Mammalia, Carnivora): Appearance of the Eurasian Beardog Ysengrinia in North America Robert M

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2002 Intercontinental Migration of Neogene Amphicyonids (Mammalia, Carnivora): Appearance of the Eurasian Beardog Ysengrinia in North America Robert M. Hunt Jr. University of Nebraska-Lincoln, [email protected]

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Hunt, Robert M. Jr., "Intercontinental Migration of Neogene Amphicyonids (Mammalia, Carnivora): Appearance of the Eurasian Beardog Ysengrinia in North America" (2002). Papers in the Earth and Atmospheric Sciences. 547. https://digitalcommons.unl.edu/geosciencefacpub/547

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Intercontinental Migration of Neogene Amphicyonids (Mammalia, Carnivora): Appearance of the Eurasian Beardog Ysengrinia in North America

ROBERT M. HUNT, JR.1

CONTENTS Abstract ...... 2 Introduction ...... 2 Abbreviations ...... 4 Early History of Amphicyonidae in North America ...... 5 Early Neogene Amphicyonines ...... 6 History of Discovery of North American Ysengrinia ...... 7 Geographic and Geologic Distribution of North American Ysengrinia ...... 8 Systematics ...... 11 Ysengrinia Ginsburg, 1965 ...... 11 Ysengrinia americana (Wortman, 1901), new combination ...... 14 Postcranial Osteology ...... 26 Basicranial Anatomy ...... 43 Dentition and Feeding ...... 47 Acknowledgments ...... 49 References ...... 49

1 Research Associate, Division of Paleontology, American Museum of Natural History; Professor, Geological Sci- ences; and Curator, Vertebrate Paleontology, University of Nebraska, Lincoln, NE 68588-0549.

ABSTRACT At the beginning of the Neogene a remarkable faunal turnover occurred within the North American carnivore community. The dominant larger Oligocene carnivores (creodonts, nimravid cats, the amphicyonid Daphoenus) became extinct during the late Oligocene and were replaced in the early Miocene by amphicyonine amphicyonids and hemicyonine ursids that entered North America from Eurasia. During a ®ve million-year interval from ϳ23 to 18 Ma, large amphicyonines appear in late Arikareean and early Hemingfordian faunas of the North American midcontinent. Although most fossils are from western Nebraska and southeastern Wyoming, occurrences of amphicyonines at several sites in the eastern United States (Dela- ware, Florida) indicate that they rapidly established a broad geographic distribution in North America during the early Miocene. This report describes and summarizes the North American specimens of the rare immigrant amphicyonine Ysengrinia, the ®rst large amphicyonine to enter the New World. Ysengrinia exists in North America from ϳ23 to 19 Ma, becoming extinct at the end of the late Arika- reean. A single species of Ysengrinia is recognized in North America: Y. americana (Wortman, 1901), comb. nov., restricted to the late Arikareean of western Nebraska and southeastern Wyoming. The North American hypodigm includes the only known complete skull of the genus, associated with a mandible and partial postcranial skeleton. Because most Eurasian occurrences of Ysengrinia are limited to mandibles or isolated teeth of single individuals, intraspeci®c variation in teeth and skeleton in these carnivores has been dif®cult to determine. The more complete North American specimens provide estimates of dental and osteological variation in Ysengrinia, and suggest that the North American species is dimorphic. Skeletal remains of early Miocene New World Ysengrinia are most often found in riparian and waterhole environments.

INTRODUCTION prising large amphicyonine beardogs, hemi- Faunal turnover profoundly altered inte- cyonine ursids, and diverse species of the am- grated mammalian communities at various phicyonid Daphoenodon. times during the Neogene in both North The temnocyonine amphicyonids were the America and Eurasia. These turnover events only major group of large carnivorans to produced changes in faunal composition span the Paleogene-Neogene boundary in throughout the Holarctic region that eventu- North America, apparently unaffected by this ally in¯uenced the southern continents, ®rst North American large carnivore turnover Africa in the early Miocene, and later South event (NALCTE). Temnocyonines ®rst ap- America in the Plio-Pleistocene. On each oc- peared in the early Arikareean (ϳ29±30 Ma) casion, extinction of multiple lineages was and diversi®ed into several lineages (Hunt, followed by the appearance of a new faunal 1998b) that attained their maximum size association. Nowhere is this pattern more ev- (ϳ40±80 kg) in the late Arikareean. The sub- ident than in the turnover of large carnivor- family became extinct at the end of the late ans during the Neogene of North America. Arikareean in North America. Large carnivorans Ͼ200 kg did not exist in By the mid-Miocene, creodonts were re- the New World at the beginning of the Neo- duced to relict species in Africa, southern gene. The largest carnivores of the North Asia, and Europe (Barry, 1980, 1988; Gins- American late Paleogene were an aggregation burg, 1980; Morales et al., 1998). Nimravids of diverse, mid-sized (Ͻ100 kg in most cases) were represented in the mid- to late Miocene nimravid cats, creodonts, and amphicyonids. of Eurasia and North America by a single This carnivoran assemblage became extinct subfamily, the Barbourofelinae (Geraads and during the late Oligocene with the gradual GuÈlecË, 1997), of which only a few species disappearance of Nimravinae, creodonts (Barbourofelis fricki, North America, to ϳ6 (Hyaenodontidae), and the daphoenine am- Ma; nimravid, Asian Siwaliks, to ϳ7.4 Ma; phicyonid Daphoenus. In the early Miocene a Barry and Flynn, 1989) persisted to near the new community of large carnivorans appeared end of the epoch. The numerous genera and in North America (®g. 1, NALCTE), com- species of late Eocene-Oligocene Nimravi- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 3

Fig. 1. Temporal ranges of large Oligocene and early Miocene carnivores in North America, demonstrating the faunal turnover event at the Paleogene-Neogene boundary (Global Polarity Time Scale from Berggren et al., 1995). Abbreviations: NALCTE, North American large carnivore turnover event; GPE, last appearance in Great Plains; JDE, last appearance in John Day Formation, Paci®c Northwest; Ma, Mega-annum. 4 AMERICAN MUSEUM NOVITATES NO. 3384 nae found in North America and Eurasia tocene ursid-felid-canid association (Hunt and were extinct by ϳ24±25 Ma, prior to the Tedford, 1993). Miocene. This report is one in a series of publica- By the end of the early Miocene, amphi- tions that explores the early Neogene radia- cyonids and hemicyonines dominated niches tion of the Amphicyonidae in the New for large carnivores on the northern conti- World. Earlier studies reviewed the Oligo- nents (Hunt, 1998a, 1998b; Ginsburg and cene amphicyonids of North America (Hunt, Morales, 1998). During the mid-Miocene, 1996, 1998b, 2001), the evolution of the these were the ®rst Neogene carnivorans to family in North America (Hunt, 1998b), and attain sizes Ͼ200 kg: among the largest of the intercontinental migration of the large these arctoids were Amphicyon ingens of amphicyonine Amphicyon to the New World North America, and the European Amphi- in the early Miocene (Hunt, in press). Here cyon giganteus and hemicyonine Dinocyon I brie¯y review the early history of amphi- thenardi. By the mid-Miocene several am- cyonids in North America (the temnocyoni- phicyonids, including a large species of Am- nes and endemic daphoenines); describe the phicyon, had entered Africa and rapidly pen- faunal turnover event (NALCTE, ®g. 1) at etrated to the southern limit of the continent the Paleogene-Neogene boundary when cre- (Arrisdrift fauna, Namibia: Hendey, 1978; odonts, nimravine cats, Daphoenus, and tem- Morales et al., 1998). nocyonines were replaced by immigrant am- Amphicyonids and hemicyonines contin- phicyonines and hemicyonines; and place on ued to dominate the carnivoran fauna of Ho- record the ®rst of the large immigrant am- larctica into the late Miocene. But within the phicyonines to appear in North America, the late Miocene, during the Clarendonian land Eurasian beardog Ysengrinia. mammal ``age'' of North America and the Vallesian of Europe, both groups became ex- ABBREVIATIONS tinct. Relict taxa of amphicyonids survived in Africa at Lothagam (Kenya) to at least Anatomical ϳ6.5 Ma (Werdelin, 1999), and on the Indian A alisphenoid subcontinent in the Siwalik Group to ϳ7.4 BO basioccipital Ma (Barry et al., 1982: 112), but failed to eam osseous external auditory meatus reach South America. After ϳ9 Ma, late gf postglenoid foramen Miocene (Turolian, Hemphillian) faunas on h hypoglossal (condyloid) foramen the northern continents lacked amphicyonids ips inferior petrosal venous sinus and hemicyonines altogether; they were re- M mastoid process me mastoid-exoccipital suture placed by large ursids (Agriotherium, In- p petrosal promontorium darctos), felids, and canidsÐlineages that pcf posterior carotid foramen heralded the eventual rise to prominence of pg postglenoid process these families in the Plio-Pleistocene. plf posterior lacerate foramen Ecological roles occupied by amphicyon- pp paroccipital process ids and hemicyonines on the northern conti- T ectotympanic nents were eventually ®lled in the Pleisto- cene/Holocene by ursine bears (Ursidae, Ur- Institutional sus, Thalarctos, Arctodus, Tremarctos), the great cats (Felidae, Panthera, Smilodon, Di- ACM Pratt Museum, Amherst College, Mas- nobastis), wolves (Canidae, Canis), and hy- sachusetts enas (Hyaenidae, Crocuta, Hyaena, Para- AM Department of Mammalogy, American hyaena, Pachycrocuta, Chasmaporthetes). Museum of Natural History, New York Thus, the early to mid-Miocene interval in AMNH Division of Paleontology, American Museum of Natural History, New York North America is identi®ed by a discrete as- CM Division of Vertebrate Fossils, Carne- sociation of large amphicyonids and hemi- gie Museum of Natural History, Pitts- cyonines that intervenes between the late Eo- burgh cene-Oligocene creodont-nimravid-Daphoen- CNHM Field Museum of Natural History, Chi- us association and the late Miocene to Pleis- cago 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 5

Fig. 2. Ysengrinia americana (Wortman, 1901), new combination; holotype palate with left P2±M2, right P3±M3, YPM 10061, upper Arikaree Group, collected in 1875 by H.C. Clifford in northwest Nebraska (see appendix 1). Scale bar, 1 cm.

F:AM Frick Collection, American Museum of (Hunt, 1996). The late Eocene to mid-Oli- Natural History, New York gocene (Duchesnean±Chadronian through FSL FaculteÂ des Sciences, UniversiteÂde Whitneyan) species all belong to the endemic Lyon, Lyon MGL MuseÂe Guimet d'Histoire Naturelle, North American subfamily Daphoeninae, Lyon comprising four genera (Daphoenus, Da- NMB Naturhistorisches Museum, Basel phoenictis, Brachyrhynchocyon, Parada- PaN Museo PaleontoloÂgico de Valencia, phoenus). Daphoenus is the oldest New Universidad de Valencia World amphicyonid, appearing in the Du- SMNS Staatliches Museum fuÈr Naturkunde, chesnean, and is the most plesiomorphic in Stuttgart UNSM University of Nebraska State Museum, dental, cranial, and postcranial features. The Lincoln small hypercarnivore Daphoenictis is ®rst re- USNM Department of Paleobiology, Smithson- corded in the later Duchesnean (Hunt, 1996; ian Institution, Washington, D.C. ®g. 2). Daphoenus, Daphoenictis, and Bra- YPM Peabody Museum, Yale University, chyrhynchocyon all occur in the Chadronian, New Haven and the latter two genera are not known after ZM Division of Mammals, University of that time. Paradaphoenus is ®rst certainly Nebraska State Museum, Lincoln known in the Orellan (early Oligocene) and, EARLY HISTORY OF THE together with Daphoenus, it continued AMPHICYONIDAE IN NORTH through the Whitneyan into the early Arika- AMERICA reean (late Oligocene; Hunt, 2001). These The ®rst North American amphicyonids genera, then, comprise a New World amphi- appear in the late Eocene at ϳ39±40 Ma cyonid assemblage characteristic of the late 6 AMERICAN MUSEUM NOVITATES NO. 3384

Eocene to late Oligocene interval, all smaller the Arikareean NALMA (30 Ma± ϳ18.8 Ma, carnivorans of less than 20 kg. MacFadden and Hunt, 1998; Tedford et al., In North America the only signi®cantly 1996). Therefore, late Arikareean temno- larger carnivores that occurred in this fauna cyonines, which are all younger than ϳ22.9 were the massive endemic Chadronian creo- Ma, are among the oldest Neogene amphi- dont Hemipsalodon (Mellet, 1969; Gustaf- cyonids in North America. Temnocyonines son, 1986) and the largest species of North (and species of Daphoenodon) are the most American Hyaenodon, H. megaloides and H. frequently encountered New World amphi- horridus of the Chadronian and Orellan, with cyonids in the earliest Miocene when the skull lengths of 25±40 cm (Mellett, 1977). subfamily is represented by three lineages These creodonts were the only species that (Temnocyon, Mammacyon, and an unde- approached and, in some cases, exceeded scribed genus). 100 kg. A few early Arikareean nimravid In Europe, the haplocyonines are related cats were of comparable size, with males to the Temnocyoninae, and evolved similarly possibly approaching 100 kg. However, the specialized dentitions in parallel at about the small size of most carnivores at this time is same time (Bonis, 1973; Bonis and Guinot, in marked contrast to the many large ungu- 1987). lates (brontotheres, rhinoceroses, entelo- Near the Oligocene-Miocene boundary, donts) in the late Eocene-Oligocene of North the beardog Daphoenodon appears in North America. America (®g. 1). Early occurrences are pri- By the beginning of the Arikareean (ϳ29± marily in Florida where a small species, D. 30 Ma), the character of the amphicyonid notionastes, has been identi®ed by fragmen- fauna had begun to change. The North Amer- tary remains coming from a number of Ari- ican temnocyonine amphicyonids ®rst appear kareean ®ssure ®lls and karst sinkholes in the earliest Arikareean (Hunt, 1998b), the (Frailey, 1979). This species is also known most primitive species showing a resem- from east Texas, suggesting a restricted Gulf blance to Daphoenus. The last record of Da- Coastal Plain range (Albright, 1996). Da- phoenus (ϳ28.5 Ma in the Great Plains, ϳ27 phoenodon, however, is better known from a Ma in the John Day beds, Oregon) is almost succession of chronospecies from upper Ari- concurrent with the ®rst appearance of tem- karee and lower Hemingford Group sedi- nocyonines at ϳ29.5 Ma in the John Day ments in western Nebraska and southeastern Formation, Logan Butte, Oregon (®g. 1). Wyoming (Hunt, 1998b). These fossils are Temnocyonines diversify and increase in found in ¯uvial, waterhole, and eolian sedi- size throughout the Arikareean (®g. 1), but ments of a semiarid continental interior. The are absent from earliest Hemingfordian fau- oldest of the Great Plains species is repre- nas and are therefore presumed extinct by sented by an undescribed mandible from the ϳ18.5 Ma. The largest species probably at- type area of the Harrison Formation, esti- tained ϳ40±90 kg. They are best represented mated at ϳ22±23 Ma, and hence close to the in the Arikaree Group of the Great Plains and Oligocene-Miocene boundary. It directly John Day beds of the Paci®c Northwest, with precedes in time a population sample of the rare occurrences from Florida and California. holotype species, D. superbus, from the wa- Temnocyonines are the only group of large terhole bonebed and carnivore dens at Agate carnivorans that bridge the temporal hiatus National Monument (Peterson, 1910; Hunt, that occurs between the Paleogene and Neo- 1990). The genus is known only from North gene large carnivore associations in North America, and possibly is derived from the America (®g. 1). They span the interval be- endemic North American Oligocene da- tween the last occurrence of endemic Da- phoenine Daphoenus. phoenus (ϳ27 Ma) and the ®rst appearance of Daphoenodon and immigrant amphicyon- EARLY NEOGENE AMPHICYONINES ines (ϳ23 Ma). The Oligocene-Miocene boundary, placed at ϳ22.9±23.8 Ma in west- In the early Neogene three European am- ern Europe (Steininger et al., 1989, 1996, phicyonine genera appear successively in the 1997; Shackleton et al., 2000), occurs within New World at ϳ23 Ma (Ysengrinia), ϳ19.2 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 7

