multituberculates from the wasatchian land-mammal age, early eocene, of western north america

Multituberculates from the Wasatchian Land-Mammal Age, Early Eocene, of Western NorthAmericaAuthor(s): David W. KrauseSource: Journal of Paleontology, Vol. 56, No. 2 (Mar., 1982), pp. 271-294Published by: SEPM Society for Sedimentary GeologyStable URL: http://www.jstor.org/stable/1304455 .

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JOURNAL OF PALEONTOLOGY, V. 56, NO. 2, P. 271-294, 14 TEXT-FIGS., MARCH 1982

MULTITUBERCULATES FROM THE WASATCHIAN LAND-MAMMAL AGE, EARLY EOCENE, OF WESTERN NORTH AMERICA

DAVID W. KRAUSE Museum of Paleontology, The University of Michigan, Ann Arbor 48109

ABSTRACT-Wasatchian multituberculates have been discovered in five major areas within the West- ern Interior of North America. Particularly large samples have been recovered from the Bighorn Basin of northwestern Wyoming and the Four Mile Creek area of northwestern Colorado. Multitu- berculate taxa now known from Wasatchian horizons include the neoplagiaulacids Ectypodus tardus, Ectypodus cf. E. childei, Parectypodus lunatus n. sp., Parectypodus simpsoni, and Neoplagiaulacidae genus and species indeterminate, and the large eucosmodontid Neoliotomus ultimus. Parectypodus (=Charlesmooria) childei, a European species that may also be represented in North America, is transferred to Ectypodus. Ectypodus tardus and Neoliotomus ultimus were probably derived from Clarkforkian E. powelli and N. conventus, respectively. Ectypodus cf. E. childei and Parectypodus lunatus have no known ancestors in North America. Parectypodus lunatus, the most common early Wasatchian multituberculate, appears to have given rise to the later, larger P. simpsoni. More complete material of Neoliotomus than previously available indicates that it is the most primitive known, yet latest occurring, eucosmodontid in North America.

Discovery of specimens of a small neoplagiaulacid(s) from a late Wasatchian horizon in the Wind River Basin, Wyoming, provides the first documentation of multituberculates of that age; all other records are from the early and middle Wasatchian.

INTRODUCTION

MULTITUBERCULATES have one of the longest known histories among mammalian orders. They reached their acme in relative abundance and diversity in the Torrejonian (middle Paleocene) and Tiffanian (late Paleocene) but declined precipitously immediately thereafter. Multituberculates comprise only a minor com- ponent of the North American mammalian fuana by Clarkforkian (latest Paleocene-earliest Eocene) time, where they are represented by only six known species (Krause, 1980). From this point onward, multituberculates lingered in the fossil record until their last known occurrence in the early Oligocene (Ostrander, Jones and Cape, 1979; Krish- talka et al., in prep.). The objective of this study is to document the taxonomic diversity and evolutionary relationships of North American Multituberculata during the Wa- satchian Land-Mammal Age (early Eocene).

The evolutionary history of post-Clarkfor- kian multituberculates is poorly known. This is due, at least in part, to their small size, which renders discovery uncommon using nor- mal surface prospecting methods. All post- Clarkforkian multituberculates, except Neo- liotomus, are very small neoplagiaulacids. In recent years the technique of screen washing large volumes of fossiliferous sediment to collect small mammalian remains has been in- Copyright ( 1982, The Society of Economic Paleontologists and Mineralogists and The Paleontological Society 2 71

creasingly employed and has shown multituberculates to be more common in Clarkforkian and later strata than previously recognized. Even in screen-washed samples, however, only the largest of the cheek teeth (P4) are usually represented. Upper fourth premolars and M1 occur next in abundance while p1-3 and M2 are rare.

The relatively large samples now available from individual localities in the Four Mile Creek area of northwestern Colorado and the Bighorn Basin of northwestern Wyoming provide the first opportunity to study variability within Wasatchian multituberculate species, and to resolve some of the difficulties that have historically attended their discrimination. In addition, the well-exposed and continuous stratigraphic section in the Bighorn Basin permits a temporal ordering of multituberculate- producing localities. Almost all of the collections of multituberculates from Wasatchian localities in the Western Interior of North America were available for this study. Impor- tant samples from the Bitter Creek area (Wa- satch Formation, Washakie Basin, Wyoming) and from University of Arizona localities 7745 and 7747 (San Jose Formation, San Juan Basin, New Mexico) are currently under study by B. Waters and R. A. Haskin, respectively. Mul- tituberculates from Wasatchian equivalent (Ypresian, in part) localities in England and

0022-3360/82/0056-0271$03.00

1



DAVID W. KRAUSE

France (Kiihne, 1969; Savage, 1971; Sloan, 1981) are also not reviewed here.

ABBREVIATIONS

Institutions: AMNH-American Museum of Natural

History, New York. BMNH-British Museum of Natural His-

tory, London. CM-Carnegie Museum of Natural

History, Pittsburgh. MCZ-Museum of Comparative Zoolo-

gy, Harvard University, Cam- bridge.

PU-Princeton University, Princeton. UCMP-University of California Museum

of Paleontology, Berkeley. UM-University of Michigan Museum

of Paleontology, Ann Arbor. USGS-United States Geological Survey,

Denver. UW-University of Wyoming, Laramie.

YPM-Yale Peabody Museum, Yale University, New Haven.

Localities: All localities are prefaced by above institutional acronyms except as follows:

FG-UM locality in the Foster Gulch area of the northern Bighorn Ba- sin.

SC-UM locality in the Sand Coulee area of the northern Bighorn Ba- sin.

Y-M-Joint YPM-UM locality in the central Bighorn Basin.

Measurements: H-Height. L-Length.

W-Width. S-Number of serrations on P4. C-Number of cusps (for derivation

of cusp formulae see Simpson, 1929, p. 104).

All measurements are in millimeters (mm) and were taken on a Bausch and Lomb stereo zoom microscope with a disc micrometer; all values are rounded to tenths.

GEOGRAPHIC AND STRATIGRAPHIC FRAMEWORK

Specimens of Wasatchian multituberculates have been recovered from at least five major areas in western North America (Text-fig. 1):

River Basin L._ _ _- --

..- ----- "~

Four Mile I __ Creek

!j| KANSAS

L --- t - - _ a- \ r ,

) ARIZONA I I -_

-- i {> _J 0 : o 200 400 KM

h4- 0 -

TEXT-FIG. 1--Major multituberculate-bearing areas in Wasatchian deposits of western North Amer- ica.

1) Bighorn Basin of northwestern Wyoming (Willwood Formation).-In 1914 Granger (p. 205) defined the Wasatchian biostratigraphic subzone, the "Sandcouleean", in part by "the last appearance of the primitive order Multi- tuberculata." This was based on the discovery in the northern Bighorn Basin of specimens of Neoliotomus ultimus, which were not described until some 14 years later (Granger and Simpson, 1928). Jepsen (1930) described two new multituberculate species, Ectypodus tardus and Parectypodus simpsoni, specimens of which were discovered fortuitously while ex- cavating the remains of much larger animals from quarries in the central Bighorn Basin. H. Seton and W. Stein, while collecting for Har- vard University (MCZ) in 1939, found additional specimens of these two species in the Dorsey Creek and Elk Creek areas.

Jepsen and his field parties from Princeton University collected several specimens of Wa- satchian multituberculates from the central and northern parts of the Bighorn Basin during extensive prospecting between 1930 and 1970. The most significant PU collections of multituberculates come from two localities:

272



WASATCHIAN MULTITUBERCULATES

Hackberry Hollow (=UM locality SC-192) and Bone Hill (=UM locality FG-17). Jepsen's ef- forts in the northern Bighorn Basin were re- sumed in 1975 by field parties under the direction of P. D. Gingerich of the University of Michigan. Of 126 Wasatchian UM localities that have produced mammals in the Sand Coulee area of the northern Bighorn Basin, only 26 have yielded multituberculates. In addition, Wasatchian multituberculates have been found at three localities in the Foster Gulch area southeast of the settlement of Will- wood, in the northern Bighorn Basin.

Small samples of multituberculates were recovered from three localities (CM localities 150, 676, 681) west of Basin and Manderson (central Bighorn Basin) by J. L. Kay and J. A. Dorr, Jr. and their field parties from the Carnegie Museum of Natural History in 1952 and 1953. These are currently being described by L. Krishtalka. In 1961, E. L. Simons, then of Yale University, began an intensive annual field program to collect fossil mammals in the central Bighorn Basin. This effort has resulted in the discovery of 474 fossil localities, 240 of which have been recently correlated on the basis of relative position in a measured stratigraphic section (Schankler, 1980). Included in this central Bighorn Basin section are several localities discovered by a joint expedition led by Simons and Gingerich in 1974.

Beginning in 1973, T. M. Bown, then of the University of Wyoming, studied the stratigraphy, sedimentology, and paleontology in the Sand Creek-No Water Creek area of the southeastern Bighorn Basin (Bown, 1979) and, more recently, in the area of the Fifteenmile Creek drainage with K. D. Rose.

Many of the Bighorn Basin localities that have yielded multituberculates can be correlated on the basis of detailed stratigraphic sections measured by P. D. Gingerich, K. D. Rose and myself in the northern part (Ginger- ich, Rose and Krause, 1980), D. M. Schankler and S. L. Wing in the central part (Schankler, 1980) and T. M. Bown in the southeastern part (Bown, 1979). The multituberculate-producing localities for which stratigraphic information is available are listed in Text-fig. 2. It should be noted that the bottom of each section in Text-fig. 2 starts at a different level. The zero meter level in the northern section marks the Clarkforkian-Wasatchian boundary; the base of the Willwood Formation lies

375 m below this level (Rose, 1979). No Clark- forkian mammals hve been recovered in the central and southeastern parts of the Bighorn Basin. Instead, Wasatchian mammals are found within the basal Willwood rocks in these areas. The zero meter levels for the central and southeastern sections are therefore at the Fort Union-Willwood contact, which is conformable in some areas and unconformable in others (Bown, 1979).

