Some Middle Cenomanian (Upper Cretaceous) 

Acanthoceratid Ammonites from the 

Western Interior of the 

United States

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445
Some Middle Genomanian (Upper Cretaceous) 

Acanthoceratid Ammonites from the 

Western Interior of the 

United States

By WILLIAM A. COBBAN

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445

Ammonites of the genera

Calycoceras, Acanthoceras, Plesiacanthoceras, fa

and Protacanthoceras from the Frontier Formation fand equivalent rocks are described fe>\ ^THP^P- £

- \ and illustrated

UNITED STATES GOVERNMENT PRINTING OFFICE, W A S H I N G T O N : 1 9 8 7
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging-in-Publication Data

Cobban, William Aubrey, 1916-

Some Middle Cenomanian (Upper Cretaceous) Acanthoceratid Ammonites from the Western Interior of the 

United States.

(U.S. Geological Survey professional paper ; 1445

Bibliography: p.

Includes index.

Supt. of Docs, no.: I 19.16:1445

1. Acanthoceratidae. 2. Paleontology Cretaceous. 3. Paleontology United States. I. Geological Survey 

(U.S.) II. Title. III. Series: Geological Survey professional paper ; 1445. 

QE807.A5C625 1987 564'.53 86-600103

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425 

Denver, CO 80225
CONTENTS

Abstract .................................

Introduction ..............................

Previous work on acanthoceratid ammonites . . . 

Localities at which fossils were collected ......

Systematic descriptions ....................

Subfamily Acanthoceratinae de Grossouvre

Genus Calycoceras Hyatt ............

Genus Acanthoceras Neumayr ........

Genus Cunningtoniceras Collignon ....

Genus Plesiacanthoceras Haas ........

Genus Protacanthoceras Spath .......

Zonation of acanthoceratid ammonites ........

References cited ...........................

Index ....................................

Page

1

1

1

3

3

4

4

5

8

15

18

23

24

27

ILLUSTRATIONS

[Plates follow index]

PLATE 1. Calycoceras and Acanthoceras

2. Acanthoceras

3. Protacanthoceras and Acanthoceras

4-8. Cunningtoniceras

9. Protacanthoceras and Cunningtoniceras

10. Protacanthoceras and Plesiacanthoceras

11-13. Plesiacanthoceras

	Page

FIGURE 1. Map of part of Western Interior showing localities of fossil collections 2

2. Suture of Calycoceras (Gentoniceras) leonense (Adkins) ............. 5

3. Scatter diagram of umbilical ratios of Acanthoceras bellense Adkins . 6

4. Histogram of diameters at base of body chambers of Acanthoceras bellense

Adkins .................................................. 7

5. Suture of Acanthoceras bellense Adkins ......................... 7

6. Scatter diagram of ribs per half whorl of Acanthoceras muldoonense Cobban and Scott ............................................ 8

7. Map showing localities of Cunningtoniceras amphibolum (Morrow) ... 10

8. Scatter diagram of umbilical ratios of Cunningtoniceras amphibolum amphibolum (Morrow) and C. amphibolum fallense Cobban, n. subsp 14

9. Histogram of diameters at base of body chambers of Cunningtoniceras amphibolum fallense Cobban, n. subsp .......................... 15

10. Map of Wyoming showing localities of Plesiacanthoceras wyomingense

(Reagan) ................................................. 17

11. Histogram of diameters at base of body chambers of Protacanthoceras hosei

hosei Cobban, n. subsp ..................................... 19

12. Suture of Protacanthoceras hosei hosei Cobban, n. subsp ........... 19

13. Histogram of diameters at base of body chambers of Protacanthoceras hosei

sheridanense Cobban, n. subsp .............................. 20

14. Suture of Protacanthoceras hosei sheridanense Cobban, n. subsp ..... 20

15. Histogram of diameters at base of body chambers of Protacanthoceras

vetula Cobban, n. sp ....................................... 21

in
IV CONTENTS

Page

FIGURE 16. Suture of Protacanthoceras vetula Cobban, n. sp ..................... 21

17. Histogram of diameters at base of body chambers of Protacanthoceras

alzadense Cobban, n. sp .......................................... 22

18. Suture of Protacanthoceras alzadense Cobban, n. sp .................. 22

19. Suture of Protacanthoceras fisherense Cobban, n. sp .................. 23
SOME MIDDLE CENOMANIAN (UPPER CRETACEOUS)

ACANTHOCERATID AMMONITES FROM THE

WESTERN INTERIOR OF THE UNITED STATES

By WILLIAM A. COBBAN

ABSTRACT

The ammonite family Acanthoceratidae de Grossouvre is 

represented in the Western Interior region by many genera. Species 

and subspecies of Calycoceras, Acanthoceras, Cunningtoniceras, 

Plesiacanthoceras, and Protacanthoceras are important guide fossils 

to narrow zones of middle Cenomanian age in southeastern Montana, 

northeastern Wyoming, western South Dakota, and central Kansas. 

In this region, the ammonite zonation through most of the middle 

Cenomanian seems to be, from oldest to youngest, a zone of Acanthoceras muldoonense Cobban and Scott, a zone of Acanthoceras 

bellense Adkins and Calycoceras leonense (Adkins), a zone of Cunningtoniceras amphibolum (Morrow) with subzones of C. amphibolum 

amphibolum and C. amphibolum fallense (n. subsp.), and a zone of 

Plesiacanthoceras wyomingense (Reagan).

In this report, Acanthoceras muldoonense, A. bellense, and 

Calycoceras leonense are described from the northern part of the 

Western Interior for the first time. Cunningtoniceras amphibolum, 

originally assigned to Acanthoceras, is described in more detail and 

divided into the nominate subspecies and the new subspecies C. amphibolum fallense. The earliest whorls of Plesiacanthoceras wyomingense, previously unknown, are described as well as all the later 

growth stages. The small genus, Protacanthoceras, is represented by 

several new species and one new subspecies. Protacanthoceras fisheri 

is found in the zone of Acanthoceras bellense, P. vetula occurs in the 

subzone of Cunningtoniceras amphibolum amphibolum, and P. hosei 

hosei and P. hosei sheridanense are found in the subzone of C. amphibolum fallense. Protacanthoceras alzadense is associated with 

Plesiacanthoceras wyomingense.

INTRODUCTION

The family Acanthoceratidae de Grossouvre (1894) includes ammonites that have strong ornament of umbilical and ventrolateral tubercles and, in many genera, 

midventral (siphonal) tubercles as well. Ribs are usually conspicuous at some growth stage and can be the 

dominant ornament. The family ranges from the lower 

Cenomanian to the Coniacian and has a worldwide 

distribution. Acanthoceratid ammonites were the dominant forms in the Cenomanian of many parts of the 

world.

Most genera of ammonites of Cenomanian and Turonian age in the Western Interior belong to the Acanthoceratidae. Specimens are abundant in places, 

especially in silty limestone concretions in the Frontier 

Formation of Wyoming and southern Montana and in 

limestone concretions in the Belle Fourche Shale around 

the flanks of the Black Hills. Specimens in the limestone 

concretions are usually uncrushed, and many retain part 

or much of their shell material, which has generally been 

converted to calcite. At a few localities, nacreous 

aragonitic shell material has been retained.

Many of the species have been poorly known because 

of brief descriptions and lack of enough illustrations to 

show growth stages and variation in form and ornament. Other species have been undescribed. The present 

report was undertaken to more firmly define a few of 

the earlier named species, and to describe some of the 

new forms.

All specimens described in this report are kept in the 

National Museum of Natural History (USNM) in 

Washington, D.C., and have USNM catalog numbers. 

Plaster casts of the holotypes are in the U.S. Geological 

Survey's reference collections at the Federal Center, 

Denver, Colo. Robert E. Burkholder, of the U.S. Geological Survey, made all the photographs. The author 

made the drawings of sutures.

PREVIOUS WORK ON 

ACANTHOCERATID AMMONITES

Ammonites of the family Acanthoceratidae were not 

recorded from the Western Interior of the United States 

until 1877, when White (1877, p. 201, 202) described the 

new species Ammonites loevianus from New Mexico 

and figured specimens from Utah that he assigned to 

Buchiceras swallovi (Shumard). Later in that century, 

Stanton (1893) described the new species Acanthoceras
UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

110° 108° 106° 104° 102° 100° 9f

44°

40°-

Billings^

MONTANA

x 20934, 24319

22871 V I

D6933, 21364 

-.Buffalo

,08318

22804.

D5869, D8841

WYOMING

: D9801, 23459

D5900, D8442 X

oCasper

LasKO

QLaramie 

CHEYENNEO

ODENVER

COLORADO

SOUTH DAKOTA

Q Pierre

o Rapid City

D7370

oChadron

NEBRASKA

KANSAS X 12510 

X D4428

100 150 200 MILES

100 200 KILOMETERS

FIGURE 1. Map of part of the Western Interior of the United States showing localities of fossil collections. Numbers are U.S. Geological

Survey Mesozoic localities.

kanabense. In the early part of the next century, Hyatt 

(1903) described as new Metoicoceras whitei and M. 

kanabense from Utah, and Henderson (1908) described 

the new species Acanthoceras cohradoensis from Colorado. Acanthoceratids had not been noted north of Colorado until Reagan (1924) described a species from the 

Frontier Formation of Wyoming that he named 

Metoicoceras wyomingensis. A little later Reeside 

(1927) recorded, but did not illustrate, an acanthoceratid 

fauna from Colorado. An important paper was that by 

Morrow (1935), who described the new species Acanthoceras amphibolum, Mammites wingi, M. rectangulus, and Pseudaspidoceras cornucostale from the 

Graneros Shale and Greenhorn Limestone of central

Kansas. Haas (1949, 1951, 1963, 1964) contributed 

much to our knowledge of the acanthoceratids of the 

Frontier Formation of Wyoming in describing the new 

species and subspecies Mantelliceras canitaurinum, 

Metoicoceras whitei praecox, Dunveganoceras pondi, 

and D. conditum, and in erecting the new genus 

Plesiacanthoceras. Acanthoceratid ammonites from farther north, in central Montana, were treated by me (Cobban, 1953), and included the new species and subspecies 

Metoicoceras mosbyense, M. muelleri, Dunveganoceras 

albertense montanense, andZ). parvum. A new species, 

Paracompsoceras landisi, and many splendid examples 

of Calycoceras naviculare (Mantell), from the Greenhorn 

Limestone of Colorado, were also described by me
SYSTEMATIC DESCRIPTIONS

(Cobban, 1971). The largest work that includes many 

acanthoceratid ammonites was on the ammonites from 

the Graneros Shale and Greenhorn Limestone of the 

Pueblo area of Colorado (Cobban and Scott, 1972). New 

species described were Calycoceras (Conlinoceras) gilberti, 

Acanthoceras muldoonense, A. granerosense, Kanabiceras 

puebloense, andAmpakabites cottignoni. Many previously 

named species of Calycoceras, Pseudocalycoceras, Tarrantoceras, Acanthoceras, Euomphaloceras, Kanabiceras, 

Metoicoceras, Watinoceras, and Mammites were described 

and illustrated in that paper. The most recent work concerning acanthoceratid ammonites is that of Cobban and 

Hook (1983a) in which the new genus Morrowites was proposed and the new species M. subdepressus was described. 

Illustrations of some of the earlier named species can be 

found in many papers (Cobban, 1971, 1975, 1977, 1983, 

1984b, Cobban and Hook, 1979,1983a, 1983b; Hook and 

Cobban, 1981, 1982; Hattin, 1965a, 1965b, 1968, 1975, 

1977; Hattin and Siemers, 1978; Kauffman, 1977; Kauffman and others, 1976; Kauffman and Powell, 1977; 

Merewether and others, 1979).

LOCALITIES AT WHICH 

FOSSILS WERE COLLECTED

The ammonites described or reported on in this report 

came mainly from 17 localities in southern Montana, the 

northeast quarter of Wyoming, southwestern South 

Dakota, and central Kansas (fig. 1). The U.S. Geological 

Survey Mesozoic locality number, names of collectors, 

year of collection, locality, and stratigraphic position are 

as follows (prefix D indicates Denver Mesozoic locality 

numbers; the rest are Washington, D.C., Mesozoic locality numbers):

Locality 

number

D4428.

D5869.

D5900.

D6933.

D7370.

Locality

W. A. Cobban, 1964. Beside road in the NWJ/4 sec. 3, T. 16 

S., R 10 W, Ellsworth County, Kans. Graneros Shale, from 

brown calcarenitic limestone 3.4 m (11 ft) below the bentonite marker bed near the top.

W. A. Cobban, 1966. About 2.5 km (IVz mi) southwest of 

Osage near the center of sec 17, T. 46 N., R. 63 W, Weston 

County, Wyo. Belle Fourche Shale, from a gray calcareous 

concretion 33.8 m (111 ft) below a 0.6-m-thick bed of bentonite.

W. A. Cobban, 1967. Head of Elm Creek in WV4 sec. 14, T. 

36 N., R. 62 W, Niobrara County, Wyo. Belle Fourche 

Shale, from limestone concretions 3.6 m (12 ft) below bentonite marker bed.

W. A. Cobban, 1969. North of Gay Creek in the SEH sec. 

18, T. 58 N., R. 88 W, Sheridan County, Wyo. Frontier 

Formation, from limestone concretions developed along 

the Soap Creek Bentonite Bed.

W. A. Cobban, 1970. About 6.7 km (4 mi) southeast of Hot 

Springs in the NEVi sec 34, T. 7 S., R. 6 E., Fall River 

County, S. Dak. Belle Fourche Shale, from limestone concretions at top of bentonite marker bed.

Locality 

number

D8318.

D8442.

D8841.

D9801.

12510.

20934.

21364.

22804.

22871.

23459.

24319.

Locality

E. A. Merewether, 1971. SWJ/4 sec 22, T. 52 N., R. 67 W., 

Crook County, Wyo. Belle Fourche Shale, from limestone 

concretions at base of bentonite marker bed

E. A. Merewether, 1972. NWW sec. 35, T. 37 N., R. 62 W., 

Niobrara County, Wyo. Belle Fourche Shale, from limestone concretions at base of bentonite marker bed.

W. A. Cobban, 1966. About 2.8 km (! 3/4 mi) west of Osage 

in the SWVi sec. 8, T. 46 N., R. 63 W., Weston County, 

Wyo. Belle Fourche Shale, from a gray calcareous concretion at same stratigraphic position as D5869.

E. A. Merewether, 1975. South of Lone Bear road in the 

SWVi sec. 13, T. 42 N., R. 82 W, Johnson County, Wyo. 

Frontier Formation, from dusky-red ferruginous concretions about same stratigraphic position as locality 23459.

N. W. Bass, W. W Rubey, and J. B. Reeside, Jr., 1924. Bank 

of Smoky Hill River 4 km (21A mi) south of Wilson, 

Ellsworth County, Kans. Graneros Shale, from limestone 

concretion 1.2 m (4 ft) below top.

W. A. Cobban, 1947. East flank of Soap Creek dome and 

4.5 km (2.8 mi) east of West Fork of Soap Creek in the 

SEVi sec. 35, T. 6 S., R. 32 E., Big Horn County, Mont. 

Upper part of Belle Fourche Member of Cody Shale, from 

silty concretions just below Soap Creek Bentonite Bed.

W. A. Cobban, 1947. From bentonite pit in the SWVi sec. 

17, T. 58 N., R. 88 W, Sheridan County, Wyo. Frontier 

Formation, from limestone concretions developed along 

the Soap Creek Bentonite Bed.

R K. Hose and Theodore Scott, 1950. Dry Muddy Creek 

in center of sec. 1, T. 48 N., R 83 W, Johnson County, 

Wyo. Frontier Formation, from brown-weathering septarian very fine grained sandstone concretions 38 m (125 

ft) below top.

J. B. Reeside, Jr., G T. Moore, and W. A. Cobban, 1949. About 

9.6 km (6 mi) northeast of Alzada in the SEVi sec. 6, T. 

9 S., R. 59 E., Carter County, Mont. Belle Fourche Shale, 

from light-gray-weathering limestone concretions in upper part.

W. A. Cobban, 1959; Cobban, J. R. Gill, and R T. Fleisher, 

1966. Near head of Fisher Draw about 4.5 km (2.7 mi) 

south of Kaycee in sec. 25, T. 43 N., R. 82 W, Johnson 

County, Wyo. Frontier Formation, from concretions of 

calcareous siltstone 6 m (20 ft) above a 2.7 m-thick bed 

of bentonite.

W. A. Cobban, 1947. NWV4 sec. 31, T. 7 S., R 33 E., Big 

Horn County, Mont. Frontier Formation, float on Soap 

Creek Bentonite Bed.