Ma (Cynelos), and ϳ18.5±18.8 Ma (Amphi- tition (®g. 2), an upper canine, and a calca- cyon). These North American ®rst occur- neum of a young adult beardog, discovered rences are interpreted as Eurasian immigrants in northwest Nebraska in 1875 by H.C. Clif- because of their earlier presence in Europe ford, at that time in the employ of O.C. and their more advanced stage of evolution Marsh of Yale University (appendix 1). The relative to the earliest Old World species. amphicyonid palate was later designated the There are no plausible ancestors for these holotype of ``Amphicyon'' americanus by Ja- amphicyonines among North American bear- cob Wortman (1901). dogs. Cynelos and Ysengrinia have been re- Wortman's (1901) published paper report- ported previously from the latest Arikareean ed that the palate was found in the ``Loup of western Nebraska (Hunt, 1972, 1998b), Fork beds, Niobrara River, Nebraska'' and dated at ϳ19.2 Ma. Recently discovered ev- did not mention Clifford or the 1875 date of idence of Ysengrinia in older late Arikareean collection, information recorded only in the rocks of western Nebraska, estimated at ϳ23 YPM catalogue. Casts of the palate which I Ma, indicates an earlier entry into North had previously examined in various muse- America. Amphicyon is the last of the three ums were poorly executed. In December genera to appear, ®rst known from early 2000, I examined the original specimen: its Hemingfordian sediments in northern Colo- exceptional preservation has prompted this rado and northwest Nebraska at ϳ18.5±18.8 review of the genus in North America, sup- Ma (Hunt, in press; MacFadden and Hunt, plementing (and superceding in part) my ear- 1998). lier remarks (Hunt, 1998b). Because all other Ysengrinia occurs in both the late and lat- North American specimens of Ysengrinia est Arikareean intervals in North America discovered since 1875 can be attributed to a (ϳ23±18.8 Ma). Cynelos ®rst appears in the single species, Wortman's (1901) species- latest Arikareean (ϳ19.2 Ma), represented by group term serves as the name-bearer for the two teeth found in waterhole bonebeds at hypodigm. Hence, the palate (YPM 10061) Agate Fossil Beds National Monument, becomes the holotype of the North American Sioux County, Nebraska (Hunt, 1972: ®g. species, Ysengrinia americana, comb. nov. 6B, D). Cynelos and Amphicyon are also pre- Following Clifford's discovery of the ho- sent in the early Hemingfordian, but are rare, whereas they are the common large amphi- lotype, no new material of Ysengrinia came cyonines of the late Hemingfordian. The ro- to light in North America until several foot bust Cynelos idoneus is present in the late and limb bones were found in early Miocene Hemingfordian Sheep Creek Formation of upper Arikaree rocks of western Nebraska by western Nebraska where it is accompanied O.A. Peterson from 1904 to 1908. These by the even larger Amphicyon frendens. were initially attributed to large canids by These two genera persist as large carnivorans Peterson (1910). Hunt (1972) later described in the early Barstovian. Cynelos is not found isolated teeth, an edentulous mandible, and in the mid-Barstovian and is presumed to be some postcranials (including Peterson's spec- extinct. Amphicyon survives into the mid- imens), recognizing them as amphicyonids Barstovian at Horse and Mastodon Quarry, and referring them to (?)Ysengrinia Gins- Colorado, but by ϳ14 Ma is also extinct. burg, 1965. Although Peterson (1910) and Amphicyon and Cynelos are replaced in the Hunt (1972) initially attributed these fossils late Barstovian by the amphicyonids Pseu- to the Harrison Formation, Hunt (1978, docyon and Ischyrocyon (Hunt, 1998b), best 1985, 1990) later referred the localities to the represented at sites in the Great Plains and lower part of the overlying Upper Harrison California. Both genera are no longer in ev- beds, based on lithostratigraphic revision of idence by the end of the Clarendonian (ϳ9 the upper Arikaree Group in its type area in Ma). Sioux County. In 1937, collectors from the Frick Labo- HISTORY OF DISCOVERY OF NORTH ratory (AMNH) discovered an associated AMERICAN YSENGRINIA skull, mandible, and postcranials of a large In North America the ®rst record of Ysen- adult Ysengrinia in the Upper Harrison beds grinia is a palate with nearly complete den- of southeastern Wyoming (®g. 3), but it re- 8 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 3. Ysengrinia americana, paratype cranium and associated mandible, F:AM 54147, Upper Har- rison beds, 25 Mile District, latest Arikareean, Goshen County, Wyoming. mained unidenti®ed. This individual (F:AM Miocene waterhole environment in which 54147) demonstrates for the ®rst time an as- scattered skeletal remains of a variety of sociated upper and lower dentition, the form mammals were buried. The teeth and bones of the skull, and a damaged but largely intact of a large amphicyonid similar to Ysengrinia basicranium, features unknown in Old World americana were intermixed with these re- Ysengrinia. The postcranials were limited to mains. In a recent summary of amphicyonid cervical vertebrae and forelimb elements, but diversity in North America (Hunt, 1998b), I nevertheless reveal a short-footed, robust allocated this large Bridgeport amphicyonid skeleton, similar to the postcrania of Amphi- to Ysengrinia. Discovery of the exceptionally cyon (Ginsburg, 1961; Hunt, in press). No preserved palate and dentition of Wortman's complete skull is known from the Old World; holotype of ``Amphicyon'' americanus dem- the Wyoming skull is the ®rst of its kind. onstrates that the early Hemingfordian University of Nebraska excavations from Bridgeport carnivore is better allocated to an- 1974 to 1990 at Harper Quarry and other other taxon (Hunt, in preparation). nearby latest Arikareean sites in western Ne- braska produced additional remains of Ysen- GEOGRAPHIC AND GEOLOGIC grinia (Hunt 1978, 1990). Ysengrinia was DISTRIBUTION OF NORTH AMERICAN common in waterhole and riparian environ- YSENGRINIA ments of this age. In addition to these latest Arikareean fossils, a large collection of iso- All North American specimens of Ysen- lated teeth, mandibles (most edentulous), and grinia are from nonmarine sediments of late unassociated postcranials were excavated by or latest Arikareean age in western Nebraska the University of Nebraska State Museum and southeastern Wyoming (®g. 4). The ear- from the early Hemingfordian Bridgeport liest North American record of Ysengrinia is Quarries, Morrill County, Nebraska, during a mandible with p3±m2 from late Arikareean 1932±1940. These quarries sampled an early ¯uvial sediments at Wildcat Ridge, south of 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 9

Fig. 4. Geographic distribution of Ysengrinia in the North American midcontinent. Localities 1±5, latest Arikareean; locality 6, late Arikareean: 1, Harper Quarry; 2, University Quarry at Agate National Monument and American Museum±Cook Quarry; 3, Morava Ranch Quarry; 4, 25 Mile District of Frick Laboratory, AMNH; 5, Lay Ranch beds (an Upper Harrison paleovalley) at Spoon Butte; 6, UNSM Locality Sf-105; HC, the geographic area where H.C. Clifford collected the holotype (YPM 10061) of Y. americana, possibly from Morava Ranch Quarry (appendix 1). All localities are in strata of the upper Arikaree Group.

Gering, Nebraska (Harrison Formation, esti- Ysengrinia apparently was an important mated age, ϳ23 Ma). scavenger-predator. A latest Arikareean sample of Ysengrinia From higher stratigraphic levels within the includes fossils from the waterhole bonebeds Upper Harrison beds of latest Arikareean (ϳ19.2 Ma: University Quarry at Agate Na- age, only three occurrences are knownÐ(1) tional Monument, Hunt, 1972, 1990; Harper an associated partial postcranial skeleton Quarry, Hunt, 1978; Morava Ranch Quarry, (USNM 186993) from the Lay Ranch beds Coombs and Coombs, 1997; AMNH-Cook (Hunt, 1985) west of Spoon Butte, Goshen Quarry, Hunt, 1972) that occur in the basal County, Wyoming; (2) isolated teeth and Upper Harrison beds along the valley of the postcranials of one or two individuals from Niobrara River in Sioux and Box Butte the Lay Ranch beds east of Spoon Butte; and Counties, Nebraska. If Clifford's holotype (3) the associated skull, mandible, and partial palate of Y. americana was also found at Mo- skeleton (F:AM 54147, paratype of Y. amer- rava Ranch Quarry, which seems probable, icana) from Upper Harrison beds, Goshen it is of the same age. Seven to ten individuals County, Wyoming, ϳ15 miles (24 km) north- are known from these waterholes where west of Spoon Butte. 10 AMERICAN MUSEUM NOVITATES NO. 3384

Ysengrinia americana is accompanied by form, and a few phalanges (Hunt, 1972: ®gs. other large carnivorans in the latest Arika- 8, 9, 10A, 11). The depositional environment reean Upper Harrison fauna of western Ne- of Morava Ranch Quarry fossils has been de- braska and southeastern Wyoming. Ysengri- scribed by Coombs and Coombs (1997) as a nia americana, Daphoenodon superbus, and waterhole in a ¯uvial setting. The diagnostic a temnocyonine are found in the Agate Quar- M1 of Ysengrinia americana is known from ries local fauna (Hunt, 1985, 1990), collected Morava Ranch Quarry and from American from waterhole deposits and carnivore dens Museum±Cook Quarry (Hunt, 1972: ®g. at the base of the Upper Harrison in Sioux 10A, B). These molars are nearly identical to County. At higher stratigraphic levels in the the M1 of the holotype and paratype. Despite Upper Harrison beds of southeastern Wyo- the lack of teeth in the Morava Ranch man- ming, Y. americana and two large unde- dible, its deep-jawed, robust form, the size scribed amphicyonid species are associated and spacing of the alveoli, and the placement with faunas age-equivalent to the Niobrara of the mental foramina demonstrate a corre- Canyon local fauna (Hunt, 1985, 1990). Also spondence to the mandible of the Y. ameri- present in the Upper Harrison is the giant cana paratype. mustelid, Megalictis ferox (Hunt and Skol- Although Ysengrinia is uncommon in Up- nick, 1996), and two species of large tem- per Harrison sediments (Lay Ranch beds, nocyonine amphicyonids representing the Hunt, 1985) ®lling the Lay Ranch paleoval- terminal members of their respective lineag- ley at Spoon Butte, the few scattered occur- es. Both paleofelids (Nimravidae) and neo- rences include an associated partial hindlimb felids (Felidae) are absent from these assem- that establishes the proportions of femur to blages (Hunt and Joeckel, 1988), and con- tibia, and provides insight into the functional sequently several of these arctoid carnivorans anatomy of the hindfoot. This partial skele- apparently occupied the niches for large cat- ton of a large individual, probably male, was like predators. discovered and excavated in 1972 west of The Harper Quarry waterhole assemblage Spoon Butte by R.J. Emry and M.F. Skinner (Harper Quarry local fauna: Hunt, 1978, for the Smithsonian Institution. In the same 1985, 1990) produced the most numerous paleovalley east of the butte, a partial man- postcranial remains of Y. americanaÐal- dible of a much smaller individual was found though at least four individuals are represented, there were no articulated elements. by UNSM in 1983, suggesting that sexual No crania or mandibles have been found, dimorphism was an attribute of Y. americana only isolated teeth. Scavenging at the water- populations. Evidence of dimorphism occurs hole is everywhere evident, suggesting that not only in the Lay Ranch beds in south- skulls were fragmented and scattered. eastern Wyoming but also at Harper Quarry Ysengrinia americana is present but rare in northwest Nebraska where marked size in the waterhole bonebeds in the vicinity of differences are evident in some postcranial Agate Fossil Beds National Monument bones. (Hunt, 1972). A robust metacarpal was found Finally, a large ``canid'' humerus (CM in the waterhole bonebed at University Hill 2400) was reported by Peterson (1910: ®g. in 1904, but no remains have come from the 56) from a quarry 8±10 miles east of the Ag- quarries at Carnegie Hill and the nearby car- ate Quarries. This humerus was later re®g- nivore den site (Hunt et al., 1983; Hunt, ured and described by Hunt (1972) and at- 1990). At the American Museum±Cook tributed to (?)Ysengrinia. Peterson's quarry Quarry waterhole, located a few kilometers has never been relocated, and no other fossils north of the Agate waterhole bonebed, Ysen- from this quarry were identi®ed in the col- grinia is represented by a calcaneum and lections of the Carnegie Museum (Pitts- M1. burgh), despite Peterson's (1910: 262) state- Fragmentary remains of Y. americana at ment that the ``quarry . . . contains a similar Morava Ranch Quarry include an edentulous fauna to that of the Agate Spring Fossil mandible (F:AM 25423), isolated M1, a par- Quarries''. The anatomy of the distal humer- tial innominate, distal humerus, ectocunei- us indicates referral to Y. americana. 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 11