Schankler (1980) has provided a detailed biostratigraphic zonation within the central Bighorn Basin based on the entire mammalian fauna. Schankler's type of analysis has yet to be applied to the northern and southeastern parts of the basin. The biostratigraphic zonation scheme utilized here is that developed by Gingerich and Simons (1977) and Gingerich (1980a), based on successive species of the adapid primate genus Pelycodus. Gingerich has subdivided the Wasatchian Land-Mam- mal Age into five biochrons, which are, from oldest to youngest, Pelycodus ralstoni, P. mckennai, P. trigonodus, P. abditus and P. jarrovii. Within the limitations noted by Schankler (1980, p. 101), the most serious of which is the gradual and therefore arbitrary nature of the species boundaries, this scheme remains the most useful for correlation among basins within the Western Interior and within different parts (north, central and southeastern) of the Bighorn Basin. Overall changes in the mammalian faunas from different basins in western North America and even from different areas within the Bighorn Basin have yet to be documented, and therefore the data base for a comprehensive biostratigraphic zonation of the Wasatchian at the faunal level remains unattained.

As stated by Gingerich (in Gingerich, Rose and Krause, 1980, p. 62), "Pelycodus ralstoni is confined to the lowest 130 m of the Clark's Fork Basin Wasatchian. Its descendant P. mckennai is found from 135 m to 425 m above the base of the Wasatchian. P. trigonodus is derived from P. mckennai, and it occurs from 430 m to the highest levels at about 600 m above the base of the Wasatchian. . .. Pely- codus abditus . . . has not been found in the Clark's Fork Basin." Based on the data from Schankler (1980, fig. 3), P. ralstoni is not found in the central Bighorn Basin, the P. mckennailP. trigonodus couplet spans the 50-440 m range, P. abditus is found from ap-

273



DAViD W. KRAUSE

NORTHERN BIGHORN BASIN

2560

1480

1124

640 644

CENTRAL BIGHORN BASIN

('1

0 Z3

,t

4Z

U1) Z3

0

1Z2

cclr

350

870

120 1,544

4 7,38,304i

180

TO

2900

146 0

90b,1190

17f

4'

1250 60 60

I I I

U) U) 0~ U)

Cr, t.1) 1 K ~

Kcccc

U) Z

Z U) 5 O

li.- -.-- ~ Qj (- Q-;F

SOUTHEASTERN BIGHORN BASIN

2080 2080?

I 460 16'b1 16b 1

U)bb 16Cj Is

44'1 0 22? :Bt 3 K 370 37,760 cc 280

r U) . . . . . . . ... .. . . . . . . . . . . . . . . . . .. . . Kcc........

. . . . . .. . . . .. . . . . . . . .. . . . . . . . . . . . . . . . .. . . .. . . . . .. . . .

TEXT-FIG. 2-Stratigraphic distribution of multituberculate-bearing localities in the northern, central and southeastern parts of the Bighorn Basin. Meter levels in the three areas are not comparable (see text). Localities in the northern Bighorn Basin are all UM localities with the prefix SC-. Type localities in the central Bighorn Basin (designated by T) are PU localities; 90b, 119 and 290 are YPM localities; and 146 is a Y-M locality. Localities in the southeastern Bighorn Basin are all UW localities with the prefix V-730. Stratigraphic levels were determined from Rose (1979) and unpublished information for the northern Bighorn Basin; from Schankler (personal commun., 1980) for the two type localities and YPM 290 and from Schankler (1980) for the remaining localities in the central Bighorn Basin; and from Bown (1979) for localities in the southeastern Bighorn Basin. Solid circles designate localities of known stratigraphic level; open circles designate localities of estimated position. Transitions between Pelycodus biochrons of Gingerich (1980a) (P. raistoni, P. mckennai, P. trigonodus, and P. abditus) are indicated by stippled divisions, which are continuous if well known and broken if estimated.

274

600m

5OOm-

U1) :2

0

K cc Q,

I

LuI

LuL

0-

T

CD

H

H

Co

400m-

300m-

200m-

133'

161'

38, 210'(

0 U)

0 K .

.. . .. . .. . lOOm-

Om-




proximately 410 to 650 m, and P. jarrovii occurs from approximately 650 m to 700 m. Bown (1979, see also footnote p. 80; 1980) has recognized P. ralstoni, P. mckennai, and P. trigonodus in the southeastern Bighorn Basin; the later species P. abditus and P. jarrovii have not been found there. Meter levels for approximate boundaries between P. ralstoni and P. mckennai and between P. mckennai and P. trigonodus are not available but Bown (1979) has noted that the first occurrence of P. trigonodus is at the 590 ft (180 m) level. This is much lower than the first occurrence of P. trigonodus in the northern part of the basin. Gingerich (in Bown, 1980, p. 135), however, reidentified the specimens of Pelycodus at the 590 ft level as P. mckennai, a species that had not yet been described at the time of Bown's (1979) writing.

The research of Gingerich and Simons (1977), Bown (1979), Rose (1979), Gingerich (1980b), Gingerich, Rose and Krause (1980), and Schankler (1980) has yielded the following tentative conclusions concerning bio- and lithostratigraphic correlation of Willwood For- mation rocks among the three areas of the Big- horn Basin (summarized in Schankler, 1980): a) the upper part of the formation has been truncated by erosion in the southeast and north, b) the lowest part of the formation is missing in the central section, c) the central section is typified by a lower rate of sediment accumu- lation than in the northern part, and d) the onset of deposition of Willwood sediments is time transgressive, beginning much earlier in the north. Multituberculates, because of their uncommon occurrence in Wasatchian deposits, are not very reliable biostratigraphic in- dicators. However, it is noteworthy that none of the above conclusions are controverted by the multituberculate evidence now available.

In the northern part of the Bighorn Basin, Ectypodus tardus and Neoliotomus ultimus are long-ranging species, spanning most of the Pelycodus ralstoni and P. mckennai biochrons. Parectypodus lunatus first appears slightly later in the record than E. tardus and N. ultimus (but still within the P. ralstoni biochron) and extends into the P. mckennai biochron. Parectypodus lunatus probably gave rise to Parectypodus simpsoni, which endured into the P. trigonodus biochron.

In the central Bighorn Basin, multituberculate fossils are rare, presumably a reflection

of their small size and the relatively little screen washing performed in that area (most of the specimens of neoplagiaulacids from this area are dentary fragments). Parectypodus lunatus is absent from localities of known stratigraphic position but it is represented at CM locality 681, five miles west of Basin. No multituberculates have been recovered in association with either Pelycodus abditus or P. jarrovii in the central Bighorn Basin.

The occurrence of multituberculates in Bown's (1979) No Water fauna of the southeastern Bighorn Basin reflects an apparently dense distribution relative to the central and northern parts of the basin. This is due, at least in part, to the intensity of screen washing methods utilized by Bown. Of the 14 localities shown in Text-fig. 2 that have yielded multituberculates in the southeastern Bighorn Ba- sin, eight (57%) were screen washed. This compares to six of 23 (26%) localities screen washed in the north, and zero of six (0%) for the central part of the basin. Furthermore, none of the southeastern localities above 100 m (the highest is at 180 m) were screen washed, which may account for the absence of P. simpsoni in this area.

2) Four Mile Creek area of northwestern Colorado (Hiawatha Member of Wasatch For- mation).-McKenna (1960a) described the mammalian fauna from 30 localities in the Four Mile Creek area. Of these localities, six were quarries that produced small samples of multituberculates (Table 1). A large collection of multituberculates from East Alheit Pocket Quarry has been recovered by AMNH field parties since 1960. The distribution of multituberculate taxa in the six quarries suggests rather strongly that Despair Quarry, and probably Kent Quarry, are somehow different from the others. Whether this reflects temporal or ecological factors is not known. The presence of Ectypodus tardus, Parectypodus lunatus and Neoliotomus ultimus, and the absence of Parectypodus simpsoni in the Four Mile quarries suggests correlation with early Wasatchian faunas in the Bighorn Basin. This is corroborated by the occurrence of Pelycodus mckennai at East Alheit Pocket Quarry (Gin- gerich and Simons, 1977).

3) Powder River Basin of northeastern Wy- oming ("Wasatch Formation").-Delson (1971) described samples of fossil mammals collected by H. E. Wood in the early 1950's from 122

275



DAVID W. KRAUSE

TABLE 1-Distribution of multituberculate taxa in quarries in the Four Mile Creek area, northwestern Colorado. ? denotes questionable identification.

Ectypodus Ectypodus cf. Parectypodus Neoplagiaulacidae Neoliotomus Quarry tardus E. childei lunatus gen. & sp. indet. ultimus

Despair X East Alheit X X X Kent X? Sand X X X X Timberlake X X X West Alheit X X X

localities in the Powder River Basin. Multi- tuberculates are represented by a single specimen of Parectypodus lunatus from the Dry Well locality and one of Neoliotomus ultimus from the Bozeman locality. Specimens of Pe- lycodus from the Powder River Basin have been referred to P. mckennai (Gingerich and Simons, 1977).

4) Williston Basin of southwestern North Dakota (Golden Valley Formation).-Jepsen (1963) described a small collection of fossils from this area but no multituberculates were discovered until West (1973) screen washed matrix from Jepsen's White Butte locality in 1972. Included in West's sample were two isolated teeth here identified as Parectypodus lunatus. Gingerich and Simons (1977) have referred three isolated teeth from this locality to Pelycodus trigonodus. If my and their identi- fications are correct, this represents the only co-occurrence of Parectypodus lunatus and Pelycodus trigonodus. Elsewhere, P. lunatus is found only with the earlier species of Pely- codus, P. ralstoni and P. mckennai (see above).