SYSTEMATIC DESCRIPTIONS

In the descriptions, umbilical diameters are usually 

given as ratios to the shell diameters. In the drawings 

of sutures, the heavy straight line marks the middle of 

the venter as well as the middle of the external lobe. The 

umbilical shoulder is indicated by the curved dashed line, 

and the umbilical seam is marked by the smaller curved 

solid line. Only the major sutural elements are identified; 

E stands for the external lobe, L stands for the lateral 

lobe, and E/L stands for the saddle that separates these 

lobes.
UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

Phylum MOLLUSCA

Class CEPHALOPODA

Order AMMONOIDEA

Suborder AMMONITINA

Superfamily ACANTHOCERATACEAE de Grossouvre,

1893 [1894]

Family ACANTHOCERATIDAE de Grossouvre, 1893 [1894] 

Subfamily ACANTHOCERATINAE de Grossouvre,

1893 [1894] 

Genus CALYCOCERAS Hyatt, 19OO

Calycoceras (Gentoniceras) leonense (Adkins)

Plate 1, figures 1-17; text figure 2

1928. Eucalycoceras leonense Adkins, University of Texas Bulletin

2838, p. 240, pi. 28, fig. 1; pi. 29, fig. 3. 

1928. Metacalycocerast sp. 2. Adkins, University of Texas Bulletin

2838, p. 242, pi. 28, fig. 2; pi. 29, fig. 2.

1942. Eucalycoceras leonense Adkins. Moreman, Journal of Paleontology, v. 16, no. 2, p. 207. 

1969. Eucalycoceras (Proeucalycoceras) leonense Adkins. Thomel,

Academic des Sciences [Paris], Comptes Rendus Hebdomadaires des Seances, Series D, Sciences Naturelles, v. 268, no.

4, p. 650. 

1972. Eucalycoceras (Proeucalycoceras) leonense Adkins. Thomel,

Memoires de la Societe Geologique de France, n. ser., v. 51,

Memoire 116, p. 81. 

1972. Calycoceras leonense (Adkins). Cobban and Scott, U.S.

Geological Survey Professional Paper 645, p. 60, pi. 3, figs.

1-4.

This species is characterized by its sparse ribbing and 

by the persistence of tuberculation well on to the adult 

body chamber. The species is small for the genus.

The holotype came from the basal part of the Eagle 

Ford Group (Upper Cretaceous) in Bell County in eastcentral Texas. Adkins (1928, p. 240) did not give its 

diameter, but a plaster cast suggests a diameter of about 

46 mm and an umbilical ratio of 0.28. The specimen consists of most of an outer whorl; inner whorls are not exposed. Whorl section is stout and about as broad as 

high. Flanks are very broadly rounded and merge evenly into the more narrowly rounded venter. The umbilical 

shoulder is narrowly rounded, and the umbilical wall is 

steep. Ribs, which alternate in length, are narrow, 

rounded, straight, and rectiradiate; all cross the venter 

transversely and strongly. Primary ribs begin at the umbilical seam and rise into conspicuous bullae on the umbilical shoulder. Secondary ribs arise on the inner third 

of the flank and, on crossing the venter, are as strong 

as the primaries. All ribs support small inner and outer 

ventrolateral and siphonal tubercles. Inner ventrolateral 

tubercles weaken and disappear on the younger half of 

the whorl. The last half whorl has 15 ribs of which 8 are 

primaries that bear umbilical bullae. From the type 

locality of C leonense, Adkins (1928, p. 242, pi. 28, 

fig. 2; pi. 29, fig. 2) figured another ammonite as 

Metacalycoceras? sp. 2. This specimen, which is poorly 

preserved, consists of half a whorl about 66 mm in

diameter. Ribs are narrow, rectiradiate, and alternate in 

length; they number 14. The specimen is probably a 

fragment of a large C. leonense as previously suggested 

(Cobban and Scott, 1972, p. 60).

The late L. W. Stephenson, formerly of the U.S. Geological Survey, made two collections of C. leonense from 

the type locality in Bell County, Tfex. These collections 

(USGS Mesozoic Iocs. 11845 and 13577) have 22 

specimens suitable for the determination of one or more 

of the following measurements: umbilical ratio, diameter 

at base of the body chamber, and number of ribs in half 

a whorl. Umbilical ratios range from 0.27 to 0.37 and 

show a gradual increase with growth. Ribs per half whorl 

range from 12 to 17, averaging 14. Diameters at the base 

of body chambers could be determined for 13 of the 

specimens. These diameters range from 30 to 58 mm, 

with most in the 36-46 range. Dimorphism cannot be 

demonstrated with the material at hand.

Ammonites that seem referable to C. leonense occur 

at few localities in the Western Interior region. The 

largest collection is from a limestone concretion in the 

Belle Fourche Shale at locality D8841 near Osage, Wyo., 

on the west flank of the Black Hills uplift (fig. 1). TWentyeight of the specimens from this concretion are suitable 

for rib counts and for the determination of either the 

umbilical ratio or the diameter at the base of the body 

chamber or both. The specimens range in diameter from 

23 to 72 mm. Umbilical ratios range from 0.25 to 0.38, 

and show a slight increase with growth.

The smallest entire whorl examined from locality 

D8841 has a diameter of 23 mm and an umbilical ratio 

of 0.29 (pi. 1, figs. 3-5). Ornament, which is well developed on this whorl, consists of 23 narrow primary and 

secondary ribs, umbilical bullae, inner and outer ventrolateral tubercles, and siphonal tubercles. Ribs arch 

forward a little on crossing the venter on the older part 

of the whorl, but on the younger part, the ribs cross the 

venter more transversely. Ventrolateral and siphonal 

tubercles are nodate and about equal in size on the older 

part of the whorl, but on the younger part, the outer 

ventrolateral and siphonal tubercles become somewhat 

clavate and a little larger than the nodate inner ventrolateral ones. A smaller whorl, only partly exposed, 

has equal-sized clavate outer ventrolateral and siphonal 

tubercles and pointed, nodate inner ones all well developed at a diameter of about 7 mm (pi. 1, figs. 6, 7). Inner 

ventrolateral tubercles weaken and disappear on the 

larger shells at some diameter from 25 to 32 mm. The 

outer ones and the siphonal tubercles persist on to the 

older part of the adult body chamber before weakening 

and disappearing. Ribs remain narrow and conspicuous 

to the adult aperture. Most are rectiradiate and straight 

to slightly flexuous. An occasional specimen may have 

some rursiradiate ribbing (pi. 1, fig. 12) or some
SYSTEMATIC DESCRIPTIONS

prorsiradiate ribbing (pi. 1, fig. 15). Ribs number 12-17 

per half whorl, averaging 12.

Body chambers occupy about half a whorl. Diameters 

at the base of body chambers could be either measured 

or estimated for 20 specimens from locality D8841 near 

Osage. These diameters ranged from 26.5 mm to 

51.0 mm, with most in the 32-44 mm range. Clustering 

of diameters into two dimorphic groups could not be 

demonstrated with the material at hand. The largest 

complete adult in the collection (hypotype USNM 

388091) has a diameter of 72 mm and an umbilical ratio 

of 0.38 (pi. 1, figs. 12, 13). Diameter at the base of its 

body chamber is 51 mm. An occasional fragment in the 

collection indicates still larger specimens (pi. 1, figs. 16, 

17).

The suture of the holotype is not preserved. An external suture of one of the specimens from locality 

D8841 is shown in figure 2. The lateral lobe (L) is short, 

and the E/L saddle is very broad and shallow.

The specimens from Osage (loc. D8841) are assigned 

to C leonense, although they differ a little from the collections from Bird Creek (Iocs. 11845 and 13577). The 

Osage specimens tend to be slightly more evolute 

(average umbilical ratio of 0.33 compared to 0.31) and 

a little more sparsely ribbed (average half whorl rib 

count of 12 compared to 14.5). These differences may 

be due to the great distance of 1,560 km (970 mi) that 

separates the Osage and Bird Creek localities, or possibly the localities may not be the same age. In their 

sparse ribbing and in the size of their umbilici, the Osage 

specimens resemble an ammonite from the Woodbine 

Formation (Upper Cretaceous) of Texas that was identified as Acanthoceras barcusi Jones by Stephenson 

(1952, p. 203, pi. 44, figs. 9-11). The Woodbine specimen 

differs mainly in having thicker ribs and in retaining 

tuberculation to a larger diameter. The holotype of A. 

barcusi (Jones, 1938, p. 117, pi. 6, figs. 2, 3, 8, 9) is a 

larger and more robust shell 83 mm in diameter that retains tuberculation to a much greater diameter than on 

any specimens from Osage. Jones' holotype and

E/L

FIGURE 2. Last external suture of Calycoceras (Gentoniceras) 

leonense (Adkins) at a diameter of 34 mm from the Belle Fourche 

Shale at locality D8841 (fig. 1). Hypotype USNM 388087.

Stephenson's specimen seem better assigned to 

Calycoceras because of their rounded whorls and ribs 

of alternate lengths.

Fossils associated with C. leonense at locality D8841 

include Acanthoceras bellense Adkins, Borissiakoceras 

orbiculatum Stephenson, Inoceramus arvanus Stephenson, and Drepanochilus sp.

Types Hypotypes USNM 388087-388093.

Genus ACANTHOCERAS Neumayr, 1875 

Acanthoceras bellense Adkins

Plate 1, figures 18, 19; plate 2; text figure 5

1928. Acanthoceras bellense Adkins, University of Texas Bulletin 

2838, p. 245, pi. 30, figs. 1, 2.

1942. Acanthoceras bellense Adkins. Moreman, Journal of Paleontology, v. 16, no. 2, p. 203.

Acanthoceras bellense is a moderate-sized species that 

is characterized by its conspicuous tuberculated phragmocone and by its sparsely ribbed body chamber.

The holotype came from the basal part of the Eagle 

Ford Group of east-central Texas. Adkins did not give 

its size, but a plaster cast indicates a diameter of about 

91 mm. The type is an undeformed phragmocone that 

is badly corroded on one side as well as on much of the 

opposite side and on the older half of the venter (pi. 1, 

figs. 18,19). Much of the cross section of the outer whorl 

is rather rounded and about as high as wide, but near 

the larger end, the section becomes more subquadrangular with very broadly rounded flanks and venter and 

more narrowly rounded ventrolateral shoulder. The umbilicus, which has a ratio of 0.26, has a well-rounded 

shoulder that merges evenly into the rounded, sloping 

wall. Ornament on the outer whorl consists of low, narrow ribs; weak umbilical bullae; stronger inner and outer 

ventrolateral tubercles; and very weak siphonal clavi on 

a low, rounded siphonal ridge. Details of the ornament 

on the older half of the outer whorl cannot be determined owing to the eroded condition. Ribs on the 

younger half of the whorl are mostly of equal strength, 

rectiradiate, and very slightly flexuous. A few raised 

striae separate some of the ribs. Ribs begin at the umbilical seam, rise into low umbilical bullae on the lower 

part of the flank, and rise again into equal-sized nodate 

inner ventrolateral tubercles and clavate outer ones. 

These tubercles are matched by weak, clavate siphonal 

tubercles located directly across the venter. Adkins 

noted that only parts of the suture were visible.

The holotype came from hard calcarenitic limestone 

that was originally assigned to the Flag Member of the 

Eagle Ford (Adkins, 1928, p. 246), later to the Tarrant 

Formation (Moreman, 1942, p. 204), and more recently 

to the Bluebonnet Member of the Lake Waco Formation (Adkins and Lozo, 1951, p. 130). Ammonites
UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

associated with the holotype were described by Adkins 

(1928) as the new species Acanthoceras hnsdalei, A. 

stephensoni, and Eucalycoceras leonense. At a later 

date, Moreman (1942) described A. validum and A. pepperense as additional new species from the type locality of A. bellense.

Ammonites that seem assignable to A. bellense have 

been found in only one small area in the Western Interior 

of the United States. This area, in the Osage oil field 

on the west flank of the Black Hills uplift in western 

Wyoming, has two localities of A. bellense 1.4 km apart 

(fig. 1, Iocs. D5869, D8841). The larger collection (D8841) 

contains 84 specimens suitable for the determination of 

one or more of the following measurements: umbilical 

ratio, diameter at the base of the body chamber, and the 

number of umbilical and ventrolateral tubercles per half 

whorl. Phragmocones are well preserved, but body 

chambers are crushed.

The smallest whorls examined from locality D8841 

have diameters of slightly less than 10 mm (pi. 2, figs. 

9-11, 24, 25). At these diameters, whorls are subquadrate and wider than high with flattened flanks and 

very broadly rounded venter. Ornament is well established and consists of low rectiradiate ribs that support 

weak umbilical bullae, pointed inner ventrolateral 

tubercles, somewhat clavate outer ones, and clavate 

siphonal tubercles. One individual (hypotype USNM 

388097) seems to have a weak constriction that crosses 

the venter transversely at a diameter of about 5 mm (pi. 

2, fig. 11). At a diameter of 9.8 mm, this specimen has 

13 ventrolateral tubercles per whorl. As the shell 

enlarges, the whorl section becomes slightly more quadrate, although all whorls seem to be a little wider than 

high with the greatest width at the umbilical shoulder 

(pi. 2, figs. 1-8). Umbilical ratios range from 18 to 29 

percent of the diameter in the 20-70 mm size group, and 

from 23 to 28 percent at larger diameters (fig. 3). Umbilical bullae, ventrolateral tubercles, and siphonal clavi 

persist to the end of the adult phragmocone.

Ventrolateral tubercles number 8 to 12 per half whorl 

at diameters of 10-40 mm, 7-11 at diameters of 40-50 

mm, and 6-9 at larger diameters. All ornament on the 

adult body chamber weakens except for the umbilical 

bullae and the inner ventrolateral tubercles (pi. 2, figs. 

28, 29). The latter enlarge into short, stout outward 

directed horns. On some individuals, the outer ventrolateral tubercles and the siphonal ones disappear on the 

body chambers. On others, a low siphonal ridge may persist on the body chambers. An occasional very weak, 

nontuberculate rib may lie on the venter between two 

tuberculate ribs. These rare secondary ribs were not 

observed on specimens of less than 33 mm diameter. 

None of the adult specimens has the aperture completely preserved. One crushed specimen, (unfigured hypotype USNM 388107), about 97 mm in diameter, has a 

nearly complete body chamber that occupies a third of 

a whorl. Ornament on the flank of this body chamber 

consists of four umbilical bullae located well out on the 

flank and a final flange-like, fairly narrow, rectiradiate 

rib that supports an umbilical bulla. The first three umbilical bullae are matched by large, thick, clavate inner 

ventrolateral tubercles, weak outer ventrolateral clavi, 

and weak siphonal clavi. These tubercles disappear 

abruptly, and the fourth umbilical bulla is matched by 

a fairly broad, transverse ventral rib that is thickened 

and accentuated a little on the ventrolateral shoulder. 

The terminal flange is broken off on the venter, but on 

a fragment of another body chamber (unfigured hypotype USNM 388108), the flange rises high above the 

venter.

The specimens of A. bellense from locality D8841 are 

dimorphic. Diameters at the base of body chambers 

could be measured or estimated for 52 specimens. These 

measurements revealed a grouping in the 30-62 mm 

range and in the 74-88 mm range (fig. 4). Most measurements are in the smaller size range, but these are due 

to the better preservation of the smaller specimens. 

There are many fragments of body chambers of

30

20

10

20 30 40 50 60 70 

DIAMETER, IN MILLIMETERS

80 90 100 110

FIGURE 3. Scatter diagram showing umbilical ratios of 62 specimens of Acanthoceras bellense Adkins from the Belle Fourche Shale at locality

D8841 (fig. 1).
SYSTEMATIC DESCRIPTIONS

30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

DIAMETER AT BASE OF BODY CHAMBER, IN MILLIMETERS

FIGURE 4. Histogram showing diameters at base of body chambers of the 53 measurable specimens of Acanthoceras bellense

Adkins from the Belle Fourche Shale at locality D8841 (fig. 1).

specimens that would fall in the 74-88 mm range, but 

these lack attached phragmocones necessary for 

diameter measurements.

Although most specimens resemble the bulk of those 

shown on plate 2, there are some unusual variants. An 

occasional individual may have the ventrolateral 

tubercles raised a little above the venter, and in this manner, it shows some resemblance to A. muldoonense. An 

unusual specimen is part of a small phragmocone that 

is well ornamented on the older part and nearly smooth 

on the younger part (pi. 2, fig. 18).

Adkins (1928, p. 245) gave only a brief description of 

part of the external suture of A. bellense without an illustration. The complete external suture of a hypotype 

(USNM 388109) from locality D8841 is shown in figure 

5. The suture is typical of the genus.

Fossils associated with Acanthoceras bellense at 

localities D5869 and D8841 include the ammonites 

Calycoceras (Gentoniceras) leonense (Adkins) and 

Borissiakoceras orbiculatum Stephenson, the bivalve Inoceramus arvanus Stephenson, and the gastropod 

Drepanochilus sp.

7>pes.-Hypotypes USNM 388094-388109.

FIGURE 5. External suture of Acanthoceras bellense (Adkins) at a 

whorl height of 25.7 mm from the Belle Fourche Shale at locality 

D8841 (fig. 1). Hypotype USNM 388109.

1972. 

(1973)

Acanthoceras muldoonense Cobban and Scott

Plate 3, figures 7-34

Acanthoceras muldoonense Cobban and Scott, U.S. Geological 

Survey Professional Paper 645, p. 67, pi. 4, figs. 1, 3; pi. 7, 

figs. 1-13; pL 11, figs. 12, 13; text figs. 27, 28.

This species is characterized by sparse ribbing on 

adults, by early loss of siphonal and outer ventrolateral 

tubercles, and by the development of the inner ventrolateral tubercles into upward projected horns on the 

outer whorl. The species was based on fragments of internal molds from ferruginous concretions in the upper 

part of the Graneros Shale of south-central Colorado.