SYSTEMATICS ®g. 17). The m2 is elliptical in occlusal view, ORDER CARNIVORA BOWDICH, 1821 robust, but not enlarged relative to m1; the m2 trigonid is large and moderately elevated DIVISION ARCTOIDEA FLOWER, 1869 relative to the short, low talonid (the rect- FAMILY AMPHICYONIDAE TROUESSART, 1885 angular m2 of Amphicyon, Cynelos, and most species of Daphoenodon differs in having a Ysengrinia Ginsburg, 1965 more elongated, wider talonid). The principal TYPE SPECIES: Ysengrinia gerandiana (Vi- trigonid cusp is a massive, slightly labially ret). placed protoconid. A thin crest runs antero- INCLUDED SPECIES: Ysengrinia americana lingually from the protoconid to form an ar- (Wortman), comb. nov., Y. tolosana (Noulet), cuate rim at the front of the tooth that ter- Y. depereti (Mayet), Y. valentiana Belinchon minates at the location of a very reduced or and Morales, ?Y. ginsburgi Morales, Pick- absent paraconid. The swollen metaconid is ford, Soria, and Fraile. much smaller than the taller protoconid and KNOWN DISTRIBUTION: Early Miocene (late is separated from it by a shallow cleft or val- to latest Arikareean) of southeastern Wyo- ley. The posteriorly tapering m2 talonid ap- ming and western Nebraska; late Oligocene- pears to be much reduced relative to the ro- early Miocene of France (MP 30, MN1±3); bust trigonid; the m2 talonid displays a early Miocene of Germany; late early Mio- prominent, ridged, labially placed hypocon- cene of Spain (MN4); ?late early Miocene of id. There is no entoconid. The labial faces of southwest Africa (MN4). the m2 hypoconid and protoconid are DIAGNOSIS: Mid-sized to large (ϳ40±150 smoothly rounded whereas the inner faces of kg) deep-jawed amphicyonines (anteriorly these cusps are lingually inclined and ¯at. deep mandibles do not occur in daphoenines) The dental formula is 3-1-4-3/3-1-4-3 (tem- in which the posterior molars (M2±3, m2±3) nocyonine amphicyonids and canids have are not enlarged to the degree observed in lost M3). mid-Miocene Amphicyon (table 1). M2±3/m2±3 are not enlarged, but remain Anterior premolars (p1±3, P1±3) are low, subordinate in size to M1/m1. Thus, Ysen- reduced, differing from North American tem- grinia differs from both Old and New World nocyonines and Daphoenodon in which the mid-Miocene Amphicyon species (Old World anterior premolars are well-developed; p4 in A. giganteus, A. major, New World A. fren- Ysengrinia is not reduced, has a tall principal dens, A. ingens) in lacking greatly enlarged cusp equal in height to the m1 paraconid, and posterior molars. Ysengrinia differs from a well-developed posterior accessory cusp contemporary species of Cynelos in being above an expanded cingulum shelf; p4 has a much larger. rounded posterior margin (Daphoenodon has EUROPEAN SPECIES OF YSENGRINIA: Ysengri- a squared posterior margin) and, as noted by nia was created by Ginsburg (1965) for two Bonis (1973), a nearly rectilinear mesial face. mandibles and a tentatively referred rostrum The m1 is robust, wide, carnassiform, with from St.-GeÂrand-le-Puy (Allier, France) that massive trigonid and prominent low talonid had been originally referred by Viret (1929) (m1 in contemporary Cynelos is much small- to Pseudocyon gerandianus. Viret did not er and less robust); a slightly swollen m1 present a compelling rationale for assigning metaconid is present and is situated at the the three specimens to Pseudocyon. Ginsburg same height as the paraconidÐit becomes pointed out that the rostrum could not rep- somewhat reduced in Y. depereti but is pre- resent Pseudocyon, since upper molars had sent in Amphicyon and Daphoenodon; the been found in association with a typical low- m1 talonid has a prominent labially placed, er dentition of Pseudocyon (Kuss, 1965: ®g. ridgelike hypoconid, bordered internally by a 79) at Ponsan-Soubiran, France, and these low shelf lacking a de®ned entoconid cusp. molars were different from those in Viret's The m2 is considered diagnostic and oc- rostrum. Therefore, Ginsburg (1965) created curs in a mandible of Y. gerandiana (MGL a new genus, Ysengrinia, for the mandibles St.-G. 2848), the type species of Ysengrinia, and rostrum from St.-Gerand, and the species ®gured by Viret (1929: pl. VII, ®g. 1, text- thus became Ysengrinia gerandiana (Viret). 12 AMERICAN MUSEUM NOVITATES NO. 3384

Ginsburg (1966) next placed two addition- zones MP30±MN1, Y. gerandiana in MN2, al species in Ysengrinia:``Amphicyon'' to- Y. depereti in MN3, and the recently discov- losanus Noulet from the Aquitanian of Paul- ered Y. valentiana from Spain (Belinchon hiac, and ``Pseudocyon'' depereti Mayet and Morales, 1989) in MN4 (table 1). from the early Burdigalian of Chilleurs-aux- Neither Viret (1929) nor Ginsburg (1965) Bois. These two species were previously re- selected a type specimen from the two man- ferred to Arctamphicyon by Kuss (1965), but dibles and the rostrum comprising Viret's hy- this assignment was sensibly questioned by podigm of Y. gerandiana. Although Kuss Bonis (1973), who noted that because the ho- (1965: 141f.) placed this hypodigm in Pseu- lotype of Arctamphicyon is an isolated M2 docyonopsis as a subspecies (P. landesquei from the Siwaliks, and the types of tolosanus gerandianus), a generic attribution later re- and depereti are mandibles without associ- futed by Bonis (1973), he did select from ated upper dentitions, comparison was not Viret's hypodigm the mandibular fragment possible. Referral of these species to Arctam- with p2±m1 (FSL 213828: Viret, 1929: pl. phicyon is without merit. Nor can tolosana, VII, ®g. 3) as the holotype of gerandiana depereti,orgerandiana be placed in Pseu- (appendix 2). docyon as this genus is presently de®ned.2 Only a few fossils attributed to Ysengrinia In his monograph on Aquitanian mammals have been reported from the Aquitanian of of the Agenais district, France, Bonis (1973: Germany. The mandible from FloÈrsheim re- 97±100) reviewed Ysengrinia tolosana.He ferred to Y. tolosana by Bonis (1973) is sim- included in it Aquitanian fossils from Le ilar to the Paulhiac mandible, and displays a Cammas, France (the holotype mandible of p4 resembling that of the North American Noulet); from Paulhiac, France (the lower paratype of Ysengrinia americana. A pair of teeth of a single individual except for a re- mandibles from Ulm-Westtangente, ®rst il- ferred canine); and a mandible from FloÈrsh- lustrated by Heizmann (1992; also Heizmann eim, Germany. These fossils established the et al., 1996), are similar to both North Amer- characteristics of the lower dentition. Bonis ican and European mandibles of Ysengrinia. (1973: 99) suggested that Viret's mandible These mandibles were recently placed in a (with m2, MGL St.-G. 2848) of Y. gerandi- new genus, Crassidia, by Heizmann and ana might be included in Y. tolosana, based Kordikova (2000), who also placed Crassi- on the similar size and form of m2 in the two dia in a new tribe, Ysengriniini, together species. However, Ginsburg (1999), Morales with Ysengrinia and Amphicyonopsis. et al. (1998), and Ginsburg et al. (1991) con- The mandibles of Crassidia are associated tinued to employ Y. gerandiana as a species with only a few upper teeth: P3±4 and an M1 distinct from Y. tolosana. Ginsburg (1999) fragment. However, Heizmann and Kordikova recognized Y. tolosana in European mammal also decided that the holotype of Amphicyon intermedius H. von Meyer, 1849, an isolated 2 Pseudocyon sansaniensis is based on a mandible M1 from the Aquitanian SuÈûwasserkalk near from Sansan, an apparent female, and on a referred male Ulm, Germany, probably belongs to the same mandible from Ponsan-Soubiran (Kuss, 1965: ®g. 79). species as the mandibles. For this material These Pseudocyon mandibles display an m2 trigonid they established the species Crassidia inter- crowded to the front of the tooth, and a long m2 talonid with a relatively ¯at occlusal surface. The m2 hypoconid media. Meyer's M1 is similar in size and form is a low cusp placed close to the labial margin of the to M1 of Y. americana (Hunt, 1972: ®g. 10A), tooth. Moreover, the principal cusp of p4 is low, well but differs in lacking the thickened lingual below the height of the m1 paraconid, whereas in Ysen- cingulum of the North American species and grinia it is a tall cusp approximating the m1 paraconid its distinctive placement posterolingual to the in height. In Ysengrinia the m2 trigonid occupies the entire anterior half of the tooth, the cusps are not crowd- protocone. No complete upper molars are un- ed to the front of the tooth, and the short talonid has a ambiguously associated with lower teeth of broad, labial hypoconid occupying more of the talonid Ysengrinia in Europe. surface than in Pseudocyon. The m2 form and reduced In addition to Ysengrinia, there were other p4 distinguish Pseudocyon from Ysengrinia. Although Pseudocyon eventually entered North America at ϳ15.5 large beardogs in the Aquitanian of western Ma (Hunt, 1998b), it does not occur in Arikareean or Europe. Most of these fossils are from Hemingfordian faunas of the New World. France. In the Agenais district, Bonis (1973) 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 13

TABLE 1 Dental Measurements (in mm) of North American and European Species of Ysengrinia

recognized a true Amphicyon at Laugnac cyon crassidens. Bonis (1973) noted a num- (MN 2b, ϳ35 km south of Paulhiac), cur- ber of features of the lower dentition that dif- rently designated as Amphicyon laugnacensis fered from the large amphicyonines of the (Ginsburg, 1989: 104; 1999: 116), and also Agenais. My examination of the holotype a large anteriorly deep mandible from Gar- m1, a maxilla, and a cast of a mandible from rouch (MN1), the holotype of Amphicyon as- Viret's hypodigm (1929: pl. 3) in Lyon, in- trei (Kuss, 1962; Ginsburg, 1999: 144). Fos- dicates that these fossils are not referrable to sils of large Aquitanian beardogs are also Ysengrinia. Recently, Heizmann and Kordi- known from the Allier basin, France, north- kova (2000) placed Viret's specimens of A. east of the Agenais. Viret (1929) described crassidens in Crassidia. remains of a large deep-jawed amphicyonine AFRICAN AND ASIAN SPECIES OF YSENGRINIA: from Langy, which he assigned to Amphi- Two maxillae (one edentulous) and a man- 14 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 5. Holotype dentition of Ysengrinia americana (Wortman, 1901), YPM 10061, upper Arikaree Group, northwest Nebraska: A, left P2±M2, M3 alveoli; B, right P3±M3. Stereophotographs. Scale bars, 1 cm. dible from the Arrisdrift fauna, Namibia proportionately from these teeth in Y. amer- (MN4a, early Miocene), were recently re- icana: the P4 is smaller, M1 larger, and M2 ferred to Ysengrinia ginsburgi by Morales et much smaller and narrower than these teeth al. (1998). If correctly assigned, this is the in North American Ysengrinia, and they do ®rst and only record of the genus in Africa. not seem to correspond to expected upper Heizmann and Kordikova (2000), however, dentitions of Y. tolosana and Y. gerandiana questioned referral of the holotype mandible from the equivalent interval (MN1±2) in Eu- to Ysengrinia based on features of p4±m2 rope. Because the upper dentiton of Euro- that differ from most species of the genus. pean Ysengrinia is not certainly known, more There are two Asian records of Ysengri- complete material will be required to con®rm nia: a maxilla with P4±M2, from the upper the presence of the genus in Asia. part of the Askazansor Formation, Betpak- dala, Kazakhstan (early Miocene, MN1±2, Ysengrinia americana (Wortman, 1901), Bonis et al., 1997), and an isolated M1 from new combination the Korematsu Formation (ϳ15.6±16.3 Ma), Figures 2, 3, 5±7, 9±22, 24A, table 1 southwestern Japan (Kohno, 1997). The Jap- anese molar, as noted by Kohno, is quite HOLOTYPE: YPM 10061, palate with right young to belong to the genus, which previ- P3±4, M1±3, alveoli for P1±2; left C, P2±4, ously was not recorded in rocks younger than M1±2, alveoli for P1 and M3 (®gs. 2, 5). The ϳ17 Ma. The form of the molar differs from Yale catalogue also records a calcaneum with M1 of Y. americana, but is extremely similar the palate, but it was not with the holotype to M1 of Hemingfordian Cynelos (e.g., Cy- in the Yale collection, and Wortman (1901) nelos idoneus, holotype maxilla, AMNH does not mention a calcaneum in his initial 18912), whose age better corresponds to the description. age of the Korematsu Formation. The P4± HOLOTYPE LOCALITY: From the Yale Pea- M2 in the maxilla from Kazakhstan differ body Museum Catalogue of Mammalia, Nos. 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 15

10001 to 14975: ``YPM 10061, accession no. Morava Ranch Quarry, Box Butte County, 704, H.C. Clifford, 1875, palate and teeth, Nebraska; American Museum±Cook Quarry calcaneum''. Probably found by Clifford in and University Quarry, Sioux County, Ne- upper Arikaree rocks of the Niobrara River braska; and some specimens from the Lay valley, northwestern Nebraska, near the Sid- Ranch beds, an Upper Harrison paleovalley ney±Red Cloud Agency trail in March 1875. ®ll extending from Goshen County, Wyo- The holotype was apparently collected from ming, eastward into Sioux County, Nebraska. an 1875 excavation that was reopened in From the Harrison Formation: UNSM Lo- 1940 by the Frick Laboratory as the Morava cality Sf-105, Wildcat Ridge, Scottsbluff Ranch Quarry and was further explored in County, Nebraska (®g. 4). 1975 by M.C. Coombs (appendix 1). HARPER QUARRY: Dental: all isolated HOLOTYPE HORIZON: Based on preserva- teethÐM2, l. (UNSM 44674); I3, l. (UNSM tion of the teeth and palate, and on infor- 44687); upper C, r. (UNSM 44670); lower C, mation from the Yale Peabody Museum ar- r. (UNSM 44672); m1 talonid, r. (UNSM chives, the stratigraphic units from which 44671); m2, r. (UNSM 44673); m3, l. Clifford could have obtained the holotype are (UNSM 44676); Postcranial: innominate, the early Miocene Harrison Formation and partial, l. (UNSM 44626); innominate, par- Upper Harrison beds of the upper Arikaree tial, r. (UNSM 44627); baculum (UNSM Group. If the holotype is in fact from Morava 44629); femur, r. (UNSM 44624); femur, Ranch Quarry, it was collected in the basal proximal, r. (UNSM 44625); femur, l. Upper Harrison beds. (UNSM 44690); tibiae, l. (UNSM 44620, PARATYPE: F:AM 54147, a complete skull 44622); tibiae, r. (UNSM 44621, 44623); cal- with right I3, C, P1±M2, left damaged I2±3, caneum, l. (UNSM 44692); calcanea, r. C, damaged P1±3, intact P4±M2; M3 pre- (UNSM 44631, 44632); astragalus, l. sumably present, but lost from skull (®gs. 3, (UNSM 44630); metatarsal 1, r. (UNSM 6). The skull is associated with a right man- 44640); metatarsal 1, proximal, l. (UNSM dible with worn canine, damaged p1±2, al- 44641); metatarsal 2, l. (UNSM 44637, veoli for p3, and intact p4±m3 (®gs. 3, 7). 44639); metatarsal 3, r. (UNSM 44636); Associated postcranials: axis, third to ®fth metatarsal 4, l. (UNSM 44635); metatarsal 4, cervical vertebrae, right humerus, proximal r. (UNSM 44638); metatarsal 5, r. (UNSM left and right ulnae, distal left radius, left sca- 44633, 44634); scapula, partial, l. (UNSM pholunar, a proximal phalanx (pathologic), 44607, 44608); humerus, l. (UNSM 44606); right metacarpal 1, left metacarpal 5, and a ulnae, r. (UNSM 44603±44605); radii, l. distal metapodial. (UNSM 44600, 44601); radius, r. (UNSM PARATYPE LOCALITY: 25-Mile District of 44691); juvenile radius, diaphysis, r. (UNSM the Frick Laboratory (AMNH), Goshen 44602); scapholunars, r. (UNSM 44609, County, Wyoming, collected by C.H. Falken- 44693); scapholunar, l. (UNSM 44610); un- bach in 1937 from the ``Middle Brown ciform, r. (UNSM 44666); metacarpal 2, l. Sand''. (UNSM 44616); metacarpal 2, r., without PARATYPE HORIZON: Detailed stratigraphic distal end (UNSM 44619); metacarpal 4, r. information identifying the collecting locali- (UNSM 44617); metacarpal 4, l., without ty was not recorded in 1937; however, the distal end (UNSM 44618); metacarpal 5, r. ``25-Mile District'' was Falkenbach's ®eld (UNSM 44611, 44614, 44615); metacarpal 5, term for a collecting area 18 miles south and r., proximal (UNSM 44613); metacarpal 5, l. 7 miles east of the town of Lusk, Goshen (UNSM 44612); proximal phalanges (UNSM County, Wyoming. Exposures that he named 44656±44659, 44665); median phalanges ``Middle Brown Sand'' in this area are re- (UNSM 44660±44664, 44678); atlas verte- ferred to the Upper Harrison beds of Peterson brae (UNSM 44644, 44645); cervical verte- (1907, 1909; Hunt, 1990). The Upper Har- bra (UNSM 44642); thoracic vertebra rison beds are of latest Arikareean age. (UNSM 44643); lumbar vertebrae (UNSM REFERRED SPECIMENS: From the Upper 44646±44655, 44668); caudal vertebra, par- Harrison beds: Primarily from Harper Quar- tial (UNSM 44667); sacrum (UNSM 44628). ry, Sioux County, Nebraska, but also from NIOBRARA CANYON: Dental: partial 16 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 6. Ysengrinia americana, paratype cranium, F:AM 54147, Upper Harrison beds, 25 Mile Dis- trict, latest Arikareean of Goshen County, Wyoming. A, dorsal view; B, ventral view. maxilla with M1, broken P4, l. (F:AM MORAVA RANCH QUARRY: Dental: 54149), from volcaniclastic loess lithofacies, isolated M1, l. (F:AM 25420); mandible, type area, Upper Harrison beds, Sioux Coun- edentulous, r. (F:AM 25423); Postcranial: ty, Nebraska. innominate, r. (ACM 9761); humerus, distal, 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 17

