U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2006−1250

A USGS Zonal Table for the Upper Cretaceous Middle

Cenomanian-Maastrichtian of the Western Interior of

the United States Based on Ammonites, Inoceramids,

and Radiometric Ages
A USGS Zonal Table for the Upper Cretaceous Middle

Cenomanian−Maastrichtian of the Western Interior of the

United States Based on Ammonites, Inoceramids, and

Radiometric Ages

By William A.Cobban, Ireneusz Walaszczyk, John D. Obradovich, and Kevin C. McKinney

Open-File Report 2006–1250

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2006

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Suggested citation:

Cobban, W.A., Walaszczyk, Ireneusz, Obradovich, J.D., and McKinney, K.C., 2006, A USGS zonal table for the Upper 

Cretaceous middle Cenomanian−Maastrichtian of the Western Interior of the United States based on ammonites, 

inoceramids, and radiometric ages: U.S. Geological Survey Open-File Report 2006-1250, 45 p.
A USGS Zonal Table for the Upper Cretaceous Middle CenomanianMaastrichtian of the Western Interior of the United States Based on 

Ammonites, Inoceramids, and Radiometric Ages 

William A. Cobban1, Ireneusz Walaszczyk2, John D. Obradovich, and Kevin C. 

McKinney1 

1 U.S. Geological Survey, Denver Federal Center, MS 980, Denver, CO. 80225. USA. Email: kcmckinney@usgs.gov. 2 Faculty of Geology, University of Warsaw, Al. Zwirki I 

Wigury 92, PL-02-089 Warszawa, Poland. E-mail: i.walaszcyk@uw.edu.pl.

Introduction

This provisional table (fig. 1) is based mainly on the molluscan fossil record of

the central and northern parts of the Western Interior of the United States. Some of the 

ammonite zones are known in Europe, such as Watinoceras devonense, Collignoniceras 

woollgari, Prionocyclus germari, Scaphites hippocrepis, Didymoceras stevensoni, and 

Didymoceras cheyennense, whereas more than one-half of the inoceramid zones are 

known also in Europe. A few of the ammonite zones are known from only a few 

localities, but the diagnostic species may occur in abundance. Among these are the zones 

of Acanthoceras granerosense, A. bellense, Dunveganoceras problematicum, Burroceras 

clydense, Watinoceras devonense, Collignoniceras praecox, and Scaphites mariasensis. 

All fossils listed in the table are in the national collection housed in Building 810 at the 

Federal Center, Denver, Colo. 

1
This zonation is based on field work by U.S. Geological Survey geologists and 

their collections of fossils. There are other Western Interior zonations by paleontologists 

outside the USGS, especially the many works of E.G. Kauffman and associates 

(Kauffman et al., 1994). 

figure 1 (chart attached to page 47 at the end of volume)

2
The present zonation was founded mainly on the extensive collection of fossils 

made by the following USGS personnel, in alphabetical order: C.E. Erdmann, J.R. Gill, 

E.R. Landis, E.A. Merewether, C.M. Molenaar, F. Peterson, J.D. Powell, J.B. Reeside, 

Jr., and G.R. Scott. Special thanks go to Stephen C. Hook (Atarque Geologic Consulting, 

Socorro, N. Mex.) for much cooperative work with Cobban on the Cretaceous 

stratigraphy and fossils of New Mexico and Trans-Pecos Texas, while Hook was 

employed by the New Mexico Bureau of Mines and Mineral and Mineral Resources 

during 1976-1981. 

Different molluscan zonations of Upper Cretaceous ammonites and inoceramids 

have been shown in tables in numerous publications beginning with the broad zonation of 

Stephenson and Reeside’s (1938) 10 zones to the present one of 67 zones. The zonation 

begins with a great transgression of the epeiric sea early in the middle Cenomanian and 

ending in the late Maastrichtian. In general, each successive zonation was a revision of 

the next older one and usually added more refinement by the subdivision of zones or the 

recognition of new zones. In the following discussion on the construction of the present 

zonation, only the more important changes are treated. For simplicity, each zone is 

designated by a single name of a species. Subspecies names are not used, although some

of the species in the table were considered as subspecies in earlier tables (Hook and 

Cobban, 1981; Cobban and Hook, 1983; Cobban, 1984, 1988b). In the present report, the 

words ammonite and inoceramid are applied both as a noun and an adjective, which 

seams to be in general use these days. 