The holotype (USNM 163941) is a small crushed adult 

that has a diameter of 143 mm and an umbilical ratio 

of 0.25. Most of the body chamber and the last two septate whorls are preserved. Diameter at the base of the 

body chamber is about 88 mm. The body chamber consists of a little more than half a whorl ornamented by 

weak ribs of equal length that support umbilical bullae 

well out on the flank and clavate ventrolateral horns. 

There are seven umbilical bullae and eight ventrolateral 

horns in half a whorl.

The smallest specimen in the type lot has a diameter 

of 12.5 mm. Fragments of the largest specimens in the 

type lot suggest that A. muldoonense attained diameters as much as 200 mm.

Sutures are not preserved on the holotypa The external suture of a paratype (Cobban and Scott, 1972, text 

fig. 28) is typical of Acanthoceras in its general appearance; it has a broad, bifid E/L saddle and narrower, 

bifid, rectangular L.

Specimens of Acanthoceras muldoonense from the 

Frontier Formation of north-central Wyoming are 

preserved better than those from the type area in Colorado. The largest collection from the Frontier is from
8 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

concretions of calcareous siltstone at locality 23459 near 

Kaycee (fig. 1). Here 42 specimens, mostly 8-40 mm in 

diameter, were collected that are suitable for measurements of diameter, umbilicus, and number of umbilical 

and ventrolateral tubercles in half a whorl. At the smallest diameter observed, 3.7 mm, whorls are smooth and 

broader than high with broadly rounded venter and 

flanks. Ornament, in the form of weak transverse ventral ribs, first appears at some diameter between 4.5 and 

6.3 mm. Within half a whorl of the appearance of ribbing, nodate siphonal and outer ventrolateral tubercles 

form on the ribs. By a diameter of 11 or 12 mm, the 

flanks become flattened and bordered by a row of weak, 

nodate inner ventrolateral tubercles. At this diameter, 

ribs have become stronger and forwardly arched a little 

as they cross the venter. Every other rib tends to be 

longer and extends to the umbilical wall. By a diameter 

of 15-20 mm, whorls are about as high as wide with flattened flanks and venter. Ribs become transverse on 

crossing the venter, and the siphonal and outer ventrolateral tubercles become somewhat clavate. Umbilical 

bullae may appear on the longer ribs of some specimens. 

Inner ventrolateral tubercles, which are nodate and 

smaller than the outer ones, are located on the upper 

part of the flank. As the shell enlarges, the inner ventrolateral tubercles migrate upward to a position above 

the venter, where they become larger than the outer ones 

(pi. 3, figs. 22-24). For about a quarter of a whorl or less, 

the outer tubercle is reduced to a small swelling on the 

side of the larger inner tubercle before disappearing (pi. 

3, fig. 24). The outer tubercles and the siphonal tubercles 

disappear at some diameter between 30 and 40 mm. At 

this size, the inner ventrolateral tubercles become 

clavate and rise farther above the venter (pi. 3, fig. 27). 

At larger diameters, the tubercles form prominent clavate horns that are directed upward and a little outward 

(pi. 3, figs. 33, 34). Umbilical bullae migrate out to the 

middle of the flank, where they are usually prominent 

and nodate (pi. 3, fig. 34). Ribs become equal in length 

at diameters greater than 50 mm. The 42 specimens

from locality 23459 reveal a gradual decrease in rib density with growth (fig. 6).

Nearly all specimens from locality 23459 are phragmocones. Diameters at the base of the few body 

chambers range from 11 to 21 mm. These specimens are 

probably immature inasmuch as adult ornament and 

crowded terminal sutures are lacking.

Ribs on the outer septate whorl and on the body 

chamber weaken considerably between the umbilical 

bullae and the ventrolateral horns as well as across the 

venter. On a few specimens, a very low, broad, flat rib 

connects opposite ventrolateral horns, and this rib may 

be raised a little along the edges to form a weak looped 

rib (pi. 3, fig. 29).

Acanthoceras muldoonense has a whorl section much 

like that of A cornigerum Crick (1907, p. 207, pi. 13, fig. 

1, la), especially like the whorl section drawn by Matsumoto (in Matsumoto and others, 1957, text fig. 5). 

Crick's South African species, however, is more evolute, 

and the ribs are narrower and more numerous.

The holotype and paratypes of Acanthoceras muldoonense came from iron-stained chamosite ironstone 

concretions in the Graneros Shale 4-6 m (13-20 ft) above 

the Thatcher Limestone Member in south-central Colorado. Specimens from the Frontier Formation in northcentral Wyoming occur in ferruginous concretions of 

calcareous siltstone. Other fossils in these concretions 

are scarse but include an occasional poorly preserved 

inoceramid and one fragment of Turrilites cf. T. scheuchzerianus Bosc.

Types. Hypotypes USNM 388110-388122.

Genus CUNNINGTONICERAS Collignon, 1937 

Type species. Ammonites cunningtoni Sharpe, 1855.

Collignon (1937, p. 40) defined this genus to include 

ammonites that have a rectangular whorl section, 

multiplication of ribs and tubercles on the venter, and

15

_j 

cc 

O

llO

LLJ 5 

Q.

10 20 30 40 50 

DIAMETER, IN MILLIMETERS

60 70 80

FIGURE 6. Scatter diagram showing number of ribs per half whorl of Acanthoceras muldoonense Cobban and Scott from a bed of concretions in the Frontier Formation at locality 23459 near Kaycee, Wyo. (fig. 1).
SYSTEMATIC DESCRIPTIONS

later loss of the ventral ornament accompanied by the 

enlargement of the ventrolateral tubercles. Collignon 

included in the genus Ammonites cunningtoni Sharpe, 

Acanthoceras cunningtoni var. inermis Pervinquiere, 

A. cunningtoni var. cornuta Kossmat, A. diadema 

Spath, Ammonites meridionalis Stoliczka and its 

varieties africana Pervinquiere and tuberculata 

Pervinquiere, Acanthoceras lonsdalei Adkins, A. latum 

Crick, A. quadratum Crick, and A. aberrans Kossmat.

Cunningtoniceras has usually been considered a 

junior synonym of Euomphaloceras Spath (1923, p. 144, 

footnote 2) by most ammonitologists (e.g., Wright, 

1957, p. L414; Matsumoto, in Matsumoto and others, 

1969, p. 270; Kennedy, 1971, p. 90). I believe the two 

genera are distinct enough to retain separate names. 

Cunningtoniceras has more Acanthoceras-]ike whorls 

with rectangular sections and a suture characterized by 

L usually narrower than the E/L saddle; whereas, Euomphaloceras has more depressed, rounded whorls and a 

suture featured by L generally broader than the E/L 

saddle. Cunningtoniceras is apparently the older form. 

Kennedy (1971, p. 102) recorded the cunningtoni-inerme 

group in both the Turrilites costatus Assemblage and 

T. acutus Assemblage of the middle Cenomanian ^4ca«- 

thoceras rhotomagense Zone. Euomphaloceras euomphalum (Sharpe), the type for the genus Euomphaloceras, occurs in the upper Cenomanian Eucalycoceras 

pentagonus/Calycoceras naviculare Assemblage Zone. 

The same order of genera is apparent also in the 

Western Interior of the United States. Cunningtoniceras is well established in the middle Cenomanian 

Thatcher Limestone Member of the Graneros Shale 

(Cobban and Scott, 1972, p. 30, recorded as Euomphaloceras cf. E. cunningtoni); whereas, upper Cenomanian rocks in the same area contain Euomphaloceras 

(Kanabiceras) septemseriatum (Cragin).

The type of Cunningtoniceras, by absolute tautonymy, is Ammonites cunningtoni Sharpe (1855, p. 35, 

pi. 15, fig. 2a-c) from the middle Cenomanian Lower 

Chalk at Upton Scudamore, near Warminster, in 

southern England. Sharpe described the species briefly and gave its dimensions as "Diameter, 6 inches; 

width, 3 J/4 inches; height of aperture, 2V* inches." The 

specimen was illustrated by drawings of the lateral and 

front views. Kennedy (1971, p. 92, 93) has more fully 

described the type, which is a phragmocone that consists of one complete whorl; the inner whorls are not 

preserved. The intercostal whorl section, at the larger 

end, is much broader than high. Ornament on the side 

of the whorl consists of 11 broad, low, rectiradiate ribs, 

each of which supports a strong bullate umbilical tubercle and a larger nodate ventrolateral tubercle or horn 

that is directed upwards and outwards. Regarding ornament on the venter, Kennedy (1971, p. 93) observed 

that

At the smallest diameter visible there are 2 strong clavate upper 

ventro-lateral tubercles and 1 or 2 small rounded tubercles en a spirally 

elongate siphonal swelling, connected to the upper ventro-lateral 

tubercles by a broad low rib.

Between the long ribs there are 1 or 2 short intercalated ribs, extending across the venter only. These bear a rounded siphonal tubercle, 

or, in some cases, 2 smaller tubercles. With increasing size the intercalated ventral ribs disappear, as do the siphonal tubercles, whilst 

the ventro-lateral horn and upper ventro-lateral tubercle combine to 

form a large bituberculate horn. The siphonal region between the horns 

is depressed.

Cunningtoniceras amphibolum (Morrow)

Plates 4-8; plate 9, figures 48-63

Cunningtoniceras amphibolum is a moderate sized, 

somewhat evolute ammonite that has quadrate whorls 

with flattened flanks and very broadly rounded venter. 

Ribs are straight and rectiradiate to prorsiradiate; they 

are long and short on the innermost whorls and equal 

in length on the outer whorls. The ribs on the inner 

whorls bear umbilical bullae or bullate umbilical 

tubercles, nodate inner ventrolateral tubercles, and 

clavate outer ventrolateral and siphonal tubercles. On 

later whorls, the outer ventrolateral tubercles weaken 

and disappear, and the siphonal tubercles gradually 

weaken and merge into a low siphonal ridge. Inner ventrolateral tubercles become larger on the outer whorls 

and, on the body chamber of large adults, rise into prominent horns that are directed outward and upward. The 

species seems to be dimorphic. Cunningtoniceras amphibolum is widely distributed in the Western Interior 

from south-central Montana south to the vicinity of El 

Paso, Tex. (fig. 7).

Ammonites loevianus White (1877, p. 201, pi. 19, fig. 

la, b), from New Mexico, is closely related to if not identical to Cunningtoniceras amphibolum. White's species 

was treated briefly by Stanton (1893, p. 178, pi. 43, figs. 

3, 4), but since then the species has seldom been mentioned in the literature; the name is best considered a 

nomen oblitum.

Molluscan fossils usually found with C. amphibolum 

include Inoceramus arvanus Stephenson, /. rutherfordi 

Warren, Ostrea beloiti Logan, and Borissiakoceras 

reesidei Morrow. In the southern part of the Western 

Interior, a more varied ammonite fauna occurs with C. 

amphibolum. Important ammonites from that region are 

Desmoceras (Pseudouhligella) aff. D. japonicum Yabe, 

Paracompsoceras landisi Cobban, Thrrantoceras rotatile 

Stephenson, and Turrilites acutus americanus Cobban 

and Scott (Cobban, 1977).
10 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

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FIGURE 7. Map showing localities (x) where Cureremgtomceras amphibolum (Morrow) has been found.
SYSTEMATIC DESCRIPTIONS 11

Cunningtoniceras amphibolum amphibolum (Morrow)

Plate 4; plate 5, figures 1-25

1935. Acanthocerasl amphibolum Morrow, Journal of Paleontology, v. 9, no. 6, p. 470, pi. 49, figs. 1-4, 6; pi. 51, 

figs. 3, 4; text fig. 4.

1942. Acanthoceras alvaradoense Moreman, Journal of Paleontology, v. 16, no. 2, p. 205, pL 32, fig. 6; text figs. 2o, 2t.

1952 (1953). Acanthoceras hazzardi Stephenson, U.S. Geological 

Survey Professional Paper 242, p. 201, pi. 48, figs. 1, 

2; pi. 49, fig. 4.

1955. Euomphaloceras alvaradoense (Moreman). Stephenson, 

U.S. Geological Survey Professional Paper 274-C, 

p. 63, pi. 7, figs. 1-9.

1960. Acanthoceras amphibolum Morrow. Matsumoto, 

Kyushu University Faculty of Science, Science 

Reports, Geology, v. 5, no. 1, p. 41, text fig. 5b-d.

1960. Acanthoceras hazzardi Stephenson. Matsumoto, Kyushu 

University Faculty of Science, Science Reports, 

Geology, v. 5, no. 1, p. 41, text fig. 5a

1960. Acanthoceras alvaradoense Moreman. Matsumoto, 

Kyushu University Faculty of Science, Science 

Reports, Geology, v. 5, no. 1, p. 41, text fig. 6a-c.

1963. Paracanthoceras amphibolum (Morrow). Haas, American Museum Novitates 2151, p. 18.

1964. Plesiacanthoceras [amphibolum (Morrow)]. Haas, Journal of Paleontology, v. 38, no. 3, p. 610.

1965. Plesiacanthoceras amphibolum (Morrow). Hattin, Kansas Geological Survey Bulletin 178, pi. 4, figs. J, K; 

pi. 5, figs. C-F.

1965. Plesiacanthoceras amphibolum (Morrow). Hattin, 

Geological Society of America Field Conference 

Guidebook, Upper Cretaceous stratigraphy, paleontology, and paleoecology of western Kansas, Annual 

Meetings, 1965, text fig. 3 (photo 8).

1966. Acanthoceras amphibolum Morrow. Matsumoto and

Obata, National Science Museum [Tokyo] Bulletin, v.

9, no. 1, p. 45, text figs. 4-6. 

1966. Acanthoceras hazzardi Stephenson. Matsumoto and

Obata, National Science Museum [Tokyo] Bulletin, v.

9, no. 1, p. 45, text fig. 7.

1968. Plesiacanthoceras [amphibolum Morrow]. Laporte, Ancient environments (Prentice-Hall), text fig. 6-10H.

1969. Acanthoceras amphibolum Morrow. Matsumoto, 

Muramoto, and Takahashi, Kyushu University Faculty of Science Memoirs, Series D, Geology, v. 19, no. 

2, p. 266, pi. 31, fig. la, b.

1972 (1973). Acanthoceras amphibolum Morrow. Cobban and Scott, 

U.S. Geological Survey Professional Paper 645, p. 65 

(part).

1977. Acanthoceras alvaradoense Moreman. Cobban, U.S. 

Geological Survey Professional Paper 1009, p. 24, pi. 

6, figs. 1-7, 11-20; text fig. 6.

1977. Acanthoceras amphibolum Morrow. Hattin, The Mountain Geologist, v. 14, nos. 3-4, p. 183, fig. 13.

1978. Acanthoceras amphibolum Morrow. Hattin and Siemers, 

Kansas Geological Survey Guidebook Series 3, fig. 

5 (photo 14).

1979. Acanthoceras alvaradoense Moreman. Merewether, Cobban, and Cavanaugh, The Mountain Geologist, v. 16, 

no. 3, pi. 1, figs. 3-7.

1985. Acanthoceras amphibolum Morrow. Zaborski, Bulletin 

of the British Museum (Natural History), Geology 

Series, v. 39, no. 1, p. 35, figs. 38-41.

Morrow (1935) illustrated four syntypes from the upper part of the Graneros Shale of central Kansas as well 

as a plaster cast of a large adult in the National Museum 

of Natural History, Washington, D.C. The four syntypes, 

which are well-preserved, uncrushed, internal molds, apparently all came from one or more limestone concretions at one locality. In addition to good photographs 

of these four syntypes, Morrow (1935, text fig. 4) presented a drawing of the whorl section of the largest of 

them. At a later date, Matsumoto (1960, text fig. 5BD) showed a new drawing of this whorl section as well 

as drawings of the whorl sections of two other syntypes. 

Morrow's description of his species is generalized and 

based on other specimens as well as the syntypes. Three 

of the syntypes are worthy of more detailed descriptions.

The smallest syntype (pi. 4, figs. 1-3), which has a 

diameter of 27.3 mm and an umbilical ratio of 0.25, consists of a phragmocone and nearly half a whorl of body 

chamber. Diameter at the base of the body chamber is 

19.3 mm. The last septa are not crowded, which suggests 

that the specimen is immature. Ornament is strong on 

the outer whorl, where ribs are mostly of equal length 

and number 15. Longer ribs arise from nodate umbilical 

bullae, and all ribs bear nodate inner ventrolateral 

tubercles and clavate outer ventrolateral and siphonal 

tubercles. All clavate tubercles are asymmetric with 

steep adoral slopes. The tuberculated ribs cross the 

venter as broad folds slightly arched forward.

The second smallest syntype (pi. 4, figs. 4-6), which 

is herein designated as the lectotype, has a diameter of 

55.8 mm and an umbilical ratio of 0.28; it is chiefly a 

phragmocone with a bit of the body chamber. Matsumoto (1960, fig. 5B) has drawn its squarish whorl section. Diameter at the base of the body chamber is 

53 mm. Inasmuch as the last septa are not crowded, the 

specimen may represent an immature individual. Ribs 

on the outer whorl number 18 and are prorsiradiate and 

equal in length. The ribs begin on the steep umbilical 

wall, rise into umbilical bullae on the lower part of the 

flank, cross the flank with slight forward inclination, and 

rise again into nodate to clavate inner ventrolateral 

tubercles and clavate outer ones, which are set forward 

a little. Opposite ventrolateral tubercles may or may not 

be connected across the venter by weak, poorly defined 

ribs that support weak clavate siphonal tubercles. These 

scarcely visible ventral ribs are separated by faint 

secondary ventral ribs that have outer ventrolateral and 

siphonal tubercles.