Fig. 7. Mandibles of Daphoenodon superbus (UNSM 44688, Harper Quarry) and Ysengrinia americana (paratype, F:AM 54147). A, lateral view; B, medial view. 18 AMERICAN MUSEUM NOVITATES NO. 3384 l. (F:AM 25421); ectocuneiform, r. (ACM drainage in the company of numerous other 9390); proximal phalanges (F:AM 25433, late Arikareean mammals. ACM 9392, and F:AM ®eld no. Har. 211- DIAGNOSIS: Upper molars particularly di- 80); median phalanx (F:AM ®eld no. Har. agnosticÐM1 with occlusal outline of isos- 211-80). celes triangle, paracone taller than metacone, AMERICAN MUSEUM±COOK QUAR- protocone a low V-shaped platform with lin- RY: Dental: isolated M1, l. (AMNH 81049); gually directed apex, arms of the V continue Postcranial: calcaneum, r. (CM 2211). as thin enamel ridges to the bases of para- UNIVERSITY QUARRY (Agate Fossil cone and metacone; there is no strong de- Beds National Monument): Postcranial: velopment of a metaconule as occurs in Am- metacarpal 5, r. (CM 1897). phicyon; a thickened posterolingual cingu- LAY RANCH BEDS: West of Spoon lum is particularly characteristicÐthere is no Butte, Goshen County, Wyoming: (1) an as- thickening of the anterior cingulum which is sociated partial skeleton and isolated canine not enlarged and merges smoothly with the of a single individual (USNM 186993). Den- expanded posterolingual cingulum; a shallow tal: upper C, r.; Postcranial: right and left basin occurs between the posteromedial base scapulae, the left femur, tibia, and astragalus, of the protocone and the enlarged posterolin- a navicular and pisiform; (2) an isolated gual cingulum; M2 noticeably smaller than proximal phalanx (UNSM 6030-79). M1; M2 metacone slightly to strongly re- East of Spoon Butte, Sioux County, Ne- duced relative to paracone; metaconule not braska: (1) isolated lingual half of M1 and a enlarged; well-developed lingual cingulum metatarsal 2, l. (both UNSM 6109±79); (2) surrounding protocone; M3 much smaller partial right mandible with p4 and alveoli of than M2, apparently undergoing reduction the canine and p1±3 (UNSM 7131-83). (in contrast to Amphicyon and Cynelos); P4 UNSM LOCALITY Sf-105: Dental: (1) robust with slightly reduced anterolingually mandible, r. with p3±m2 (UNSM 26584). directed protocone; paracone with sharp KNOWN DISTRIBUTION: Late to latest Ari- enamel ridge descending anterior face and kareean of Sioux, Box Butte, and Scottsbluff fusing with cingulum; P4 parastylar cusp ab- counties, Nebraska, and Goshen County, sent (present in Amphicyon) but short length Wyoming (®g. 4). Harper Quarry, University of cingulum enlarged immediately labial to Quarry, and the American Museum±Cook terminus of descending enamel ridge, creat- Quarry are excavated in waterhole bonebeds ing a pseudoparastyle; anterior premolars that ®lled with tuff, ®ne sand, silt, and lime somewhat reduced; P3 narrow, its length ex- mud (Hunt, 1978, 1990). Morava Ranch tended by developed anterior and posterior Quarry occurs in a ®ne-grained ¯uvial chan- cingula; vertical crease in the enamel occurs nel ®ll (Coombs and Coombs, 1997). Fossils at posterolingual corner of P3; snout short from these quarries comprise an older Upper and constricted at level of P2 (width at P2, Harrison fauna from the base of the unit. ϳ50 mm, width at M1, ϳ92±98 mm in ho- Fossils from the Lay Ranch beds near Spoon lotype and paratype); P1±2/p1±2 small; an- Butte are slightly younger and come from terior mandible deep below p1±3; prominent ®ne-grained ¯uvial sediments ®lling a broad p4 with posterior accessory cusp but without Arikaree paleovalley of Upper Harrison age anterior accessory cusp; m1 robust with tall (Hunt, 1985, 1990). The locality that pro- trigonid, prominent metaconid, talonid dom- duced the paratype skull, mandible, and skel- inated by tall, ridgelike, labially placed hy- eton can only be approximately located; poconid and no entoconid; m2 not enlarged however, matrix on the fossils indicates that relative to m1 (m2 description as for the ge- they came from a volcaniclastic loess litho- nus); m3 a robust, broad, ¯at enamel plat- facies of the Upper Harrison beds, and ex- form. Upper canine slightly elongate, with plains the relative degree of completeness of sharp posterior and anterolingual enamel this skeleton (see Hunt, 1990, for descrip- ridges. tions of Upper Harrison lithofacies). The Distinguished from Y. depereti by smaller mandible from UNSM locality Sf-105 was average size of m1±m2 (®g. 8, table 1), and found in a ¯uvial channel ®ll of a major by m2 form; from Y. tolosana by the form 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 19

Fig. 8. Lower molar dimensions (m1, m2, length and width in mm) of North American Ysengrinia americana and European species of Ysengrinia. A sample of the latest Arikareean amphicyonid Da- phoenodon superbus is included to demonstrate the extent of variation in these measurements in a single species from a limited stratigraphic interval. Statistical data for D. superbus, m1 length and width (N ϭ 13): range, 24.2±27.4 mm, 11.1±12.0 mm; mean, 25.6, 11.5 mm; 1 SD, 0.93, 0.25. D. superbus,m2 length and width (N ϭ 8): range, 13.9±17.4 mm, 9.8±11.5 mm; mean, 15.1, 10.4 mm; 1 SD, 1.20, 0.57. of p4. The p4 in Y. americana lacks the near- pearance of the skull: the small volume of ly rectilinear mesial face of Y. tolosana and the braincase is remarkable relative to the is longer relative to m1 length than in most size of the skull, resulting in a particularly Y. tolosana and Crassidia intermedia (p4/m1 prominent sagittal crest for attachment of ratio, Y. americana, 0.66±0.71; Y. tolosana, massive temporal muscles, and an exception- 0.61; C. intermedia, ϳ0.62; however, the ally low occipital region of very small area. FloÈrsheim mandible of Y. tolosana has a ratio The frontal region is only moderately in¯ated of ϳ0.70, based on measurements in Kuss, and its surface is not domed, but is rather 1965). In the Y. americana paratype (F:AM ¯at. The basicranium is anteroposteriorly 54147), a ®ne enamel ridge runs from the short, but is poorly preserved, revealing little principal cusp of p4 directly to the anterior detail; the mastoid processes were at least edge of the tooth and is not diverted toward moderately developed. The auditory bulla the lingual face as in Y. tolosana; in other Y. was evidently ossi®ed and of small volume, americana individuals the ridge is more sim- with a laterally prolonged bony external au- ilar in its course to Y. tolosana. Ysengrinia ditory meatus ϳ1 cm in length. tolosana also tends to have a wider m2 than The dentitions of the holotype palate (®g. Y. americana (®g. 8). 5) and paratype skull (®g. 9), with its asso- DESCRIPTION: The paratype cranium is the ciated deep, robust mandible, show that Y. only complete skull of the genus (®gs. 3, 6). americana had reduced anterior premolars. It is distinguished from its contemporary, This differs from the species of Daphoeno- Daphoenodon, by larger size, greater basilar don and the large contemporary temnocyon- length of the skull (ϳ30 cm), short snout ine amphicyonids of the early Miocene, all with reduced premolars, and by the relatively of which retain fully developed premolars. small braincase surmounted by a long, dor- In North America there is only a single soventrally prominent sagittal crest. Before it individual (F:AM 54147, paratype) with an was recognized as Ysengrinia, several inves- associated upper and lower dentition (®gs. 3, tigators commented on the ``primitive'' ap- 9B). The skull has a short rostrum, broad- 20 AMERICAN MUSEUM NOVITATES NO. 3384 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 21 ened at the level of the large canines, an ex- sible trend toward reduction of M2±3 in panded frontal region, and a small braincase time. The protocone forms the lingual apex relative to overall cranial size. M1±2 in the of a low V-shaped platform which is sur- paratype and holotype are particularly diag- rounded by the thickened tonguelike lingual nostic (®gs. 5, 9); isolated M1s of this type cingulum. M2 varies in anteroposterior are also reported from the American Muse- length in different individuals but not in the um±Cook Quarry and Morava Ranch Quarry pattern of its cusps. (Hunt, 1972: ®g. 10A, B). M2 is not enlarged M3 is preserved only in the holotype, relative to M1. M1 is transversely extended, where it is markedly smaller than M2. The forming an isosceles triangle in occlusal paracone, metacone, and protocone are very view, with a distinctive lingual cingulum low cusps, the metacone reduced relative to characteristic of the North American species. the others. M3 is surrounded by a distinct The cingulum is thin anterior to the proto- cingulum, thicker lingually and in the par- cone but is thickened and enlarged lingual astylar area. and posterolingual to that cusp. A shallow P4 is a relatively narrow shearing carnas- basin separates the thickened posterolingual sial with a low but distinct protocone. The cingulum from the base of the protocone. most distinctive feature of P4 in the holotype The M1 paracone is taller than the metacone; is a ®ne enamel ridge that descends the an- its anterolingual face has a prominent wear terior face of the paracone to the cingulum. facet (F:AM 25420) produced by shear Labial to this point of contact the cingulum against the posterior surface of the m1 tri- is conspicuously thickened as a pseudopar- gonid. In older individuals this cusp cuts a astyle. Although P4 is known only in the ho- deep groove in the labial face of the m1 tal- lotype and paratype of Y. americana, it dif- onid (visible in paratype m1). The protocone fers from the relatively shorter, more robust forms the lingual apex of a V-shaped plat- P4 of New World Amphicyon which invari- form whose arms surround a shallow proto- ably displays a true parastylar cusp at the cone basin. The arms of the V continue lat- base of the paracone. M1 length/ P4 length erad as thin ridges (pre- and postprotocristae) ratios of the para- and holotype of Y. amer- to the bases of the paracone and metacone. icana are 0.76 and 0.82, respectively, where- The paraconule and metaconule are either as in early Hemingfordian Amphicyon (F:AM absent or only weakly developed. The en- 25400, UNSM 1570-59) this ratio is 0.92. larged metaconule of Amphicyon does not P1±3 are reduced in Y. americana, de- occur. M1 is similar in form to the holotype creasing in size from P3 to P1, each with a M1 of ``Amphicyon'' intermedius from the low, central cusp and no accessory cusps German Aquitanian (Kuss, 1965: ®g. 75, (®g. 9B). P2±3 each have two roots; P1 is SMNS 4568), recently designated the holo- single-rooted. P3 in the holotype shows a se- type of Crassidia intermedia (Heizmann and lective thickening of the cingulum at the an- Kordikova, 2000), but differs in occlusal de- terior and posterior ends of the tooth, and tails. also a sharp crease in the enamel of the pos- M2 is smaller than M1, subrectangular, terolingual face that continues into the cin- and transversely extended by an expanded gulum. P3 in Y. americana is taller and lingual cingulum. The metacone is smaller somewhat narrower than P3 in Amphicyon. than the paracone, less so in the holotype There are short diastemata between P1±P2 M2, more so in stratigraphically younger in- (ϳ5±6 mm) and P2±3 (ϳ7 mm). The snout dividuals (F:AM 54147), suggesting a pos- is conspicuously narrowed at the level of P2.