3
Constructing the Zonation 

Much of the early stratigraphic work in the Western Interior of the United States 

was along the Missouri River, where steamboat travel from St. Louis to Fort Benton was 

available. The general order of much of the Cretaceous sedimentary rocks was 

determined in the 1850s. At first the formations were numbered 1 to 5 from oldest to 

youngest. In 1861 F.B. Meek and F.V. Hayden gave the following geographic names to 

the sequence (Waage, 1975, p. 60): 

Eocene Fort Union or Great Lignite Group 

Cretaceous

Upper Series {

Lower Series {

Formation No. 5. Fox Hills beds 

Formation No. 4. Fort Pierre Group 

Formation No.3. Niobrara Division 

Formation No.2. Fort Benton Group 

Formation No.1. Dakota Group 

Coal Measures 

In 1876 Hayden proposed the name Colorado group for the strata between the Dakota and 

Fox Hills groups along the Front Range in Colorado. C.A. White (1878) emended this 

definition to include only the Fort Benton and Niobrara groups. Later G.H. Eldridge 

(1888, 1889) gave the name Montana group to rocks in central Montana equivalent to the 

Fort Pierre Shale and Fox Hills Sandstone of the Dakotas. Fossils reported on in the late 

4
1800s were usually assigned to some one of the few named formations, such as “upper 

part of the Fort Pierre group” (Meek, 1876a), or the fossils were grouped under a 

formational name such as “Colorado fauna” or “Montana fauna” (Stanton, 1894, 1909). 

During the 1920s Reeside authored several papers on Cretaceous molluscan faunas from

the Western Interior in which he related many of the species to the European stages of the 

Cretaceous. These papers included important works on ammonite faunas (Reeside, 

1927a,b). 

Stephenson and Reeside (1938), in comparing the Upper Cretaceous of the 

Western Interior and Gulf regions, recognized 10 molluscan zones in the Western 

Interior, of which most of their record was in the pre-Campanian part. Their zonation is 

summarized in the following illustration (fig. 2) based on their original figure 3 and 

adjacent pages. 

5
Figure 2. Upper Cretaceous stages, Western Interior formations with fossil zones 1-10, 

and important molluscan species (modified from Stephenson and Reeside, 1938, p.1636-

38). Reeside repeated this zonation in 1944 (Reeside, 1944). 

6
Strata of Colorado age (Cenomanian-Santonian) in Montana and in the Black 

Hills area were investigated by Cobban in the 1940s. A sequence of 20 zones was 

established (Cobban, 1951a, fig. 2). This zonation was applied by Cobban and Reeside 

(1952) in their Geological Society of America’s correlation of Cretaceous formations of

the Western Interior, Chart 10b. In addition to the Colorado Group, the chart included 

nine ammonite zones in the Montana Group. The Upper Cretaceous part of the chart is 

shown below (the zonation was repeated by Reeside, 1957, table 1). 

7
8
Figure 3. Upper Cretaceous stages and formations of the Gulf coastal plain and Western 

Interior with fossil zones mostly from northern part of Western Interior. Part of chart 10b 

of Cobban and Reeside (1952). 

Extensive field work by G.R. Scott and Cobban in the late 1950s in the Pierre 

Shale mainly along the Front Range area of Colorado made possible a more refined 

zonation of the Montana Group. The three Campanian zones of Baculites asperiformis, B. 

gregoryensis, and B. compressus of the GSA chart were subdivided into the following 13 

zones (Scott and Cobban, 1959; see also Cobban, 1958a,b): 

Figure 4. Campanian zones of Baculites asperiformis-B. compressus of Cobban and 

Reeside (1952, chart 10b) and ammonite zonation of Pierre Shale of northeastern 

Colorado. Modified from Scott and Cobban (1959, fig. 3). 

9
The baculitid sequence was refined further following a taxonomic study by Cobban (1962 

a,b). 

In the early 1960s, H.A. Tourtelot was in charge of a geochemical investigation of 

the Pierre Shale of the northern Great Plains and the equivalent stratigraphic rocks farther 

west. J.R. Gill (1922-1972), a superb fossil collector, did much of the field work of this 

project. The following sequence, based mainly on Baculites, was determined for the 

Montana Group (Gill and Cobban, 1965). 

Figure 5. Campanian and lower Maastrichtian ammonite zonation and formations in 

central Montana. From Gill and Cobban (1965, fig. 3, in part). 

10
Baculites reduncus, a curved species, was later found to occupy a position between B. 

gregoryensis and B. scotti (Cobban, 1977). 