The third syntype (Morrow, 1935, pi. 49, fig. 1), of 

which Matsumoto (1960, fig. 5C) has shown its whorl 

section, is half a specimen of 95 mm diameter with an 

umbilical ratio of 0.30. Most of the outer whorl is unchambered and probably represents the older half of a
12 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

body chamber that had a diameter of about 70 mm at 

its base. Ribs on the last half whorl numbered about 

10. These ribs begin near the umbilical seam and slant 

forward to the umbilical shoulder, where they rise into 

umbilical bullae on the lower part of the flank. The ribs 

then bend back slightly before crossing the flank. Each 

rib terminates in a prominent inner ventrolateral tubercle, which is clavate on the older part of the whorl and 

horn-like on the younger part. Very weak clavate outer 

ventrolateral tubercles are present on the older end of 

this half whorl, but these weaken further and disappear. 

A low siphonal ridge is present on the entire half whorl. 

On the older part of the whorl, the siphonal ridge is 

weakly beaded by faint forwardly arched ventral riblets.

Innermost whorls of Cunningtoniceras amphibolum 

were not illustrated by Morrow. According to Morrow 

(1935, p. 470, 472), whorls at a diameter of 2 mm are 

wider than high and broadly rounded, and they are 

smooth except for a row of pointed, conical lateral 

tubercles. These tubercles migrate ventrally as the shell 

enlarges, and by a diameter of 5 mm, they become the 

inner ventrolateral row. At this diameter outer ventrolateral and siphonal tubercles appear, as well as ribs. 

The whorl assumes a subquadrate section by a diameter 

of 15 mm.

The suture is typical of the genus in that it is only 

moderately digitate with broad bifid E/L and a rectangular bifid L. Morrow (1935, pi. 51, figs. 3, 4) illustrated two external sutures.

Fossils from Kansas in the collections of the U.S. 

Geological Survey at the Denver Federal Center include 

only one specimen (hypotype USNM 388123) from the 

type locality of C. amphibolum. This specimen (pi. 4, 

figs. 7-9), from locality 12510 (fig. 1), is preserved exactly like Morrow's syntypes. The specimen may be 

nearly complete; it has a diameter of 72 mm and an umbilical ratio of 0.30. The last half whorl is a body 

chamber that has a diameter of 51.3 mm at its base. 

Septa are uniformly spaced, which suggests an immature individual. Whorls are subquadrate and a little 

wider than high. Ornament on the outer whorl consists 

of 17 equal rounded ribs that are narrower than the interspaces and have umbilical bullae, nodate inner ventrolateral tubercles, and clavate outer ventrolateral and 

siphonal ones. Siphonal tubercles, although weakening, 

persist to the end of the specimen. On the older part 

of the outer whorl, the clavate siphonal tubercles are 

separated by a smaller nodate siphonal tubercle located 

on a faint secondary ventral rib (pi. 4, fig. 8).

Morrow's four syntypes came from the upper part of 

the Graneros Shale on the "south bank of Smoky Hill 

River south of Wilson, Ellsworth County, Kansas". 

(Morrow, 1935, p. 473). On the Wilson 7 1/2-minute quadrangle, the collection is from the S1/2S1/2 sec. 31, T. 14 S.,

R. 10 W., about 4 km (2Vz mi) south of Wilson. The collection made by N. W. Bass and others at this locality 

(fig. 1, loc. 12510) was said to have come from "4 feet 

below top of Graneros Shale" (original label with the 

collection). Hattin (1965a, p. 76, 77) measured a section 

nearby and noted the presence of C. amphibolum in the 

Graneros Shale about 4.8 m (16 ft) below a thick 

widespread bed of bentonite referred to as the bentonite 

marker bed, which lies about 0.9 m below the top of the 

Graneros Shale at this locality.

Hattin (1965a, pi. 4, figs. J, K; pi. 5, figs. C-F) illustrated several good examples of C. amphibolum from 

3.4 m (11 ft) below the bentonite marker bed at a locality 12 km (8 mi) southeast of the type locality of the 

species. Among them is a large body chamber of half 

a whorl about 210 mm in diameter (Hattin, 1965a, pi. 

5, figs. C, E). Ornament is sparse and consists of five 

very widely spaced straight, rectiradiate ribs of which 

all but the final one have umbilical bullae and ventrolateral horns. Outer ventrolateral tubercles and 

siphonal tubercles have disappeared at this large size. 

Opposite horns are connected across the venter by 

broad, low, flat, transverse ribs, which are raised a little along the margins to form looped ribs. The final rib 

at the aperture is narrow and forms a flange like that 

of a specimen from near Pueblo, Colo. (Cobban and 

Scott, 1972, pi. 10, fig. 16).

A collection made by me at Hattin's locality (fig. 1, 

loc. D4428) revealed marked dimorphism in adult 

specimens of C. amphibolum (pi. 4, figs. 10, 11). Adult 

body chambers are characterized by a loss of the outer 

ventrolateral and siphonal tubercles and by the development of the inner ventrolateral tubercles into horns. 

Diameters at the base of the few measurable adult body 

chambers range from 53 to 115 mm.

Earliest whorls are either not visible or not well 

enough preserved for study in the collection from locality D4428. An excellent collection from the Graneros 

Shale at locality D5900 (fig. 1) southwest of the Black 

Hills in eastern Wyoming includes many small whorls 

(pi. 5, figs. 1-25). The earliest whorl examined, at a 

diameter of 1 mm, is smooth, well rounded, and wider 

than high. Tubercles appear at some diameter around 

3 mm. At diameters of 5-9 mm nodate, equal-sized inner and outer ventrolateral and siphonal tubercles form 

a forwardly arched row across the venter bounded on 

the adoral side by a low constriction. There are 5-7 rows 

per half whorl; the rows are well separated by smooth 

areas. At some diameter between 9 and 12 mm, ribs 

develop along the tubercles, and another row of tubercles 

usually arises on the adoral side of the constriction, or 

the constriction disappears, and a weak untuberculated 

rib may form midway between the tuberculated ribs. 

These rib arrangements and constrictions were not
SYSTEMATIC DESCRIPTIONS 13

mentioned by Morrow. On the early whorls from locality D5900, ribs usually lengthen to the umbilicus at a 

diameter of about 10 mm, and umbilical bullae arise at 

diameters from 7 to 12 mm.

Forty specimens, 7-117 mm in diameter, from locality D5900 are suitable for determination of two or more 

of the following measurements: diameter of shell, 

diameter of umbilicus, diameter at base of body 

chamber, and number of ribs per half whorl. Diameters 

at the base of body chambers, which could be determined for 17 specimens, ranged from 13.3 to 114 mm. 

Sixteen of these specimens have measurements of 

13.3-44.7 mm, but inasmuch as none of these has 

crowded terminal sutures or ventrolateral horns, they 

may represent immature individuals. Ribs on the specimens from locality D5900 are mostly of uniform length 

and number 8-14 in half a whorl, averaging 9.1. Fifteen 

of the specimens have at some growth stage secondary 

ribs on the venter. These ribs are weaker than the 

primary ones and usually support weak outer ventrolateral and siphonal tubercles. Only one secondary 

rib separates the primaries. Secondary ribs on the venter 

were not observed at diameters larger than 41 mm.

Morrow did not record the presence of secondary ribs 

and tubercles on the venter of C. amphibolum, nor did 

he record the presence of constrictions on the earliest 

whorls. These facts led to considerable confusion as to 

the concept of the species. A form, now known to be 

younger than C. amphibolum amphibolum, occurs at 

many localities in the Western Interior of the United 

States. Adults cannot be separated from those of C. amphibolum amphibolum, but the inner whorls generally 

lack constrictions and extra ventral ornament. Specimens of this type were considered as Acanthoceras amphibolum; however, those with constrictions and extra 

ventral ornament were assigned to A. alvaradoense 

Moreman (Cobban, 1977, p. 23, 24). Acanthoceras amphibolum and A. alvaradoense are the same subspecies 

and should be assigned to Cunningtoniceras. The slightly younger specimens that usually lack extra ventral ornament are herein assigned to the new subspecies C. 

amphibolum fallense.

Cunningtoniceras amphibolum amphibolum has been 

found at many localities in the Western Interior. A 

number of localities are clustered in the central part of 

Kansas (fig. 7), where the subspecies occurs as undeformed specimens in limestone concretions or as flattened impressions in shale in the upper part of the 

Graneros Shale below the bentonite marker bed. Farther 

northwest, near the central eastern boundary of Wyoming, limestone concretions below the bentonite marker 

bed in the upper part of the Graneros Shale, contain excellent specimens of C. amphibolum amphibolum (fig. 

1, loc. D5900). The subspecies has not been positively

identified farther west in Wyoming or southward in Colorado. However, it occurs at many localities in westcentral New Mexico, where it was recorded as Acanthoceras alvaradoense in the Clay Mesa Tongue of the 

Mancos Shale (Cobban, 1977, table 1 and p. 24). The 

subspecies is also abundant and well preserved in 

calcarenite at the base of the Boquillas Formation in 

New Mexico just west of El Paso, lex. (fig. 1, loc. 

D10142), where it was recorded as A. alvaradoense 

(Strain, 1976, p. 82). 

Types.-Hypotypes USNM 388123-388135.

Cunningtoniceras amphibolum fallense Cobban, n. subsp.

Plate 5, figures 26, 27; plates 6-8; plate 9, figures 48-63

1972. Acanthoceras amphibolum Morrow. Cobban and Scott, p. 65 

(1973) (part), pi. 9; pi. 10, figs. 12-16; text fig. 26. 

1976. Acanthoceras amphibolum Morrow. Kauffman, Cobban, and 

(1978) Eicher, Museum d'Histoire Naturelle de Nice Annales, v.

4, p. XXIII. 39, figs. 1, 2. 

1977. Acanthoceras amphibolum Morrow. Cobban, U.S. Geological

Survey Professional Paper 1009, p. 23, pi. 8, figs. 8, 9; pi.

12, figs. 10-12, 15-23; text fig. 5. 

1977. Acanthoceras amphibolum Morrow. Kauffman, The Mountain

Geologist, v. 14, nos. 3-4, pi. 15, figs. 1, 2. 

1979. Acanthoceras amphibolum Morrow. Merewether, Cobban, and

Cavanaugh, The Mountain Geologist, v. 16, no. 3, pi. 1, figs.

1, 2, 8, 9.

This chronologic subspecies usually lacks multiplication of ventral ornament. Like the nominate subspecies, 

C. amphibolum fallense is dimorphic. Many of the microconchs seem to be slightly more slender and more 

evolute than similar sized microconchs of C. amphibolum 

amphibolum (fig. 8). The holotype (pi. 5, figs. 26, 27) and 

several of the figured paratypes (pi. 6) of C. amphibolum 

fallense came from limestone concretions developed 

along the bentonite marker bed near the top of the Belle 

Fourche Shale at locality D7370 in southwestern South 

Dakota (fig. 1). This collection contains 19 specimens 

24-150 mm in diameter that are suitable for the determination of three or more of the following measurements: diameter of the shell, diameter of the umbilicus, 

diameter of the base of the body chamber, and the 

number of ribs in half a whorl.

The holotype (pi. 5, figs. 26, 27) is a small adult 

macroconch 132 mm in diameter with an umbilicus of 

51.4 mm (ratio 0.39). The specimen, an uncrushed internal mold badly weathered on one side, is made up of a 

nearly complete body chamber and the outer IVz whorls 

of the phragmocone. Innermost whorls are not preserved. The last septate whorl has a rectangular intercostal section that is slightly higher than wide with 

flattened flanks and venter and steep umbilical wall. 

Ribs, which number 18 on this whorl, are straight,
14 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

40, 

DC 30

=i20

OQ

10

10 20 30 40 50 

DIAMETER, IN MILLIMETERS

60 70 80

FIGURE 8. Scatter diagram of umbilical ratios of Cunningtoniceras amphibolum amphibolum ( ) from the Belle Fourche Shale at 

locality D5900 (fig. 1) and C. amphibolum fallense (x) from the Belle Fourche Member at locality 20934 (fig. 1).

rounded, prorsiradiate, equal in length, and narrower 

than the interspaces. Each rib begins on the outer part 

of the umbilical wall, rises into a forwardly inclined bulla 

on the narrowly rounded umbilical shoulder, crosses the 

flank, and rises again into a conspicuous nodate inner 

ventrolateral tubercle. From there, a forwardly arched, 

broad, very low swelling crosses the flattened venter. 

This swelling supports low, clavate outer ventrolateral 

and siphonal tubercles on the older part of the whorl, 

but these disappear on the younger part. Diameter of 

the phragmocone at the base of the body chamber is 

102.4 mm. The body chamber, which occupies half a 

whorl, has a squarish section with broadly rounded 

flanks and venter, well-rounded umbilical shoulder, and 

gently sloping umbilical wall. Ornament consists of 5 

straight, rectiradiate ribs, 4 of which bear prominent 

nodate umbilical tubercles and inner ventrolateral horns 

that are directed upward and outward. The fifth or final 

rib forms a flange that curves forward on crossing the 

venter. Ribs on the body chamber are much farther 

apart than those on the phragmocone. Opposite ventrolateral horns are connected across the venter by broad, 

flat areas that may or may not be elevated a little. Only 

the ventral margin of the aperture is preserved; it is 

broadly convex forward. Sutures on the holotype are 

poorly preserved, but they seem typical of the species. 

Of the 19 specimens suitable for measurements from 

locality D7370, only one shows extra ventral ornament. 

This specimen, which is half a whorl of 36 mm diameter, 

has weak nontuberculated ventral ribs alternating with 

the stronger tuberculated primary ribs. Occasional 

specimens have closely spaced riblets on the venter and

flanks (pi. 6, figs. 1-4, 7), and on one individual, these 

riblets seem to have replaced the normal ribbing on part 

of the whorl (pi. 6, fig. 7).

The specimens from locality D7370 are dimorphic. 

Microconchs have body chambers characterized by loss 

of outer ventrolateral and siphonal tubercles and with 

or without the development of inner ventrolateral horns. 

Outer ventrolateral and siphonal tubercles weaken and 

disappear on the last quarter of the outer septate whorl, 

or at the base of the body chamber, or on the older part 

of the body chamber. Ventrolateral horns form only on 

the larger microconchs. The 14 specimens that can be 

considered as microconchs have the following diameters 

in millimeters (rounded) at the base of the body 

chambers: 36, 45, 51, 55, 57, 60, 60, 64, 68, 73, 73, 74, 

75, and 77. Macroconchs, represented by only 5 specimens, resemble the larger microconchs in their horn 

development. Diameters in millimeters (rounded) at the 

base of the body chambers range from 102 (holotype) 

to an estimated 210.

The specimens from locality D7370 are from the 

southeast flank of the Black Hills uplift in Fall River 

County, S. Dak., which is the source of the subspecies 

name. Associated fossils include abundant Inoceramus 

arvanus Stephenson and Ostrea beloiti Logan, a single 

small hamitid, and numerous Borissiakoceras reesidei 

Morrow and Protacanthoceras hosei Cobban, n. sp.

Another large collection of C. amphibolum fallense (pi. 

7) is from very fine grained sandstone concretions in the 

upper part of the Frontier Formation at locality 22804 

in north-central Wyoming (Hose, 1955, p. 100). Thirtytwo specimens from 18 to 123 mm in diameter are
SYSTEMATIC DESCRIPTIONS 15

suitable for measurements. Only 4 of these, which have 

diameters of 27-36 mm, have slight multiplication of 

ventral ornament. Diameters at the base of the body 

chambers could be determined or estimated for 27 

specimens (fig. 9). Fifteen of these, which have diameters 

of 18.3-51 mm at the base of the body chamber, may 

be considered microconchs because outer ventrolateral 

and siphonal tubercles disappear at or near the base of 

the body chamber. Inner ventrolateral tubercles persist 

on the body chamber, where they become large and conspicuous but not horn-like. Only one of the microconchs 

has crowded terminal sutures. Specimens that may be 

considered macroconchs have diameters at the base of 

body chambers of 61-123 mm. Body chambers have ventrolateral horns. Even these specimens seem to be 

dimorphic with 10 of them that have diameters at the 

base of the body chamber of 61-94 mm and with 2 that 

have diameters of 110 and 123 mm.

The subspecies attains diameters of nearly 200 mm. 

One of the large specimens (pi. 8) from locality D8442 

(fig. 1) shows a rejuvenation of cunningtonicerid ventral 

ornament at a very large diameter.

