550.5 FI n.s. no. 33 F1ELD1ANA Geology NEW SERIES, NO. 33 The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part III. The Perissodactyls Steven M. McCarroll John J. Flynn William D. Turnbull CO CT) CL. LU CO March 29, 1996 Publication 1474 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY Information for Contributors to Fieldiana General: Fieldiana is primarily a journal for Field Museum staff members and research associates, although manuscripts from nonaffiliated authors may be considered as space permits. The Journal carries a page charge of $65.00 per printed page or fraction thereof. Payment of at least 50% of page charges qualifies a paper for expedited processing, which reduces the publication time. Contributions from staff, research associates, and invited authors will be considered for publication regardless of ability to pay page charges, however, the full charge is mandatory for nonaffiliated authors of unsolicited manuscripts. 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Author-generated changes in page proofs can only be made if the author agrees in advance to pay for them. ( fffllS PUBLICATION IS PRINTED ON ACID-FREE PAPER. ILLINOIS LIBP \T URBANA-CHAMrv GEOLOGY FIELDIANA Geology NEW SERIES, NO. 33 The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part III. The Perissodactyls Steven M. McCarroll John J. Flynn William D. Turnbull Department of Geology Field Museum of Natural History Roosevelt Road at Lake Shore Drive Chicago, Illinois 60605-2496 Accepted July 6, 1995 Published March 29, 1996 Publication 1474 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 1 996 Field Museum of Natural History ISSN 0096-2651 PRINTED IN THE UNITED STATES OF AMERICA GEOLOGY LIBRARY Table of Contents Abstract 1 Introduction 1 Abbreviations and Institutions 5 Systematic Paleontology 5 Orohippus sp 5 Epihippus gracilis 6 Telmatherium sp 8 Mesatirhinus sp 8 Metarhinus sp 11 Dolichorhinus sp 13 Brontotherioidea indeterminate 15 Isectolophus latidens 15 Eomoropus amarorum 15 Helaletes nanus 18 Dilophodon minusculus 20 Hyrachyus modestus 22 Hyrachyus eximius 25 Triplopus cubitalis 26 Trip/opus implicates 26 cf. Forstercooperia minuta 28 Hyracodontidae indeterminate 28 Amynodon advenus 28 BlOSTRATIGRAPHY 30 Conclusions 34 Acknowledgments 34 Literature Cited 35 Appenddc 1 : Field Museum Localities Cited in Text 38 Appendix 2: Metarhinus sp. Specimens from the Monospecific Titanothere Quarry Reported by Turnbull and Martill (1988) 38 List of Illustrations 1 . Regional location map 2 2. Washakie Formation location map 2 3. General stratigraphic correlation of the Washakie, Bridger, and Uinta forma- tions 3 4. pm 55790, Orohippus sp. pm 55311, Epihippus gracilis 7 5. pm 27939, Mesatirhinus sp 9 6. pm 36045, Mesatirhinus sp 10 7. pm 3935 and pm 35932, Metarhinus sp. . . 12 8. pm 3870, Dolichorhinus sp 14 9. pm 55925, Isectolophus latidens. pm 1670 and pm 2082, Eomoropus amaro- rum 16 10. pm 55951, Helaletes nanus, pm 55709, Dilophodon minusculus 19 11. pm 55710 and pm 37284, Hyrachyus modestus. pm 26128, Hyrachyus eximius 24 12. pm 28365, Triplopus cubitalis. cm 18464, Triplopus implicatus 27 13. pm 1088, Amynodon advenus 29 List of Tables 1 . Comparative dental measurements of selected middle Eocene perissodactyl taxa 20 2. Length-width measurements of all lower cheektooth specimens reported here 21 3. Length-width measurements of all upper cheektooth specimens reported here 23 4. Currently recognized chronologic distri- butions of selected North American mid- dle and late Eocene perissodactyl taxa ... 3 1 5 . Stratigraphic distribution within the Wash- akie Formation of perissodactyl taxa re- ported here 32 The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part III. The Perissodactyls Steven M. McCarroll John J. Flynn William D. Turnbull Abstract Eighteen perissodactyl taxa have been identified in the Field Museum collections from the Washakie Formation, Washakie Basin, Wyoming: Orohippus sp., Epihippus gracilis, Telma- therium sp., Mesatirhinus sp., Metarhinus sp., Dolichorhinus sp., Brontotherioidea indeter- minate, Isectolophus latidens, Eomoropus amarorum, Helaletes nanus, Dilophodon minusculus, Hyrachyus modestus, Hyrachyus eximius, Triplopus cubitalis, Triplopus implicates, cf. For- stercooperia minuta, Hyracodontidae indeterminate, and Amynodon advenus. At present, the Washakie Formation is divided into two members: the lower Kinney Rim Member and the upper Adobe Town Member. The Adobe Town Member is informally divided into lower, middle, and upper units, with the Bridgerian-Uintan North American Land Mammal "Age" boundary currently placed between the lower and middle units. The Kinney Rim Member contains Mesatirhinus sp., Helaletes nanus, Hyrachyus modestus, and Hyrachyus eximius. Helaletes nanus and Hyrachyus modestus occur throughout the Bridg- erian, and their usefulness in defining finer temporal divisions is thus limited. Hyrachyus eximius elsewhere is limited in age to the late Bridgerian. Its occurrence near the base of the Kinney Rim Member indicates the lack of early Bridgerian age sediments in the Washakie Formation. Telmalherium sp., Mesatirhinus sp., Isectolophus latidens, Hyrachyus modestus, and Hyrachyus eximius are present in the lower unit of the Adobe Town Member, also considered to be late Bridgerian in age. Metarhinus sp., Dolichorhinus sp., Eomoropus amarorum, Dilophodon min- usculus, Triplopus cubitalis, Triplopus implicatus, cf. Forstercooperia minuta, and Amynodon advenus occur only in the middle unit of the Adobe Town Member. All these taxa have early Uintan first occurrences except Dilophodon minusculus and Hyrachyus eximius, which have late Bridgerian first occurrences, and Amynodon advenus, which has an earliest Uintan first occurrence. Additionally, Dilophodon minusculus and Hyrachyus eximius are known from earliest Uintan deposits elsewhere. This apparent overlap of late Bridgerian taxa with early Uintan taxa in the middle unit of the Adobe Town Member indicates that the Shoshonian Subage of the Uintan North American Land Mammal "Age" may be present within the middle unit of the Adobe Town Member in addition to the lower unit, as previously suggested by Flynn (1986). The presence of the Uintan taxon Epihippus gracilis from the upper unit of the Adobe Town Member indicates only an undifferentiated Uintan age. Among perissodactyls, the future discovery of Colodon or Epitriplopus (both late Uintan first appearance taxa) from the upper unit of the Adobe Town Member would indicate the presence of the early-late Uintan boundary within the Washakie Formation. Introduction sin of northwestern Colorado (Roehler, 1 973). This paper deals only with the Washakie Formation The Washakie Formation consists of fluvial rocks within the Washakie Basin as defined by the Rock of Eocene age cropping out in the Washakie Basin Springs uplift to the west, the Cherokee Ridge to of southwestern Wyoming and the Sand Wash Ba- the south, the Sierra Madre uplift to the east, and FIELDIANA: GEOLOGY, N.S., NO. 33, MARCH 29, 1996, PP. 1-38 1 t IDAHO ROCK SPRINGS UPLIFT WAMSUTTER ARCH I WASHAKIE BASIN j SIERRA MAMS MTS WYOMING I COLORADO CHEROKEE RIDGE AND WASH BASIN Fig. 1 . General location map showing geographic re- lationship of the Washakie, Green River (containing the Bridger Basin), and Uinta basins (from Roehler, 1973). the Wamsutter arch to the north (Fig. 1). Corre- lation of the Washakie Formation between the Sand Wash Basin and the Washakie Basin, however, is discussed briefly. Within the Washakie Basin (Fig. 2) the Washakie Formation crops out in an area of about 680 square miles in the geographic center of the basin (Roehler, 1973). Granger (1909) divided the Washakie Forma- tion into two lithostratigraphic units, the lower Washakie A and the upper Washakie B. Washakie A corresponded faunally with faunas from the Bridger C-D, and Washakie B corresponded fau- nally with faunas from the Uinta A-B. As later defined by Roehler (1973), the Washakie For- mation is divided into two members, the lower Kinney Rim Member (-900 ft/270 m thick) and the upper Adobe Town Member (~ 2,300 ft/700 m thick). In addition, the Adobe Town Member is divided into three informal units: lower, middle, and upper (Fig. 3). Granger's Washakie A is equiv- alent to Roehler's lower unit of the Adobe Town Member, and Granger's Washakie B is equivalent to Roehler's middle unit of the Adobe Town Member. The Kinney Rim Member of Roehler's section was considered to be the uppermost part of the Green River Formation by Granger ( 1 909). Granger did not recognize rocks stratigraphically higher than those capping Haystack Mountain, but subsequent work by Roehler (1973) and Turnbull (1972) showed a sequence of beds near the geo- graphic center of the basin to be stratigraphically higher than the top of Haystack Mountain; the uppermost of these rocks are the upper unit of the Adobe Town Member. N Twg /K HAYSTACK MT ^r -^"Ht^ SAND '' HVP^i BUTTE « jZr J ^Cs« 1 8 s z pine v / Ty^y jk BUTTE ( 1 S*^ ^S \ 1 / f /{ \f /*^dobe}*-i ir * 1 ill X \ TOWN \ 1 i-4 #\ K C*S Twg VJW Twka ? Twg \\V^_ %CZ"" Twkk WYOMING -^^ Tpe COLORADO 1 1 I 0 5 MILKS I Fig. 2. Detailed map of study area showing outcrop extent of the Washakie Formation members and informal units. Major physiographic features are also shown. Abbreviations as follows: Twg = Wasatch and Green River formations; Twkk = Washakie Formation, Kinney Rim Member; Twka = Washakie Formation, Adobe Town Member; Tpe = post-Eocene rocks (from Roehler, 1973). FIELDIANA: GEOLOGY 3& s =3 i fl CO Bridger Formation Twin Buttes Member Black Forks Member Vfeshakie Formation Granger, 1909 UashakieB Washakie A Washakie Formation Roehler, 1973 upper middle lower Kinney Rim Member Washakie Formation This Paper upper middle lower Kinney Rim Mem Uinta Formation Myton Member ^Jfagonhound Member Fig. 3. Generalized correlation of the Washakie, Bridger, and Uinta formations to the North American Land Mammal Ages. The upper Bridger Formation is shown to include earliest Uintan time, based on the biostratigraphic results of Evanoff et al. (1994) and the stratigraphic correlations of Roehler (1992). Roehler (1973) speculated that some lower por- tion of the Kinney Rim Member was early Bridg- erian in age and that the upper unit of the Adobe Town Member was possibly late Uintan in age. These age assignments were tentative, based on lithostratigraphic changes, and have not been borne out by subsequent faunal evidence. Recently, McCarroll et al. (1993, 1996) have shown that no definitive faunal evidence supports an early Bridg- erian age for the Kinney Rim Member, and it should be considered late Bridgerian in age (al- though to date, no specimens have come from the lowest 30 m of this member). In addition, no de- finitive faunal evidence supports a late Uintan age for the upper unit of the Adobe Town Member, and it should be considered early Uintan in age. Fossil vertebrates were first collected from the Washakie Formation in the 1870s (for complete histories see Roehler, 1973, and Turnbull, 1978). Fossil mammals are found throughout the for- mation but are rare in the Kinney Rim Member and very rare in the upper unit of the Adobe Town Member. No comprehensive faunal revisions of the Washakie Formation faunas have been pro- duced, as has been the case for other western North American faunas (for example, the lower Eocene Wasatch and Wind River faunal revisions of Mat- thew & Granger, 1915). Even so, selected Wash- akie Formation taxa have been included in various taxonomic descriptions and revisions, or taphon- omic reports (Osborn, 1929, titanotheres; Whee- ler, 1961, uintatheres; Radinsky, 1967a, Hyraco- dontidae; Turnbull & Martill, 1988, Mesatirhinus [= Metarhinus of this paper]; Turnbull, 1 99 1 , Pro- toptychus). Collection efforts by the Field Museum in the Washakie Formation were begun in the late 1 940s by Rainer Zangerl. Zangerl's main interest was the collection of the varied reptilian fauna. One of Zangerl's field assistants was William D. Turnbull, who is now Curator Emeritus at fmnh. Over the past four decades (although not every year) Turn- bull has made an extensive collection of the mam- malian fauna (Turnbull, 1972). This report con- centrates on specimens in the fmnh collections (and a few from cm) and is not an inclusive report of all Washakie Formation perissodactyl speci- mens in other collections (see Turnbull, 1978, for a discussion of Washakie Formation collections in other institutions). In addition, many of the McCARROLL ET AL: THE PERISSODACTYLS more complete titanothere specimens are still not identifiable to genus, as they do not preserve di- agnostic characters. These and unidentifiable post- cranial specimens are not included in this study. Such exclusions explain the small number of spec- imens in this study, although fossils are much rarer in the Washakie Formation than in the Bridger Formation. For our purposes, the most important of the older fmnh collections are: 1) A small but very important fauna from the Kinney Rim Member. Roehler (1973) recog- nized the Kinney Rim Member as distinct from the underlying Green River Formation, and more characteristic of, and assignable to, the Washakie Formation. Prior to Turnbull's col- lecting, no fossils were known from the section of rocks now placed within the Kinney Rim Member. 2) The rim below the Adobe Town Rim. Within this set of beds, Flynn (1986) postulated the presence of the Shoshonian Subage (earliest Uintan) of the Uintan North American Land Mammal "Age" (NALMA) within the Wash- akie Formation. ("Age" is in quotation marks because the NALMAs are not based on cor- responding time stratigraphic stages.) 