5) Wind River Basin of central Wyoming (Indian Meadows and Wind River Forma- tions).-G. Winterfeld of the University of Wyoming discovered an isolated P4 of Parec- typodus lunatus in the East Fork area (UW locality V-80076, Indian Meadows Formation) of the western Wind River Basin and kindly made it available for inclusion in this study. Earlier reports (Love, 1939; Keefer and Troy- er, 1956) on vertebrate fossils from the Indian Meadows Formation indicate an early Was- atchian age (Keefer, 1965).

Isolated teeth of a small neoplagiaulacid(s) have recently been discovered by R. Stucky (University of Colorado, Boulder) from the Deadman Butte locality, Wind River Forma- tion, eastern Wind River Basin, Natrona County. These specimens are significant be-

cause of their association with Lambdotherium and Shoshonius (R. Stucky, personal commun., 1981), thereby indicating the first and only occurrence of Lostcabinian (late Was- atchian) multituberculates. The teeth will be identified and described elsewhere by Stucky and L. Krishtalka (CM).

SYSTEMATIC PALEONTOLOGY

Synonymies in this section are restricted to published records of taxa cited in formal treat- ments of individual local faunas. They do not include citations from secondary sources (e.g., Van Valen and Sloan, 1966, figs. 4 and 5).

Current diagnoses of the neoplagiaulacid genera discussed in this study are given in Sloan (1981).

Class MAMMALIA Linnaeus, 1758 Order MULTITUBERCULATA Cope, 1884

Suborder PTILODONTOIDEA Sloan & Van Valen, 1965

Family NEOPLAGIAULACIDAE Ameghino, 1890 Genus ECTYPODUS Matthew & Granger, 1921

Type species.-Ectypodus musculus Mat- thew and Granger.

Included species.-Ectypodus tardus (Jep- sen), E. powelli Jepsen, E. lovei (Sloan), E. childei (Kiihne), E. szalayi Sloan.

ECTYPODUS TARDUS (Jepsen, 1930) Text-fig. 3; Tables 2-4

Parectypodus tardus JEPSEN, 1930, p. 121, P1. II, figs. 1-4.

Ectypodus tardus (in part), MCKENNA, 1960a, p. 36, figs. 12d, f.

Parectypodus sp. A (in part), BOWN, 1979, p. 52, fig. 39c (M1'2), d (P4M2 only).

Ectypodontid, sp. indet., BOWN, 1979, p. 53. Parectypodus childei (in part), SLOAN, 1981, p.

137, text-fig. 6.8A (M1 only).

Holotype.-PU 13265, right dentary with P4M1 from 1.5 mi southeast of Dorsey Creek

276




A A

B ~~..

2mm

ci'

2 mm

E

F

2 mm - -

TEXT-FIG. 3-Ectypodus tardus, LI1, UM 74664, in A, labial and B, lingual views; RI2, UCMP 44908, in C, labial and D, lingual views; LP4, PU 17674, in E, labial and F, lingual views; and left upper dentition, I3-M2, PU 17674, in G, occlusal view.

and 2 mi south of old Otto-Basin road, Big Horn County, Bighorn Basin, Wyoming.

Localities and referred specimens. -Four Mile Creek area: East Alheit Pocket Quarry (AMNH 59613, 59626, 80401, 80413, 80414, 80416, 80418, 80424, 80426, 80431-80433, 80445, 80451, 80905, 80911, 80913, 80914, 80916, 80930, 80933, 80934; UCMP 44005, 44019); Sand Quarry (UCMP 44892, 59041); Timberlake Quarry (UCMP 44882, 44906,

44908, 59044); West Alheit Pocket Quarry (UCMP 44004).

Bighorn Basin: PU locality 1.5 mi southeast of Dorsey Creek and 2 mi south of old Otto- Basin Road (PU 13265-holotype, and PU 13265a); UM localities SC-6 (UM 72917), SC- 38 (UM 74664-74671, 74676, 74677), SC-64 (UM 74661, 74662), SC-133 (UM 68116), SC- 161 (UM 68676), SC-192 = PU Hackberry Hollow locality (PU 14724, 16522, 17674,

277

G 711

I

-



DAVID W. KRAUSE

TABLE 2-Dental measurements, serration counts, and cusp formulae of Ectypodus tardus from Wasatchian localities in the Bighorn Basin, Wyoming, and the Four Mile Creek area, Colorado.

H I

L P4 W

S L

M, W C L

M2 W C

J2 H W L W

p2 L W

P3 L W L

P4 W C L

M' W C L

M2 W C

N

3 3

41 30 39

7 7 7 4 5 5 3 3 2 2 4 4 4 3 7 7 7

14 13 13 4 4 4

OR

0.8-0.9 0.5-0.6 2.5-3.4 0.9-1.2 10-11

1.6-1.9 0.7-0.9 7-8:4-5 1.0-1.1 0.8-0.9

3-4:2 0.7-0.8

0.5 0.8-0.9

0.7 0.8-0.9 0.6-0.7 0.7-0.8 0.5-0.6 1.9-2.2 0.6-0.8 2-3:6

2.2-2.5 1.1-1.3

7-8:8-11:3-8 0.9-1.1 1.0-1.1

1:3:3

17675, 18187, 23067, 23068, UM 73879), SC- 210 (UM 72166, 72272-72277, 72581-72584, 72594-72596, 74674); UW localities V-73016a

(UW 6547, 6550-6552, 6554, 6556 (M1'2 only), 6558, 6562 (P4M2 only), 6563, 6564, 6571-6573), V-73016b (UW 6574), V-73022

(UW 10442), V-73037 (UM 76481, UW 10432, 10436); CM localities 676 (CM 12131-12133, 12300), 681 (CM 12108, 12117, 12123, 17464, 17465); Y-M locality 146 (UM 63833); YPM

locality 370 = UW locality V-73016 (YPM 30791, 31162); Dorsey Creek area, Bighorn

County (MCZ 20742, 20749); Elk Creek area, Bighorn County (MCZ 20750).

Age and distribution.-Early Wasatchian

Pelycodus ralstoni and P. mckennai biochrons; Colorado and Wyoming.

Revised diagnosis.-Small species of Ecty- podus (means of cheek tooth lengths generally 10-15% smaller than those of E. powelli). Dif- fers from E. musculus and E. szalayi in absence of P3. Lower fourth premolars differ from those of E. childei in having lower first serration, lower crown, less expanded exodaenodont lobe, and slightly smaller mean size. Differs from E. lovei in being about 15%

larger (molar lengths) and in having a greater number of cusps on M1. Measurements, serration counts, and cusp formulae are given in Tables 2-4.

Description.-The lower incisors of E. tardus are much as in E. powelli but have slightly shorter and relatively more robust crowns (Text-fig. 3A, B). The curvature of the entire tooth is also less than in incisors of E. powelli.

The peg-prop P3 is absent in E. tardus (con- tra Sloan, 1979, 1981). It is reconstructed as

being present in figs. 2 and 3 of Sloan (1979) but there is no trace of P3, or its alveolus, in the 14 specimens preserving this region of the

dentary. The lower cheek teeth of the holotype of E. tardus have been described and illustrated by Jepsen (1930, pl. II, figs. 1-4). Krish- talka (in prep.) has, in addition, provided thorough descriptions of P4-M2 in small samples of E. tardus from the central Bighorn Basin. The larger samples now available dis-

play a large amount of variation in shape (see discussion below).

The upper dentition of E. tardus has never been thoroughly described. Upper and lower dentitions can be confidently associated on the basis of PU 16522, which preserves a crushed palate and right dentary.

TABLE 3-Measurements, serration counts, and cusp formulae of associated lower dentitions of Ectypodus tardus, Bighorn Basin, Wyoming.

P4 M, M2

Specimen Locality L W S L W C L W C

CM 12300 CM loc. 676 2.6 1.1 10 1.8 0.9 7:4 1.1 0.9 4:2 PU 13265 Type locality 3.0 0.9 10 1.9 0.8 7:4 1.0 0.9 3:2 PU 17675 UM loc. SC-192 2.8 1.2 10 1.7 0.9 7:4 1.0 0.9 4:2 UM 76481 UW loc. 73037 2.8 1.0 11 1.7 0.7 8:5 - - -

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TABLE 4-Measurements and cusp formulae of associated upper dentitions of Ectypodus tardus from UM locality SC- 192 (=PU Hackberry Hollow locality), Bighorn Basin, Wyoming.

pi p2 p3 p4 Ml M2

Specimen L W L W L W L W C L W C L W C

PU 14724L 0.8 0.7 0.8 0.8 0.8 0.6 2.0 0.8 3:6 2.5 1.1 8:10:3 1.0 1.1 1:3:3 PU 14724R 0.8 0.7 0.8 0.7 0.8 0.6 2.0 0.8 3:6 2.4 1.1 8:10:4 0.9 1.1 1:3:3 PU 16522 - - 0.8 0.6 0.8 - 1.9 0.7 2:6 2.2 - ?:9?:3 - - PU 17674 0.9 0.7 0.9 0.7 0.8 0.6 1.9 0.8 3:6 2.3 1.1 7:9:4 1.0 1.1 1:3:3

The upper central incisor (I2) of E. tardus is the only tooth in the upper dentition that has not been found in association with other teeth. Three isolated specimens (UCMP 44908; UM 72596, 74670) are tentatively referred. They are similar to I2 in E. powelli (see Krause, 1980) but are smaller. The crown of I2 is much shorter than that of I, and the root is n-shaped rather than elliptical in cross-section (Text-fig. 3C, D). The crown is set at a slight angle to the root so that the roots of left and right I2 would have converged distally and the crowns would have paralleled one another.