Cunningtoniceras amphibolum fallense has been 

found at many localities in the Western Interior. Specimens are exceptionally well preserved in limestone concretions developed along a widespread thick bed of 

bentonite in the upper part of the Belle Fourche Shale 

in the Black Hills area of western South Dakota, eastern 

Wyoming, and southeastern Montana. This bed of bentonite was informally referred to as the gray-red bentonite by M. N. Bramlette and W W. Rubey (in Moore, 

1949, fig. 18; also see Robinson and others, 1964, p. 53); 

it has also been designated as bed F by Knechtel and 

Patterson (1955; 1962, p. 982). Farther northwest, in 

south-central Montana, this bed was formally named the 

Soap Creek Bentonite Bed of the Belle Fourche Member 

of the Cody Shale (Knechtel and Patterson, 1952; 1956, 

p. 18). In this area, limestone concretions associated with 

the bentonite locally contain well-preserved specimens 

of C. amphibolum fallense, some with nacreous shells. 

At one locality (fig. 1, loc. 24319), specimens lying on

40 65 90 115 125 

DIAMETER AT BASE OF BODY CHAMBER, IN MILLIMETERS

FIGURE 9. Histogram showing diameters at base of body chambers 

of the 27 measurable specimens of Cunningtoniceras amphibolum 

fallense Cobban, n. subsp., from the Frontier Formation at locality 

22804 (fig. 1).

the Soap Creek Bentonite Bed have been replaced by silica 

derived from the bentonite. In eastern Colorado, a widely 

distributed bed of bentonite that is probably a continuation 

of the Soap Creek Bed, has been informally referred to as 

the marker bentonite bed and considered as the base of the 

Greenhorn Limestone (Cobban and Scott, 1972, p. 16, fig. 

10). Concretionary limestone developed along this bed of 

bentonite contains C. amphibolum fallense. This 

subspecies occurs in sandstone farther southwest in the 

northern and west-central parts of New Mexico.

Types Holotype USNM 388136, paratypes USNM 

388137-388151.

Genus PLESIACANTHOCERAS Haas, 1964

Type species. Metoicoceras wyomingensis Reagan, 

1924.

This genus, originally named Paracanthoceras Haas 

(1963, p. 2), was renamed Plesiacanthoceras by Haas 

(1964), after he found that his earlier name was preoccupied by Paracanthoceras Furon (1935, p. 59). The 

original generic description (Haas, 1963, p. 2, 3) is as 

follows:

Involute in youth, becoming increasingly more evolute with growth. 

Whorl section rectangular to subquadratic, with gently convex flanks 

and truncate venter. Ornamentation consisting of radial ribs which 

gradually disappear, circumumbilical tubercles gradually shifting away 

from umbilical shoulder and developing into horns, inner and outer 

lateroventral tubercles, outer ones more pronouncedly elongated spirally; both eventually merging into large horns that point outward and 

upward. Inconspicuous median tubercles, present in youth only, forming an intermittent keel which soon fades. Suture line characterized 

by particularly high outer main stem of very large external saddle and 

by wide first lateral lobe which is mostly bifid.

Plesiacanthoceras has been considered a synonym of 

Acanthoceras by several authors (Matsumoto, 1960, 

p. 43; Matsumoto and Obata, 1966, p. 45-47; Kennedy, 

1971, p. 85; Juignet and Kennedy, 1976, p. 113). However, 

I believe that the very early loss of siphonal tubercles 

and the development of conspicuous nodate umbilical 

tubercles and ventrolateral horns seem distinctive 

enough from Acanthoceras to retain the separation. 

Plesiacanthoceras was derived from Cunningtoniceras 

by an earlier loss of siphonal tubercles and by the upward projection of the outer ventrolateral clavi well 

above the middle of the venter on the intermediate inner whorls. The inner whorls of Plesiacanthoceras are 

much like those of Dunveganoceras; whereas, the outer 

whorl of Plesiacanthoceras is like that of horned Cunningtoniceras. Plesiacanthoceras is transitional from the 

older Cunningtoniceras to the younger Dunveganoceras. 

The genus is known from rocks of late middle Cenomanian age in the Western Interior.
16 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

Plesiacanthoceras wyomingense (Reagan)

Plate 10, figures 48-82; plates 11-13

1924. Metoicoceras wyomingensis Reagan, Pan-American Geologist,

v. 41, no. 3, p. 181, pi. 19, figs. 1, 2. 

1946. Prionotropis woollgari Meek (Inon Mantell) forma typical

Haas, American Museum of Natural History Bulletin, v.

86, art. 4, p. 153,157,161,164,172,185,197, pi. 14, fig. 11. 

1949. Collignoniceras woollgari (Meek, non Mantell) forma typical

Haas, American Museum of Natural History Bulletin, v.

93, art. 1, p. 29, footnote 2. 

1949. "Mammites" n. sp. Haas, American Museum of Natural

History Bulletin, v. 93, art. 1, p. 28. 

1949. Dunueganoceras sp. indet. Haas, American Museum of Natural

History Bulletin, v. 93, art. 1, p. 30, pi. 15, figs. 1-3; text

fig. 10.

1951. Acanthoceras? n. sp. Cobban. American Association of Petroleum Geologists Bulletin, v. 35, no. 10, p. 2182, text fig. 2.

1952. Acanthocerasl sp. A. Cobban and Reeside, Geological Society of America Bulletin, v. 63, no. 10, p. 1017, chart 10B.

1955. Acanthoceras athabascense Warren and Stelck, Research Council of Alberta Report 70, p. 71, pi. 6, figs. 5, 6; pi. 7, figs. 

1, 3, 4; pi. 8, figs. 1-3; pi. 9, fig. 2.

1958. Acanthoceras? wyomingense (Reagan). Cobban, Wyoming 

Geological Association Guidebook 13th Annual Field Conference, Powder River Basin, p. 118, text fig. 2.

1963. Paracanthoceras wyomingense (Reagan). Haas, American 

Museum Novitates 2151, p. 3, text figs. 1-12.

1964. Plesiacanthoceras wyomingense (Reagan). Haas, Journal of

Paleontology, v. 38, no. 3, p. 610. 

1966. Acanthoceras wyomingense (Reagan). Matsumoto and Obata,

National Science Museum [Tokyo] Bulletin, v. 9, no. 1,

p. 45-47. 

1968. Plesiacanthoceras wyomingense (Reagan). Hattin, Journal of

Paleontology, v. 42, no. 4, p. 1084, text figs. 3, 4.

1975. Acanthoceras wyomingense (Reagan). Hattin, Kansas Geological Survey Bulletin 209, pi. 4, figs. D, F.

1976. Plesiacanthoceras wyomingense (Reagan). Kauffman, Cobban,

(1978) and Eicher, Annales du Museum d'Histoire Naturelle de 

Nice, v. 4, pi. 5, figs. 15, 16.

1977. Plesiacanthoceras wyomingense (Reagan). Kauffman, The 

Mountain Geologist, v. 14, nos. 3-4, pi. 22, figs. 15, 16.

1979. Plesiacanthoceras wyomingense (Reagan). Merewether, Cobban, and Cavanaugh, The Mountain Geologist, v. 16, no. 3, 

pi. 1, figs. 15, 16.

The holotype, Stanford University 119, is a poorly 

preserved, worn, internal mold of half a phragmocone. 

Haas (1963, p. 4), who examined the type, gave its 

diameter as 120 mm, its umbilicus as 18 mm (0.15), its 

height as 50.5 mm, and its width as 38 mm. Whorl section is rectangular with flattened flanks and venter and 

low, sloping umbilical wall. Ornament, which is fairly 

weak, consists of about 5 umbilical bullae and 10 equalsized inner and outer ventrolateral tubercles. Inner ventrolateral tubercles are nodate to slightly clavate, and 

outer ones are clavate; the latter ones rise above the flat, 

somewhat depressed venter. The specimen came from 

the Frontier Formation somewhere northwest of Casper, 

Wyo.

Plesiacanthoceras wyomingense is widely distributed 

mainly in Wyoming (fig. 10). Most collections are from 

silty concretions in the Frontier Formation, but the best 

preserved specimens are from limestone concretions in 

the Belle Fourche Shale along the north and northwest 

flanks of the Black Hills.

A collection from locality 22871, near Alzada, Mont, 

(fig. 1), includes many minute ammonites, some of which 

are probably juveniles of P. wyomingense. The shells of 

many of these juveniles are damaged at the base of the 

body chamber, probably owing to the work of some sort 

of predator. The smallest specimen that seems assignable to this species is a juvenile 10.4 mm in diameter 

(pi. 10, figs. 48-50). This specimen (hypotype USNM 

388152) has a quarter of the body chamber preserved. 

The outer septate whorl is wider than high with very 

broad gently rounded venter, narrow flattened flanks, 

well rounded umbilical shoulder, and steep umbilical 

wall. Ornament on the older half of this septate whorl 

consists of 5 low, rounded, rectiradiate ribs that support 

small, pointed, nodate inner and outer ventrolateral 

tubercles matched by low siphonal clavi. A low, barely 

visible, slightly trituberculate secondary ventral rib 

crosses the venter transversely between the primary ones. 

The body chamber of this juvenile has a more quadrangular section. Ribs begin from umbilical bullae located 

on the umbilical shoulder, and the inner ventrolateral 

tubercles become a little clavate. Faint secondary ventral ribs were observed on another juvenile (hypotype 

USNM 388153), on which the secondaries disappeared 

at a diameter of 10.5 mm (pi. 10, figs. 51-53).

As the shell enlarges, the intercostal whorl section 

becomes more slender, and most specimens 18-160 mm 

in diameter have subrectangular intercostal sections 

higher than wide with the greatest width at the umbilical 

shoulder (pi. 10, figs. 63-82).

Ribs are conspicuous only on juveniles that have 

diameters less than 80 mm. On these specimens, ribs are 

alternately long and short. The longer ribs begin on the 

umbilical wall and bend forward a little to the umbilical 

shoulder, where they rise into conspicuous bullae. The 

ribs then bend back slightly and cross the flank rectiradially or prorsiradially. Shorter ribs arise at the umbilical shoulder or about midflank. All ribs become broad 

at the ventrolateral shoulder and cross the venter transversely as low, wide bulges. Each rib supports a nodate 

to slightly clavate inner ventrolateral tubercle and a 

clavate outer one and, on the smaller specimens, a weak 

clavate siphonal tubercle. The outer ventrolateral ones 

are asymmetric with steep adoral sides. Ventrolateral 

tubercles number 8-12 per half whorl.

As the shell enlarges, secondary ribs disappear, and
111°

SYSTEMATIC DESCRIPTIONS

109° 107°

17

105°

45'

IDAHO I

MONTANA

7C~x 

0

Sheridan

T~~T~ ____ 

X* X,

X

Basin^

X X

o

Buffalo Gillette ! x Sundance° (ft

0 |____ '2

,_ J iWoitando ^VVUIIOIIU O X*

J L_,

^"L i I 

ThermopoliSQ x1 , I X I "^- v-L-^-f Newcastle 0 p

WYOMING x

1 Jxx

-j 15

i

L

, Green River

 1

x X

O ' 

iTorrington

XRawlins

X

I I

I

1 -

"

I 

~1

QCHEYENNE INEI

«_ L " "

UTAH COLORADO

I 

100

100 150

I

I I 

150 200 KILOMETERS

200 MILES

i

FIGURE 10. Map of Wyoming showing localities (x) where Plesiacanthoceras wyomingense (Reagan) has been found.

the umbilical tubercles become stronger and nodate and 

migrate out onto the lower part of the flank (pi. 11, 

fig. 13; pi. 12, fig. 2). Outer ventrolateral tubercles 

become weak and disappear at some diameter between 

110 and 150 mm. As these tubercles disappear, the inner ventrolateral tubercles enlarge into conspicuous 

clavate horns that are directed outwards and a little upwards (pi. 11, figs. 12,13). Various growth states can be 

seen on two individuals (hypotype USNM 388165 on 

pi. 11, figs. 3-7 and pi. 12, and hypotype USNM 388167 

on pi. 11, figs. 10-13).

Ribs on the larger adults are usually very low, flat, 

and inconspicuous; they may disappear at midflank or 

on the venter. On some specimens, low looped ribs connect opposite ventrolateral horns, or they may connect 

the horns to the umbilical nodes. A fragment of a septate whorl (hypotype USNM 388168) that retains its 

shell material revealed slightly raised growth lines 

crossed at right angles by closely spaced fine spiral lines 

(pi. 13, fig. 4).

Large adults of half a whorl or more are not present 

in the collection from locality 22871, although there are
18 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

several fragments of large body chambers. For illustrations of a complete adult, the reader is referred to Haas 

(1963, text figs. 10-12). The species is probably dimorphic, although this cannot be proven with the material 

at hand.

Some specimens from the Frontier Formation of southcentral Wyoming differ from those from the Belle Fourche Shale of the Black Hills area in that siphonal clavi 

are retained to diameters of 70-110 mm. In this respect, 

the specimens are like one of the paratypes of Acanthoceras athabascense Warren and Stelck (1955, pL 7, fig. 1).

The suture is much like that of Acanthoceras. The 

lateral lobe (L) and adjoining saddles show well on one 

of the specimens figured by Haas (1963, fig. 8) as well 

as on the large phragmocone shown in plate 12 of the 

present report.

Ammonites associated with P. wyomingense at locality 22871 include two species originally described from 

Texas as Acanthoceras cuspidum Stephenson (1952, 

p. 202, pi. 50, figs. 1-4) and Borissiakoceras orbiculatum 

Stephenson (1955, p. 64, pL 6, figs. 1-4). The former came 

from the Woodbine Formation, and the latter came from 

the basal beds of the Eagle Ford. Kennedy (1971, p. 97, 

121) regarded A. cuspidum as a Protacanthoceras, but 

later Wright and Kennedy (1980, p. 99) considered it as 

a possible Dunveganoceras. Two specimens of B. orbiculatum from locality 22871 were illustrated by Kennedy and Cobban (1976, pL 1, figs. 3, 4). Other ammonites 

from locality 22871 include Moremanoceras, Hamites (pi. 

11, fig. 2), Anisoceras, Scaphites, and small undescribed 

genera as well as a new species of Protacanthoceras 

described herein as P. alzadense.

The ammonite described by Stephenson (1952, p. 204, 

pi. 49, fig. 3; pi. 51, figs. 8-11) as Mammitest bellsanus 

from the Templeton Member of the Woodbine Formation 

of north Texas is better assigned to Plesiacanthoceras. 

The species differs from P. wyomingense in having a more 

involute shell, a lesser excavated venter, and a weaker 

ornament.

Types.-'USNM 220381, 388152-388169.

Genus PROTACANTHOCERAS Spath, 1923

Type species. Ammonites bunburianus Sharpe, 1853.

Protacanthoceras was named by Spath (1923, p. 144) 

for a stock of small acanthoceratid ammonites. A generic 

diagnosis was not given. Four earlier named species were 

assigned to the genus by Spath; Protacanthoceras 

triseriale (J. de C. Sowerby), P. compressum (JukesBrowne), P. bunburianum (Sharpe), and P. hippocastanum 

(J. de C. Sowerby). The genus has been recently treated 

in detail by Wright and Kennedy (1980), who gave the 

following diagnosis:

Small. Adult at diameters of 15-50 mm. Moderately involute, compressed to depressed, flat-sided or round-whorled, bearing primary and 

intercalated ribs, typically with prominent umbilical and inner ventrolateral tubercles and closely spaced clavate outer ventrolateral and 

siphonal tubercles; tuberculation declines as the end of the body 

chamber and the ribs become broad and flat. Dimorphic, microconchs 

generally less densely and more strongly ribbed than macroconchs, 

although both show essentially similar styles of ornament. In a few 

species some or all tuberculation except for the umbilical is suppressed 

during part or all of ontogeny. Suture simple, with broad bifid L and 

smaller bifid U2. E/L larger, bifid; L/U2 small, simple. Auxiliaries may 

be pseudoceratitic.

Wright and Kennedy (1980, p. 70) noted that Protacanthoceras ranges from the lower part of the middle 

Cenomanian to the middle of the upper Cenomanian. 

Most specimens have come from southern England, and 

a few have been found in France and Madagascar.

Protacanthoceras hosei Cobban, n. sp.

Plate 9, figures 1-47; text figures 12, 14

This small species has a body chamber ornamented 

by fairly coarse ribs and tubercles that persist to the 

aperture. Ribs are straight on small specimens and flexuous on larger ones. Clavate outer ventrolateral and 

siphonal tubercles are conspicuous on the body 

chamber. Early whorls may have a slight cunningtoniceratid aspect. The species is named for Richard 

K. Hose who collected the type lot while he was with 

the U.S. Geological Survey. Two forms of the species 

are distinguished, P. hosei hosei and P. hosei 

sheridanense, n. subsp.

Protacanthoceras hosei hosei Cobban, n. subsp.

Plate 9, figures 1-27; text figure 12

This form of the species is characterized by its fairly 

slender whorls and by its flexuous ribbing. The type lot, 

from the Frontier Formation in northern Wyoming at 

locality 22804 (fig. 1), contains 25 specimens suitable 

for the determination of three or more of the following 

measurements; diameter, umbilicus, diameter at base 

of the body chamber, and number of umbilical and ventrolateral tubercles in half a whorl. Diameters at the 

base of the body chambers could be determined for 20 

of the specimens; these measurements ranged from 

10-16.6 mm (fig. 11). Five specimens have approximated terminal septa at diameters of 16.7, 17.2, 18.3, 

21.5, and 22.2 mm.