← Fig. 9. A, Upper dentition of a daphoenine amphicyonid, F:AM 27568, Upper Harrison beds, 18 Mile District, Goshen County, Wyoming. This species with developed premolars is representative of all other Upper Harrison amphicyonids in contrast to the reduced premolars of Ysengrinia. Scale bar, 1 cm. B, Upper dentition of Ysengrinia americana, paratype, F:AM 54147, Upper Harrison beds, 25 Mile District, Goshen County, Wyoming. Note reduced premolars 1±3. 22 AMERICAN MUSEUM NOVITATES NO. 3384

I2, much smaller than I3, exists only as a broken root; I1 was present but was lost from the premaxilla. The mandible is represented by the paratype (®g. 7) and a previously described edentulous mandible (F:AM 25423) from Morava Ranch Quarry (Hunt, 1972: ®gs. 8, 9). The depth of the paratype mandible is remarkable: 56 mm below the m2 trigonid, 50.7 mm below p2 (the holotype of Daphoenodon superbus, a female, CM 1589, measures 30.3 and 24.5 mm, respectively; a large male D. superbus, UNSM 700-82, measures 38.6 and 29.5 mm). Both the holotype and F:AM 25423 have a broad shallow trough, ϳ2cm in greatest width, extending along the length of the internal surface of the mandible from below p3 to a short distance behind m3. The considerable force developed by the masseter complex during occlusion of the carnassials and molars is indicated by the deep masse- teric fossa bordered by conspicuously thickened ventral and anterior margins of the ascending ramus. A rugose angular process Fig. 10. Stereophotographs of unworn right upper canine, Ysengrinia americana, UNSM projects backward and is de¯ected medially. 44670, Harper Quarry, latest Arikareean, Sioux Only the medial half of the robust articular County, Nebraska. Lateral view. Scale bar, 1 cm. condyle is preserved; it is placed at the level of the toothrow. Characteristic of the species are two large Upper and lower canines of the paratype close-spaced mental foramina ϳ1 cm apart are robust teeth, blunted by heavy wear. on the labial surface of the mandible: the Abrasion by the lower canine has produced posterior foramen occurs below the anterior a ¯at wear surface along the length of the root of p3, the anterior foramen below p2. anterointernal face of the upper canine. The A partial mandible of Y. americana (®g. posterior face of the lower canine is recip- 11, UNSM 26584) from UNSM locality Sf- rocally grooved by the upper canine, and the 105 lacks the ascending ramus and ventral anterointernal face of the lower canine is border so that the depth of the jaw cannot be deeply worn by the action of the large I3. An determined. However, p3±m2 are well-pre- unworn upper canine (®g. 10) from Harper served and unworn (®g. 12) and show a Quarry is 103 mm in length; at the crown marked similarity to these teeth in Y. tolo- base the anteroposterior length is 23.3 mm, sana (NMB Pa 951) from Paulhiac. Both in and width is 17.4 mm; crown height is 45.8 UNSM 26584 and in the paratype, p1±3 are mm. Thin sharp enamel ridges traverse the reduced in size relative to the posterior cheek length of the posterior and anterolingual fac- teeth. Only alveoli and roots are preserved in es of the upper canine. This canine is iden- the paratype, but their size and spacing in- tical in form and size to the unworn upper dicate that they progressively diminished in canine of the holotype (YPM 10061). The size from p3 to p1. The p2 was a very small anteriorly deep, massive mandible of Y. (length, 8.5 mm in paratype; alveolus length, americana (F:AM 54147, F:AM 25423) is in 6.2 mm in UNSM 26584), low, elliptical part the product of the development of robust tooth with a single apical cusp. canines in this carnivore. The paratype p4 is an elongate premolar The incisors are evident only in the para- whose posterior margin contacted the carnas- type. I3 is large but blunted by heavy wear. sial. The prominent central cusp is ¯anked 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 23

Fig. 11. Ysengrinia americana, partial right mandible with p3±m2, UNSM 26584, Harrison For- mation, late Arikareean, Scottsbluff County, Nebraska. A, lateral view; B, medial view. Scale bars, 1 cm. by a strong posterior accessory cusp and a the talonid is heavily worn in the paratype, low heel with a small cingulum cusp. A thin an m1 talonid from Harper Quarry (UNSM enamel ridge runs down the anterior face of 44671, ®g. 13A) and a complete m1 from the tooth to a weak enamel swelling. The UNSM Loc. Sf-105 (®g. 12) are unworn and pro®le of the anterior face is not rectilinear show a blunt swollen hypoconid ridge bor- as in Y. tolosana, but is mesially extended. dered internally by a short shelf with a very This tooth is the most variable in the denti- weak entoconid. In the paratype m1, the pos- tion: in UNSM 26584 the p4 is short and terolabial face of the tall protoconid and ad- rather broad (®g. 12), and in UNSM 7131- jacent anterolabial part of the talonid display 83 the p4 is intermediate in length and width, a deep wear groove produced by action of falling between the short, broad p4 of UNSM the M1 paracone. The marked size difference 26584 and the more elongate p4 of F:AM between the m1 of the paratype and UNSM 54147. Illustrations of p4 in European spe- 44671 suggests that the teeth of Y. americana cies also seem to show this variation. are sexually dimorphic. The m1 is robust with a tall trigonid and Occlusion of P4, M1, and m1 result in a low wide talonid. The paraconid is placed number of vertically oriented shear surfaces directly anterior to the tall protoconid; the that demonstrate a slicing action. Crushing is prominent metaconid is somewhat retracted simultaneously accomplished by occlusion of posterolingual to the protoconid. Although M1±2 with m2±3 and the m1 talonid. Verti- 24 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 12. Ysengrinia americana, occlusal view of p4±m2, UNSM 26584, Harrison Formation, late Arikareean, Scottsbluff County, Nebraska. Stereophotographs. Scale bar, 1 cm.

cal wear surfaces associated with carnassial crushing platform ϳ35 mm in length in the shear, and the depth of the wear groove along paratype. the labial face of m1 produced by the M1 paracone, are better developed than in North COMPARISON OF NEW AND OLD WORLD American early Miocene Amphicyon. SPECIES The m2 is subrectangular with a broad tri- A comparison of Y. americana with the gonid and narrower talonid; m2 is not elon- European species of Ysengrinia is essentially gated relative to m1 (®gs. 7, 11, 12, 13B). limited to the lower dentition and mandible The m2 trigonid occupies the anterior half of because European holotypes of Y. tolosana, the tooth and is not crowded to the front of Y. gerandiana, and Y. depereti are mandibles the tooth, as in Pseudocyon. The protoconid without associated upper teeth. No popula- is the most prominent cusp, connected by a tion samples in Europe allow us to adequate- smooth enamel arc to the low paraconid ly assess dental variation within a species, ridge. A low rounded metaconid is separated and no postcrania have been attributed to the from the protoconid by a distinct crease in genus with certainty. All Ysengrinia species the enamel. The m2 trigonid surface forms a apparently show a modest reduction of the shallow basin sloping linguad. The m2 tal- anterior premolars (p1±3), a trait common to onid is a low platform with a labially placed many amphicyonines. Because p1±4 are not hypoconid ridge. The internal surface of the preserved in the holotype mandible of Y. de- hypoconid slopes toward the lingual edge of pereti, this inference is based on the size of m2; there is no talonid basin or entoconid. premolar alveoli. The Y. tolosana holotype The form of m2 in Y. americana is nearly lacks the anterior part of the mandible but identical to m2 of Paulhiac Y. tolosana the referred mandible from Paulhiac (NMB (NMB Pa 951); the lower dentition of these Pa 951) shows reduced anterior premolars. two species is extremely similar. Thus, identi®cation of Ysengrinia rests The m3 is elliptical, robust, with an irreg- heavily on p4±m3. ular surface of nearly uniform height on North American Y. americana shares cer- which individual cusps are no longer distinct. tain dental and mandibular traits with the Eu- The m2±3 and m1 talonid together form a ropean Y. tolosana. In particular, m1±m2 of 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 25

Fig. 13. Ysengrinia americana: A, m1 talonid, right (labial view), UNSM 44671; B, isolated m2, right (labial view), UNSM 44673, both from Harper Quarry, latest Arikareean, Sioux County, Nebraska. These are the largest molars attributed to Y. americana and probably belong to a male. Scale bar for both molars, 1 cm. the Y. americana paratype (F:AM 54147), of the lower dentition and the shape of the and the m1±m2 of a referred mandible mandibles indicate that these are distinct spe- (UNSM 26584), are nearly identical in form cies. and dimensions to these teeth in Paulhiac Y. The p4 in the Y. americana paratype from tolosana (NMB Pa 951) described by Bonis the Upper Harrison beds is longer than the (1973). To estimate dental variation expected short p4 of Paulhiac Y. tolosana (NMB Pa in a single amphicyonid species contempo- 951), and it lacks the rectilinear pro®le of the raneous with Ysengrinia,m1(Nϭ 13) and Paulhiac p4. However, Y. americana from m2 (N ϭ 8) dimensions were plotted for Da- the Harrison Formation (UNSM 26584) also phoenodon superbus; this sample comes has a short p4. The Y. americana paratype from a limited stratigraphic interval in the p4 appears more similar in form to p4 of the lower part of the Upper Harrison beds, Sioux FloÈrsheim Y. tolosana mandible (Kuss 1965: County, Nebraska. Figure 8 shows these ®g. 55). It seems that Y. americana and the measurements for D. superbus, Y. ameri- European species include both short, wide cana, and the European species of Ysengri- p4s and more elongate, narrow p4s; until a nia. The m1±m2 measurements of Y. amer- larger number of individuals from a single icana are closely grouped with those of Y. stratigraphic level is available, the explana- tolosana and Y. gerandiana, and could be re- tion of this variation in p4 remains uncertain. garded as within the expected range of a The Y. depereti holotype from Chilleurs- somewhat variable species. However, details aux-Bois (MN3b, Mus. OrleÂans 785) is dis- 26 AMERICAN MUSEUM NOVITATES NO. 3384 tinguished from Y. americana by its larger to those of living lions (Panthera leo, table m2. Also, the principal cusps of the Y. de- 2). Although there is no association of a pereti m2 terminate in sharp, anteroposterior complete radius or ulna with the humerus of crests, and the protoconid and metaconid are Y. americana, F:AM 54147 includes two joined by thin transverse enamel crests; in Y. proximal ulnae, a distal radius, and a com- americana (F:AM 54147, UNSM 26584) and plete humerus from one individual that can in Y. tolosana (NMB Pa 951) these cusps are be used to estimate forelimb proportions. The more rounded and the crests less sharply de- humeroradial index (Davis, 1964: 93) cal- ®ned. In Y. depereti the m2 protoconid and culated for F:AM 54147 is ϳ89.3, and for metaconid are joined anteriorly by a low ar- the largest unassociated humerus and radius cuate enamel rim that forms the anterior bor- from Harper Quarry it is 90.6. These values der of this tooth; the two cusps and the rim are most similar to humeroradial indices of surround a well-de®ned trigonid basin. Ysen- living lions (90.0±94.0, table 2). Although grinia americana (F:AM 54147, UNSM the radius of Y. americana is shorter than the 26584) and Y. tolosana (NMB Pa 951) lack humerus, its humeroradial index exceeds the this de®ned basin of Y. depereti, and have a range of the index for living ursids (78.3± shallower trigonid basin the margins of 86.3) and tigers (P. tigris, 80.7±86.4), dem- which blend smoothly into the peripheral onstrating a relatively longer lower forelimb cusps. The m2 of Y. americana and Y. tolo- in Ysengrinia and in living lions. sana are narrower than the broad m2 of Y. However, a shorter lower hindlimb in depereti. The two former species also have a Ysengrinia americana, relative to lions hypoconid that ®lls most of the talonid, leav- (83.7±89.3) and tigers (83.4±87.6), is re¯ecting only a narrow inner talonid margin. In Y. ed in the femorotibial index of 79.8 for the depereti the wider m2 talonid has a labially only known associated hindlimb (USNM restricted, sharp hypoconid ridge, bordered 186993). Using the median values for the lingually by a broad, low talonid shelf. lengths of all Y. americana femora and tib- There is an evident af®nity shared by the iae, the femorotibial index is Ͻ82, whereas teeth of Y. americana and Y. tolosana, and in lions and tigers it is Ͼ82. On the other among the m2s of Y. americana, Y. tolosana, hand, Y. americana has a somewhat longer and Y. gerandiana. However, given our in- tibia relative to those of living North Amer- complete knowledge of the upper dentition, ican Ursus americanus (71.4±75.9), Ursus skull, and postcranial skeleton of the Euro- arctos (68.2±71.9), the large Kodiak Island pean species, speculation about the relation- Ursus (67.9±73.9), and the polar bear Thal- ships among these nominal species is pre- arctos (73.9±74.4). Thus, the lower limb mature. (epipodial) segments in Ysengrinia appear to be somewhat longer than those of the living POSTCRANIAL OSTEOLOGY North American bears. The humeroradial and femorotibial indices Postcranial bones of Ysengrinia were well of Ysengrinia describe a heavily muscled, represented at the Harper Quarry waterhole short-footed carnivore without cursorial spe- bonebed, Sioux County, northwest Nebraska cializations of the limbs and feet. In cursorial (Hunt, 1978). Also, a partial forelimb was canids (Canis lupus, C. latrans, table 2) the associated with the Y. americana paratype humeroradial index ranges from 97.2 to cranium and mandible (FAM 54147) from 104.4, and the femorotibial index from 96.5 the 25 Mile District, and an associated partial to 100.9. In the long-legged Chrysocyon bra- hindlimb (USNM 186993) was found west chycrus of South America, both indices ex- of Spoon Butte, both from Goshen County, ceed 100. Thus, Ysengrinia was not propor- southeastern Wyoming. tioned as in living larger cursorial carnivor- The morphology of the foot and limb ans such as wolves, but more closely ap- bones shows some similarities to those of proached the limb indices of the large cats. large living ursids. However, the proportions However, Y. americana differed from them of the epipodial (radius, tibia) to propodial in lacking their more elongate tibia and tar- (humerus, femur) elements are more similar sus. 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 27

SCAPULA: An enormous scapula associated quarries (®g. 15). The humerus is similar to with the partial hindlimb (USNM 186993) that of large ambulatory ursids which can from the Lay Ranch beds west of Spoon move swiftly over short distances, and which Butte, Wyoming, measures 28 cm from the retain considerable mobility of the forelimb. dorsal border of the glenoid to the point The bone is robust, including a particularly where the scapular spine intersects the ver- massive diaphysis, created in part by the in- tebral border (®g. 14A). The scapular spine sertion of brachialis (long head), cephalohu- is extremely broad, ϳ3 cm in height at its meralis, and pectoral muscles along the del- midpoint; it terminates inferiorly in a well- toid-pectoral crests to produce a broad sur- developed acromion and more subdued me- face of attachment that extends for 20 cm tacromion process. Internal to the acromion along the anterior face of a humerus 30 cm the base of the scapular spine is broadened in length. The distal end of the humerus is to enclose the suprascapular artery and nerve transversely widened as in ursids by well- within a bony foramen. This foramen is not developed lateral and medial epicondyles present in large ursids or felids in which the continuous with the supracondylar ridges for artery lies anterior to the edge of the scapular the origin of major extensors and ¯exors of spine without bony enclosure. The large spe- the wrist and digits. The medial epicondylar cies of Panthera show moderate develop- region is developed as a rugose process, and ment of the acromion and metacromion, but as a result the shallow olecranon fossa of Y. Ysengrinia is most similar to Ursus arctos, americana is somewhat extended medially. U. americanus, and Thalarctos maritimus in A similar asymmetric olecranon fossa is pre- which the metacromion is not well differen- sent in living Ursus and in North American tiated. early Miocene Amphicyon but the fossa is The outer surface of the scapula re¯ects deeper and more dorsally extended than in the great mass and thickness of the muscles Ysengrinia. The deep olecranon fossa of Ur- of the rotator cuff that stabilized the huge sus and Amphicyon allows a more secure shoulder of Ysengrinia. Despite breakage, a locking of the anconeal process of the ulna prominent postscapular fossa for the sub- in the fossaÐthe contact of the lateral face scapularis muscle, similar to that in ursids, of the anconeal process with the side of the was present along the caudal margin of the olecranon fossa creates a bony stop mecha- scapula at its junction with the vertebral bor- nism that prevents lateral bending of the el- der. The ventral border of the scapula is bow joint. Ysengrinia americana has a some- thickened and laterally re¯ected to accom- what more primitive articulation of distal hu- modate the subscapularis minor within a merus with ulna. broad shallow sulcus along its ventral mar- Ysengrinia retains an entepicondylar fora- gin. Within the infraspinous fossa an ellipti- men for the brachial artery and median cal muscle scar 7.5 cm in length and 2.5 cm nerve, whereas in living Ursus the bony bar in greatest width, placed slightly posterior to enclosing the vessel and nerve is lost and the the midpoint of the fossa, may have con- foramen is open medially. tained a separate belly of infraspinatusÐno RADIUS-ULNA: The radius and ulna of Y. similar scar occurs in ursids or felids. americana are known from complete speci- Dimensions of the glenoid fossa of the mens at Harper Quarry (®g. 16). The para- scapula convey a sense of the mass of the type skeleton includes only a distal radius forequarters of these large carnivorans (table and proximal parts of the two ulnae (®g. 17); 3). The glenoid area of Ysengrinia americana however, they compare with the Harper is similar to that of some Thalarctos mariti- Quarry elements. The radius and ulna are mus, falling below the dimensions of large similar to these bones in large living ursids Ursus arctos but above those of Panthera leo and felids but there are some noteworthy dif- and P. tigris. ferences. The massive construction of radius HUMERUS: The humerus was previously and ulna, the thick diaphyses, and prominent described (Hunt, 1972: 16f.), based on a rugosities for interosseous ligaments indicate well-preserved example (CM 2400) collected the powerful muscular forces transmitted to by O.A. Peterson (1910) east of the Agate the lower limb skeleton. The radii of Ursus 28 AMERICAN MUSEUM NOVITATES NO. 3384