A study of the early Campanian ammonite Scaphites hippocrepis (DeKay) and the 

late Santonian and earliest Campanian S. leei Reeside revealed that both species occurred 

as three chronologic subspecies each numbered I-III (Cobban, 1969). Scaphites 

hippocrepis first appeared as zones I to III on a chart by Gill et al., 1970, table 1; see also 

Gill and Cobban, 1973, fig. 12). 

By the early 1960s, a zonation of the Colorado Group was fairly well established. 

The sequence was shown well in a study of the ammonite family Binneyitidae. 

Figure 6. Ammonite zones for the part of the Upper Cretaceous and position of 

Binneyites and Borissiakoceras (Cobban, 1961, table 1). 

11
A little later, the ammonite Clioscaphites saxitonianus (McLearn) was determined to 

form a zone between C. vermiformis and Scaphites depressus (Scott and Cobban, 1962), 

and the ammonite Acanthoceras?wyomingense (Reagan) was placed in 

Plesiacanthoceras (Haas, 1964). 

The stratigraphy and paleontology of the Niobrara Formation in the Pueblo area 

of Colorado was investigated by Scott and Cobban (1964). Part of their table 3 is shown 

here. 

12
Figure 7. Upper Turonian-lower Campanian stages, molluscan fossil zones, and 

formations of the Pueblo, Colorado, area. From Scott and Cobban (1964, part of table 3). 

This was an early attempt to integrate ammonite and inoceramid zonation. 

Inoceramus aff. I. perplexus is now considered Mytiloides scupini (Heinz), Inoceramus 

erectus and I. deformis are now placed in Cremnoceramus, I. stantoni is considered a 

junior synonym of I. undabundus, I. cordiformis is assigned to Cordiceramus, I. platinus

is a nomen nudum (poorly defined species), and I. patootensis is probably 

13
Sphenoceramus lundbreckensis. The ammonites Barroisiceras and Prionocycloceras? are 

Forresteria. 

In the course of mapping the geology of many quadrangles in the eastern one-half 

of Colorado, G.R. Scott refined the stratigraphic units and collected numerous fossils. 

The middle Cenomanian Graneros Shale and the upper Cenomanian and lower Turonian 

Greenhorn Limestone received much attention that resulted in Professional Paper 645 

(Cobban and Scott, 1972). The middle Cenomanian into the base of the middle Turonian 

rock sequence and fossil zones of the Pueblo area were given in the following table: 

14
Figure 8. Ammonite zonation of Cenomanian and part of Turonian of the Western 

Interior and Pueblo, Colorado, area, and the rock sequence at Pueblo (Cobban and Scott, 

1972, table 4). 

Calycoceras (Conlinoceras) gilberti Cobban and Scott was a new name given to 

the Calycoceras sp. of previous reports. Two new species of ammonites, Acanthoceras 

granerosense and A. muldoonense, marked middle Cenomanian zones between C. 

gilberti and A. amphibolum. Dunveganoceras pondi (Haas), from the base of the upper 

Cenomanian of Wyoming and Montana, was not found in the Pueblo area, but 

Calycoceras? canitaurinum (Haas), restricted to the pondi zone, is common at Pueblo. 

Seiponoceras gracile (Shumard), a straight ammonite and the immediate ancestor of 

Baculites, was believed to occupy the rest of late Cenomanian time. The zones of 

Watinoceras coloradoense Henderson, Mammites nodosoides (Schlüter), and 

Collignoniceras woollgari (Mantell), were assigned to the Turonian. 

Calycoceras (Conlinoceras) gilberti appeared as a zone in many publications 

during the decade following the Cobban and Scott Pueblo paper. In that paper (Cobban 

and Scott, 1972, p. 62), attention was drawn to the close resemblance of gilberti to the 

two ammonites from the Woodbine Formation of Texas described by Walter Adkins 

(1928) as the new species Metacanthoceras? tarrantense and Acanthoceras wintoni. 

Cobban and Scott believed the two Texas fossils were one species (tarrantense) and 

assignable to Calycoceras (Conlinoceras). Cobban and Hook (1983, table 1) raised 

15
Conlinceras to full generic rank and replaced gilberti by tarrantense because the latter 

was more widely distributed. 

The middle Cenomanian ammonite Acanthoceras alvaradoense Moreman was 

added to the zoned sequence between A. muldoonense and A. amphibolum (Merewether, 

et al., 1975), but later it was treated as a subspecies of A. amphibolum (Cobban and 

Hook, 1983, table 1; Cobban, 1984, fig. 2), and after 1984, A. alvaradoense was no 

longer used as a zone. 