3) Haystack Mountain. Many of the classic Uin- tan age collections from the Washakie For- mation were made from Haystack Mountain (Mammoth Buttes of Cope). Cope (1884) dis- tinguished Haystack Mountain as the eastern tip of the Mammoth Buttes; subsequent usage refers to this entire linear feature (see Fig. 2) as Haystack Mountain (Turnbull, 1 978, p. 581). In addition to these three major efforts, Turn- bull has collected throughout the basin and from within the entire stratigraphic section. More recent Field Museum collecting efforts be- gan in the summer of 1990, under the direction of John J. Flynn and William D. Turnbull, and continue to the present. As with the earlier efforts, reconnaissance collecting has encompassed the en- tire stratigraphic section and much of the areal extent of the Washakie Formation. Concentrated collection efforts have been made in the southern and southeastern portions of the basin (areas un- dercollected historically, Turnbull, 1972). Of par- ticular interest is a series of red beds (the middle red beds of Roehler, 1973) that have produced a fauna rich in smaller taxa (insectivores, primates, rodents, creodonts) but few perissodactyls to date. Stratigraphically, these red beds are approximately equivalent to the less fossiliferous beds of the rim below the Adobe Town Rim, which is exposed in the northwestern portion of the basin, and the Wil- low Creek Rim, which is exposed in the north- eastern part of the basin. Also of note is a small mammalian fauna from the upper unit of the Ado- be Town Member that at present indicates an early Uintan age for the upper unit. This fauna will be reported elsewhere (McCarroll, 1995, in prep.). The Washakie Formation is important because of its well-preserved fossil fauna and the presence of the Bridgerian-Uintan NALMA boundary within the formation. When fossils were first dis- covered in western North America, the larger and most productive basins were heavily collected and many of the NALMAs were a direct result of this early work. As we understand more about the NALMAs, it becomes imperative that we also try to tie them together so that the transitions and boundaries between them can be documented, de- fined, and dated. A recent example of this kind of work is Flynn's (1986) assessment of the Bridg- erian-Uintan transition in western North Amer- ica. Flynn (1986) used biostratigraphy, magnetic polarity stratigraphy, and radioisotopic dating to correlate the Bridgerian-Uintan transition be- tween the Washakie Formation, the Aycross and Tepee Trail formations of northwestern Wyo- ming, and the marine and continental La Jolla and Poway groups of southern California. Flynn (1986) named the Shoshonian (earliest Uintan) a subage of the Uintan NALMA. The Shoshonian was de- fined (see Flynn, 1986, p. 380) by the first ap- pearance of Amynodon and characterized by the co-occurrence of what previously had been re- garded as typically late Bridgerian or early Uintan taxa. These taxa tended to be (but were not exclu- sively) smaller-bodied Bridgerian taxa (i.e., Hyop- sodus, primates, rodents) and larger-bodied Uin- tan taxa (i.e., perissodactyls). The Uintan NALMA has gone through many changes since its inception (summarized in Krish- talka et al., 1987). Herein, we recognize three biochronologic divisions of the Uintan NALMA: 1) the earliest Uintan or Shoshonian, 2) the early Uintan, and 3) the late Uintan. At present, there is no known fauna from the Uinta A lithostrati- graphic unit of the Uinta Basin, and the age of Uinta A strata relative to the Shoshonian and oth- er Uintan temporal subdivisions is not well un- derstood. A portion (or all) of the Uinta A strata may be time equivalent to the earliest Uintan. The Bridgerian NALMA, by contrast, has had a fairly FIELDIANA: GEOLOGY straightforward history (Krishtalka et al., 1987). The Bridgerian is divided into three biochrono- logic divisions: 1) earliest Bridgerian or Gardner- buttean, 2) early Bridgerian, and 3) late Bridgerian. Historically, the Washakie Formation has been temporally correlated with varying portions of the Bridger and Uinta formations (see Fig. 3). In this paper and a previously published abstract (McCarroll, 1994) we concentrate on the peris- sodactyls for the following reasons, all of which relate to the biostratigraphic and biochronologic usefulness of the perissodactyls: 1 ) The stratigraphic distribution of perissodactyls is fairly even throughout the formation. Pri- mates are much more common finds (abun- dance) in any particular field season, but their distribution within the formation is limited to one or two productive layers within the lower unit of the Adobe Town Member. 2) The taxonomic diversity of perissodactyls is relatively high. To date, we have recovered 1 8 perissodactyl taxa from the Washakie Forma- tion. To use primates as an example once again, we find only four genera and four species of primates known to date. 3) Taxonomic revisions of the perissodactyls have been fairly numerous, resulting in elucidation of the combination of primitive and derived characters by which these taxa can be recog- nized. Unfortunately, in this respect some specimens reported here can only tentatively be assigned to a taxon, as they do not preserve some of the defining characters. In addition, revisions are needed for some perissodactyl groups (see Schoch, 1989). The present paper is not a systematic revision. Even so, we discuss problems involving perissodactyl systematics, specifically morphological characters used to define taxa. Abbreviations and Institutions L indicates length; W, width. Bed numbers are those of Roehler (1973) (or Granger, 1909, as noted). Many specimens are not given specific bed numbers because of the difficulty of determining exactly which bed a specimen was collected from; most of the beds numbered by Roehler (1973) are not laterally continuous. Molarization terminol- ogy is that of Radinsky (1967a). Cusp terminology is that of Hooker (1989, Fig. 1). Detailed locality information for locality abbreviations cited in the text is given in Appendix 1 (except those listed in Turnbull, 1978). All specimen measurements are in millimeters (mm), amnh = American Museum of Natural History, cm = Carnegie Museum of Natural History, fmnh or fm = Field Museum of Natural History, jjf = John J. Flynn, NALMA = North American Land Mammal Age, pm or p = fmnh fossil mammal collection, ucmp = Univer- sity of California Museum of Paleontology, Berke- ley, uw = The Geological Museum, The Univer- sity of Wyoming, wdt or klwdt = William D. Turnbull or Kubet Luchterhand, ypm = Yale Pea- body Museum, ypm-pu = Princeton University (now housed at the Peabody Museum of Natural History, Yale University). Systematic Paleontology Order Perissodactyla Owen, 1848 Infraorder Hippomorpha Wood, 1927 Superfamily Equoidea Grey, 1821 Family Equidae Grey, 1821 Orohippus sp. Marsh, 1872 (Fig. 4A) Referred Specimens— pm 55790, isolated left M1, from Loc. jjf 7-26-92-1, Twka,; pm 39944, paired lower jaws with partial right and left M3 from Loc. fm-6-83-klwdt, Twka,. Description— pm 55790 (Fig. 4A) is an almost complete left M1 lacking only the parastyle. It ap- pears to be an M1 rather than an M2 because of its square outline and a hypocone that is slightly more prominent than the protocone. If pm 55790 were a P4, one would expect a more prominent protocone and a smaller hypocone. A small me- sostyle is present. Small but distinct paraconule and metaconule are present, which may appear larger in less worn specimens of the same size and taxon. Discussion — Granger (1908) differentiated Orohippus from Hyracotherium (= Eohippus) by the progressive molarization of the premolars in Orohippus. He recognized 1 0 species of Orohippus. More recently, Kitts (1957) revised the genus and recognized only five species. Compared to the measurements reported by Kitts (1957) for Orohippus, pm 55790 (see Table 3) is outside the size ranges of the much larger O. McCARROLL ET AL: THE PERISSODACTYLS major and O. agilis; it is within the size range of O. pumilus. It is slightly smaller than measure- ments reported for O. progressus and O. sylvaticus, although only one M1 measurement was reported for O. progressus by Kitts (1957). pm 55790 may represent a small individual of O. sylvaticus, as it is morphologically indistinguishable from ypm 1 1322, a specimen of O. sylvaticus preserving P2- M1 figured by Kitts (1957, Fig. 8A,B). As stated previously, pm 55790 is also within the size range of O. pumilus, a taxon previously known only from Bridger B beds of the Bridger Formation (Kitts, 1957). pm 55790 is from the rim below the Adobe Town Rim that is thought, based on other taxa (Granger, 1 909), to be late Bridgerian in age. At present, the limited Washakie material assignable to Orohip- pus prevents a definitive species-level identifica- tion. At present, taxa restricted to the Bridger B beds of the Bridger Formation are unknown from the Washakie Formation. If future specimens in- dicate the undisputed presence of O. pumilus from the rim below the Adobe Town Rim, either the temporal range of O. pumilus should be revised to include the late Bridgerian or, less likely, given current knowledge of the temporal distribution of taxa, the age of a portion of the lower unit of the Adobe Town Member may be older (early Bridg- erian) than presently recognized (late Bridgerian). Epihippus gracilis (Marsh, 1871) (Fig. 4B,C) Referred Specimen— pm 55311, left dentary with dP,-M2 with the unerupted M3 exposed in the lingual surface of the dentary, from Loc. jjf 7-21-90-1, Twka3. Description— pm 55311 (Fig. 4B,C) possesses a diastema between the canine alveolus and the root of dP, . Two foramina are present on the labial surface of the dentary. The larger anterior mental foramen is under the diastema and the smaller posterior mental foramen is directly under dP2. pm 5531 1 is missing dP,, which appears to be single-rooted. dP2 possesses a metaconid-meta- stylid complex; this area is too worn to determine with certainty if the metaconid and metastylid were distinct, but a small posterior extension of enamel from this area leads us to think that they were. The protoconid is small and the paracristid and protocristid are not well developed. The cristid obliqua is complete, intersecting the posterolabial base of the metaconid-metastylid complex. The hypoconid is well developed with a hypolophid connecting it to a very small entoconid. A small postcristid branch extends posteriorly from the small entoconid. The postcristid branch appears to be notched, separated from the main body of the tooth by a wear facet. Distinct cingula are not present. dP3 and dP4 are more molarized than dP2, with better developed protocristid and paracristid; the paracristid descends anterolingually from the pro- toconid and bends sharply lingually near the mid- line of the tooth. This pattern is repeated in the remaining, more posterior teeth. The entoconid on dP3 and dP4 is better developed than that of the dP2, appearing as a distinct cusp. The proto- cristid branch is also more distinct and located more medially but is still slightly linguad of the tooth midline. The metaconid and metastylid are distinct cusps; the metaconid on dP3 is at the mid- line of the tooth but more linguad on dP4 than on dP3. Small anterior, posterior, and lingual cingula are present on dP3 and they are slightly larger on dP4. M, and M2 are distinctly more squared than the deciduous premolars, which are narrower anteri- orly, giving them a trapezoidal outline. As on DP^, the area between the postcristid branch and the posterior edge of the entoconid forms a small an- teroposteriorly oriented groove, slightly lingual to the midline of the tooth. Well-developed cingula are present on both M, and M2, although they are slightly reduced labially on M2. Discussion— Granger (1908) recognized only two species of Epihippus: E. gracilis and E. parvus. He distinguished E. parvus from E. gracilis by its smaller size, greater development of the parastyle, and its compressed mesostyle. Granger (1908) did not recognize E. uintensis (= Orohippus uintensis) and considered it synonymous with E. gracilis. MacFadden (1980), in a study of the perisso- dactyls of the Tepee Trail Formation of north- western Wyoming, recognized both E. gracilis and E. uintensis, differentiating the two solely on the basis of size. MacFadden (1980) found no mor- phologic or size differences between E. parvus and E. gracilis and considered E. parvus to be syn- onymous with E. gracilis. Length-width plots for Epihippus P4's (see MacFadden, 1 980, Fig. 3) show two discrete size populations, the larger E. uin- tensis and the smaller E. gracilis. The more im- portant measure for distinguishing the species is tooth width, as the P4 lengths for the two species overlap. FIELDIANA: GEOLOGY ^Br Fig. 4. A, Orohippus sp., pm 55790, isolated left M1, in occlusal view (fmnh neg. 858 1 3). B-C, Epihippus gracilis, pm 5531 1, left dentary with dP,-M2. B, Lateral view (fmnh neg. 85824.27). C, Occlusal view (fmnh neg. 85825.6). McCARROLL ET AL: THE PERISSODACTYLS pm 5531 1 is confidently assigned to Epihippus based on the degree of loph development of the molars, which is typical for Epihippus. pm 5531 1 is too small to be E. uintensis, and is assigned to E. gracilis solely on the basis of size (see Table 2). pm 5531 1 is from the upper unit of the Adobe Town Member, a unit that produces few mammal fossils. Epihippus gracilis is currently known from throughout the entire Uintan elsewhere, and its occurrence here indicates a Uintan age assignment for the upper unit. Infraorder Titanotheriomorpha Hooker, 1989 Superfamily Brontotherioidea Marsh, 1873 Our discussion of the Washakie Formation ti- tanotheres will be limited to the generic level. A good generic-level revision of the group has re- cently been published (Mader, 1989). That revi- sion included generic diagnoses based on numer- ous primitive and derived characters, allowing us to confidently identify the specimens in this study. We consider only taxa represented by complete or partial skulls for this titanothere section, because many of the taxa are indistinguishable on the basis of dentition and because Mader's (1989) revision showed most of the diagnostic derived, generic characters to be cranial. The species-level taxon- omy of titanotheres is still in need of extensive and thorough revision, and we therefore will not attempt species-level identifications. All dental measurements of titanothere specimens are given in the respective taxic descriptions rather than in a separate table; following Mader (1989), only P2- M3 measurements are