Two upper third incisors are known; one is preserved with the cheek tooth dentition of PU 17674 (Text-fig. 3G), the other associated with the palate and dentary of PU 16522. I3 is a very small, simple, unicuspid tooth, as it is in E. powelli (Krause, 1980).

The three cusps of pl are situated anteriorly, posterolabially, and posterolingually. The pos- terolabial cusp is slightly anterior to the pos- terolingual one. P2 and P3 each bear four cusps, arranged in a 2:2 fashion. P3 is consistently smaller, lower, and relatively more elongate than pl and P2.

The referral of unassociated upper fourth premolars to E. tardus is problematical. There are clearly two size clusters of P4 among early Wasatchian neoplagiaulacids, the smaller one presumably belonging to E. tardus. Within this smaller group, however, there is consid- erable variability. One of the teeth, CM 12108, was previously assigned to Parectypodus childei by Krishtalka (in prep.). CM 12108 exhibits several Parectypodus-like features, according to Sloan's (1981) revised diagnosis of the genus, but it is too small to belong to the early Wasatchian species of Parectypodus. The upper fourth premolars here assigned to E. tardus exhibit the following features: 1) cusp formula 2-3:6; 2) ultimate or penultimate cusp highest in principal row; 3) anterior slope

straight or slightly convex; 4) posterior slope straight or slightly concave; and 5) postero- basal cuspule moderately developed, weak, or absent. Although these character states have been used to differentiate neoplagiaulacid genera (Sloan, 1981), the same variability was observed in upper fourth premolars of Clark- forkian E. powelli (Krause, 1980).

Distinct morphological differences between the upper molars of E. tardus and the Was- atchian species of Parectypodus were not observed. They were separated primarily on the basis of size, both by measurement and by outlines drawn using a camera lucida. The outlines of M1 in the largest quarry sample (East Alheit Pocket Quarry) show some evidence of bimodality (Text-fig. 4). The internal row on M1 of E. tardus, like that of Parectypodus lunatus n. sp., is nearly complete, originating op- posite one of the first three cusps of the middle row (usually the third).

M2 of E. tardus is of typical neoplagiaulacid form and has a cusp formula of 1:3:3.

Discussion.-Jepsen (1930) named and described Ectypodus tardus on the basis of two specimens excavated from a Wasatchian quarry in the central Bighorn Basin. The circum- scription of this species has become vague with the discovery of thousands of specimens and recognition of many new species of early Ter- tiary neoplagiaulacids since 1930 and, therefore, a re-analysis of the species is attempted here.

The largest sample of Wasatchian multituberculates now available from a single locality is that from East Alheit Pocket Quarry in the Four Mile Creek area. The majority of specimens in this sample was collected after McKenna's (1960a) major study of the Four Mile fauna. In that analysis McKenna had available only small samples of multituberculates from six different quarries. The samples were comprised entirely of isolated teeth, many

279



DAVID W. KRAUSE

A B A East Alheit Pocket Quarry

2mm - II

2mm

TEXT-FIG. 4-Camera lucida outline drawings of occlusal profile of nine upper first molars of neoplagiaulacids from East Alheit Pocket Quarry, Four Mile Creek area, Colorado. A indicates interpreted groupings with larger group being referred to Parectypodus lunatus, smaller group to Ectypodus tardus. Cross-hatched area shows area of overlap. B illustrates ungrouped profiles. Specimens were oriented about a line (vertical in figure) passing through the apices of the second and antepenultimate cusps in the middle row and were registered about a point midway along the length of the crown.

of which exhibit breakage or signs of post- mortem abrasion. McKenna treated the small neoplagiaulacids from the six quarries as a single sample, found a gradation of size in the

length of P4 and also in shape, and referred the entire sample to Ectypodus tardus. The coefficient of variation of 6.6 for the length of P4 in this sample was a reasonable one for a single species. The much larger collection now available from East Alheit Pocket Quarry permits a test of this conclusion. Although there is indeed an intergradation of lengths of P4, when camera lucida outlines of these teeth are superimposed, two definite groupings can be noted; a generally larger, high-crowned form, and a smaller, low-crowned form (Text-fig. 5A). This bimodality was also recognized by McKenna (personal commun., 1978) and Sloan (1981) in the larger East Alheit sample. These same two groups also occur at several other quarries in the Four Mile Creek area, includ-

ing Sand (Text-fig. 5B), Timberlake and West Alheit Pocket quarries. The smaller, low- crowned form is here referred to E. tardus sen-

B Sand Quarry

2mm - II

TEXT-FIG. 5-Camera lucida outline drawings of labial profiles of complete, unworn (or only slightly worn) lower fourth premolars of neoplagiaulacids from A, East Alheit Pocket Quarry (N = 44) and B, Sand Quarry (N = 3), Four Mile Creek area, Colorado. The larger, high-crowned form is referred to Parectypodus lunatus; the smaller, low- crowned form to Ectypodus tardus. Specimens were oriented about a line (horizontal in figure) passing through the anteriormost point on the ledge above the anterobasal concavity and, pos- teriorly, through the dorsal margin of the poster- olabial shelf. They were registered about a point midway along the length of the crown.

su stricto while the larger, high-crowned form is referable to a new species of Parectypodus (see below).

It should be noted, however, that although both Sloan (1981) and I recognize the presence of two small neoplagiaulacid species in the East Alheit Pocket Quarry sample, our divisions between those two species appear to be different. Sloan's E. tardus has a larger P4 (x length = 3.06 mm, N = 26 in his study versus 2.77 mm, N = 11 reported here), and a greater variability in length of P4 (2.5-3.5 mm versus 2.6-3.0 mm) and number of serrations on P4 (9-12 versus 10-11). Sloan's criteria for di- vision of the East Alheit neoplagiaulacid sam-

280




2mm

TEXT-FIG. 6-Camera lucida outline drawings of labial profiles of complete, unworn (or only slightly worn) lower fourth premolars of Ectypodus tardus from localities in the Bighorn Basin, Wyo- ming, and the Four Mile Creek area, Colorado. Specimens oriented and registered as in Text-fig. 5.

ple were not explicitly stated and he did not provide a list of specimens allocated to E. tardus.

E. tardus may still be a composite aggre- gation of species, despite the recognition of two additional species (Parectypodus lunatus and Ectypodus cf. E. childei) within the sample from the Four Mile quarries originally assigned to E. tardus by McKenna (1960a). The vast majority of lower fourth premolars assigned to E. tardus from the Bighorn Basin are similar in size and shape to those of E. tardus sensu stricto from East Alheit Pocket Quarry. Only PU 13265, the holotype, and UM 63833 differ, perhaps significantly (Text- fig. 6). The P4 in the holotype appears to be slightly higher anteriorly than in most Bighorn Basin lower fourth premolars of E. tardus and is at the upper extreme of their range in length (3.0 mm). UM 63833 is similar to the holotype in shape, except for a slightly more rounded anterior margin, but it is considerably longer (3.4 mm). These morphological differences can be reflected taxonomically in one of four ways: 1) the entire sample is monospecific; 2) the holotype and UM 63833 are referable to E. tardus while the majority of lower fourth premolars, including those from the Four Mile quarries, should be assigned to a new species; 3) UM 63833 represents a new species whereas the remaining specimens belong to E. tardus; or 4) three (or more) distinct species are represented in the sample, two (or more) of which would be new. Another piece of evidence bearing on this problem is that there is no apparent polymodality in size or shape from other tooth positions. The sample is therefore, provision-

A B

2 mm _ 1

TEXT-FIG. 7-Ectypodus cf. E. childei. RP4, UCMP 44023, in A, labial and B, lingual views.

ally and conservatively, interpreted as repre- senting a single, highly variable species, although my suspicion is that further collecting will produce evidence for a new species currently represented only by UM 63833.

The close similarities between E. tardus and the Tiffanian and Clarkforkian species E. powelli have been noted by previous workers. McKenna (1960a), Van Valen and Sloan (1966), and Krause (1980) regarded E. powelli as a probable ancestor of E. tardus. Krishtalka (in prep.) even suggests that the two species were conspecific, in which case E. powelli Jepsen (1940) would become the junior synonym. Krishtalka may be correct but the average di- mensions of teeth of E. tardus are consistently smaller than those of Clarkforkian E. powelli (Krause, 1980, tables 3 and 4) and the two species are therefore retained here.

It should also be noted that the molars of the late Eocene E. lovei are very similar to those of E. tardus (Sloan, 1966; Krishtalka and Black, 1975) but, on average, are slightly smaller and have fewer cusps. It is possible that E. lovei is the end-member of a lineage consisting of E. powelli, E. tardus, and E. lovei that decreased in size through time. Ow- ing to the parallelism exhibited in the molars of neoplagiaulacid species, fourth premolars of E. lovei will be required to test this hypothe- sis.

Ectypodus cf. E. childei, new combination Text-fig. 7; Table 5

Localities and referred specimens.-Four Mile Creek area: Despair Quarry (AMNH 59691, 88831; UCMP 44007, 44008, 44022-44024); Kent Quarry (UCMP 44041 questionably referred).

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DAVID W. KRAUSE

TABLE 5-Dental measurements, serration counts and cusp formulae of Ectypodus cf. E. childei from the Four Mile Creek area, Colorado, and of Ectypodus childei from the Abbey Wood fauna, southern England.

P4 P4

Specimen Locality L W S L W C

AMNH 59691 Despair Quarry 3.2 1.2- UCMP 44007 Despair Quarry 3.1 - 11 UCMP 44008 Despair Quarry 3.1 1.3 11 UCMP 44022 Despair Quarry -1.4 UCMP 44023 Despair Quarry 3.2 1.4 11- UCMP 44024 Despair Quarry - 2.7 1.0 1:6 UCMP 44041 Kent Quarry 2.9 1.1 11- - BMNH 15131 Abbey Wood 3.1 1.1 11- BMNH 26617 Abbey Wood 2.9 - 11

Age and distribution. -Early Wasatchian Pelycodus mckennai? biochron; Colorado.

