Norte Mountains of 

West Texas 

[Stratigraphic positions shown in figs. 4, 7, 8. and 9] 

Conodonts1 

Sample 2 3 4 5 6 7 8 9 10 11 12 13 

Section I 

USGS 29395-PC ..... X X X X X 

USGS 29396-PC ..... X X 

USGS 29397-PC ..... X X X 

USGS 29398-PC ..... X X 

USGS 29399-PC ..... X X 

USGS 29400-PC ..... X X X 

Section III 

USGS 29808-PC ..... X X X X 

USGS 29809-PC ........ X X X 

USGS 29810-PC ........ X X 

USGS 29811-PC ......................................... X 

USGS 29812-PC ....................... X X 

USGS 29813-PC ....................... X 

USGS 29814-PC ........... X 

USGS 29815-PC ........... X 

USGS 29816-PC ........... X 

USGS 29817-PC ........... X 

USGS 29818-PC ........... X 

USGS 29819-PC ........... X 

Section IV 

USGS 2940 1-PC ..... X 

USGS 29402-PC ..... X X 

USGS 29403-PC ..... X X XX 

USGS 29404-PC ..... X X X X 

USGS 29405-PC ........ X 

USGS 29406-PC ........ X X 

USGS 29407-PC2 •.•••••••• X 

USGS 29408-PC2 •••••••••. X X 

USGS 29409-PC2 •••••••••• X 

USGS 29410-PC2 .••••••..• X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

XX 

X 

X 

X 

X 

X 

X 

X 

X 

X 

1 Conodont species are indicated by numbers, as follows: 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

1, Neogondolella idalwensis (Youngquist, Hawley, and 

Miller) 

2, Neogondolella serrata (Clark and Ethington) 

3, Neogondolella aserrata Clark and Behnken 

4, Neostreptognathodus prayi Behnken 

5, Neostreptognathodus sulcoplicatus (Youngquist. Hawley, and Miller) 

6, Neostreptognathodus newelli Wardlaw and Collinson 

7. Hindeodus excavatus (Behnken) 

8. Hindeodus sp. 

9, Sweetina festiva (Bender and Stoppel) 

10, Sweetina sp. 

11, Sweetognathus iranicus Kozur. Mostler, and RahimiYazd 

12, Sweetognathus sp. 

13, Xaniognathus abstractus (Clark and Ethington) 2 Sample from extension of section IV into Altuda Formation, in 

ascending order. 

tered occurrences of Sweetina, Neostreptognathodus, and 

Sweetognathus are also present. These faunas are diagnostic 

of offshore facies. The lime mudstones at the base of the 

Altuda Formation contain a fauna that is almost entirely and 

abundantly Hindeodus but includes very rare elements of 

Sweetina and Sweetognathus. These faunas are diagnostic 

Leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas All 
SECTION Ill 

o USGS 29819-PC 

UNIT 18 

o USGS 29818-PC 

UNIT 1 7 ALTUDA 

FORMATION 

200 FT 

100 

0 

UNIT 16 

_ ....

- o USGS 29817-PC / 

/ / 

/ / 

o USGS 29816-PC' 

/ 0. / 

/ " / // ~'<. / 

/ ~~ / 

/ / 

/ / 

~'+--/ o USGS 29815-PC 

o USG§ 29814-PC / 

o USGS 29813-PC 

/ 

/ 

......--.-........-., o USGS 29812-PC 

UNlT 13 

~ LIMESTONE OR LIMEY 

[] SANDSTONE OR SANDY 

(B SILTSTONE OR SILTY 

/ 

SECTION IV 

.. 

/ ·.~: ::.~· 

/ · ... 

/ 

· .. ·. ~ t I • 

SECOND 

. ·. · .. SANDSTONE 

.... 1,,' 

· .. · .. 

·.· •. 

MEMBER, 

WORD 

FORMATION 

~ STROMATOLITIC 

0 LEAF FOSSILS 

r;:.;) RECRYSTALLIZED 

MUDSTONE AND SHALE OR MUDDY 

CONGLOMERATE OR CONGLOMERA TIC 

TRACHYTE SILL 

Figure 9. Measured sections Ill and IV, units 13 through 18, and explanation of lithic 

symbols. 

A 12 Shorter Contributions to Paleontology and Stratigraphy 
of near-shore facies. Skeletal wackestones and packstones 

sampled throughout the remainder of the formation yield 

faunas dominated by Neogondolella, like those recovered 

from the Road Canyon and Willis Ranch, and indicative of 

offshore facies. Only one sample was taken from a sparsely 

skeletal bed of the laminated lime mudstone at the top of the 

formation, and it contains a sparse fauna of Neogondolella, 

Xaniognathus, Hindeodus, and Sweetina, which indicates 

an offshore facies. 

These generalized facies are only relative and may be 

strongly related to energy regimes of the depositional 

environment (that is, offshore corresponds to lower energy 

depositional environments). But it is clear that faunas from 

the Cathedral Mountain Formation seem to consistently 

indicate higher energy, nearer shore deposition than faunas 

from the Road Canyon, Word, and Altuda Formations, with 

the exception of faunas at the base of the Altuda, which also 

indicate nearer shore deposition. 

DEPOSITIONAL SETTING 

The clastic-dominated deposition of the Del Norte 

and Glass Mountains has generally been considered to be 

basinal (recently, Ward and others, 1986; Ross, 1986). The 

rocks described here for the northern Del Norte Mountains 

are better explained as part of a generally marine-fan delta 

complex. The Cathedral Mountain Formation appears to 

represent deposition of the fluvial (lower delta plain)-

dominated fan delta. The Road Canyon Formation appears 

to have been the result of a major marine incursion by 

shelfal carbonates. The first sandstone member of the Word 

Formation marks the return of a distal fluvial-dominated fan 

delta. The remainder of the Word Formation and the Altuda 

Formation appear to represent deposition of a distal tidaldominated fan delta. The nearby Marathon folded belt 

would have been an excellent source. This fan delta 

depositional model is not unlike the well-documented fan 

delta complexes developed along the Ouachita thrust belt 

(Thompson, 1982) and along the Amarillo-Wichita uplift 

(Dutton, 1982) in the Pennsylvanian. The probably arid 

climate of the Permian in West Texas (Newell and others, 

1953) would support the development of a fan delta 

complex. 

Cathedral Mountain Formation 

Unit 1 (interbedded coarse siltstone, fine sandstone, 

and carbonates), unit 2 (fine sandstone, coarse siltstone, 

and discontinuous carbonate beds), unit 3 (skeletal carbonate), and unit 4 (interbedded very fine to fine sandstone and 

carbonate) represent deposition in a laterally variable 

marine distal fan delta lobe plain. The coarsening-upward 

sequences represent distal fan belt lobes, and overlying 

carbonates represent abandonment of the lobes. Fine sandstone, siltstone, and silty wackestones to packs tones represent generally marine interlobe plain deposition characterized by variably distributed outwash sands, relatively quiet 

water silt deposition, and carbonate tidal channel and 

shallow shelf deposition. 

Unit 5 (interbedded mudstone, coarse siltstone, fine 

sandstone, and carbonates) represents distal delta front and 

prodelta deposition. 

Unit 6 (sandy conglomerate) represents a return of fan 

delta lobe deposition. 

The abundant delicate leaf fossils in unit 2 and the 

upper part of unit 5 and the intermediate conodont biofacies 

in all the carbonates support the depositional interpretation. 

Road Canyon Formation 

Skeletal carbonate and minor sandstone and shale 

represent shallow marine shelf deposition that includes 

small incursions of distal delta front and prodelta deposition. The basal beds of skeletal packstone containing rip-up 

clasts indicate probable transgressive sedimentation over 

the fan delta lobe plain due to a local relative rise in sea 

level. 

Word Formation 

The first sandstone member, unit 8 (pebbly, very fine 

to coarse sandstone, and discontinuous conglomerate beds), 

appears to represent lower delta plain deposition, rare 

channel conglomerates, and common overflow and sheet 

flow pebble beds. 

In the Willis Ranch Member, unit 9 (cherty, sandy 

carbonate and minor siltstone), unit 10 (interbedded siltstone, sandstone, lime mudstone, and discontinuous skeletal carbonate beds), unit 11 (stromatolitic lime mudstone), 

and unit 12 (interbedded sandstone, siltstone, mudstone, 

and carbonate) are interpreted as an incursion of shallow 

shelf carbonate deposition, perhaps due to a relative rise in 

sea level followed by shallow tidal flat deposition accompanied by carbonate tidal channels and shallow subtidal and 

supratidal stromatolitic lime mudstone deposition. 

The second sandstone member, unit 13 (very fine to 

medium sandstone), represents very shallow to exposed 

tidal flat deposition. 

Altuda Formation 

Unit 14 (interbedded carbonate and mudstone) and 

unit 15 (interbedded carbonate and siltstone) represent 

marine tidal flat deposition that may be attributed to a slight 

relative rise in sea level. The units become coarser and more 

skeletal upward, perhaps indicative of slightly more open 

circulation to the tidal flat. 

leonardian-Wordian Deposition in the Northern Del Norte Mountains, West Texas A 13 
Unit 16 (mudstone and minor discontinuous carbonate beds) and unit 17 (interbedded carbonate and mudstone) 

represent shallow mud flat and carbonate tidal channel 

deposition. Tidal channels increase in size and abundance 

upwards. 

Unit 18 (interbedded lime mudstone and mudstone) 

appears to represent shallow subtidal to supratidal tidal flat 

deposition. 

The deposition of the Willis Ranch Member and the 

second sandstone member of the Word Formation and the 

Altuda Formation represents a complex of distal tidal flat 

deposition, far removed from the fan delta complex, which 

probably represents cutoff, abandonment, and migration of 

active fan delta deposition. The tidal flat is variously 

represented by sand, carbonate, and mud deposition in 

apparent shallowing-upward and deepening-upward 

sequences. The Willis Ranch Member and the second 

sandstone member of the Word Formation represent a 

shallowing-upward sequence dominated by carbonate at its 

base and sand at its top. Most of the Altuda Formation 

represents a generally deepening-upward sequence initiated 

by a possible marine incursion marked by interbedded 

skeletal carbonates and mudstones followed by mudstones. 

The mudstones are increasingly cut by carbonate tidal 

channels toward the top. The uppermost part of the Altuda 

Formation represents a shallowing-upward sequence of 

laminated lime mudstones and mudstones. 

REFERENCES CITED 

Behnken, F. H. , 197 5, Leonardian and Guadalupian (Permian) 

conodont biostratigraphy in western and southwestern United 

States: Journal of Paleontology, v. 49, p. 284-315. 

Clark, D.L., and Behnken, F.H., 1979, Evolution and taxonomy 

of the North American Upper Permian Neogondolella serrata 

complex: Journal of Paleontology, v. 53, p. 263-275. 

Cooper, G.A., and Grant, R.E., 1972, Permian brachiopods of 

West Texas, pt. I: Smithsonian Contributions to Paleobiology, no. 14, p. 1-231. 

Cys, J.M., and Mazzullo, S.J .. 1978, Lithofacies and sedimentation of Lower Permian carbonate of the Leonard Mountain 

area, western Texas: A discussion: Journal of Sedimentary 

Petrology, v. 48, p. 1363-1368. 

Dutton, S .P., 1982, Pennsylvanian fan-delta and carbonate deposition, Mobeetie field, Texas Panhandle: Bulletin of the 

American Association of Petroleum Geologists, v. 66. p. 

389-407. 

A 14 Shorter Contributions to Paleontology and Stratigraphy 

Flawn, P.T., Goldstein, A., Jr., King, P.B., and Weaver, C.E., 

1961, The Ouachita System: University of Texas Publication 

6120. 401 p. 

Flores, R.M., McMillan, T.L.. and Watters, G.E., 1977, Lithofacies and sedimentation of Lower Permian carbonate of the 

Leonard Mountain area. western Texas: Journal of Sedimentary Petrology, v. 47, p. 1610-1622. 

---1981, Lithofacies and sedimentation of Lower Permian 

carbonates of the Leonard Mountain area, Glass Mountains, 

western Texas: Reply, in Marathon-Marfa region of west 

Texas, symposium and guidebook: Midland, Tex., Society of 

Economic Paleontologists and Mineralogists, Permian Basin 

Section, p. 169-181. 

Grant, R.E., and Wardlaw, B.R., 1984, Redefinition of the 

Leonardian-Guadalupian boundary in the regional stratotype 

for the Permian of North America: International Geological 

Congress, 27th, Moscow 1984, Abstracts, v. 1, p. 58. 

King, P.B .. 1931, The geology of the Glass Mountains, Texas, pt. 

1. Descriptive geology: University of Texas Bulletin 3038, 

167 p. 

Mamay, S.H., Miller, J.M .. and Rohr, D.M., 1984, Late Leonardian plants from West Texas: The youngest Paleozoic 

plant megafossils in North America: Science, v. 223, p. 

279-281. 

Newell, N.D., Rigby, J.K., Fischer, A.G., Whiteman, A.J., 

Hickox, J.E., and Bradley, J.S., 1953, The Permian reef 

complex of the Guadalupe Mountains region, Texas and New 

Mexico-A study in paleoecology: San Francisco, W.H. 

Freeman, 236 p. 

Ross, C.A., 1986, Paleozoic evolution of southern margin of 

Permian basin: Geological Society of America Bulletin, v. 

97. p. 536-554. 

Rudine, S.F., Faliskie, R.A., Rohr, D.M .. Wardlaw, B.R., and 

Grant, R.E., 1988, Major unconformity defines WordianCapitanian boundary (Upper Permian) in Glass and Del Norte 

Mountains, Texas: Geological Society of America Abstracts 

with Program, v. 20, p. A122-A123. 

Thompson, D.M., 1982, Atoka Group (Lower to Middle Pennsylvanian), northern Fort Worth basin, Texas: Terrigeneous 

depositional systems, diagenesis, and reservoir distribution 

and quality: Texas Bureau of Economic Geology Report of 

Investigations 125, p. 1-62. 

Ward, R.F., Kendall, C.G.St. C., and Harris, P.M., 1986, Upper 

Permian (Guadalupian) facies and their association with 

hydrocarbons-Permian Basin, West Texas and New Mexico: Bulletin of the American Association of Petroleum 

Geologists, v. 70, p. 239-262. 

Wardlaw, B.R., and Collinson, J.W., 1984, Conodont paleoecology of the Permian Phosphoria Formation and related rocks 

of Wyoming and adjacent areas, in Clark, D.L., ed., Conodont biofacies and provincialism: Geological Society of 

America Special Paper 196, p. 263-281. 
Chapter B 

Variation and Ontogeny of 

Calycoceras (Proeucalycoceras) 

canitaurinum (Haas, 1949) from the 

Upper Cretaceous (Cenomanian) 

of the Western Interior of the 

United States 

By WILLIAM A. COBBAN and W. JAMES KENNEDY 

Description and illustrations of an important upper 

Cenomanian index ammonite from the Western Interior of the 

United States 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to Paleontology and Stratigraphy 

CONTENTS 

Abstract Bl 

Introduction Bl 

Localities of collections Bl 

Conventions B4 

Systematic paleontology B4 

Superfamily ACANTHOCERAT ACEAE de Grossouvre B4 

Family ACANTHOCERATIDAE de Grossouvre 84 

Subfamily ACANTHOCERATINAE de Grossouvre B4 

Genus Calycoceras Hyatt B4 

Subgenus Proeucalycoceras Thomel B5 

Genus Calycoceras (Proeucalycoceras) canitaurinum (Haas) B5 

References cited B7 

PLATES 

[Plates follow References cited] 

1--4. Calycoceras (Proeucalycoceras) canitaurinum (Haas) 

FIGURES 

1. Map of part of the Western Interior of the United States showing localities where 

Calycoceras (Proeucalycoceras) canitaurinwn (Haas) has been collected B2 

2. Sketch showing whorl sections of a specimen of Calycoceras (Proeucalycoceras) 

canitaurinum (Haas) from U.S. Geological Survey Mesozoic locality D7913 B6 

Contents Ill 

Variation and Ontogeny of Calycoceras 

(Proeucalycoceras) canitaurinum (Haas, 1949) from 

the Upper Cretaceous (Cenomanian) of the Western 

Interior of the United States 

By William A. Cobban and W. james Kennedy 

Abstract 

Mantelliceras canitaurinum Haas, 1949 was originally 

described from the basal part of the Cody Shale near 

Greybull, Wyo. The species, which belongs to the genus 

Calycoceras Hyatt, 1900, subgenus Proeucalycoceras 

Thomel, 1972, shows considerable variation. This upper 

Cenomanian index fossil is known from north-central 

Montana south to southwestern New Mexico and possibly 

to Trans-Pecos Texas. 

INTRODUCTION 

Calycoceras (Proeucalycoceras) canitaurinum 

(Haas, 1949) is a large, ornate ammonite that was first 

described as Mantelliceras canitaurinum from the basal part 

of the Cody Shale near Greybull, Wyo. (Haas, 1949, p. 9, 

pls. 1-3; pl. 4, figs. 1, 2, 4; text figs. 1-4), where it was 

associated with Metoicoceras praecox (Haas, 1949) and 

Dunveganoceras pondi Haas, 1949. The last-named species 

is widely used as the index fossil for the lowest zone of the 

upper Cenomanian in the northern part of the Western 

Interior in north-central and south-central Wyoming, along 

the flanks of the Black Hills in southwestern South Dakota 

and northeastern Wyoming, and, less commonly, in eastern 

Colorado and central Kansas. The species has not been 

found farther south. In contrast, C. (P.) canitaurinum has a 

much wider geographic distribution (text fig. 1) that extends 

from north-central Montana to New Mexico and possibly to 

Trans-Pecos Texas. In the southern area, where Dunveganoceras pondi is absent, C. (P.) canitaurinum serves as the 

zonal index fossil for the interval (Cobban, 1984, fig. 2). 

Haas's type specimens, which consist of fragmentary adults 

up to 290 mm in diameter, lack the early whorls. We here 

describe abundant new collections that illustrate the ontogeny, intraspecific variation, and dimorphism within the 

species. 

The fossils described in this report are kept in the 

U.S. National Museum of Natural History (USNM) m 

Manuscript approved for publication November 16, 1988. 

Washington, D.C. All specimens have USNM catalog 

numbers. Plaster casts of a few of the specimens are at the 

Federal Center in Denver, Colo. We thank R.E. Burkholder 

(retired from the U.S. Geological Survey) for assistance 

with the photography, and Kennedy acknowledges the 

assistance of the staff of the Geological Collections, Oxford 

University Museum and the Department of Earth Sciences, 

Oxford, U.K., and the financial support of the Natural 

Environment Research Council (U.K.), the Royal Society, 

and the Astor Fund (Oxford). 

LOCALITIES OF COLLECTIONS 

Localities at which Calycoceras (Proeucalycoceras) 

canitaurinum have been collected in the Western Interior 

are shown in figure 1. The U.S. Geological Survey (USGS) 

Mesozoic locality number, name( s) of collectors, year of 

collection, locality, and stratigraphic assignment are as 

follows (prefix D indicates Denver Mesozoic locality numbers; all others are Washington, D.C., Mesozoic locality 

numbers): 

D1155 

21368 

21850 

D11753 

W.A. Cobban, 1956. Northern side of Black 

Coulee southwest of Carter in the SI/2 NEI/4 

sec. 17, T. 23 N., R. 6 E., Chouteau County, 

Montana. Marias River Shale, from a gray 

septarian limestone concretion 7. 6 m below 

top of Floweree Member. 

W.A. Cobban, 1947. North of Woody Creek 

in the NEI/4 SEI/4 sec. 20, T. 3 S., R. 32 E., 

Big Hom County, Montana. Cody Shale, 

from septarian limestone concretions in shale 

unit 29.5 to 34.0 m above base. 

J.B. Reeside, Jr., and D.A. Andrews, 1938. 

East of Herren Gulch in SWI/4 SEI/4 sec. 9, T. 

53 N., R. 92 W., Big Hom County, Wyoming. Cody Shale, from silty concretions 24.4 

m above base. 

W.D. Greene, D. Nobel, R.E. Burkholder, 

and W.A. Cobban, 1963. Northeast of Greybull in the NWl/4 quarter ofT. 53 N., R. 92 

W., Big Hom County, Wyoming. Frontier 

Variation and Ontogeny of Calycoceras (Proeucalycoceras) canitauninum 81 
112° 

49° 

48° 

46° 

44° 

42° 

40° 

38° 

36° 

34° 

32° 

110° 10SO 106° 104° 102° 100° 98° 

- - - - - - - - - - - - - - ~~~~ - - - - - - - - - - - - - -

e XD1155 

Great Falls 

MONTANA 

UNITED! STATES 

NORTH DAKOTA 

•Bismarck 

•Billings '---- --------------

X 21368 

:-----------

21850, Dll ;s;--os388 \~ X 23064 

X e ;y-D8298 21818 x Moorcroft ~D8392 

SOUTH DAKOTA 

• Pierre 

Greybull• X Buffalo D8320 I 

D9821 D9898xx~5~28 • Rapid City 

Newcastle 

WYOMING D

835il D9336 Casper ,-- - - --- - --- - --- ~ '-'V" -

X • eDouglas 

D8912 }• Alcova x D8913 X D6956 D8501 

D8914 >s( D10428 

XD9760 xD7913 

• xzzgso 

/ Rawlins ' NEBRASKA 

L _ _ __ _ __ _ _ __ Cheyenni _j_ 1 ----- ----, 

: • K<emmling ~~' ___________ -

UTAH 

I XD7403 XD1816 

D7404 • Denver 

XD60 

COLORADO 

D3967 

D12558xe 

Pueblo 

KANSAS 

X D10395 

• Russell 

---,'- I - --- - --- - --- - --- -,-- - - -- --------

ARIZONA 

.cuba 

XD3667 

I Gallup X D6209 • 

• X D7339 D6210 Santa Fe xD7348 XD5327 D7349 X X D5344 

: XD8875 D5741 • Albuquerque 

xD5786 

NEW MEXICO 

Dll024x Silver City 

• Socorro 

I ~D11185 

xlD101os 

e D10106 , Deming D10186 

-- j_ r ---c:--------0-

MEXICO- ~ 0 

TEXAS 

OKLAHOMA 

'~-, 

50 100 150 200 MILES 

100 200 300 KILOMETERS 

96° 

Figure 1. Part of the Western Interior of the United States showing localities where 

Calycoceras (Proeucalycoceras) canitaurinum (Haas) has been collected. Numbers are 

U.S. Geological Survey Mesozoic localities. 

82 Shorter Contributions to Paleontology and Stratigraphy 
21818 

D9821 

D8388 

D8343 

D8320 

D8298 

D8392 

D9898 

D5928 

D8359 

23064 

D9336 

D8912 

Formation, from sandstone concretions near 

top. 

S.K. Fox and R.W. Murphy, 1949. Eastfacing scarp on Potato Ridge in the NWI/4 sec. 

14, T. 51 N., R. 91 W., Big Horn County, 

Wyoming. Frontier Formation, from large, 

brown sandstone concretions 4 to 6 m below 

top. 

E.A. Merewether, 1975. NEI/4 NWI/4 sec. 12, 

T. 48 N., R. 83 W., Johnson County, Wyoming. Frontier Formation, from unit of shale 

and lenticular coarse-grained sandstone. 

E.A. Merewether, 1972. Sec. 20, T. 56 N., 

R. 67 W., Crook County, Wyoming. Belle 

Fourche Shale, from a septarian limestone 

concretion. 

E.A. Merewether, 1971. NEI/4 NEI/4 sec. 33, 

T. 55 N., R. 67 W., Crook County, Wyoming. Belle Fourche Shale, from shale unit 12 

to 21.6 m below top. 

E.A. Merewether, 1971. Northwest of Oil 

Butte in the NEI/4 SEI/4 sec. 21, T. 52 N., R. 

67 W., Crook County, Wyoming. Belle 

Fourche Shale, about 30 to 45 m below top. 

E.A. Merewether, 1971. SWI/4 NWI/4 sec. 14, 

T. 51 N., R. 67 W., Crook County, Wyoming. Belle Fourche Shale. 

E.A. Merewether and W.A. Cobban, 1972. 

SE1/4 NWl/4 sec. 33, T. 50 N., R. 66 W., 

Crook County, Wyoming. Belle Fourche 

Shale, from a unit of septarian limestone 

concretions. 

E.A. Merewether, 1976. Osage oil field in 

SWI/4 sec. 8, T. 46 N., R. 64 W., Weston 

County. Wyoming. Greenhorn Formation, 

from tan-weathering calcarenite at base. 

W.H. Cobban and W.A. Cobban, 1967. 

Osage oil field in the SWI/4 sec. 17, T. 46 N., 

R. 63 W., Weston County, Wyoming. Greenhom Formation, from limonitic concretions 

16.7 m above base. 

E. A. Merewether, 1971. NEl/4 NWI/4 sec. 7, 

T. 42 N., R. 60 W., Weston County, Wyoming. Basal part of Greenhorn Formation. 

J.B. Reeside, Jr., H.R. Christner, and W.A. 

Cobban, 1950. Belle Fourche Reservoir in the 

Wl/2 sec. 31, T. 9 N., R. 4 E., Butte County, 

South Dakota. Greenhorn Formation, from 

basal bed. 

E.A. Merewether, 1974; E.A. Merewether 

and W.A. Cobban, 1984. Emigrant Gap in the 

SEI/4 NWl/4 sec. 32, T. 34 N., R. 81 W., 

Natrona County, Wyoming. Frontier Formation, from concretions about 2. 7 m below a 

2.7-m-thick bed of bentonite. 

E.A. Merewether, 1973. SWI/4 SWI/4 sec. 32, 

T. 30 N., R. 82 W., Natrona County, Wyoming. Frontier Formation, about 9 m above a 

3-m-thick bed of bentonite in Belle Fourche 

Member. 

D8913 

D8914 

D6956 

D10428 

D9760 

D8501 

D7913 

22950 

D7403 

D7404 

D1816 

D60 

D3967 

D12558 

E.A. Merewether, 1973. SEl/4 NEI/4 sec. 31, 

T. 30 N., R. 82 W., Natrona County, Wyoming. Frontier Formation, from soft sandstone 

in Belle Fourche Member. 

E.A. Merewether, W.J. Kennedy, and W.A. 

Cobban, 1973. SEI/4 NEI/4 sec. 31, T. 30 N., 

R. 82 W., Natrona County, Wyoming. Frontier Formation, from brown-weathering sandy 

limestone concretions at top of soft sandstone 

in Belle Fourche Member. 

W.A. Cobban, 1969. SWI/4 SWI/4 sec. 10, T. 

26 N., R. 80 W., Carbon County, Wyoming. 

Frontier Formation, from brown-weathering 

limestone concretions in a shale unit in the 

upper part 13.7 to 18.3 m below a 0 .4-m-thick 

bed of micaceous bentonite. 

E.A. Merewether, 1977. SEl/4 SWl/4 sec. 16, 

T. 25 N., R. 78 W., Carbon County, Wyoming. Frontier Formation, below Wall Creek 

Member. 

E.A. Merewether and W.A. Cobban, 1975. 

NEI/4 NEI/4 sec. 35, T. 24 N., R. 76 W., 

Albany County, Wyoming. Frontier Formation, from calcarenite bed in Belle Fourche 

Member. 

E.A. Merewether, 1972. NEI/4 NWI/4 sec. 6, 

T. 30 N., R. 71 W., Converse County, 

Wyoming. Greenhorn Formation. 

E.A. Merewether, 1971. SWl/4 NEI/4 sec. 30, 

T. 22 N., R. 86 W., Carbon County, Wyoming. Frontier Formation, about 18 m below 

top. 

J.B. Reeside, Jr., H.R. Christner, and W.A. 

Cobban, 1950. Grenville dome in NEI/4 sec. 

27, T. 21 N., R. 86 W., Carbon County, 

Wyoming. Frontier Formation, from brownweathering limestone concretions along a 0. 5-

m-thick bed of bentonite 22.8 m below base of 

Wall Creek Member. 

G.A. Izett and G.R. Scott, 1969. Center of 

sec. 31, T. 1 N., R. 80 W., Grand County, 

Colorado. Benton Shale, 60.6 m below base 

of Juana Lopez Member. 

G.A. Izett and G.R. Scott, 1969. Center of 

sec. 31, T. 1 N., R. 80 W., Grand County, 

Colorado. Benton Shale, from thin calcarenite 

63 m below base of Juana Lopez Member. 

G.R. Scott and J.D. Wells, 1958. NEI/4 SEl/4 

sec. 12, T. 1 S., R. 71 W., Boulder County, 

Colorado. Greenhorn Limestone, from Lincoln Member. 

G.R. Scott, 1954. Deer Creek in the NEI/4 

SWI/4 sec. 4, T. 6 S., R. 69 W., Jefferson 

County, Colorado. Greenhorn Limestone, 

from Lincoln Member. 

W.A. Cobban, 1957. SEI/4 SWI/4 sec. 30, T. 

20 S., R. 65 W., Pueblo County, Colorado. 

Greenhorn Limestone, from Lincoln Member. 

W.A. Cobban, 1984. Wl/2 SWI/4 sec. 25, T. 

20 S., R. 66 W., Pueblo County, Colorado. 

Variation and Ontogeny of Ca/ycoceras (Proeuca/ycoceras) canitauninum 83 
D10395 

D3667 

D6209 

D6210 

D5327 

D5344 

D5741 

D7339 

D7348 

D7349 

D8875 

D6184 

Greenhorn Limestone, from Lincoln Member. 

W.A. Cobban, 1977. Bunker Hill in the NEtf4 

NEtf4 sec. 13, T. 13 S., R. 13 W., Russell 

County, Kansas. Graneros Shale, from upper 

part. 

R.E. Burkholder and W.A. Cobban, 1961. 

NEtf4 NWtf4 sec. 23, T. 19 N., R. 1 W., 

Sandoval County, New Mexico. Dakota Sandstone, from large sandstone concretions at top 

of Twowells Tongue. 

C.H. Dane and E.R. Landis, 1967. Highway 

44 about 3.4 km south of Holy Ghost Spring, 

Sandoval County, New Mexico. Dakota Sandstone, from Twowells Tongue. 

C.H. Dane and E.R. Landis, 1967. About 0.7 

km south-southeast of Holy Ghost Spring, 

Sandoval County, New Mexico. Mancos 

Shale, from 4.5 m below top of Whitewater 

Arroyo Tongue. 

W.A. Cobban, 1966. Just northwest of Armijo Lake, Sandoval County, New Mexico. 

Dakota Sandstone, from basal part of Twowells Tongue. 

W.A. Cobban, 1966. Bottom of arroyo below 

(east of) Paguate-Seboyeta road in the NWtf4 

NEl/4 sec 29, T. 11 N., R. 5 W., Valencia 

County, New Mexico. Mancos Shale, from 

glauconitic, calcareous sandstone concretions 

14 to 15.5 m below top of Whitewater Arroyo 

Tongue. 

W.A. Cobban, 1967. At road bend just southwest of McCartys in the SEl/4 SWtf4 sec. 27, 

T. 10 N., R. 8 W., Valencia County, New 

Mexico. Mancos Shale, from a sandy concretion a few feet below the top of the Whitewater Arroyo Tongue. 