presented. Telmatherium sp. Marsh, 1872 Referred Specimen— pm 56049, almost com- plete skull (partially prepared), from Loc. jjf 8-11- 93-1, Twka,. Description— pm 56049 is a large titanothere with a P2-M3 length greater than 160 mm. The unprepared nature of the specimen prevents an accurate P2-M3 measurement at this time. The sagittal crest is well developed. Discussion— pm 56049 is assigned to Telma- therium based on its size and well-developed high, narrow sagittal crest, pm 56049 is within the size range of Dolichorhinus. Dolichorhinus, however, possesses a low, broad sagittal crest (Mader, 1 989). Mesatirhinus sp. Osborn, 1908 (Figs. 5A,B, 6A,B) Referred Specimens— pm 27939, complete skull with upper dentition, from Loc. fm-1 1-70-wdt, Twkk, bed 527; pm 27938, partial juvenile skull preserving P1, dP2"*, M'-2, and indication of the crypt of M3, from Loc. fm-1 1-70-wdt, Twkk, bed 527; pm 36045, almost complete skull and skele- ton, from Loc. fm-2-72-wdt, Twka^ Description— pm 27939 (Fig. 5A,B) is a me- dium-sized titanothere with a P2-M3 length of 137.0 mm. pm 27939 has a very small diastema between the canine and the P1 alveolus. Both P''s are missing, and P2-P4 are unmolarized. The orbit is only moderately developed, and a broad sub- orbital protuberance is present. The zygomatic arch is moderately large and curved. The skull of pm 36045 (Fig. 6A,B) is almost complete, missing only portions of the anterior dentition, portions of the molars, and a small por- tion of the sagittal crest and the left frontal-nasal boundary. P2-M3 length is 135.2 mm. pm 36045 possesses fairly robust nasals, which are slightly flared distally. The nasal incision, which is crushed, appears to extend back to the posterior border of the M1. The orbital area is also crushed, but ap- pears not to have been enlarged. The suborbital protuberance is long and well developed. The right canine is present and has moved out of the alve- olus by approximately xh inch. This makes the canine appear enlarged when actually it is fairly small. Very small upper diastemas are present be- tween the canine and the I3 and P1. Mader (1989) was unable to corroborate the as- sertion by Osborn (1929) that Mesatirhinus pos- sessed incipient horns, pm 36045 possesses what appears to be an "incipient" horn on the right side of the skull near the frontal-nasal boundary. This area is not preserved on the left side of the skull. The "incipient" horn of pm 36045 might be an artifact of crushing. Osborn often ignored defor- mation due to crushing, and his observation of incipient horns in specimens assigned to Mesati- rhinus may have been a result of postdepositional deformation of certain specimens. Comparisons with other skulls, however, indicate that the in- cipient horns of pm 30645 are real and not an artifact of crushing. FIELDIANA: GEOLOGY Fig. 5. Mesatirhinus sp., pm 27939, complete skull. A, Dorsal view (fmnh neg. 85824.7). Arrow indicates large suborbital protuberance characteristic of Mesatirhinus. B, Lateral view (fmnh neg. 85824.16). McCARROLL ET AL: THE PERISSODACTYLS Fig. 6. Mesatirhinus sp., pm 36045, almost complete skull. A, Dorsal view (fmnh neg. 8581 1). Arrow 1 indicates posteriormost extension of the lateral nasal incision; arrow 2 indicates anteriormost extension of the orbit. Note that the lateral nasal incision does not reach back to the orbit, characteristic of Mesatirhinus. B, Lateral view (fmnh neg. 85812). 10 FIELDIANA: GEOLOGY Discussion— According to Mader (1989), Mes- atirhinus is distinguished from Metarhinus by the morphology of the nasal and orbital regions. In Mesatirhinns the lateral nasal incision does not extend as far back as the orbital region, in contrast to the condition in Metarhinus. Mesatirhinus pos- sesses a prominent suborbital protuberance, and the orbit is not prominent. In contrast, Metarhinus possesses a small suborbital protuberance and the orbit is prominent. Even though pm 36045 is dor- soventrally crushed, the orbits are clearly not pro- nounced. In addition, the lateral nasal incision does not extend as far posterior as the rim of the orbit. pm 27939 is moderately crushed, affecting direct comparison with Mader's ( 1 989) generic diagnosis of Mesatirhinus. Characters used by Mader (1 989) that are also present in pm 27939 include small canines, very small upper diastema, unmolarized premolars, well-developed suborbital protuber- ance, and no hypocone on M3. The nature of the nasals is difficult to determine because of crushing. It appears, however, that after correcting for crush- ing the nasals would have been flared distally. pm 27938 and pm 27939 are from the Kinney Rim Member, and pm 36045 is from the lower unit of the Adobe Town Member. Mesatirhinus is currently known from the Bridgerian elsewhere (Mader, 1989). Metarhinus sp. Osborn, 1908 (Fig. 7A,B,C) Referred Specimens— pm 3935, anterior half of skull with right and left P'-M3, from Loc. fm-3- 57-wdt, Twka2; pm 56023, left half of skull with C-M3, from Loc. fm-6-58-wdt, Twka2. pm num- bers for the skull (n = 1 5), lower jaw (n = 27), isolated teeth (n = 85), and postcranial specimens (n = 106) from a monospecific titanothere (Me- tarhinus) assemblage are given in Appendix 2. This assemblage has been described by Turnbull and Martill (as Mesatirhinus) (1988); all specimens from this quarry are from Loc. fm-12-70-wdt, Twka2, bed 643 or low in bed 644. Because it is from a single catastrophic event, this assemblage provides an important record of variation within a single titanothere taxon, comparable to single locality samplings of modern animals. This is in contrast to the typical time-averaged accumula- tion samples of most titanothere taxa. Additional study of the paleobiology of this assemblage is planned for a future date. One specimen (pm 35932) from the quarry is figured here (Fig. 7C) to further document the generic assignment of the quarry sample. Description— pm 3935 (Fig. 7A,B) is a medi- um-sized titanothere with a P2-M3 length of 144.0 mm. pm 3935 possesses a prominent orbit and a deep nasal incision that reaches back to the front of the orbital region. There is a small but obvious suborbital protuberance. The nasal region is slight- ly crushed and it is difficult to discern whether the nasals are constricted at the base. Although the nasals appear to be slightly constricted at the base, it is possible that if the skull were uncrushed the constriction would appear greater; alternatively, the apparent constriction now present may be a result of crushing, in which case the uncrushed skull would have no constriction. pm 35932 (Fig. 7C) is a poorly preserved, crushed skull from the Metarhinus quarry. It possesses a large bony orbit, small suborbital protuberance, and a nasal incision that reaches back to the orbit. The P2-M3 length is 157.0 mm. Discussion— Overall, the nasals of pm 3935 are most similar to the spoon-shaped nasals of Me- tarhinus rather than the unconstricted, distally flared nasals of Mesatirhinus or the shorter, ta- pered nasals of Rhadinorhinus. The tips of the nasals do seem to taper slightly, giving them a distinct spoon shape; this tapering is not the same as in Rhadinorhinus, in which the nasals taper from their base to their tips. Of titanotheres pos- sessing a suborbital protuberance, Metarhinus is the only one in which it is small; Mesatirhinus, Rhadinorhinus, and Dolichorhinus all possess a large suborbital protuberance. The lateral nasal incision in pm 3935 and pm 35932 extends back to the orbital region, as described for Metarhinus (Mader, 1989). The posterior extension of the na- sal incision may in part be attributed to crushing of surrounding bones, although we think it is clear that the nasal incision reached the orbital region in this specimen. The crushing in pm 3935 is most extensive on the right side. This crushing may have displaced the lateral nasal incision further poste- riorly than it actually was, on the less crushed left side; however, the lateral nasal incision still reach- es the anteriormost portion of the prominent orbit. Generic assignment of the titanothere quarry sample of Turnbull and Martill (1988) is changed from Mesatirhinus to Metarhinus. These speci- mens were assigned to Mesatirhinus prior to Mad- er's (1989) revision. The small suborbital protu- berance, large bony orbit, and deep nasal incision all indicate Metarhinus rather than Mesatirhinus. pm 3935, pm 56023, and the quarry sample are McCARROLL ET AL: THE PERISSODACTYLS 11 Fig. 7. Metarhinus sp., pm 3935, anterior half of skull. A, Dorsal view (fmnh neg. 85805). B, Lateral view (fmnh neg. 85806). Arrow 1 indicates posteriormost extension of the lateral nasal incision; arrow 2 indicates anteriormost extension of the orbit. Note that the lateral nasal incision does reach back to the orbit and the orbit is well defined by a raised bony rim, both characteristic of Metarhinus. (Figure continued on page 13.) 12 FIELDIANA: GEOLOGY Fig. 7 (continued). C, pm 35932, lateral view (fmnh neg. 85982). from the middle unit of the Adobe Town Member. Metarhinus is currently known from the Uintan elsewhere (Mader, 1989), including the Shoshon- ian (earliest Uintan) Subage (Flynn, 1986). pm 56023 is from near the base of the middle unit of the Adobe Town Member and, based on the dis- tribution of other taxa, probably represents an ear- liest Uintan (Shoshonian Subage) occurrence of Metarhinus rather than an early Uintan occur- rence. The same may be true of pm 3935, although it is from slightly higher in the section. The quarry sample (Appendix 2) is stratigraphically higher, in strata inferred to be early Uintan in age (based on other taxa). Dolichorhinus sp. Hatcher, 1895 (Fig. 8A,B) Referred Specimens— pm 3870, complete skull, from Loc. fm-2-57-wdt, Twka2; pm 3873, com- plete skull, from Loc. fm-6-57-wdt, Twka2. Description— pm 3870 (Fig. 8A,B) is a com- plete skull missing only the right and left I1-2. pm 3870 is a large titanothere with a P2-M3 length of 179.1 mm. pm 3870 possesses six upper incisors and large pointed canines. A small diastema is present between I3 and the canine, and a larger diastema exists between the canine and P1. P' has a single cusp, whereas P2-3 possess two labial and a single lingual cusp. M1-3 lack metaconules and protoconules, and M3 possesses a small hypocone. The nasals broaden very slightly from their base and are slightly spoon-shaped. Two small horns are present dorsally and slightly anterior of the orbit. A large suborbital protuberance is present, subdivided into a smaller anterior flange and a larger posterior flange. The distinction between the two flanges, and their difference in size, are not as great in pm 3870 as we observed in other speci- mens of Dolichorhinus from the Uinta Formation (p 12175, p 12182). A broad shelf, rather than a sharp sagittal crest, defines the top of the cranium. pm 3870 is only slightly crushed, the most exten- sive crushing being on the posterior dorsal portion of the skull. A second complete skull (pm 3873) is almost identical to pm 3870. pm 3873 shows a greater distinction, as well as a greater difference in size, between the anterior and posterior suborbital pro- tuberances, pm 3873 is much less crushed than pm 3870 and the rounded nature of the cranial vertex is more obvious. There are two "pits" posterolin- gual to the horns above the orbit; these are not discernible on pm 3870. Discussion— Dolichorhinus has the most de- rived features of any Eocene titanothere discussed by Mader (1989). pm 3873 and pm 3870 may be confidently assigned to Dolichorhinus based on the presence in both specimens of all the unique de- rived characters that Mader (1989) assigned as diagnostic of the genus. These derived features are "hyperdolichocephalic skull; large suborbital pro- tuberance with a small anterior flange and a larger posterior flange; small angular horn at frontonasal McCARROLL ET AL: THE PERISSODACTYLS 13 Fig. 8. Dolichorhinus sp., pm 3870, complete skull. A, Dorsal view (fmnh neg. 85810). Arrow indicates low, broad sagittal crest typical of Dolichorhinus. Compare this to the sharply defined sagittal crest of Mesatirhinus in Figure 5A. B, Lateral view (fmnh neg. 85809). 