Description and discussion.-Included here are lower fourth premolars that were previously referred to Ectypodus tardus by Mc- Kenna (1960a) and that are, in many ways, intermediate morphologically between those assigned to Ectypodus tardus and Parectypo- dus lunatus in this study (Text-fig. 7). Lower fourth premolars of E. cf. E. childei have a higher first serration, higher crown, more expanded exodaenodont lobe, and larger mean size than lower fourth premolars of E. tardus (Text-fig. 8A). Conversely, they have a lower first serration, lower crown, finer serrations, and a smaller mean size than those of P. lunatus. Unlike both P. lunatus and E. tardus, lower fourth premolars of E. cf. E. childei possess a prominent and distinctive lingual ridge descending from the first serration.

The specimens from Despair and Kent quarries are most similar to lower fourth premolars of E. childei from Abbey Wood in southern England (Kiihne, 1969). Their profiles are compared in Text-fig. 8B. The only complete, unworn P4 from Despair Quarry is almost identical in outline to the two specimens from Abbey Wood, except for the slightly less steep anterior slope. A more thorough evaluation of the possible conspecificity of the two forms requires larger samples. The rea- sons for referring Charlesmooria childei to Ectypodus, rather than to Parectypodus, are given below in the section on Parectypodus lunatus, a species that Sloan (1981) also referred to childei but which is recognized as new and distinct in this paper.

The single, isolated P4 from Despair Quarry (UCMP 44024) conforms to Sloan's (1981) revised generic diagnosis of Ectypodus in having

straight anterior and posterior slopes, the ultimate cusp in the middle row highest on the crown, and a cusp formula of 1:6 (see Mc- Kenna, 1960a, fig. 13a). It must be noted,

2 mm -~~~~~~~~~~~~~~~~~~~~~~~

B

2mm

TEXT-FIG. 8-A, camera lucida outline drawing of labial profile of P4 (UCMP 44023) of Ectypodus cf. E. childei (heavy single line) from Despair Quarry, Four Mile Creek area, Colorado, compared with those of Parectypodus lunatus (larger, high-crowned form-stippled, N = 36) and Ec- typodus tardus (smaller, low-crowned form-stippled, N = 8) from East Alheit Pocket Quarry, Four Mile Creek area, Colorado. B, camera lucida outline drawing of labial profile of P4 (UCMP 44023) of Ectypodus cf. E. childei (broken line) from Despair Quarry, Four Mile Creek area, Colorado, compared with those (BMNH 15131, 26617) of Ectypodus childei from the Abbey Wood fauna, England. Specimens oriented and registered as in Text-fig. 5.

282




however, that these characters appear to be quite variable when large samples are considered and may not be particularly useful in generic diagnoses.

The provenance of E. cf. E. childei in the Four Mile Creek area from only Despair and Kent quarries (in which E. tardus and P. lunatus have not been found) strongly suggests that those sites are not equivalent either tem- porally or ecologically (or both) to the other Four Mile sites.

Genus PARECTYPODUS Jepsen, 1930

Type species.-Parectypodus simpsoni Jep- sen.

Included species.-Parectypodus trovessar- tianus (Cope), P. sinclairi (Simpson), P. laytoni (Jepsen), P. sloani Schiebout, P. sylviae (Rigby), P. clemensi Sloan, P. vanvaleni Sloan, P. lunatus n. sp.

PARECTYPODUS LUNATUS n. sp. Text-fig. 9; Tables 6, 7

Ectypodus tardus (in part), MCKENNA, 1960a, p. 36, figs. 12a, b, and 13b.

Parectypodus sp. A, BOWN, 1979, p. 52, fig. 39c (P4 only), d (M, only).

Parectypodus sp., DELSON, 1971, p. 322; WEST, 1973, p. 749.

Ectypodus cf. tardus (in part), BOWN, 1979, p. 53. Parectypodus childei (in part), SLOAN, 1981, p.

137, text-fig. 6.8A (P4M1 only).

Holotype.-AMNH 59648, left dentary fragment with P4M1; from East Alheit Pocket Quarry (UCMP V-5357c), Four Mile Creek area, Moffat County, Colorado.

Localities and hypodigm.-Four Mile Creek area: East Alheit Pocket Quarry (AMNH 59606, 59609, 59611, 59614, 59615, 59623, 59627, 59628, 59630, 59635, 59648 (holotype), 80087, 80094, 80108, 80400, 80402-80409, 80411, 80412, 80415, 80417, 80419-80421, 80423, 80425, 80427-80430, 80434-80437, 80439-80443, 80446-80450, 80452-80469, 80471-80479, 80481-80483, 80485-80499, 80901-80903, 80906-80910, 80912, 80917, 80918, 80920-80924, 80927, 80929, 80931, 80932, plus numerous uncatalogued fragments; UCMP 44006, 44013, 44015, 44016, 44778, 44912; West Alheit Pocket Quarry (UCMP 44009-44011, 45832-45840, 45871, 59039, 59040); Sand Quarry (AMNH 80035; UCMP 44890, 44893-44898); Timberlake

Quarry (UCMP 44775, 44798, 44852, 44870-44873, 44883, 44884, 44886, 44887, 44904, 44909-44911, 44914, 59038).

Bighorn Basin: CM locality 681 (CM 12109, 28954); PU locality 3 mi southeast of mouth of Pat O'Hara Creek (PU 13332); UM localities FG-18 (UM 74672, 74673, 74675, 74679), SC- 12 (UM 69595, 74663), UW localities V-73016a (UW 6548, 6549, 6553, 6555, 6556 (P4 only), 6557, 6559-6561, 6562 (M1 only), 6566, 6568- 6570; V-73016b (UW 6575, 6576); V-73016c (USGS 2549 (M1 only)); V-73020a (UW 6963); V-73038 (UW 10438); V-73044 (UW 10376, 10437); V-73078 (UW 10439); YPM locality 370 = UW locality V-73016 (YPM 31163, 31201, 31207).

Powder River Basin: Dry Well locality (AMNH 56306).

Williston Basin: White Butte locality (AMNH 93475, 93476).

Wind River Basin: UW locality V-80076 (UW 14561).

Horizons.-Early Wasatchian Pelycodus ralstoni and P. mckennai biochrons (questionably also in the P. trigonodus biochron); Hia- watha Member of Wasatch Formation (Four Mile Creek area, northwestern Colorado), Willwood Formation (Bighorn Basin, northwestern Wyoming), "Wasatch Formation" (Powder River Basin, northeastern Wyoming), Golden Valley Formation (Williston Basin, southwestern North Dakota), and Indian Meadows Formation (Wind River Basin, central Wyoming).

Etymology.-lunatus, Latin, shaped like a crescent moon; in reference to the high, ar- cuate profile of P4.

Diagnosis.-Medium-sized species of Par- ectypodus, 15-20% smaller (mean length of P4) than, but otherwise morphologically similar to, P. simpsoni. Differs from P. laytoni in absence of P3; in addition, P4 has a narrower anterior base, fewer serrations, less expanded exodaenodont lobe, and a regular pattern of ridges posterolabially. Measurements, serration counts, and cusp formulae are given in Tables 6 and 7.

Description.-The lower central incisors of P. lunatus are very similar to those of E. tardus but are larger in crown height, width, and length.

P3, or an alveolus for this tooth, is absent in the seven specimens (AMNH 59609, 59611, 80094; CM 12109; PU 13332; UCMP 44006,

283



DAVID W. KRAUSE

E ---?.;c?.?? ? : ::' ?`? .?lr.-=, : -?rs-? --- ?1??--????.?. ? ? . ? ? ?. ? : :':

A ?: ????:?I- ? :1

:iF: B ??: F

?;P ?;.:'?.???:;?*f;; .-:?-.: ??;: ?:?r???-i

H

/. I

TEXT-FIG. 9-Parectypodus lunatus, n. sp. LI,, UCMP 59040, in A, labial and B, lingual views; left dentary fragment with P4M1, AMNH 59648, holotype (serrate margin of P4 restored from AMNH 80428), in C, labial and D, lingual views; RM1_2, UM 74675, in E, occlusal view; LP4, UM 74675, in F, labial and G, lingual views; and left upper dentition, pl-2 (AMNH 80087-reversed), P34 (UM 74675), M1 (AMNH 59623), in H, occlusal view. All scales are 2 mm in length.

45839) preserving the anterior part of the den- liable quantitative estimate of variation from tary. a single locality (Table 7). In labial profile the

The large sample of lower fourth premolars serrate crest of P4 is high and convex anteriorly from East Alheit Pocket Quarry permits a re- to approximately the fifth serration and then

284




TABLE 6-Dental measurements, serration counts and cusp formulae of Parectypodus lunatus from Wasatch- ian localities in the Four Mile Creek area, Colorado, the Bighorn Basin, Wyoming, the Powder River Basin, Wyoming and the Williston Basin, North Dakota.

H 11 W W

L P4 W

S L

M1 W C L

M2 W C L W

p2 L W

p3 L W L

P4 W C L

M1 W C L

M2 W C

N

10 10 95 82

102 13 14 15 3 3 3 2 2 4 4 1 1

16 17 19 8 9 8 1 0 1

OR

0.9-1.0 0.6-0.7 2.9-3.8 1.1-1.5

9-12 1.8-2.2 0.9-1.1 6-8:4

1.1-1.2 1.0-1.1

4:2 1.2-1.3 0.9-1.0 1.1-1.3

0.9 1.1 0.7

2.4-2.7 0.9-1.1 1-4:5-7 2.4-2.8 1.1-1.4

7-8:9-10:4-8 1.3

?:?:3

x

0.93 0.69 3.37 1.28

1.98 1.01

1.17 1.07

1.25 0.95 1.20 0.90

2.48 0.99

descends posteroventrally in a more nearly straight line. The anterior margin of the crown below the first serration is quite variable; in some specimens it is smoothly curved in profile view, in others it is distinctly angled above the anterobasal concavity, which is very shallow in this species owing to the absence of P3. Two specimens (AMNH 80452, 80466) bear an ac- cessory serration anteriorly, below the level of the first "true" serration. This "pseudoserra- tion" does not give rise to any ridges and is similar to those observed in a sample of Mim- etodon silberlingi from Roche Percee (Krause, 1977).