The holotype (USNM 388170) is a complete adult 

20.5 mm in diameter with an umbilical diameter of 

4.7 mm (0.23) (pi. 9, figs. 13-15). Most of the sheU material is retained, and the base of the body chamber is not 

visible. The intercostal section of the body chamber is 

subquadrangular with flattened flanks, broadly rounded
SYSTEMATIC DESCRIPTIONS 19

10 11 12 13 14 

DIAMETER, IN MILLIMETERS

15 16

FIGURE 11. Histogram showing diameters at the base of 

body chambers and number of specimens of Protacanthoceras hosei hosei Cobban, n. subsp., from the Frontier 

Formation at locality 22804 (fig. 1).

venter, rounded umbilical shoulder, and sloping umbilical 

wall. Ornament consists of narrow, slightly prorsiradiate 

ribs, umbilical bullae, nodate inner ventrolateral tubercles, 

and nodate to clavate outer ventrolateral and siphonal 

tubercles. Ornament on the first quarter of the outer 

whorl is somewhat reminiscent of Cunningtoniceras in 

that weaker secondary ribs are present, and these have 

smaller ventrolateral and siphonal tubercles. On the rest 

of the whorl, most ribs are equal in length and arise from 

bullae located on the umbilical shoulder. Each rib crosses 

the flank to a nodate inner ventrolateral tubercle. From 

there, the ribs broaden greatly and bend forward crossing the venter as broad, forward arched folds that support clavate outer ventrolateral and siphonal tubercles. 

The siphonal tubercles on the body chamber are asymmetric in that the adoral part is steep, and the adapical 

part is gently sloping. Ornament is strong on most of 

the body chamber, but just before the aperture, the ornament weakens a little, and, on the final rib, ventrolateral and siphonal tubercles become low and nodate. 

The smallest whorls of the nominate subspecies examined are partly exposed on an unfigured paratype 

(USNM 388180). At a diameter of 2 mm, the whorls are 

broader than high with broadly rounded venter and wellrounded flank. The whorls are smooth except for rows 

of small nodate ventrolateral tubercles that number 5 in 

half a whorl. These tubercles become the inner ventrolateral ones on larger whorls. Nodate outer ventrolateral and siphonal tubercles arise along with the ribs 

at some diameter less than 6 mm (pL 9, fig. 1). At this 

size, the ribs cross the venter transversely and are usually 

bounded on their adoral side by a constriction (pi. 9, figs. 

1, 25). As the shell enlarges, ribs become more closely 

spaced, and constrictions disappear, and by a diameter

of 8 mm, outer ventrolateral and siphonal tubercles 

become asymmetrically clavate with the adoral side 

steepest. Umbilical bullae become distinct by a diameter 

of 15 mm; they number 4-6 per half whorl at diameters 

of 15-20 mm and 5-9 at larger diameters. Ventrolateral 

and siphonal tubercles number 8-11 per half whorl 

without any obvious change in number with growth.

The apertural margin is usually incomplete or damaged. A large paratype from a limestone concretion at 

the top of the Soap Creek Bentonite Bed at locality 

D7370 in eastern Wyoming (fig. 1) has an aperture that 

features a ventral lappet (pi. 9, fig. 22).

The suture is typical of the genus (fig. 12). The external lobe (E) is fairly broad; the lateral lobe (L) is smaller 

and shallower than E; and the E/L saddle is broad and 

bifid.

Of the described species of Protacanthoceras, P. hosei 

most closely resembles P. tuberculatum Thomel (1972, 

p. 101, pi. 32, figs. 9-12). Both species have similar 

robust ornament, but P. tuberculatum has ribs of alternate lengths on the outer whorl, which is rarely seen on 

that whorl of P. hosei. In addition, P. tuberculatum has 

fewer ribs. Some slender individuals of P. hosei (pi. 9, 

figs. 19, 20) recall slender specimens of P. bunburianum 

(Sharpe, 1853, p. 25, pi. 9, figs. 3a-c), but Sharpe's 

holotype shows a great weakening of the tuberculation 

on the younger part of the body chamber.

The type lot of P. hosei hosei came from sandy concretions in the upper part of the Frontier Formation at 

locality 22804 in north-central Wyoming (fig. 1). Hose 

(1955, p. 99-101) measured the Frontier Formation at 

this locality and listed the following important fossils 

names updated in square brackets at locality 22804: 

Inoceramus prefragilis Stephenson [/. rutherfordi Warren], Ostrea sp. [O. beloiti Logan], Borissiakoceras 

reesidei Morrow, B. n. sp., and Acanthocerast amphibolum Morrow [Cunningtoniceras amphibolum 

fallense Cobban and Protacanthoceras hosei hosei 

Cobban].

Types Holotype USNM 388170, paratypes USNM 

388171-388180.

FIGURE 12. Next to last external suture of Protacanthoceras hosei 

hosei Cobban, n. subsp., from the Frontier Formation at locality 

22804 (fig. 1). Paratype USNM 388173 (pi. 9, figs. 6-9).
20 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

Protacanthoceras hosei sheridanense Cobban, n. subsp.

Plate 9, figures 28-47; text figure 14

This form is more robust and a little more sparsely 

ribbed than the nominate subspecies. The type lot, from 

locality D6933 (fig. 1) in Sheridan County in northern 

Wyoming, consists of 20 specimens suitable for 

measurements. Smaller specimens are present in the collection of ammonites from this locality, but these cannot be separated with certainty from very small inner 

whorls of the associated Cunningtoniceras amphibolum 

fallense. Diameters of the 20 specimens range from 5.7 

to 16.4 mm. All have parts of the body chambers, and 

diameters at the base of 18 could be determined. These 

diameters ranged from 3.6 to 14.7 mm. Approximated 

terminal sutures were observed on only three specimens 

at diameters of 5.3, 5.4, and 14.1 mm. Diameters at the 

base of the body chambers of the 17 specimens do not 

reveal any conspicuous grouping, which suggests that 

many of the specimens are immature (fig. 13).

3 4 5 6 7 8 9 10 11 12 13 14 

DIAMETER, IN MILLIMETERS

FIGURE 13. Histogram showing diameters at the base of body 

chambers and number of specimens of Protacanthoceras hosei 

sheridanense Cobban, n. subsp., from the Frontier Formation at locality D6933 (fig. 1).

The holotype (USNM 388171) is a stout individual 

16.4 mm in diameter with an umbilicus of 2.9 mm (0.17) 

(pi. 9, figs. 31-33). Its whorl section is quadrate about 

as high as wide with flat flanks, very broadly rounded 

venter, and narrowly rounded umbilical wall. The body 

chamber, which occupies the last half whorl, has a 

diameter at its base of about 10 mm. Ribs on the last 

complete whorl number 12 and are rounded and mostly straight and rectiradiate on the flanks. Most arise 

from bullate to nodate umbilical tubercles located on 

the umbilical shoulder. Each rib rises into a prominent 

nodate to clavate inner ventrolateral tubercle. From this 

tubercle the rib broadens on crossing the venter, where 

it supports a conspicuous clavate outer ventrolateral 

tubercle and a similar-sized siphonal clavus. These 

clavate tubercles are asymmetric with the forward side 

steepest. Ribs cross the venter transversely on the

phragmocone, but on the body chamber, the ribs become 

increasingly projected forward as they approach the 

aperture. At one place the venter is a little pathologic 

owing to the fusion of two of the outer ventrolateral 

tubercles into a single clavus as well as the fusion of the 

two adjacent siphonal tubercles into a single clavus. The 

aperture is not preserved, but the great reduction in size 

of the last inner ventrolateral tubercle suggests that 

very little of the body chamber is missing.

The 20 specimens from locality D6933 have 6-10 ventrolateral tubercles per half whorl, averaging 7.3. On the 

smallest whorls observed, tubercles are nodate and are 

located on low, narrow ribs well separated by smooth 

areas (pi. 9, figs. 41, 42). An occasional individual may 

have a weak rib on the venter between two stronger 

tuberculated ribs (pi. 9, fig. 39). As the whorls enlarge, 

the ventral tubercles become clavate and more uniformly 

spaced (pi. 9, figs. 30, 33, 45).

Only bits of the suture are visible on the holotype. 

Most of the external suture of a very small paratype 

(USNM 388188) that has the last four septa approximated is shown in figure 14. The suture is as simple 

as that of the nominate subspecies. Protacanthoceras 

asgeirri Wright and Kennedy (1980, text fig. 47) has a 

similar suture.

The type lot of Protacanthoceras hosei sheridanense 

came from limestone concretions that formed along the 

Soap Creek Bentonite Bed in the upper part of the Frontier Formation at locality D6933 near the northern 

boundary of Wyoming (fig. 1). Associated fossils include 

Cunningtoniceras amphibolum fallense, Borissiakoceras 

reesidei Moreman, Inoceramus rutherfordi Warren, and 

Ostrea beloiti Logan.

Types. Holotype USNM 388181, paratypes USNM 

388182-388188.

FIGURE 14. Fourth from last external suture of a small paratype 

(USNM 388188) of Protacanthoceras hosei sheridanense Cobban, 

n. subsp., from a limestone concretion in the Soap Creek Bentonite 

Bed at locality D6933 (fig. 1).
SYSTEMATIC DESCRIPTIONS 21

Protacanthoceras vetula Cobban, n. sp.

Plate 10, figures 1-28; text figure 16

Characteristic features of this new species include its 

robust shell and its nodate tubercles. Early whorls have 

constrictions like those of Protacanthoceras hosei.

The type lot is from limestone concretions in the upper part of the Belle Fourche Shale at locality D5900 

on Old Woman anticline southwest of the Black Hills 

in eastern Wyoming (fig. 1). The species name vetula is 

Latin for old woman.

Twenty-eight specimens from locality D5900 are 

preserved well enough for measurements of the diameters of the shell, umbilicus, and base of the body 

chamber. These specimens range in size from 8.0 to 

16.8 mm. Diameters at the base of the body chambers 

range from 6.4 to 12.4 (fig. 15). Seven specimens have 

crowded septa at the end of the phragmocone at diameters of 8.6, 8.9, 9.0, 9.0, 10.0, 10.2, and 10.6 mm. All 

specimens are involute with umbilical ratios of 0.12-0.19. 

Body chambers are about as high as wide or a little 

broader. Flanks are flattened, and venters are broadly 

rounded. Ornament on mature body chambers consists 

of weak umbilical bullae and strong forwardly arched

10, 

7 8 9 10 

DIAMETER (mm)

11 12

FIGURE 15. Histogram showing diameters at the 

base of body chambers and the number of 

specimens of Protacanthoceras vetula Cobban, n. 

sp., from the Belle Fourche Shale at locality D5900 

(fig. 1).

E/L

FIGURE 16. Last external suture of Protacanthoceras vetula Cobban, 

n. sp., from the Belle Fourche Shale at locality D5900 (fig. 1). 

Holotype USNM 388189 (pi. 10, figs. 14-17).

ventral ribs that bear small inner and outer ventrolateral 

and siphonal tubercles. These tubercles number 5-13 in 

half a whorl, averaging 9. Inner whorls are ornamented 

by narrow tuberculate ribs that number 5 or 6 in half 

a whorl. These ribs begin on the outer part of the flank 

and cross the venter transversely at first and with forward arching later. Each rib bears small nodate inner 

and outer ventrolateral and siphonal tubercles, which 

are about equal in size and spacing. A conspicuous constriction bounds the adoral side of the rib (pi. 10, figs. 

3, 7,18, 23, 24, 28). The venter between the constriction 

and the next rib may be smooth (pi. 10, figs. 3, 28) or 

it may contain a faint nontuberculate rib (pi. 10, fig. 15).

The holotype (USNM 388189) is a complete adult 

15.5 mm in diameter with an umbilicus of 2.0 mm (0.13) 

(pi. 10, figs. 14-17). About two-thirds of the outer whorl 

is body chamber. Two crowded septa mark the end of 

the phragmocone. The venter on the last quarter whorl 

of the phragmocone is crossed by five forwardly arched 

tuberculate ribs that are bounded on their adoral side 

by narrow shallow constrictions. Under very oblique 

lighting, a faint nontuberculate rib can be detected in 

the area separating the constriction and the next tuberculate rib. This type of ornament persists on to the older 

part of the body chamber, but on the younger part, the 

faint rib rapidly increases in height and becomes tuberculate. Ribbing and tuberculation are abruptly reduced 

near the aperture, which is marked by a ventral lappet 

(pi. 10, fig. 14). The suture of the holotype (fig. 16) is 

typical of the genus. In its details, the suture resembles 

that of a paratype of P. tuberculatum mite Wright and 

Kennedy (1980, text fig. 3A).

The early whorls of P. vetula that have widely spaced 

narrow tuberculate ventral ribs resemble similar early 

whorls of P. asgeirri Wright and Kennedy (1980, figs. 

20, 21), P. arkelli arketti Wright and Kennedy (1980, fig. 

24), and P. tuberculatum Thomel as figured by Wright 

and Kennedy (1980, fig. 28). In addition, the early whorls
22 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

of P. arkelli arkelli have constrictions. Protacanthoceras 

vetula, however, is much smaller and more involute than 

the European species and has smoother flanks.

The type lot was collected from limestone concretions 

near the top of the Belle Fourche Shale 3.6 m (12 ft) 

below the bentonite marker bed at locality D5900 (fig. 

1). Associated fossils include Inoceramus arvanus 

Stephenson, Ostrea beloiti Logan, Cunningtoniceras amphibolum amphibolum (Morrow), Thrrantoceras settardsi 

(Adkins), Borissiakoceras orbiculatum Stephenson, and 

a juvenile desmoceratid ammonite.

Types.-Kolotype USNM 388189, paratypes USNM 

388190-388197.

Protacanthoceras alzadense Cobban, n. sp.

Plate 10, figures 29-47; text figure 18

This species differs from Protacanthoceras hosei in its 

smaller size, in its smaller umbilicus, and in its weaker 

ornament. The type lot, from limestone concretions in 

the Belle Fourche Shale at locality 22871, near Alzada, 

Mont. (fig. 1), contains 30 specimens suitable for 

measurements of the base of the body chambers. These 

measurements range from 5.2 to 9.4 mm (fig. 17).

The holotype (USNM 388198) is a small but complete 

internal mold 11.6 mm in diameter that has an umbilicus 

of 1.3 mm (0.11) (pi. 10, figs. 29-32). The body chamber,

81 

678 

DIAMETER (mm)

FIGURE 17. Histogram showing diameters at the base 

of body chambers and the number of specimens of 

Protacanthoceras alzadense Cobban, n. sp., from the 

Belle Fourche Shale at locality 22871 (fig. 1).

E/L

1 mm

FIGURE 18. Part of the penultimate external suture of the holotype 

(USNM 388198) of Protacanthoceras alzadense Cobban, n. sp., from 

the BeUe Fourche Shale at USGS Mesozoic locality 22871 (fig. 1).

which occupies about two-thirds of a whorl, has a diameter of 5.6 mm at its basa Cross section of the outer septate whorl is broader than high with broadly rounded 

venter, slightly flattened flanks, well rounded umbilical 

shoulder, and steep umbilical wall Cross section of the 

body chamber is more quadrate with flatter flanks and 

narrower, but flattened venter. Ornament on the younger 

part of the outer septate whorl consists of small, pointed, 

nodate inner ventrolateral tubercles and similar sized but 

weaker outer ones that number 6 or 7 per half whorl In 

addition to these two rows of tubercles, ribs are present 

on the body chamber. Each rib begins at the umbilical 

shoulder, crosses the flank a little prorsiradially to the inner ventrolateral tubercle, and then becomes stronger and 

bends forward a little more to the outer tubercla Each 

rib then becomes weaker and broader as it crosses the 

venter transversely to connect opposite outer ventrolateral 

tubercles. A very low clavate siphonal tubercle is present 

on each of these ribs. On the older two-thirds of the body 

chamber, inner and outer ventrolateral tubercles are 

nodate, but on the younger third, the inner ones weaken 

and disappear, and the outer ones become a little clavate 

and persist to the aperture. The aperture is normal and 

lacks constrictions and extensions.

The last two septa of the holotype are approximated. 

A complete external suture is not exposed. E/L is broad 

and symmetrically divided by a deep spade-shaped loba 

L is narrower than E/L and divided by several shallow indentations (fig. 18). The general configuration and simplicity is much like the suture of Protacanthoceras proteus 

Wright and Kennedy (1980, text fig. 57A).

The smallest whorls examined have diameters of 6.2 and 

6.5 mm. Ornament on the smaller of these specimens (unfigured paratype USNM 388204) consists of weak rectiradiate ribs that begin at the umbilical shoulder and 

trend straight across the flank, where they rise into conspicuous pointed, nodate inner ventrolateral tubercles. 

From these tubercles, a weak rib crosses the venter 

transversely and supports weak nodate outer ventrolateral 

tubercles and slightly smaller nodate to somewhat clavate
ZONATION OF ACANTHOCERATID AMMONITES 23

siphonal tubercles. There are 6 of these tuberculate ribs 

in half a whorl. Interspaces between the ribs are several 

times wider than the ribs. The other specimen (paratype 

USNM 388201) differs in that ribs are of alternate 

lengths, and the longer rise into more conspicuous inner ventrolateral tubercles (pi. 10, figs. 39, 40). Only the 

longer ribs cross the venter, where they bear nodate 

outer ventrolateral and siphonal tubercles.