W.A. Cobban, 1969. Mount Powell in the Etf2 

NWtf4 sec. 8, T. 14 N., R. 13 W., McKinley 

County, New Mexico. Mancos Shale, from a 

0.6-m-thick bed of fine-grained sandstone 

11.5 m below top of Whitewater Arroyo 

Tongue. 

W.A. Cobban, 1970. West of Whitewater 

Arroyo in the NEl/4 sec. 17, T. 12 N., R. 19 

W., McKinley County, New Mexico. Mancos 

Shale, from a limestone concretion 8.2 m 

above base of Whitewater Arroyo Tongue. 

W.A. Cobban, 1970. West of Whitewater 

Arroyo in the NEl/4 sec. 17, T. 12 N., R. 19 

W., McKinley County, New Mexico. Mancos 

Shale, from a limestone concretion 10 m 

above base of Whitewater Arroyo Shale 

Tongue. 

W.A. Cobban, 1973. State Route 32 in the 

NWtf4 sec. 18, T. 9 N., R. 17 W., McKinley 

County, New Mexico. Mancos Shale, from 

Whitewater Arroyo Tongue. 

W.A. Cobban, 1967. NWtf4 sec. 15, T. 4 N., 

R. 20 W., Catron County, New Mexico. 

Mancos Shale, from a concretionary limestone 

84 Shorter Contributions to Paleontology and Stratigraphy 

D5786 

D11024 

D11185 

D10105 

D10106 

D10186 

bed in Whitewater Arroyo Tongue. 

E.R. Landis and W .A. Cobban, 1967. SEl/4 

sec. 33, T. 3 N., R. 5 W., Socorro County, 

New Mexico. Mancos Shale, from a thin bed 

of sandstone 24 m below top of Whitewater 

Arroyo Tongue. 

S.C. Hook, J.R. Wright, R.R. Cobban, and 

W.A. Cobban, 1977. Cane Spring Canyon in 

the NWtf4 SEtf4 sec. 8, T. 17 S., R. 15 W., 

Grant County, New Mexico. Colorado Formation, from siltstone 3 m above base. 

S.C. Hook, J.R. Wright, R.R. Cobban, and 

W.A. Cobban, 1977. SEtf4 NEl/4 sec. 36, T. 

17 S., R. 13 W., Grant County, New Mexico. 

Colorado Formation. 

S.C. Hook, E.R. Landis, and W.A. Cobban, 

1976. NWl/4 NWl/4 sec. 18, T. 21 S., R. 8 

W., Luna County, New Mexico. Colorado 

Formation, from a basal 1.5-m-thick sandstone bed. 

S.C. Hook, 1976; S.C. Hook, D.E. Tabet, 

and J.R. Wright, 1977. NWtf4 NWl/4 sec. 18, 

T. 21 S., R. 8 W., Luna County, New 

Mexico. Colorado Formation, from silty limestone 1.8 m above base. 

S.C. Hook and W.A. Cobban, 1977. NWtf4 

NWtf4 sec. 18, T. 21 S., R. 8 W., Luna 

County, New Mexico. Colorado Formation, 

from limestone concretions 3.4 m above base. 

CONVENTIONS 

Dimensions of specimens are given in millimeters 

and are indicated as follows: D, diameter; Wb, whorl 

breadth; Wh, whorl height; Wb: Wh, ratio of whorl breadth 

to height; and U, umbilical diameter. Numbers in parentheses are percentages of the diameters. The suture terminology of Wedekind ( 1916) as described by Kullmann and 

Wiedmann (1970) is followed, where E is the external lobe, 

L is the lateral lobe, U is the umbilical lobe, and I is the 

internal lobe. 

SYSTEMATIC PALEONTOLOGY 

Superfamily ACANTHOCERA T ACEAE de 

Grossouvre, 1894 

Family ACANTHOCERATIDAE de Grossouvre, 

1894 

Subfamily ACANTHOCERA Tl NAE de 

Grossouvre, 1894 

Genus Cafycoceras Hyatt, 1900 

(Synonym: Metacalycoceras Spath, 1926) 

Type species.-By designation under the Plenary 

Powers (ICZN Opinion no. 557) Ammonites navicularis 

Mantell, 1822, p. 198, pl. 22, fig. 5 (ICZN Specific Name 

no. 1633). 
Subgenus Proeucalycoceras Thome!, 1972 

Type species.-By original de~ignation Calycoceras 

(Eucalycoceras) besairiei Collignon, 1937 (p. 37, pl. 3, 

figs. 1-4; pl. 8, fig. 5), from the Cenomanian of Madagascar. 

Diagnosis.-The subgenus includes medium- to 

large-sized dimorphic species that have compressed to 

depressed whorls. Juveniles have dense, sometimes flattopped ribs, alternately long and short, displaying umbilical, inner and outer ventrolateral and siphonal tubercles. 

Ribs dominate in compressed individuals, whereas tubercles are more important in depressed ones; siphonal tubercles may be lost at an early ontogenetic stage. Ornament 

changes abruptly on the last part of the phragmocone and 

early part of the adult body chamber, where there are 

moderate to very strong, distant, well-rounded ribs that 

cross the venter transversely. Umbilical bullae are present 

on the long ribs, ventrolateral tubercles are weak or absent, 

and the whorl section is rounded to subquadrate. 

Genus Calycoceras (Proeucalycoceras) 

canitaurinum (Haas, 1949) 

Plate 1, figures 1-12; plate 2, figures 1-12; plate 3, 

figures 1-7; plate 4, figures 1, 2; text figure 2. 

1949. Mantelliceras canitaurinum Haas, p. 9, pis. 1-3; 

pl. 4, figs. 1, 2, 4; text figs. 1-4. 

1949. Mantelliceras sp. indet., Haas, p. 14, pl. 4, figs. 

3, 5. 

1972. Mantelliceras (Bunburyiceras) canitaurinum 

(Haas). Thome I, p. 46. 

1973. Calycoceras? canitaurinum (Haas). Cobban and 

Scott, p. 60, pl. 21, fig. 2. 

1975. Calycoceras? canitaurinum (Haas). Hattin, pl. 4, 

figs. A, C. 

1977a. Calycoceras? canitaurinum (Haas). Cobban, p. 

23' pl. 21' fig. 17. 

1977b. Calycoceras? canitaurinum (Haas). Cobban, fig. 

5i. 

1977. Calycoceras? canitaurinum (Haas). Hattin, p. 

184, text fig. 5 (4). 

1978. Calycoceras? canitaurinum (Haas). Hattin and 

Siemers, text fig. 6 (4). 

Types. - Holotype, here designated, is AMNH 

26413:1, the original of Haas (1949, pl. 1, figs. 1, 2); the 

holotype and a number of paratypes are all from the lower 

part of the Cody Shale about 9. 7 km east and 11.3 km north 

of Greybull, Wyo., in the north-central part ofT. 53 N., R. 

92 W., in the upper Cenomanian Dunveganoceras pondi 

zone. 

Material. -About 120 specimens from 47 localities 

in the Western Interior were examined. Sixteen specimens 

(USNM 422686-422700) from four localities (USGS 

Mesozoic localities 21818, 21850, D7913, and D11753) in 

Wyoming are described in this report. 

Dimensions.-Dimensions of 11 specimens are as 

follows: 

USNM no. 0 1 (mm) Wb(mm) Wh (mm) Wb: Wh U2 (mm) 

422686 ..... 24.9(100) c 16.7(67.1) 11.0(44.2) 

422687 ..... 29.5(100) c 18.7(53.7) 14.0(47.5) 

422688 ..... 34.8(100) c 17.5(50.3) 18.7(53.7) 

422689 ..... 50.3( 100) c 23.3(46.3) 27.3(54.3) 

422690 ..... 51.0(100) c 26.4(51.8) 24.0(47.1) 

422691 ..... 60.8(100) c 32.0(52.6) 27.5(45.2) 

422692 ..... 64.3(100) c 29.2(45.4) 31.3(48. 7) 

422693 ..... 84.3(100) c 42.3(50.2) 38.3(45.4) 

422694 ..... 96.0( 100) c 45.5(47.4) 46.5(48.4) 

422695 ..... 100.3(100) c 74.5(74.2) 41.9(41.8) 

97.5(100)ic 67.2(68.9) 39.0(40.0) 

422696 ..... 110.5(100) c 75.5(68.3) 52.3(47.3) 

107.3(100)ic 66.5(62.0) 48.8(45.5) 

1 c, costal diameter; ic, intercostal diameter. 2 --, Measurements not possible. 

1.51 5.8(23.3) 

1.36 27.0(23.6) 

.94 6.8(19.5) 

.85 9.7(19.3) 

1.1 -- ( --) 

1.16 14.3(23.5) 

.93 10.7(16.6) 

1.1 19.2(22.8) 

.98 23.3(24.3) 

1.78 30.0(29.9) 

1.72 30.0(30.8) 

1.44 30.6(27.7) 

1.36 30.6(28.5) 

Description.-Large; specimens interpreted as macroconchs are up to 300 mm in diameter and are incomplete. 

Specimens interpreted as microconchs are rarer and have 

diameters up to 150 mm at the end of the phragmocone. The 

earliest growth stages seen are at diameters of 25 to 50 mm 

(pl. 1, figs. 1-6); these growth stages show a wide range of 

morphological variation from compressed with weak ornament to depressed with strong ornament. This variability 

continues through middle growth and extends through most 

of the phragmocone whorls (pl. 1, figs. 10-12; pl. 3, figs. 

1-3). 

In compressed juveniles, such as USNM 422688 (pl. 

1, figs. 1-3), coiling is moderately involute, and U= 19.5 

percent of the diameter. The umbilicus is shallow and 

displays an outwardly inclined umbilical wall and a broadly 

rounded umbilical shoulder. The ratio of costal whorl 

breadth to height is 0. 94, the greatest breadth being at the 

umbilical bullae. Perched on the umbilical shoulder are 11 

to 12 bullae per whorl that give rise to blunt prorsiradiate 

ribs, singly or in pairs; the adapertural rib of any given pair 

is weaker than the adapical one. One and rarely two shorter 

ribs intercalate between the bullate ones, generally arise 

below midflank, and sometimes tenuously link to the 

umbilical shoulder. Hypo type USNM 422687 has 26 ribs 

per whorl at a diameter of 34 mm, USNM 422690 has 34 at 

a diameter of 50 mm, and USNM 422692 has an estimated 

40 at a diameter of 66 mm. At small sizes, the ribs develop 

a small inner ventrolateral tubercle linked by a thickened rib 

to a feebly clavate outer ventrolateral one. A strong rib 

passes straight across the flat, broad venter and supports a 

feebly clavate siphonal tubercle that is slightly weaker than 

the outer ventrolateral tubercles (pl. 1, figs. 1, 3, 4). 

Siphonal tubercles disappear at a diameter of 37 mm in 

USNM 422690, 41 mm in USNM 422692, and 47 mm in 

USNM 422689. Inner ventrolateral tubercles disappear at 

an equally early stage ( 43 mm in USNM 422690 and lesser 

Variation and Ontogeny of Calycoceras (Proeucalycoceras) canitauninum 85 
....-------.......... , ------------ " \ 

20 mm 

'\. 

\ 

\ 

I 

\ 

\ 

\ 

\ 

\ 

I 

25mm 

I 

/60mm 

---

I 

I 

I 

l 

I 

I / 

-/ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

112mm 

Figure 2. Whorl sections at whorl heights of 25, 60, and 112 mm of a specimen (USNM 422691) of Calycoceras 

(Proeucalycoceras) canitaurinum (Haas) from U.S. Geological Survey Mesozoic locality 07913 (text fig. 1). See 

plate 2, figures 7 and 8, for views of inner whorls. 

diameters in other specimens). When the inner ventrolateral 

tubercles are lost, the whorl sides become more flattened; 

the ribs broaden and flatten and become wider than the 

interspaces on both flank and venter from diameters of as 

little as 45 mm in USNM 422689 and as much as 85 mm in 

USNM 422694. At this stage, these compressed specimens 

have a very distinctive appearance. As size increases, the 

ribs become markedly flexuous, broadened, and crowded, 

and flattening is especially obvious on the outer flank and 

ventrolateral shoulder. Thirty-six ribs per whorl are present 

in USNM 422694 at a diameter of 105 mm and 40 to 42 in 

USNM 422692 at the same diameter. The ventrolateral 

tubercles decline and disappear, leaving a flattened venter 

crossed by flattened bandlike ribs that are much wider than 

the interspaces (pl. 2, figs. 9, 10); this feature is diagnostic 

in middle growth. Toward the end of the phragmocone, 

these ribbonlike flat-topped ribs are replaced by narrower, 

rounder ribs, separated by wider interspaces on the venter. 

A feebly clavate ventrolateral horn appears that bounds a 

flattened to slightly concave venter. On the flanks, the ribs 

coarsen markedly, to a density of 28 per whorl and 13 on 

the last half whorl of the phragmocone of USNM 422697 

(pl. 4). The ribs become coarse, distant, and prorsiradiate 

86 Shorter Contributions to Paleontology and Stratigraphy 

and regularly alternate long and short. Each long rib has a 

strong umbilical bulla, and a midlateral bulla develops with 

growth. Neither is present on the shorter ribs. 

A series of passage forms links this extreme of 

variation to the depressed, coarsely ribbed specimens like 

those shown in plate 2 (figs. 11, 12), plate 3 (figs. 1-3), and 

text figure 2, which are characterized by very depressed 

whorl sections. Ratios of whorl breadth to height are 1. 51 in 

USNM 422686 at a diameter of 24.9 mm, 1.36 in USNM 

422687 at 29.5 mm, 1.78 in USNM 422695 at 100.3 mm, 

and 1.44 in USNM 422696 at 110.5 mm. Coiling is 

evolute, U varying between 23.3 and 30.8 percent of 

diameter in the above specimens. The inner ventrolateral 

tubercles of the preceding whorl are housed in notches in 

the umbilical wall of the succeeding one. In USNM 

422686, 28 ribs per whorl correspond to 12 sharp umbilical 

tubercles from which primary ribs arise singly or in pairs 

and develop strong conical inner ventrolateral tubercles and 

feebly clavate, weaker outer ventrolateral and siphonal rows 

linked by a strong transverse rib. Some nonbullate primaries 

are also present and have a full complement of ventrolateral 

and siphonal tubercles, as may some of the shorter intercalated ribs, although others may lack the inner ventrolaterals. 
As diameter increases, this coarse ornament persists. The 

siphonal tubercles are lost at a diameter of as little as 45 

mm, although the ribs may be elevated at midventer beyond 

this diameter. The ribs are strong, narrow, and rectiradiate 

to rursiradiate and regularly alternate long and short. Strong 

umbilical bullae may migrate out to an inner flank position, 

as they do in USNM 422695 (pl. 3, figs. 1-3). A pronounced flare and then a bulla develop at midflank, and 

well-differentiated inner and outer ventrolateral tubercles 

persist to a diameter of 115 mm in USNM 422695 (pl. 3, 

figs. 1-3) but merge progressively into the ribs from a 

diameter of 65 mm in USNM 422696 (pl. 2, figs. 11, 12). 

Even these coarsely ornamented specimens pass through a 

stage of broad, flat-topped, ribbonlike ventral ribs, such as 

USNM 422700, where the adapical and adapertural edges 

of the ribs are separated by a median groove, and poorly 

differentiated riblets loop across the venter on the surface of 

the main rib. 

On mature body chambers, the ribbing coarsens 

markedly, as few as 12 ribs being present on the last half 

whorl. The ribs are strong, blunt, distant, and alternately 

long and short. Long ribs begin on the umbilical wall and 

rise into subspinose umbilical bullae that migrate out to a 

low flank position toward the adult aperture. Each rib 

supports a lateral bulla and short ventrolateral horn. The 

shorter ribs generally lack the lateral bulla. The venter is 

concave in costal section at this stage. All ribs flatten on 

crossing the venter and may show feeble division into a pair 

of riblets that loop between the horns. The umbilical and 

lateral bullae appear to decline toward the adult aperture, 

but none of our specimens are complete. 

The suture line, which has been well illustrated by 

Haas (1949, figs. 1-4), is moderately incised; E is narrow, 

E/L is broad and asymmetrically bifid, and L is narrow. 

Discussion.-The adult whorls of C. (P.) canitaurinunz, which have coarse, alternately long and short ribs, are 

immediately distinguishable from all other Western Interior 

acanthoceratid species. 

Juveniles of some variants show a remarkable similarity to certain C. (Ne-..vboldiceras) Thomel (1972), but 

early loss of siphonal tubercles in C. (P.) canitaurinum 

distinguishes it from C. (N.) newboldi newboldi (Kossmat, 

1897, p. 5 (112), pl. 1 (12), figs. 2, 3; pl. 3 (14), fig. 2), 

and C. (N.) newboldi spinosum (Kossmat, 1897, p. 7 (114), 

pl. 2 (13), figs. 2, 3; pl. 3 (14), fig. 1 ). C. (N.) planecostatum (Kossmat, 1897, p. 9 (116), pl. 2 (13), fig. 1) nuclei 

may be very close to those of certain C. (P.) canitaurinum 

(for example, pl. 1, figs. 6-8, 10-12), but the rounded 

flanks and rounded, flexuous ribs of planecostatum separate 

the two. 

REFERENCES CITED 

Cobban, W.A., 1977a, Characteristic marine molluscan fossils 

from the Dakota Sandstone and intertongued Mancos Shale, 

west-central New Mexico: U.S. Geological Survey Professional Paper 1009, 30 p., 29 pis. 

---1977b, Fossil mollusks of the Dakota Sandstone and 

intertongued Mancos Shale of west-central New Mexico, in 

Guidebook 28, San Juan Basin III: Socorro, New Mexico 

Geological Society, p. 213-220. 

---1984, Mid-Cretaceous ammonite zones, Western Interior, 

United States: Bulletin of the Geological Society of Denmark, v. 33, p. 71-89. 

Cobban, W.A., and Scott, G.R., 1972 (1973), Stratigraphy and 

ammonite fauna of the Graneros Shal~ and Greenhorn Limestone near Pueblo, Colorado: U.S. Geological Survey Professional Paper 645, 108 p., 39 pis. 

Collignon, M., 1937, Ammonites ceomaniennes du sud-ouest de 

Madagascar: Annales Geologiques de Madagascar, no. 8, p. 

29-72, pis. 1-11. 

de Grossouvre, A., 1893 (1894), Les ammonites de la craie 

superieure, pt. 2, Paleontologie, in Recherches sur la craie 

superieure: Carte Geologique Detaillee de la France 

Memoires, 264 p., 39 pis. (1893 imprint). 

Haas, 0., 1949, Acanthoceratid Ammonoidea from near Greybull, Wyoming: American Museum of Natural History Bulletin, v. 93, art. 1, 39 p., 15 pis. 

Hattin, D.E., 1975, Stratigraphy and depositional environment of 

Greenhorn Limestone (Upper Cretaceous) of Kansas: Kansas 

Geological Survey Bulletin 209, 128 p., 10 pis. 

---1977, Upper Cretaceous stratigraphy, paleontology, and 

paleoecology of western Kansas: The Mountain Geologist, v. 

14, nos. 3--4, p. 175-218. 

Hattin, D.E., and Siemers, C.T., 1978, Upper Cretaceous stratigraphy and depositional environments of western Kansas: 

American Association of Petroleum Geologists and Society 

of Economic Paleontologists and Mineralogists Annual Meeting, Oklahoma City 1978, Kansas Geological Survey Guidebook Series 3, 102 p. 

Hyatt, A., 1900, Cephalopoda, in von Zittel, K.A., Textbook of 

palaeontology (translated from German by C.R. Eastman): 

London, MacMillan, p. 502-604. 

Kossmat, F., 1897, Untersuchungen tiber die stidindische Kreideformation: Beitrage Palaontologie und Geologie OsterreichUngarns und des Orients, v. 11. p. 1--46 (108-153), pis. 1-8 

(12-19). 

Kullmann, J., and Wiedmann, J., 1970, Significance of sutures in 

phylogeny of Ammonoidea: University of Kansas Paleontological Contributions Paper 47, 32 p. 

Mantell, G.A., 1822, The fossils of the South Downs, or 

illustrations of the geology of Sussex: London, Lupton Relfe, 

327 p., 42 pis. 

Spath, L.F., 1926, On new ammonites from the English Chalk: 

Geological Magazine, v. 63, no. 740, p. 77-83. 

Tho mel, G., 1972, Les Acanthoceratidae cenomaniens des 

chaines subalpines meridionales: Memoires de la Societe 

Geologique de France, n.s., v. 51. Memoire 116, 204 p., 88 

pls. 

Wedekind. R., 1916, Uber Lobus, Suturallobus und Inzision: 

Zentralblatt ftir Mineralogie, Geologie, und Palaontologie, 

B, for 1916, p. 185-195. 

Variation and Ontogeny of Calycoceras (Proeucalycoceras) canitauninum 87 

PLATES 1-4 
PLATE 1 

Calycoceras (Proeucalycoceras) canitaurinum (Haas) (p. BS). 

[All figures natural size] 

Figures 1-3. Hypotype USNM 422688, from the upper part of the Frontier Formation at USGS Mesozoic locality 

D11753 (text fig. 1 ). 

4, 5, 9. Hypotype USNM 422690, from the basal part of the Cody Shale at USGS Mesozoic locality 21850 

(text fig. 1). 

6-8. Hypotype USNM 422692, from near the top of the Frontier Formation at USGS Mesozoic locality 

21818 (text fig. 1 ). 

10-12. Hypotype USNM 422693, from near the top of the Frontier Formation at USGS Mesozoic locality 

21818 (text fig. 1). 
U.S. GEOLOGICAL SURVEY 

3 

2 

6 7 

10 11 

CALYCOCERAS 

4 

BULLETIN 1881-B, PLATE 1 

5 

9 

12 
PLATE 2 

Calycoceras (Proeucalycoceras) canitaurinum (Haas) (p. 85). 

[All figures natural size] 

Figures 1- 3. Hypotype USNM 422687, from the upper part of the Frontier Formation at USGS Mesozoic locality 

D11753 (text fig. 1). 

4-6. Hypotype USNM 422686, from the upper part of the Frontier Formation at USGS Mesozoic locality 

011753 (text fig. 1). 

7, 8. Hypotype USNM 422691, from the upper part of the Frontier Formation at USGS Mesozoic locality 

D7913 (text fig. 1). See text figure 2 for whorl section. 

9, 10. Hypotype USNM 422698, from near the top of the Frontier Formation at USGS Mesozoic locality 

D11753 (text fig. 1). 

11, 12. Hypotype USNM 422696, from near the top of the Frontier Formation at USGS Mesozoic locality 

011753 (text fig. 1). 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-B, PLATE 2 

3 4 5 6 

2 

8 

7 

11 12 

CALYCOCERAS 
PLATE 3 

Calycoceras (Proeucalycoceras) canitaurinum (Haas) (p. 85) 

[All figures natural size] 

Figures 1-3 . Hypotype USNM 422695, from near the top of the Frontier Formation at USGS Mesozoic locality 

21818 (text fig. 1). 

4, 5. Hypotype USNM 422689, from near the top of the Frontier Formation at USGS Mesozoic locality 

D11753 (text fig . 1). 

6, 7. Hypotype USNM 422699, from near the top of the Frontier Formation at USGS Mesozoic locality 

D11753 (text fig . 1). 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-B, PLATE 3 

4 

3 

CALYCOCERAS 
PLATE 4 

Calycoceras (Proeucalycoceras) canitaurinum (Haas) (p. 85). 

[Both figures natural size] 

Figures 1, 2. Hypotype USNM 422697, from the basal part of the Cody Shale at USGS Mesozoic locality 21850 (text 

fig. 1). 
N 

Chapter C 

Observations on the 

Cenomanian (Upper 

Cretaceous) Ammonite 

Calycoceras (Calycoceras) 

obrieni Young, 1957 from 

Arizona and New Mexico 

By WILLIAM A. COBBAN and W. JAMES KENNEDY 

Description of an upper Cenomanian marker ammonite from 

the southern part of the Western Interior of the United States 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to Paleontology and Stratigraphy 

CONTENTS 

Abstract Cl 

Introduction Cl 

Age and occurrence of Calycoceras (Calycoceras) obrieni Cl 

Repositories of specimens Cl 

Conventions Cl 

Systematic paleontology C3 

Family ACANTHOCERATIDAE de Grossouvre C3 

Subfamily ACANTHOCERATINAE de Grossouvre C3 

Genus and subgenus Calycoceras Hyatt C3 

Calycoceras (Calycoceras) obrieni Young C3 

References cited C4 

PLATES 

[Plates follow References cited] 

1-5. Calycoceras (Calycoceras) obrieni Young 

FIGURE 

1. Columnar section of the upper part of the Twowells Tongue of the Dakota Sandstone 

exposed in the eastern side of Cottonwood Canyon, Apache County, Arizona, 

showing U.S. Geological Survey Mesozoic fossil locality numbers and the more 

diagnostic molluscan fossils C2 

Contents Ill 

Observations on the Cenomanian (Upper 

Cretaceous) Ammonite Calycoceras (Calycoceras) 

obrieni Young, 1957 from Arizona and New Mexico 

By William A. Cobban and W. James Kennedy 

Abstract 

Calycoceras (Calycoceras) obrieni Young, 1957 is 

revised on the basis of new collections from the upper 

Cenomanian Metoicoceras mosbyense zone of Arizona 

and New Mexico, and differences between it and C. (C.) 

naviculare (Mantell, 1822) are described. 

INTRODUCTION 

Calycoceras obrieni Young, 1957 (p. 1171, pl. 150, 

figs. 1-4; text figs. lf, h) is a large, densely ribbed 

ammonite originally described on the basis of a single badly 

preserved specimen from the lower part of what Keith 

Young termed the "Mesaverde Formation" in eastern 

Apache County, Arizona. Subsequent authors followed 

Matsumoto (1959, p. 81; Kennedy, 1971, p. 73) in regarding C. obrieni as a synonym of C. (C.) naviculare (Mantell, 

1822), an important upper Cenomanian marker fossil in 

many parts of the world. We have redescribed Calycoceras 

obrieni on the basis of new, well-preserved specimens that 

show it to be a valid species, if closely allied to C. (C.) 

naviculare, of which it may be the ancestor. 

The fossils described in this report are kept in the 

U.S. National Museum of Natural History (USNM) in 

Washington, D.C. All specimens have USNM catalogue 

numbers. Plaster casts of a few of the specimens are at the 

Federal Center, Denver, Colo. We thank R.E. Burkholder, 

retired from the U.S. Geological Survey (USGS), for taking 

the photographs. Kennedy acknowledges the assistance of 

the staff of the Geological Collections, Oxford University 

Museum and the Department of Earth Sciences, Oxford, 

U.K., and the financial support of the Natural Environment 

Research Council (U.K.), the Royal Society, and the Astor 

Fund (Oxford). 

AGE AND OCCURRENCE OF CAL YCOCERAS 

(CAL YCOCERAS) OBRIEN/ 

The holotype of C. obrieni and other fossils described 

by Young were collected by R.K. Deford and others in 

Manuscript approved for publication November 16, 1988. 

1955 in the El/2 sees. 3 and 10, T. 10 N., R. 31 E., eastern 

Apache County, Arizona, from 21 to 27m above the base 

of what was then termed the "Mesaverde Formation." 

Young regarded the formation as either upper Cenomanian 

or lower Turonian and certainly close to the boundary of the 

two stages. He recorded Metoicoceras defordi Young, 

1957, Calycoceras obrieni Young, 1957, Dunveganoceras(?) sp. A, and Dunveganoceras(?) n.sp. B and illustrated a specimen of Exogyra columbella Meek. 

The sandstone unit that yielded this fauna is now 

referred to as the Twowells Tongue of the Dakota Sandstone, and the generalized stratigraphic relationships of the 

unit have been discussed by Landis and others (1973). 

Some 27 m of the Twowells Tongue are exposed in the 

Cottonwood Canyon area that yielded the type material. 

The lower 18 m are unfossiliferous, but the upper part 

yielded a series of faunas, as text figure 1 summarizes. 

Metoicoceras mosbyense Cobban, 1953 (of which M. 

defordi Young, 1957 is a synonym) ranges throughout most 

of the interval and co-occurs with C. (C.) obrieni, firmly 

establishing it as mosbyense zone. The highest ammonite 

fauna, from concretions above the Pycnodonte newberryi 

coquina, is poorly preserved but includes Pseudaspidoceras 

cf. flexuosum Powell, 1963 and Mytiloides sp.; this assemblage is early Turonian. Reexamination of Young's original 

material plus new collections shows that Dunveganoceras(?) n.sp. B of Young is a fragmentary Mammites, 

probably of the group of M. powelli Kennedy, Wright, and 

Hancock, 1987; 'Ye believe it to be derived from the highest 

fossil horizon and to be early Turonian, not a contemporary 

of C. obrieni. 

REPOSITORIES OF SPECIMENS 

The following abbreviations are used to indicate the 

repositories of specimens cited in the text: TMM, Texas 

Memorial Museum, Austin; USNM, National Museum of 

Natural History, Washington, D.C. 

CONVENTIONS 

Dimensions of specimens are given in millimeters 

and are indicated as follows: D, diameter; Wb, whorl 

Observations on the Cenomanian Ammonite Calycoceras (Calycoceras) obrieni Cl 
EXPLANATION 

Sandstone 

Shale 

Concretionary 

sandstone 

I._;'~"' ~"'I Shell beds 

... 

~·;~~.-.; ~~·,-t:~~~~ 

06175. Sandstone concretions containing Pseudaspidoceras d. flexuosum, 

Mammites sp., Pycnodonte newberryi, and Mytiloides sp. 

30-cm-thick bed of Pycnodonte newberryi lumachelle. 

06174. 90-cm-thick bed of sandstone crowded with Exogyra levis and an 

occasional Metoicoceras mosbyense. 

06173. 30-cm-thick ledge of highly fossiliferous sandstone. Calycoceras obrieni, 

Metoicoceras mosbyense, Exogyra levis, Lopha, Pinna, Callistina, 

Homomya, and other bivalves. 

06177. Pinna petrina 

·':·.~ r:" ~~ r; "'::..., ,_;_.;~~~. 06176. ldonearca, Callistina, Homomya, and other bivalves. 

· .... 

06171 . 30-cm-thick ledge of concretionary sandstone containing an occasional 

Metoicoceras mosbyense. 

Figure 1. Upper part of the Twowells Tongue of the Dakota Sandstone exposed in the eastern side of 

Cottonwood Canyon in the NEV4 SE1f4 sec. 3, T. 10 N., R. 31 E., Apache County, Arizona, showing U.S. 

Geological Survey Mesozoic fossil locality numbers and the more diagnostic molluscan fossils. 

C2 Shorter Contributions to Paleontology and Stratigraphy 
breadth; Wh, whorl height; Wb: Wh, ratio of whorl breadth 

to whorl height; and U, umbilical diameter. Numbers in 

parentheses are percentages of the diameters. 