 The ammonite Nigericeras scotti Cobban was added to the lower Turonian 

zonation just below a zone of Watinoceras coloradoense-Vascoceras birchbyi (Cobban 

and Hook, 1979, fig. 1), and the ammonite Neocardioceras juddii (Barrois and Guerne) 

was added at the base of the Turonian just beneath the scotti zone (Hook and Cobban, 

1981, fig 1). An investigation of the Cenomanian and Turonian strata and fossils of 

England by Wright and Kennedy (1981) revealed that the juddii zone marked the top of 

the Cenomanian, and, accordingly, Cobban and Hook (1983, table 1) raised the 

Cenomanian boundary to fit the European placement. The types of N. scotti came from a 

bed of limestone in the Bridge Creek Member of the Greenhorn Limestone in 

southeastern Colorado (Cobban, 1972). Collections made from that locality show that the 

species occurs a little higher in the formation than N. juddii. N. scotti is now considered 

the top of the Cenomanian in the Western Interior (Cobban, 1988a, fig 13; Kennedy and 

Cobban, 1990, fig. 3). It should be noted that N. scotti has been found only in a single bed 

at three localities in southeast Colorado and, questionable, from a specimen in southwest 

16
New Mexico. According to Gale (1989), the N. juddii Zone involves perhaps 300 kyr of 

time. 

Acanthoceras bellense Adkins (1928), a species described from the basal part of 

the Eagle Ford Formation of Texas, was found later in the Belle Fourche Shale of the 

Black Hills area in eastern Wyoming, where it forms a zone between the zones of A. 

muldoonense and A. amphibolum (Cobban, 1987, p. 24). Associated ammonites at the 

Wyoming localities include Paraconlinoceras leonense (Adkins), a species now known 

from the Mancos Shale of west-central New Mexico. 

Vascoceras birchbyi Cobban and Scott (1972) was described from the Bridge 

Creek Member of the Greenhorn Limestone of the Pueblo area of Colorado, and assigned 

to the Watinoceras coloradoense Zone. On some charts of the 1970s, both species were 

listed together as an early Turonian zone indice, but later V. birchbyi was applied alone 

because it was more widely distributed, as in the following table from Cobban and Hook 

(1983). 

17
Figure 9. Cenomanian-Turonian ammonite sequence in the Western Interior (Cobban and 

Hook, 1983, table 1). In the above figure, the ammonite Pseudaspidoceras flexuosum

18
Powell (1963), described from Trans-Pecos Texas, was added at the base of the Turonian 

just below V. birchbyi, and the poorly defined ammonite Subprionocyclus percarinatus 

(Hall and Meek) was replaced by the much better defined Collignonoceras praecox

(Haas, 1946; Kennedy et al., 2001). The table also shows the application of the ammonite 

Subfamily Collignoniceratinae for the Turonian in the southern part of the Western 

Interior with Prionocyclus quadratus at the top of the Turonian. That species, described 

from the Sage Breaks Member of the Carlile Shale of the Black Hills area (Cobban, 

1953), has appeared on numerous tables from 1979-1994, when it was replaced by P. 

germari. 

The upper Cenomanian Sciponoceras gracile Zone was divided into a lower 

subzone of Vascoceras diartianum (d’Orbigny) and an upper subzone of 

Euomphaloceras septemseriatum (Cragin) (Cobban, 1988b, fig. 2), and these were treated 

later as regular zones (Obradovich, 1994; Cobban and Larson, 1997), when S. gracile

was found to range through the zones of V. diartianum-Neocardioceras juddii (Cobban et 

al., 1989). 

Extensive field work by Hook and Cobban in southwestern New Mexico revealed 

a zone of the ammonite Burroceras clydense Cobban, Hook and Kennedy, between the 

zones of Sciponoceras gracile [Euomphaloceras septemseriatum] and Neocardioceras 

juddii (Cobban et al., 1989), and since then clydense has appeared in the zonal schemes 

(Kennedy and Cobban, 1991a, fig. 2; Obradovich, 1994, fig. 2), and has replaced 

Vascoceras cauvini of earlier reports as noted by Cobban (1990, fig. 2). 