The specimens from locality 22871 were associated 

with Plesiacanthoceras wyomingense as well as the genera Moremanoceras, Boris siakoceras, Hamites, Anisoceras, Scaphites, and small undescribed genera. 

Inoceramus prefragilis Stephenson is also found at this 

locality.

Types.-Holotype USNM 388198, paratypes USNM 

388199-388204.

Protacanthoceras fisherense Cobban, n. sp.

Plate 3, figures 1-6; text figure 19

This small species of Protacanthoceras has a strongly ribbed adult body chamber. The types are from the 

Frontier Formation at the head of Fisher Draw south 

of Kaycee in northern Wyoming (fig. 1, loc. 23459).

The holotype (USNM 388110) is a nearly complete 

adult 14.5 mm in diameter that has most of the body 

chamber preserved, but not the aperture (pi. 3, figs. 4-6). 

The umbilicus is very small with a diameter of only 

1.1 mm and a ratio to the shell diameter of 0.08. Its well 

rounded umbilical wall grades evenly into the more 

broadly rounded umbilical shoulder. The last half whorl 

of the phragmocone is visible; its cross section is wider 

than high with broadly rounded flanks and venter. Ornament on its older half consists of weak, narrow, tuberculate, rectiradiate ribs that arise at the umbilical 

shoulder and become strongest on crossing the venter. 

These ribs, which are fairly equal in length, support 

small bullate outer ventrolateral and siphonal tubercles. 

On the younger half of the phragmocone, ornament 

gradually strengthens. The body chamber, which occupies a full half whorl, is about as high as wide with 

flattened flanks and rounded venter. Ornament is conspicuous and consists of 11 narrow, flexuous ribs of 

about equal length and strength. Each rib bends forward at the ventrolateral shoulder and crosses the venter 

with slight forward arching. Low, bullate outer ventrolateral tubercles and equal-sized nodate siphonal 

tubercles are present on each rib. The suture (fig. 19) is 

comparable to other species of the genus. The lateral 

lobe (L) is rather deeply bifid and narrower than the bifid 

E/L saddle.

A robust paratype (USNM 388111), from the same 

locality as the holotype, has small nodate to bullate

inner ventrolateral tubercles on the outer whorl of the 

phragmocone (pL 3, figs. 1-3). These tubercles weaken and 

gradually disappear on the body chamber. Like the holotype, the incomplete body chamber of the paratype occupies a full half whorl and is ornamented by 11 strong 

ribs that arch forward on crossing the venter. In addition to the weak inner ventrolateral tubercles on the older 

part, the ribs bear low, blunt, bullate outer ventrolateral 

tubercles and low, blunt, nodate siphonal tubercles.

Protacanthoceras fisherense is represented by only a 

few specimens, all from locality 23459 (fig. 1), where it 

occurs with Acanthoceras muldoonense Cobban and 

Scott. The conspicuous ribbing on the adult body 

chamber easily distinguishes P. fisherense from other 

species of the genus.

Types.-Holotype USNM 388110, paratype USNM 

388111.

E E/L L

FIGURE 19. Third from last external suture of the holotype 

(USNM 388110) of Protacanthoceras fisherense Cobban, n. sp., 

from the Frontier Formation at USGS Mesozoic locality 23459 

(fig. 1).

ZONATION OF 

ACANTHOCERATID AMMONITES

That Plesiacanthoceras wyomingense occurs in rocks 

above those containing Cunningtoniceras amphibolum 

has been known since 1951 (Cobban, 1951, fig. 2), when 

the former was referred to as Acanthoceras? n. sp. and 

the latter as Acanthoceras? amphibolum. In the Pueblo 

area of Colorado, A. muldoonense was found below C. 

amphibolum (Cobban and Scott, 1972, p. 26-30, table 4).

Stratigraphic studies and additional collections of 

fossils made in the early 1970's revealed that the species 

referred to as A. amphibolum consists of two forms, an 

older one that has more siphonal and outer ventrolateral 

tubercles on the venter of the inner whorls than inner 

ventrolateral ones, and a younger one that tends to have 

equal numbers of tubercles. The older form was typical 

of Acanthoceras alvaradoense Moreman (1942, p. 205, 

pi. 32, fig. 6; text fig. 2 O, T), a species described from 

the basal part of the Eagle Ford Group of Texas. The
24 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

younger form was thought to be A. amphibolum s.s. 

Western Interior specimens were assigned to one or the 

other of these, and two zones were recognized, an older 

one of A. alvaradoense and a younger one of A. amphibolum (for example, Merewether and Cobban, 1972, 

table 1; Cobban and Scott, 1972, p. 33; Obradovich and 

Cobban, 1975, table 1). Because differences in the adult 

body chambers of A. amphibolum and A. alvaradoense 

cannot be distinguished, the two forms have recently 

been treated as one species, A. amphibolum, with A. 

alvaradoense considered as a subspecies of it (Cobban and 

Hook, 1983a, table 1; Cobban, 1984a). A zone of A. amphibolum was recognized with subzones of A. amphibolum alvaradoense and A. amphibolum amphibolum. 

The present investigation revealed that the type specimens of Morrow's A. amphibolum as well as other 

specimens from central Kansas have multiplication of 

ribs and tubercles on the venter of the inner whorls like 

that of Moreman's A. alvaradoense and that all these 

specimens should be more properly assigned to Cunningtoniceras. Inasmuch as the Acanthoceras amphibolum 

alvaradoense of recent reports is the same as A. amphibolum s.s., a new name is needed for the late form of 

the species. Cunningtoniceras amphibolum fallense is 

proposed herein for it.

Acanthoceras bellense Adkins has not been previously considered in the ammonite zonation of the Western 

Interior. This species is known from a very limited area 

near Osage, Wyo., on the west flank of the Black Hills 

(fig. 1, Iocs. D5869, D8841). The position of this fossil in 

the middle Cenomanian acanthoceratid sequence is not 

clear. At locality D5869, A. bellense occurs with 

Calycoceras (Gentoniceras) leonense (Adkins) 9.1 m (30 ft) 

above a bed of dusky-red ferruginuous concretions that 

contains Eocogyra columbella Meek, a bivalve that may 

be restricted to the middle Cenomanian zone of Calycoceras (Conlinoceras) tarrantense (Adkins) (Cobban, 

1977, table 2). Cunningtoniceras amphibolum occurs at 

locality D5869 27.4 m (90 ft) above A. bellense. Near 

Pueblo, Cola, Calycoceras (Conlinoceras) gilberti Cobban 

and Scott, a close relative of C. tarrantense and probably 

of the same age, occurs in ferruginous concretions about 

a meter below the lowest occurrence of Acanthoceras muldoonense (Cobban and Scott, 1972, p. 7). It seems likely 

that A. bellense lies some place between the zones of A. 

muldoonense and Cunningtoniceras amphibolum.

The middle Cenomanian acanthoceratid sequence in 

the Western Interior is probably as follows:

Plesiacanthoceras wyomingense 

Cunningtoniceras amphibolum

(at top)

C. amphibolum fallense

C. amphibolum amphibolum

Acanthoceras bellense

Acanthoceras muldoonense

Calycoceras (Conlinoceras) tarrantense (at bottom)

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26 UPPER CRETACEOUS ACANTHOCERATID AMMONITES, WESTERN INTERIOR, UNITED STATES

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INDEX

[Italic page numbers indicate major references]

Acanthocerataceae ............

Acanthoceratid sequence ......

Acanthoceratidae de Grossouvre 

Acanthoceratinae .............

Page 

........... 4

........... 24

........... 1,4

........... 4

Acanthoceras ................................. 3,15

aberrans ................................. 9

alvaradoense .......................... 11,13,23,24

amphibolum ..................... 1,2,11,13,19,23,24

alvaradoense .......................... 24

amphilbolum ......................... 24

athabascense .............................. 16,18

barcusi ................................... 5

bellense ........................... 5, 24; pis. 1,2

coloradoensis ............................. 2

cornigerum................................ 8

cunningtoni var. cornuta.................... 9

var. inermis ........................... 9

cuspidum ................................ 18

diadema ................................. 9

granerosense .............................. 3

hazzardi .................................. 11

kanabense ................................ 1

latum .................................... 9

lonsdalei ................................. 6,9

muldoonense ...................... 3,7,23,24; pl.3

n. sp. .................................... 16,23

pepperense ............................... 6

quadratum ............................... 9

rhotomagense Zone ........................ 9

sp. A .................................... 16

stephensoni ............................... 6

validum .................................. 6

wyomingense ............................. 16

Age, Cenomanian, middle ................. 1,9,15,18,24

Coniacian ................................ 1

TUronian ................................. 1

Alzada, Carter County, Mont. ................. 3,16,22

alzadense, Protacanthoceras ................. 22; pi. 10

Ammonites africana ........................... 9

bunburianus .............................. 18

cunningtoni .............................. 8,9

loevianus ................................. 1,9

meridionalis .............................. 9

tuberculata ............................... 9

Ampakabites collignoni ........................ 3

amphibolum, Cunningtoniceras ............ 9; pis. 4-8,9

amphibolum, Cunningtoniceras amphibolum . 11; pis. 4,5 

amphibolum fallense, Cunningtoniceras ..... 13; pis. 5-9

Anisoceras ................................... 18,23

Assemblage, Eucalycoceras pentagonus/Calycoceras

naviculare ........................ 9

Turrilites acutus .......................... 9

Turrilites costatus ......................... 9

Associated fossils, Acanthoceras amphibolum ..... 19

Acanthoceras bellense ...................... 5

cuspidum ............................ 18

lonsdalei ............................. 6

muldoonense ......................... 23

stephensoni ........................... 6

validum .............................. 6

Anisoceras ............................... 18,23

Borissiakoceras ........................... 19,23

Borissiakoceras orbiculatum .............. 5,7,18,22

reesidei ........................... 9,14,19,20

Calycoceras (Gentoniceras) teonense ......... 7,24

Cunningtoniceras amphibolum .............. 22

fallense ............................. 15,19,20

Desmoceras (Pseudouhligella) D. japonicum .. 9 

desmoceratid ammonite, juvenile ............ 22

Drepanochilus sp. ......................... 5,7

Associated fossils Continued

Eucalycoceras leonense ..................... 6

Exogyra columbella ....................... 24

Hamites .................................. 18,23

Inoceramus arvanus ................... 5,7,9,14,22

prefragilis ............................ 19,23

rutherfordi .......................... 9,19,20

Moremanoceras ........................... 18,23

Ostrea beloiti ....................... 9,14,19,20,22

Paracompsoceras landisi .................... 9

Plesiacenthoceras wyomingense ............. 23

Protacanthoceras alzadense ................. 18

hosei ................................ 14

hosei ............................ 19

Scaphites ................................. 18,23

Tarrantoceras rotatile ...................... 9

sellardsi .............................. 22

Turrilites acutus americanus ................ 9

Turrilites cf. T. scheuchzerianus ............. 8

B 

Bed F, Belle Fourche Shale ..................... 15

Bell County, Texas ............................. 4

Belle Fourche Member, Cody Shale .............. IS

Belle Fourche Shale ......................... 1,4,13,22

Alzada, Mont. ............................ 22

bentonite marker bed ...................... 22

Black Hills .............................. 15,16,18

upper part ............................... 21

bellense, Acanthoceras ...................... 5; pis. 1,2

Bentonite bed, Belle Fourche Shale .............. 15

Bentonite marker bed, Graneros Shale ........... 12,13

Big Horn County, Mont. ....................... 3

Bird Creek ................................... 5

Black Hills, Belle Fourche Shale ................ 1,16,18

west flank ......................... 4,6,12,13,14,24

Bluebonnet Member, Lake Waco Formation ...... 5

Boquillas Formation, New Mexico ............... 13

Borissiakoceras ............................... 23

n. sp. .................................... 19

orbiculatum ............................ 5,7,18,22

reesidei ............................... 9,14,19,20

Buchiceras swallovi ............................ 1

bunburianus, Ammonites ...................... 18

Calycoceras ................................... 3

(Conlinoceras) gilberti ..................... 3,24

tarrantense ........................... 24

(Gentoniceras) leonense ............... 4,1,24; pi. 1

naviculare ................................ 2

Cenomanian .................................. 1

middle ................................ 9,15,18,24

Clay Mesa Tongue, Mancos Shale ............... 13

Cody Shale, Soap Creek Bentonite Bed .......... 15

Collignoniceras woollgari ....................... 16

Coniacian .................................... 1

Crook County, Wyo. ........................... 3

Cunningtoniceras ............................. 8,15,18

amphibolum ................... 9,22,23; pis. 4-8,9

amphibolum ...................... 11; pis. 4,5

fallense .................. 13,19,20,24; pis. 5-9

cunningtoni, Ammonites ....................... 8,9

D

Definition of terms ............................ 3

Descriptions, systemic .......................... 3

Desmoceras (Psendouhligella) D. japonicum .......... 9

Drepanochilus sp. ............................. 5,7

Dry Muddy Creek, Johnson County, Wyo. ........... 3

Page 

Dunveganoceras ............................... 15,16

albertense montanense ..................... 2

conditum ................................. 2

parvum .................................. 2

pondi .................................... 2

Eagle Ford Formation........................... 5,18

Eagle Ford Group ............................. 4,23

Ellsworth County, Kansas....................... 3,12

Elm Creek, Niobrara County, Wyo................... 3

England ...................................... 18

Eucalycoceras leonense......................... 4,6

Eucalycoceras pentagonus/Calycoceras naviculare

Assemblage Zone ................. 9

Euomphaloceras .............................. 3,9

alvaradoense .............................. 11

cunningtoni .............................. 9

euomphalum ............................. 9

(Kanabiceras) septemseriatum ............... 9

Exogyra columbella ........................... 24

Fall County, South Dakota ..................... 14

Fisher Draw, Kaycee, Johnson County, Wyo ...... 3,23

fisherense, Protacanthoceras .................... 23;p\.3

Flag Member, Eagle Ford Fromation............. 5

Formations, Belle Fourche Shale ..... 1,4,13,75,16,18,21,22

Boquillas Formation ....................... 13

Cody Shale, Belle Fourche Member .......... 15

Soap Creek Bentonite Bed.............. 3,75,19

Eagle Ford Formation ..................... 5,18

Frontier Formation ............ 1,2,7,8,14,16,18,19,23

Soap Creek Bentonite Bed .............. 20

Graneros Shale,...................... 2,3,7,11,12,13

Thatcher Limestone Member............ 8,9

Greenhorn Limestone ...................... 2,3,15

Lake Waco Foundation..................... 5

Lower Chalk.............................. 9

Mancos Shale, Clay Mesa Tongue............ 13

Tarrant Formation ......................... 5

Woodbine Formation, Templeton Member..... 5,18

Fossil localities................................ 3

Fossil sequence................................ 24

France........................................ 18

Frontier Formation........................... 1,2,16,18

Fisher Draw, Wyo.......................... 23

north-central Wyoming................. 7,8,14,18,19

Soap Creek Bentonite Bed.................. 20

G, H 

Gay Creek, Sheridan County, Wyo............... 3

Gentoniceras, Calycoceras leonense............... 4

Graneros Shale............................. 2,3,7,12,13

Thatcher Limestone Member................... 8,9

upper part................................ 11

Greenhorn Limestone .......................... 2,3,15

Hamites ...................................... 18,23

hosei, Protacanthoceras .................... 78;pl.9

sheridanense, Protacanthoceras.............. 20;p\.9

Hot Springs, Fall River County, S. Dak............... 3

I, K 

Inoceramus arvanus ....................... 5,7,9,14,22

prefragilis ................................ 19,23

rutherfordi............................... 9,19,20

Kanabiceras puebloense......................... 3

Kaycee, Wyo................................... 3,8,23

27
28 INDEX

Lake Waco Formation, Bluebonnet Member. 

leonense, Eucalycoceras. .....................

Calycoceras (Gentoniceras). ..............

Localities, fossil.............................

loevianus, Ammonites.......................

Lone Bear road, Johnson County, Wyo........

Lower Chalk ...............................

M

Mammites ..................................

bellsanus ...............................

n. sp....................................

rectangulus .............................

wingi ..................................

Madagascar ................................

Mancos Shale, Clay Mesa Tongue..............

Mantelliceras canitaurinum ...................

Metacalycoceras .............................

Metoicoceras ...............................

kanabense ..............................

mosbyense ..............................

muelleri ................................

whitei ..................................

praecox ............................

wyomingensis............................. 2,15,16

Montana, southeastern......................... 15

Moremanoceras................................ 18,23

Morrowites. ................................... 3

subdepressus .............................. 3

muldoonense, Acanthoceras..................... 7;pl.3

N, O

Niobrara County, Wyo.