The anterior upper premolars of P. lunatus, like the other teeth, are generally larger than those of E. tardus from the same localities. The major distinguishing feature, however, is the presence of only three cusps, rather than four, on P2 of P. lunatus.

As in E. tardus, P4 of P. lunatus exhibits a wide range of morphological variability in the position of the highest cusp on the crown (ultimate or penultimate), shape of the anterior (straight to convex) and posterior (straight to

TABLE 7-Dental measurements, serration counts and cusp formulae of Parectypodus lunatus from East Al- heit Pocket Quarry, Four Mile Creek area, Colorado.

N OR x SD CV

L 68 2.9-3.8 3.35 .18 5.4 P4 W 54 1.1-1.4 1.25 .08 6.4

S 73 9-11 10 L 4 1.9-2.1 2.03 .10 4.9

M1 W 5 1.0-1.1 1.04 .05 4.8 C 5 6-7:4 7:4

p L 1 1.2 - W 1 0.9

p L 1 1.2 - W 1 0.9 -

L 10 2.4-2.6 2.46 .07 2.8 P4 W 11 0.9-1.1 0.95 .07 7.4

C 11 1-4:5-6 2:6 L 5 2.4-2.8 2.62 .15 5.7

M1 W 6 1.1-1.4 1.28 .10 7.8 C 5 7-8:9-10:4-8 7:9:4

concave) slopes, and development of the anterobasal cusp (weak to strong, but always present). In general, however, upper fourth premolars of P. lunatus are larger than those of E. tardus and have a better developed anterobasal cusp and a more consistently straight anterior slope.

Both upper and lower molars of P. lunatus are morphologically very similar to those of E. tardus and discrimination of molar phena is extremely difficult, being based primarily on size. As an example, camera lucida outlines of the upper first molars of neoplagiaulacids from East Alheit Pocket Quarry are illustrated in Text-fig. 4. The larger upper first molars are tentatively referred to P. lunatus, the smaller ones to E. tardus. The possibility of course exists that the molar sample may include specimens of Ectypodus cf. E. childei as well.

Discussion.-Sloan (1981) regarded the species of Parectypodus from East Alheit Pocket Quarry as conspecific with Charles- mooria childei, named and described by Kiihne (1969) from the early Eocene Blackheath beds of Abbey Wood in southern England. In the same paper (p. 133), Sloan revised the diagnosis of Parectypodus as "Neoplagiaulacidae with relative height of first serration [of P4] more than 0.45" and "labial height of enamel at exodaenodont lobe approximately equal to or greater than standard length." The only two lower fourth premolars of Charlesmooria childei known meet neither of these criteria; the relative height of the first serration is only

285



DAVID W. KRAUSE

0.42 and the labial height at the exodaenodont lobe is only 0.80 times that of the standard length. In these and other features lower fourth premolars of C. childei fall within the limits given in Sloan's revised diagnosis of Ectypo- dus; Charlesmooria is therefore considered here to be a junior synonym of that genus, rather than of Parectypodus.

The large neoplagiaulacid species from East Alheit Pocket Quarry is not conspecific with the Abbey Wood species and does, in fact, meet Sloan's criteria for the definition of Pa- rectypodus. It is therefore referred to that genus.

Parectypodus lunatus and E. tardus are contemporaneous and co-occur in several localities in the Four Mile Creek area and in the Bighorn Basin. The two species are very similar morphologically and overlap in size; they have consequently proved difficult to distin- guish. McKenna (1960a, p. 36) examined camera lucida outlines of 35 lower fourth premolars from the Four Mile localities and concluded that "the smaller teeth are relatively lower crowned than the larger ones, but no definite groupings were noted." A much larger sample from a single locality, East Alheit Pocket Quarry, does indeed reveal at least two groups (Text-fig 5A), thus suggesting that McKenna's groupings were obscured because he examined specimens from five different localities, not all of which are necessarily at the same stratigraphic horizon or sample the same paleoen- vironment. In any case, the differences between the two species are subtle and are even less obvious when teeth from positions other than P4 are studied. Assignments of specimens other than lower fourth premolars to either P. lunatus or E. tardus must therefore be regarded as tentative.

Specimens of P. lunatus from the Bighorn Basin are, on average, larger than those from the Four Mile Creek area. This may reflect temporal or geographic variation but larger samples from the Bighorn Basin and a better knowledge of the associated faunas are required to more fully assess its significance.

Sloan (1981) regarded his Parectypodus childei (= P. lunatus + Ectypodus childei + Ectypodus cf. E. childei in this paper) as being close to the ancestry of Parectypodus lovei. Parectypodus lovei is best regarded as a species of Ectypodus (Krishtalka and Black, 1975). Ectypodus lovei is clearly not derivable from

Parectypodus lunatus (unless, of course, Ec- typodus is diphyletic, but this does not appear to be the case). On current knowledge it is not possible to determine if E. lovei was derived from E. childei or near E. childei. E. childei is known exclusively from lower fourth premolars whereas E. lovei is known primarily from molars (Krishtalka and Black, 1975); a complete P4 of E. lovei or Ectypodus sp. is now known but is, as yet, undescribed (Krish- talka, in prep.).

Sloan (1981) stated that the Tiffanian species Parectypodus sloani and P. laytoni were close to the ancestry of his P. childei. Parectypodus sloani and, particularly, P. laytoni both show specializations of P4 that probably remove them from consideration as ancestors of P. lunatus, and certainly remove them from the ancestry of E. childei and E. cf. E. childei. Schiebout (1974) suggested that P. sloani could have been ancestral to P. laytoni; both species have lower fourth premolars with similar profiles but P. sloani has fewer serrations on P4 and fewer cusps in the external row of P4. P. lunatus, however, retains a low number of serrations on P4, a relatively low number of cusps on P4, and does not show the specializations in shape of P4 that are seen in P. laytoni, namely a wide anterior base and a greatly expanded exodaenodont lobe. The ancestry of P. lunatus remains unknown.

PARECTYPODUS SIMPSONI Jepsen, 1930 Table 8

Parectypodus simpsoni JEPSEN, 1930, p. 120, P1. I, figs. 1-3; P1. II, fig. 8.

Localities and referred specimens.-Big- horn Basin: PU locality in Gray Bull beds between Elk Creek and "South Elk Creek," Big- horn County (PU 13242-holotype, PU 13242a); PU Hackberry Hollow locality = UM locality SC-192 (PU 23014); UM localities SC- 35 (UM 71742), SC-64 (UM 72821), SC-112 (UM 72982), SC-148 (UM 67345), SC-256 (UM 73559); YPM locality 290 (YPM 24955); Dor- sey Creek area, Bighorn County (MCZ 20741).

Age and distribution.-Early Wasatchian Pelycodus mckennai and P. trigonodus biochrons; Wyoming.

Revised diagnosis.-Larger than all other species of Parectypodus except P. trovessar- tianus, which is considerably (about 30%) larger still. As in P. lunatus, P3 is absent (P3

286




TABLE 8-Dental measurements, serration counts and cusp formulae of Parectypodus simpsoni from the Bighorn Basin, Wyoming.

P4 M, M2

Specimen Locality L W S L W C L W C

PU 13242 Type locality 4.4* 1.5 13 2.3 1.2 8?:4 - - PU 13242a Type locality 4.0 1.5 12 - - PU 23014 UM loc. SC-192 4.3 1.4 13 - - - UM 67345 UM loc. SC-148 4.1 1.5 12 - - UM 71742 UM loc. SC-35 - - - 2.4* 1.1 9:4? 1.4* 1.2 4?:3 UM 72821 UM loc. SC-64 4.2 1.4 13 - - - UM 73559 UM loc. SC-256 4.1 1.5 13 - - - YPM 24955 YPM loc. 290 4.6* 1.4 13 - - MCZ 20741 Dorsey Creek 4.1 1.6 13 - -

* Estimated.

is known or inferred to be present in other species of the genus-condition unknown for P. sylviae and P. vanvaleni). Measurements, serration counts, and cusp formulae are given in Table 8.

Description and discussion.-Previously, only the holotype and paratype of P. simpsoni were known (Jepsen, 1930, pl. I, figs. 1-3 and pl. II, fig. 8). There is suggestive evidence, from the addition of the new sample of lower fourth premolars, that more than one species may be represented. PU 13242a, MCZ 20741, and UM 67345, 72821, 72982, and 73559 appear to be slightly higher-crowned, relative to their length, and have a more erect anterior margin. YPM 24955 and PU 13242 and 23014, which are also the longest teeth, exhibit the contrasting character states. The bimodality in these conditions is, however, not clear-cut and is less extreme than the end-points in variability exhibited by the large sample of lower fourth premolars of P. lunatus from East Al- heit Pocket Quarry. The outlines of the entire sample of complete, unworn lower fourth premolars of P. simpsoni are compared with those of P. lunatus in Text-fig. 10.

The lower second molar of P. simpsoni was previously unknown but is represented by a heavily worn and broken tooth in PU 71742, where it is preserved in a jaw fragment with M,. The upper dentition remains undiscov- ered.

Parectypodus simpsoni appears to be closely related to P. lunatus. The lateral profiles of P4 in the two species are nearly identical but, relative to P. lunatus, P. simpsoni is larger and has a greater number of cusps on M1 and M2. Furthermore, all occurrences of P. simpsoni of known stratigraphic position in the Bighorn

Basin are higher (younger) than those of P. lunatus (Text-fig. 2). The close morphological resemblance and the temporal juxtaposition of the two species suggest that P. lunatus may be the immediate ancestor of P. simpsoni.