19
The ammonite genus Forresteria Reeside (1932), named for the deceased Robert 

Forrester, Salt Lake City, Utah, can be used for zoning the upper part of the Turonian and 

the lower Coniacian in Colorado, Utah, and New Mexico, where scaphitid ammonites of 

that age are scarce in contrast to their abundance farther north. Forresteria in the Western 

Interior was treated by Kennedy and Cobban (1991b). The sequence of species related to 

the inoceramid zonation seems to be as follows, although the total range of each 

Forresteria species is unknown at present: 

Stage Forresteria Inoceramid species 

Lower 

Coniacian 

alluaudi 

brancoi and hobsoni

Cremnoceramus crassus crassus 

C. crassus inconstans 

C. deformis dobrogensis

C. deformis erectus 

Upper 

Turonian (part) peruana

C. waltersdorfensis 

Mytiloides scupini 

Figure 10. Occurance of species of Forresteria in the Western Interior and the 

inoceramid zone in which they have been found. 

A few tables have Forresteria as zones in the Western Interior (Cobban and Hook, 1989; 

Obradovich, 1994; Hancock et al., 1994). 

20
Some Stage Boundaries 

The Cenomanian-Turonian boundary in the Western Interior has an interesting history. 

Reeside (1944) used the ammonite Metoicoceras whitei as the lowest zone of the 

Turonian, and listed the bivalve Gryphaea newberryi among the underlying Cenomanian 

fossils. Metoicoceras whitei Hyatt (1903) is now considered a synonym of M. 

geslinianum (d’Orbigny, 1841), and G. newberryi is now assigned to the genus 

Pycnodonte and occurs with M. geslinianum. The straight ammonite Sciponoceras 

gracile (Shumard) was included with M. whitei in the basal zone of the Turonian by 

Cobban (1951a,b, fig. 2), but in their GSA paper(1952), Cobban and Reeside showed 

only S. gracile as a zonal fossil. From 1952 to 1972, the S. gracile Zone was shown in 

many publications as the basal zone of the Turonian. But in 1972, Cobban and Scott 

placed it at the top of the Cenomanian, and designated Watinoceras coloradoense

(Henderson) as the basal Turonian zone. As noted earlier, Pseudaspidoceras flexuosum

was recognized as the basal Turonian zone from 1983-1991, when W. devonense Wright 

and Kennedy (1981), a species described from the base of the Turonian of England, was 

recorded from just below the P. flexuosum Zone in the Pueblo area, Colorado (Kennedy 

and Cobban, 1991a,b, fig. 2; see also Kennedy et al., 2000, fig. 6; 2005, fig. 8). 

The Turonian Stage was not subdivided in the Western Interior until 1978, when 

Kauffman et al. recognized lower, middle, and upper substages. The boundary between 

the middle and upper substages was placed at the contact between the zone of 

Inoceramus howelli-Prionocyclus hyatti below and the zone of Inoceramus dimidius21
Prionocyclus macombi above. The boundary between the middle and upper Turonian 

remained stable from 1978-2000 until Walaszczyk, while studying Western Interior 

inoceramids at the Denver Federal Center, found that the European I. costellatus Woods

(1912) of authors, widely used as a guide to the base of the upper Turonian, was the same

species as I. perplexus Whitfield (1877) of the Western Interior zone of Scaphites 

whitfieldi. Walaszczyk and Cobban (2000), accordingly, considered the S. whitfieldi-I. 

perplexus Zone as the base of the upper Turonian and lowered the I. dimidius-P. 

macombi Zone (including the zone of Scaphites ferronensis and S. warreni) to the upper 

part of the middle Turonian. 

The Campanian-Maastrichtian boundary has also been a problem. In their 1952 GSA 

paper, Cobban and Reeside placed the boundary at the base of the Baculites baculus Zone 

following the judgment of George Jeletzky of the Geological Survey of Canada (in 

Cobban and Reeside, 1952, p. 1026-27). The Maastrichtian zonation proposed, from the 

oldest to the youngest was as follows: Baculites baculus, B. grandis, and then a gap 

followed by Discoscaphites nicolletii, and D. nebrascensis. The lower part of the gap was 

filled by Sphenodiscus (Coahuilites)-Discoscaphites n. sp. (Gill and Cobban, 1966, table 

2), who assigned the D. nicolletii of the earlier reports to Hoploscaphites nicolletii. The 

use of Sphenodiscus (Coahuilites) disappeared in the late 1980s, and the Discoscaphites 

n. sp. became Hoploscaphites aff. nicolletii (Cobban et al., 1992, fig. 1; Obradovich, 

1994, fig. 2). The latter species was described by Landman and Waage (1993) as H. 

birkelundi (spelling corrected to birkelundae by Landman and Cobban, 2003), and the 

species name has appeared on numerous tables since 1997, as in the following table: 

22
Figure 11. Coniacian-Maastrichtian ammonite sequence in the Western Interior in which 

the zones were numbered 1-38 (Merewether et al., 1997, part of figure 4) 

The Campanian Maastrichtian boundary in the above table was placed at the base 

of the Baculites eliasi Zone following a recommendation by Kennedy and Cobban (1993, 

fig. 4), but it was raised again to the base of the baculus Zone as a result of an 

23
investigation of Western Interior inoceramid bivalves (Walaszczyk et al., 2001). 