14 FIELDIANA: GEOLOGY boundary over orbit; rounded cranial vertex with no sagittal crest" (Mader, 1989, p. 468). Both pm 3873 and pm 3870 are from high within the middle unit of the Adobe Town Member. Doli- chorhinns is currently known from the Uintan elsewhere (Mader, 1989). Its occurrence here in- dicates an undifferentiated Uintan age assignment for the middle unit of the Adobe Town Member. Brontotherioidea indeterminate Referred Specimen— pm 1 676, partial skull and associated bone fragments, from Loc. fm-6-56- wdt, Twka2. Description— pm 1676 is approximately the same size as pm 36045 (Mesatirhinus), but is miss- ing the orbital and nasal regions; the suborbital protuberance is as well developed as in pm 36045, although there is a more obvious division into smaller anterior and larger posterior flanges, sim- ilar to those in some specimens of Dolichorhinus. Preserved portions of the maxillary indicate that the lateral nasal incision was deep, possibly reach- ing back to the orbits. Discussion— pm 1676 cannot be confidently as- signed to a taxon because the uniquely diagnostic parts of the nasal and orbital regions are not pre- served, pm 1 676 could be assigned to Mesatirhinus or Rhadinorhinus based on its size and the prom- inent suborbital protuberance. The specimen, however, is from the middle unit of the Adobe Town Member, which is thought to be earliest to early Uintan in age. If pm 1676 is Mesatirhinus, it would be the first Uintan occurrence of the taxon (see Mader, 1989). Alternatively, pm 1676 could be assigned to Rhadinorhinus, which is known from the Uintan of the Uinta Formation. The specimen also possesses a deep nasal incision, also a char- acter of Rhadinorhinus (Mader, 1989). IfPM 1676 is Rhadinorhinus, it would represent the first re- port of the genus from outside of the Uinta For- mation of the Uinta Basin. Infraorder Moropomorpha Schoch, 1984 Family Isectolophidae Peterson, 1919 Isectolophus latidens (Osborn, Scott, & Speir, 1878) (Fig. 9A) Referred Specimen— pm 55952, associated RM1"3, LM2-3, partial R&LM3, from Loc. jjf 8- 1 3- 93-1, Twka,. Description— M' of pm 55952 (Fig. 9 A) is nar- rower posteriorly than anteriorly, the paracone is the most prominent cusp, and the parastyle is rounded and well developed. M2 is also narrower posteriorly and the parastyle is larger and more prominent than in M1. In M3 the metaloph is ex- tended lingually compared to that of M1 and M2, giving M3 a more trapezoidal outline. The para- style is flattened and less prominent than on M1-2. Prominent anterior, posterior, and lingual cingula are present on all upper molars. Both M3's are incomplete, lacking the anterior portion of the tooth. The hypolophid is well de- veloped, with the cristid obliqua intersecting the protocristid slightly lingual to the protoconid. A large, well-developed hypoconulid is present, with a large notch in the posterolabial corner. Discussion— Isectolophus differs from Homo- galax in the lack of protoconules and metaconules on M1-3 (rarely present in Homogalax), the lack of a metastylid on M,_3, and in being larger in size (Radinsky, 1963). At present, two species of Is- ectolophus are recognized, /. latidens and /. an- nectens. They are differentiated by the larger size and the consistent presence of two lingual cusps on P3 in /. annectens. Without the preservation of P3 we can use only size to distinguish between /. latidens and /. annectens. On the basis of size (see Tables 2 and 3) we assign pm 55952 to /. latidens, as all measurements fall within the range reported for that species and outside the range of/, annec- tens (Radinsky, 1963). pm 55952 is from the lower unit of the Adobe Town Member. The occurrence of /. latidens (pm 55952), a late Bridgerian taxon elsewhere, from the lower unit of the Adobe Town Member in- dicates a late Bridgerian age assignment for this unit. Superfamily Chalicotherioidea Gill, 1872 Family Chalicotheriidae Gill, 1872 Eomoropus a ma ro rum (Cope, 1881) (Fig. 9B-H) Referred Specimens— pm 1670, left dentary fragment with P4-M3, from Loc. fm-3-56-wdt, Twka2; pm 2082, associated postcrania, including proximal end of femur, distal ends of tibia and fibula, astragalus, calcaneum, navicular, cuboid, lateral cuneiform, internal cuneiform, three com- McCARROLL ET AL: THE PERISSODACTYLS 15 Fig. 9. See legend on opposite page. 16 FIELDIANA: GEOLOGY Fig. 9. A, Isectolophus latidens, pm 55925, right M1-3 found in association, in occlusal view (fmnh neg. 85808). B-H, Eomoropus amarorum. B, pm 1670, left dentary fragment with P4-M,, in occlusal view (fmnh neg. 85814). C-D, pm 2082, anterior (fmnh neg. 85978) and posterior (fmnh neg. 85977) views of right tibia and fibula; note the well-developed fibula compared to the figured type specimen (see Osborne, 1913, Fig. 7). E-G, pm 2082, internal (fmnh neg. 85981), anterior (fmnh neg. 85980), and external (fmnh neg. 85979) views of right tarsus. H, pm 2082, three sesamoids (fmnh neg. 85976). plete metatarsals (II, III, IV), two podials, and three sesamoids, from Loc. fm-1-56-wdt, Twka2. Description -The P4 of pm 1670 (Fig. 9B) has a prominent metaconid and a small but distinct metastylid; the entoconid is very small. M, is worn and heavily damaged, but a well-developed en- toconid is indicated by an upturn in the partial crown surface near the posterior lingual corner of the tooth. M2_3 are almost complete, with well- developed metastylids and very prominent ento- conids compared to M,. Small cingula are present along the anterior edge of M2_3. M,_2 possess small hypoconulids; the posterior end of M3 is broken, but the presence of a well-developed hypoconulid is indicated by the surface features that are pre- served. pm 2082 (Fig. 9C-H) comprises an almost com- plete distal right hind limb. There is a proximal McCARROLL ET AL: THE PERISSODACTYLS 17 half of a badly crushed femur. Its head is attached by a short neck and has a well-developed foveal pit. Most of the greater trochanter is present; its anterior portion reaches a height equal to that of the head, while the posterior, broken portion ex- ceeds the height of the head. As in the type (amnh 5096, using Osborn's 1913 figures and descrip- tions), there is a marked fossa on the posterior surface. Second and third trochanters are similarly developed as in the type, although the latter is incomplete and may have extended a bit farther down the shaft than it does on the type (amnh 5096). Length of the preserved proximal half is 260.0 mm, the distance from the head to the tip of the third trochanter is 150.0-160.0 mm, and the distance from the head to the middle of the second trochanter is 100.0-1 10.0 mm. The tibia and fibula of pm 2082 (Fig. 9C,D) also correspond well with the type, except for one sig- nificant difference: the fibula of pm 2082 has a robust shaft and the type does not. Osborn (1913, p. 271) stated that "A distinctive feature is the marked reduction of the fibula; the lower portion of the shaft is so slender as to indicate that the central portion may have been incomplete. In Mo- ropus the fibula has a complete shaft." We suspect that Osborn may have misinterpreted a weathered or incomplete shaft, in which case pm 2082 may give a better idea of the condition of the fibula of Eomoropus than does the type. The tarsus of pm 2082 is almost complete (Fig. 9E-G). The three metatarsals, astragalus, and cal- caneum have the same features and proportions as in the type. The same is true for the navicular, except that the facet for articulation with the cal- caneum indicates a weaker articulation than Os- born noted for the type. Furthermore, in pm 2082 the cuboid articulates with the dorsal internal sur- face of the astragalus, and it is only on the surface that the two could be even slightly separated by the navicular. The posterior extension of the cu- boid is a somewhat more massive and pronounced process than Osborn figured (1913, Fig. 4— B2). The ectocuneiform (= external, or tarsal III) is broader than deep, and not as quadrate on its an- terior face as is that of the type. The mesocunei- form (= middle, or tarsal II) is small and abbre- viated, as Osborn described it in the type. Osborn (1913, Fig. 4— B3) showed a bone he took to be the entocuneiform (= internal, or tarsal I), but that to us resembles a sesamoid, pm 2082 has three sesamoid bones (Fig. 9H), but unfortunately they were prepared free without their positions relative to the rest of the foot being noted, pm 2082 has no obvious facets which would indicate the pres- ence of an entocuneiform. The three metatarsals (II, III, IV) are complete bones. On the distal end each shows exactly the same sort of division into a keeled sesamoidal posterior face and a smoothly convex anterior phalangeal face, which Osborn describes for the metacarpals of the type. The best preserved of the two podial bones may belong to the fourth toe, as it makes a fair articulation with metatarsal IV. Discussion— The most recent revision of Eo- cene chalicotheres is that of Lucas and Schoch (1989). They recognized Eomoropus amarorum and Grangeria anarisus from the western United States, and E. quadridentatus and G. canina from the People's Republic of China. Radinsky (1964) recognized the same taxa, as well as a third Chinese species, G.l major, which Lucas and Schoch (1989) synonymized with G. canina. Both Radinsky (1964) and Lucas and Schoch (1989) referred pm 1670 to E. amarorum, but did not discuss the specimen in detail. Its size (see Table 2) indicates that it should be assigned to a species of the smaller genus Eomoropus rather than of the larger genus Grangeria. According to Lucas and Schoch (1989), E. amarorum differs from E. quadridentatus in the more molariform premolars of E. quadridentatus, and in differences between P2"* and P2 of the two species. P2 is not preserved in pm 1 670, so direct comparisons cannot be made. P4 is preserved, but we have found no comparative discussions of P4 morphology between E. ama- rorum and E. quadridentatus. We have not been able to examine specimens of E. quadridentatus for comparison. Barring evidence to the contrary, we follow Radinsky (1964) and Lucas and Schoch (1989) and assign pm 1670 to E. amarorum. pm 2082 agrees well enough with Osborn's (1913) de- scription of the type that we also assign it to E. amarorum. Both pm 1 670 and pm 2082 are from the middle unit of the Adobe Town Member. Eomoropus amarorum is currently known from the early Uin- tan elsewhere (Lucas and Schoch, 1989); its oc- currence here indicates an early Uintan age as- signment for some part of the middle unit of the Adobe Town Member. Superfamily Tapiroidea Burnett, 1830 Family Helaletidae Osborn, 1892, in Osborn and Wortman, 1892 Helaletes nanus (Marsh, 1871) (Fig. 10 A) referred specimen— pm 55951 isolated right M3, from Loc. fm-3-74-wdt, Twkk. 18 FIELDIANA: GEOLOGY A ! 5 cm B Fig. 10. A, Helaletes nanus, pm 55951, isolated right M3> in occlusal view (fmnh neg. 85815). B, Dilophodon minusculus, pm 55709, right M'-3 found in association, in occlusal view (fmnh neg. 85825.7). Description— pm 55951 (Fig. 10A) is almost complete, lacking only broken metaconid and en- toconid tips. The roots lack only the proximal tips, and the posterior half of the tooth root shows a bony reinforcement under the hypoconulid char- acteristic of an M3. pm 55951 is distinctly bilophodont. The pro- toconid is very slightly anterior to the metaconid, whereas the hypoconid is distinctly more anterior than the entoconid. Both the paralophid and the protocristid are small, with the paralophid more pronounced and descending anteriorly from the protoconid, then turning sharply lingually. The protolophid is distinctly notched, while the hy- polophid is only slightly notched. No lingual or labial cingula are present. A small anterior cin- gulum is present, starting lingually where the par- alophid descends to the base of the metaconid, and running labial I \ around the base of the pro- tocone. A hypoconulid is present. It is medially situated, but closer to the entoconid than to the hypoconid. Small ridges connect the hypoconulid to the entoconid and the hypoconid. The ridge extending to the hypoconid is the longer of the two. Discussion— Helaletes is a small- to medium - McCARROLL ET AL: THE PERISSODACTYLS 19 Table 1 . Comparative dental measurements (in mm) of selected middle Eocene perissodactyl taxa. Taxon LM"3 LM..3 LP'-M3 Source Isectolophus annectens 46.8 Radinsky, 1963 Isectolophus latidens — 40.4 — Radinsky, 1963 Helaletes nanus 31.6 — — Radinsky, 1963 Helaletes intermedins 44.4 — — Radinsky, 1963 Dilophodon minusculus — 28.0 — Radinsky, 1963 Dilophodon leonatus — 25.1 — Radinsky, 1963 Hyrachyus modestus 45-50 — — Radinsky, 1967b Hyrachyus eximius 64 — — Radinsky, 1967b Triplopus cubitalis — 35 — Radinsky, 1967a Triplopus implicatus — 46 — Radinsky, 1967a Amynodon advenus 93-131 90-117 — Wall, 1982 Forstercooperia grandis 84-97 84-97 — Lucas etal., 1981 Forstercooperia minuta 71-79 71-75 — Lucas etal., 1981 Fouchia elyensis 19.2 18.6 — Emry, 1989 Palaeosyops — — 129-165 Mader, 1989 Telmatherium — — 160-190 Mader, 1989 Mesatirhinus — — 128-145 Mader, 1989 Metarhinus — — 138-145 Mader, 1989 Rhadinorhinus — — 143-148 Mader, 1989 Dolichorhinus — - 164-193 Mader, 1989 sized helaletid. According to Radinsky ( 1 963), He- laletes is characterized by the following combi- nation of characters: canines small; P1 simple; P2^* submolariform with the metaloph less prominent than the protoloph and a tendency for the hypo- cone to separate off from the protocone; metacone of M1-2 slightly convex to flat and slightly short- ened; M3 metaloph relatively short; P, absent; tri- gonids of P2_4 low but with long paracristids; small entoconid present on P^; M3 retains a hypocon- ulid; greatly enlarged nasal incision. At present, two species of Helaletes are recog- nized: H. nanus and H. intermedins. They are dis- tinguished from each other most readily on the basis of size (see Table 1). In addition, the P3 me- taloph of H. nanus extends toward an incipient hypocone, in contrast to H. intermedius, where the metaloph extends toward the protocone, bypass- ing the hypocone (Radinsky, 1963). pm 55951 is referred to H. nanus on the basis of size (see Table 2) and the presence of an M3 hypoconulid. pm 55951 is small for H. nanus com- pared to measurements reported by Radinsky (1963), and is smaller than any measurements re- ported for H. intermedius. pm 55951 is closer in size to reported measurements (Radinsky, 1963) of Dilophodon minusculus than to either species of Helaletes; however, D. minusculus lacks an M3 hypoconulid. pm 5595 1 comes from the Kinney Rim Member, the lowest unit of the formation. Helaletes nanus is currently known from the Bridgerian elsewhere, and its occurrence here indicates an undifferen- tiated Bridgerian age assignment for the Kinney Rim Member. Dilophodon minusculus Scott, 1883 (Fig. 10B) Referred Specimens— pm 55709, associated right M1-3, from Loc. jjf 7-25-92-1, Twka2; pm 5571 1, isolated left M3, from Loc. fm-6-56-wdt, Twka2. DESCRiPTiON-The M1 of pm 55709 (Fig. 10B) has a posterolabially directed metastyle and a me- tacone that is very slightly convex labially. The parastyle is very distinct, with a notch between it and the paracone. Anterior and posterior cingula are present, as is a cingulum labial to the meta- cone. In pm 55709, the M2 differs from the M1 in having a broader notch between the parastyle and paracone (this may be due to differences in wear stage), a metacone that is very slightly concave labially, and a slightly larger parastyle. The M3 of pm 55709 has a very small metacone that is also more lingually deflected than in M1-2. In addition, the labial surface of the metacone is flat and has no associated cingulum. The posterior cingulum of M3 is smaller than in M1 or M2. pm 5571 1 is very similar to pm 55709 but has a more robust parastyle and metastyle. pm 5571 1 is longer than pm 55709 (Table 3). Discussion— Dilophodon is a very small hela- letid. According to Radinsky (1963), Dilophodon is recognized by the following combination of 20 FIELDIANA: GEOLOGY c a i So c 5 I 2 2 I I III II v> en © qo I © vb* ""II "^> oo so f> ^ >o <N O "* I*» i i ^ f> I I 32 III II I ■"". *-. 