NEOPLAGIAULACIDAE?, genus and species indeterminate

Locality and referred specimen.-Four Mile Creek area: Sand Quarry (UCMP 44900).

Description and discussion.-UCMP 44900 is an anterior fragment of a left M1 described and figured by McKenna (1960a, fig. 14), who referred it to Ectypodus cf. E. hazeni. Ecty- podus hazeni, a species known only from Tif- fanian horizons, has since been transferred to Neoplagiaulax (Van Valen and Sloan, 1966). Numerous specimens of multituberculates re-

2mm

TEXT-FIG. 10-Camera lucida outline drawings of labial profiles of complete, unworn (or only slightly worn) lower fourth premolars of Parectypodus simpsoni (N = 6) from various localities in the Bighorn Basin, Wyoming, compared to those of Parectypodus lunatus (stippled, N = 36) from East Alheit Pocket Quarry, Four Mile Creek area, Colorado. Specimens oriented and registered as in Text-fig. 5.

287



DAVID W. KRAUSE

10 mm

TEXT-FIG. 11-Neoliotomus ultimus. Reconstruction of labial view of dentary and left lower dentition (I1, P3-4, M1_2). Based on AMNH 16103 (holotype), PU 16145m, UM 65503, and UM 74644.

covered since McKenna's work in the Four Mile Creek area and elsewhere in Wasatchian deposits of western North America have failed to add documentation of this taxon. Without fourth premolars identification and definition of this species are not possible, but that it represents a form other than those already recognized in the Wasatchian of western North America is indicated by its relatively large size, as McKenna noted.

Suborder TAENIOLABIDOIDEA Sloan & Van Valen, 1965

Family EUCOSMODONTIDAE (Jepsen, 1940) Subfamily EUCOSMODONTINAE Jepsen, 1940

Genus NEOLIOTOMUS Jepsen, 1930

Eucosmodon (in part), MATTHEW AND GRANGER, 1921, p. 1.

Neoliotomus, JEPSEN, 1930, p. 122.

Type species.-Neoliotomus conventus Jep- sen.

Included species. -Neoliotomus ultimus (Granger and Simpson).

Revised diagnosis.--Large eucosmodontid, much larger than all other members of the

family except Eucosmodon. Differs from Eu- cosmodon in retaining P3 and pl and in having two roots on each of p2'3. Further differs from Stygimys in retaining P3, two roots on each of pl-3, and a simple crown on I2; from Penta- cosmodon in retaining P3 and in having unreduced P4 (based on length of P4:M1); from Microcosmodon in retaining P3 (P3 is lost in later species of Microcosmodon-see Krause, 1980), a simple crown on I2, and unreduced fourth premolars; and from Asian eucosmodontids Bulganbaatar, Kryptobaatar, Tugrig- baatar, Nemegtbaatar and Buginbaatar in having more serrations on P4 and more cusps on P4 and molars (where known), and in having a more complete internal row of cusps on M1.

NEOLIOTOMUS ULTIMUS (Granger & Simpson, 1928)

Text-figs. 11-13; Table 9

Eucosmodon ultimus GRANGER AND SIMPSON, 1928, p. 2, figs. 1, 2.

Undescribed genus and species cf. Prochetodon sp., MCKENNA, 1960a, p. 38, fig. 15a, b.

288




5mm

B .^^-^^^^^^irs: .

TEXT-FIG. 12-Neoliotomus ultimus. RI2, UW " 10434, in A, lingual, and B, labial views. -

Neoliotomus ultimus, MCKENNA, 1960a, p. 40, fig... :::j| 16b, c; DELSON, 1971, p. 322; BOWN, 1979, p. 52, fig. 39a, b.

Localities and referred specimens.-Four :-i Mile Creek area: East Alheit Pocket Quarry (AMNH 59617, 80101); Sand Quarry (UCMP 44766, 44794, 44899); Timberlake Quarry (UCMP 44869, 44874); West Alheit Pocket. i Quarry (UCMP 44003); unknown locality 5 mm (UCMP 59043 and uncatalogued AMNH P3).

Bighorn Basin: AMNH locality 3 mi south- f east of mouth of Pat O'Hara Creek (AMNH 16103-holotype); AMNH locality in upper beds at head of Big Sand Coulee (AMNH/ 16098, 16782, 16783); CM locality 150 (CM . . ... -.

12184); PU locality 6 mi south of Powell (PU 16144); PU Bone Hill locality (PU 16145a-n and uncatalogued P4); PU Simpson-Lewellyn "' .-. locality (PU 19860); UM localities FG-18 (UM ' . 74647-74649, 74657), FG-22 (UM 74650), FG- - 25 (UM 74651-74655, 74659, 74660), SC-1 (UM 63294a-c), SC-3 (UM 64553), SC-4 (UM 65144, 72711, 72847, 72888), SC-6 (UM 64868, 74643), SC-7 (UM 74644, 74645), SC-17 (UM & i 73735), SC-38 (UM 76482), SC-44 (UM 74656), ' SC-47 (UM 65503), SC-54 (UM 71411), SC- 123 (UM 66860, 67068, 74658), SC-125 (UM 66873), SC-304 (UM 74646); USGS locality D-

TEXT-FIG. 13-Neoliotomus ultimus. Reconstruc- ' tion of occlusal view of left upper dentition. Based on USGS 2476 (pl), UM 65144 (PV3-reversed, P4), UM 72847 (M1), and YPM 30550 (M2).

289



DAVID W. KRAUSE

TABLE 9-Dental measurements, serration counts, and cusp formulae of Neoliotomus ultimus from Wasatchian localities in the Bighorn Basin, Wyoming, and the Four Mile Creek area, Colorado.

H 11

H W L

P4 W S L

M, W C L

M2 W C

W

Pl W C L

p2 W C L

p2 w

P3 W C L

P4 W C L

M1 W C L

M2 W C

N

23 23 10 14 12 6 7 6 4 4 4 5 5 1 1 1 5 5 5 4 3 4 5 5 5 1 2 1 2 2 2

OR

6.0-7.8 2.0-2.9

10.6-12.6 3.5-4.1 13-15

6.6-7.3 2.9-3.6 6:4-5

3.8-4.8 3.0-3.6 4-5:2

3.4-4.4 2.7-3.1

3.9 3.0 3

3.5-3.9 3.2-3.9

1-2:2 3.3-3.7 2.8-3.2 1-2:2

7.6-8.6 3.0-3.5 1:9-11

9.3 4.1-4.3

8:8:9 4.3-4.7 3.4-3.8

4:3

1186 (USGS 2158); UW localities V-73016b (UW 6577, 6578), V-73020a (UW 10435), V- 73022 (UW 6976), V-73027 (UW 7015), V- 73028 (UW 10431), V-73046 (UW 10429), V- 73060 (UW 10428), V-73076 (UW 10430, 10433), V-73090 (UW 10434); YPM localities 48 (YPM 23065, 23805), 90b (YPM 23068), 119 (YPM 30550), 474 (USGS 2476), south of Worland (YPM 17979), and unspecified (YPM 30549).

Power River Basin: AMNH Bozeman locality (AMNH 56305).

Age and distribution.-Early Wasatchian Pelycodus ralstoni and P. mckennai biochrons; Colorado and Wyoming.

Revised diagnosis.-P4 smaller than in N. conventus and P4 with fewer cusps in the middle row. Morphology of molars and incisors as in N. conventus, insofar as known. Measure- ments, serration counts and cusp formulae are given in Table 9.

Description.-The lower dentition of N.

ultimus has been adequately described by Granger and Simpson (1928), McKenna (1960a) and Bown (1979).

The upper dentition is less well known; only P4 has been correctly identified previously (Bown, 1979). The additional material now available indicates that specimens thought to be an upper incisor and P3 by Bown (1979) and ?P3 by McKenna (1960a) have been mis- identified. The "upper incisor" (UW 10431) identified by Bown is instead a very worn specimen of II. Isolated upper incisors (UCMP 59043; UM 74643, 74645, 74652, 74653, 74657; and UW 10434) that probably do pertain to N. ultimus occur in samples from the Bighorn Basin and the Four Mile area. They are tentatively identified as upper central incisors (I2). The upper central incisors are much smaller than the lowers and, unlike the latter, have a subtriangular rather than an elliptical root and do not exhibit a restricted band of enamel along the anterolabial surface of the tooth (compare Text-figs. 11 and 12). The apex of I2 is not bifid as in some other eucosmodontid genera (Stygimys, Microcosmodon).

Of the anterior upper premolars only pl has not been found in direct association with other teeth of N. ultimus. The upper first premolar is represented by an isolated tooth (USGS 2476) that accords well in size with the other upper premolars. That pl was present in N. ultimus is clearly indicated by a strong anterior interdental wear facet on P2 of UM 65144, a maxillary fragment containing p24.

The tooth identified by Bown as P3 (UW 6578) of N. ultimus is probably a deciduous anterior upper premolar (position unknown) and that identified by McKenna (1960a, fig. 16a) as ?P3 (UCMP 44875) of N. ultimus is a right P3 of Phenacolemur.

In addition to UW 6578, specimens (UCMP 44794, 44874) referred by McKenna (1960a) to an undescribed genus and species cf. Proche- todon sp. are deciduous anterior upper premolars and it seems likely that they pertain to N. ultimus (Krause, 1980) rather than to some multituberculate species that is unknown from other teeth. The positions of these deciduous anterior upper premolars cannot be determined at present.