SYSTEMATIC PALEONTOLOGY 

Family ACANTHOCERATIDAE de Grossouvre, 

1894 

Subfamily ACANTHOCERATINAE de 

Grossouvre, 1894 

Genus and Subgenus Calycoceras Hyatt, 1900 

Type species.-ICZN Opinion 557, 1959, name no. 

1633; Ammonites navicularis Mantell, 1822, p. 198, pl. 22, 

fig. 5. 

Calycoceras (Calycoceras) obrieni Young, 1957 

Plates 1-5 

1957. Calycoceras obrieni Young, p. 1171, pl. 150, figs. 

1-4; text figs. lf. h. 

1959. Calycoceras obrieni Young. Matsumoto, p. 81. 

1971. Calycoceras obrieni Young. Kennedy, p. 73 

1972. Calycoceras obrieni Young. Thomel, p. 52. 

1981. Calycoceras obrieni Young. Wright and Kennedy. 

p. 36. 

T_'.'pe. - Holotype by monotypy is TMM 18469 from 

the Twowells Tongue of the Dakota Sandstone in the upper 

Cenomanian Metoicoceras mosbyense zone of Cottonwood 

Canyon, sec. 3, T. 10 N., R. 31 E., Apache County, 

Arizona. 

Material.-Three topotypes (including hypotypes 

USNM 422680-422681) collected by W .A. Cobban at 

USGS Mesozoic locality D6173 in the NEl/4 SEI/4 sec. 3, T. 

10 N., R. 31 E., Apache County, Arizona; one hypotype 

(USNM 422679) collected by Cobban at USGS Mesozoic 

locality Dl2163 in the SEl/4 SEl/4 sec. 28, T. 1 N., R. 21 

W., Catron County, New Mexico; and two hypotypes 

(USNM 422678 and 422683) collected by Cobban at USGS 

Mesozoic locality Dl2070 in the SEI/4 SWl/4 sec. 30, T. 10 

N., R. 30 E., Apache County, Arizona. 

Dimensions.-Dimensions of five of the six specimens described herein are as follows: 

USNM no. 0 1 (mm) Wb2 (mm) Wh2 (mm) Wb: Wh2 U (mm) 

422678 ........ 114.0 (100) c 64.2 (56.3) 43.8 (38.4) 

108.0 (100) ic 54.2 (50.2) 41.7 (38.6) 

422679 ........ c 42.5 31.0 

73.5 48.0 

ic 66.0c 46.0 

422680 ........ 90.0 (100) c 57.0 (63) 37.0 (·+1.1) 

422681 ........ 167 (100) c -- (--) -- (--) 

422682 ........ 157 (100) c 104.0 (66.2) 65 (41.4) 

147.5 (100) ic 82.5 (55.9) 57 (38.6) 

1 c, costal diameter; ic, intercostal diameter. 2 --, measurements not possible. 

1.47 

1.30 

1.37 

1.53 

1.43 

1.54 

1.6 

1.45 

38.0 (33.3) 

37.8 (35.0) 

26.7 (29.7) 

47.7 (28.5) 

42.0 (26.8) 

42.0 (28.5) 

Description.-USNM 422679 shows the early phragmocone whorls and replaced shell preserved at a diameter of 

72 mm (pl. 1, figs. 4, 5). Coiling is evolute; 33 percent of 

the previous whorl is covered, the inner ventrolateral 

tubercles of the preceding whorl being housed in shallow 

notches in the umbilical wall of the succeeding one. The 

umbilicus is deep, comprises 29 percent of the diameter, 

and has a flattened wall. The whorl section is depressed 

reniform in intercostal section, the greatest breadth occurring just outside the umbilicus, and the flanks and venter are 

broadly and evenly rounded. There are 13 rectiradiate to 

feebly rursiradiate primary ribs per whorl visible in the 

umbilicus and 15 per whorl at a diameter of 72 mm. These 

ribs arise at the umbilical seam and strengthen across the 

umbilical wall, where they are rounded and separated by 

wide interspaces. The ribs strengthen markedly across the 

umbilical shoulder into strong umbilical bullae. which form 

the point of greatest width of the whorl in costal section. A 

strong, narrow, high rib connects to a smaller, sharp, inner 

ventrolateral bulla, the rib profile being markedly concave 

in profile between the bullae. A lower rib passes straight 

across the venter to the corresponding inner ventrolateral 

bulla on the opposite flank without diminution in strength or 

development of outer ventrolateral or siphonal tubercles at 

the smallest diameter visible, estimated to be 33 mm. These 

strong bullate primaries are separated by two to four 

nontuberculate ribs. Some extend down to the umbilical 

seam but are much weaker than the primaries; others arise at 

levels from inner to outer flank, and some are feebly linked 

to the bullate primaries. These incipient secondary and 

intercalated ribs strengthen across the ventrolateral shoulder, and all ribs are equally developed across the venter, to 

give a total rib density of 40 to 42 per whorl at a diameter 

of 63 mm. 

Between diameters of 42 and 63 mm (this interval is 

concealed in the specimen), the venter flattens, and feeble 

outer ventrolateral bullae appear, initially little more than an 

angulation in the rib profile. The ribs broaden and coarsen 

markedly from this diameter and become markedly rursiradiate. USNM 422680 is a somewhat distorted internal 

mold 100 mm in diameter (pl. 1, figs. 1-3). It is less 

depressed than USNM 422679 but shows a comparable 

ornament and ontogenetic development and has 17 bullate 

primaries and a total of 38 ribs per whorl. 

USNM 422681 continues the ontogeny (pl. 3). It is 

167 mm in maximum costal diameter, has just over half a 

whorl of body chamber preserved, and is an internal mold. 

There are 27 ribs on the outer whorl. Twelve ribs arise at the 

umbilical seam and develop into umbilical bullae that 

strengthen markedly and migrate outward as size increases. 

These ribs give rise to very coarse, rursiradiate ribs that are 

high and flared across the flanks. The latter ribs bear 

well-differentiated outer ventrolateral bullae that are connected across the venter by a broad, coarse rib that is 

slightly sunken between the ventrolateral tubercles when 

Observations on the Cenomanian Ammonite Calycoceras (Calycoceras) obrieni C3 
viewed in profile. At the beginning of the outer whorl, these 

strong bullate primaries are separated by two intercalated 

ribs; the adapical ribs are short, whereas the adapertural 

ones are long and extend in some cases to the umbilical 

seam, although they are not bullate. In the last 120° of body 

chamber, only a single intercalated rib is present, arising on 

the outer flank and having a ventral development comparable to that of the primaries. 

USNM 422682 is a complete adult displaying a 

preserved shell; the maximum costal diameter is 196 mm 

(pls. 4, 5). Ornament is the same as that of USNM 422681, 

but the flares on the primary ribs on the flank are very 

pronounced and yield a costal whorl breadth to height ratio 

of up to 1. 6. The ribs sharpen and narrow markedly, and the 

umbilical bulla weakens on the last primary rib before the 

aperture. 

USNM 422678 and 422683 (pl. 2, figs. 1-6) are from 

the Twowells Tongue 17 km southwest of the type locality 

of C. (C.) obrieni in the SWl/4 SEl/4 SWl/4 sec. 30, T. 10 

N., R. 30 E., in Apache County, Arizona. Both appear to 

represent a slender form of C. (C.) obrieni. USNM 422678 

is 114 mm in maximum costal diameter, 240° of the last 

whorl being body chamber. The coiling is evolute; U is 

33.3 percent of the costal diameter and 35.0 percent of the 

intercostal diameter, and the umbilical wall is rounded. The 

whorl section is depressed reniform in intercostal section, 

and the whorl breadth to height ratio is 1. 30, the greatest 

breadth occurring just outside the umbilical shoulder. The 

costal ratio is 1.47, the greatest breadth being at the 

umbilical bullae. At the smallest diameter visible in the 

umbilicus of the specimen, 14 to 15 primary ribs arise at the 

umbilical seam, where they are broad, strong, rounded, and 

rursiradiate. At the smallest diameter, there is a strong 

umbilical bulla and a slightly weaker inner ventrolateral 

bulla, linked by a high rib, as in specimens already 

described, and the tuberculate ribs are separated by two 

intercalated ribs. The inner ventrolateral tubercle has 

already disappeared by an estimated diameter of 40 mm. 

Twenty primary ribs are present on the outer whorl. All 

arise at the umbilical seam, strengthen across the umbilical 

wall, and develop into prominent umbilical bullae, which 

give rise to pairs of narrow, sharp, rursiradiate ribs separated by single intercalated ribs that arise below midflank. 

Well-differentiated outer ventrolateral bullae are present to 

a diameter of 85 mm, connected across the venter by a 

broad, transverse rib. The venter remains flattened beyond 

85 mm, but the ventrolateral tubercles efface, although this 

effacement may, in fact, reflect wear on the surface of the 

specimen. USNM 422683 is wholly septate and slightly 

crushed, the maximum preserved diameter being 91 mm. 

Nineteen ribs are present on the last half whorl; they are 

fewer and coarser than those in USNM 422678, are long 

and short, and do not arise in pairs from bullae, so that the 

specimen is intermediate in ribbing strength and character 

between USNM 422682 and USNM 422678. 

C4 Shorter Contributions to Paleontology and Stratigraphy 

Discussion. -C. (C.) obrieni has been treated as a 

synonym of C. (C.) naviculare (Mantell, 1822), as the 

introduction noted. On the basis of the new material 

described here, the two species can be distinguished as 

follows. Taking descriptions of Western Interior C. (C.) 

naviculare by Cobban ( 1971) and those of European material by Kennedy (1971) and Wright and Kennedy (1981) as 

the basis, the inner whorls of C. (C.) obrieni generally have 

a narrower venter and show a more gradual increase in 

whorl breadth. Intercostal section is similar in middle and 

later growth, but large specimens have much coarser ribs 

that are expanclP':! into marked lateral flanges (pis. 3-6). 

Outer ventrolateral tuberculation or angulation is more 

marked, and there is commonly a significant depression in 

the ribs over the venter. 

REFERENCES CITED 

Cobban, W.A., 1953, Cenomanian ammonite fauna from the 

Mosby sandstone of central Montana: U.S. Geological Survey Professional Paper 243-D, p. D45-D55, pis. 6-12. 

---1971, New and little-known ammonites from the Upper 

Cretaceous (Cenomanian and Turonian) of the Western Interior of the United States: U.S. Geological Survey Professional Paper 699, 24 p. , 18 pis. 

de Grossouvre, A., 1894, Les ammonites de la craie superieure, 

pt. 2, Paleontologie, in Recherches sur la craie superieure: 

Carte Geologique Detaillee de la France Memoires, 264 p., 

39 pis. (1893 imprint.) 

Hyatt, A., 1900, Cephalopoda, in von Zittel, K.A., Textbook of 

paleontology (translated from the German by C.R. Eastman): 

London, Macmillan, p. 502-604. 

Kennedy, W .J., 1971, Cenomanian ammonites from southern 

England: Palaeontology Special Papers, no. 8, 133 p., 64 pis. 

Kennedy, W.J., Wright, C.W., and Hancock, J.M., 1987, Basal 

Turonian ammonites from West Texas: Palaeontology, v. 30, 

p. 27-74, pis. 1-10. 

Landis, E.R., Dane, C.H., and Cobban, W.A., 1973, Stratigraphic terminology of the Dakota Sandstone and Mancos 

Shale, west-central New Mexico: U.S. Geological Survey 

Bulletin 1372-J, 44 p. 

Mantell, G.A., 1822, The fossils of the South Downs, or 

illustrations of the geology of Sussex: London, Lupton Relfe, 

327 p., 42 pls. 

Matsumoto, T., 1959, Upper Cretaceous ammonites of California, 

pt. 2: Memoires of the Faculty of Science, Kyushu University, ser. D, Geology, special v. 1, 172 p., 41 pis. 

Powell, J.D., 1963, Cenomanian-Turonian (Cretaceous) ammonites from Trans-Pecos Texas and northeastern Chihuahua, 

Mexico: Journal of Paleontology, v. 37, p. 1217-1232, pis. 

166-171. 

Thomel, G., 1972, Les Acanthoceratidae cenomaniens des 

chaines subalpines meridionales: Memoires de la Societe 

Geologique de France, n. s. , v. 51 , Memoire 116, 204 p. , 88 

pls. 

Wright, C.W., and Kennedy, W.J., 1981, The Ammonoidea of 

the Plenus Marls and the Middle Chalk, in Publication no. 

560: London, Palaeontographical Society, v. 134, 148 p., 32 

pls. 

Young, K., 1957, Cretaceous ammonites from eastern Apache 

County, Arizona: Journal of Paleontology, v. 31, p. 1167-

1174, pis. 149-150. 
PLATES 1-5 
PLATE 1 

Calycoceras (Calycoceras) obrieni Young (p. C3). 

[All figures natural size] 

Figures 1-3. Hypotype USNM 422680, from the Twowells Tongue of the Dakota Sandstone at USGS Mesozoic 

locality D6173. 

4, 5. Hypotype USNM 422679, from the Twowells Tongue at USGS Mesozoic locality D12163. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-C, PLATE 1 

3 

2 

4 5 

CALYCOCERAS 
PLATE 2 

Calycoceras (Calycoceras) obrieni Young (p. C3). 

[All figures natural size] 

Figures 1- 3. Hypotype USNM 422683 , from the Twowells Tongue of the Dakota Sandstone at USGS Mesozoic 

locality D12070. Figure 2 is a Latex peel of the inner dorsum area. 

4-6. Hypotype USNM 422678 , from the Twowells Tongue of the Dakota Sandstone at USGS Mesozoic 

locality D12070. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-C, PLATE 2 

3 

4 

2 

5 6 

CALYCOCERAS 
PLATE 3 

Calycoceras (Calycoceras) obrieni Young (p. C3). 

[Both figures natural size] 

Figures 1, 2. Hypotype USNM 422681, from the Twowells Tongue of the Dakota Sandstone at USGS Mesozoic 

locality 06173. 
N 
PLATE 4 

Calycoceras (Calycoceras) obrieni Young (p. C3) 

[Figure natural size] 

Hypo type USNM 422682, from the Two wells Tongue of the Dakota Sandstone at USGS Mesozoic locality D6173. See 

plate 5 for end views. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881- C, PLATE 4 

CALYCOCERAS 
PLATE 5 

Calycoceras (Calycoceras) obrieni Young (p. C3). 

[Figure natural size] 

Hypotype USNM 422682, from the Twowells Tongue of the Dakota Sandstone at USGS Mesozoic locality D61 73. See 

plate 4 for side view. 
CS. GEOLOGICAL SURVEY BULLETIN 1881-C, PLATE 5 

CALYCOCERAS 

Chapter D 

Revision of the Nucula percrassa 

Conrad, 1858 Group in the Upper 

Cretaceous of the Gulf and 

Mid-Atlantic Coastal Plains: An 

Example of Bias in the 

Nomenclature 

By G. LYNN WINGARD and NORMAN F. SOHL 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to Paleontology and Stratigraphy 

CONTENTS 

Abstract Dl 

Introduction Dl 

Coastal Plain Upper Cretaceous Nuculidae D2 

Mode of occurrence and abundance of Cretaceous Coastal Plain nuculids D3 

Previous work on the Nunda percrassa lineage D3 

Acknowledgments DS 

Materials and methods DS 

Discriminant analysis D6 

Implications for paleontologists D9 

Systematic paleontology Dll 

Summary and conclusions D17 

References cited D17 

Appendix 1. Nuculid species from the Upper Cretaceous of North America D20 

Appendix 2. Description of collection localities D22 

PLATES 

[Plates follow References cited] 

1. Type specimens of species of Nucztla 

2. Comparison of external morphologies of NuCitla percrassa Conrad 

3. Comparison between upper Maastrichtian specimens of Nucula percrassa Conrad 

and Nucula severnensis Wingard and Sohl, n.sp. at various growth stages 

4. Comparison of Nucula percrassa Conrad arranged in descending stratigraphic 

order 

5. Comparison of four species of Upper Cretaceous Nucztla 

6. Articulated specimens showing variations in shell obesity and lunule and escutcheon 

morphology 

7. Adductor and pedal muscle scar systems 

FIGURES 

1-3. Locality maps showing samples collected in: 

1. Tennessee and Mississippi D6 

2. Alabama and Georgia D6 

3. Mary land D7 

4. Diagrams showing measurement of the characters D7 

5. Plot showing discriminant analysis of the data grouped by "species" DS 

6. Columnar diagram showing stratigraphic positions of samples, ranges of species 

in previous papers and in this report, and the five stratigraphic levels used in 

analyzing Gulf Coast samples D9 

7. Plot showing discriminant analysis of the data grouped by collection locality DlO 

8. Histogram showing discriminant analysis of the data grouped by region DlO 

9. Plot showing discriminant analysis of the data grouped by stratigraphic position DlO 

10. Histogram showing discriminant analysis of the data on topotypes of Nucztla 

percrassa and N. tippahensis D12 

11. Schematic diagram showing the musculature of the Nucztla percrassa group D13 

Contents Ill 
IV Contents 

TABLES 

1. Occurrence of Nucztla (N.) percrassa at selected localities of the Haustator bilira 

Assemblage Zone (Maastrichtian) of the Coastal Plain D3 

2. Summary statistics for the Nucztla (N.) percrassa group D4 

3. Classification results for discriminant analysis of data grouped into three ''species'' of 

Nucula occurring within the upper Maastrichtian DS 

4. Classification results for discriminant analysis of data grouped by State Dll 

5. Classification results for discriminant analysis of data grouped by region Dll 

6. Mean values of the morphologic characters of Nucztla percrassa at each stratigraphic 

level Dll 

7. Classification results for discriminant analysis of data grouped by stratigraphic 

level D12 

8. Classification results for discriminant analysis of data on topotypes of Nucula 

percrassa and Nuczda tippahensis D12 
Revision of the Nucula percrassa Conrad, 1858 

Group in the Upper Cretaceous of the Gulf and 

Mid-Atlantic Coastal Plains: An Example of Bias 

the Nomenclature 

. tn 

By G. Lynn Wingard and Norman F. Sohl 

Abstract 

A discriminant analysis of Nucula percrassa Conrad, 

N. slackiana Gabb, N. tippahensis Harbison, and N. sp. 

was conducted to resolve questions about their taxonomic, geographic, and stratigraphic relationships. The 

specimens analyzed were from lower Campanian through 

upper Maastrichtian units of the Gulf and Mid-Atlantic 

Coastal Plains. The results indicate that there are no 

genetically based morphologic features that can distinguish between N. percrassa, N. slackiana, and N. tippahensis; therefore, these three names are synonymized 

within the single concept N. percrassa Conrad, 1858 as 

here revised. An insufficient number of specimens prevented N. cibolensis Stephenson and N. chatfieldensis 

Stephenson (upper Campanian and Maastrichtian, Texas) 

from being included in the statistical analysis, but the 

available specimens show no significant morphological 

differences from N. percrassa as defined here. N. cibolensis and N. chatfie/densis were consequently synonymized 

with N. percrassa. The fourth group, N. sp. (previously 

regarded as a juvenile), was determined during the analysis to be a separate species, named N. severnensis n.sp. 

The methods by which paleontologists define species and select type specimens change as knowledge 

increases. This study illustrates instances of nomenclatural 

biases based on assumed stratigraphic or geographic 

isolation of populations or on typological differences. The 

existence of such biases can have profound effects on the 

calculation of rates of evolution and extinction. For the 

Nuculidae, the bias was toward shorter species durations 

and increased species diversity. This study indicates the 

importance of establishing fossil species by the objective 

examination of preserved morphologic differences. Until 

consistent, reproducible taxonomies are constructed, 

paleontologists should proceed cautiously with inductive 

conclusions about the evolution and extinction of organisms. 

Manuscript approved for publication November 16, 1988. 

INTRODUCTION 

Nucula has been known in marine Cretaceous rocks 

of North America ever since Morton (1833, p. 292) 

recognized specifically indeterminate molds in what is now 

the Merchantville Formation (lower Campanian) in the 

vicinity of Bordentown, N.J. , as belonging to this genus. 

By 1893, Boyle (1893, p. 200-203) listed 24 described 

North American species that were primarily from the Upper 

Cretaceous of the Western Interior and the Atlantic and Gulf 

Coastal Plains (see app. 1 for a complete listing); 29 

additional Cretaceous species were described subsequently. 

There has been no overall synthesis of these Cretaceous 

species, nor have there been any redescriptions or analyses 

of most of them since their original descriptions. N. 

truncata Gabb, 1864 (non Nilsson, 1827) was renamed 

Acila demessa by Finlay (1926, p. 522), and N. perequalis 

Conrad, 1860 is placed by us in the Nuculanidae (see 

discussion in the next section). All other species originally 

placed in Nucula are still assigned to that genus and to the 

family Nuculidae. 

In a study of late Maastrichtian Mollusca of the 

Atlantic and Gulf Coastal Plains, Sohl and Koch (1983) 

realized that confusion exists as to the number of species of 

Nucztla that are present in the fauna and the characters that 

previous workers used to distinguish the species. The 

species were described at times when correlations of the 

units in which they are found were less well known than 

they are now, and we have determined that some species 

names are artifacts of a provincial nomenclature. The 

present study utilizes the many new collections made 

throughout the Coastal Plains and applies techniques of 

morphometric analysis to solve taxonomic questions. 

Our survey of the literature on fossil and living 

marine bivalves convinced us of the great morphologic 

similarity between extant species of Nucula and those of 

many fossil deposits of Cretaceous and Tertiary ages. 

Therefore, this study may also serve as an example of 

analytical techniques that can be applied to other groups of 

mollusks that show very conservative character state 

changes over long periods of time. 

Revision of the Nucula percrassa Conrad, 1858 Group D1 
Coastal Plain Upper Cretaceous Nuculidae 

Species assigned to the Nuculidae have been 

described from Gulf and Atlantic Coastal Plain formations 

(see app. 1) ranging in age from Cenomanian through the 

Maastrichtian. Geographically, they range from occurrences on the Banquereau Banks off Nova Scotia to Mexico. All species have been assigned to Nucztla, except for 

Acila banquereauensis Stephenson, 1936 and A. (Truncacila)? chicotana Stephenson, 1952. It is doubtful that all 

these Late Cretaceous species should be included in Nucula 

ss. As Allen and Hannah (1986, p. 225) stated, ''From the 

earliest writings to the present, malacologists have experienced great difficulty in separating clearly and defining 

adequately the proto branch taxa .... " We believe that a 

number of clear distinctions can be made among the 

Cretaceous Coastal Plain species that have been lumped 

under Nucz.tla (Nucztla). For example, representatives of all 

three major groups proposed by Schenk (1934) are present: 

(1) forms having a crenulate ventral margin, (2) forms 

having a smooth ventral margin, and (3) forms having a 

divaricate ornamentation. Schenk recognized six genera of 

nuculids as subdivisions of these three major groupings. 

Five additional proposed taxa were viewed as being of 

questionable rank or position. Subsequently, two other 

schemes of nuculid classification have appeared. Keen 

(1969) recognized 10 genera within the family, whereas 

Allen and Hannah ( 1986) accepted only 3. The disparity in 

numbers between these two classifications exists because 

Allen and Hannah did not treat the eight genera and 

subgenera that are known only from the fossil record. In 

addition, they incorrectly ascribed Keen's classification to 

Newell in their references. Despite these shortcomings, the 

diagnoses that Allen and Hannah provided are more useful 

than those of Keen because they contrast the same characters between taxa. Keen's diagnoses suffer from a lack of 

detail and a lack of uniformity; she failed to contrast the 

same features between all taxa. 

Despite these failings, most of the adequately 

founded and described Late Cretaceous nuculids of the 

Coastal Plains can be placed in existing genera or subgenera. The most common group of species are those allied to 

Nucula percrassa Conrad, 1858, which consists of forms 

exhibiting a subovate to subtrigonal valve outline, a crenulate inner ventral margin, an oblique ligament, and a 

flat-lying radial sculpture (pl. 1, figs. 1-10). The sum of 

characters indicates placement of these species in Nucula 

(Nucula). The species described below may all be assigned 

to this subgenus. 

A second grouping is characterized by Nucula amica 

Gardner, 1916 (pl. 5, figs. 4, 7, 9) and is united in having 

a subtrigonal valve outline, a crenulate inner ventral margin, an internal ligament, a short chondrophore, and a 

strongly defined comarginal lirae; fainter raised radial 

02 Shorter Contributions to Paleontology and Stratigraphy 

elements cross the comarginal lirae and lend the shell 

surface a subcancellate appearance. This group is assignable to Nucula on the basis of shape and hinge characters 

but finds no parallel in ornament among the subgenera of 

the genus. 

The third grouping is typified by species such as 

Nucula cuneifrons Conrad, 1860 (pl. 5, figs. 1, 5, 6, 8) that 

are trigonally subovate in valve outline and display a 

noncrenulate ventral margin and fine, closely spaced 

comarginal ribs. This group is similar to N. (Leionucula) 

Quenstedt, 1930 in possessing an oblique resilifer but 

differs in possessing distinct raised comarginal ribs (pl. 5, 

fig. 8). Quenstedt (1930, p. 112), in his diagnosis of the 

subgenus, stated that the shells are characteristically 

smooth. Schenk (1934, p. 34), in his description of the type 

species of Leionucuta (N. albensis d'Orbigny, 1844), stated 

that, "although there are concentric growth stages, the shell 

is without definite ribs." If such a definition is adhered to, 

another assignment is needed for N. cuneifrons. The strong 

comarginal elements of N. cuneifrons are similar to thr 

ornament found on Nucula castor d'Orbigny, 1850, the 

type species of Nuculoma Cossmann, 1907. In fact, Allen 

and Hannah (1986, p. 229) considered Leionucula a synonym of Nuculoma; they described the outer layer of shell 

as "smooth, glossy, [and] without radial elements." As the 

illustrations of the type species Nucula castor provided by 

Cossmann (1907, pl. 2, figs. 14-15) and Schenk (1934, pl. 

4, fig. 5) indicate, the outer shell surface bears close spaced 

collabral threads. Although the hinge structures of the two 

are similiar, Cossmann emphasized that Nuculoma is 

"Lithodomous shaped" and thus almost subquadrate, as 

opposed to the decidedly subtrigonal shape of Leionucula. 

In sum, the group of species allied to Nucula cuneifrons 

shows some features that are common to both these taxa but 

more that are akin to Leionucula. 

The fourth species group encompasses those species 

assigned by Stephenson (1936, 1952) to Acila and characterized by divaricate sculpture. This group of nuculids is the 

rarest in the Coastal Plains. 

One species, Nucula perequalis Conrad, 1860, and 

its junior objective synonym, N. eufaulensis Gabb, 1860, 

stand alone in character. Shells of this species are rare and 

poorly known. Stephenson (1941, pl. 8, figs. 7-9) has 

presented illustrations and described the species but has 

omitted several features that we believe cast doubt on 

current assignment of the species. We have examined two 

well-preserved topotypes and find that they lack nacreous 

shell layers and possess a shallow pallial sinus. Such 

characters suggest that this species is better placed among 

the Nuculanacea. Of the four groups accepted as nuculids, 

it is the N. percrassa group that is the most common and 

persistent in the Cretaceous deposits of the Coastal Plains 

and will be the subject of the following discussions. 
Table 1. Occurrence of Nucula (N.) percrassa at selected localities of the Haustator bilira 

Assemblage Zone (Maastrichtian) of the Coastal Plain 

Total no. No. of N. percrassa 

No. of bivalve of bivalve specimens of specimens, 

Locality genera/species specimens N. percrassa in percent 

Owl Creek Formation, Miss., ........ 

USGS 707, 25423, loc. 19. 

Providence Sand, Ga., ............... 

USGS 6412, 25935. loc. 22. 

Severn Formation, Md.: 

USGS 28858, loc. 25 ........... 

USGS 32772, loc. 24 ........... 

USGS 32775, loc. 23 ........... 

Mode of Occurrence and Abundance of 

Cretaceous Coastal Plain Nuculids 

66/78 

48/76 

36/41 

39/62 

53/68 

The four groups of nuculids defined above all occur 

most commonly in the Upper Cretaceous of the Coastal 

Plains in micaceous, clayey, fine sands deposited on the 

inner shelf in shallow marine waters of normal salinity. 

They occur only rarely in lagoonal clays, in coarse sand, 

and in deeper water, middle to outer shelf chalky deposits. 

Their preservation in the inner shelf deposits is excellent. 

Aragonitic shell material is still present, including the 

lustrous mother-of-pearl inner nacreous shell layers. Preservation as phosphatic internal molds is moderately common in the basal reworked beds of the transgressive phases 

of the Coastal Plain depositional cycles. Such molds, when 

well preserved (pl. 7, figs. 7, 9), replicate muscle scar 

patterns especially well. 

Nuculids only rarely form a major element of Coastal 

Plain bivalve associations. Some measure of their frequency 

of occurrence and individual abundance can be gauged from 

Sohl and Koch's (1983) study of the late Maastrichtian 

fauna of the Haustator bilira Assemblage Zone. During that 

study, the fauna from 642 localities within this zone, 

representing a full spectrum of shelfal environments, was 

analyzed, and over 110,000 specimens of mollusks were 

identified. Nucula occurred in the collections from 97 

localities (15 percent of the total). A total of 2,206 

specimens of Nuctda was identified, or about 2 percent of 

all molluscan specimens identified (table 1). Considering 

that over 600 species and 287 genera of mollusks have been 

recognized in the fauna of the Haustator bilira Assemblage 

Zone, a total of 2 percent for the specimens of Nucttla is a 

significant representation. 

Among the species of Nucula that are present, N. 

percrassa constitutes about 75 percent of the total specimens of the Nuculidae at the 97 localities. At some of these 

localities, N. percrassa may be among the most abundant of 

bivalves, as table 1 shows. All of the localities listed in 

table 1 are representative of the intermixed mud and fine 

2,005 186 9 

4,215 148 3.5 

2.120 167 8 

2,953 259 9 

3,052 200 6.5 

sand facies in which aragonitic shells are preserved and 

molluscan diversity is high. The unconsolidated sediment 

can be washed and sieved and the smallest species recovered. In coarse sand or chalk facies, nuculids are commonly 

absent or usually constitute only a fraction of a percent of all 

bivalve specimens. 

Another facet of the Nucttla (N.) percrassa lineage on 

the Coastal Plains is shell size. In comparison with other 

species of Nucula, both extant and fossil, this species 

includes specimens that must be considered among the 

giants of the genus. The largest specimen measured is 45 

mm in length and comes from the Ripley Formation of the 

Chattahoochee River Valley near Eufaula, Ala. An examination of extant nuculids in the collections of the Division 

of Mollusks of the U.S. National Museum of Natural 

History (USNM NH) turns up only one specimen, N. 

mirabilis Adams and Reeve, 1850, from the Sea of Japan, 

that reached such a size ( 44 mm) (USNM NH Division of 

Mollusks no. 204519). A specimen of N. iphigenia Dall, 

1896 from the Gulf of Panama (USNM NH Division of 

Mollusks no. 122896) was 35 mm long. The majority of 

extant species ranged between 6 and 25 mm in length. The 

largest recorded nuculid that we are aware of was cited by 

Schenk (1934, footnote p. 46) as a specimen of Acila 

(Acila) divaricata (Hinds), 1843, housed in the collections 

of the University of Berlin, that attained a length of 49 mm. 