TABLE 2 Limb Bone Lengths (in mm) and Limb Proportions of the North American Amphicyonid Ysengrinia americana Compared with Other Amphicyonids, and Living Ursids, Felids, and Canids 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 29

TABLE 2 (Continued)

and large Panthera all show a strong cur- into the olecranon fossa of the humerusÐthis vature of the diaphysis; in Ysengrinia the is apparent from the greater dorsal extent of massive columnar radius has almost no cur- the articulation surface on the lateral face of vature. The articulation of the distal humerus the anconeal process in Amphicyon. Similar- with the radius-ulna is most similar to the ly, in Ursus the lateral articulation surface of con®guration in living ursids. The smoothly the anconeal process extends far dorsad, concave radial notch of the ulna and the con- nearly to the tip of the olecranon process. In vex articular margin of the radial head indi- Y. americana, however, the articulation sur- cate a degree of rotation of the radius around face on the lateral face of the anconeal pro- the ulna (supination-pronation) similar to cess does not extend as far dorsad as in Am- large ursids. A massive subrectangular radial phicyon and Ursus. None of the Ysengrinia tuberosity for attachment of the biceps ten- radii possess a radial exostosis like that don suggests the power of this rotation. Mus- known for Daphoenodon and Daphoenus. cle scars for the interosseous ligaments are CARPALS: The carpus is represented by left particularly developed. The radius and ulna and right scapholunars (®g. 18) and by a differ from those of early Hemingfordian right unciform from Harper Quarry: all are North American Amphicyon in that the radius heavy, massive bones, indicating the consid- of the latter is more slender and not as mas- erable force transmitted through the fore- sive, and its proximal ulna ®ts more deeply limb. A scapholunar of the same type is also 30 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 14. A, Left scapula of Ysengrinia americana, USNM 186993, Lay Ranch beds, west of Spoon Butte, Goshen County, Wyoming, associated with femur-tibia of ®gure 20. B, Metatarsals 1±5 of a composite pes, Y. americana, Harper Quarry, Upper Harrison beds, Sioux County, Nebraska. From right to left: MT1, UNSM 44640; MT2, UNSM 44639; MT3, UNSM 44636; MT4, 44638; MT5, UNSM 44634. C, Right innominate (above), Y. americana, ACM 9761, Morava Ranch Quarry, Box Butte 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 31 present in the paratype (®g. 19). The dorsal smoothly concave, articulating with the prox- surface of the scapholunar is smoothly con- imal ends of the large metacarpals 4 and 5. vex, without diagnostic features. However, Metacarpal 5 determines the minimum num- the ventral surface displays a distinctive to- ber of individuals (N ϭ 4) of Ysengrinia pre- pography that can be compared with that of sent in Harper Quarry, and also demonstrates ursids and large felids, produced by the ar- dimorphism in the foot: UNSM 44611 and ticulations with the unciform, magnum, trap- 44615 are about the same length, but the for- ezoid, and trapezium. mer (female) is gracile whereas the latter In living Ursus, three facets on the ventral (male) is much thicker and more robust (®g. surface can be recognized: an unciform facet 18A, B). The greatest width of the proximal and magnum facet are sharply demarcated, end of metacarpal 5 in these individuals is are aligned fore-aft, and occupy the lateral 25.2, 23.7, 23.3, 23.0, and 22.9 mm. It is a half of the ventral surface; a conjoined quad- short robust bone, comparing in anatomical rate facet for trapezoid-trapezium is con®ned detail to the metacarpal 5 of ursids, but in to the medial half of this surface. In Panthera living ursids and large felids the bone is leo and P. tigris the unciform and magnum much longer than in Ysengrinia. facets are crowded to the lateral side of the Metacarpal 1, clearly reduced in size, is scapholunar, leaving a large triangular area associated with the paratype cranium and for the trapezoid-trapezium articulation. The mandible (F:AM 54147). Although metacar- pattern of facets on the ventral surface of the pal 3 is not known, the reduced size of meta- Ysengrinia scapholunar (®g. 19A, B) is sim- carpal 1 and the lengths of the ®fth metacar- ilar to Panthera and is distinct from the de- pals suggest that the forefoot was probably rived pattern found in Ursus. In addition, in paraxonic. Ursus the trapezoid is smaller than the tra- The metacarpals (®gs. 18A±D, 19C, D) pezium, but in Panthera the trapezoid is larg- demonstrate that Ysengrinia had a short fore- er. In the lion the trapezoid extends along the foot. Anatomical details of the metacarpals front of the scapholunar to the medial border, are extremely similar to those of living ursids hence the trapezium is restricted to the pos- such as Ursus arctos and U. americanus. teromedial corner of the scapholunar. In Ur- Metacarpal 2 from Harper Quarry is most sus, however, the trapezoid lacks this medial similar to this bone in Ursus. The strongly extension, and the trapezium intervenes at developed interlocking overlap of the edge the anteromedial corner of the scapholunar. of metacarpal 2 on metacarpal 3 seen in large The unciform was also preserved at Harp- felids is not present in Ysengrinia. Similarly, er Quarry: its geometry and facet pattern are the facets of the proximal end of metacarpal most like large extant species of Ursus.A 4 duplicate those of Ursus and differ from pisiform was associated with the partial skel- those of large felids. In one important ana- eton from Spoon Butte; it conforms exactly tomical detail, Ysengrinia metacarpals differ to this bone in large Ursus. It is of interest from those of Ursus. In ursids a prominent because the ligament thought to be respon- elliptical scar occurs on the posterior surface sible for a prominent elliptical scar on the of the diaphysis of metacarpal 4 immediately posterior surface of metacarpal 4 originates below the articular head; this scar is always from the pisiform (®g. 18, see below). situated above the midpoint of the diaphysis METACARPALS: Metacarpals 2 and 4 were of the metacarpal. In amphicyonids it occurs found at Harper Quarry, metacarpals 1 and 3 more distally on the shaft of the metacarpal were not; however, there are ®ve ®fth meta- where it is closer to the midpoint of the di- carpals, including four of the right side. The aphysis, often extending below it. The scar distal surface of the unciform is broad and apparently represents an attachment for a lig-

← County, Nebraska; baculum of large undescribed amphicyonid (middle), UNSM 5-1-9-32SP, Bridgeport Quarries, Morrill County, Nebraska; baculum (below), UNSM 44629, length, 24 cm, Y. americana, Harper Quarry, Upper Harrison beds, Sioux County, Nebraska. 32 AMERICAN MUSEUM NOVITATES NO. 3384

TABLE 3 Comparative Measurements (in mm) of the Scapula in North American Early Miocene Amphicyonids and Large Living Ursids and Felids

ament of the carpus (the medial distal acces- the smaller are those of the side toes. There sory ligament of canids running from the pi- is no evidence of retractile claws. The ungual siform to metacarpal 4 may be comparable: phalanges were not preserved. see Miller et al., 1964: 225), which joins an VERTEBRAE: Vertebrae were found only at accessory carpal bone (pisiform) to the pal- Harper Quarry. There were a large number mar aspect of metacarpal 4. of lumbar vertebrae (N ϭ 11), but only two PHALANGES: Because the available phalan- of the atlas, one cervical and one thoracic. ges are not associated with metapodials, it This may be due to the destruction of the rib cannot be determined whether they belong to cages and thoracics during scavenging of the the fore- or hindfoot. Considered as a group, carcasses at the waterhole. the 17 phalanges from Harper and Morava The lumbars have elongate centra as in Ranch quarries are similar to those of large Panthera, unlike the short ones of living ur- ursids. The proximal phalanges are particu- sids. Although the transverse processes are larly massive and broad. Intermediate pha- mostly broken, some show the downward langes are smaller and more dorsoventrally sweep typical of large Panthera, whereas compressed; they display a strong process at others are directed more laterad as in ursids. the center of the dorsal edge of the proximal However, the base of these processes tends end for attachment of the extensor tendons to be situated lower on the centrum than in of the digits, and the ventral surface is ¯at. ursids, much as in large living felids. Large The smaller intermediate phalanges show a accessory processes also occur on the ante- moderate degree of asymmetry not seen in rior lumbars of Ysengrinia but are absent on the large ones; the large intermediate phalan- the most posterior, just as in large ursids and ges belong to the central digits 3±4 whereas felids. Situated laterad of the posterior zyg- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 33

was a pronounced dorsoventral bending of the vertebral column when running. The lumbar zygapophyses are set close to the midline in Ysengrinia, very similar to the zygapophyseal spacing of Panthera. The cervical vertebra (6th) differs from those of both large extant felids and ursids in slightly greater height of the neural arch, but its general form is much like that of Ur- sus arctos of similar size. Although the centrum is proportionately more elongated than that of U. arctos, the form, orientation, and surface area of the zygapophyses and details of the neural spine, arch, and transverse processes are con®gured as in that species. The atlas vertebra is nearly identical to the atlas of a Siberian tiger (P. tigris). These both differ from the atlas of living ursids which fuse the anterior edge of the transverse process with the anterior margin of the vertebra. When fused, the transverse process encloses a foramen that is placed between the transverse foramen and canal (in the process) and the intervertebral foramen at the anterior end of the vertebra, a specialized trait of ursine ursids not seen in Y. americana. The thoracic vertebra is damaged but appears to be the last thoracic anterior to the anticlinal vertebra. It does not differ signi®- cantly from this vertebra in either ursids or felids. A single elongate caudal vertebra indicates the presence of a long tail in Y. americana. SACRUM: A nearly intact sacrum from Harper Quarry (UNSM 44628) is the only known example of this segment of the vertebral column in the genus. It is made up of three vertebrae, the most common number in Carnivora. The Ysengrinia sacrum compares Fig. 15. Anterior view of left humerus, Ysen- well with those of P. leo and P. tigris which grinia americana (probable male, CM 2400), from 8 to 10 miles (ϳ13±16 km) east of the Agate also include three sacral vertebrae. Davis Quarries, ?Arikaree Group, Sioux County, Ne- (1964: 112) suggested that the longer sacrum braska, compared with a distal left humerus (prob- of Ursus, in which four to six vertebrae are able female, F:AM 25421) of the same species commonly incorporated, was ``associated from Morava Ranch Quarry, Upper Harrison with increased horizontal thrust on the pelvis beds, Box Butte County, Nebraska. Scale bar, 1 .... Extending the sacrum posteriorly in- cm. creases the attachment area for the multi®dus and sacrospinalis muscles. The main action of . . . these muscles is to extend the verte- apophyses, these processes reinforce the bral column when acting on the vertebrae, or zone of spinal ¯exure at, and posterior to, the to extend the pelvis when acting on the sa- anticlinal vertebra, indicating together with crum. These actions are obviously important the orientation of the zygapophyses that there for spinal ®xation .... It seems likely that 34 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 16. Radius (UNSM 44600, left) and ulna (UNSM 44604, right) of Ysengrinia americana, Harper Quarry, Upper Harrison beds, Sioux County, Nebraska. A, anterior view of radius, lateral view of ulna; B, posterior view of radius, medial view of ulna. reduction in tail length is a consequence of expense of the basal tail muscles''. The short increased sacral length, although critical data tails of ursids with long sacra contrast with are lacking. If sacral length is increased to the very long tails of amphicyonids and spe- provide additional area for the spinal erec- cies of Panthera, which all have short triver- tors, this area could be provided only at the tebral sacra. 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 35

Fig. 17. Distal radius and proximal ulna of Y. americana paratype, F:AM 54147, Upper Harrison beds, 25 Mile District, Goshen County, Wyoming. Scale bar, 1 cm.

INNOMINATE: Two innominates, damaged thigh in this heavily muscled amphicyonid. by scavengers, were found in Harper Quarry, However, the overall form of the Y. ameri- and a more complete innominate occurred at cana innominate most closely parallels this Morava Ranch Quarry (®g. 14C). Those bone in large living felids. In P. leo and P. from Harper Quarry are from individuals tigris the ilium and ischium are more antero- larger than the Morava Ranch specimen. The posteriorly aligned than in living ursids in innominate is massive, the bone very thick, which a ¯ared ilium and short, everted is- particularly surrounding the acetabulum. The chium are typical. acetabular diameter for each of the three in- BACULUM: A large baculum at Harper dividuals is 49.0, 47.8, and 45.2 mm (table Quarry measured 24 cm in length (®g. 14C), 4). Despite breakage, the ilium is most sim- lacking only the tip of about 1 cm. Although ilar to the elongate ilium of large living fe- not associated with other elements, it dem- lids. The ischium is also long, not shortened onstrates that males are present in the bone- as in some carnivores such as Ailuropoda, bed, and supports the inference that skeletal and the ischial tuberosity for the hamstrings dimorphism is sexual. The Y. americana bac- was well-developed but not everted as in liv- ulum is nearly perfectly straight for its prox- ing ursids. The most evident similarity to the imal 18 cm, then curves downward for its ursid innominate is the widened ventral sur- distal 5 cm, hence it differs from the smaller face of the ilium anteromedial to the rectus but entirely straight baculum of Ursus (a Ko- femoris tuberosity for the origin of the iliacus diak Island U. arctos baculum measures only muscle. This probably re¯ects a very large 15.2 cm in length). A weak urethral grove in iliopsoas muscle complex for ¯exion of the the ventral surface of the bone begins about 36 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 18. Ysengrinia americana: A, metacarpal 5 (UNSM 44611, female); B, metacarpal 5 (UNSM 44615, male); C, metacarpal 2 (UNSM 44619); D, metacarpal 4 (UNSM 44617); E, scapholunar (UNSM 44609); F, pisiform (USNM 186993). Metacarpals and scapholunar are from Harper Quarry, Sioux County, Nebraska. Pisiform is from Lay Ranch beds, west of Spoon Butte, Goshen County, Wyoming.