However, in regard to the sequence at Tercis, France, which has the Global Standard 

Stratotype Section and Point for the Campanian-Maastrichtian Stage boundary, the base 

of the Maastrichtian should be placed high in the Baculites eliasi Zone (Walaszczyk et 

al., 2002). The latter placement of the boundary is accepted for the present table, although 

strontium isotope stratigraphy would have it a little lower within the Baculites jenseni

Zone (McAuthor et al., 1992). 

Inoceramid Zonation 

Although a few inoceramid species were included in earlier reports (Stephenson and 

Reeside, 1938; Cobban and Reeside, 1952), including a late Turonian-Coniacian 

sequence (Merewether et al., 1975, table 1), the first detailed zonation of Western Interior 

Late Cretaceous inoceramids was by Kauffman et al. (1978) in which the inoceramids 

were treated by E.G. Kauffman, the ammonites by Cobban, and the Foraminifera by D.L. 

Eicher. Their zonal sequence was summarized in the following figure: 

24
Figure 12. Early Cenomanian-early Coniacian integrated zonation of ammonites, 

inoceramids, and foraminifera (Kauffman et al., 1978, xxiii-16). 

25
A zonation for the middle Cenomanian-lower Coniacian that has an inoceramid 

species for each ammonite was presented in the following paper on south-central New 

Mexico modified from Cobban (1986): 

Figure 13. Integrated ammonite and inoceramid zonation for the middle Cenomanian into 

the lower Coniacian of New Mexico (Cobban, 1986, modified from fig. 2). 

26
The Western Interior inoceramids were thoroughly investigated by Walaszczyk 

during parts of 1998-1999, while he was in Denver on a Fulbright Foundation research 

fellowship. The inoceramid zonation (upper Cenomanian-Maastrichtian) in the present 

table is based on his work (Walaszczyk and Cobban, 2000; Walaszczyk et al., 2001; 

Walaszczyk and Cobban, in Kennedy et al., 2000; Walaszczyk and Cobban, 2006a,b, in

press). Minor changes include an undescribed species referred to as Inoceramus aff. 

dimidius in the older part of the I. dimidius Zone of earlier reports. At the base of the 

middle Cenomanian, I. macconnelli Warren 1930a is used in place of the synonym I. 

eulessanus Stephenson 1953 of earlier tables. 

27
Origin of Generic Names of Ammonites 

Most of the generic names of ammonites end in ceras (Greek, keras, horn) or ites (Greek, 

ites, stone) 

Acanthoceras. Greek, akanthos, prickly; for its shell with several rows of nodes. 

Neumayr, 1875. 

Baculites. Latin, baculum, rod or staff; for its straight shell. Lamarck, 1799. 

Burroceras. For Big Burro Mountains, Grant County, New Mexico. Cobban, et al., 1989. 

Clioscaphites. Greek, kleio, close; for the tightly enrolled shell. Cobban, 1952. 

Collignoniceras. For the French Général Maurice Collignon, who authored many papers 

on ammonites, especially those from Madagascar. Breistroffer, 1947. 

Conlinoceras. For James P. Conlin (1908-1972), Fort Worth, Texas, who collected and 

carefully documented numerous Cretaceous fossils, and donated them to the 

USGS. Cobban and Scott, 1972. 

Desmoscaphites. A scaphitid ammonite that has the early whorls with constrictions 

resembling the constrictions in the ammonite Desmoceras. Reeside, 1927b. 

Didymoceras. Greek, didymos, double, for the two growth forms. Hyatt, 1894. 

Dunveganoceras. For the Dunvegan Formation, Alberta, Canada. Warren and Stelck, 

1940. 

Euomphaloceras. Greek, eu, true; omphalor, navel; probably from the navel-like 

umbilicus of the ammonite. Spath, 1923. 

Exiteloceras. Greek, exitglos, becoming extinct. Hyatt, 1894. 

28
Hoploscaphites. Greek, hoplo, shield; for the shield-like appearance of laterally 

compressed scaphitid ammonites. Nowak, 1911. 

Jeletzkyites. For Jurij Alexandrovich Jeletzky, (1915-1988), paleontologist with the 

Geological Survey of Canada from 1948-1988. Riccardi, 1983. 