Schenk also provided seven tables of measurements of 

fossil and living species indicating that most species fall 

within the length ranges that we found in our survey. A 

comparison of Schenk's tables with the measurements of N. 

(N.) percrassa provided in table 2 indicates that this 

Cretaceous species must be classed among the largest of all 

known nuculid species. 

Previous Work on the Nucu/a percrassa Lineage 

Nucula percrassa Conrad, 1858 and Leda slackiana 

Gabb, 1860 have been a particular source of confusion and 

controversy since their original descriptions (compare pl. 1, 

Revision of the Nucula percrassa Conrad, 1858 Group 03 
Table 2. Summary statistics for the Nucula (N.) percrassa group 

[The three left-hand columns show data for species as previously defined; these categories were tested in the 

discriminant analysis portion of this paper. The two right-hand columns represent species as defined in this paper. 

Note the proximity of the mean, median, and mode values, which is indicative of a normal distribution] 

Previous usage This paper 

N. percrassa N. s/ackiana N. tippahensis N. percrassa N. severnensis 

Conrad Gabb of Gardner Harbison Conrad n.sp 

Height, in millimeters 

Number of cases ..... 237 83 40 360 61 

Mean ................ 16.81 19.39 20.74 17.84 9.75 

Median .............. 17.00 20.00 21.25 18.00 10.00 

Mode ................ 17.00 20.00 23.00 18.00 9.00 

Standard deviation .... 3.94 2.51 3.34 3.88 1.62 

Range ............... 22.50 13.50 16.00 23.50 10.50 

Minimum value ...... 5.50 10.00 13.00 5.50 4.50 

Maximum value ...... 28.00 23.50 29.00 29.00 15.00 

Length, in millimeters 

Number of cases ..... 232 81 40 353 61 

Mean ................ 26.94 28.03 31.93 'I7 .76 12.75 

Median .............. 27.00 28.00 33.00 28.00 13.00 

Mode ................ 27.00 30.00 34.00 30.00 13.00 

Standard deviation .... 6.29 3.51 4.95 5.82 2.18 

Range ............... 36.00 20.00 20.00 36.00 12.50 

Minimum value ...... 8.00 14.00 21.00 8.00 5.50 

Maximum value ...... 44.00 34.00 41.00 44.00 18.00 

Hinge angle, in degrees 

Number of cases ..... 178 67 40 285 49 

Mean ................ 119.36 107.52 117.01 116.25 93.26 

Median .............. 119.00 108.50 116.25 116.50 94.00 

Mode ................ 119.00 108.50 114.00 119.00 98.00 

Standard deviation .... 7.50 6.44 5.64 8.55 7.40 

Range ............... 41.00 30.00 25.50 42.00 37.00 

Minimum value ...... 95.00 94.00 103.00 94.00 75.00 

Maximum value ...... 136.00 124.00 128.50 136.00 112.00 

Anterior angle, in degrees 

Number of cases ..... 175 69 40 284 47 

Mean ................ 53.06 60.17 54.44 54.98 62.31 

Median .............. 52.50 61.00 52.50 55.00 62.00 

Mode ................ 50.00 57.00 59.00 50.00 60.00 

Standard deviation .... 7.58 6.67 8.01 7.99 6.44 

Range ............... 44.00 33.50 37.00 44.00 28.00 

Minimum value ...... 37.00 41.50 40.00 37.00 48.00 

Maximum value ...... 81.00 75.00 77.00 81.00 76.00 

Posterior angle, in degrees 

Number of cases ..... 178 68 40 286 47 

Mean ................ 72.46 80.16 74.40 74.57 89.13 

Median .............. 72.00 79.50 76.00 75.00 88.00 

Mode ................ 70.00 79.00 80.00 79.00 92.00 

Standard deviation .... 7.35 6.40 7.47 7.82 7.35 

Range ............... 37.00 28.00 31.00 41.00 30.00 

Minimum value ...... 55.00 68.00 59.00 55.00 77.00 

Maximum value ...... 92.00 96.00 90.00 96.00 107.00 

04 Shorter Contributions to Paleontology and Stratigraphy 
figs. 1-2, and pl. 2, figs. 3, 5-6, 9, with pl. 1, figs. 3-6, 

and pl. 2, figs. 1-2, 4). Conrad (1858, p. 327) named and 

described N. percrassa in 1858 from Cretaceous deposits in 

Tippah County, Mississippi, but, in contrasting it with other 

taxa, stated only that it was "very unlike any other species." 

In 1860, Gabb named L. slackiana (placed in Nucula as N. 

slackiana by Gabb (1876, p. 318)) for a mold collected in 

Upper Cretaceous beds of "Crosswicks," N.J. By 1876, 

Gabb (1876, p. 318) began to question his own identification and stated " ... but from its size and shape I have little 

doubt it will prove identical with percrassa." 

Gardner (1916, p. 511) took the opposite position in 

her study of the Cretaceous deposits of Maryland and stated 

that Nucula slackiana "is not Nucula percrassa." She 

believed that the two species represented geographically 

restricted species, distinguished on characteristics of height, 

convexity of umbo, and ventral margin. Stephenson (1955) 

agreed with her conclusions. Richards (1958) reviewed the 

literature on N. percrassa and N. slackiana and concluded 

that a more careful study needed to be done to determine 

whether the two forms are conspecific. Differences between 

the height-length ratios of N. percrassa and N. slackiana 

might not be enough to consider the two forms a distinct 

species, according to Speden (1970). He believed that a 

statistical study might show whether they are conspecific, 

subspecies, or distinct species. 

Harbison (1945) contributed to the taxonomic splitting of the percrassa lineage when she named Nuntla 

tippahensis from Maastrichtian-age deposits of the Ripley 

Formation in Mississippi (pl. 1, figs. 7-10; pl. 2, figs. 7-8, 

10-11). She stated that a "new specific name is used, as the 

form appears to be significant stratigraphically" (see pl. 4 

for stratigraphic comparison). Three species names-two 

conceived in part on the basis of being geographic isolates 

and the third on the basis of being stratigraphically restricted-have thus been established. 

Occurring in deposits with either Nucula percrassa or 

N. slackiana is a small, trigonaL previously unnamed 

species of Nucula, similiar in form to N. arnica Gardner 

( 1916, p. 514) but differing in its lack of strong co marginal 

ribs (compare pl. 5, figs. 2, 11, to pl. 5, figs. 4, 7, 9). The 

near absence of immature forms of N. percrassa and N. 

slackiana raises the possibility that this Nucula sp. is a 

juvenile form, but the analysis presented herein indicates 

that it is a separate species, which we name N. severnensis 

n.sp. 

The purpose of this study is to clarify the taxonomic, 

geographic, and stratigraphic relationships of the abovementioned species of Nucula Lamarck for the time interval 

from early Campanian through Maastrichtian. The morphologic characteristics used to differentiate the taxa by the 

original authors were applied in discriminant analyses to 

compare specimens grouped by taxonomic assignment, 

geographic locality, and stratigraphic position. 

Acknowledgments 

We express our gratitude to John Pojeta (U.S. Geological Survey, Washington, D.C.), Carl Koch (Old 

Dominion University, Norfolk, Va.), and Martin Buzas 

(Smithsonian Institution, Washington, D.C.) for their thorough reviews of the manuscript and for their numerous 

suggestions for its improvement. Philip Wirtz (George 

Washington University, Washington, D.C.) provided 

extensive instruction and assistance in the analytical portion 

of this paper. The comments and suggestions made in the 

early phases of this study by Anthony Coates and Diane 

Lipscomb (also of George Washington University) are 

appreciated. Thanks are also due to Robin Espenschade 

(U.S. Geological Survey volunteer) for her help in the 

compilation of appendix 1. 

MATERIALS AND METHODS 

Four hundred and eighty-three specimens were 

selected randomly from U.S. Geological Survey and 

USNM NH collections containing well-preserved Nucula 

spp. (text figs. 1, 2, 3; app. 2). Specimens were measured 

for length, height, hinge angle, anterior angle, and posterior 

angle. To facilitate the angular measurements and to circumvent the problems caused by using calipers to measure 

height and length on rounded specimens, reproductions 

were made by placing the specimens on a Litton Royfax 

copier. The illustration obtained allowed a grid to be 

constructed around the specimen and precise measurements 

to be taken, according to the method illustrated in text 

figure 4. When specimens were too small to copy, a camera 

Iucida was used to trace the specimens, and the same 

measurements were taken. The methods used to measure 

specimens worked only on preserved shells; thus, the 

possibility of using internal molds, including topotypes of 

N. slackiana from New Jersey, was eliminated. 

For this analysis, four taxonomic categories were 

tested: (1) Nucula percrassa Conrad, (2) N. slackiana Gabb 

of Gardner, (3) N. tippahensis, and (4) N. sp., later 

identified as N. severnensis n.sp. Identifications of N. 

percrassa and N. slackiana are made by following the 

convention in use since 1916 (Gardner, 1916); specimens 

from the Upper Cretaceous of the eastern Gulf Coast were 

placed in N. percrassa, whereas specimens from the Upper 

Cretaceous of the mid-Atlantic Coastal Plain were designated N. slackiana. In addition, Nucula from Pleasant 

Ridge Lake, Miss. , and the surrounding area in Maastrichtian beds of the Ripley Formation were assigned to N. 

tippahensis, and small, thin, trigonal specimens were 

placed inN. sp. The data were analyzed by means of the 

discriminant analysis program contained within the Statistical Package for the Social Sciences (SPSS Inc., 1983), on 

the George Washington University IBM-4341. 

Revision of the Nucula percrassa Conrad, 1858 Group 05 
/ ... --4®-1 

I / I 

I I I 1

-..1 I • Bolivar 

1 Selmer I 

Hardeman I • I i I McNairy I 

1 Middleton• I 

1

1 

• Pocahontas 

J_EJiti~SS~~--.1-- -- -----1..,.-~~~X-~AP MISSIS&IPPI I corinth! \ 

I I • I " I I I .. J 18®L Alcorn Tishomingo 1 F1

alker• -1 I / 

1--J ~ 1 7 1 I luka • / I . Tip~19 Lr--------lt. I Ripley •\l::JI I t ~: 

I I I Q./< Dumas Bloneville.® 1 I en,~ 

j_

1 1~-11,116 Prentiss 1 ~•m 

~--- -s.7 "f>T' • I (J)I< Keownville 8 91 Wheeler I (/) -J I •/Q\ ' I -•< I New Albany• 12--'01 1

___J-----, !El i Union I , ____ l_ __ i 

1------- IISaltil~o 2 ®I 

1

, I Sher~aniil I I I I 

Pontotoc 1 ~ee 1 Jta.::1::a /1 

I Pontotoc • 1 Tupelo 1 

I I I : I I I I I I I I l--------~-~---j _______ , 

1 

0 16 32 

KM 

Figur~ 1. Sa~ples collecte~ in Tennessee and Mississippi. 

L_ocal1ty regrster (app. 2) grves exact description of locations. Text figure 6 gives stratigraphic position of samples. 

DISCRIMINANT ANALYSIS 

The first discriminant analysis compared the morphologic characteristics of three "species'' of Nucula occurring 

in the upper Maastrichtian: N. percrassa, N. slackiana, and 

N. severnensis n. sp. The overlap of points between N. 

percrassa and N. slackiana plotted along the first and 

second canonical discriminant axes is illustrated in text 

figure 5 and could have been predicted by examining the 

univariate statistics presented in table 2 or by visually 

examining the specimens. Despite this overlap, N. percrassa is correctly classified in the statistical sense by its 

morphologic characteristics 78.2 percent of the time and N. 

slackiana 89.2 percent of the time (table 3). The Maryland 

samples containing specimens of N. slackiana were collected from the same formation and within several miles of 

each other (text figs. 3, 6), whereas the specimens of N. 

percrassa were collected from four States (text figs. 1, 2) 

and were distributed across a 430-km (300-mi) spread. The 

higher percentage of correctly classified (again, in the 

statistical sense) N. slackiana is therefore predictable. 