6 cm from the proximal end and continues to the distal tip; however, the terminal 4±5 cm of the groove deepens and widens, open- ing at the distal end of the baculum which ¯ares to form a bifurcated tip. In large living felids the baculum is quite short (ϳ1 cm) and small. FEMUR: There are three complete femora of Y. americana, one from the Lay Ranch beds at Spoon Butte, two from Harper Quar- ry. The two complete bones from Harper Quarry differ in size, one large and robust (UNSM 44624), the other a more gracile femur from a much smaller individual (UNSM 44690). These are probably male and female: the diameter of the femoral head (41.1 and 40.0 mm, respectively) is nearly equal, but Fig. 19. Scapholunars and metacarpals of Y. the width of the proximal femoral neck (69.8 americana: A, scapholunar, F:AM 54147, para- vs. 61.0 mm, measured at the level of the type; B, scapholunar, UNSM 44610, Harper Quar- lesser trochanter) and the midshaft width of ry; C, metacarpal 5, and D, metacarpal 1, both the diaphysis (43.0 vs. 35.3 mm) differ ap- from F:AM 54147, paratype. Scale bar, 1 cm. preciably. The femur from Spoon Butte is an 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 37

TABLE 4 Comparative Measurements (in mm) of the Innominate in North American Early Miocene Amphicyonids and Some Living Felids, Ursids, Hyaenids, and Canids 38 AMERICAN MUSEUM NOVITATES NO. 3384 even larger individual, probably a male marily in a more elongate diaphysis. Living (USNM 186993, diameter, femoral head, large ursine bears and Y. americana share a 46.2 mm; width of proximal femoral neck, particularly robust tibia. However, the prin- 71.0 mm; diaphyseal width, 45.4 mm) , and cipal distinction between living ursids on the is associated with a tibia (®g. 20), providing one hand, and Y. americana and large felids the only known femorotibial index for a sin- on the other, involves the distal articular sur- gle individual of Y. americana (79.8, table face of the tibia: the wider and shorter as- 2). tragalus of Ursus corresponds to a shallower, The femur is columnar and straight, its di- wider articulation surface on the distal tibia, aphysis of nearly equal diameter throughout whereas this surface is narrower and more its length, re¯ecting the body weight sup- deeply grooved in Y. americana, P. leo, and ported by the hindlimb and its muscular P. tigris. These latter three species also show power. It shares some similarities with fem- a more fore-aft alignment of the trochlear ora of large living ursids, but compares most grooves on the distal tibia for reception of closely with those of living felids. It differs the astragalus than is found in living ursids. from femora of extant ursids in the following In addition, there is a tight registration be- features: (1) in Ursus arctos, U. americanus, tween distal tibia and astragalus in the large and T. maritimus the femoral diaphysis is rel- felids and Y. americana, but the ®t is looser, atively slender and more elongate than in less congruent, in large ursids in which in- YsengriniaÐthe bone tapers to a gracile mid- tervening soft tissue must compensate for the shaft diaphysis, widening at the distal end, slack registration in the living animal. even in the largest living ursids; (2) the distal If we calculate the femorotibial index for femoral condyles in Ursus are low and the hindlimbs from Harper Quarry (using the broad, whereas Ysengrinia shares the taller, largest femur and tibia) and from Spoon narrower distal condyles of Panthera leoÐ Butte, the range of values (79.8±81.6) for Y. the intercondylar depression or groove is americana falls between living ursids (67.9± deep and symmetric in Ysengrinia, shallow 75.9) and the large living species of Panth- to deep and asymmetric in Ursus; (3) the era (P. leo, 83.7±89.3; P. tigris, 83.4±87.6), deep pits or scars for the lateral and medial indicating that, relative to the hindlimb pro- heads of the gastrocnemius situated on the portions of living bears, the Y. americana tib- dorsal margin of the lateral and medial fem- ia is elongated, approaching the felid ratios oral condyles face posteriorly in Ursus but (table 2). have a shallower and more lateral orientation TARSALS: An astragalus (®g. 21) is asso- in Ysengrinia and large living felids; (4) the ciated with the tibia of the Spoon Butte Ysen- distal end of the femur in living bears is grinia. Three calcanea and an astragalus asymmetric, due to the more expanded me- come from Harper Quarry, and a somewhat dial epicondylar regionÐin large living fe- larger calcaneum from American Museum± lids and Ysengrinia the distal end of the fe- Cook Quarry. A right ectocuneiform from mur is symmetric. The femur of Y. ameri- Morava Ranch Quarry (®g. 21) is the only cana compares particularly well with the other tarsal element in these collections. femora of P. leo and P. tigris but is some- The astragali of living bears and Ysengri- what more robust in large males. nia are markedly different. In plantigrade Ur- TIBIA: The tibia is the best represented sus the astragalar trochlea is broadened and limb bone of the species: there are four from the neck is shortened signi®cantly relative to Harper Quarry and one associated with the Y. americana. The Ysengrinia astragalus re- femur from Spoon Butte (USNM 186993). sembles that of large living felids in which a Although the Spoon Butte femur is larger narrow trochlea with well-de®ned trochlear than the femora from Harper Quarry, the tib- ridges is positioned above a longer neck. In ia (®g. 20) associated with this femur is Y. americana, however, the neck is not quite shorter and somewhat more robust than any as elongated as in felids and is not as narrow, of the Harper Quarry tibiae. The general and the sustentacular facet is not restricted to form of the tibia is most similar to those of the more dorsal part of the neck as it is in large living felids; the felid tibia differs pri- digitigrade cats. In living Ursus the area oc- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 39 (USNM 186993), Lay Ranch beds, west of Spoon Butte, Goshen County, tibia, medial view; femur, posterior view. B, Ysengrinia americana tibia, lateral view; femur, anterior view; A, Fig. 20. Associated right femur and tibia, Wyoming: 40 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 21. Ysengrinia americana: A, ectocuneiform (ACM 9390); B, carpal cuneiform (USNM 186993); C, metatarsal 5 (UNSM 44634, male); D, metatarsal 5 (UNSM 44633, female); E, astragalus (UNSM 44630, female); F, astragalus (USNM 186993, male). cupied by the sustentacular facet extends dis- facet remains separate from the anterior facet tally farther along the neck, an anatomical in three out of four calcanea, they are slightly trait typical of ursid plantigrady. The Y. conjoined in the largest individual (CM americana astragalus lacks the astragalar fo- 2211). In large plantigrade ursids (U. arctos, ramen which is often lost in carnivorans that T. maritimus) the medial and anterior artic- approach or have attained digitigrady in the ular facets of the calcaneum are conjoined hindfoot (this foramen is occasionally pre- (Stains, 1973), presumably due to body sent in digitigrade felids, e.g., UNSM 16656, weight transmitted downward through the P. tigris, Siberian tiger). superposed astragalus. The fusion of these The three calcanea from Harper Quarry calcaneal facets does not occur in digitigrade are of about the same size and can articulate felids. appropriately with the astragalus from Harp- Other features of calcaneum and astragalus er Quarry (®g. 21E). This astragalus is ϳ7% are more typical of digitigrade carnivores: smaller than the large astragalus from Spoon (1) the general form of these bones closely Butte (®g. 21F), a measure of dimorphism in approaches that of P. tigris and P. leo, but this species. The calcanea are not anatomi- differs primarily in being more robust, mas- cally specialized for a fully digitigrade sive; (2) the relatively narrow parallel-sided stance: (1) the distal calcaneum below the and grooved trochlea of the astragalus and sustentaculum is not as short as in living ur- its tight registration and arc of rotation on the sids but is not as elongated as in large digi- distal tibia are as in the large digitigrade fe- tigrade Panthera; (2) the posterior surface of lids; (3) the sustentacular facet of the astrag- the sustentaculum is not as deeply grooved alus remains con®ned largely or entirely to for a ¯exor tendon of the digits (¯exor hal- the neck of the astragalus as in felids and lucis longus) as in digitigrade felids and ca- does not continue dorsad to the summit of nids in which the distal calcaneum is medio- the trochlea as in large ursids; (4) the cal- laterally narrower; (3) although the medial caneum of plantigrade Ursus arctos is dis- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 41 tally broader and has a proportionately larger facet in large species of Panthera, which is sustentaculum relative to Ysengrinia, pre- prolonged ventrad as a narrow linear crest. sumably due to its greater weight-bearing In Ursus arctos the dorsal facet is much larg- role; (5) the peroneal tubercle of the distal er and rectangular, extending nearly to the calcaneum, involved in eversion of the plan- rear of the bone; its form in these bears is a tigrade hindfoot, is prominently developed in specialization of the plantigrade tarsus. The large living ursids but remains only of mod- convex surface of the dorsal facet in large est size in large digitigrade felids and Y. Ursus indicates a greater degree of move- americana. ment between the cuboid and ectocuneiform Ysengrinia americana does not show the than in P. tigris, P. leo, and Y. americana in specializations of calcaneum and astragalus which a more planar surface suggests more for plantigrady found in living ursids, but limited motion between these bones. The two neither has it achieved the fully digitigrade ventral facets are present in large living ur- calcaneum-astragalus of large living felids sids, but the dorsal facet is conjoined with and canids. In Y. americana the entire sole the anterior ventral facet, forming a broad of the hindfoot may have occasionally con- surface of articulation with the cuboid, a fea- tacted the substrate when standing at rest, but ture not evident in large felids. In Y. ameri- when in motion adopted a more elevated cana the anteroventral facet is much smaller, ``subdigitigrade'' stance. This is suggested and a posteroventral facet is added in the by measurements of the arc of rotation of the beardog which is absent in P. tigris. The pos- astragalus on the distal tibia (table 5; see terior process of the ectocuneiform is prom- Wang, 1993). These data were used to esti- inently developed in Ysengrinia and the great mate the amount of plantar and dorsi¯exion cats but is very reduced in Ursus. The medial of the hindfoot on the lower limb. The ex- face of the ectocuneiform in large living fe- treme plantar ¯exion observed in digitigrade lids, ursids, and Y. americana is similar in canids (73±76Њ) is not achieved in most liv- having an elongate dorsal facet for the me- ing plantigrade ursids (37±47Њ). Y. ameri- socuneiform and two separate anterior and cana (47±50Њ) shows a somewhat greater de- posterior ventral facets for the head of meta- gree of plantar ¯exion than seen in these ur- tarsal 2. The ventral surface of the ectocu- sids. The maximum amount of rotation of the neiform for articulation with the head of astragalus on the tibia, measured in degrees metatarsal 3 most resembles that in P. tigris. of arc, occurs in digitigrade canids and felids METATARSALS (®g. 14B): The form of the (80±96Њ); ursids and Y. americana show a proximal heads of the metatarsals and the an- lower range of values (54±66Њ), with the ex- atomical detail of the articular facets are de- ception of the carnivorous polar bear (74Њ). veloped as in large Ursus (U. arctos). Dif- However, a digitigrade stance is not neces- ferences are: (1) a somewhat closer registra- sarily accompanied by high values for plan- tion of the proximal articulations in Ursus; tar ¯exion, as shown by brown and spotted (2) a reduction in size of metatarsal 1 in Y. hyenas (table 5) relative to canids and felids. americana relative to Ursus; (3) a paraxonic The ectocuneiform (®g. 21), known only hindfoot in Ysengrinia, similar to large living from Morava Ranch Quarry, differs consid- Panthera in which metatarsals 3±4 are the erably from the low, tabular ectocuneiform longest and of about equal length (metatar- of Ursus, resembling much more closely this sals 2 and 5 are shorter), whereas in Ursus bone in Panthera leo and P. tigris. Moreover, the hindfoot is not paraxonic, the longest the form of the ectocuneiform and its cuboid metatarsals are 5±4, diminishing progressive- facets allows a reliable estimation of the ly in length through metatarsals 3±2±1. Di- form of the cuboid. The lateral face of the Y. morphism in Ysengrinia (®g. 21C, D) is americana ectocuneiform shows three sepa- demonstrated by 2 ®fth metatarsals of equal rate facets for articulation with the cuboid: length from Harper Quarry, one robust the largest is the nearly quadrate dorsal facet (UNSM 44634), the other gracile (UNSM which is typical of amphicyonids; there are 44633). also smaller anterior and posterior ventral The orientation and relative lengths of the facets. This differs from the smaller dorsal metacarpals and metatarsals in large living 42 AMERICAN MUSEUM NOVITATES NO. 3384

TABLE 5 Comparative Measurements (in degrees of arc) of the Rotation of Astragalus on Distal Tibia in the Early Miocene Amphicyonid Ysengrinia and in Living Ursids, Felids, Canids, and Hyaenids

ursids (Ursinae) re¯ect the turning-in of their Hough, 1948) and to ursids (Ginsburg, feet, a specialization of ursine bears not 1961). Such skeletal correspondences have found in other Carnivora. This is interpreted been interpreted by some workers as evi- as a secondary modi®cation of the planti- dence of direct relationship to these groups. grade stance of early Tertiary carnivorans. However, comparisons with postcrania of a SUMMARY: The nearly complete represen- broad spectrum of fossil and extant Carniv- tation of the postcranial skeleton of Y. amer- ora suggest that many of the resemblances of icana provides the ®rst de®nitive evidence of Y. americana to large living ursids in fact its size, stance, and gait. The robust, massive re¯ect their shared arctoid ancestry. On the limb elements and stout vertebral column in- other hand, the ``felid'' traits of this beardog dicate a large, heavy, muscular carnivore. At (table 6: scapholunar, lumbar vertebral col- ®rst the postcranial skeleton of Ysengrinia umn, sacrum, and tail, pelvis, hindlimb ele- americana appears to be a composite of fea- ments) are regarded here as primitive carni- tures found in both large living felids and voran postcranial features scaled to large ursids, integrated with features exclusive to size, or, with regard to fore- and hindlimb amphicyonids (table 6). Earlier studies of proportions, as ecological adaptations of this amphicyonid postcranial skeletons remarked particular species. In fact these ``felid'' traits on resemblances to felids (Hatcher, 1902; are almost certainly early arctoid skeletal fea- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 43

TABLE 6 proximal metapodials, and phalanges. The Summary Comparison of Postcranial Traits of the amphicyonid skeleton indicates that the fam- Early Miocene Amphicyonid Ysengrinia americana ily evolved independently of both ursids and Relative to Postcrania of Large Living Ursids felids during the Cenozoic, yet paralleled the and Felids large species of these groups in a number of adaptive traits related to the life mode of large terrestrial carnivorans. Ysengrinia americana fossils are consis- tently found in waterhole and ¯uvial settings, suggesting that the animal was a frequent visitor to these places, probably preying on and scavenging mammals congregating at such water sources. The postcranial skeleton indicates that Ysengrinia was an ambush predator that relied on a burst of speed to overtake its prey, and on its grasping, powerful forelimbs and huge canines to dispatch these animals.