Mammites. Latin, mamma, breast, teat; for the ornament of nipple-like nodes. Laube and 

Brüder, 1887. 

Neocardioceras. Greek, neos, young; for a Cretaceous ammonite younger than the 

somewhat similar Jurassic ammonite Cardioceras. Spath, 1926. 

Nigericeras. For Niger, Africa. Schneegans, 1943. 

Plesiacanthoceras. Greek, plesios, near; for its resemblance to the ammonite 

Acanthoceras. Haas, 1964. 

Prionocyclus. Greek, priono, saw; kyklios, circular; for resemblance to a circular saw. 

Meek, 1871. 

Pseudaspidoceras. Greek, pseudes, false; for resemblance to the ammonite Aspidoceras, 

but not that genus. Hyatt, 1903. 

Scaphites. Latin, scapha, light boat; for its resemblance to a boat that has both ends 

curved. Parkinson, 1811. 

Vascoceras. Latin, vas, vessel; for resemblance to a vessel. Choffat, 1899. 

Watinoceras, For Watino, Alberta, Canada. Warren, 1930a. 

29
Origin of Species Names of Ammonites 

Origin of the names is followed by the author’s name and date (see References) 

albertense. For Alberta, Canada. Warren, 1930b. 

amphibolum. Greek, amphibolus, doubtful; for the assignment doubtfully to 

Acanthoceras. Morrow, 1935. 

asperiformis. Latin, asper, rough, forma, shape; for its ornament. Meek, 1876a. 

baculus. Latin, baculum, rod or staff. Meek and Hayden, 1861; Meek, 1876a. 

bassleri. For Harvey Bassler (1883-1950), paleontologist, who collected the type 

specimen. Reeside, 1927b. 

bellense. For Bell County, Texas. Adkins, 1928. 

birchbyi. For the late William H. Birchby, Pueblo, Colorado, who did bed-by-bed 

collecting from the Greenhorn Limestone in the Pueblo area, and then donated his 

fossils to the USGS. Cobban and Scott, 1972. 

birkelundae. For Tove Birkelund (1939-1986), Copenhagen, Denmark, paleontologist 

who wrote many papers on Cretaceous cephalopods including a monograph on 

ammonites from Greenland. Landman and Waage, 1993. 

cheyennense. For Cheyenne River in west-central South Dakota. Meek and Hayden, 

1856. 

choteauensis. For Choteau, Montana, where the holotype was found nearby. Cobban, 

1952 

30
clinolobatus. Latin, clino, slant or inclined, lobus, lobe; for the lateral lobe of the suture 

slanted at an angle to the axis of the shell. Elias, 1933. 

clydense. For Clyde Canyon in the Big Burro Mountains, Grant County, New Mexico. 

Cobban, et al. (1989). 

compressus. French, compresse, compress, for its compressed cross-section. Say, 1820. 

conditum. Latin, conditus, hidden, for the paratype specimen that was hidden in the back 

of a drawer in the Department of Geology, University of Wyoming. Haas, 1951. 

cuneatus. Latin, wedge-shaped; for the cross-section of the shell. Cobban, 1962b. 

depressus. Latin, pressed down; for the depressed cross-section of the shell. Reeside,

1927c. 

devonense. For the Devon coast, south-west, England. Wright and Kennedy, 1981. 

diartianum. Name given to a Turonian ammonite, probably from France. d’Orbigny, 

1850. 

eliasi. For Maxim Kondradovich Elias (1889-1982), for his excellent stratigraphic and 

paleontologic investigations of the Pierre Shale of western Kansas. Cobban, 

1958b. 

erdmanni. For Charles Edgar Erdmann (1897-1971), USGS geologist, he and his 

assistants made over 500 carefully located geographically and stratigraphically 

collections of fossils from the Sweetgrass Arch and Disturbed Belt of 

northwestern Montana. Cobban, 1952. 

ferronensis. For the Ferron Sandstone Member of the Mancos Shale of central Utah. 

Cobban, 1952. 

flexuosum. Latin, flexuosus, bending; for the fossil’s flexuous ribbing. Powell, 1963. 

31
germari. For Professor Ernst Friederich Germar (1786-1853), mineralogist and 

entomologist and director of the Mineralogical Museum at Halle, Germany. 

Reuss, 1845. 

grandis. Latin, large; for the large size of species. Hall and Meek, 1856. 

granerosense. For the Graneros Shale that provided the type. Cobban and Scott, 1972. 

gregoryensis. For the Gregory Member of the Pierre Shale, Lyman County, South 

Dakota. Cobban, 1951b. 

hippocrepis. Greek, hippo, horse; krepis, shoe; for the horseshoe-shaped cross-section. 