Relatively high classification values for N. percrassa and 

D6 Shorter Contributions to Paleontology and Stratigraphy 

N 

~~~p t 

o 4 8 1 

KM ALABAMA 

RUSSELL CO. 

---, STEWART CO. ... ...,_ 

!:\ 

\ .. , 

'~ GEORGIA l..__ ____ _ 

BARBOUR CO. 

.. --L. 

~--- 1 

I 

I 

I 

I 

I 

I 

~AN DOLPH 

I CO. 

I 

'-L, 

HENRY CO. IJ 

I L ___ _ 

CLAY CO. 

Figure 2. Samples collected in Alabama and Georgia. 

Locality register (app. 2) gives exact description of locations. Text figure 6 gives stratigraphic positions of 

samples. 

N. slackiana do not eliminate the possibility that the two 

forms represent only one species. The relatively high 

confidence level of 90 percent statistically correct classification was selected because the discriminant analysis program is designed to maximize the differences between 

groups; consequently, any degree of overlap between 

groups is significant. In addition, the classification phase is 

performed with the same specimens from which the groups 
' /"" ,, MARYLAND 

' " ' " 

/ 

/ 

J / 

/ Prince 

4 

Figure 3. Samples collected in Maryland. Locality register 

(app. 2) gives exact description of location. Text figure 6 

gives stratigraphic positions of samples. 

were originally discriminated. These two factors combine to 

make groups appear more discrete than they actually are. 

(For a complete description of discriminant analysis, see the 

discussion by Davis (1973, p. 442-456, fig. 7.3).) On the 

basis of the overlap of characters illustrated in text figure 5, 

of visual inspection of the specimens, and of classification 

values of less than the 90-percent confidence level, we 

concluded that N. percrassa Conrad and N. slackiana 

Gardner represent end members of the same species. 

Nucula severnensis n.sp. forms a fairly discrete group 

on the plot of the canonical discriminant functions (text fig. 

5), particularly along function 1, which accounts for 72.59 

percent of the variance among the three groups. During the 

classification phase , 60 out of 61 specimens of N. severnensis n.sp. (98.4 percent) were correctly identified in the 

statistical sense (table 3). A morphological examination of 

immature specimens of N. percrassa eliminated the possibility that N. severnensis n.sp. was a juvenile N. percrassa 

(compare pl. 3, figs. 1-10, with pl. 3, figs. 11-19). N. 

severnensis was therefore identified as a new species within 

the Upper Cretaceous of Maryland and the Gulf Coast, and 

it was not included in any further analyses. 

A plot on the first and second canonical discriminant 

functions of the data for N. percrassa and N. slackiana, 

grouped by State from the uppermost Maastrichtian collections (level 5 on text fig. 6), illustrates a clustering of 

centroids and an overlap of all regions (text fig. 7). 

Accurate predictions of the collection locality, based on 

observations of the shell morphology, can be made only 

66.39 percent of the time (table 4). The Maryland speciFigure 4. Measurement of the characters. A, Length (1) is 

measured as the maximum distance from the anterior end 

to the posterior end. Height (2) is measured along a line 

perpendicular to length and passing through the maximum extent of the beak. B, Hinge angle (3) is measured at 

the intersection of two lines tracing the anterior and 

posterior rows of teeth. C, Anterior angle (4) and posterior 

angle (5) are measured by constructing lines perpendicular to maximum length and passing just to the inside of the 

anterior and posterior muscle scars; measured angles best 

fit the exterior margin of the shell and touch the margins 

at the perpendiculars. 

mens again form the most discrete group because of the 

geographic proximity of the collections, 84.1 percent being 

correctly classified statistically. Surprisingly, the distribution of points along canonical discriminant function 1 

(accounting for 91.18 percent of the variance) and the 

classification results revealed a coupling of Maryland with 

Alabama and Mississippi with Georgia. Since the Alabama 

and Georgia samples were collected from opposite banks of 

the same river (text fig. 2), it was expected that the analysis 

would indicate a high degree of similarity between these 

samples. These results further substantiate the contention 

that N. slackiana specimens collected in Maryland are 

Revision of the Nucula percrassa Conrad, 1858 Group D7 
C\1 

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co 

u 

-4 -2 0 2 4 

4 

2 

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Canonical Discriminant Function 

Figure 5. Discriminant analysis of the data grouped by 

"species": 1, Nucula percrassa (89 specimens in the analytical phase, ~56 in t~e classificatiC?n phase); 2, N. slacklana (67 specrmens rn the analytrcal phase, 83 in the 

classification phase); 3, N. severnensis n.sp. (46 specimens in the analytical phase, 61 in the classification 

phase). Canonical discriminant function 1 accounts for 

72.59 percent of the variance and function 2 for 27.41 

percent. The standardized canonical discriminant function 

coefficients for functions 1 and 2 are as follows. Function 

1: height, - 0.06206; length, 0.61079; hinge angle, 0.67047; 

anterior angle, - 0.13185; posterior angle, -0.05775. Function 2: height, 1.98636; length, - 1.24781; hinge angle, 

- 0.20987; anterior angle, - 0.03229; posterior angle, 

0.05318. Asterisks mark the centroids. 

members of the same species as the Gulf Coast specimens 

assigned toN. percrassa. No justification exists for identifying a specimen as N. percrassa solely because it is found 

in Alabama or as N. slackiana because it is found in 

Maryland. 

An analysis of the Maryland specimens versus the 

gulf specimens was performed to determine if a morphological gradient exists between the regions. Text figure 8 

illustrates the gradation from one group to the other and the 

presence of the centroids in the region of superposition. 

Despite the statistically correct classification of 87.39 

percent of the specimens (table 5), the analysis lends 

support to the idea of a continuous morphological gradient 

of specimens. 

To document whether splitting was occurring on a 

stratigraphic basis, the Gulf Coast Upper Cretaceous stratigraphic column was divided into five groups (text fig. 6). 

The morphologic characteristics of Nucula at each level 

were compared. Gradational changes in the mean values of 

the morphologic characters are not discernible moving up 

the stratigraphic column (table 6), nor do the plots along the 

canonical discriminant functions 1 and 2 reveal a linear 

pattern (text fig . 9). Instead, the centroids are clustered, and 

the territories are at least partially superimposed. Visual 

inspection of the specimens does not reveal any distinctive 

differences (pl. 4). During the classification phase of the 

analysis, only 46.04 percent of the specimens were grouped 

correctly in the statistical sense (table 7). These results 

indicate a period of nearly 15 Ma in which virtually no 

recognizable morphologic change occurred in the species N. 

percrassa. 

The data from stratigraphic level 3 come entirely 

from specimens assigned to Nucula tippahensis. Other than 

the larger-than-average size (see height and length values in 

tables 2 and 6) of the specimens from level 3, N. tippahensis does not stand out as a distinct identifiable species either 

in the plot (text fig. 9) or in the classification results (table 

7). Harbison (1945) named N. tippahensis on the basis of 

characteristics that differentiated it from topotype specimens of N. percrassa . An analysis comparing topotype N. 

percrassa to topotype N. tippahensis was performed. Even 

though topotypes of N. percrassa are morphologic end 

members of the percrassa population, a plot of N. tippahensis along canonical discriminant function 1 overlaps that 

of N. percrassa (text fig . 10). Classification results revealed 

that 88.60 percent of the specimens would be correctly 

identified in the statistical sense (table 8). The partial 

superposition of this plot, the lack of distinctive characters 

in comparison with the entire Late Cretaceous suite as a 

whole, classification values below the 90th percentile, and 

Table 3. Classification results for discriminant analysis of data grouped into 

three "species" of Nucula occurring within the upper Maastrichtian (level 5, 

text fig. 6) 

[Discriminant analysis plot is seen in text fig . 5] 

Actual group 

N. percrassa ... . ...... . 

N. slackiana . .......... . 

N. severnensis . . ..... . . . 

Total number 

of cases 

156 

83 

61 

Predicted group membership,1 

number of cases (percentage of cases) 

N. percrassa N. slackiana N. severnensis 

122 (78.2) 

7 (8.4) 

0 (0.0) 

30 (19.2) 

74 (89.2) 

1 (1.6) 

4 (2.6) 

22 (4.0) 

60 (98.4) 

1 Percentage of "grouped" cases correctly classified: 85.33 percent. 

08 Shorter Contributions to Paleontology and Stratigraphy 
z 

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ville 

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Figure 6. Stratigraphic positions of samples (see text figs. 

1-3 for geographic distribution), ranges of species in 

previous papers and in this report, and the five stratigraphic levels used in analyzing Gulf Coast samples (Maryrand samples were not included in the stratigraphic analHarbison's (1945, p. 78) own description of Owl Creek N. 

percrassa as "senile ," imply that specimens identified as N. 

tippahensis are actually members of the N. percrassa 

population. It is possible that topotypes of N. percrassa 

from the Owl Creek Formation represent a certain stage in 

the ontogeny of the species or possibly ecophenotypes. 

Since height and length were the primary discriminating variables in our analysis, one concern of this investigation was that specimens were actually being classified 

by growth stage. The emphasis placed on height and length 

in the original species descriptions of Nucula percrassa, N. 

slackiana, and N. tippahensis should have caused earlier 

authors to be concerned that they were actually identifying 

different phases in an ontogenetic sequence. Division by 

age group was not a problem in this investigation, however, 

as evidenced by the lack of mixing between groups in the 

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ysis). Numbered symbols in State columns reflect the 

relative stratigraphic positions within a given formation of 

the fossil samples cited. References are as follows: A and 

D, Wade (1926); B, Gardner (1916); C, Harbison (1945). 

analysis of State, regional, and stratigraphic data. If such a 

separation were occurring, the juveniles from all the groups 

would be mixed together and would form a plot isolated 

from that of the adults. 

IMPLICATIONS FOR PALEONTOLOGISTS 

Several points of evolutionary significance emerge 

from this analysis of Nucula percrassa. First, a period of 15 

Ma of evolutionary stasis has occurred for N. percrassa. 

Accordingly, the species has only limited biostratigraphic 

utility. In addition, the taxonomic splitting of the N. 

percrassa lineage demonstrates the problems that can arise 

when previously published species lists are used in calculating evolutionary rates. 

Revision of the Nucula percrassa Conrad, 1858 Group 09 
C\1 

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-c 

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Canonical Discriminant Function 

Figure 7. Discriminant analysis of the data grouped by 

collection locality: 1, Mississippi (58 specimens in the 

analytical phase, 109 in the classification phase); 2, Georgia (27 specimens in the analytical phase, 37 in the classification phase); 3, Alabama (4 specimens in the analytical 

phase, 10 in the classification phase); 4, Maryland (66 

specimens in the analytical phase, 82 in the classification 

phase). Canonical discriminant function 1 accounts for 

91.18 percent of the variance and function 2 for 8.27 

percent. The standardized discriminant function coefficients are as follows. Function 1: height, -1.77200; 

length, 1.42646; hinge angle, 0.51961; anterior angle, 

0.09156; posterior angle, -0.17803. Function 2: height, 

0.74754; length, 0.13677; hinge angle, 0.33494; anterior 

angle, 0.07115; posterior angle, -0.22586. Asterisks mark 

the centroids. 

Stratigraphic or geographic separation of populations 

often influences paleontologists to assume the presence of a 

new species, despite a lack of change in the preserved 

morphology of the separated groups. A type of circular 

reasoning can develop when a paleontologist makes such 

assumptions about evolutionary change. To determine when 

or if a new species has evolved in a lineage, an author might 

apply a previously calculated average rate of evolution for 

that group. Later, this author's data may be included in a 

recalculation of the average rate for that group of organisms, or they may be used to further substantiate the 

accuracy of this rate. The original rate used by the author 

may not have been accurate in the first place, especially if 

it had been based on previously published species lists. For 

e»ample, if rates of evolution were calculated for the Late 

Cretaceous Nuculidae by using the published record, the 

results would be biased toward a shortened duration for 

species; in addition, species diversity for the Nuculidae 

would be too high. Methods of defining species that are 

based on assumptions can introduce a nomenclatural bias 

Dl 0 Shorter Contributions to Paleontology and Stratigraphy 

16 16 

~ 

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0' 8 8 G) 

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u. 4 4 

-4 -2 0 2 4 

Canonical Discriminant Function 1 

Figure 8. Discriminant analysis of the data grouped by 

region: 1, Gulf Coast region (89 specimens induded in the 

analytical phase, 156 in the classification phase); 2, Maryland (66 specimens in the analytical phase, 82 in the 

classification phase). Canonical discriminant function 1 

accounts for 100 percent of the variance. The standardized 

discriminant function coefficients are as follows: height, 

1.72698; length, -1.30692; hinge angle, -0.46599; anterior angle, -0.01744; posterior angle, 0.15842. Asterisks 

mark the centroids. 

C\1 3 c: 

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Canonical Discriminant Function 

Figure 9. Discriminant analysis of the data grouped by 

stratigraphic position; 1 represents the ordest stratigraphic level, and 5 represents the youngest (see text fig. 

6 for exact position of levels). The numoer of specimens 

included in the analytical and classification phases are 32 

for level 1, 25 for level 2, 40 for level 3, and 25 for level 4. 

For level 5, 89 specimens were included in the analytical 

phase and 156 in the classification phase. Canonica discriminant function 1 accounts for 65.97 percent of the 

variance and function 2 for 30.01 percent. The standardized canonical coefficients are as follows. Function 1: 

height, 1.62370; length, -1.00906; hinge angle, - 0.48111; 

anterior angle, 0.03953; posterior angle, -0.04751. Function 2: height, 0.17464; length, 0.55760; hinge angle, 

0.70151; anterior angle, - 0.08734; posterior angle, 

0.33718. Asterisks mark the centroids. 
Table 4. Classification results for discriminant analysis of data grouped by State 

[Discriminant analysis plot shown in text fig. 7] 

Predicted group membership,1 

Total number 

number of cases (percentage of cases) 

Actual group of cases Mississippi Georgia Alabama Maryland 

Mississippi ............. 109 68 (62.4) 35 (32.1) 2 (1.8) 4 (3. 7) 

Georgia ................ 37 10 (27 .0) 18 (48.6) 1 (2. 7) 8 (21.6) 

Alabama ............... 10 0 (0.0) 1 (10.0) 3 (30.0) 6 (60.0) 

Maryland ............... 82 1 (1.2) 8 (9.8) 4 (4.9) 69 (84.1) 

1 Percentage of "grouped" cases correctly classified: 66.39 percent. 

Table 5. Classification results for discriminant analysis of 

data grouped by region 

[Discriminant analysis plot shown in text fig. 8] 

Actual group 

Total 

number 

of cases 

Gulf Coast . . . . . . . . . . . . 156 

Maryland.............. 82 

Predicted group membership, 1 

number of cases 

(percentage of cases) 

Gulf Coase 

133 (85.3) 

7 (8.5) 

Maryland 

23 (14.7) 

75 (91.5) 

1 Percentage of ''grouped" cases correctly classified: 87.39 percent. 2 Includes samples collected from Mississippi, Alabama, and 

Georgia. 

into our understanding of evolutionary processes and ultimately will obscure information on the rates of morphologic 

change with time. 

Two basic paleontological concepts are at the heart of 

the problems raised here: (1) the definition of species and 

(2) the selection of type specimens. The question of how to 

define species has been debated at great length (Lovtrup, 

1979; McAlester, 1962; Weller, 1961; Wiley, 1978), but, 

for paleontologists, usually only the preserved hard parts of 

specimens are available for recognizing and defining species. The discrimination of a new fossil species should be 

based solely on preserved morphologic differences and 

should take into account a reasonable amount of intraspecific variation. Measurement of morphologic differences is 

an objective and testable data base available to paleontologists. The species description should include the statistical 

range of variation seen within the population, and care 

should be taken to ensure that the type specimen does not 

represent an end member of the population, as was the case 

with Nucula percrassa. 

Statistical programs currently available to paleontologists offer a means of analyzing morphologic variability 

and may assist in the recognition of new species. Previous 

work needs to be critically reexamined in light of new ideas 

and methods. Until consistent, reproducible taxonomies are 

constructed, we should proceed cautiously with our inductive conclusions about the mode and tempo of evolution. 

Table 6. Mean values of the morphologic characters of 

Nucula percrassa at each stratigraphic level (gradational 

changes in characters not discernible) 

[Level 1 is the oldest, and level 5 is the youngest. Exact position of each 

level shown in text fig. 6] 

Stratigraphic 

level 

Height, Length, __ A_ng_l_e_, i_n_d_e_g_re_e_s __ 

in mm in mm Hinge Anterior Posterior 

1 ................... 17.75 

2 ................... 15.84 

3 ................... 20.74 

4 ................... 19.82 

5 ................... 15.84 

Group means 1 ••.•.•• 17.53 

26.34 112.45 54.61 

26.54 122.06 49.44 

31.93 117.01 54.44 

31.30 121.46 53.18 

25.97 120.15 53.21 

27.86 118.77 53.20 

1 For all stratigraphic levels combined. 

SYSTEMATIC PALEONTOLOGY 

73.84 

71.56 

74.70 

72.26 

72.05 

72.73 

Class RIVAL VIA Linne, 1758 

Subclass PALEOTAXODONT A Korobkov, 1954 

Order NUCULOIDA Dall, 18891 

Family NUCULIDAE Gray, 1824 

Genus Nucula Lamarck, 1799 

Subgenus Nucu/a (Nucu/a) Lamarck, 1799 

T_vpe species. -Area nucleus Linne, 1758, by monotypy. 

Discussion. -The presence of crenulations on the 

inner ventral margin and the presence of well-developed 

external radial ribs suggest placement of both Nucula 

percrassa and N. severnensis in the subgenus N. (Nucula) 

rather than in other subgenera that occur in the Cretaceous. 

These species lack the highly oblique resilifer and smooth 

external surface of N. (Leionucula) Quenstedt, 1930 and the 

strong, raised radial ribs of N. (Pectinucula) Quenstedt, 

1930. 

In addition to the presence of the diagnostic crenulations and external radial ribs, the muscle scar pattern is 

similiar to that displayed on the specimen of the type 

1 nom. transl. et correct. Newell, 1965 (ex suborder Nuculacea, 

Dall, 1889. 

Revision of the Nucu/a percrassa Conrad, 1858 Group 011 
Table 7. Classification results for discriminant analysis of data grouped by stratigraphic 

level 

[Level 1 is the oldest, and level 5 is the youngest. Exact position of each level shown in text fig. 6. Discriminant 

analysis plot shown in text fig. 9] 

Predicted group membership,1 

Total number 

number of cases (percentage of cases) 

Actual group of cases Level 1 Level 2 Level 3 Level 4 Level 5 

Level 1 ................ 32 20 (62.5) 3 (9.4) 6 (18.8) 0 (0.0) 3 (9.4) 

Level 2 ................ 25 1 (4.0) 13 (52.0) 2 (8.0) 3 (12.0) 6 (24.0) 

Level 3 ................ 40 4 (10.0) 2 (5.2) 20 (50.0) 11 (27.5) 3 (7.5) 

Level4 ................ 25 2 (8.0) 4 (16.0) 7 (28.0) 9 (36.0) 3 (12.0) 

Level 5 ................ 156 17 (10.9) 38 (24.4) 16 (10.3t) 19 (12.2) 66 (42.3) 

1 Percentage of "grouped" cases correctly classified: 46.04 percent. 

1 

8 8 

>o 

0 6 6 t:: 

Q) 

:::J 

C' 4 4 

Q) 

... 

LL. 2 2 

-4 -2 0 2 4 

Canonical Discriminant Function 1 

Figure 10. Discriminant analysis of the data on topotypes 

of (1) Nucula percrassa (41 specimens in the analytical 

phase, 74 in the classification phase) and (2) N. tippahensis 

(40 specimens in both phases). Canonical discriminant 

function 1 accounts for 100 percent of the variance, and 

the standardized coefficients are distributed as follows: 

height, 1.05776; length, -0.10033; hinge angle, -0.11865; 

anterior angle, -0.13217; posterior angle, 0.18210. Asterisks mark tile centroids. 

species Area nucleus Linne, 1758, as figured by Schenk 

(1934, pl. 5, figs. 1, la). Muscle scar patterns are exceptionally well displayed on the valve interiors of specimens 

of Nucula percrassa. The clarity of these impressions is 

enhanced because of both the large size and the especially 

thick shell of the species. They are less deeply impressed 

and clear on the interiors of the smaller and thinner shelled 

valves of N. severnensis. Text figure 11 illustrates the 

general placement of these muscle scars on the interior of 

the shell and the descriptive terms applied. Plate 7 shows 

representative specimens illustrating the variation in shape 

and number of scars of certain types. 

The anterior and posterior adductor muscle scars are 

the largest and most deeply impressed. As text figure 11 

indicates, the areas of attachment of both quick and catch 

muscles can commonly be distinguished on the surface of 

the adductor scars. The specimens shown on plate 1 (figs. 

1, 5, 8) and plate 7 (figs. 2, 5, 6) show the separation 

reasonably well. The area covered by the catch muscle 

012 Shorter Contributions to Paleontology and Stratigraphy 

Table 8. Classification results for discriminant analysis of 

data on topotypes of Nucula percrassa and Nucula tippahensis 

[Discriminant analysis plot shown in text fig. 10] 

Total 

Predicted group membership,1 

number of cases 

(percentage of cases) 

number Nucula Nucula 

Actual group of cases percrassa tippahensis 

Nucula percrassa . . . . . . 74 

Nucula tippahensis. . . . . 40 

66 (89.2) 

5 (12.5) 

8 (10.8) 

35 (87.5) 

1 Percentage of "grouped" cases correctly classified: 88.60 percent. 

(smooth) is greater than that occupied by the quick muscle 

(striated) that lies toward the shell interior. 

Muscles that control the movement of the foot are 

distributed over the dorsal surface of the valve interior. All 

such scars lie dorsal to a line connecting the center points of 

the adductor scars. The paired anterior protractor muscle 

scars are situated immediately ventral to the hinge plate and 

posterior to the posterior-dorsal margin of the anterior 

adductor muscle (text fig. 11; pl. 7, figs. 7, 9, 11). In both 

Nucula percrassa and N. severnensis, the anterior protractor muscle scars are elongate, the anterior end being 

expanded into a ventrally extended hooklike insertion area 

(pl. 7, figs. 8, 9, 11). 

The anterior pedal retractor muscle scars consist of a 

gently curvilinear series of circular to oval scars extending 

over the upper part of the shell interior between the 

posterior end of the anterior adductor and the ventralmedian muscle scar (text fig. 11; pl. 7, figs. 2, 4, 5, 11). In 

Nucula percrassa, the number of such scars ranges between 

three (pl. 1, fig. 1) and six (pl. 1, fig. 9). The number may 

vary between different valves of the same individual, as an 

articulated specimen (pl. 7, figs. 8, 10, 11) shows. On this 

individual, the right valve (pl. 7, fig. 10) possesses four 

anterior pedal retractor muscle scars and the left valve five 

(pl. 7, fig. 11). N. severnensis most commonly has only one 

round to dorsal-ventrally elongated scar (pl. 7, fig. 3), but, 
PA 

8 

Figure 11. Musculature of the Nucula percrassa 

group. AA, anterior adductor (shaded area is quick 

muscle, white area is catch muscle); AP, anterior 

protractor; AR, anterior pedal retractors; DM, dorsalmedian muscle; PA, posterior adductor (shaded area 

is quick muscle, white area is catch muscle); PE, pedal 

elevator muscle; PL, pallial line; PR, posterior pedal 

rarely, a second generally rounded scar may occur (text fig. 

11). The scar or scars lie close to a line drawn from the 

center of the anterior adductor to the ventral-median scar, 

but the anterior scar is closer to the anterior adductor than to 

the ventral-median scar, and the second scar is at a midpoint 

on that line. 

The next set of muscles appearing in a posterior 

direction are the dorsal-median (=median muscle scar of 

Schenk, 1934) and ventral-median muscles. Both occur 

well above, or dorsal to, a line connecting the center of the 

adductor scars. The ventral-median scar (text fig. 11) 

(=central muscle scar of Schenk, 1934) is generally circular, less pronounced, and smaller than the dorsal-median 

scar (pl. 1, figs. 5, 8, 9; pl. 4, figs. 2, 3, 6; pl. 7, figs. 4, 

5, 6). The dorsal-median scar ranges in shape from nearly 

circular (pl. 1, fig. 4; pl. 4, fig. 6) to dorsal-ventrally 

elongate (pl. 1, fig. 9; pl. 4, figs. 2, 3; pl. 7, figs. 5, 11). 

The function of the dorsal-median and ventral-median 

muscles is conjectural. Heath (1937, p. 14) stated that the 

greater number of muscle strands of the dorsal muscle 

retractor; VM, ventral-median muscle. A, Outline of 

right valve interior of N. severnensis (USNM 423847) 

illustrated on plate 7, figure 3. B, Left valve interior of 

N. percrassa (USNM 423832) illustrated on plate 7, 

figure 2. C, Dorsal view of internal mold of N. per- crassa (USNM 423833) illustrated on plate 7, figure 9. 

extend into the pedal tissue; the ventral muscle strands form 

part of the posterior part of the visceral sac wall, a few 

fibers being attached "superficially to the upper portions of 

the foot." Driscoll (1964, p. 63) suggested that these 

muscles may, by contraction, reinforce the action of the 

pedal retractors or that they may simply form a firm 

attachment of the pericardia! region of the shell. 

There is another cluster of small muscle scars within 

the umbonal cavity (PE, text fig. 11). These scars are best 

seen on internal molds, where they form prominences on 

the surface of the umbonal region (pl. 7, figs. 7, 9). In 

Nucula percrassa, these scars number from two to five and 

are aligned in a track from the base of the resilifer trending 

anteriorly and ventrally toward the dorsal-median muscle 

scar. The two dorsalmost scars are the strongest, the 

strength of the others decreasing away from the umbo. 

When only two scars are present, they represent the 

dorsalmost pair. The number of scars may vary between the 

valves of the same individual; for example, five scars are 

present on the left valve and four on the right valve of the 

Revision of the Nucu/a percrassa Conrad, 1858 Group 013 
internal mold shown as figure 9 on plate 7. In N. severnensis, equivalent scars have been seen only on the largest 

individuals, where they consist of two closely spaced scars 

in the dorsalmost part of the umbonal cavity slightly 

anterior to the base of the resilifer. Their trend is dorsalventral; they do not form an anteriorly inclined track, as 

they do inN. percrassa. Heath (1937, p. 14) stated that 

"several authors have described muscles in Anodonta, 

Cardium, etc., which are termed levator peidis, 'Fussheber ,' or merely 'Heber.' These are attached to the shell in 

the neighborhood of the umbo, but we have no detailed 

information as to their distribution .... In the case of the 

protobranchs they may reinforce the pedal retractors." 

Pojeta (1987, p. 406, figs. 14.98D, E) has provided clear 

illustrations of similarly placed muscle scars, termed pedal 

elevators, in the genus Astarte that serve to raise the foot 

into the shell. 

A final set of pedal muscles, the posterior pedal 

retractors, are located on the posterior dorsal slope, immediately ventral of the posterior hinge teeth and near the 

anterior dorsal margin of the posterior adductor (text fig. 

11 C). On both Nuczila percrassa and N. severn ens is, the 

scars are shallowly impressed and narrowly elongate, following a track parallel to the margin of the hinge plate (pl. 

7, figs. 7, 8, 10, 11). 

Earlier in this paper, it was stated that four species 

groups of nuculids could be distinguished in the Cretaceous 

deposits of the Gulf and Atlantic Coastal Plains. These 

groupings were distinguished on the basis of obvious 

characters of external ornament and the presence of crenulations on the ventral margin. All are, however, linked by 

characters of the family Nuculidae, including general features of dentition, possession of an internal ligament, and a 

nacreous inner shell layer. They are also allied in having a 

corresponding pattern of muscle impressions on the interior 

of the valves. In the groups of which Nucztla arnica and N. 

cuneifrons are representative, muscle scar patterns are more 

difficult to delineate than they are in the N. percrassa 

group, mainly because the shells are smaller and thinner. 

Specimens have been seen, however, in which both anterior 

and posterior pedal retractors are discernible, anterior pedal 

retractors and dorsal-median scars are present, and all are in 

the same relative placement on the respective valves, as 

they are in theN. percrassa group. Thus, although the base 

plan is repetitive, the shape and number of scars may vary. 

Although little emphasis has been placed on the 

conchological character of muscle scar patterns by neontologists or paleontologists dealing with Mesozoic or Tertiary 

nuculids, those dealing with Paleozoic members of the 

superfamily have, in recent years, emphasized their character and placement. Although the prime driving force for 

this interest has been the interpretation of proper shell 

orientation, it also leads to interpretation of functional 

morphology and phylogenetic speculation. 

014 Shorter Contributions to Paleontology and Stratigraphy 

Driscoll ( 1964) pointed out that a group of Mississippian protobranchs that he studied possessed muscle scar 

patterns analogous to those present in many living forms but 

markedly different, especially in number, from those 

present on Ordovician species. He suggested a trend toward 

reduction of the number of muscle scars from the early to 

the late Paleozoic, the arrangement of those scars centering 

on a modem mode by at least the Mississippian. Further 

examples of Ordovician paleotaxodonts having multiple 

muscle scars have been presented by Bradshaw (1970). In 

all these Ordovician bivalves, it is somewhat difficult to 

directly ascribe the presumed pedal muscle to individual 

scars of more recent forms. Both Bailey (1983) and Bradshaw ( 197 4) have described Devonian nuculids. The figures 

presented by Bailey (1983, fig. 30) of the musculature 

attachment in Nuculoidea deceptriformis Bailey, 1983 show 

an arrangement that fundamentally parallels that of the 

Cretaceous species described here, lacking only the pedal 

elevator group. 

As the preceding paragraph has made obvious, the 

general relative arrangement of the pedal muscle attachment 

was arrived at early in nuculid evolution, but much remains 

to be investigated. For example, Heath (1937, pl. V, fig. 

39) indicated that, in Acila divaricata, the anterior pedal 

protractors and anterior pedal retractors are clustered 

together. This grouping is certainly different from that of 

Nucztla percrassa (text fig. 11), in which the retractors are 

well separated, as they are in the Devonian forms mentioned above. Because Acila appears after the origin of 

these other groups, one might question whether this clustering may reflect some phylogenetic trend or is only of 

functional significance. The presence of such differences 

among the later nuculids does indicate that further work is 

needed to understand the range of differences among living 

and fossil nuculids. A study of muscle scar patterns may 

provide criteria pertinent to developing a stable taxonomic 

arrangement of the Nuculacea. 

Nucula percrassa Conrad, 1858 

Plate 1, figures 1-10; plate 2, figures 1-11; plate 3, 

figures 1-10; plate 4, figures 1-10; plate 5, 

figures 3, 10; plate 6, figures 1, 2, 4-16; 

plate 7, figures 1, 2, 4-11. 

Nucula percrassa Conrad, 1858, p. 327, pl. 35, fig. 4. 

Conrad, 1868, p. 725. Gabb, 1876, p. 318. Whitfield, 

1885, p. 102, pl. 11, figs. 2, 3. Weller, 1907, p. 369, 

pl. 29, figs. 1-5. Wade, 1926, p. 39, pl. 8, figs. 1-4. 

Roberts, 1931, p. 404, pl. 68, figs. 1, 2. Stephenson, 

1955, p. 106, pl. 15, figs. 4-7. Richards, 1958, p. 59, 

pl. 10, figs. 1, 2, 4. Speden, 1970, p. 33, pl. 2, figs. 

4-11. 

Leda slackiana Gabb, 1860, p. 397, pl. 69, fig. 36. 

Nuculana slackiana Conrad, 1868, p. 725. 
Nucula slackiana Gabb, 1876, p. 318. Whitfield, 1885, p. 

103, pl. 11, figs. 2, 3. Gardner, 1916, p. 511, pl. 19, 

figs. 1-4. Richards, 1958, p. 60, pl. 10, figs. 3, 5, 6. 

Nucula chatfieldensis Stephenson, 1941, p. 73, pl. 8, figs. 

11' 12. 

Nucula cibolensis Stephenson, 1941, p. 72, pl. 8, fig. 10. 

Nucula tippahensis Harbison, 1945, p. 77, pl. 2, figs. 10, 

11. 

Diagnosis.-Elongate, subelliptical shell; beak lying 

at posterior one-third of shell; posterior-dorsal margin 

straight and steeply angled; posterior margin truncate; 

anterior-dorsal margin straight and gently inclined; closely 

spaced radial striations and comarginal growth lines; hinge 

angle wide (average value 116°). 

Description. -Shell equivalve and variably convex; 

degree of convexity increases with age; elongate, subelliptical, and inequilateral in outline, beak lying posterior to 

midlength; opisthogyrate. Lunule long, proportionally narrow, and poorly defined; escutcheon broad, rather short, 

distinctly outlined. Posterior-dorsal margin straight and 

inclined steeply away from beak; posterior ridge present and 

more sharply defined at younger growth stages; posterior 

margin truncate. Anterior-dorsal margin straight to very 

slightly convex and inclined gently away from beak; anterior margin elongate and smoothly curved. Ventral margin 

usually gently curved and crenulate; occasionally a posterior flattening causes an increased convexity of shell surface 

that accentuates toward posterior end. Surface ornamentation consists of closely spaced, radial, incised striations 

over anterior two-thirds of shell, becoming raised fine 

ridges over posterior third, and comarginal growth lines that 

become more prominent ventrally. Interior shell material is 

nacreous. Chevron-shaped taxodont dentition; anterior 

series shows a dramatic increase in size and height of teeth 

along the anterior-dorsal margin, becoming smaller and 

shorter as anterior-ventral margin is approached; posterior 

series shows a slight increase in size and a dramatic increase 

in height of teeth posteriorly but decreases toward the 

posterior-ventral margin; 23 to 31 teeth are present in 

anterior series and 8 to 12 in posterior series. Hinge angle 

formed by intersection of anterior and posterior series is 

wide (average 116°); anterior hinge plate convex toward 

valve interior immediately anterior to beak, then proceeds 

in a nearly straight line toward anterior-ventral margin; 

posterior hinge plate is straight to slightly concave toward 

valve interior. Resilifer lies below anterior series of teeth 

and in line with posterior series, forming a distinct spoonshaped pit that extends into valve interior past hinge plate; 

on left valve, resilifer rises up from pit, above posterior row 

of teeth, to form a toothlike process in line with posterior 

series; correspondingly, a slight recess is found on right 

valve. Isomyarian adductor muscle scars vary from shallow 

to deep impressions, depending somewhat on growth stage. 

Pallial line is usually distinct and parallels ventral margin of 

shell, often making a sharp bend at posterior end of shell. 

Pedal retractor and protractor muscle scars are commonly 

visible above midline of inner valve surface; anterior 

adductor muscle scar is commonly most prominent. Prodissconch resembles adult form. 

Discussion. -As herein defined, Nucula percrassa is 

a morphologically variable species. The objective range of 

variability is discussed in the statistical analysis portion of 

this study and can be seen by examining table 2. The 

observable range of variability of overall shape and hinge 

angle is well exemplified by a comparison of figures 1 and 

5 on plate 1. These two specimens typify the morphologic 

end members, figure 1 being the extreme of proportional 

elongation relative to height and also having a hinge angle 

greater than that of the specimen represented by figure 5. 

Intermediate morphologies are illustrated on plate 1 (figs. 8, 

9), plate 3 (figs. 2, 3, 6), and plate 4 (figs. 4, 5, 8, 9). 

Variation in the prominence of the umbonal area, flattening, 

or subsinusing of the posterior-ventral margin can be seen 

by comparing the figures on plate 2 and plate 6. The 

specimens shown on plate 1 (figs. 1, 2), plate 2 (fig. 5), and 

plate 6 (figs. 9, 10) especially show the character cited in 

the original description by Conrad (1858, p. 327) as "basal 

margin rounded, slightly contracted anteriorly [posteriorly]." Flattening of the outline of the ventral margin is 

especially well seen in some specimens among populations 

from the Owl Creek Formation of Mississippi but is 

occasionally also seen on other specimens, particularly 

those from the Coon Creek Tongue of the Ripley Formation 

of Tennessee (pl. 2, fig. 8). Similar inbending of the ventral 

margin has also been noted in other species of Nucula, often 

accompanied by extreme thickening of the shell material, 

and has been judged to be a gerontic feature (Stephenson, 

1941, p. 73). 

A number of other species that have been described 

from the Cretaceous rocks of the Coastal Plain appear to be 

related to Nucula percrassa. N. cibolensis Stephenson, 

1941 is from the Kemp Clay (late Maastrichtian) and is, 

according to the author, differentiated from N. percrassa in 

being larger and proportionally shorter, having more 

rounded posterior and anterior margins, and lacking a faint 

posterior radiating sulcus. N. chatfieldensis Stephenson 

(1941, p. 73) is described from somewhat compressed 

specimens from the Nacatoch Sand (Maastrichtian) of 

Texas. It was distinguished on the basis of being less 

elongate than N. percrassa and coming from a stratigraphic 

position lower than that of the type locality. Internal shell 

features and hinge character are poorly known for both 

these Texas species, but both appear to fall within the range 

of morphologic variablility of N. percrassa, as it is conceived herein. 

Nucula stantoni Stephenson, 1923, described from 

the Black Creek Formation (Campanian) at Snow Hill, 

N.C., is also a member of theN. percrassa lineage. It was 

differentiated from N. percrassa primarily because it is 

Revision of the Nucula percrassa Conrad, 1858 Group 015 
more trigonal in outline and smaller in size, both characters 

that need to be tested with a suite of specimens larger than 

what is currently available. N. prepercrassa Stephenson, 

1956 was described from the lower part of the Eutaw 

Formation on Ochillee Creek in Chattahoochee County, 

Georgia. The rocks at this locality are of lower to middle 

Santonian age (Sohl and Smith, 1980, p. 398). Stephenson 

(1956, p. 234) noted the similarity to N. percrassa but 

stated that it differed "in that the shell is much thinner, the 

hinge is narrower, the chondrophore is larger and projects 

farther inward .... '' Too few specimens of this species exist 

to determine how consistent these differences are, but there 

is no doubt that both are closely related members of the 

same lineage. 

One additional species probably related to Nucula 

percrassa has been described by Stephenson ( 194 7) and 

named N. nulla. All known specimens were recovered from 

well cores at a depth between 2, 730 and 2, 750 ft in the 

Avent No. 1 well in Grenada County, Mississippi. Stratigraphically, they come from beds of probable early Campanian age. All known specimens are small (less than 5 mm 

in length) and have a crenulate ventral margin. The internal 

features are unknown save for the dentition, which is of 

Nunda type. Comparison with N. severnensis is discussed 

in the description of that species. In sum, the relationship to 

other described species is unsure, and specimens may 

represent only immature members of a described species. 

Occurrence. -Alabama: Ripley Formation, loc. 13; 

Providence Sand, loc. 20. Delaware: Matawan Formation, 

Severn Formation. Georgia: Blufftown Formation, loc. 3; 

Ripley Formation, locs. 14, 15; Providence Sand, loc. 22. 

Maryland: Severn Formation, locs. 23-25. Mississippi: 

Coffee Sand, locs. 1, 2; Ripley Formation, locs. 5-12; Owl 

Creek Formation, locs. 16-19. Missouri: Owl Creek Formation. New Jersey: Magothy Formation, Merchantville 

Formation, Woodbury Formation, Marshalltown Formation, Wenonah Formation. South Dakota: Fox Hills Formation. Texas: Nacatoch Sand, Corsicana Marl, Kemp Clay. 

Stratigraphic range.-Middle lower Campanian 

through Maastrichtian. 

T'.';pes.- Holotype Nucula percrassa, Academy of 

Natural Sciences of Philadelphia (ANSP); hypotypes 

USNM 32713, 128084, 128085, and 423803-423837. 

Holotype N. slackiana, ANSP; hypotypes USNM 131858. 

Holotype N. tippahensis, USNM 103751. 

Nucu/a severnensis n.sp. 

Plate 3, figures 11-19; plate 5, figures 2, 11; 

plate 6, figure 3; plate 7, figure 3. 

Diagnosis.- Subtrigonal shell, posterior margin 

inclined steeply away from beak. Faint radial striations and 

comarginal growth lines ornament surface. Hinge angle 

approximates a right angle. 

016 Shorter Contributions to Paleontology and Stratigraphy 

Description. -Shell is equivalve, slightly to moderately convex, and subtrigonal in outline; beak lies posterior 

to midlength; opisthogyrate. Lunule elongate narrow and 

indistinctly margined; escutcheon proportionally broad, distinct. Posterior-dorsal margin is inclined steeply away from 

beak; margin is straight to slightly convex outward; posterior ridge may be sharp and well defined; posterior margin 

is truncate. Anterior-dorsal margin is slightly curved and 

inclined away from the beak at a more gentle angle than 

posterior margin; anterior margin truncate. Ventral margin 

is gently curved and crenulate. Surface ornamentation 

consists of comarginal growth lines and faint incised radial 

striations commonly becoming raised lines on posterior 

quarter. Interior shell material is nacreous. Chevron-shaped 

taxodont dentition; anterior teeth increase in size and height 

anteriorly, becoming smaller and shorter as anterior-ventral 

margin is approached; posterior series shows a slight 

increase in size of teeth and an increase in height toward 

middle of posterior hinge plate, decreasing toward ventral 

margin; 22 to 29 teeth occur in anterior series; 10 to 12 teeth 

are present in posterior series. Hinge angle formed by 

intersection of anterior and posterior series of teeth approximates a right angle (average=93°); anterior hinge plate is 

convex in toward valve interior, following curvature of 

anterior-dorsal margin; posterior hinge plate is straight to 

slightly concave toward valve interior. Resilifer lies below 

anterior series of teeth and in line with posterior series and 

forms a triangular-shaped, basally flattened pit that extends 

somewhat into valve interior past hinge plate; on left valve, 

resilifer rises up from recess, above posterior series of teeth 

to form a toothlike process in line with posterior series; in 

an analogous position on right valve is a small recess. 

Isomyarian adductor muscle scars usually form shallow 

depressions. Pallial line faint and somewhat obscured by 

radial striations visible on interior of shell surface. Pedal 

muscles usually distinctly impressed. Prodissconch ressembles adult form. 

Discussion.-The primary difference between 

Nunda percrassa and N. severn ens is is shape; N. percrassa 

is subelliptical, whereas N. severnensis is subtrigonal (compare pl. 3, figs. 1-10, with pl. 3, figs. 11-19). This 

difference in shape is even more pronounced when internal 

molds of the two species are compared (pl. 7, figs. 1-6). An 

examination of the mean values for the hinge angles of the 

two species in table 2 provides a less subjective way of 

expressing this difference in shape. The average value of 

the hinge angle in N. percrassa is 116°, giving the species 

its subelliptical appearance. The subtrigonal shape of N. 

severnensis is produced by an average value of 93° for the 

hinge angle. The hinge angle is the primary discriminating 

variable in the discriminant analysis comparing N. percrassa to N. severnensis (text fig. 5); the standardized 

canonical discriminant function coefficient is 0. 67 for 

function 1, which accounts for about 73 percent of the 

variance between the species. Length, the second most 
important discriminating variable in the analysis of the two 

species (standardized canonical discriminant function coefficient is 0.61 ), is intuitively tied to the value of the hinge 

angle; the wider the angle, the greater the length. An 

additional component of the difference in shape between N. 

percrassa and N. severnensis is the anterior margin. InN. 

percrassa, it is elongate and smoothly curved, an average 

value for the angle of the anterior-ventral margin being 55° 

(table 2), whereas, inN. sevemensis, the anterior margin is 

truncate, an average value for the angle of the anteriorventral margin being 62° (table 2). The angle of the 

anterior-ventral margin is the third most important discriminating variable along function 1 in the discriminant analysis of the species (standardized canonical discriminant 

function coefficient is -0.13 ). 

Additional variations between Nuntla percrassa and 

N. severnensis can be seen along the hinge plate. In N. 

percrassa, the anterior series of teeth bends slightly toward 

the interior of the valve in the region of the umbo and then 

continues in a nearly straight line toward the anterior margin 

(pl. 4, figs. 2, 3, 7). The anterior series of teeth in N. 

severnensis gradually curves toward the interior of the shell 

as it approaches the anterior margin, following the curvature of the anterior-dorsal margin (pl. 3, figs. 12, 13, 15, 

18). The resilifer of N. percrassa is spoon shaped and 

extends proportionally farther past the hinge plate than the 

triangular-shaped, basally flattened resilifer of N. severnensis (compare pl. 3, fig. 7, pl. 4, fig. 3, and pl. 7, fig. 8, 

with pl. 3, figs. 12, 15, 18). 

Nucz.tla H'altonensis Stephenson (1941, p. 74), from 

the N acatoch Sand of Texas, is somewhat simi liar to N. 

severnensis in its trigonal outline and fine, faint, comarginal 

ribbing. Because features of the hinge and interior are 

unknown, close comparison of the two is impossible, given 

the available specimens. The holotype (USNM 76295), a 

small (6.8 mm long, 5 mm high) bivalved specimen, differs 

from N. sevemensis in having a more concave posteriordorsal margin and a more rounded escutcheon margin. In 

these characters, it appears morphologically closer to N. 

stantoni Stephenson, 1923, from the Black Creek Formation of North Carolina, than toN. severnensis. 

Occurrences. -Alabama: Providence Sand, loc. 20. 

Georgia: Ripley Formation, loc. 14; Providence Sand, locs. 

21, 22. Maryland: Severn Formation, locs. 23-25. 

Stratigraphic range.-Middle through upper Maastrichtian. 

T_vpes. -Holotype, USNM 423838. Paratypes, 

USNM 423839-423847 (shown); USNM 423848-423853 

(not shown). 

SUMMARY AND CONCLUSIONS 

A discriminant analysis of the Nucula percrassa 

lineage has clarified the taxonomic, geographic, and stratigraphic relationships within the group. Morphologic characters deemed important by the original authors of the 

species were used as the discriminating variables in the 

analysis to test the validity of the authors' assumptions. The 

results indicate that N. percrassa Conrad, N. slackiana 

Gabb, and N. tippahensis Harbison are all members of the 

same species. Consequently, we suggest that the names N. 

slackiana Gabb and N. tippahensis Harbison be treated as 

synonyms of N. percrassa Conrad. Occurring with N. 

percrassa in beds of Maastrichtian age from Maryland and 

the Gulf Coast is N. severnensis n. sp., named and described 

within this paper. This species had previously been surmised to be a juvenile N. percrassa or N. slackiana. 

Discriminant analysis was thus shown to be a very simple, 

graphic means of testing previously defined species; we 

hope that this technique will be utilized in similiar studies in 

the future. 

The results of this study raise issues relevant for all 

paleontologists, especially our methods of defining species 

and selecting type specimens. Because morphologic similarities between individuals and populations are the only 

testable data available to paleontologists, identifications of 

new species should be based solely on morphologic divergence. Prior assumptions of stratigraphic or geographic 

isolation are not valid criteria for distinguishing species. 

Ideally, a holotype representing the median of a population 

should be selected, and paratypes should represent the full 

suite of morphologic divergence, especially end members. 

The statistical range of variation seen within a population 

should be included in the species description. Only by 

reaching a consensus on these issues can we develop a 

consistent, reproducible data base. 

The continued use of the published species record to 

extrapolate conclusions about evolutionary processes and 

rates could bias our calculations and conceal important facts 

about the real processes of biological change. The published 

record of the Nuculidae contains a bias toward shortened 

species durations and too much diversity. No doubt, future 

studies will reveal similar evidence regarding the reliability 

of the published record for other groups of organisms. 

Meanwhile, we should proceed cautiously with our inductive conclusions about evolutionary processes. 

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of Texas: University of Texas Publication 4101, 641 p. 

---1947, New Upper Cretaceous fossils from Mississippi and 

Texas, pt. 1, Fossils from two deep wells in Mississippi: U.S. 

Geological Survey Professional Paper 210-E, p. E161-E196. 

---1952, Larger invertebrate fossils of the Woodbine Formation (Cenomanian) of Texas: U.S. Geological Survey Professional Paper 242, 226 p. 

---1955, Owl Creek (Upper Cretaceous) fossils from Crowleys Ridge, southeastern Missouri: U.S. Geological Survey 

Professional Paper 274-E, p. E97-E140. 

---1956, Fossils from the Eutaw Formation, Chattahoochee 

River region, Alabama-Georgia: U.S. Geological Survey 

Professional Paper 274-J, p. J227-J250. 

Stephenson, L.W., and Monroe, W.H., 1940, The Upper Cretaceous deposits: Mississippi State Geological Survey Bulletin 

40, 296 p. 

Veatch, 0., and Stephenson, L.W., 1911, Preliminary report on 

the geology of the Coastal Plain of Georgia: Georgia Geological Survey Bulletin 26, 466 p. 

Wade, B., 1926, The fauna of the RiP.ley Formation on Coon 

Creek, Tennessee: U.S. Geological Survey Professional 

Paper 137, 272 p. 

Weller, J.M., 1961, The species problem: Journal of Paleontology, v. 35, no. 6, p. 1181-1192. 

Weller, S., 1907, A report on the Cretaceous paleontology of New 

Jersey: Geological Survey of New Jersey, Paleontology ser., 

V. IV, 1106 p. 

Whitfield, R.P., 1885, Brachiopoda and Lamellibranchiata of the 

Raritan clays and greensand marls of New Jersey: U.S. 

Geological Survey Monograph IX, 338 p. 

Wiley, E. 0., 1978, The evolutionary species concept reconsidered: Systematic Zoology, v. 27, p. 17-26. 

Revision of the Nucula percrassa Conrad, 1858 Group 019 
APPENDIX 1. NUCULID SPECIES FROM THE UPPER CRETACEOUS OF NORTH 

AMERICA 

Species name Formation (if known) Locality 

Acila banquereauenis . . . . . . . . . . . . . ..................... Nova Scotia 

Acila demessa . . . . . . . . . . . . . . . . . . . . ..................... California 

Acila (Truncacila) 

Acila (T.) demessa haidana ....... Haida 

Acila (T.) princeps ............... Moreno Formation 

Acila (T.)'? chicotana ............ Woodbine Formation 

British Columbia. Oregon 

California 

Texas 

Nucula (Acila) tuberculata . . . . . . . . ..................... California 

Nucula amica ................... Monmouth Formation Maryland 

Nucula assiniboiensis ............ Montana Group Alberta 

Nunda bellastriata . . . . . . . . . . . . . . . ..................... Texas 

Nucula cancellata . . . . . . . . . . . . . . . . ..................... Nebraska 

Nunda catherina . . . . . . . . . . . . . . . . . ..................... Kansas 

Nucula chatfieldensis ............ Nacatoch Sand Texas 

Nuntla chickasaensis . . . . . . . . . . . . . ..................... Texas 

Nuntla ciboloensis . .............. Kemp Clay Texas 

Nuczda coloradoensis ............ Colorado Group Colorado 

Nunda cunei.frons . . . . . . . . . . . . . . . . ..................... Alabama 

Nuntla distorta . . . . . . . . . . . . . . . . . . . ..................... Tennessee 

Nuczda dowlingi ................. Colorado Group British Columbia 

Nuntla equilateralis . . . . . . . . . . . . . . ..................... Nebraska 