'I Ov 00 O I I O I o SO I W> on r-' Os so I I I I I I I 00 SO I oo r-' I 22 i I 00 I I I r- PO «n-: I I I I l q r- r-' vo Os OO q "■> so >/■> 00 00 I sd I I - I I I <N I I III I I I I I Ml M I I I I I Ml I I - I I 3 sj ^, ~ — cL^ S->0 §"0 2<^ S,— irt — SO* 300-S-* '% U O C i -3 .s McCARROLL ET AL: THE PERISSODACTYLS 21 characters: premolar molarization retarded com- pared to the Helaletes-Colodon line; M1-2 meta- cone lingually displaced, slightly convex labially, and with a small labial cingulum; short lower post- canine diastema; P, absent; M3 hypoconulid not present. At present, two species of Dilophodon are rec- ognized, D. minusculus (late Bridgerian) and D. leotanus (late Uintan). They are distinguished (Ra- dinsky, 1963) from each other based on the fol- lowing: size (see Table 1); P2 with two labial cusps in D. leotanus, only one in D. minusculus; P3-^ relatively nonmolariform in D. minusculus, sub- molariform in D. leotanus; symphysis begins an- terior to P2 in D. minusculus, whereas it is pos- terior to P2 in D. leotanus; P2^» long and narrow in D. minusculus compared to short and narrow in D. leotanus. Both specimens reported here compare well with D. minusculus measurements reported by Radin- sky (1963). D. leotanus, a late Uintan form, is smaller than D. minusculus, but the size difference is not great (see Table 1). Even so, pm 55709 and pm 5571 1 are closer to D. minusculus than to D. leotanus (see Table 3). In addition, the concavity of M1-2 metacones of pm 55709 are closer to D. minusculus, as D. leotanus has more convex M1-2 metacones. Radinsky (1963) recognized no early Uintan species of Dilophodon and did not preclude the evolution of the late Uintan D. leotanus directly from the late Bridgerian D. minusculus. Black (1979) reported D. leotanus from the late Eocene Badwater Creek Fauna of central Wyo- ming. The sizes of the upper and lower molars of those specimens are closer to D. minusculus, whereas the anterior teeth are closer in size to D. leotanus. The possibility thus exists that D. leo- tanus molars overlap in size with those of D. min- usculus, and if specimens are found without the anterior dentitions preserved, the two taxa may be confused. Schiebout (1977) reports Dilophodon sp. indet. from the La Jolla and Poway groups of San Diego County, California. Schiebout considers these specimens intermediate between D. minusculus and D. leotanus. "Early Uintan" (now considered ear- liest Uintan [Flynn, 1986]) D. minusculus is re- ported from the Tepee Trail Formation of north- western Wyoming by MacFadden (1980). Both specimens reported here were collected low within the middle unit of the Adobe Town Mem- ber, both from approximately bed 630. Dilopho- don minusculus is currently known from the late Bridgerian to earliest Uintan elsewhere, and D. leotanus is known from the late Uintan elsewhere (Radinsky, 1963). Assuming that D. leotanus is derived from D. minusculus, this leaves us with no species of Dilophodon from the early Uintan. Flynn (1986) lists Dilophodon, presumably D. minusculus, based on MacFadden (1980), as a characteristic earliest Uintan taxon but gives no species-level data or discussion. This is an im- portant distinction here because both pm 55709 and pm 557 1 1 are from low within the middle unit of the Adobe Town Member, previously thought to be early Uintan. The co-occurrence of D. min- usculus with characteristic early Uintan taxa would indicate an earliest Uintan, rather than late Bridg- erian or early Uintan, age for some lower portion of the middle unit of the Adobe Town Member. Superfamily Rhinocerotoidea Gill, 1872 Hyrachyus modestus (Leidy, 1870) (Fig. 11A,B) Referred Specimens— pm 37284, RM2 in max- illary fragment, from Loc. fm- 1 1 -70-wdt, Twkk, bed 527; pm 55358, LP2"4 in maxillary fragment with possibly associated postcranial fragments, from Loc. jjf 7-24-90-1, Twka,; pm 55710, RP3- M3 in dentary fragment, from Loc. jjf 7-24-90-1, Twka^ pm 55712, RM2 with associated dentary fragment, from Loc. fm-1-58-wdt, Twka,; pm 55959, left dentary fragment with P4 and partial M2, from Loc. jjf 7-28-92-2, Twka,. Description— pm 55710 (Fig. 1 1A) preserves a portion of the symphysis showing a diastema be- tween the canine and P,. The symphysis extends beneath the anterior half of P2. The posterior men- tal foramen is located beneath the anterior half of M3. pm 55710 is the most complete H. modestus dentary in the fmnh collections, possessing the right P3-M3. The alveoli of the anterior premolars indicate that P, was single-rooted and P2 was prob- ably small, unmolarized, and double-rooted. P3 has a well-developed protocristid and a small, sharply curved paracristid; the hypolophid and en- toconid are small and poorly developed; the hy- poconid is distinct but lower than the metaconid and protoconid. P4 is larger and more molarized than P3; the hypolophid and entoconid are more developed but still lower than the metaconid and protoconid. 22 FIELDIANA: GEOLOGY a a. i c o d r- q 06 o\ I I I I I I £ 2 I £ I II 2 I i I I 2 I — ism I I I I I I I I 1 1 1 2 00 1 m I CO On CO <S <«■ Tt 2 l I 2 i 1 1 vd 1 r- Tf — « wo 2 1 1 2 1 1 c* d I I I I I I I 2 I I 2 r- <r> od od I I II I od II I I I I I I I I I *5 .c 1 s 1 5 I232322S22S2* -C — oo g.'T C oo p S * O O ■O r- "Q oo <N O co O oo oo "" ©» c o «*> CO >. £5*2=2^23 i McCARROLL ET AL: THE PERISSODACTYLS 23 Fig. 11. A, Hyrachyus modestus, pm 55710, right dentary fragment with P3-M3, in occlusal view (fmnh neg. 85816). B, Hyrachyus modestus, pm 37284, right maxillary fragment with M2, in occlusal view (fmnh neg. 85817). C, Hyrachyus eximius, pm 26128, isolated left M3, in occlusal view (fmnh neg. 85777.1 1). M,_3 are very similar, becoming progressively larger in size from M, to M3. The molar proto- cristids and hypolophids are almost equal in size, compared to those of the premolars, in which the protocristids and hypolophids differ in size. The hypolophid on M3 runs slightly more diagonally across the tooth rather than more transversely as in M[_2. M3 lacks a hypoconulid. pm 55358 is a left maxillary fragment preserving P2 and the lingual half of P3-^. All three premolars are nonmolariform with no indication of a second lingual cusp. P2 has two indistinct labial cusps. pm 37284 (Fig. 1 IB) is a right maxillary frag- ment preserving a complete M2. It possesses a slightly concave labial metacone, with a small la- bial cingulum. The metacone is deflected lingually to the midline of the tooth. The paracone is the most prominent cusp of the tooth. The parastyle is large and distinct from the paracone. The pro- toloph is long and possesses a small paraconule, which is slightly labial to the midline of the tooth. The metaloph is much shorter than the protoloph and possesses a very small metaconule positioned along the midline of the tooth. A distinct ridge runs from the paracone toward the center of the tooth. Discussion— A combination of characters is used to recognize Hyrachyus. These include: re- 24 FIELDIANA: GEOLOGY tention of P,; nonmolariform to submolariform premolars; no M3 hypoconulid; and size (Radin- sky, 1967b). At present, two species of North American Hyrachyus are recognized, H. modestus and H. eximius. Both species are reported here from the Washakie Formation. They are distin- guished from each other on the basis of size (see Table 1) (Radinsky, 1967b). Schoch (1989, p. 310) considered Radinsky's revision of Hyrachyus to one genus and two species to be too "lumped," but gave no species-level revisions. Until further taxonomic revision, we follow Radinsky (1967b). pm 55710, a right dentary with P3-M3 and al- veoli of P,_2, cannot be assigned to Helaletes nan- us, as its M3 lacks a hypoconulid. Length-width measurements of the specimens reported here (see Tables 2 and 3) compare well with those given by Radinsky ( 1 967b) for H. modestus from the Bridg- er Formation. Radinsky (1967b) doubted all pre- vious reports of Hyrachyus from the Washakie Formation, giving either incorrect locality data or misidentification of Triplopus specimens as the reason(s). He stated that Triplopus specimens are easily confused with Hyrachyus, especially when M3 is not preserved. This presents a problem, however, as no spec- imens of//, modestus reported here preserve M3. Hyrachyus modestus is the smallest species of Hy- rachyus, and it overlaps in size with Triplopus im- plicatus, also known from the Washakie Forma- tion. A second species of Triplopus from the Washakie Formation, T cubitalis, is much smaller than H. modestus (see Table 1) (Radinsky, 1967a). pm 55710 has an M,_3 length of 47.2 mm, only slightly larger than T. implicatus reported by Ra- dinsky (1967a) (see Table 1). Unfortunately, no discrete morphological characters are known to distinguish Hyrachyus and Triplopus lower den- titions. This makes the identification of lower den- titions of these two taxa tentative, leaving both //. modestus and T. implicatus from the Washakie Formation of little biostratigraphic utility. We ten- tatively assign these specimens to Hyrachyus mo- destus rather than Triplopus implicatus because of the late Bridgerian age of the Washakie Formation strata in which they occur, including the Kinney Rim Member (pm 37284) and from the lower unit of the Adobe Town Member (pm 55701, 55358, 55712). Hyrachyus modestus has a late Bridgerian last occurrence elsewhere (Krishtalka et al., 1987, and references therein), whereas Triplopus impli- catus has an early Uintan first occurrence else- where (Table 4). Hyrachyus eximius Leidy, 1871 (Fig. 1 1Q Referred Specimens— pm 26128, isolated left M3, from Loc. fm-1 1-70-wdt, Twkk, bed 527; pm 55867, weathered fragments of what was probably a complete skeleton, including partial left and right M3, from Loc. jjf 7-28-92-1, Twka,. Description— pm 26128 (Fig. 11C) has a dis- tinct protoloph and metaloph. The protocone and hypocone are only slightly deflected posteriorly with reference to the paracone and metacone. A well-developed metastyle runs perpendicular to the metaloph. The paracone is large and distinct from the rest of the ectoloph. The parastyle is large, with a deep notch separating it from the paracone. The tooth is moderately worn, with a distinct groove separating the paracone and the protocone on the occlusal surface. No labial or lingual cingula are present. Small anterior and posterior cingula are present. pm 55867 is very similar to pm 26 1 28. The meta- style is slightly larger and the anterior and poste- rior cingula are slightly larger. In addition, a small cingulum is present lingually between the proto- cone and hypocone. All these differences may be attributed to differences in wear stages between the two specimens, with pm 55867 being much less worn than pm 26128. The parastyle and par- acone are broken on pm 55867, thereby limiting comparison with pm 26128. Discussion— pm 26128 is a left M3 and is con- fidently assigned to H. eximius, firmly establishing the presence of the genus Hyrachyus in the Wash- akie Formation, contrary to the conclusions of Ra- dinsky (1967b). This specimen (see Table 3) falls within the observed size range reported for the species by Radinsky (1967b). In addition, posses- sion of a metacone perpendicular to the metaloph and a large robust parastyle with a deep groove separating it from the paracone distinguish it from Triplopus. pm 26128 is from bed 527, near the base of the Kinney Rim Member. At present, the temporal range of H. eximius elsewhere consists of a late Bridgerian first occurrence and an earliest Uintan last occurrence. The presence of H. eximius near the base of the Kinney Rim Member indicates that the lower part of the Washakie Formation is late Bridgerian or younger, and the early-late Bridg- erian boundary is below bed 527 and probably lies within the underlying Green River Formation (see biostratigraphic section for further discussion). McCARROLL ET AL: THE PERISSODACTYLS 25 Family Hyracodontidae Cope, 1879 Triplopus cubitalis (Cope, 1880) (Fig. 12A) Referred Specimens— pm 28365, right dentary fragment with P3-M3, from Loc. fm- 1 2-70-wdt, Twka2; pm 55708, a fragmentary left dentary with P3-M3, from Loc. jjf 7-25-92-2, Twka2, bed 630. Description— pm 28365 (Fig. 12A) is moder- ately bilophodont, with well-developed paralo- phids and metalophids. Both the P3 and P4 have small hypolophids, making the metalophids the most prominent feature of the posterior half of these teeth. On P4, however, there is a small pos- terolingual swelling, indicating an incipient ento- conid. This swelling is separated from the small hypolophid by a small groove. Such a swelling could be considered a small cingulum rather than an incipient entoconid; it should be noted, how- ever, that no cingula are present in this position on any other tooth except for a very small pos- terolingual cingulum on M3. Small anterolingual cingula are present on P3 and P4. For all the teeth the protolophid is higher than the hypolophid; this is true even for M,, the most heavily worn tooth. In addition to the complete teeth, the alveoli are preserved for P, and P2. P2 is double-rooted and the posterior mental foramen lies directly beneath it. The P, alveolus is incomplete on its anterior border, and it may be single- or double-rooted. Radinsky (1967a, Fig. 1) shows P[ to be single- rooted in T. cubitalis. pm 55708 is very similar to pm 28365, differing only in being slightly larger (see Table 2). Discussion— Triplopus is a small hyracondon- tid recognized (Radinsky, 1967a) by the following combination of characters: dentition unreduced; incisors equal in size and spatulate; premolars nonmolariform to submolariform; M3 with small metacone; and a tridactyl manus. Two species of Triplopus are currently recog- nized from the Washakie Formation, T cubitalis and T. implicatus (Radinsky, 1967a). They are distinguished from each other on the basis of size (see Table 1) and are assigned to Triplopus rather than Hyrachyus because of their Uintan age in the Washakie Formation and known ranges else- where, pm 55708 is assigned to T. cubitalis rather than T. implicatus because of its smaller size (see Table 2). pm 55708 is from ~bed 630, near the base of the middle unit of the