DeKay, 1828. 

hyatti. For Alpheus Hyatt (1838-1901), eminent American paleontologist. Stanton, 1894. 

jenneyi. For Walter Proctor Jenney (1849-1921), geologist-in-charge of an exploring 

expedition of the Black Hills in 1875. Whitfield, 1877. 

jenseni. For the late Fred Scott Jensen, USGS geologist in the early 1960s who collected 

the type specimens. Cobban, 1962b. 

juddii. For the English geologist “M. le professeur Judd.” Barrois and de Guerne, 1878. 

leei. For Willis Thomas Lee (1864-1926), USGS geologist, who collected the type 

specimen. Reeside, 1927b. 

maclearni. For Frank Harris McLearn (1885-1964). prominent paleontologist of the 

Geological Survey of Canada. Landes, 1940. 

macombi. For Captain John N. Macomb (1810-1889), in command of the U.S. 

Topographical Engineers San Juan exploring expedition in New Mexico in 1859. 

Meek, 1876b. 

32
mariasensis. For Marias River in north-central Montana, where the holotype was 

collected from the river bank. Cobban, 1952. 

muldoonense. For Muldoon Hill in Pueblo County, Colorado, about 30 kilometers 

southwest of Pueblo and site of “Muldoon Man” carved out of gypsum and then 

buried to be “discovered” later by the perpetrator for a money-making display. 

Cobban and Scott, 1972. 

nebrascensis. For Nebraska Territory. Owen, 1852. 

nicolletii. For Joseph Nicolas Nicollet (1786-1843), French immigrant scientist, who 

explored and mapped the upper Mississippi River Valley and collected 

Cretaceous fossils in South Dakota in 1839. Morton, 1842. 

nigricollensis. Latin, nigra, black; collis, hill, for the Black Hills of South Dakota. 

Cobban, 1952. 

nodosoides. Latin, nodosus, full of knots; for the nodate ornament. Schlüter, 1871. 

obtusus. Latin, blunt; for the ornament of node-like arcuate ribs or blunt nodes. Meek, 

1876a. 

perplexus. Latin, puzzling; for the difficulty in separating the species from other early 

Campanian species. Cobban, 1962a. 

pondi, For. W.F. Pond, Greybull, Wyoming, who assisted Otto Haas in the field. Haas, 

1949. 

praecox. Latin, prae, before; for the accelerated development of its ornament in contrast 

to other related species. Haas, 1946. 

preventricosus. Latin, prae, before; for occurence before (below) the species ventricosus. 

Cobban, 1952. 

33
problematicum. Greek, problema, problem or puzzle; for taxonomic status of the 

ammonite Dunveganoceras problematicum. Cobban, 1988a. 

reduncus. Latin, curved; for the curved form. Cobban, 1977. 

reesidei. For John Bernard Reeside, Jr. (1889-1958), eminent USGS paleontologist. Elias, 

1933. 

saxitonianus. For Saxitonia “the Rocky Mountain country.” McLearn, 1929. 

scotti. For Glenn R. Scott, retired USGS geologist, who added much to our knowledge of 

the Cretaceous rocks and fossils of the Western Interior. Cobban, 1958b; 1972). 

septemseriatum. Latin, septum, partition; seria, pot; for its resemblance to a chambered 

pot. Cragin, 1893. 

stevensoni. For Professor John James Stevenson (1841-1924), who “has done so much 

good work among Cretaceous rocks of the West.” Whitfield, 1877. 

tarrantense. For Tarrant County, Texas. Adkins, 1928. 

ventricosus. Latin, ventricose swelling; for the inflated form. Meek and Hayden, 1862. 

vermiformis. Latin, vermiculatus, worm-like; probably from its fanciful resemblance to a 

coiled caterpillar. Meek and Hayden, 1862. 

warreni. For Lieutenant Gouverneur Kemble Warren (1830-1882), Corps of 

Topographical Engineers, who led a geographical and geological survey of the 

Black Hills in 1857. Meek and Hayden, 1860. 

whitfieldi. For Robert Parr Whitfield (1828-1910), long-time curator of geology and 

invertebrate paleontology at the American Museum of Natural History, who 

described many Cretaceous fossils. Cobban, 1952. 

woollgari. For Thomas Woollgar, “esteemed friend” of Gideon Mantell, 1822. 

34
wyomingense. For the State of Wyoming. Reagan,1924. 

35
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