Nunda ermani . . . . . . . . . . . . . . . . . . . ..................... Alaska 

Nucula eufalensis. . . . . . . . . . . . . . . . . ..................... Alabama 

Nunda evansi...... . . . . . . . . . . . . . . ..................... Nebraska 

Nunda gabbi . ................... Knoxville Formation California 

Nunda guadalupae . . . . . . . . . . . . . . . ..................... Mexico 

Nucula haydeni. . . . . . . . . . . . . . . . . . . ..................... Texas 

Nunda hornbyensis . ............. Nanaimo Formation Ottawa 

Nucula larimerensis . ............. Fox Hills Formation Colorado 

Nunda microconcentrica ......... Ripley Formation Tennessee 

Nucula microstriata .............. Monmouth Formation Maryland 

Nunda momnouthensis........... . ..................... New Jersey 

Nucula nacatochana ............. Nacatoch Sand Texas 

Nuntla obsoletastriata . . . . . . . . . . . . ..................... Nebraska 

Nucula pectinata . . . . . . . . . . . . . . . . . ..................... British Columbia 

Nunda pectinata cretae . . . . . . . . . . . ..................... Greenland 

Nucztla percrassa ................ Owl Creek Formation Mississippi 

Nuntla perequalis . . . . . . . . . . . . . . . . ..................... Alabama 

Nunda planomarginata . . . . . . . . . . . ..................... Nebraska 

Nucula prepercrassa . . . . . . . . . . . . . . ..................... Georgia 

Nunda richardsoni . . . . . . . . . . . . . . . ..................... British Columbia 

Nucula rivulana ................. Woodbine Formation Texas 

Nunda scitula. . . . . . . . . . . . . . . . . . . . ..................... Nebraska 

Nuczda serrata . . . . . . . . . . . . . . . . . . . ..................... Texas 

Nunda severnensis n.sp .......... Severn Formation Maryland 

Nucula slwlsa ................... Woodbine Forn1ation Texas 

Nunda slackiana . . . . . . . . . . . . . . . . . ..................... New Jersey 

Nucztla soltaria. . . . . . . . . . . . . . . . . . . ..................... California 

Nucula stantoni .................. Black Creek Formation North Carolina 

Nucula storrsi ................... Knoxville Formation California 

Nucztla subnasuta. . . . . . . . . . . . . . . . . ..................... Colorado 

Nucula subplana................. . ..................... Nebraska 

Nucula tenuisculpta. . . . . . . . . . . . . . . ..................... California 

Nuczda tippahensis . .............. Ripley Formation Mississippi 

Nucula traskana . . . . . . . . . . . . . . . . . . ..................... British Columbia 

Nucula truncata . . . . . . . . . . . . . . . . . . ..................... California 

Nucztla ventricosa . . . . . . . . . . . . . . . . ..................... Colorado 

Nucula waltonensis .............. Nacatoch Sand Texas 

Nuczda l-veldensis ................ Fox Hills Formation Colorado 

Nuntla whitfieldi ................ Cliffwood beds New Jersey 

1 References are as follows: 

020 Shorter Contributions to Paleontology and Stratigraphy 

Author(s) 1 

Stephenson ( 1936) 

Finlay ( 1927) 

Schenk (1936) 

Schenk ( 1943) 

Stephenson ( 1953) 

Gabb (1873) 

Gardner (1916) 

Landes ( 1940) 

Shumard ( 1861) 

Meek and Hayden ( 1856) 

Cragin (1894) 

Stephenson ( 1941) 

Cragin (1895) 

Stephenson (1941) 

Stanton (1894) 

Conrad ( 1860) 

Gabb (1860) 

McLearn ( 1919) 

Meek and Hayden ( 1856) 

Eichwald (1871) 

Gabb (1860) 

Meek and Hayden ( 1856) 

Stanton (1895) 

Bose (1910) 

Shumard ( 1859) 

Whiteaves ( 1896) 

Reeside ( 1928) 

Wade (1926) 

Gardner (1916) 

Whitfield ( 1885) 

Stephenson ( 1941) 

Meek and Hayden ( 1856) 

Whiteaves ( 1879) 

Donovan (1953) 

Conrad (1858) 

Conrad ( 1860) 

Meek and Hayden (1856) 

Stephenson (1956) 

Whiteaves ( 1896) 

Stephenson (1953) 

Meek and Hayden ( 1856) 

Shumard (1859) 

Wingard and Sohl (this paper) 

Stephenson ( 1953) 

Gabb (1876) 

Gabb (1869) 

Stephenson ( 1923) 

Stanton (1895) 

Hall and Meek (1855) 

Meek and Hayden ( 1856) 

Gabb (1873) 

Harbison (1945) 

Meek (1858) 

Gabb (1864) 

Hall and Meek ( 1855) 

Stephenson ( 1941) 

Reeside (1928) 

Weller ( 1907) 
Bose, E., 1910, Boletin Instituto Geologico de Mexico, no. 25, p. 120. 

Conrad, T.A., 1858, Journal of the Academy of Natural Sciences of Philadelphia, v. 3, p. 327. 

---1860, Journal of the Academy of Natural Sciences of Philadelphia, v. 4, p. 281. 

Cragin, F.W., 1894, American Geologist, v. 14, p. 4. 

--1895, Colorado College Studies, no. 5, p. 49-68. 

Donovan, D.T., 1953, Meddeleser om Gronland, v.lll, no. 4, p. 87. 

Eichwald, E., 1871, Geonostisch-paleontologische Bemerkungen uber die Halbinsel Mangischlak und die Aleutischen 

lnseln, St. Petersburg, Buchdr. der Kaiserlichen Akademie der Wissenschaften, p. 126-127. 

Finlay, H.J., 1927, Royal Society of New Zealand Transactions and Proceedings, v. 57, p. 522. 

Gabb, W.M., 1860, Journal of the Academy of Natural Sciences of Philadelphia, v. 4, p. 396-397. 

---1864, Paleontology: San Francisco, Geological Survey of California, v. 1, p. 198-199. 

---1869, Paleontology: San Francisco, Geological Survey of California, v. 2, p. 197. 

---1873, Transactions of the American Philosophical Society, v. 15, p. 255. 

---1876, Proceedings of the Academy of Natural Sciences of Philadelphia, p. 318. 

Gardner, J.A., 1916, Systematic paleontology, Upper Cretaceous: Maryland Geological Survey, Upper Cretaceous 

[Volume], p. 514-515. 

Hall, J., and Meek, F.B., 1855, Memoirs of the American Academy of Arts and Sciences, v. 5, p. 384--385. 

Harbison, A., 1945, Proceedings of the Academy of Natural Sciences of Philadelphia, v. 97, p. 77. 

Landes, R.W., 1940, Geological Survey of Canada Memoir 221, p. 131. 

McLearn, F.H., 1919, Canada Department of Mines and Canada Geological Survey, Museum Bulletin 29, p. 9. 

Meek, F.B., 1858, Transactions of the Albany Institute, v. 4. p. 39. 

Meek, F.B., and Hayden, F.V .. 1856, Proceedings of the Academy of Natural Sciences of Philadelphia, p. 84-85,275. 

Reeside, J.B., 1928, Journal of the Washington Academy of Sciences, v. 18, no. 11, p. 306-307. 

Schenk. H.G., 1936. Geological Society of America Special Paper 4, p. 50. 

---1943, Journal of Paleontology, v. 17, no. 1, p. 63. 

Shumard, B.F .. 1859, Transactions of the Academy of Sciences of St. Louis, v. 1, p. 602-603. 

---1861, Proceedings of the Boston Society of Natural History, v. 8, p. 202-203. 

Stanton, T.W., 1894, U.S. Geological Survey Bulletin 106. p. 94. 

--1895, U.S. Geological Survey Bulletin 133, p. 51-52. 

Stephenson, L.W., 1923, North Carolina Geologic and Economic Survey, v. 5. pt. 1, p. 79. 

---1936, Geological Society of America Bulletin, v. 47. p. 387. 

---1941, Texas University Publication 4101, p. 72-74. 

---1953, U.S. Geological Survey Professional Paper 242. p. 54-56. 

---1956, U.S. Geological Survey Professional Paper 274-J, p. J234. 

Wade, B .. 1926, U.S. Geological Survey Professional Paper 137. p. 40. 

Weller, S., 1907, New Jersey Geologic Survey, Cretaceous Paleontology, p. 371. 

Whiteaves, J.F., 1879, Canada Geologic Survey, Mesozoic Fossils, v. 1, pt. 2, p. 161. 

---1896, Proceedings and Transactions of the Royal Society of Canada, v. 1, sec. 4, p. 122. 

Whitfield, R.P., 1885, U.S. Geological Survey Monograph 9. p. 102. 

Revision of the Nucula percrassa Conrad, 1858 Group 021 
APPENDIX 2. DESCRIPTION OF COLLECTION LOCALITIES 

The following locality descriptions are organized in stratigraphic order within each formation. Each description 

includes the U.S. Geological Survey (USGS) Mesozoic collection number(s), followed in parentheses by the collector and 

the date of collection. 

CAMPANIAN 

Coffee Sand 

Locality 1. USGS Mesozoic collection 9501 (L. W. 

Stephenson, 1915). Ten kilometers (6 mi) 

east of Booneville on road to Hare's old mill 

site (on Big Brown Creek) in Prentiss 

County, Mississippi. Well-preserved fossils 

were collected from the lower 1.5 m (5 ft) of 

a 13.7-m (45-ft) section; Stephenson and 

Monroe (1940, p. 159) described the sediment as a dark-gray, compact, finely micaceous, glauconitic sand. These beds are in 

the lower part of the Coffee Sand. 

Locality 2. USGS Mesozoic collections 17254 (W.H. 

Monroe, 1936), 17809 (L.W. Stephenson 

and W.H. Monroe, 1938), 25483 (L.W. 

Stephenson and N.F. Sohl, 1955), and 

26338 (N.F. Sohl and H.I. Saunders, 1956). 

Roadcut on north-facing slope of Mantachie 

Creek Valley, 3.2 km (2 mi) due west of 

Ratliff in Lee County, Mississippi, SI/2, sec. 

9, T. 8 S., R. 7 E. Abundant fossils are 

found in the first meter of a 10. 7-m (35-ft) 

section of massive, dark-colored, micaceous, glauconitic, clayey sand. These beds 

lie in the middle of the lower Coffee Sand, 

stratigraphically above locality 1. 

Blufftown Formation 

Locality 3. USGS Mesozoic collections 6405 (L.W. 

Stephenson, 1909) and 26033 (N.F. Sohl 

and H.I. Saunders, 1955). Type locality of 

the Blufftown Formation. Bluffs on the left 

bank of the Chattahoochee River at Blufftown, 45.6 km (28.5 mi) above Eufaula 

landing, and 50 km (31.25 mi) below 

Columbus in Stewart County, Georgia (Julia 

quadrangle, 84 °57' 45" N., 32°11' W.). 

Stephenson (Veatch and Stephenson, 1911, 

p. 135) described the lower 3m (10ft) of the 

section as a "gray, calcareous, finely arenaceous, fossiliferous clay"; overlying this 

lower layer is 13.7 m (45 ft) of a "gray, 

calcareous, glauconitic sand'' with concretionary layers. Fossils listed were recovered 

D22 Shorter Contributions to Paleontology and Stratigraphy 

from the lower 13.7 m (45ft). The remaining 45.7 m (150 ft) of section consists of a 

''gray, calcareous, marine sand," overlain by 

a weathered, unconsolidated sand. 

MAASTRICHTIAN 

Ripley Formation, Coon Creek Tongue 

Locality 4. USGS Mesozoic collections 10198 (B. 

Wade, 1917) and 25406 (N.F. Sohl, 

1950-53). Type locality of the Coon Creek 

Tongue of the Ripley Formation. The old 

Dave Week's place, on Coon Creek, 5.6 km 

(3.5 mi) south of Enville, 12 km (7.5 mi) 

north of Adamsville, and 198m (660ft) east 

of the main Henderson-Adamsville road, in 

the northeastern part of MeN airy County, 

Tennessee. Wade (1926, p. 9-10) described 

the 9.1-m (30-ft) section along the banks of 

Coon Creek as consisting of a dark bluishgreen and gray, clayey, glauconitic, micaceous, medium fine sand; concretionary 

masses may form locally. 

Locality 5. USGS Mesozoic collections 18078 (L.C. 

Conant, A. Brown, and W.H. Monroe, 

1939), 18616 (L.W. Stephenson and W.H. 

Monroe, 1941), and 25411 (N.F. Sohl, 

1950-52). Scraped area along the northern 

side of the dam at Pleasant Ridge Lake in 

Union County, Mississippi, NWl/4 NEI/4 

NEl/4 sec. 11, T. 6 S., R. 4 E. Collections 

were made from the lower 3m (10ft) of the 

section, which consists of a blue-gray, silty, 

calcareous, micaceous, glauconitic, very 

fossiliferous sand and a layer of crab-bearing 

concretions near its base. The overlying 

layer is a dark-gray, silty, micaceous, ironstained clay interbedded with a mediumgrained sand. 

Locality 6. USGS Mesozoic collection 711 (T.W. Stanton, 1889). Bed of Hall Branch of Tallahatchie River on the old C.R. Hall farm, 

near Molino in Union County, Mississippi, 

sec. 5, T. 6 S., R. 4 E. Stanton described, in 

his field notes, the 396-m (0.25-mi) exposure along the creek bed as "an almost 

continous exposure of dark clay marl, 10 or 

15 feet [3-4.6 m] thick." 
Locality 7. USGS Mesozoic collection 25410 (N.F. 

SohL 1950-1952). Roadcut in east-facing 

slope of Hall Branch, 1.4 km (0.9 mi) west 

of Molino in Union County, Mississippi, 

SWl/4 NEl/4 sec. 8, T. 6 S., R. 4 E. This 

locality is 0.8 km (0.5 mi) north of locality 

6. The sample was collected from the lowest 

bed of the Coon Creek exposed at this 

outcrop-a blue-gray, silty, micaceous, calcareous, glauconitic, fossiliferous sand. This 

bed most likely correlates with the bed sampled at locality 6, but an exact determination 

is impossible. The lower bed is overlain by 

4.2 m (14 ft) of Coon Creek interbedded 

sands and clays, capped by 48 m (16 ft) of 

the McNairy Sand. 

Locality 8. USGS Mesozoic collection 6873 (L. W. 

Stephenson, 1910). Lee's old mill site, roadcut on northeast-facing slope of Tallahatchie 

River valley, 3.2 km (2 mi) north-northeast 

of Keown ville, on the road to Molino in 

Union County, Mississippi, NWl/4 NEl/4 sec. 

17, T. 6 S., R. 4 E. Five beds of the upper 

portion of the Coon Creek Tongue crop out 

at this locality (see Sohl, 1960, p. 30-31, 

locs. 14, 15, and 16, for complete section). 

The first 10.4 m (34.5 ft) of the section 

consists of a micaceous sand, interbedded 

with clay and alternating between fossiliferous and noncalcareous beds, overlain in tum 

by a thin (0. 2 m) layer of blue-black, sandy, 

laminated, micaceous, carbonaceous clay. 

Nine meters (30ft) of McNairy Sand rests on 

top of the Coon Creek beds. An incomplete 

section was exposed in 1910, but the sample 

that Stephenson collected then probably 

came from bed 4, a blue-black, massive, 

silty, micaceous, glauconitic, fossiliferous 

sand. This unit is stratigraphically higher 

than the beds described at localities 6 and 7. 

Locality 9. USGS Mesozoic collection 25409 (N.F. 

Sohl, 1950-52). Locality description same as 

that for locality 8. This sample was also 

collected from bed 4. 

Locality 10. USGS Mesozoic collection 25407 (N.F. 

Sohl, 1950-52). Roadcut on northeast-facing 

slope of Hall Creek, a tributary of the Tallahatchie River, 4.6 km (2.9 mi) (airline) 

southwest of Dumas in Tippah County, Mississippi, center Sl/2 NWl/.:~ sec. 34, T. 5 S., 

R. 4 E. The sample was collected from the 

lowermost unit of the 11-m (37-ft) section, 

which is a blue-gray, medium-grained, silty, 

clayey, micaceous, glauconitic, highly fossiliferous sand containing many large fossil 

concretions. Four additional Coon Creek 

beds overlie unit 1 and consist of alternating 

sands and clays (see Sohl, 1960, p. 28, loc. 

6, for the complete section). The section is 

topped with a layer of McNairy Sand. 

Ripley Formation, upper marine sands 

Locality 11. USGS Mesozoic collection 708 (T. W. Stanton, 1889). Bullock's old overshot mill, 3.2 

km (2 mi) south of Dumas in Tippah County, 

Mississippi, sec. 36, T. 5 S., R. 4 E. 

Stanton, in his field notes, stated that fossils 

were collected from "8 or 10 feet [2.4-3.0 

m] of dark marl" at water level. Although the 

outcrop was overgrown by 1910 when L.W. 

Stephenson visited the site, he placed the 

collection in the Coon Creek Tongue 

(Stephenson and Monroe, 1940, p. 188). 

Sohl argues that the matrix and fauna present 

could just as easily be placed in the upper 

part of the Ripley; the presence of the outcrop "20 or 30 feet" [6.1-9.1 m] below a 

ferruginous limestone layer, most likely the 

Keownville Limestone Member of the Ripley, suggests this possibility (Sohl, 1960, p. 

28, loc. 5). 

Locality 12. USGS Mesozoic collection 26339 (N.F. 

Sohl and H.I. Saunders, 1956). Roadcut on 

secondary road on the north-facing slope of 

the South Branch of Wilhite Creek, 3. 7 km 

(2.3 mi) southeast of Keownville in Union 

County, Mississippi, SEl/4 NWl/4 sec. 33, T. 

6 S., R. 4 E. Fossils occur in a gray, 

micaceous, glauconitic, clayey fine sand 

about 2m thick and located 63.5 em (25 in) 

below the Chiwapa Sandstone Member of 

the Ripley. 

Locality 13. USGS Mesozoic collection 857 (T. W. Stanton, 1891). Chattahoochee River, between 

Eufaula and Barbour Creek, 3.2 km (2 mi) 

below Eufaula landing in Barbour County, 

Alabama. The collector provided no additional information. Before construction of 

the Walter F. George Dam at Fort Gaines, 

Ga., there were numerous exposures of fossiliferous, dark-gray, clayey sand of the 

Ripley Formation along the Chattahoochee 

River bluffs in this area. Which of these 

exposures is represented by Stanton's collection is unsure, but, presumably, it would 

have come from beds less than 1 m below 

locality 14. 

Locality 14. USGS Mesozoic collection 28431 (N.F. 

Sohl and R.L. Rieke, 1961). Bluffs of the 

Revision of the Nucula percrassa Conrad, 1858 Group D23 
Chattahoochee River, left bank about 3.2 km 

(2 mi) below the Central of Georgia railroad 

crossing in Quitman County, Georgia. Collections were made from a 3-m section of 

dark-gray, sparingly glauconitic, micaceous, 

clayey fine sand. 

Locality 15. USGS Mesozoic locality 25991 (N.F. Sohl 

and H.I. Saunders, 1955). Bluffs of Chattahoochee River. left side about 396 m (0.25 

mi) above the mouth of Barbour Creek at 

water level and 6.4 km (4.0 mi) south of 

Eufaula in Quitman County, Georgia. Collected from a 2.5-m section consisting of 

blue-black. very micaceous, glauconitic, 

clayey fine sand. 

Owl Creek Formation 

Locality 16. USGS Mesozoic collection 25424 (N .F. 

Sohl, 1951-53). Head of ravine, underpass. 

and roadcut just north of road fork 1.2 km 

(0.75 mi) south of Dumas in Tippah County. 

Mississippi, center of eastern edge of SElf-+ 

sec. 24. T. 5 S., R. 4 E. The 2.4-m (8-ft) 

exposure of the Owl Creek at this section 

overlies 49.8 m (166ft) of the Ripley and is 

overlain by 1. 8 m ( 6 ft) of the Prairie 

Bluff(?) Chalk (see Sohl. 1960, p. 29-30, 

loc. 47. for complete section). The Owl 

Creek at this locality is a blue-gray. silty. 

micaceous. glauconitic, calcareous. fossiliferous sand. 

Locality 17. USGS Mesozoic collection 713 (T.W. Stanton, 1889). Exposures in Walnut Creek bed, 

Braddock's farm. on south-facing slope of 

Walnut Creek valley 6 km (3.75 mi) eastsoutheast of Falkner in Tippah County, Mississippi, NElf-+ SElf-+ SElf-+ sec. 16. R. 3 S., T. 

4 E. Two and one-half meters (8 ft) of the 

Ripley is overlain by 7.65 m (25.5 ft) of the 

Owl Creek: 7.2 m (24 ft) of the Clayton 

Formation tops the section. The sample was 

collected from the 2. 7-m-thick (9-ft-thick) 

lower bed of the Owl Creek, which Stephenson (Stephenson and Monroe. 1940, p. 233) 

described as a blue-gray. calcareous. argillaceous. very fine sand containing abundant 

fossil shells. 

Locality 18. USGS Mesozoic collection 25422 (N.F. 

Sohl. 1950-53). Roadcut on north-facing 

slope of a tributary to Fourth Creek. 1.4 km 

(0.9 mi) north of Providence School in 

Tippah County, Mississippi. NElf-1 NWlf-1 

sec. 27. T. 2 S., R. 4 E. Sample was 

collected from a 6-m (20-ft) layer of blue024 Shorter Contributions to Paleontology and Stratigraphy 

gray, silty. micaceous, glauconitic, very fossiliferous sand of the Owl Creek, overlain by 

about 9 m (30ft) of the Clayton (Paleocene). 

Locality 19. USGS Mesozoic collections 707 (T. W. 

Stanton. 1889), 6464 (L.W. Stephenson, 

1909), and 25423 (N.F. Sohl, 1950). Bluffs 

on right bank of Owl Creek, 4 km (2.5 mi) 

northeast of Ripley in Tippah County, Mississippi, Nl/2 SEI/-1 sec. 7, T. 4 S., R. 3 E. 

This location is the type locality for the Owl 

Creek Formation. Five and eight-tenths 

meters (16 ft) of the Owl Creek is exposed 

here, overlain by 6.9 m (23ft) of the Clayton 

(Paleocene). Stephenson (Stephenson and 

Monroe, 1940, p. 232) described the lithology as dark greenish-gray, fine, compact, 

tough, massive, micaceous. calcareous, 

argillaceous. slightly glauconitic sand containing large numbers of well-preserved 

shells, including many genera and species. 

Providence Sand 

Locality 20. USGS Mesozoic collection 25921 (N.F. 

Sohl and H.I. Saunders. 1955). Bluffs of 

White Oak Creek at bridge of Barbour 

County Route 47 and Alabama State Route 

95 at the Barbour-Henry County line in 

Alabama. SElf-+ SWI/-1 sec. 8, T. 9 N., R. 29 

E. Collected from about 2 m of blue-black, 

coarse, sparingly glauconitic, clayey, fineto medium-grained sand exposed in stream 

bed and banks. 

Locality 21. USGS Mesozoic collection 855 (T.W. Stanton, 1891). Chattahoochee River at mouth of 

Pataula Creek in Georgia. Stanton described 

the outcrop in his field notes as "25 or 30 feet 

[7. 6-9.1 m] of blue sandy clay interrupted 

midway by 4 feet [1.2 m] of coarse gray 

sandstone." 

Locality 22. USGS Mesozoic collections 6412 (L.W. 

Stephenson. 1909) and 25935 (N.F. Sohl 

and H.I. Saunders, 1955). One and fourtenths kilometers (0.9 mi) above the mouth 

of Pataula Creek at the "Narrows,'' right 

bank 180 m (200 yd) below the waterfalls, 

Clay County, Georgia. Stephenson (Veatch 

and Stephenson, 1911, p. 184) described the 

section as 6.9 m (23 ft) of ''dark greenish 

gray, massive, micaceous, argillaceous, 

marine sand with indurated ledges" 0.3 to 

1.8 m (1-6 ft) apart, overlain by 3.6 m (12 

ft) of "brownish, weathered, argillaceous, 

marine sand." 
Severn Formation 

Locality 23. USGS Mesozoic collection 32775 (N.F. 

Sohl, 1971 ) . Excavations for Landover Mall 

shopping center near intersection of Maryland Route 202, Interstate 95. and Brightseat 

Road in Prince Georges County, Maryland. 

Collection is from the upper part of a 4-m 

(13.2-ft) section of dark gray. micaceous, 

fine sand. 

Locality 24. USGS Mesozoic collection 32772 (N.F. 

Sohl and E.G. Kauffmann, 1961-62). Exposures in small drainage ditch on the Wilson 

Dairy Farm south of Sheriff Road (Gardner's 

(1916) Brightseat locality) in Prince Georges 

County, Maryland. Collection is from the 

upper part of a 6-m-thick (19.8-ft-thick) 

section of gray, very micaceous, clayey, fine 

sand. 

Locality 25. USGS Mesozoic collection 28858 (N.F. 

Sohl, W.O. Ross, H.I. Saunders, and E.L. 

Y ochelson, 1960). Excavations immediately 

west of bridge of Interstate 95 and just north 

of Central A venue, within cloverleaf 

approach and exit, in Prince Georges 

County, Maryland. Sample is from the 

medial part of a 3.5-m (11.6-ft) section of 

gray, micaceous, clayey fine sand. 

Revision of the Nucula percrassa Conrad, 1858 Group 025 

PLATES 1-7 
PLATE 1 

Type specimens of species of Nucula 

Figures 1-10. Nucula percrassa Conrad: all specimens X2. 

1, 2. Interior and exterior views of left valve of topotype figured by Stephenson ( 1955. pl. 15. figs. 

4-7), from the Owl Creek Formation at locality 19. USGS 707. USNM 128084. Note 

position of insertion of anterior pedal protractor muscle (AP). 

3-6. Gardner's hypotype of N. slackiana. from the Severn Formation. 1.6 km ( 1 mi) west of 

Friendly in Prince Georges County, Maryland. USNM 131858. 

3, 4. Exterior and interior views of right valve. Note well-developed dorsal median (DM) 

and ventral-median (VM) muscle scars. 

5, 6. Interior and exterior views of left valve. Note the division of the anterior adductor 

into quick (QJ and catch (C) muscles. 

7, 8. Exterior and interior views of right valve of Harbison's holotype of N. tippalzensis, from the 

Coon Creek Tongue of the Ripley Formation at locality 5. USNM 103751. 

9, 10. Interior and exterior views of left valve of a topotype of N. tippahensis Harbison, from the 

Coon Creek Tongue of the Ripley Formation at locality 5. USGS 25411. USNM 423803. 

Note the large number of anterior pedal retractor muscle scars (AR). 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 1 

5 

NUCULA 
PLATE 2 

Comparison of external morphologies of Nucula percrassa Conrad 

Figures 1-11. Nunda percrassa Conrad; all specimens X2. 

I, 2, 4. Specimens of N. percrassa classified as N. s/ackiana Gabb of Gardner for the 

discriminant analysis, from the Severn Formation at locality 25. USGS 28858. 

1. Exterior view of right valve. USNM 423804. 

2. Exterior view of right valve. USNM 423805. 

4. Exterior view of left valve. USNM 423806. 

3, 5, 6, 9. Specimens of N. percrassa Conrad, classified as N. percrassa for the discriminant 

analysis. 

3. Exterior view of right valve, from the Providence Sand at locality 22. USGS 

25935. USNM 423807. 

5. Exterior view of right valve of a topotype, from the Owl Creek Formation at 

locality 19. USGS 707. USNM 20688. 

6. Exterior view of left valve, from the Providence Sand at locality 22. USGS 

25935. USNM 423808. 

9. Exterior view of left valve, from the Coon Creek Tongue of the Ripley Formation 

at locality 4. USNM 32713. Figured by Wade (1926, pl. 8, fig. 1). 

7, 8, 10, 11. Specimens of N. percrassa, classified as N. tippahensis Harbison for the discriminant 

analysis. 

7. Exterior view of left valve, from the Coon Creek Tongue of the Ripley Formation 

at locality 9. USGS 25409. USNM 423809. 

8. Exterior view of right valve, from the Coon Creek Tongue of the Ripley 

Formation at locality 10. USGS 25407. USNM 423810. 

10. Exterior view of left valve of a topotype , from the Coon Creek Tongue of the 

Ripley Formation at locality 5. USGS 25411. USNM 423811. 

11. Exterior view of right valve, from the Coon Creek Tongue of the Ripley 

Formation at locality 10. USGS 25407. USNM 423812. Note strong radial ribs 

exposed by exfoliation of outer shell layers. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 2 

NUCULA 
PLATE 3 

Comparison between upper Maastrichtian specimens of Nucula percrassa Conrad 

and Nucula severnensis Wingard and Sohl, n.sp. (stratigraphic 

level 5, text fig. 6) at various growth stages 

Figures 1- 10. Nucula percrassa Conrad; all specimens X3. 

I. Exterior view of left valve , from the Severn Formation at locality 23. USGS 32775 . USNM 

423813. 

2, 3. Exterior and interior views of right valve , from the Providence Sand at locality 20. USGS 

25921. USNM 423814. 

4, 5. Interior and exterior views of left valve, from the Severn Formation at locality 24. USGS 

32772. USNM 423815. 

6, 7. Exterior and interior views of left valve , from the Owl Creek Formation at locality 16. 

USGS 25424. USNM 423816. 

8. Exterior view of left valve , from the Owl Creek Formation at locality 18 . USGS 25422. 

USNM 423817. 

9. Exterior view of right valve of a topotype , from the Owl Creek Formation at locality 19. 

USGS 6464. USNM 423818. 

10. Interior view of right valve, from the Providence Sand at locality 22. USGS 25935. USNM 

423819. 

11-19. N. severnensis Wingard and Soh!, n.sp. ; all specimens X3. 

11 , 12. Exterior and interior views of right valve of the holotype , from the Severn Formation at 

locality 25. USGS 28858. USNM 423838. 

13. Interior view of right valve of a paratype , from the Severn Formation at locality 23 . USGS 

32775 . USNM 423839 . 

14. Exterior view of left valve of a paratype , from the Severn Formation at locality 23 . USGS 

32775 . USNM 423840. 

15 , 16. Interior and exterior views of left valve of a paratype , from the Providence Sand at locality 

22. USGS 25935 . USNM 423841. 

17. Exterior view of right valve of a paratype , from the Providence Sand at locality 22. USGS 

25935. USNM 423842. 

18 , 19. Interior and exterior views of right valve of a paratype , from the Providence Sand at locality 

20 . USGS 25921. USNM 423843. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 3 

NUCULA 
PLATE 4 

Comparison of Nucula percrassa Conrad arranged tn 

descending stratigraphic order 

Figures 1-10. Nucula percrassa Conrad; all specimens x2. (Text fig. 6 shows stratigraphic levels and exact positions 

of samples.) 

1. Exterior view of left valve of a topotype, from the Owl Creek Formation at locality 19, 

stratigraphic level 5. USGS 707. USNM 20688. 

2. Interior view of right valve , from the Providence Sand at locality 22, stratigraphic level 5. 

USGS 25935. USNM 423820. 

3, 4. Interior and exterior views of right valve, from the Ripley Formation at locality 11, 

stratigraphic level 4. USGS 708. USNM 423821. 

5, 6. Exterior and interior views of right valve classified as Nucula tippahensis Harbison for the 

discriminant analysis, from the Coon Creek Tongue of the Ripley Formation at locality 10, 

stratigraphic level 3. USGS 25407. USNM 423822. Resilifer is broken. 

7, 8. Interior and exterior views of right valve, from the Coon Creek Tongue of the Ripley 

Formation at locality 4, stratigraphic level 2. USGS 25406. USNM 423823. 

9. Exterior view of right valve, from the Blufftown Formation at locality 3, stratigraphic level 1. 

USGS 26033. USNM 423824. 

10. Exterior view of right valve from the Coffee Sand at locality 2, stratigraphic level 1. USGS 

17254. USNM 423825. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 4 

NUCULA 
PLATE 5 

Comparison of four species of Upper Cretaceous Nucula 

Figures I, 5, 6, 8. Nucula cuneifrons Conrad. 

1. Interior view of right valve ( x 1.5), from the Coon Creek Tongue of the Ripley Formation 

at locality 6. USGS 711. USNM 423854. Note oblique inclination of resilifer. 

5. Exterior view of left valve , scanning electron microscope (SEM) ( x 25), from the 

Providence Sand at Ft. Gaines in Clay County, Georgi a. USGS 32250. USNM 423855. 

6. Interior view of left valve (X3), from the Severn Formation at locality 25. USGS 28858 . 

USNM 423856. 

8. Exterior view of right valve ( X4), from the Severn Formation at locality 23. USGS 32775. 

USNM 423857 . Note closely spaced, round-topped - llabral ribs. 

2, 11. N. severnensis Wingard and Sohl , n.sp ., specimens from the Ripley Formation at Mercer's Mill, 

Tobannee Creek in Quitman County , Georgia . USGS 27878 . 

2. Interior view of left valve of a paratype , SEM (X40). USNM 423844. 

11. Exterior view of right valve of a paratype , SEM (X24). USNM 423845. 

3, 10 . N. percrassa Conrad , specimens from the Ripley Formation at Mercer's Mill , Tobannee Creek in 

Quitman County, Georgia. USGS 27878. 

3. Exterior view of right valve, SEM (X 10). USNM 423826. 

10 . Interior view of left valve , SEM (X44). USNM 423827. 

4, 7, 9. N . arnica Gardner. 

4. Exterior view of right valve ( X4), from the Severn Formation at locality 25. USGS 28858 . 

USNM 423858. 

7. Exterior view of left valve , SEM (X20) , from the Severn Formation at locality 25. USGS 

28858 . USNM 423859. Note strong collabral ribs on umbonal region, in contrast to figures 

3, 5, and 11. 

9. Interior view of right valve, SEM X32) , from the Ripley Formation at Mercer's Mill, 

Tobannee Creek in Quitman County, Georgia. USGS 27878 . USNM 423860 . 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 5 

NUCULA 
PLATE 6 

Articulated specimens showing variations in shell obesity 

and lunule and escutcheon morphology 

Figures I, 2, 4-16. Nucu/a percrassa Conrad; all specimens X2. 

I, 4. Dorsal hinge view of specimens classified as N. s/ackiana Gabb of Gardner for the 

discriminant analysis, from the Severn Formation at locality 24. USGS 32772. 

I . USNM 423828. 

4. USNM 423829. 

2. Dorsal hinge view of specimen classified as N. tippahensis Harbison for the 

discriminant analysis, from the Coon Creek Tongue of the Ripley Formation at 

locality 6. USGS 711. USNM 20843. 

5, 7, 8. Topotype specimen classified as N. percrassa for the discriminant analysis, from 

the Owl Creek Formation at locality 19. USGS 707. USNM 20688. Youthful 

specimen does not exhibit shell thickening characteristic of more mature members 

of the population. 

5. Dorsal hinge view. 

7. Posterior view. 

8. Anterior view. 

6, 9, 10. Topotype specimen classified as N. percrassa for the discriminant analysis, from 

the Owl Creek Formation at locality 19. USGS 707. USNM 20688. Specimen 

illustrates senile characteristic of shell thickening, which produces a flattened 

ventral margin. 

6. Dorsal hinge view. 

9. Posterior view. 

10. Anterior view. 

11, 13, 14. Specimen classified as N. percrassa for the discriminant analysis, from the Owl 

Creek Formation at locality 17. USGS 713. USNM 20802. Specimen exhibits a 

lesser degree of shell thickening than the topotype specimen in figures 9, 10, and 

12. 

11 . Dorsal hinge view. 

13. Posterior view. 

14. Anterior view. 

12, 15, 16. Specimen classified as N. percrassa for the discriminant analysis, from the 

Providence Sand at locality 22. USGS 25935. USNM 423830. 

12. Dorsal hinge view. 

15. Posterior view. 

16. Anterior view. 

3. Nucu/a severnensis Wingard and Soh!, n.sp. (X3); dorsal hinge view of a paratype, from the 

Providence Sand at locality 20. USGS 25921. USNM 423846. 
U.S. GEOLOGICAL SURVEY BULLETIN 1881-D, PLATE 6 

NUCULA 
PLATE 7 

Adductor and pedal muscle scar systems 

Figures 1, 2, 4- 11. Nucula percrassa Conrad. 

1. Latex mold ( x 1.5) of left valve interior of a topotype, from the Owl Creek 

Formation at locality 19. USGS 25423. USNM 423831. 

2. Latex mold ( x 2) of left valve interior of specimen, from the Coon Creek Tongue of 

the Ripley Formation at locality 4. USGS 25406. USNM 423832. 

4, 9. Internal mold (X2), from the Prairie Bluff Chalk at Braggs in Lowndes County, 

Alabama. USGS 30669. USNM 423833. 

4. View of right valve interior. 

9. Dorsal hinge view. 

5, 6. Latex molds (X 1.5) of specimens, from the Ripley Formation at locality 13. USGS 

857. 

5. Right valve interior. USNM 423834. 

6. Left valve interior. USNM 423835. 

7. Dorsal hinge view of internal mold ( x 2), from the Prairie Bluff Chalk at Braggs in 

Lowndes County, Alabama. USGS 30668. USNM 423836. 

8, 10, 11. Articulated specimen ( X2), from the Coon Creek Tongue of the Ripley Formation at 

locality 4 .USGS 25406. USNM 423837. 

8. Interior view through the ventral shell gape of hinge, resilifer, and muscle 

scars. 

10. Interior view through the ventral shell gape of the muscle scars of the right 

valve. 

11. Interior view through the ventral shell gape of the muscle scars of the left 

valve. 

3. Nucula severnensis Wingard and Sohl, n.sp. Latex mold (X 2) of right valve interior of specimen, 

from the Providence Sand at White Oak Creek at the Barbour-Henry County line, Alabama (near 

loc. 20). USGS 25993. USNM 423847. 

AA, anterior adductor; AP, anterior protractor; AR, anterior pedal retractor; C, catch portion of adductor muscle; OM, 

dorsal-median muscle; PA, posterior adductor; PE, pedal elevator muscle; PR, posterior pedal retractor; Q, quick 

portion of adductor muscle; VM, ventral median muscle. 
U.S. GEOLOGICAL SURVEY 

NUCULA 

BULLETIN 1881-D, PLATE 7 

OM 

PE 

Chapter E 

HUM Lithosome: An 

Example of Regional 

Stratigraphic Synthesis in the 

Mississippian of the Western 

Interior of the United States 

By WILLIAM j. SANDO 

Development of a regional depositional model using the 

I ithosome concept 

U.S. GEOLOGICAL SURVEY BULLETIN 1881 

Shorter Contributions to Paleontology and Stratigraphy 

CONTENTS 

Abstract El 

Introduction El 

Acknowledgments E2 

Lithosomes E2 

Definition E2 

Operational procedure E3 

HUM lithosome E3 

Reference section and definition E3 

Regional relations with other lithosomes E3 

Chronometric regional geometry E7 

Thickness variation E7 

Origin E7 

References cited E14 

PLATE 

1. Chronometric lithofacies profiles of the HUM lithosome. Upper Mississippian of 

Utah, Idaho, and Wyoming, Western Interior region of the United States (In 

pocket) 

A. Profiles A-A', B-B', and C-C' across the depositional strike of the HUM 

lithosome 

B. Profile D-D' along the depositional strike of the HUM lithosome 

FIGURES 

1. Reference section of the HUM lithosome near Twelve Mile Pass, Tooele County, 

Utah E4 

2. Mississippian time scale and biozonations used in chronometric analysis of the HUM 

lithosome ES 

3. Chronometric interval map showing the areal distribution of the HUM lithosome E6 

4. Map showing thickness variation of the HUM lithosome E13 

TABLES 

1. Catalog of stratigraphic section control points for figures 3 and 4 and plate 1A and 

1B ES 

2. Correlations and reference sections for other lithosomes shown on plate 1A and 

1B E12 

Contents Ill 

HUM Lithosome: An Example of Regional 

Stratigraphic Synthesis in the Mississippian of the 

Western Interior Region of the United States 

By William J. Sando 

Abstract 

The rules governing formal stratigraphic nomenclature are justifiably committed to producing a stable classification based on geologic mapping and mappability. 

However, regional stratigraphic syntheses based on correlation of stratigraphic sections may conflict with the 

classification of rock units founded on geologic mapping. 

When a conflict occurs, it may be difficult to resolve 

without abandoning useful geologic maps or remapping 

the geology. The lithosome concept affords a practical 

solution to problems of stratigraphic nomenclature that 

arise from regional stratigraphic studies of Mississippian 

rocks in the Western Interior of the United States. 

The informal term lithosome refers to a vertically and 

horizontally segregated body of sedimentary rock, characterized by its lithic content and inferred genetic significance, that mutually intertongues with one or more rock 

bodies of different lithic constitution. An analysis of the 

HUM lithosome in the Upper Mississippian of Utah, 

Idaho, and Wyoming is an example of how the lithosome 

concept can be used to communicate ideas about regional 

stratigraphic and depositional relationships. 

The HUM lithosome is a large body of marine quartz 

sandstone and subtidal carbonate rock in the Antler foreland basin of the Western Interior. It is composed mostly 

of terrigenous detritus supplied by rivers that carried this 

sediment westward across the Madison paleokarst plain 

from sources in the Transcontinental arch area to the 

Antler basin in Late Mississippian time. The HUM has the 

form of an offshore delta shelf deposit similar to that of 

the present Nile delta, but no deltaic plain deposits are 

preserved. Carbonate factories that originated on local 

sea-floor highs and on a large positive area in Idaho and 

northern Utah contributed significant amounts of carbonate sediment to the HUM depositional complex. 

INTRODUCTION 

Formal lithostratigraphic units recognized in the Mississippian of the Western Interior region traditionally have 

been founded on geologic mapping. Most of the older units 

Manuscript approved for publication November 16. 1988. 

currently in use were originally defined and named in 

mining districts in order to describe local geologic history, 

interpreted from geologic mapping, before the advent of 

regional stratigraphic studies. Extensions of these units 

beyond their type localities commonly resulted from subsequent mapping that proceeded radially from these nomenclatural centers with limited information available to determine regional implications. Regional geologic maps (2° 

sheets and State maps) compiled from quadrangle maps and 

other local maps extended the formal nomenclature. This 

procedure resulted in a stable formal stratigraphic nomenclature that is deeply ingrained in the common geologic 

language of the area. 

The benefits of this historical development of the 

lithostratigraphic nomenclature are obvious. The inherent 

stability of the nomenclature minimizes problems in communication among most geologists working in the region. 

The names of the units depicted on most maps are familiar 

to all. and most geologists need not concern themselves 

with new names or new combinations of old names when 

they want to work in a given local area. 

Regional stratigraphic synthesis based on correlation 

of stratigraphic sections may result in recognition of rock 

units that do not coincide with units recognized on existing 

geologic maps. The requirements of geologic mapping for 

definition and identification of rock units tend to emphasize 

criteria of local rather than regional significance. The 

mapping geologist must deal with the entire geologic 

sequence of the map area, whereas the regional stratigrapher focuses on only a small fraction of that sequence. 

Inferred geologic history, depositional environment, and 

age relationships, which are prohibited by the North American Stratigraphic Code (North American Commission on 

Stratigraphic Nomenclature, 1983) as criteria for defining 

formal rock units, may be useful assets for the regional 

stratigrapher. Regionally significant rock units too thin to 

be mapped at conventional mapping scales may be obscured 

by inclusion in larger formal units recognized for mapping. 

Nomenclatural precedence established by previous mapping 

may effectively limit changes in stratigraphic classification 

based on new evidence or reinterpretation of old evidence. 

HUM Lithosome: An Example of Regional Stratigraphic Synthesis E1 
My regional stratigraphic analyses of the Western 

Interior Mississippian have now reached a stage of development where it has become almost impossible to communicate new regional lithostratigraphic concepts without 

drastically altering much of the stable formal lithostratigraphic classification recognized widely by other geologists. In most cases, the regional synthesis has resulted in 

the consolidation of local units into areally more extensive 

regional units and the consequent abandonment of some 

older names, some of which were proposed by myself and 

my colleagues in earlier studies. Occasionally, the need for 

new names to designate previously unrecognized units has 

been indicated. New concepts of geologic history and 

depositional environment inferred from the rocks have 

played a major role in the definition and recognition of the 

rock bodies. 

The North American Stratigraphic Code (North 

American Commission on Stratigraphic Nomenclature, 

1983, p. 850-851 ) has provided a solution to this dilemma 

by permitting the use of various kinds of informal stratigraphic units for "innovative approaches in regional stratigraphic studies." H.E. Wheeler and V.S. Mallory (in 

Fischer and others, 1954: also Wheeler and Mallory, 1956), 

faced with the same dilemma, proposed the term "lithosome'' to address the same problems that I have encountered. This paper presents a procedure for using lithosomes 

as informal units to describe regional stratigraphic relations 

in the Mississippian of the Western Interior. 

Acknowledgments 

Early fieldwork on the HUM sequence was done in 

the company of J.T. Dutro, Jr., to whom I am indebted for 

many contributions to the basic data in Idaho, western 

Wyoming, and northern Utah. I am likewise indebted to 

C.A. Sandberg and R.C. Gutschick for their contributions, 

made during joint field studies in Utah and Idaho. I thank 

Mackenzie Gordon, Jr., for sharing with me his data on 

critical stratigraphic sections in Utah. I am grateful to K.R. 

Moore for dedicated assistance in field and laboratory. I 

thank B .L. Mamet for foraminiferal zone determinations 

and Sandberg for conodont zone determinations. My thanks 

are also extended to Dutro, G.A. Izett, W.J. Perry, J.A. 

Pierce, F.G. Poole, N.F. SohL D.J. Stanley, J.I. Tracey, 

and B.R. Wardlaw for stimulating discussions of the 

concepts and for technical review of the manuscript. 

LITHOSOMES 

Definition 

Lithosome is one of the many terms that were coined 

during the published discussions of stratigraphic nomenclaE2 Shorter Contributions to Paleontology and Stratigraphy 

ture that preceded formulation of the American Code of 

Stratigraphic Nomenclature by the American Stratigraphic 

Commission (1961 ). Wheeler and Mallory (1953) called 

attention to the interrelations of rock units that affect 

definitions of formal stratigraphic units and focused on 

recognition of the arbitrary cutoff as a principle in defining 

formal units. A critique of this concept by A. G. Fischer (in 

Fischer and others, 1954) led Wheeler and Mallory (in 

Fischer and others, 1954, p. 929) to propose the term 

lithosome to distinguish lithic units that are "verticolaterally" segregated (group, formation, member) as 

opposed to those that are laterally segregated (facies). As a 

followup to the 1954 debate, Wheeler and Mallory (1956) 

presented an expanded discussion of these two kinds of 

lithic unit and formally defined the term lithosome as "a 

lithostratigraphic body which is mutually intertongued with 

one or more bodies of differing lithic constitution" (Wheeler 

and Mallory, 1956, p. 2719). 

Moore (1957, p. 1787-1789) altered Wheeler and 

Mallory's original definition of lithosome to read "(I) an 

independent body of genetically related sedimentary deposits of any sort, or, alternatively, (2) a spatially segregated 

part of any genetically related body of sedimentary deposits, in which this part is distinguished by some noteworthy 

characters or combination of characters judged important 

enough to merit separation." Moore believed that lithosome 

is a synonym of Caster's (1934) magnafacies, which was 

defined as ''a major, continuous, and homogeneous belt of 

deposits that is distinguished by similar lithologic and 

paleontologic characters and that extends obliquely across 

time planes or through several defined chronostratigraphic 

units" (Bates and Jackson, 1980, p. 375). Moore's definition of lithosome deemphasized the intertonguing character 

of its lateral margins and injected genetic homogeneity into 

the concept. 

Weller (1958, p. 613) rejected Caster's magnafacies 

as a useful term because he believed that it is merely a 

"rock-stratigraphic unit' coinciding with formation, group, 

or member, depending on the size of the rock body to which 

it is applied.'' Weller (1958, p. 635-636) also rejected the 

term lithosome because he concluded that it would have 

little practical application and that it coincided essentially 

with the terms lithofacies and facies. L.L. Sloss (in Weller, 

1958, p. 624) defined lithosome as a "body of sediment 

deposited under uniform physico-chemical conditions." 

The lithosome, as originally conceived by Wheeler 

and Mallory, offers a practical solution to the problem of 

distinguishing natural rock bodies that have been given 

different formal names (group, formation, member) in 

different geographic areas because of the historical development of the nomenclature. Although almost all lithostratigraphic units are inherently diachronous, Caster's magnafacies does not seem appropriate as a general term for such 

rock bodies, because it refers to a facies geometry characterized by large-scale diachroneity. The essential character-
istics of a lithosome embodied in Wheeler and Mallory's 

( 1956) original definition and augmented by Moore ( 1957) 

and Sloss (in Weller, 1958) are (1) lithic identity, (2) 

vertical and lateral segregation, (3) genetic identity, and (4) 

intertonguing relationships with other bodies of differing 

lithic constitution. I propose a revised definition of lithosome as a vertically and horizontally segregated body of 

sedimentary rock, characterized by its lithic content and 

inferred genetic significance. which mutually intertongues 

with one or more bodies of differing lithic constitution. A 

lithosome may or may not be demonstrably diachronous as 

measured by its transgression of time planes based on 

biozones or physical means of measuring time. Mappability 

is not a requirement for recognition of a lithosome. 

Operational Procedure 

Communicating concepts of regional stratigraphic 

and depositional models by means of lithosomes is facilitated by using a system of nomenclature independent of the 

formal stratigraphic classification in order to avoid confusion between the two systems. However, because most 

lithosomes are lithologically and stratigraphically equivalent to formal stratigraphic units at some localities. recognition is enhanced by using names related to familiar formal 

names. In this paper. a lithosome name is derived by 

contracting the geographic name of the formal stratigraphic 

unit that is most typical of the lithosome and printing it in 

capital letters. The reference section for a lithosome may be 

the type section of a formal stratigraphic unit, or it may be 

a more representative locality discovered during later 

regional studies. 

In the example described below, I have chosen the 

name HUM lithosome, derived from the Humbug Formation of Utah, to designate a body of quartz sandstone and 

carbonate rock in the Upper Mississippian of Utah, Idaho, 

and Wyoming. The HUM lithosome is founded on a 

reference section where its vertical boundaries coincide 

with those of the formal unit. The HUM lithosome is then 

projected from its reference section into other areas by 

analyzing detailed stratigraphic sections. Age relationships 

of its vertical boundaries are determined biometrically, 

where possible, or by lithostratigraphic correlation with 

sections where the boundaries are dated by fossils. Lateral 

boundaries are determined by regional lithostratigraphic 

analysis of the total time interval occupied by the lithosome 

throughout its lateral extent. 

HUM LITHOSOME 

Reference Section and Definition 

The reference section for the HUM lithosome is on 

the south side of Topliff Hill, near Twelve Mile Pass, at the 

north end of the East Tintic Mountains in central Utah, 

where it coincides with the Humbug Formation (Tower and 

Smith, 1899) as mapped by Morris and Lovering (1961). A 

stratigraphic section measured by Mackenzie Gordon, Jr., 

H.M. Duncan. and H.T. Morris (fig. 1) serves as a 

description of the reference section. The HUM lithosome in 

this section is composed of approximately 200 m of fine- to 

medium-grained calcareous quartz sandstone interbedded 

with mostly subtidal and fossiliferous limestone and sandy 

limestone. Corals, brachiopods, and foraminifers, which 

are the most common fossils, indicate a zonal range of 

Composite Zones 17 to 18 in the zonation system of Sando 

(1985) (fig. 2). This zonal range places the HUM in the 

Upper Mississippian (middle and late Visean of the European scale) at the reference locality. 

The HUM lithosome in its reference section is overlain by the GREAB lithosome and underlain by the UNJO 

lithosome, units that coincide with the Great Blue Limestone and the Uncle Joe Member of the Deseret Limestone, 

respectively, as mapped by Morris and Lovering (1961) in 

the Tintic district. 

Regional Relations with Other Lithosomes 

The HUM lithosome occupies a large area in southeast Idaho. western Wyoming, and Utah (fig. 3), where it is 

composed of rocks currently mapped as Humbug Formation 

over most of Utah and includes parts of the Brazer Limestone in northern Utah; parts of the Wells Formation in 

northeast Utah, western Wyoming, and southeast Idaho; 

parts of the Little Flat and Aspen Range Formations in 

southeast Idaho; and a part of the Amsden Formation in 

western Wyoming (pl. 1A, 1B). It is bounded on the west 

by laterally equivalent rocks of the WOOM lithosome, 

which includes strata currently mapped as Woodman Formation (western Utah), Great Blue Limestone (western 

Utah), Chainman Shale (western Utah and eastern Nevada), 

and Deep Creek Formation (southeast Idaho). On the east, 

the HUM lithosome interfingers with the DAR lithosome, 

which includes strata currently mapped as Darwin Sandstone Member of the Amsden Formation (western Wyoming), Morgan Formation (northwest Colorado), and Molas 

Formation (southwest Utah). 

Detailed descriptions and discussion of the many 

lithosomes that were deposited during the total time interval 

of HUM deposition in the study area are beyond the scope 

of this report. The relations of these units to formal 

stratigraphic units in control sections are shown on plate 

1A and 1B. Table 2 provides data on the locations of the 

reference sections of these lithosomes and their relations to 

formal stratigraphic units in the reference sections. 

HUM Lithosome: An Example of Regional Stratigraphic Synthesis E3 
U) 

a: 

w 

tl:i 

~ 

(/) 

(/) 

w 

z 

~ 

~ 

I 

I200-

-600 

150-- 500 

100-

50-

-400 

-300 

- 200 

1- 100 ItItItItto-~o 

w 

~ 

0 

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0 

I 

1-

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uw _a: 

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13 

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u...uu:::: w cn....Ju 

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f;;:21216 

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f- 21214 

z 

0 

i= 

<( 

z 

0 

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Q 

Cil 

, lndet [> 14 or 15 > IV 

t- 14 or 15 

_l J ~14 [> 21213 ~ 14 or 15 I> IV 

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25 

f- 21209 f- lndet. t- IIID 

35 

- 21208 -14 f- IIID 

E4 Shorter Contributions to Paleontology and Stratigraphy 

18 

17 

EXPLANATION 

Limestone. 

subtidal 

Limestone, 

algal 

Limestone, 

sandy 

Dolomite, 

fine-grained 

Dolomite, 

sandy, and 

dolomitic 

sandstone 

~ Quartz 

sandstone, 

regularly 

bedded 

[B 

Quartz 

sandstone, 

cross bedded 

J oooJ 

Limestone 

pebbles 

Chert 

nodules 

D 

Covered 

Figure 1. Reference section (UT-104) of the 

HUM lithosome near Twelve Mile Pass, 

NE1J4 sec. 22, T. 8 5., R. 3 W., Tooele 

County, Utah. Fossil collections and 

description of stratigraphic section by 

Mackenzie Gordon, Jr., H.M. Duncan, and 

H.T. Morris; foraminiferal zone determinations by B.L. Mamet. Fossil collections are 

at the U.S. National Museum of Natural 

History, Washington, D.C. PC refers to the 

Permian and Carboniferous locality file. 
w en ....J (/) 

~ <( z w (/) 

u <( z zCil z w w (/) w <( <(~ 0 (/) z l-en w w £l.. u ua: N 0 enw z ~ 0 ii:Cil -W 0 1-(/) N 

>-- 0:(/) 0:(/) iij 0 0 en a: i= w~ w Zw N :JW iij w ~w ~....J Oz 0 zen u'CO w(!J a: co z~ <(I- '<( ~ w iij w -~ (/) u u.. ON 1- <to 1-

a:- 0:(/) I~ IZ z zo ....J 

wz Ci5 w w f-Cil 1-- o- <( 0 

g,<t: ~ 1- a: a:> ~ ucn a: £l.. 

0 (/) 0 oo <( 0 a: w z za: u ~ 

C5 ~ £l.. a: 0 ::::::) 0 u UJ <( u.. a: 

z Idiognathoides sinu-

<( at ns-N eognathodns 0 0 

~i= symmeh'icus w w 20 z z i=' oa: (Part) 0 0 a: a:<( N N C:£l.. Declinognathodus z z <t o- nodulzfe1·us :::> :::> e:. ~ 

en Rhachistognatlws primus ::J 

0 

a: 

w 

u.. Adetognathus 

z nnicornis VI 

0 

CD 

a: 

<t: 

u 

a: 18 

w Cauu.sgnath ns a.. altus- a.. 

::::::) Gnathodns B girtyi 

v 

Ccwu.sgnathus altus- A Hindeodus cristulns 

CaPnsgnathns altusHindeodus IV 

penescitulns 

Taphmgnathns D en 16 ::J ual'ians 

0 c 15 a: 

w 

u.. 

z B 14 

0 III 

CD 

a: Gnathodns <t: 

u te.ranus 13 

a: 

w 

~ 

0 

....J 

Figure 2. Mississippian time scale and biozonations used in 

chronometric analysis of the HUM lithosome (from Sando, 

1985). Shading denotes part of the scale not involved in this 

study. 

HUM lithosome: An Example of Regional Stratigraphic Synthesis E5 
I 

I 

I 

I 

I ',1 ~---~---M K:----<-

1'\. 

I 

I~ "' 