Adobe Town Member. Ra- dinsky (1967a) stated that "All specimens of Tri- plopus cubitalis come from the Washakie For- mation of the Washakie Basin, Wyoming, . . . . " Thus, their presence in fmnh collections is not surprising, and adds nothing to their biochrono- logic utility. Furthermore, we have been unable to locate subsequent reports of T. cubitalis from else- where in the western interior. Triplopus implicatus (Cope, 1873) (Fig. 12B) Referred Specimens— pm 3228, isolated right M3, from Loc. fm-8-57-wdt, Twka2; cm 18464, partial skull with LP4-M3 and RP3-M3 and as- sociated dentaries, from Loc. "west rim of Adobe Town about 4 miles south of Haystack Mt." Description— pm 3228 is only moderately bi- lophodont, with a well-developed paralophid and metalophid. The paralophid is the larger of the two lophids, and runs anteriorly from the proto- conid and then lingually along the anterior margin of the tooth. The smaller metalophid runs ante- riorly from the hypoconid to the posterior base of the protoconid. The protolophid is slightly higher than the hypolophid. A small cingulum is present on the posterolingual corner of the tooth. In ad- dition, a very small, faint cingular ridge runs along almost the entire base of the tooth, being absent only on the anterior margin. In some features pm 3228 could be mistaken for an M2. The angle between the posterior and an- terior halves of the root is not as great as that seen in the M3 of other specimens of Triplopus (pm 55708, for example), but is closer to that seen in the M2. Even so, the angle is still fairly high and the thickness of the posterior half of the root is more similar to that of an M3 than to either an M2 or M,. The M3 of cm 1 8464 (Fig. 1 2B) has a very small metastyle and M1-3 have small, reduced (com- pared to Hyrachyus) parastyles. Both P3"* are sub- molariform. Discussion— Measurements of pm 3228 (see Table 2) are well within the range of those reported for the larger T. implicatus and outside of those reported for the smaller T. cubitalis (Radinsky, 1967a). pm 3228 is from the middle unit of the Adobe Town Member. As with T. cubitalis, T. implicatus is known only from the Washakie Formation and is thus of limited biochronologic utility. We sus- pect, as did Radinsky (1967a, p. 14), that larger sample sizes will result in the synonymy of Tri- 26 FIELDIANA: GEOLOGY Fig. 12. A, Triplopus cubitalis, pm 28365, right dentary fragment with P3-M3, in occlusal view (fmnh neg. 85777.19). B, Triplopus implicatus, cm 18464, right maxillary fragment with P3-M3, in occlusal view (fmnh neg. 85824.26). McCARROLL ET AL: THE PERISSODACTYLS 27 plopus species from the Uinta and Washakie for- mations. cm 1 8464 was listed by Radinsky ( 1 967a, p. 13) as a specimen of T. implicatus. He did not, how- ever, list it as a specimen preserving the upper molars (see Radinsky, 1967a, p. 12). cm 18464 does preserve the upper right and left molars. In overall morphology, cm 1 8464 is assignable to Tri- plopus and its size (see Table 3) is within the range reported for T. implicatus. cf. Forstercooperia minuta Lucas, Schoch, & Manning, 1981 Referred Specimen— pm 1682, an isolated left M3, from Loc. fm-5-56-wdt, Twka2. Description— pm 1682 is not complete, as it lacks a parastyle, the labial base of the paracone, and the anterior portion of the hypocone. The ec- toloph and metaloph are not readily distinguished, giving the tooth a generally triangular shape. The metacone intercepts the metaloph lingually just past the midline of the tooth; the metastyle is al- most perpendicular to the metaloph. The proto- loph is slightly crescent-shaped. Discussion— Forstercooperia is a medium- to large-sized hyracodontid recognized (Radinsky, 1967a) by the following combination of charac- ters: size (see Table 1); dentition unreduced com- pared to that of Hyrachyus; incisors approxi- mately equal in size and pointed; canines medium- sized and stubby; premolars nonmolariform to submolariform; M3 metacone small to absent. Wood (1938) first coined the name Forstercoop- eria for the preoccupied genus Cooperia. Radinsky (1967a) recognized five species of Forstercooperia, four from Asia and one, F.1 grandis (= Hyrachyus grandis Wood, 1934), from the Uinta and Wash- akie formations. Most recently, Lucas et al. (1 98 1) recognized only three species of Forstercooperia: F. totadentata (middle to late Eocene of Asia), F. grandis (middle to late Eocene of Asia, late Eocene of North America), and F. minuta (middle to late Eocene of Asia, late Eocene of North America). pm 1682 is almost identical morphologically to the M3 of ucmp 69722, a complete skull of F. grandis figured by Radinsky (1967a, Fig. 1 1). Its size, however (see Table 3), is closer to measure- ments reported for the smaller F. minuta and well outside the range of reported measurements for the larger F. grandis (Lucas et al., 198 1). The pau- city of specimens and the fragmentary nature of pm 1682 preclude a more confident identification. If accurate, this is the first report of F. minuta from the Washakie Formation. pm 1682 is from the middle unit of the Adobe Town Member. North American F. minuta is cur- rently known from the Galisteo Formation of north-central New Mexico, which is of Duches- nean age (Lucas et al., 1981; Lucas & Sobus, 1 989), and the Tepee Trail Formation of northwestern Wyoming, which is of Bridgerian to early Uintan age (Eaton, 1985). These age occurrences are con- sistent with an earliest-early Uintan age assign- ment for the middle unit of the Adobe Town Member, as indicated by other taxa. Hyracodontidae indeterminate Referred Specimen— pm 3937, right maxillary fragment with fragmentary F*-M2, associated at- las, from Loc. fm-8-57-wdt, Twka2. Description— pm 3937 possesses three highly fractured teeth that are interpreted here as F'-M2. P4 appears to have a large, well-separated proto- cone and hypocone, but lacks a well-developed metastyle. M1 possesses a high paracone and only a small vestige of a parastyle. The metastyle is missing, but remnants of enamel present on the ectoloph and metaloph indicate that a postero- labially deflected metastyle was present. M2 is very poorly preserved and adds no further information. Discussion— pm 3937 is assigned to the Hyra- codontidae based on overall molar morphology and size. Although it is broken and fragmentary, this specimen appears to have been larger (see Ta- ble 3) than Forstercooperia grandis and is close to measurements reported for F. totadentata from China (Lucas et al., 1981). Because of the frag- mentary nature of the specimen, we do not attempt a more specific identification. Family Amynodontidae Scott and Osborn, 1883 Amynodon advenus Marsh, 1877 (Fig. 13) Referred Specimens— pm 1088, paired right and left maxillary dentitions with RP2-M2 and LP2- M2, from Loc. given only as "Top of Haystack Mt"; pm 3874, dentary with LC-M2 and RP3-M2, from FM-8-57-WDT, Twka2; pm 1514, right dentary fragment with M3 and partial M2, associated cal- caneum and postcranial fragments, from Loc. fm- 28 FIELDIANA: GEOLOGY Fig. 13. Amynodon advenus, pm 1088, right and left maxillary dentitions (in matrix) showing RP2-M2 and LP2- M2, in occlusal view (fmnh neg. 85777.5). 10-56-wdt, Twka2; cm 9382, associated LP3-M2 and tooth fragments, from Loc. given only as "Haystack Mt."; pm 51597, left dentary fragment with partial M,_3, and associated incisors, from Loc. fm-6-73-wdt, Twka2. Description— In pm 1088 (Fig. 1 3) both second premolars and both second molars are damaged; the third molars are both missing. The fourth pre- molars are large and submolariform, and the third and fourth premolars have a continuous, heavy lingual cingulum. In pm 3874, the left and right P2 alveoli show them to be double-rooted, and the P, is absent. In addition, a distinct labial groove separates the trigonids and talonids on P4-M2. This is also true for pm 1514. However, pm 1 5 1 4 is more worn than pm 3874, making the lingual groove separating the trigonid and talonid less obvious. cm 9382 is indistinguishable from pm 1088. Discussion— Amynodon is recognized (Wall, 1982) by the following combination of characters: large double-rooted P2; a distinct labial groove separating trigonid and talonid on molars; length of upper and lower premolar series is approxi- mately half that of molar series (see Table 1); P4 large and submolariform; and M3 metastyle less labially deflected than in more derived amyno- donts. At present, only two North American spe- cies of Amynodon are recognized, A. advenus and the much smaller A. reedi (Wilson & Schiebout, 1981; Wall, 1982). The loss of P,, a large double-rooted P2, and size (see Table 2) allow the lower dentitions to be confidently assigned XoA. advenus. Unfortunately, pm 1088 lacks the diagnostic metastyle condition on M3; even so, it possesses a large submolariform P4 and is of appropriate size (see Table 3) for as- signment to A. advenus. All Amynodon specimens reported here are from the middle unit of the Adobe Town Member. Amynodon is currently known from the earliest Uintan (Shoshonian Subage) through the Duches- nean elsewhere (Krishtalka et al., 1987), although we are unsure if Amynodon has a Duchesnean last occurrence. Amynodon is currently used as the de- McCARROLL ET AL: THE PERISSODACTYLS 29 fining taxon for the base of the Uintan NALMA (Flynn, 1986). The lowest stratigraphic occurrence of Amynodon within the Washakie Formation is pm 3874 from the northwest flank of Haystack Mountain. This is stratigraphically higher than Granger's (1909) bed 1 1, which was his Bridger- ian-Uintan boundary. We discuss the position of the Bridgerian-Uintan boundary in the biostrati- graphic section of this paper. Biostratigraphy Overview Granger ( 1 909) was the first to divide the Wash- akie Formation (see Fig. 3). Granger called the lower half of the formation "Washakie A" (~260 ft/79 m, beds 1-10) and considered it to corre- spond faunally to the "Bridger C-D" based on the presence of Uintatherium, Manteoceras, Mesati- rhinus, Notharctus, Hyrachyus, and Sinopa. He called the upper half of the formation "Washakie B" (-380 ft/1 16 m, beds 12-22) and considered it to correspond faunally to the "Uinta A-B" based on the presence of Eobasileus, Achaenodon, Amy- nodon, Dolichorhinus, and Metarhinus. Granger considered the base of the Washakie Formation to be the "lower brown sandstone," a sequence of sandstones, varying in thickness, that weather to a reddish brown and form a distinct rim around much of the basin. Granger considered the summit of Haystack Mountain to be the top of the Wash- akie Formation. Haystack Mountain (as discussed by Turnbull, 1978) is a high topographic feature in the north-northeast portion of the basin, which Granger assumed included the stratigraphically highest beds in the formation. Roehler (1973) formally divided the Washakie Formation into two members, the lower Kinney Rim Member (~900 ft/270 m, beds 5 1 5-568) and the upper Adobe Town Member (« 2,300 ft/700 m, beds 569-708). He also informally divided the Adobe Town Member into lower, middle, and up- per units (see Fig. 2). As noted earlier, the Wash- akie Formation as defined by Roehler (1973) is more inclusive than Granger's (1909) concept of the Washakie Formation. Roehler's (1973) Kin- ney Rim Member and the upper unit of the Adobe Town Member were not recognized by Granger ( 1 909). Granger ( 1 909) assigned the rocks that now comprise the Kinney Rim Member to the under- lying Green River Formation. Roehler (1973) found that rocks stratigraphically below the "lower brown sandstone" (the base of Granger's Wash- akie Formation) were lithologically more similar to those of the overlying Washakie Formation than to the underlying Green River Formation. These rocks are bound below by the "persistent white ridge marker bed" (bed 515) and above by the unconformable persistent "lower brown sand- stone" (bed 569), and thus constitute a mappable unit, named the Kinney Rim Member of the Washakie Formation. Granger (1909) did not rec- ognize any rocks stratigraphically higher than those topping Haystack Mountain. Roehler (1973) and Turnbull (1972, 1978) independently recognized that rocks in the geographic center of the basin were stratigraphically higher than those of Hay- stack Mountain; this stratigraphically higher part of the section now constitutes the upper unit of the Adobe Town Member. The units of the Adobe Town Member were not formally divided by Roehler (1973) because they cannot be differen- tiated on the basis of persistent mappable beds. Based on the mammalian fauna and lithologic changes, both Roehler (1973) and Turnbull (1978) placed the early-late Bridgerian boundary within the Kinney Rim Member (Roehler at ~bed 540; Turnbull at ~540 — 559), the Bridgerian-Uintan boundary between the lower and middle units of the Adobe Town Member (bed 620; Granger's bed 1 1), and the early-late Uintan boundary between the middle and upper units of the Adobe Town Member (~bed 675). Of these boundaries, only one, the Bridgerian-Uintan boundary, was rec- ognized by Granger (1909). Granger placed this boundary in the same place Roehler (1973) and Turnbull ( 1 972) later did, between his beds 1 0 and 1 1 (bed 620 of Roehler, 1973), based on biostrati- graphic distributions of Bridgerian and Uintan taxa. Roehler's (1973) placement of the early-late Bridgerian boundary and the early-late Uintan boundary was tentative and based on lithologic changes, not the biostratigraphic occurrence of di- agnostic taxa. Two taxa, Hyrachyus near H. mo- destus and Sciuravus cf. nitidus, were used as ten- tative evidence for the placement of the early-late Bridgerian boundary in the Kinney Rim Member (Turnbull, 1972; Roehler, 1973). These taxa and their use as early Bridgerian indicators are dis- cussed in more detail later. The stratigraphic distributions within the Wash- akie Formation of the perissodactyl taxa reported here are shown in Table 5. When compared to the presently known temporal distributions of these taxa elsewhere (shown in Table 4), the following 30 FIELDIANA: GEOLOGY Table 4. Currently recognized chronologic distributions of selected North American middle and late Eocene perissodactyl