Old Woman anticline, Wyo...................... 21

Osage, Weston County, Wyo................... 3,4,5,24

Osage oil field..................... .......... 6

Ostrea beloiti............................ 9,14,19,20,22

Paracanthoceras ............................... 15

amphibolum............................... 11

wyomingense.............................. 16

Paracompsoceras landisi........................ 2,9

Plesiacanthoceras.............................. 2,75

amphilbolum.............................. 11

wyomingense....................... 7<5,23;pls.lO-13

Prionotropis woollgari.......................... 16

Proeucalycoceras, Eucalycoceras leonese.............. 4

Protacanthoceras. .............................. 18

alzadense............................. 18^;pl.lO

arkelli arkelli.............................. 21

asgeirri ................................... 20,21

bunburianum.............................. 18,19

compressum............................... 18

fisherense................................. 23;pl.3

hippocastanum............................ 18

hosei................................ 7S,19,21;pl.9

hosei.............................. 7S,19;pl.9

sheridanense.......................... 20;pl.9

proteus................................... 22

triseriale .................................. 18

tuberculatum.............................. 19,21

mite.................................. 21

vetula................................ 21,22;p\.lO

Pseudaspidoceras cornucostale....................... 2

Pseudocalycoceras............................. 3

Pueblo, Colo................................. 12,23,24

R, S

References cited. 24

Scaphites ..................................... 18,23

Sequence, acanthoceratid........................ 24

Sheridan County, Wyo.......................... 3,20

sheridanense, Protacanthoceras hosei. ........... 20;pl.9

Smokey Hill River, Kansas........................ 3,12

Soap Creek dome.............................. 3

Soap Creek Bentonite Bed, Belle Fourche Member,

Cody Shale ...................... 3,75,19

Soap Creek Bentonite Bed, Frontier Formation....... 20

South Dakota, Belle Fourche Shale............... 13

Systemic descriptions........................... 3

Tarrant Formation............................. 5

Tarrantoceras. ................................. 3

rotatile ................................... 9

sellardsi................................... 22

Templeton Member, Woodbine Formation......... 18

Terms defined................................. 3

Thatcher Limestone Member, Graneros Shale........ 8,9

Time. See Age.

Turanian...................................... 1

Turrilites acutus americanus..................... 9

acutus Assemblage......................... 9

costatus Assemblage........................ 9

scheuchzerianus............................ 8

V, W, Z

vetula, Protacanthoceras ...................... 21;p\.lO

Watinoceras................................... 3

Wilson, Kansas................................ 12

Woodbine Formation........................... 5,18

Wyoming, eastern, Belle Fourche Shale........... 15

west of Black Hills.................. 4,6,12,13,14,24

wyomingense, Plesiacanthoceras............. 7<5;pls.lO-13

wyomingensis, Metoicoceras..................... 15

Zone, Acanthoceras rhotomagense.........

Eucalycoceras pentagonus/Calycoceras 

naviculare .......................

A U.S. GOVERNMENT PRINTING OFFICE: 1987 773-047/46,063 REGION NO. 8
PLATES 1-13

Contact photographs of the plates in this report are available, at cost, from the U.S. Geological 

Survey Photographic Library, Federal Center, Denver, Colorado 80225.
PLATE 1

[All figures natural size Arrows mark base of body chambers]

FIGURES 1-17. Calycoceras (Gentoniceras) leonense (Adkins) (p. 4).

From the Belle Fourche Shale at USGS Mesozoic locality D8841 (text fig. 1). 

1, 2. Rear and side views of hypotype USNM 388087. 

3-5. Front, rear, and side views of hypotype USNM 388088. 

6-8. Front, side, and rear views of hypotype USNM 388089. 

9-11. Front, side, and rear views of hypotype USNM 388090. 

12, 13. Side and front views of hypotype USNM 388091. 

14, 15. Rear and side views of hypotype USNM 388092. 

16, 17. Rear and side views of a fragment of the largest specimen, hypotype

USNM 388093. 

18, 19. Acanthoceras bellense Adkins (p. 5).

Rear and side views of a plaster cast of the holotype from the basal part of 

the Eagle Ford Group in Bell County, lex.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 1

CALYCOCERAS AND ACANTHOCERAS
PLATE 2

[All figures natural size except as indicated. Arrow marks base of body chamber]

FIGURES 1-29. Acanthoceras bellense Adkins (p. 5).

1-3. Front, side, and rear views of hypotype USNM 388094, from USGS

Mesozoic locality D5869 (text fig. 1). 

4, 5. Front and side views of hypotype USNM 388095, from the same

locality. 

6-8. Front, side, and rear views of hypotype USNM 388096, from the

same locality. 

9-11. Rear, side, and front views, X2, of hypotype USNM 388097, from

USGS Mesozoic locality D8841 (text fig. 1). 

12-14. Front, side, and rear views of hypotype USNM 388098, from the

same locality as figures 9-11.

15, 16. Rear and side views of hypotype USNM 388099, from the same 

locality.

17. View of a cross section of a fragment of a large phragmocone. 

Hypotype USNM 388100, from the same locality as figures 1-3.

18. Side view of variant that has a nearly smooth outer whorl Hypotype

USNM 388101, from the same locality as figures 9-11. 

19-21. Rear, side, and front views of hypotype USNM 388102, from the

same locality. 

22, 23. Side and front views of hypotype USNM 388103, from the same

locality. 

24, 25. Side and front views, X2, of hypotype USNM 388104, from the

same locality. 

26, 27. Rear and side views of hypotype USNM 388105, from the same

locality. 

28, 29. Rear and side views of part of an adult body chamber. Hypotype

USNM 388106, from the same locality.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 2

ACANTHOCERAS
PLATE 3

[All figures natural size except as indicated. Arrows mark base of body chambers]

FIGURES 1-6. Protacanthoceras fisherense Cobban, n. sp. (p. 23).

1-3. Front, side, and rear views of paratype USNM 388111, from USGS

Mesozoic locality 23459 (text fig. 1). 

4-6. Rear, side, and front views of holotype USNM 388110, from the same

locality. 

7-34. Acanthoceras muldoonense Cobban and Scott (p. 7).

7-9. Rear, side, and front views of hypotype USNM 388112, from the

same locality as figures 1-3. 

10-12. Rear, side, and front views of hypotype USNM 388113, from USGS

Mesozoic locality D9801 (text fig. 1). 

13-15. Front, side, and rear views of hypotype USNM 388114, from the

same locality as figures 1-3. 

16-18. Rear, side, and front views, X2, of hypotype USNM 388115, from

the same locality. 

19-21. Rear, side, and front views of hypotype USNM 388116, from the

same locality. 

22-24. Front, side, and rear views of hypotype USNM 388117, from the

same locality. 

25, 26. Front and side views of hypotype USNM 388118, from the same

locality. 

27, 28. Rear and side views of hypotype USNM 388119, from the same

locality as figures 10-12. 

29, 30. Rear and side views of a fragment of a body chamber that has looped

ribs across the venter. Hypotype USNM 388120, from the same

locality. 

31, 32. Rear and side views of hypotype USNM 388121, from the same

locality. 

33, 34. Rear and side views of hypotype USNM 388122, from the same

locality.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 3

fttff«fff|

10 11 12

33

PROTACANTHOCERAS AND ACANTHOCERAS
PLATE 4

[All figures natural siza Arrows mark base of body chambers]

FIGURES 1-11. Cunningtoniceras amphibolum amphibolum (Morrow) (p. 11).

1-3. Rear, side, and front views of a small syntype from the Graneros

Shale near Wilson, Kans.

4-6. Front, side, and rear views of the lectotype from the same locality. 

7-9. Side, front, and rear views of hypotype USNM 388123, from USGS

Mesozoic locality 12510 (text fig. 1).

10. Side view of part of the body chamber of an adult macroconch. 

Hypotype USNM 388124, from USGS Mesozoic locality D4428 

(text fig. 1).

11. Side view of a partially crushed microconch. Hypotype USNM 

388125, from the same locality.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 4

C UNNINGTONICERAS
PLATE 5

[All figures natural size Arrows mark base of body chambers]

FIGURES 1-25. Cunningtoniceras amphibolum amphibolum (Morrow) (p. 11).

From the Belle Fourche Shale at USGS Mesozoic locality D5900 (text fig. 1). 

1-3. Front, side, and rear views of hypotype USNM 388126. 

4-6. Front, side, and rear views of hypotype USNM 388127. 

7-9. Rear, side, and front views of hypotype USNM 388128. 

10, 11. Side and rear views of hypotype USNM 388129. 

12, 13. Side and front views of hypotype USNM 388130. 

14-16. Front, side, and rear views of hypotype USNM 388131. 

17, 18. Side and rear views of hypotype USNM 388132.

19. Side view of hypotype USNM 388133. 

20-22. Front, side, and rear views of hypotype USNM 388134. 

23-25. Front, side, and rear views of hypotype USNM 388135. 

26, 27. Cunningtoniceras amphibolum fallense Cobban, n. subsp. (p. 13).

Top and side views of the holotype USNM 388136, from USGS Mesozoic 

locality D7370 (text fig. 1).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 5

CUNNINGTONICERAS
PLATE 6

[All figures natural size. Arrow points to base of body chamber]

FIGURES 1-9. Cunningtoniceras amphibolum fattense Cobban, n. subsp. (p. 13).

From the Belle Fourche Shale at USGS Mesozoic locality D7370 (text fig. 1). 

1, 2. Rear and side views of a specimen that has riblets on the ribs and

in the interspaces. Paratype USNM 388137. 

3, 4. Side and front views of another specimen that has riblets. Paratype

USNM 388138. 

5, 6. Rear and side views of paratype USNM 388139.

7. Side view of a specimen that shows loss of ribbing on part of the

outer whorl. Paratype USNM 388140. 

8, 9. Rear and side views of paratype USNM 388141.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 6

CUNNINGTONICERAS
PLATE 7

[All figures natural size. Arrows mark base of body chambers]

FIGURES 1-9. Cunningtoniceras amphibolum fallense Cobban, n. subsp. (p. 13).

From the Frontier Formation at USGS Mesozoic locality 22804 (text fig. 1). 

1-3. Rear, side, and front views of paratype USNM 388142. 

4, 5. Rear and side views of a specimen that shows loss of ornament on 

the younger end of the adult body chamber. Paratype USNM 

388143.

6. Side view of paratype USNM 388144.

7. Side view of paratype USNM 388145. 

8, 9. Rear and side views of paratype USNM 388146.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 7

CUNNINGTONICERAS
PLATE 8

[Both views natural size. Arrow marks base of body chamber]

Cunningtoniceras amphibolum fallense Cobban, n. subsp. (p. 13).

Front and side views of paratype USNM 388147, from the Belle Fourche Shale at USGS Mesozoic 

locality D8442 (text fig. 1).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 8

C UNNINGTONICERAS
PLATE 9

[All figures natural size except as indicated. Arrows mark base of body chambers]

FIGURES 1-27. Protacanthoceras hosei hosei Cobban, n. subsp. (p. 18).

1-3. Front, side, and rear views of paratype USNM 388171, from the

Frontier Formation at USGS Mesozoic locality 22804 (text fig. 1). 

4, 5. Rear and side views of paratype USNM 388172, from the same

locality. 

6-9. Front, side, rear, and top views of paratype USNM 388173, from

the same locality. 

10-12. Top, rear, and side views of paratype USNM 388174, from the same

locality. 

13-15. Front, side, and rear views of the holotype USNM 388170, from the

same locality. 

16-18. Side, rear, and top views of paratype USNM 388175, from the

same locality. 

19, 20. Side and rear views of paratype USNM 388176, from the same

locality. 

21, 22. Top and side views of paratype USNM 388177, from the Belle

Fourche Shale at USGS Mesozoic locality D7370 (text fig. 1). 

23, 24. Side and rear views of paratype USNM 388178, from the same

locality. 

25-27. Front, side, and rear views of paratype USNM 377179, from the same

locality. 

28-47. Protacanthoceras hosei sheridanense Cobban, n. subsp. (p. 20).

From the Frontier Formation at USGS Mesozoic locality D6933 (text fig. 1). 

28-30. Front, side, and rear views of paratype USNM 388182. 

31-33. Front, side, and rear views of the holotype USNM 388181. 

34-36. Rear, side, and front views, X2, of paratype USNM 388183. 

37-39. Rear, side, and front views, X2, of paratype USNM 388184. 

40-42. Rear, side, and front views, X2, of paratype USNM 388185. 

43-45. Front, side, and rear views, X2, of paratype USNM 388186. 

46, 47. Rear and side views of paratype USNM 388187. 

48-63. Cunningtoniceras amphibolum fallense Cobban, n. subsp. (p. 13).

48-56. Views of the outer whorls, intermediate whorls, and inner whorls

of paratype USNM 388148, from the Frontier Formation at USGS

Mesozoic locality 20934 (text fig. 1). 

57, 58. Front and side views of paratype USNM 388149, from the Frontier

Formation at USGS Mesozoic locality 21364 (text fig. 1). 

59-61. Rear, side, and front views of paratype USNM 388150, from the

Belle Fourche Shale at USGS Mesozoic locality D8442 (text fig. 1). 

62, 63. Side and front views of paratype USNM 388151, from the same

locality as figures 48-56.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 9

23 24 25 26 27 28 29 30 31 32 33 34 35 36

X2 ^^ X 2 

37 38 39 40

54 55 56

57

PROTACANTHOCERAS AND CUNNINGTONICERAS
PLATE 10

[All figures natural size except as indicated. Arrows mark base of body chambers]

FIGURES 1-28. Protacanthoceras vetula Cobban, n. sp. (p. 21).

From the Belle Fourche Shale at USGS Mesozoic locality D5900 (text fig. 1). 

1-3. Front, side, and rear views of paratype USNM 388190. 

4-6. Front, side, and rear views of paratype USNM 388191. 

7-10. Front, side, rear, and top views of paratype USNM 388192.

11-13. Front, side, and rear views of paratype USNM 388193.

14-17. lop, rear, side, and front views of the holotype USNM 388189.

18-20. Rear, side, and front views, X2, of paratype USNM 388194.

21-23. Front, side, and rear views, X2, of paratype USNM 388195.

24, 25. Rear and side views, X2, of paratype USNM 388196.

26-28. Rear, side, and front views, X2, of paratype USNM 388197. 

29-47. Protacanthoceras alzadense Cobban, n. sp. (p. 22).

From the Belle Fourche Shale at USGS Mesozoic locality 22871 (text fig. 1).

29-32. Side and rear views, XI and X2, of the holotype USNM 388198.

33-35. Front, side, and rear views of paratype USNM 388199.

36-38. Rear, side, and front views of paratype USNM 388200.

39, 40. Rear and side views of paratype USNM 388201.

41-43. Rear, side, and front views of paratype USNM 388202.

44-47. Front, side, rear, and top views of paratype USNM 388203. 

48-82. Plesiacanthoceras wyomingense (Reagan) (p. 16).

From the Belle Fourche Shale at USGS Mesozoic locality 22871 (text fig. 1).

48-50. Rear, side, and front views of hypotype USNM 388152.

51-53. Front, side, and rear views of hypotype USNM 388153.

54-56. Front, side, and rear views of hypotype USNM 388154.

57-59. Front, side, and rear views of hypotype USNM 388155.

60-62. Rear, front, and side views of hypotype USNM 388156.

63-65. Front, side, and rear views of hypotype USNM 388157.

66-68. Front, side, and rear views of hypotype USNM 388158.

69-71. Front, side, and rear views of hypotype USNM 388159.

72, 73. Rear and side views of hypotype USNM 388160.

74-76. Rear, side, and front views of hypotype USNM 388161.

77-79. Rear, side, and front views of hypotype USNM 388162.

80-82. Rear, side, and front views of hypotype USNM 388163.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 10

f *J0 t>

12345 

\ \

67 8 9 10 11 12 13

lit 1 X2 *mr X2 .<2 9W*

14 15 16 17 18 19 20 21 22 23

X2 V X 2 W^ X2

24 25 26 27 28

29

30 32

Jf I

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

il

48 49 50 51 52 53 54 55 56 57 58 59 60 61

62 63 64 65 66 67 68 69 70 71 72

73 74 '75 76 77 78 79 80 81 82

PROTACANTHOCERAS AND PLESIACANTHOCERAS
PLATE 11

[All figures natural siza Arrows mark base of body chambers]

FIGURES 1-13. Plesiacanthoceras wyomingense (Reagan) (p. 16).

From the Belle Fourche Shale at USGS Mesozoic locality 22871 (fig. 1). 

1, 2. Rear and side views of hypotype USNM 388164 associated with

Hamites sp. 

3-7. Views of innermost whorls and intermediate whorls of hypotype

USNM 388165. See plate 12 for views of larger whorls. 

8, 9. Side and rear views of hypotype USNM 388166. 

10-13. Views of inner and outer whorls of hypotype USNM 388167.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 11

12

PLESIACANTHOCERAS
PLATE 12

[Both figures natural size]

Plesiacanthoceras wyomingense (Reagan) (p. 16).

Rear and side views of hypotype USNM 388165, from the Belle Fourche Shale at USGS 

Mesozoic locality 22871 (text fig. 1). See plate 11, figures 3-7 for views of the inner whorls.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 12

 < '

$V?v v'* **.S
PLATE 13

[All figures natural siza Arrow marks base of body chamber]

FIGURES 1-6. Plesiacanthoceras wyomingense (Reagan) (p. 16).

From the Belle Fourche Shale at USGS Mesozoic locality 22871 (text fig. 1). 

1-3. Rear, side, and front views of hypotype USNM 220381. 

4. Rear view of hypotype USNM 388168 showing riblets and spiral

ornament on the venter.

5, 6. Side and front views of hypotype USNM 388169. A phragmocone 

of Moremanoceras is embedded in the body chamber.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1445 PLATE 13

r*

PLESIACANTHOCERAS