~~~ <t:l<t: >rE-

~~:J 

I 

I 

I 

r 

I 

I 

I 

I 

~--141 

0 

I I 11 

0 

I 

50 

50 

I I 

100 KILOMETERS 

100 MILES 

I 

Figure 3. Areal distribution of the HUM lithosome. Description of stratigraphic section control points 

is given in table 1. Structural features are from Gutschick and others (1980) and Craig and others (1979). 

E6 Shorter Contributions to Paleontology and Stratigraphy 
1\N\ __ 

EXPLANATION 

Mississippian rocks never. deposited or removed by subsequent 

erosion 

Mississippian rocks absent or buried beneath thick Cretaceous 

and Tertiary extrusive and sedimentary rocks 

HUM lithosome, including sandy carbonate facies 

WOOM lithosome 

Land during HUM time 

HUM lithosome removed by local erosion 

Lateral contact of HUM lithosome with WOOM lithosome and of 

sandy carbonate facies with main body of HUM dashed 

where inferred, sawteeth indicate interfingering 

Post-Mississippian thrust fault, dashed where inferred, sawteeth 

on upper plate 

Post-Mississippian lateral fault, dashed where inferred, arrows 

show relative movement 

Position of shore line late in HUM time, dashed where 

approximately located, hachures on landward side 

~ Majorriver 

'-=A'----.L!A' Chronometric lithofacies profile 

@ Outcrop control point, circle indicates reference section 

Subsurface control point 

Figure 3. Explanation. 

Chronometric Regional Geometry 

Chronometric lithofacies profiles across (pl. 1A) and 

along (pl. 1B) the regional depositional strike and a chronometric interval map depicting the entire areal extent of the 

lithosome (fig. 3) define the form of the HUM lithosome in 

time and space. On the interval map (fig. 3), the lithosome 

appears as a lobate body of quartz sand and sandy carbonate 

that extends westward from the shoreline of the Madison 

paleokarst plain in southwest Wyoming, northwest Colorado, and southeast Utah (see Sando, 1988, for a description of the paleokarst) to interfinger with fine terrigenous 

sediment of the WOOM lithosome, which was deposited in 

deeper water in western Utah and southern Idaho. A large 

carbonate bank that competed for depositional space with 

the sand was present in southeast Idaho and northern Utah. 

In cross-strike profiles (pl. lA), the HUM appears to 

have the form of a clastic wedge that tapers to extinction 

westward from the ancient shoreline. Because the vertical 

dimension of these profiles is time, the wedge-shaped form 

represents variation in the time of deposition rather than in 

sedimentary thickness. The wedge represents the balance 

that existed through HUM time between westward progradation of the sediment and eastward transgression of the 

sea. A profile along the depositional strike (pl. 1B) shows a 

generally tabular body that bulges notably in central Utah 

opposite a major reentrant in the shoreline in eastern Utah, 

which probably marks the mouth of a major river system 

that contributed much of the terrigenous sediment in the 

HUM. 

The base of the HUM ranges in age from the base of 

Composite Zone 14 (ca. 347 Ma) to the top of Composite 

Zone 17 (ca. 340 Ma) (pl. 1A, 1B). The oldest rocks in the 

lithosome occur adjacent to the shoreline reentrant in 

northeast Utah and in the offshore area in northeast Utah 

and southeast Idaho. The top of the HUM ranges in age 

from the top of Composite Zone 17 (ca. 340 Ma) into the 

Lower Pennsylvanian (Morrowan, ca. 318 Ma). However, 

HUM deposition was limited to Composite Zone 22 (ca. 

329 Ma) or older zones over most of its areal extent, except 

for the area immediately adjacent to the shoreline in 

northeast Utah and southwest Wyoming. Thus, although the 

maximum time of HUM deposition was approximately 29 

m. y., most of the lithosome was deposited over a time span 

of approximately 18 m.y. 