taxa. Taxon Bridgerian I in i. in EB LB EU LU Duches- nean ED Isectolophus annectens* Isectolophus latidens Eomoropus amarorum Helaletes nanus Helaletes intermedius*\ Dilophodon minusculus Dilophodon leotanus* Colodon* Forstercooperia grandisf Forstercooperia minuta Triplopus cubitalis Triplopus implicates Triplopus obliquidens* Triplopus rhinocerinus* Amynodon advenus Amynodon reedi* Hyrachyus modestus Hyrachyus eximius Epitriplopus uintensis* Orohippus Epihippus gracilis Epihippus uintensis Palaeosyops Telmatherium Mesatirhinus Metarhinus Dolichorhinus X' X1 X1 X8.I0 X8 X X9 Xs X9? X7 X7 X10 X8 X7 X7 X3 X* X3 Xic Xic X3? X10 G, Gardnerbuttean; EB, early Bridgerian; LB, late Bridgerian; S, Shoshonian; EU, early Uintan; LU, late Uintan; ED, early Duchesnean. I, Radinsky 1963; 2, Lucas et al. 1981; 3, Radinsky 1967a; 4, Wall 1982; 5, Radinsky 1967b; 6, Flynn 1983; 7, Krishtalkaet al. 1987; 8, Flynn 1986; 9, Mader 1989; 10, MacFadden 1980; 11, Lucas and Schoch 1989; 12, Robinson 1966. * Taxa not found in the Washakie Formation. t Taxa previously reported from the Washakie Formation but not present in fmnh collections. general conclusions can be made: 1) The Kinney Rim Member and the lower unit of the Adobe Town Member contain only taxa restricted to the late Bridgerian or that range broadly throughout the Bridgerian, indicating a late Bridgerian age for those units; 2) the middle unit of the Adobe Town Member contains taxa restricted to the earliest- early Uintan or that range broadly (e.g., Bridger- ian-early Uintan or early-late Uintan), indicating an earliest-early Uintan age for all or most of the unit; and 3) the only perissodactyl from the upper unit of the Adobe Town Member is Epihippus gracilis, known to range from early to late Uintan. Below we discuss each member and unit within the formation and the biochronologic significance of each taxon known from it. Kinney Rim Member Turabull (1 972) reported finding Hyrachyus near H. modestus and Sciuravus cf. nitidus from the Kinney Rim Member. He used these taxa as in- dicators of an early Bridgerian age for the lower part of the Kinney Rim Member (Roehler, 1973; Turnbull, 1978). Both H. modestus and S. nitidus range throughout the Bridgerian (Krishtalka et al., 1987) and their presence does not necessarily in- dicate an early Bridgerian age. In addition, the specimen reported as Hyrachyus near H. modestus by Turnbull ( 1 972) is pm 26 1 28 and is here thought to be H. eximius, not H. modestus (see systematic section). The Kinney Rim Member preserves Mesati- McCARROLL ET AL: THE PERISSODACTYLS 31 Table 5. Stratigraphic distribution within the Washakie Formation of perissodactyl taxa reported here. Taxon Kinney Rim Member Adobe Town Member Twka, Twka2 Twka, Orohippus sp. X Epihippus gracilis Telmatherium sp. X Mesatirhinus sp. X Metarhinus sp. X Dolichorhinus sp. X Isectolophus latidens X Eomoropus amarorum X Helaletes nanus X Dilophodon minusculus X Hyrachyus modestus X X Hyrachyus eximius X X Triplopus cubitalis X Triplopus implicatus X cf. Forstercooperia minuta X Amynodon advenus X rhinus sp., Helaletes nanus, Hyrachyus modestus, and Hyrachyus eximius. Helaletes nanus ranges throughout the Bridgerian and H. modestus occurs throughout the Bridgerian. Mesatirhinus is cur- rently restricted to the late Bridgerian (Mader, 1989). Hyrachyus eximius is currently known to have its first occurrence in the late Bridgerian (Ra- dinsky, 1967b; Gazin, 1976; although Gazin re- ported a specimen of//, eximius from just below the Sage Creek White Layer in the Bridger Basin, this layer is the dividing line between the early and late Bridgerian in the Bridger Basin). The presence of H. eximius (pm 26128) near the base of the Kinney Rim Member (bed 527) indicates that ear- ly Bridgerian -aged rocks are probably not present within the Washakie Formation, and the early- late Bridgerian boundary in the Washakie Basin lies within the underlying Green River Formation. At present, the first occurrence of//, eximius is confidently placed at the early-late Bridgerian boundary. The last occurrence of//, eximius, how- ever, is uncertain. Flynn (1983) assigned an almost complete skull and right dentary from the Wash- akie B (amnh 107978, a cast of uw 1937) to H. eximius. Hyrachyus eximius has not been recog- nized previously as occurring in the early Uintan. Upon examination of uw 1937 (fmnh 39232, also a cast of uw 1937), we agree that it is probably Hyrachyus, and not the taxon most similar to it, Triplopus; it is within the size range previously reported for H. eximius (Radinsky, 1 967b). A range extension of Hyrachyus, represented by H. exi- mius, into the early Uintan would not affect the above reasons for not recognizing early Bridgeri- an-aged rocks within the Washakie Formation. Adobe Town Member— Lower Unit The lower unit of the Adobe Town Member historically has been considered late Bridgerian in age (Granger, 1909; Roehler, 1973; Turnbull, 1978). This has been based on the occurrence of characteristic late Bridgerian taxa within the unit (e.g., Uintatherium, Mesatirhinus, Notharctus, Hyrachyus, Sinopa). More recently, in a study combining biostratigraphy, magnetic polarity stra- tigraphy, and radioisotopic dating, Flynn (1986) proposed an earliest Uintan (Shoshonian Subage) age for some upper portion of the lower unit of the Adobe Town Member. Flynn (1986) based his proposal on the finding that the Bridgerian-Uintan boundary, and earliest Uintan (Shoshonian) fau- nas, occurred within magnetochron C20R in Eo- cene sediments of the East Fork Basin area of northwest Wyoming and the San Diego area of California. Within the Washakie Formation, a re- versed polarity interval, correlated by Flynn (1986) to Chron C20R, is approximately equivalent to the lower unit of the Adobe Town Member; there- fore, the Bridgerian-Uintan boundary should lie within the lower unit. Flynn (1986, pp. 379-380) defined the Bridgerian-Uintan boundary by the first occurrence of Amynodon, and characterized earliest Uintan faunas by the co-occurrence of small-bodied taxa previously known only from the late Bridgerian or older intervals with large-bodied 32 FIELDIANA: GEOLOGY taxa previously known only from the early Uintan or younger intervals. The larger-bodied early Uin- tan taxa were predominantly, but not exclusively, perissodactyls. At present, the following perissodactyl taxa have been recovered from the lower unit of the Adobe Town Member: Orohippus sp., Telmatherium sp., Mesatirhinus sp., Isectolophus latidens, Hyrachyus modestus, and Hyrachyus eximius. The defining Shoshonian (earliest Uintan) taxon, Amynodon, is not present. Each of these other taxa is well known from late Bridgerian deposits of western North America. Although some (Hyrachyus) may have earliest Uintan last occurrences, this is insufficient evidence for demonstrating an earliest Uintan (Shoshonian) age for the lower unit of the Adobe Town Member. This unit does contain character- istic "Bridgerian" taxa (Hemiacodon gracilis, Mi- crosyops annectens, Notharctus robustior, Hyop- sodus paulus) noted as occurring in the earliest Uintan by Flynn (1986); their presence alone, however, is also insufficient evidence for dem- onstrating an earliest Uintan age for the unit. At present, the known taxa from the lower unit of the Adobe Town Member indicate a late Bridgerian age, although a Shoshonian (earliest Uintan) age is still possible for part of the unit. The absence of a definitive earliest Uintan fauna from the lower unit of the Adobe Town Member may be a taphonomic artifact. Many of the "Uin- tan" taxa used to define or characterize the earliest Uintan are larger in size (Amynodon, Metarhinus, Achaenodori). Unfortunately, the most fossilifer- ous beds known from the lower unit of the Adobe Town Member ("middle red beds" of Roehler, 1973) typically produce only smaller- bodied taxa (rodents, primates, insectivores). Preliminary analysis of the fossil material collected to date in- dicates that these beds represent paleosols— ho- rizons where there is a bias (although not exclu- sive) toward the preservation of smaller skeletal elements, especially isolated teeth and jaws (Bown & Kraus, 1981; Bown & Beard, 1990). Thus, a preservational (and potential collection) bias against larger-bodied Uintan taxa may exist. In- creasing our future collection efforts in more en- vironmentally diverse beds in the lower unit of the Adobe Town Member may yield a greater di- versity of larger-bodied taxa from the lower unit of the Adobe Town Member. Adobe Town Member— Middle Unit The middle unit of the Adobe Town Member historically has been considered early Uintan in age (Granger, 1909; Roehler, 1973; Turnbull, 1978). This has been based on the occurrence of characteristic early Uintan taxa (Eobasileus, Achaenodon, Amynodon, Dolichorhinus, Meta- rhinus) within the unit. Perissodactyl taxonomic diversity and abun- dance are highest for the Washakie Formation in the middle unit of the Adobe Town Member. The taxa present are Dolichorhinus sp., Metarhinus sp., Eomoropus amarorum, Dilophodon minusculus, Triplopus cubitalis, Triplopus implicatus, cf. For- stercooperia minuta, and Amynodon advenus. Di- lophodon minusculus has been thought to be re- stricted to the late Bridgerian (Radinsky, 1963). The remaining taxa listed above have earliest-ear- ly Uintan first occurrences (Flynn, 1986, Krish- talka et al., 1987). Thus, the middle unit of the Adobe Town Member is the only unit within the Washakie Formation where Bridgerian and Uin- tan taxa are documented to overlap in occurrence. This indicates an earliest Uintan age (Shoshonian Subage) for some lower portion of the middle unit of the Adobe Town Member. Alternatively, the occurrence of Dilophodon minusculus in the middle unit of the Adobe Town Member could be interpreted as a range extension for that taxon to include the early Uintan. The occurrence of other nonperissodactyl taxa (Hyop- sodus and Notharctus robustior) known to occur in the Bridgerian (but also in the earliest Uintan) also indicates a "Bridgerian" component to the fauna of the middle unit. Adobe Town Member— Upper Unit The upper unit of the Adobe Town Member was not included in Granger's Washakie Formation. This portion of the section was independently rec- ognized by Roehler (1973) and Turnbull (1972, 1978) as being stratigraphically above the sedi- ments capping Haystack Mountain (= top of Granger's [ 1 909] section). Thus, the upper unit is younger than the beds capping Haystack Moun- tain, but by how much is still in question. Roehler (1973) speculatively assigned a late Uintan age to the upper unit based on lithologic changes he in- terpreted as a change in "sedimentary regime." Roehler (1973) reported no fossil mammal spec- imens from the upper unit. Turnbull (1978) also reported an inadequate fossil mammal record from the upper unit and simply reiterated Roehler's speculation of a late Uintan age. Epihippus gracilis is the only perissodactyl known from the upper unit of the Adobe Town Member. The paucity of specimens makes place- McCARROLL ET AL: THE PERISSODACTYLS 33 ment of the early-late Uintan boundary within the Adobe Town Member difficult. In addition, the known temporal span of E. gracilis is the entire Uintan, which prevents further biochronologic subdivision based on its presence within the unit. Additional recent collections of nonperissodactyl taxa from the upper unit indicate the absence of late Uintan taxa from the upper unit (McCarroll et al., 1993, in press), this fauna will be reported elsewhere (McCarroll, 1995, in prep.). The currently recognized temporal distributions for selected middle and late Eocene perissodactyl species are shown in Table 4. Several taxa of late Bridgerian or early Uintan age have not been rec- ognized yet from the Washakie Formation, even though the temporal span of the formation indi- cates they could have occurred here. Palaeosyops has been reported from the Washakie Formation (Osborn, 1929), but we have no specimens of Pa- laeosyops in the fmnh collections. Helaletes in- termedins (= Desmatotherium guyotii) may in fact be known from the Washakie Formation, if the type of D. guyotii (ymp-pu 10166) is actually from the Washakie Basin rather than the Bridger Basin (see Radinsky, 1963, pp. 48-50). Radinsky (1963) commented on the rarity of H. intermedins in gen- eral. We have yet to find any specimens that we confidently assign to H. intermedins, presumably because of its rarity. Amynodon reedi, originally described from the Poway Conglomerate of San Diego, California (Stock, 1939), is now reported from early Uintan sediments of White River, Utah, and the Uinta Basin, Utah (Wall, 1982). It has not been documented in the Washakie Formation. Triplopus obliquidens and Triplopus rhinocerinus are both known from the Uinta Formation, but so far as we can tell they are absent in the Washakie Formation. This may be due in part to taxonomy; T. obliquidens of the Uinta Basin may be synon- ymous with T. implicatus of the Washakie Basin (see Radinsky, 1967a, p. 14). Dilophodon leotanus, presently restricted to the late Uintan, is not identified here from the Wash- akie Formation, but is known from several late Uintan faunas from Utah, Wyoming, and Mon- tana (Radinsky, 1963). Its absence is assumed to be due to the lack of late Uintan age sediments in the Washakie Formation. The lack of late Uintan age sediments may also explain the lack of Colo- don (late Uintan- Whitneyan) from the Washakie Formation. Ecological, paleogeographic, and climatic expla- nations could all be used to explain the absence of these taxa from the Washakie Formation. In addition, the Washakie Formation has long had the reputation for being relatively unfossiliferous, thus small sample size may also be a factor. Their presence in other geographically proximate basins and temporally equivalent formations, and the steadily growing collections from the Washakie Basin, would indicate to us that some causal mech- anism might have prevented their entry into the Washakie Basin. Unfortunately, too little is known about the detailed paleogeographic and climatic conditions at the time to confidently speculate. Furthermore, the ecologic preference and inter- actions of the taxa involved are still uncertain, and the need for taxonomic revisions of some groups hinders direct basin-to-basin comparisons. Conclusions The following biochronologic conclusions can be drawn from the perissodactyls of the Washakie Formation and their biostratigraphic distribu- tions. 