Discussion.-Jepsen (1930) considered N. conventus and N. ultimus to be contemporaneous but the type specimens of these taxa occur in faunas that are now known to be Clark-

290




forkian and Wasatchian in age, respectively (Krause, 1980). N. ultimus was apparently derived from N. conventus, the transition in- volving a diminution in size of the fourth premolars (Krause, 1980). Granger (1914) and Granger and Simpson (1928) characterized, in part, the "Sand Coulee beds" (Pelycodus ralstoni biochron) by the presence of N. ultimus, at that time considered to be the last represen- tative of the Multituberculata. N. ultimus is now known to extend also into the overlying "Lower Gray Bull" beds (Pelycodus mckennai biochron). In the three major areas of its occurrence (Bighorn Basin, Four Mile Creek area, Powder River Basin) N. ultimus is consistently found in association with either Pe- lycodus ralstoni or its successor P. mckennai. The youngest known occurrences of N. ultimus are at UM locality SC-3 (355 m above the base of the sandstone marking the Clarkforkian-Wasatchian boundary, not 160 m as stated in Gingerich, Rose and Krause, 1980) in the northern Bighorn Basin and at Yale localities YPM 119 and 90b (approximately 100 m above the Fort Union-Willwood Formation contact) in the central Bighorn Ba- sin.

Neoliotomus is the only eucosmodontid and, in fact, the only taeniolabidoid represented in the Wasatchian. It is a poorly understood genus, previously known primarily from I, and P4. The new Wasatchian material includes teeth from almost all positions and permits a re-evaluation of the relationships of Neolioto- mus.

Holtzman and Wolberg (1977) erected the subfamily Microcosmodontinae to recognize the unique phylogenetic position of Microcos- modon and Pentacosmodon within the family Eucosmodontidae. The subfamily Eucosmo- dontinae was therefore resurrected "in new usage to include eucosmodontids exclusive of Microcosmodon and Pentacosmodon" (p. 4). The new material described above, however, shows that Neoliotomus differs considerably from other known eucosmodontines (see diagnosis).

Neoliotomus is the most primitive known, yet latest occurring, eucosmodontid in North America. As in the Late Cretaceous eucosmodontids of Asia, it retains P3 and pl, two roots on each of pl-3, a simple crown on I2, and has unreduced fourth premolars. These character states serve to remove all known

North American eucosmodontids from the ancestry of Neoliotomus, despite their earlier occurrence in the fossil record (see also Mc- Kenna, 1960b). The eucosmodontine lineage, first represented by Stygimys, extends back to the Late Cretaceous in North America (Sloan and Van Valen, 1965; see also Lillegraven, 1972), while microcosmodontines, a strictly North American group date back to the Puer- can (J. D. Archibald, personal commun., 1978; P. A. Johnston, personal commun., 1979). The earliest known definite record of Neoli- otomus is from the late Tiffanian of Wyoming and Colorado (Krause, 1980). An earlier member of this lineage may be represented in the Torrejonian? Laudate fauna of California but the evidence for this is as yet meager (Mc- Kenna, 1960b). Neoliotomus apparently reached its greatest abundance in the early Wasatchian and then became extinct. The lack of an adequate ancestor in the Western Interior of North America suggests that Neo- liotomus or its immediate, unknown ancestor immigrated to this area from elsewhere or that its ancestor existed in environments not yet adequately sampled.

As mentioned, Neoliotomus shares several primitive character states with eucosmodontids from the Late Cretaceous of Asia. It is relatively derived, however, in its large size, in the possession of a high number of serrations on P4 and high number of cusps on P4 and the molars (in part a function of large size), and in the development of a nearly complete internal row of cusps on M1.

Neoliotomus is therefore derived relative to the Late Cretaceous eucosmodontines from Asia and primitive relative to those from North America. It is, however, not intermediate in either a morphological or phylogenetic sense for it has several autapomorphies (listed above) that, in addition to its late occurrence, remove it from possible ancestry of any other North American eucosmodontine (or microcosmo- dontine, for that matter), unless several re- versals have occurred. Neoliotomus and other eucosmodontids are united primarily by a single derived feature: a lower incisor with a restricted band of enamel on its ventrolabial surface, which is also the single character used to define the suborder Taeniolabidoidea (Sloan and Van Valen, 1965; Kielan-Jaworowska, 1974). This character has arisen independently in several groups of mammals, notably ro-

291



292 DAVID W. KRAUSE

L-M PRIMATE EPOCH

AGE BIOCHRONS

Q) s Z. .i

_

o

Zq ,

p, h c s P oo ? E: 'b O 9, O F o z to a o 9, C1 U C c o ac- s c gcr

o F Q o s v, o s s

o =r c a o c: 9,

P a

I I I I

EUCOSMODONTIDAE PTILODONTIDAE

I i

IT 1 ?s I I IZ I I5 L X,b 5 5~ IF1 I I Z. Z FF 5 o

t. C$C -

NEOPLAGIAULACIDAE

TEXT-FIG. 14-Distribution of latest Tiffanian, Clarkforkian and Wasatchian multituberculate species, including probable ancestor-descendant relationships. Dashed vertical lines represent times during which a particular species is not known to occur but is expected to occur at that horizon because of earlier and later occurrences. Dashed horizontal lines above and below species names represent uncer- tain time-range boundaries. Multituberculate species according to unpublished data and Sloan (personal commun., 1980) for the latest Tiffanian, Krause (1980) for the Clarkforkian, and this paper for the Wasatchian (the specimen of Neoplagiaulacidae gen. and sp. indet. from Sand Quarry is not included). Primate biochrons are from Gingerich (1976) for the Tiffanian, Rose (1979, 1980) for the Clarkforkian, and Gingerich (1980a) for the Wasatchian.

dents, phascolomyds (wombats), Daubenton- ia, tillodonts, etc. If indeed a restricted band of enamel has arisen independently more than once within the Taeniolabidoidea, that group is clearly polyphyletic (a view also shared by Kielan-Jaworowska [1974] but apparently re- jected more recently [1980]).

POST-TIFFANIAN MULTITUBERCULATE

EVOLUTION

As in the Clarkforkian, there are six species of multituberculates now known from Wa- satchian horizons in western North America. The distribution of latest Tiffanian, Clarkfor- kian, and Wasatchian multituberculates is shown in Text-fig. 14, including probable ancestor-descendant relationships. Four species lineages, comprising three genera (Pentacos- modon, Mimetodon and Neoplagiaulax) ap-

pear to become extinct in western North America before the Clarkforkian. Interesting- ly, however, Neoplagiaulax reappears in the fossil record in Wasatchian deposits of Elles- mere Island (West, Dawson and Hutchison, 1977; McKenna, 1980); Clarkforkian records of the genus are not known.

With the exception of Ptilodus sp. all species of Clarkforkian multituberculates are the same as, or appear to be descended from, Tiffanian species (Krause, 1980). Such continuity does not exist between Clarkforkian-Wasatchian multituberculate species lineages. Only Neo- liotomus ultimus and Ectypodus tardus can be derived from Clarkforkian species. Ectypodus cf. E. childei and Parectypodus lunatus appear without known ancestry in western North America; they may, in fact, represent immi- grants from Europe.

The relationship of Wasatchian multituber-

Pelycodus

jarro vii

Pelycodus

obditus

Pe ycodus

z <~

f)

I

(v0

z <

0 LL

.J

I- LL- Hi

UJ

LJ

0

LJ

w z -J O_

0o

trlgonodus

Pelyco dus

mckenna/

Pe/yc odus

ralston/

Phenacodus-

Ec to cion

cookel

P/es/adap/s

gingerichi

Plesiadapis

s'mons/

__

v,,

I -

() Z,

ob




culates to later species is difficult to assess. The post-Wasatchian history of multituberculates is restricted to unpublished records of two species in the Bridgerian (Krishtalka, personal commun., 1980), and Ectypodus lovei and Ectypodus sp. in the Uintan-Duchesnean (Krishtalka and Black, 1975), both of which survive into the Chadronian (Ostrander, Jones and Cape, 1979; Krishtalka and others, in prep.). The late-surviving members of the Multituberculata are thus exclusively small members of the Neoplagiaulacidae. There are no post-Chadronian records of multituberculates.

ACKNOWLEDGMENTS

The following individuals generously per- mitted access to specimens in their care: D. Baird and D. M. Schankler (PU); T. M. Bown (USGS); P. D. Gingerich (UM); J. Hooker (BMNH); L. Krishtalka (CM); J. A. Lillegrav- en and J. G. Eaton (UW); M. C. McKenna (AMNH); J. H. Ostrom and M. A. Turner (YPM); D. E. Savage and J. H. Hutchison (UCMP); C. R. Schaff (MCZ); R. E. Sloan and J. H. Hartman (University of Minnesota); R. Stucky (University of Colorado); and R. M. West (Milwaukee Public Museum). P. D. Gin- gerich, L. Krishtalka, and D. M. Schankler kindly shared unpublished information perti- nent to this study and, along with R. E. Sloan, provided helpful discussion. I thank L. Flynn, L. Jacobs, D. Schankler, R. Stucky and G. Winterfeld for bringing undescribed specimens of Wasatchian multituberculates to my attention. I am particularly grateful to T. M. Bown, J. A. Dorr, Jr., P. D. Gingerich, L. Krishtalka and K. D. Rose for their careful reading of an early draft of this manuscript and to W. A. Clemens, Jr. and J. A. Lille- graven for their technical reviews.

K. K. Payne drew Text-figs. 3, 7, 9, 11-13. S. M. Krause and B. H. Smith generously provided technical assistance.

Financial assistance was provided by a Rackham Predoctoral Fellowship from the University of Michigan, and travel funds were made available through a Scott Turner award from the Department of Geological Sciences, The University of Michigan. Field parties of the University of Michigan Museum of Pa- leontology, under the direction of P. D. Gin- gerich, were supported by a grant from the National Science Foundation (DEB 80-10846).

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DAVID W. KRAUSE

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multituberculates from the wasatchian land-mammal age, early eocene, of western north america

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