Thickness Variation 

An isopach map of the HUM lithosome (fig. 4) 

reveals a morphology that is generally inverse to that of the 

chronometric profiles. In this perspective, the HUM thickens westward from the ancient shoreline before interfingering with the WOOM on the west. The area of thickest 

sediment is in central and northern Utah near the western 

edge of the lithosome and opposite the pronounced shoreline reentrant. Some distortion of the regional isopach 

pattern is evident in southeast Idaho and northern Utah 

owing to the influence of the carbonate bank in that area. 

Several peculiar areas of anomalous thickness are evident a 

few tens of kilometers seaward from the ancient shoreline. 

Origin 

The provenance of the terrigenous detritus that forms 

the bulk of the HUM lithosome was the Transcontinental 

arch, a mountainous area east of the Madison paleokarst 

plain (Sando, 1988). The paucity of fine terrigenous detritus 

and the maturity of the sediment suggest that supermature 

lower Paleozoic sandstones were the principal source rocks 

(Mallory, 1967, p. G25-G27). This material was transported to the area of deposition by rivers that flowed across 

the paleokarst plain in Wyoming and Colorado (Mallory, 

1967; Sando, 1988). Some of these rivers have been 

mapped in Wyoming (Mallory, 1967; Sando, 1988), but a 

HUM lithosome: An Example of Regional Stratigraphic Synthesis E7 
Table 1. Catalog of stratigraphic section control points for figures 3 and 4 and plate 1A and 18 

Number Name 

C0-4 ...... Hells Canyon 

C0-10 ..... Jones Hole 

ID-2 ....... Black Pine Mountains 

ID-7 ....... Bannock Creek 

ID-8 ....... Paul Peak 

ID-9 ....... Gardner Canyon 

ID-13 ...... Big Canyon 

ID-14 ...... North Georgetown Canyon 

ID-15 ...... Wide Hollow 

ID-16 ...... Little Flat Canyon 

ID-17 ...... Wells Canyon 

ID-18 ...... Dry Ridge 

ID-21 ...... Little Gray Ridge 

ID-22 ...... Wolverine Canyon 

ID-23 ...... Fall Creek 

ID-25 ...... Sheep Creek 

ID-27 ...... Soda Springs Hills 

ID-61 ...... Ladd 3-24 Bennington 

ID-64 ...... Phillips No. 1 Unit 

Horseshoe Creek. 

UT-1 ....... Needle Range 

UT-2 ...... . Buckhorn Canyon 

UT-3 ....... Ophir Canyon 

Location Source 

Colorado 

Sec. 31. T. 6 N .. R. 102 W., Moffat County Thomas and others (1945) 

T. 9 N., R. 103 W .. Moffat County Bloom (1961) 

Idaho 

Sec. 25. T. 15 S .. R. 28 E .. Cassia County Smith (1983). W.J. Sando (unpublished field 

notes.l975 ). 

Sees. 12 and 13. T. 9 S.,R. 33 E .. Power 

County. 

SNE sec. 28. T. 10 S., R. 34 E .. Power 

County. 

S sec. 11 and W sec. 12. T. 16 S., R. 35 E .. 

Oneida County. 

S line SW 7. T. 10 S .. R. 44 E., Bear Lake 

County. 

Sees. 16 and 21, T. 10 S., R. 44 E .. Bear 

Lake County. 

Sees. 35 and 36, T. 9 S .. R. 39 E .. Caribou 

County. 

Sees. 17. 20. and N 29. T. 7 S., R. 40 E .. 

Caribou County. 

SW sec. 11 and SE sec. 10, T. 10 S .. R. 45 

E .. Caribou County. 

SENW sec. 6. T. 9 S., R. 45 E .. Caribou 

County. 

Sec. 18. T. 5 S., R. 43 E. ,Caribou County 

Sees. 1. 2. 10. 1 L T. 2 S .. R. 38 E .. 

Bingham County. 

SE sec. 8. T. 1 N .. R. 43 E .. Bonneville 

County. 

E sec. 28. T. 1 N .. R. 45 E .. Bonneville 

County. 

Sec. 19. T. 8 S .. R. 41 E .. Caribou County. 

SESW sec. 3, T. 12 S .. R. 43 E .. Bear Lake 

County. 

Sec. 28, T. 5 N .. R. 44 E .. Teton County 

Utah 

NW sec. 13 and SE sec. 26. T. 25 S. R. 19 

W., Millard County. 

NE 2 sec. 2 and WNWNW sec.l, T. 10 S .. 

R. 12 W .. Tooele County. 

SE sec. 22 and sec. 27. T. 5 S ... R. 4 W .. 

Tooele County. 

Trimble and Carr (1976) 

L.C. Quinn (written communication, 1981) 

Be us ( 1968). Gutschick and others ( 1980). 

Sandberg and Gutschick (1984). W.J. 

Sando (unpublished field notes. 1981, 

1982). 

Sandberg and Gutschick (1984). C.A. Sandberg (written communication. 1980). W.J. 

Sando (unpublished field notes. 1980). 

Gutschick and others ( 1980). Sando and others 

(1981 ). 

W. J. Sando (unpublished field notes. 1962, 

1982). 

Dutro and Sando (1963), Gutschick and others 

(1980), Skipp and others (1979). Sandberg 

and Gutschick (1984). 

Cressman (1964). Coffin (1982), W .J. Sando 

(unpublished field notes. 1958, 1980, 1981, 

1982). 

W.J. Sando (unpublished field notes. 1982) 

W.J. Sando (unpublished field notes. 1982) 

Allmendinger (1980). W.J. Sando (unpublished field notes. 1981, 1982). Sandberg 

and Gutschick (1984). 

W.J. Sando (unpublished field notes. 1982) 

Sando (1977), Sando and Dutro (1981) 

Armstrong (1969), W.J. Sando (unpublished 

field notes, 1982). 

G.S. Campbell (written communication, 

1980). 

Espach and Royse ( 1960) 

Gould (1959). Newman (1972). Hintze 

(1975). Sandberg and Gutschick (1980, 

1984), Gutschick and others (1980). Sandberg and others ( 1982). 

Staatz and Carr ( 1964). Poole and Sandberg 

(1977). Sandberg and Gutschick (1980. 

1984), Gutschick and others (1980). W.J. 

Sando (unpublished field notes. 1976, 

1977). 

Moyle (1959). Morris and Lovering (1961). 

Poole and Sandberg ( 1977). Sandberg and 

Gutschick ( 1980. 1984). Gutschick and others. 1980), Mackenzie Gordon, Jr. (unpublished field notes, 1953 ). 

UT-4 ....... Fitchville Ridge-Mammoth NW and SE sec. 19. T. 10 S., R. 2 W .. Juab Morris and Lovering (1961), Hintze (1975), 

Peak-Sioux Peak. County. Gutschick and others ( 1980). 

E8 Shorter Contributions to Paleontology and Stratigraphy 
Table 1. Catalog of stratigraphic section control points for figures 3 and 4 and plates 1A and 18-Continued 

Number Name 

UT-5 ....... Rock Canyon 

UT -6 ....... The Peak 

UT-7 ....... Samak 

UT-8 ....... Brazer Canyon 

UT -9 ....... Emma Canyon 

UT-10 ..... Rex Peak 

UT -12 ..... Ogden Canyon 

UT-16 ..... Rhodes Canyon 

Location 

Utah-Continued 

NE sec. 28 and NW sec. 27, T. 6 S., R. 3 

E.. Utah County. 

SWSE sec. 15. T. 3 S., R. 4 E., Wasatch 

County. 

SNENE sec. 25, T. 2 S., R. 6 E .. Summit 

County. 

Sec. 20. T. 11 N .. R. 8 E .. Rich County 

Sec. 17, T. 11 N., R. 8 E .. Rich County 

N sec. 31. T. 11 N., R. 8 E .. Rich County 

E sec. 17 and NESW sec. 16, T. 6 N .. R. 1 

E .. Weber County. 

SW sec. 3, T. 1 N .. R. 9 W .. Duchesne 

County. 

Source 

Baker (1947), Baker and others (1949), Newman (1972), Sandberg and Gutschick 

(1979, 1980), Chamberlain (1981), Gutschick and others (1980). 

Gutschick and others ( 1980) 

Dockal ( 1980), Gutschick and others ( 1980). 

Sandberg and Gutschick (1980), W.J. 

Sando (unpublished field notes, 1977, 

1978, 1980). 

Sando and others (1959), Sandberg and Gutschick ( 1979, 1984), Gutschick and others 

(1980), Norris (1981 ). 

Sando and others (1959) 

Sando and others ( 1959) 

W.J. Sando (unpublished field notes, 1961), 

B. Griffey (written communication, 1983). 

Hintze (1975), Dockal (1980) 

UT -1 7 ..... Duchesne River 1 W sec. 6 and N sec. 7. T. 1 N .. R. 8 W.. Dockal (1980) 

UT -19 ..... White Rocks 

UT-20 ..... Little Brush Creek 

UT-21 ..... Jones Hole 

UT-25 ..... Duchesne River 2 

UT-26 ..... Diamond Gulch 

UT -28 ..... Sols Canyon 

UT-29 ..... Gulf Ute Federal 1 

UT -30 ..... Split Mountain 

UT -31 ..... Whirlpool Canyon 

UT-32 ..... Phillips Two-Waters 1 

UT-33 ..... Phillips Watson B-1 

UT-34 ..... Equity Mounds Govt. 1 

UT-35 ..... Cities Service Govt. 1 

Grassy Trail. 

Duchesne County. 

SE sec. 1. T. 2 N., R. 1 W .. W sec. 7. T. 2 

N .. R. 1 E .. NW sec. 12,T. 2 N .. R. 1 

W .. SW sec. 7 and NW sec. 18. T. 2 N., 

R. 1 E., Uintah County. 

SE sec. 24 and NE sec. 25, T. 1 S., R. 21 

E., Uintah County. 

SENE sec. 13 and SWNE sec. 1, T. 3 S., R. 

25 E., Uintah County. 

SW sec. 17 and SW sec. 18, T. 1 N., R. 8 

W .. and SW. sec. L T. 1 N .. R. 9 W .. 

Duchesne County. 

SE sec. 7, SE sec. 19. SE sec. 29, and NW 

sec. 32. T. 1 S., R. 23 E., Duchesne 

County. 

Sec. 11. T. 2 N., R. 18 E., Dagget County 

Sec. 12, T. 4 S .. R. 22 E., Uintah County 

Sees. 9 and 10. T. 4 S., R. 24 E., Uintah 

County. 

Sec. 27, T. 3 S .. R. 25 E., Uintah County 

Sec. 22. T. 14 S., R. 25 E .. Uintah County 

Sec. 34. T. 9 S., R. 25 E., Uintah County 

Sec. 33. T. 15 S., R. 12 E., Carbon County 

Sec. 1. T. 16 S., R. 12 E., Emery County 

UT--43 ..... Mountain Fuel Supply Sec. 18. T. 26 S., R. 7 E .. Emery County 

South Last Chance 

Unit 1-A. 

UT--44 ..... Shell Miller Creek 1 Sec. 26, T. 15 S., R. 10 E .. Carbon County 

UT-71 ..... Three States No. 1 Sinbad Sec. 6, T. 22 S. R. 12 E .. Emery County 

UT-72 ..... Reynolds No.1 Cedar Mesa Sec. 19. T. 19 S., R. 12. E., Emery County 

UT-79 ..... Texaco No. 1 Thousand 

Lake Mountain. 

UT-88 ..... Blawn Mountain 

UT -89 ..... Shauntie Hills 

UT-91 ..... Elephant Canyon 

SW sec. 11. T. 28 S .. R. 4 E., Wayne 

County. 

SSSW sec. 32, T. 29 S .. R. 115 W., Beaver 

County. 

NW sec. 13, T. 29 S .. R. 13 W .. Beaver 

County. 

Sees. 24 and 25. T. 28 S .. R. 12 W .. Beaver 

County. 

Baker and others (1949), Kinney (1955), 

Sadlick (1957). Dockal (1980). 

Dockal ( 1980) 

Dockal (1980) 

Huddle and McCann ( 1947), Baker and others 

(1949), Sadlick (1957). 

Baker and others (1949), Kinney (1955) 

Sadlick (1955, 1957) 

Sad1ick (1957) 

Thomas and others (1945), Sadlick (1957) 

Sadlick (1957) 

Sadlick (1957) 

Sadlick (1957) 

Reid (1954). Sadlick (1957) 

Wells (1954), Sadlick (1957) 

Turnbow (1961) 

Turnbow (1961) 

Wengerd and Matheny (1958) 

Wengerd and Matheny (1958), Parker and 

Roberts ( 1963 ) 

Parker and Roberts (1963) 

Miller (1966), Hintze (1975), W.J. Sando 

(unpublished field notes, 1980). 

D.M. Lemmon 1

, (written communication, 

1963). 

D.M Lemmon (written communication, 

1963), R.C. Gutschick (written communication, 1977), W.J. Sando (unpublished 

field notes. 1977, 1980). 

HUM lithosome: An Example of Regional Stratigraphic Synthesis E9 
Table 1. Catalog of stratigraphic section control points for figures 3 and 4 and plates 1A and 18-Continued 

Number Name 

UT -92 ..... Dog Valley Peak 

UT-94 ..... North Gillson Mountains 

UT -98 ..... Cedar Valley Hills 

UT -10 1 .... Cascade Springs 

UT -104 .... Twelve Mile Pass 

UT -105 .... Silveropolis Hill 

UT-107 .... Flux 

UT -108 .... South Lakeside Mountains 

UT-109 .... Broad Canyon 

UT-110 .... Round Valley 

UT-111 .... Causey Dam 

UT-112 .... East Canyon (Porcupine 

Dam) 

UT-113 .... Dry Lake-Mount Pisgah 

UT-114 .... Leatham Hollow 

UT-1I5 .... Blacksmith Fork 

UT -I16 .... Logan Canyon 

UT-I18 .... Old Laketown Canyon 

UT-119 .... Little Mountain 

UT -121 .... Boulter Peak 

UT-122 .... Holdaway Canyon 

UT-123 .... Onaqui Mountains 

Location 

Utah-Continued 

N. sec. 17, T. 25 S., R. 6 W., Millard 

County. 

E. sec. 33, T. I3 S., R. 3 W .. Juab County 

NENENE sec. 32 and SE sec. 29. T. 6 S., 

R. I W .. Utah County. 

NW sec. I9. T. 4 S., R. 4 E .. Wasatch 

County. 

CNE sec. 22, T. 8 S., R. 3 W .. Tooele 

County. 

NESW sec. 25. T. 5 S., R. 4 W., Tooele 

County. 

CNS sec. 31. T. 1 S., R 6 W .. Tooele 

County. 

CNS sec. 31, T. I S., R. 6 W .. Tooele 

County. 

NW sec. 23, T. I N., R. 6 W .. Tooele 

County. 

Sees. 20, 21, 28. 29. and 30. T. 4 N., R. 3 

E., Morgan County. 

CNE sec. 26, T. 7 N .. R. 3 E., Weber 

County. 

NE sec. 7, NE and NW sec.17, and SE sec. 

18. T. 9 N., R 2 E., Cache County. 

Sees. 33, SE 28, and SW 27. T. 10 N .. R. I 

W., Cache County. 

NW sec. 34 and S sec. 28, T. II N., R. 2 E., 

Cache County. 

Sec. 5. T. 10 N., R. 2 E., Cache County 

Sec. 12. T. I2 N .. R. 2 E .. Cache County 

Sec. 32, T. 13 N .. R. 6 E., Rich County 

Sec. 24, T. 10 N., R. 4 W., Box Elder 

County. 

Sec. 6, T. 9 S., R. 3 W., and sec. 31, T. 8 

S., R. 3 W., Tooele County. 

SW sec. I5, T. 1I N .. R. 2 W .. Box Elder 

County. 

SE sec. 1 L T. 8 S., R. 7 W., and NW sec. 

18, T. 8 S., R. 6 W., Tooele County. 

El 0 Shorter Contributions to Paleontology and Stratigraphy 

Source 

Sandberg and Gutschick (1984). R.C. Gutschick (written communication, 1976), 

C.A. Sandberg (written communication, 

1977), W.J. Sando (unpublished field 

notes, I976, I977). 

Hintze (1975), Sandberg and Gutschick 

(1977), R.C. Gutschick (written communication, I976), C.A. Sandberg (written communication, I976), W.J. Sando (unpublished field notes. I976, 1977). 

R.C. Gutschick (written communication, 

1976), W.J. Sando (unpublished field 

notes. 1977). 

C.A. Sandberg (written communication, 

I980), W.J. Sando (unpublished field 

notes, I980). 

Mackenzie Gordon, Jr. (unpublished field 

notes, 1962). Bissell (1959). 

E.W. Tooker (written communication. 1977), 

Mackenzie Gordon, Jr. (written communication. 1978). 

Newman (1972), Sandberg and Gutschick 

(1979). W.J. Sando (unpublished field 

notes. 1975. 1977). 

Sandberg and Gutschick (1984), R.C. Gutschick (written communication, 1977), 

W.J. Sando (unpublished field notes, 1977. 

I978. I981). 

Sandberg and Gutschick (1979). W.J. Sando 

(unpublished field notes, I977). 

Williams (1943), Sadlick (1955, I959), Crittenden ( I959), Sandberg and Gutschick 

(1984), W.J. Sando (unpublished field 

notes. I96I ). 

Mullens (197I), W.J. Sando (unpublished 

field notes, I978). 

Mullens and Izett (1964), Newman (1972), 

Poole and Sandberg (1977). W.J. Sando 

(unpublished field notes, 1961, 1976, 

I980). 

Williams (1943), Williams and Yolton (1945), 

Sadlick (I955). Parks (1951), Lindsay 

(1977). W .J. Sando (unpublished field 

notes. I96L I98I ). 

Williams ( 1943). Parks ( 1951 ) . Holland 

( 1951). Poole and Sandberg ( I977), Sandberg and Gutschick ( I977). 

Williams ( I943), Mullens and Izett ( I964) 

Williams ( I943) 

Sando and others (1959). Sandberg and Gutschick ( I979), Gutschick and others ( 1980). 

W. J. Sando (unpublished field notes, I98I) 

Chamberlain ( I98I) 

Lindsay (1977), Chamberlain (1981 ), Oviatt 

(1985). 

Chamberlain ( I98I) 
Table 1. Catalog of stratigraphic section control points for figures 3 and 4 and plates 1A and 18-Continued 

Number Name 

UT -142 .... Skunk Springs 

UT -144 .... Granite Mountain 

UT -145 .... Southern Wah Wah Range 

UT-146 .... Lookout Hills 

UT -148 .... White Mountain 

UT-155 .... Big Canyon (Grasshopper 

Ridge). 

UT-158 .... Dry Canyon 

UT-159 .... El Paso Natural Gas Pack 

Saddle 1. 

UT-160 .... Phillips Huntington Unit 1 

UT-161 .... Standard Oil California, 

San Rafael Unit 2. 

WY-1 ...... Haystack Peak 

WY -2 ...... Covey Cutoff Trail 

WY-3 ...... Moffat Trail 

WY -4 ...... Mount Darby 

WY -5 ...... Cokeville Butte 

WY -6 ...... Chevron 1-18F 

WY-7 ...... Chevron 1-30F 

WY -8 ...... Hoback Canyon 

WY -9 ...... Miller Butte 

WY -10 ..... Darby Canyon 

WY-11 ..... Mountain Fuel Supply and 

Union Pacific Railroad 

19, Church Buttes Unit. 

WY-12 ..... Mobil 22-19-G, Tip Top 

Unit. 

WY -13 ..... Darwin Peak 

WY-14 ..... Phillips Canyon 

WY -15 ..... South Indian Creek 

WY-16 ..... Glory Mountain 

WY -17 ..... Martin Creek 

WY-18 ..... Shell LeRoy Unit 1 

WY-19 ..... Big Sheep Mountain 

WY -20 ..... Flat Creek-Sheep Creek 

Location Source 

Utah-Continued 

S sec. 3, T. 18 S., R. 16 W., Millard Chilingar and Bissell (1957), Sadlick (1960), 

County. Poole and Sandberg (1977), Tynan (1980), 

NW sec. 17 and N sec. 18, T. 14 S., R. 16 

W., Juab County. 

Sec. 6, T. 29 S., R. 15 W., Beaver County. 

Sees. 11, 14, 19, 24, and 25, T. 8 S., R. 7 

W., Tooele County. 

ENE sec. 9, T. 29 S., R. 13 W .. , Beaver 

County. 

SNW sec. 33 and NSE sec. 32, T. 6 S., R. 

6 W., Tooele County. 

SE sec. 27, T. 11 S., R. 1 E., Juab County 

Sec. 12, T. 18 S., R. 12 E., Emery County 

Sandberg and others (1980). 

Webster and others ( 1984) 

Miller (1966), Hintze (1975) 

Cohenour (1959), Sandberg and and Gutschick ( 1984). 

Haymond (1980) 

R.C. Gutschick (written 

1977). 

Johnson (1959) 

Reid (1954), Wells (1954) 

communication, 

Sec. 15, T. 17 S., R. 8 E., Emery County Reid (1954) 

Sec. 27, T. 23 S., R. 11 E., Emery County Reid (1954), Wells (1954) 

Wyoming 

NWNE sec. 27, T. 34 N., R. 117 W., 

Lincoln County. 

NWNE sec. 27, T. 34 N., R. 117 W., 

Lincoln County. 

NWNEsec. 3, T. 33N.,R.117W.,Lincoln 

County. 

S sec. 8 and SW sec. 7, T. 29 N., R. 115 

W., Sublette County. 

S sec. 35, T. 25 N., R. 119 W., Lincoln 

County. 

SW sec. 18, T. 18 N., R. 119 W., Lincoln 

County. 

SW sec. 30, T. 18 N., R. 119 W., Lincoln 

County. 

N sec. 2, T. 38 N., R. 115 W., Teton 

County. 

Sec 23, T. 41 N., R. ll6 W., Teton County 

Sees 14, 15, and 23, T. 43 N., R. 118 W., 

Teton County. 

Sec. 8, T. 16 N., R. 112 W., Uinta County 

NWNW sec. 19, T. 28 N., R. 113 W., 

Sublette County. 

S sec. 28, T. 40 N., R. 112 W., Teton 

County. 

SW sec. 16, T. 41 N., R. 117 W., Teton 

County. 

NE sec. 14, T. 38 N., R. 118 W., Lincoln 

County. 

SE sec. 13, T. 41 N., R. 118b W., Teton 

County. 

Sando and others (1975), Sando (1977), 

Sando and Dutro ( 1981), Gutschick and 

others (1980). 

Sando and others (1975) 

Sando and others (1975) 

DeJarnett (1984), W.J. Sando (unpublished 

field notes, 1957, 1970). 

W.J. Sando (unpublished field notes, 1982) 

Rau (1982) 

Rau (1982) 

Sando and others (197 5), Sando (1977), 

Sando and Dutro ( 1981). 

W.J. Sando (unpublished field notes, 1958, 

1970). 

Sando and Dutro (1960), Sando and others 

(1975). 

Verville and others (1973) 

Marzolf ( 1965) 

E. Blackwelder (unpublished field notes, 

1911 ). 

Sando and others (1975) 

Sando and others (1975) 

Sando and others ( 1975) 

Sec 28, T. 38 N., R. 116 W., Lincoln Love (1954), Mallory (1967) 

County. 

Sec. 32, T. 16 N., R. 117 W., Uinta Verville and Mom per ( 1960), Mallory ( 1967) 

County. 

Sec. L T. 

County. 

38 N., R. 109 W., Sublette Richmond (1945), E. Blackwelder (unpublished field notes, 1911), W.J. Sando 

(unpublished field notes, 1970). 

Sec. 2, T. 42 N., R. 115 W., Teton County Love (1954), Mallory (1967) 

HUM lithosome: An Example of Regional Stratigraphic Synthesis Ell 
Table 1. Catalog of stratigraphic section control points for figures 3 and 4 and plates 1A and 18-Continued 

Number Name Location Source 

Wyoming -Continued 

WY -22 ..... South Fork Mountain S sec. 10, T. 24 N., R. 116 W .. Lincoln W.W. Rubey (unpublished field notes. 1956) 

County. 

WY -23 ..... Sheep Creek Canyon S sec. 7, T. 33 N .. R. 115 W .. Lincoln W.W. Rubey (unpublished field notes, 1939) 

County. 

WY-24 ..... Carter Unit 1 Sec. 10. T. 26 N., R. 115 W., Lincoln American Stratigraphic Company (1959) 

County. 

WY-25 ..... Belco 30-2 Hamsfork Unit CSESE sec. 30. T. 19 N .. R. 115 W., American Stratigraphic Company (1962) 

Lincoln County. 

Table 2. Correlations and reference sections for other lithosomes shown on plate 1A and 1 B 

Lithosome Equivalent formal unit 

ASPER ............ Aspen Range Formation (upper three 

members only). 

BIGOO ............ Big Goose Member of Madison Limestone 

BULL ............. Bull Ridge Member of Madison Limestone 

DAR ............... Darwin Sandstone Member of Amsden 

Formation. 

DEL ............... Delle Phosphatic Member of Woodman 

Formation. 

DONUT ........... Doughnut Formation 

GREAB ............ Great Blue Limestone 

HORSE ............ Horseshoe Shale Member of Amsden 

Formation. 

MANCAN ......... Manning Canyon Shale 

MCKAN ........... McKenzie Canyon Limestone 

MOFAT ........... Moffat Trail Limestone Member of Amsden 

Formation. 

MONCAN ......... Monroe Canyon Limestone 

RANCH ........... Ranchester Limestone Member of Amsden 

Formation. 

TET ............... Tetro Member of Deseret Limestone. 

UNJO .............. Uncle Joe Member of Deseret limestone 

WEL .............. Wells Formation 

WOOM ............ Woodman Formation (upper two 

members only). 

E12 Shorter Contributions to Paleontology and Stratigraphy 

Reference section 

North Georgetown Canyon, sec. 16, T. 10 S., R. 44 E., Bear Lake 

County. Idaho (Sando and others, 1981 ). 

Little Tongue River (U.S. Rte. 14). Limestone. sec. 27, T. 56 N., 

R. 87 W .. Sheridan County, Wyoming (Sando. 1976b. 1982). 

Bull Lake Creek, sec. 1 LT. 2 N., Limestone. R. 4 W., Fremont 

County. Wyoming (Sando. 1968). 

Darwin Peak. sec. 28, T. 40 N., R. 112 W .. Teton County, 

Wyoming (Blackwelder, 1918: Sando and others. 1975). 

South Lakeside Mountains, sec. 6. T. 1 N., R. 8 W., Tooele 

County. Utah (Sandberg and Gutschick, 1984). 

Whiterocks Canyon. sec. 12, T. 2 N., R. 1 W., Uintah County, 

Utah (Kinney's (1955) ''black shale unit''). 

Silveropolis Hill. sec. 25. T. 5 S., R. 4 W., Tooele County, Utah 

(Mackenzie Gordon. Jr.. written communication, 1978). 

Livingston Ranch. sec. 29. T. 43 N., R. 106 W .. Fremont 

County. Wyoming (Sando and others. 1975). 

Soldier Canyon. sec. 33, T. 4 S., R. 4 W .. Tooele County, Utah 

(Gilluly. 1932). 

Bell Canyon, sec. 17, T. 11 S .. R. 10 W., Beaverhead County, 

Montana (Sando and others, 1985). 

Moffat TraiL sec. 3. T. 33 N .. R. 117 W., Lincoln County, 

Wyoming (Sando and others, 1975). 

Little Flat Canyon, sees. 17 and 20. T. 7 S., R. 40 E., Bannock 

County, Idaho (Dutro and Sando, 1963). 

Amsden Creek, sec. 34, T. 57 N .. R. 87 W., Sheridan County, 

Wyoming (Sando and others. 1975). 

Ophir Canyon, sec. 22, T. 5 S., R. 4 W., Tooele County. Utah 

(Morris and Lovering. 1961: Sandberg and Gutschick, 1980; 

Gutschick and others, 1980). 

Same as TET 

Deer Creek, sec. 33. T. 9 S .. R. 45 E .. Caribou County, Idaho 

(Cressman. 1964). 

Pool Canyon. sec. 23. T. 7 S .. R. 18 W., Tooele County, Utah 

(Harmala. 1982). 

Figure 4. Thickness variation of the HUM lithosome ..... 

(in meters). Contour interval is 100 m except for 50-

and 60-m contours indicated near the shoreline. 

Data sources are given in table 1 and figure 3. 
IDAHO -~---- UTAir---

0 50 100 MILES 

0 50 100 KILOMETERS 

CIJ 

cr: 

EXPLANATION 

~Sandy wbonate facie<! 

I 

\ 

HUM Lithosome: An Example of Regional Stratigraphic Synthesis E13 
major river in Colorado, marked by the pronounced shoreline reentrant in eastern Utah and reflected in the chronometric profiles and isopach map. has not been mapped. In 

Wyoming, a sheet sand (DAR lithosome) that rests on the 

paleokarst topography resulted from postkarst reworking of 

the river sands during eastward transgression of the sea. 

Areas of anomalously thick sediment that occupy a belt 

about 45 km wide seaward of the shoreline are interpreted 

as offshore bars and islands similar to the ones seen today 

along the Texas Gulf Coast. 

The depositional history of the HUM lithosome was 

characterized by sporadic, local, predominantly subtidal 

carbonate sedimentation over much of the depositional area. 

These carbonate deposits probably originated on local sea 

floor highs, where the growth of carbonate-secreting organisms produced small carbonate factories that were able to 

compete with the influx of sand. A large carbonate bank 

developed in southeast Idaho and northern Utah and dominated the depositional history of that area throughout most 

of HUM time. This area has been identified as a positive 

area in the earlier Mississippian rock record (Isaacson and 

others, 1985) and later became emergent (Bannock uplift of 

Sando (1976a) and Skipp and others (1979)). 

The HUM lithosome was described as a deltaic 

complex by Gutschick and others (1980. p. 126), Sandberg 

and others (1982, p. 714, fig. 17), and Sandberg and 

Gutschick (1984, fig. 5). The lobate offshore morphology 

of the HUM and its obvious relation to river sources (fig. 4) 

support a deltaic origin. On the other hand, the HUM 

includes very little clay and silt, and no evidence of deltaic 

plain deposits has been found; hence, the HUM lacks some 

important characteristics of classic modern and ancient 

deltas (see examples given by Morgan, 1970). It is similar 

to the present offshore Nile delta shelf deposits, which 

include a broad sand belt in water depths of 25 to 60 m and 

a belt of coralline algal mounds (Coleman and others, 

1981), but the Nile delta also includes a broad, onshore 

delta plain. Because the prograding HUM lithosome was 

deposited during a transgression. the typical internal deltaic 

plain morphology may have been destroyed by reworking of 

surficial deposits as the sea transgressed eastward. The 

WOOM lithosome, which forms a belt of fine-grained 

terrigenous rocks seaward from the HUM, may well represent a prodeltaic deposit, as Sandberg and others (1982, p. 

714, fig. 17) suggested. 

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HUM lithosome: An Example of Regional Stratigraphic Synthesis E17