1 ) Early Bridgerian taxa are not currently known from the Washakie Formation. The occurrence of Hyrachyus eximius, a late Bridgerian first occurrence taxon, from near the base of the Kinney Rim Member places the early-late Bridgerian boundary within the underlying Green River Formation. 2) The Kinney Rim Member and the lower unit of the Adobe Town Member both appear to be best assigned a late Bridgerian age. 3) Earliest Uintan (Shoshonian Subage) faunas may be known from the lower portion of the middle unit of the Adobe Town Member. The middle unit of the Adobe Town Member is the only unit in which larger-bodied taxa that occur in the early Uintan co-occur with smaller-bod- ied taxa that occur in the late Bridgerian, as is typical of the Shoshonian elsewhere. The upper portion of the middle unit of the Adobe Town Member is early Uintan in age. 4) Late Uintan taxa are currently unknown from the Washakie Formation. To date, no late Uin- tan first occurrence taxa are known from the upper unit of the Adobe Town Member. Acknowledgments For help in prospecting and collecting in the field we thank the field crews listed in Turnbull (1978, 34 FIELDIANA: GEOLOGY 1991) and Turnbull and Martill (1988) and more recent collectors: James Balodimas, Tamara Biggs, Steve Borysewicz, Paul Brinkman, Greg Buckley, Doreen Covey, Annette Golden, Geoff Grove, Robin Habegger, Jeff Hoke, Doug Jewell, Robert Masek, Hedy Turnbull, Susan VandenBosch, Robin Whatley, and Mary Wisz. For typing and proofreading above and beyond the call of duty we thank Elaine Zeiger (fmnh Department of Geology). For photographic illustrations we thank the fmnh Department of Photography: James Bal- odimas, Nina Cummings, Linda Dorman, John Weinstein, and Diane Alexander White. We thank Andrew H. Leman (fmnh Department of Geology) for computer production of the line drawings. The senior author thanks Janet Voight (fmnh Depart- ment of Zoology) for encouragement (and the oc- casional drink) during the course of manuscript preparation. We thank Mary Dawson (cm) for the loan of specimens in her care. We thank the Wy- oming state office of the Bureau of Land Manage- ment, especially Ranel Capron and Laurie Bryant, for help relating to our collecting permits. We thank Richard Stucky, Bryn Mader, and an anonymous reviewer for reviewing the manuscript. Literature Cited Black, C. C. 1979. Paleontology and geology of the Bad water Creek area, central Wyoming. Part 19. Per- issodactyla. Annals of the Carnegie Museum, 48(21): 391-401. Bown, T. M., and C K. Beard. 1990. Systematic lateral variation in the distribution of fossil mammals in alluvial paleosols, lower Eocene Willwood For- mation, Wyoming, pp. 1 35-1 51. In Bown, T. M., and K. D. Rose, eds., Dawn of the Age of Mammals in the Northern Part of the Rocky Mountain Interior, North America. Geological Society of America, Boul- der, Colorado. Special Paper 243. Bown, T. M., and M. J. Kraus. 1981. 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Perissodactyls from the Washakie Formation (middle-late Eocene), Washakie Basin, Wyoming. Journal of Vertebrate Paleontology, 14 (suppl. to 3): 37A. . 1995. An early Uintan fauna from the upper unit of the Adobe Town Member, Washakie Forma- tion, Washakie Basin, Wyoming. Journal of Verte- brate Paleontology, 15(suppl. to 3): 42 A. McCarroll, S. M., J. J. Flynn, and W. D. Turnbull. 1993. Biostratigraphic and magnetic polarity corre- lations of the Washakie Formation, Washakie Basin, Wyoming. Journal of Vertebrate Paleontology, 13(suppl. to 3): 49A. . 1996. A review of the biostratigraphic and magnetic polarity correlations of the Washakie For- mation, Washakie Basin, Wyoming. In Prothero, D. R., and R. J. Emry, eds., The Terrestrial Eocene-Oli- gocene Transition in North America. Cambridge Uni- versity Press, Stanford, California. Osborn, H. F. 1908. New or little known titanotheres from the Eocene and Oligocene. Bulletin of the Amer- ican Museum of Natural History, 24(32): 599-617. . 1913. Eomoropus, an American Eocene chal- icothere. Bulletin of the American Museum of Natural History, 32(14): 261-274. 1929. The titanotheres of ancient Wyoming, Dakota and Nebraska. United States Geological Sur- vey Monograph, 55(2 vols.): 1-953. Osborn, H. F., W. B. Scott, and F. Speir. 1878. Pa- leontological report of the Princeton Scientific Expe- dition of 1877. Contributions, E. M. Museum of Ge- ology and Archaeology, Princeton College, 1: 1-107. Osborn, H. F., and J. L. Wortman. 1892. Fossil mammals of the Wasatch and Wind River beds, col- lection of 1891. Bulletin of the American Museum of Natural History, 4: 81-148. Owen, R. 1848. Description of teeth and portions of jaws of two extinct anthracotheroid quadrupeds . . . with an attempt to develop Cuvier's idea of the clas- sification of pachyderms by the number of their toes. Quarterly Journal of the Geological Society of London, 4: 103-141. Peterson, O. A. 1919. Report upon the material dis- covered in the upper Eocene of the Uinta Basin by Earl Douglass in the years 1908-1909, and by O. A. Peterson in 1912. Annals of the Carnegie Museum, 12: 40-168. Radinsky, L. 1963. Origin and early evolution of North American Tapiroidea. Peabody Museum of Natural History, Yale University, Bulletin, 17: 1-106. . 1 964. Paleomoropus, a new early Eocene chal- icothere (Mammalia, Perissodactyla), and a revision of Eocene chalicotheres. American Museum of Nat- ural History Novitates, 2179: 1-28. -. 1967a. A review of the rhinocerotoid family Hyracodontidae (Perissodactyla). Bulletin of the American Museum of Natural History, 136(1): 1-45. 1967b. Hyrachyus, Chasmotherium, and the early evolution of helaletid tapiroids. American Mu- seum of Natural History Novitates, 2313: 1-23. Robinson, P. 1966. Fossil Mammalia of the Huerfano Formation, Eocene, of Colorado. Peabody Museum of Natural History, Yale University, Bulletin, 21: 1-95. Roehler, H. W. 1973. Stratigraphy of the Washakie Formation in the Washakie Basin, Wyoming. United States Geological Survey Bulletin, 1369: 1-40. . 1992. Description and correlation of Eocene rocks in stratigraphic reference sections for the Green River and Washakie Basins, southwest Wyoming. United States Geological Survey Professional Paper, 1506-D: 1-83. Schiebout, J. A. 1977. Eocene Perissodactyla from the La Jolla and Poway Groups, San Diego County, California. Transactions of the San Diego Society of Natural History, 18(13): 217-228. Schoch, R. M. 1984. Two unusual specimens of He- laletes in the Yale Peabody Museum collections, and some comments on the ancestry of the Tapiridae Per- 36 FIELDIANA: GEOLOGY issodactyla, Mammalia. Postilla, Peabody Museum, Yale University, 193: 1-20. 1989. A review of the tapiroids, pp. 298-320. In Prothero, D. R., and R. M. Schoch, eds., The Evo- lution of Perissodactyls. Oxford University Press, New York. Scott, W. B. 1883. On Desmatotherium and Dilo- phodon, two new Eocene lophiodonts. Contributions, E. M. Museum of Geology and Archaeology, Princeton College, 3: 46-53. Scott, W. B., and H. F. Osborn. 1883. On the skull of the Eocene rhinoceros, Orthocynodon, and relation of this genus to other members of the group. Contri- butions, E. M. Museum of Geology and Archaeology, Princeton College, 3: 1-22. Stock, C. 1939. Eocene amynodonts from southern California. Proceedings of the National Academy of Sciences, 25(6): 270-275. Turnbull, W. D. 1972. The Washakie Formation of Bridgerian-Uintan ages, and the related faunas, pp. 20-3 1 . In West, R. M., ed., Guidebook for Field Con- ference on Tertiary Biostratigraphy of Southern and Western Wyoming. . 1978. The mammalian faunas of the Washakie Formation, Eocene Age, of southern Wyoming. Part I. Introduction: The geology, history, and setting. Fieldiana: Geology, 33(30): 569-601. 1991. Protoptychus hatcheri Scott, 1895. The cene age of southern Wyoming. Part II. The Adobe- town Member, middle division (= Washakie B), Twka/2 (in part). Fieldiana: Geology, n.s., 21: 1-33. Turnbull, W. D., and D. M. Martill. 1988. Ta- phonomy and preservation of a monospecific titano- there assemblage from the Washakie Formation (Late Eocene), southern Wyoming. An ecological accident in the fossil record. Palaeogeography, Palaeoclima- tology, Palaeoecology, 63: 91-108. Wall, W. P. 1982. The genus Amynodon and its re- lationship to other members of the Amynodontidae (Perissodactyla, Rhinocerotoidae). Journal of Pale- ontology, 56(2): 434-443. Wheeler, W. H. 1961. Revision of the uintatheres. Peabody Museum of Natural History, Yale Univer- sity, Bulletin, 14: 1-93. Wilson, J. A., and J. A. Schiebout. 198 1 . Early Ter- tiary vertebrate faunas of Trans-Pecos, Texas: Amy- nodontidae. Texas Memorial Museum Pearce-Sel- lards, ser. 33: 1-62. Wood II, H. E. 1927. Some early Tertiary rhinoceroses and hyracodonts. Bulletin of American Paleontology, 13(50): 165-265. . 1934. Revision of the Hyrachyidae. Bulletin of the American Museum of Natural History, 67(5): 181-295. . 1938. Cooperia totadentata, a remarkable rhi- mammalian faunas of the Washakie Formation, Eo- noceros from the Eocene of Mongolia. American Mu- seum of Natural History Novitates, 1012: 1-20. McCARROLL ET AL: THE PERISSODACTYLS 37 Appendix 1: Field Museum Localities Cited in Text The following localities are cited in the text. Localities cited in the text but not listed here can be found in Turnbull (1978). Twka, jjf 7-24-90-1 Sl/z, SWA, NE'A, Sec. 19, T16N, R97W Twka, jjf 7-26-92-1 SWA, Sec. 30, T16N, R97W Twka, jjf 7-28-92-1 E'/2, Sec. 13, T13N, R96W & WVi, Sec. 18, T13N, R95W Twka, jjf 7-28-92-2 SE'A, NW'A & NE'/4, SWA, Sec. 7, T13N, R95W Twka, jjf 8-1 1-93-1 S'/2, NEVa & N'/2, SE1/., Sec. 36, T16N, R98W Twka, jjf 8-13-93-1 N'/2, NW'/4, Sec. 6, T13N, R95W & S'/2, S'/2, Sec. 31, T14N, R95W Twka2 jjf 7-25-92-1 N'/2, NW'/4, Sec. 2, T16N, R97W & SE1/., SE1/., Sec. 35, T17N, R97W Twka2 jjf 7-25-92-2 NE1/., SE1/., Sec. 36 & W'/2, NW1/., SW1/., Sec. 31, T17N, R97W Twka3 jjf 7-21-90-1 SW'/4, NE'/4, NE1/., Sec. 23, T14N, R98W Appendix 2: Metarhinus sp. Specimens from the Monospecific Titanothere Quarry Reported by Turnbull and Martill (1988) Specimens assigned here to Metarhinus from the monospecific titanothere quarry initially described by Turnbull and Martill (1988): These specimens were assigned to Mesatirhinus by Turnbull and Martill (1988), prior to Mader's (1985) revision of the Brontotheriidae. Using Mader's (1989) character sets, we amend the generic assignment to Metarhinus. Skull and maxillary specimens: pm 28012, 28345, 28348, 30384-5, 30388, 30431-2, 35931-2, 36000, 36053-4, 36072, and 1 uncatalogued skull. Dentaries: pm 28001-4, 28006-10, 28014, 28342-4, 28359A-D, 30422, 30434-5, 35928A-B, 35931, 35933, 35970, 35996, and 54422. Isolated teeth: pm 28015, 28023, 28024-31, 28039, 28347, 28350-3, 28358, 28360, 28363^, 30393- 4, 30396-400, 30413, 30417, 35938-40, 35943-51, 35953-9, 35964-8, 35971-3, 35975, 35979-81, 35998, 36004-5, 36007, 36012-4, 36016, and 36055-71. Postcranial specimens: pm 28005, 28008-9, 28013, 28037-8, 28346, 28348-9, 28354-65, 30383-7, 30389-92, 30395, 30401-16, 30418-21, 30423-30, 30433, 35924, 35928-30, 35935, 35941-2, 35952, 35960-3, 35974, 35976, 35978, 35982-6, 35989-91, 35993-5, 35997, 35999, 36001-3, 36006-11, 36015, 36023, and 36046-52. The 27 jaw specimens (MNI = 25) listed in Turnbull and Martill (1988, Table II) allowed for age estimates ranging from about 3 months to well over 1 5 years, with both sexes represented. One dentary not included in Turnbull and Martill (1988, Table II) has since turned up, which accounts for the change in numbers. 38 FIELDIANA: GEOLOGY A Selected Listing of Other Fieldiana: Geology Titles Available A Preliminary Survey of Fossil Leaves and Well -Preserved Reproductive Structures from the Sentinel Butte Formation (Paleocene) near Almont, North Dakota. By Peter R. Crane, Steven R. Manchester, and David L. Dilcher. Fieldiana: Geology, n.s., no. 20, 1990. 63 pages, 36 illus. Publication 1418, $13.00 Protoptychus hatcheri Scott, 1895. The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part II. The Adobetown Member, Middle Division (= Washakie B), Twka/2 (in Part). By William D. Turnbull. Fieldiana: Geology, n.s., no. 21, 1991. 33 pages, 12 illus. Publication 1421, $13.00 A Catalogue of Type Specimens of Fossil Vertebrates in the Field Museum of Natural History. Classes Amphibia, Reptilia, Aves, and Ichnites. By John Clay Bruner. Fieldiana: Geology, n.s., no. 22, 1991. 51 pages, 1 illus. Publication 1430, $15.00 The Ear Region in Xenarthrans (= Edentata: Mammalia). Part II. Pilosa (Sloths, Anteaters), Palaean- odonts, and a Miscellany. By Bryan Patterson, Walter Segall, William D. Turnbull, and Timothy J. Gaudin. Fieldiana: Geology, n.s., no. 24, 1992. 79 pages, 24 illus. Publication 1438, $20.00 Comparative Microscopic Dental Anatomy in the Petalodontida (Chondrichthyes, Elasmobranchii). By Rainer Zangerl, H. Frank Winter, and Michael C. Hansen. Fieldiana: Geology, n.s., no. 26, 1993. 43 pages, 35 illus. Publication 1445, $16.00 Status of the Pachypleurosauroid Psilotrachelosaurus toeplitschi Nopcsa (Reptilia, Sauropterygia), from the Middle Triassic of Austria. By Olivier Rieppel. Fieldiana: Geology, n.s., no. 27, 1993. 17 pages, 9 illus. Publication 1448, $10.00 Osteology of Simosaurus gaillardoti and the Relationships of Stem-Group Sauropterygia. By Olivier Rieppel. Fieldiana: Geology, n.s., no. 28, 1994. 85 pages, 71 illus.. Publication 1462, $18.00 Giant Short-Faced Bear (Arctodus simus yukonensis) Remains from Fulton County, Northern Indiana. By Ronald L. Richards and William D. Turnbull. Fieldiana: Geology, n.s., no. 30, 1995. 34 pages, 20 illus. Publication 1465, $10.00 Order by publication number and/or ask for a free copy of our price list. All orders must be prepaid. Illinois residents add current destination tax. 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