BASICRANIAL ANATOMY Well-preserved basicrania of early Mio- cene amphicyonids are almost entirely represented by North American specimens, with a few (Ͻ10) from western Europe; none are known from Asia or Africa. Early Miocene amphicyonids retain plesiomorphic arctoid basicrania in which the middle ear cavity has not invaded surrounding skull bones, and the auditory bulla is not greatly enlarged. In carnivorans in which the auditory bulla has expanded to accommodate an increased middle ear volume, the bulla encroaches on adjacent bones, modifying the form of the basicrani- tures that were not overprinted by postcranial um. This does not occur in these amphicyon- specializations such as those of ursine bears. ids which are distinguished by a broad ba- The undisputed anatomical specializations of sicranial axis (wide basioccipital and basi- the living ursine bears, such as their unique sphenoid) and a mastoid-occipital region un- dentition, foot anatomy, and derived planti- modi®ed by expansion of the auditory bulla. grade gait, are not seen in amphicyonids. The paratype skull of Y. americana pro- As various species of ursids and amphi- vides information on the auditory bulla and cyonids independently attained large body some surrounding features of the basicrani- size, arctoid postcranial characters were ex- um for the ®rst time (®g. 22). pressed as slightly divergent morphs, partic- AUDITORY BULLA: The auditory bulla in ularly evident in the fore- and hindfeet. For many species must have been only loosely example, living bears achieved their special- attached to the basicranium because it is of- ized form of plantigrady and the amphicyon- ten missing in otherwise intact crania. The ids a subdigitigrade stance, but their common early Miocene skulls from North America ancestry remains evident in anatomical de- that retain an intact or only slightly distorted tails of the basicranium and various postcran- auditory bulla are few, but can be divided ia. The postcranial features of the Ysengrinia into four types: (1) species referred or closely skeleton that proclaim an arctoid origin are related to Daphoenodon all display a uniform found in the scapula, humerus, baculum, morphology of the bulla similar to that of the 44 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 22. Basicranium of Ysengrinia americana, paratype (F:AM 54147): A, ventral view; B, lateral oblique view. Metric scale in A; scale bar in B is 1 cm.

D. superbus holotype skull (CM 1589); (2) cessed in the auditory region (no basicrania although known only from the paratype skull of Ysengrinia are known from the Old of Y. americana (F:AM 54147), the poorly World); (3) the relatively unspecialized bul- preserved bulla of North American Ysengri- lae of Daphoenodon and Ysengrinia differ nia evidently differed from the bulla of Da- from the bulla of early Miocene North Amer- phoenodon in having a longer bony external ican Amphicyon (F:AM 25400) where the meatal tube and in being more deeply re- middle ear cavity invades the bony ¯oor of 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 45

Fig. 23. Basicranium of Daphoenodon superbus, holotype (CM 1589), Upper Harrison Beds, Car- negie Quarry 3, Agate Fossil Beds National Monument, Sioux County, Nebraska. Stereophotographs of high-resolution cast. Scale bar, 1 cm. an enlarged external auditory meatus, there- living arctoid carnivorans, the bulla of D. su- by increasing middle ear volume (Hunt, in perbus is extremely rudimentary. The bulla press); (4) only three temnocyonine skulls re- is thin-walled, weakly attached to the skull, tain an auditory bulla, each a different spe- lacking any posterior expansion. It is formed cies; two of these skulls preserve a rudimen- mostly or entirely by an ectotympanic ele- tary crescentic ectotympanic without evident ment, and thus differs from the thick-walled, entotympanic contributions; the skull of a posteriorly and ventrally in¯ated, ankylosed third species retains a more evolved ectotym- bullae of many living arctoids that are panic bulla that probably includes small en- formed by both ectotympanic and entotym- totympanic elements. panic elements (Hunt, 1974). The presence In Daphoenodon superbus (CM 1589), a of an entotympanic contribution in Daphoen- simple, capsular bulla encloses the petrosal odon remains uncertain, but if present, it was (®gs. 23, 24B). The bulla is somewhat ven- con®ned to the posteromedial margin of the trally in¯ated in its medial half and has a bulla and was very small. short bony external auditory meatus. An os- In Y. americana (®gs. 22, 24A, F:AM seous tube for the internal carotid artery runs 54147), the weathered, partly decomposed within its medial wall; a large posterior carotid foramen at the posteromedial corner of basicranium retains remnants of the bullae, the bulla marks the entrance of the artery. basicranial axis, and petrosals. Basioccipital The osseous bulla does not extend behind a width, measured at the level of the petrosal transverse line drawn through the mastoid promontoria, is ϳ35±38 mm. Its lateral mar- processes, demonstrating that there was no gin contains the embayment for the expanded posterior expansion of the bulla. Much of the inferior petrosal venous sinus common to posterior auditory region remained uncov- amphicyonids. The petrosals are deeply inset ered. However, the bulla does extend into the in the auditory region, are small relative to anteromedial corner of the auditory region, the size of the skull, and lie medial to well- ϳ4±5 mm anterior to the level of the post- developed mastoid processes, as in North glenoid processes. Compared to the bullae of American Amphicyon.InDaphoenodon su- 46 AMERICAN MUSEUM NOVITATES NO. 3384

Fig. 24. A, Auditory region of Ysengrinia americana, paratype (F:AM 54147, ®g. 22), Upper Har- rison beds, 25 Mile District of Falkenbach, Goshen County, Wyoming; B, auditory region of Daphoen- odon superbus, holotype (CM 1589, ®g. 23), Upper Harrison Beds, Carnegie Quarry 3, Agate Fossil Beds National Monument, Sioux County, Nebraska. In Ysengrinia the auditory bulla medial to the bony external auditory meatus has been lost from the skull but is presumed to have been a low ¯ask-shaped chamber with a bony tube within its medial wall for the internal carotid artery, similar to the tube (pcf) in Daphoenodon. perbus the petrosals are not deeply inset in evidence of any extension of the middle ear the skull. cavity into surrounding basicranial bones. The bulla remnants in Y. americana con- One can conclude that the bulla of Ysengri- sist of a small part of the anterior wall and nia was a simple, rudimentary bony ectotym- the bony external auditory meatal tube which panic capsule, covering little more than the was somewhat elongated. The middle ear petrosal itself. It lacked in¯ation, ankylosis cavity did not extend into the ¯oor of the to surrounding bones, or other specializations bony meatus as occurs in Amphicyon. De- seen in various living arctoid carnivorans. spite the absence of much of the bulla, the In the Old World the only early Miocene orientation of the remaining bone suggests amphicyonid skull that preserves an intact the bulla was little if at all in¯ated, and was auditory bulla is the Jourdan cranium of Cy- not posteriorly extended. It probably reached nelos lemanensis from St.-GeÂrand, France only to the posterior margin of the petrosal (Hunt, 1977: pl. 1). Its form differs some- as in Amphicyon. The width of the capsular what from that of Daphoenodon and Ysen- part of the bulla internal to the bony meatus grinia but it also was a simple capsular struc- was no greater than 10±11 mm. There is no ture with a short bony meatal tube. The me- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 47 dial part of the bulla probably was slightly so it is uncertain if M3 was retained in this in¯ated as in D. superbus. The bulla is situ- individual, but since the holotype palate re- ated almost entirely forward of a transverse tains this tooth it probably was present in the line through the mastoid processes in the species, albeit reduced and likely nonfunc- same manner as in Ysengrinia and Daphoen- tional. However, it is in the state of the pre- odon, and there is no extension of the bulla molars that the Old World migrants differ into the posterior auditory region. As in other from the New World endemics. North Amer- amphicyonids, the bulla is formed primarily ican daphoenine and temnocyonine amphi- by the ectotympanic. Of interest is whether cyonids retain well-developed premolar bat- one or more entotympanic elements were teries in contrast to the migrant amphicyon- added to the periphery of the ectotympanic ines Ysengrinia, Cynelos, and Amphicyon as occurs in living ursids (Hunt, 1974). This that reduce the size of their anterior premo- could be determined by observing the onto- lars (P1±3 and p1±3), occasionally entirely genetic elements making up the bulla of losing p2 (®g. 9). young individuals, but no juveniles with in- Occlusion of the upper and lower tooth- tact bullae are known as fossils. Because the rows in many species of carnivorans involves Cynelos bulla is similar in form to that of close registration of the carnassials and ca- living Ursus americanus in which small en- nines. However, the carnassial teeth are not totympanics (E1,E2) are attached to the inner tightly registered when the mandibles are in margin of the ectotympanic (Hunt, 1974: pl. centric occlusion. As the jaws are brought 4), it is possible that rudimentary entotym- together, interlocking of the canines (autoc- panics contribute to the bullae of Cynelos le- clusal mechanism of Mellett, 1984) guides manensis (Hunt, 1977; Ginsburg, 1977) and the approximation of the carnassial blades. In to a species of temnocyonine from the upper many carnivorans with sectorial carnassials, John Day beds of Oregon (Fingerhut et al., registration of the chewing mandible with the 1993). corresponding upper toothrow involves a lat- PETROSAL: There are no evident anatomi- eral shift of the chewing-side mandible as cal specializations of the petrosal in early closure takes place. Precise registration of Miocene North American amphicyonids: the these teeth is effected by neuromuscular con- low promontorium and adjoining tegmen are trol and aided by a mobile mandibular sym- similar in form and proportions. Based on the physis (e.g., in canids, Scapino, 1965). How- distribution and shape of fossae and the fa- ever, in some other carnivores (the creodonts cial canal on the tegmen's surface, the audi- Hyaenodon, Patriofelis) with shearing car- tory ossicles, auditory muscles, and course nassials, the mandibular symphysis can be of the facial nerve were morphologically uni- fused, hence immobile. When this occurs, the form in these carnivorans. The anatomical chewing mandible cannot shift outward in- pattern of the tegmen is very similar to that dependently of the passive mandible, thereby of living ursids (e.g., Ursus americanus). hindering precise occlusion of the carnassial Although damaged, the petrosal of Y. teeth as the individual grows older and the americana conforms to the amphicyonid pat- teeth wear (Mellett, 1977). To compensate, tern. the upper carnassial of these creodonts ro- tates inward during the life of the animal to DENTITION AND FEEDING maintain contact with the lower shearing tooth. The dental formula of 3-1-4-3 in upper With the exception of the presence of M3, and lower jaws is consistent for nearly all the teeth of amphicyonids are broadly com- species of North American amphicyonids ex- parable in form to those of living canids, so cept the temnocyonines, which have lost M3. much so that they were classi®ed with the The migrant amphicyonines that enter North Canidae by paleontologists in the ®rst half of America from Eurasia in the early Miocene the 20th century (e.g., Simpson, 1945). In all retain the full complement of molars addition to the similarity in form and number (M1±3/m1±3). The paratype cranium of Y. of teeth, the anatomical topography of the americana lacks the maxilla posterior to M2, mandibular symphysis and temporomandib- 48 AMERICAN MUSEUM NOVITATES NO. 3384 ular joints of North American amphicyonids P1±3 show virtually no wear (p1±3 are badly also corresponds to Scapino's (1965) descrip- damaged), suggesting that P1±3/p1±3 were tion of these features in living canids. As in essentially nonfunctional. This lack of wear canids, the symphysis of amphicyonids re- on anterior premolars contrasts with the pro- mains unfused, with the exception of some nounced wear on the upper and lower ca- very old adults. Analysis of the amphicyonid nines and I3. The canines and I3 of Y. amer- feeding mechanism suggests that initiation of icana exhibit strong wear facets indicative of the bite was preceded by the autocclusal con- a mature animal. The tips of upper and lower tact of the canines, followed by precise neu- canines are blunted from heavy wear. Exten- romuscular control of carnassial registration sive wear surfaces on the mesial face of the by the jaw muscles. As the jaws came to- upper canine and on the lateral face of I3 gether, the edges of the carnassials were were produced by the insertion of the lower brought into tight registration by a slight lat- canine between these upper teeth. The lower eral adjustment of the chewing mandible, canine has been so heavily abraded that it has paralleling the mechanism described in a liv- been reduced to a rounded peg whose ante- ing canid by Scapino (1965). As an individ- rior and posterior wear surfaces penetrate the ual progressively aged, the molars and car- dentine. Similarly, the carnassials and molars nassials eventually developed subhorizontal show signi®cant wear. However, the carnas- to ¯at wear surfaces in both canids and am- sial pair has maintained near-vertical shear phicyonids. In old age, a precise occlusion surfaces, and m1 has a deep wear groove on was no longer possible or necessary because the posterolabial surface of the trigonid that the shearing blades were worn away, leaving cuts 4±5 mm downward into the labial face only broad grinding surfaces. At this point, of the talonid. This wear groove, cut by the some aged beardogs fused the mandibular tall M1 paracone, is particularly conspicuous. symphysis and employed a jaw mechanism The tips of the major cusps of carnassials and similar to the crushing occlusion found in molars show blunt wear, as does p4, but the living ursine bears. degree of wear on these teeth is not as pro- It is possible to accurately describe dental nounced as would be expected given the con- occlusion and tooth wear in several North dition of the canines and I3s. The dental wear American Neogene amphicyonids. Although pattern differs in this respect from that of a range of ontogenetic stages is lacking for Daphoenodon superbus in which wear on ca- Ysengrinia, the association of cranium and nines and I3 (relative to carnassials/molars) mandible in the Y. americana paratype, a ma- is much less pronounced (®g. 7). Ysengrinia ture adult, can be used to examine how its apparently maintained more vertical shear teeth functioned during its lifetime. As an in- planes on its carnassials for a longer interval dividual of Y. americana aged, its teeth de- during its lifespan than other contemporary veloped the greatest degree of wear in two amphicyonids such as Daphoenodon and areas of the dentition: the canines/incisors Amphicyon. and the carnassial/molar group (®gs. 6B, 7, Surprisingly, vertical carnassial shear is 9B). Incisors were gradually blunted by wear still evident in this aged adult Y. americana over time, yielding ¯at-surfaced pegs. Pre- (F:AM 54147), and the carnassials and mo- molars were not heavily worn even in old lars have not been worn to ¯at surfaces. As individuals, in which wear was limited to the the North American amphicyonids Daphoen- tip of the principal cusp on each tooth (how- odon and Amphicyon age, their tooth wear ever, on p4 both the principal and posterior patterns demonstrate that shearing occlusion accessory cusps are eventually worn ¯at). of carnassials and molars gradually trans- The degree of wear increases as one proceeds forms to a more horizontal grinding-crushing backward in the toothrow, culminating in mode. In older animals the vertical shear sur- heavily worn carnassials and molars; thus, it faces of the carnassials are entirely worn is evident that food taken into the mouth is away, and in the oldest individuals the ver- transfered to the rear where the focus of mas- tical planes of the molars (such as inner sur- tication occurred. In Ysengrinia the anterior faces of paracone-metacone) are worn ¯at. premolars are very small, and the intact right Finally, molar occlusion in aged individuals 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 49 involves the apposition of ¯at subhorizontal Roads, District V, discovered UNSM 26584; surfaces, and the carnassials are low, blunt, B. Bailey (Highway Salvage Paleontologist, rounded platforms effective only in crushing UNSM) permitted its inclusion in this report. food material. It is of particular interest that We thank the Nebraska Department of Roads the same wear progression occurs in living for continued funding of the UNSM High- canids (Canis lupus, C. latrans, various foxes way Salvage Program. and jackals) for which Scapino's jaw mech- I am particularly grateful to S. David anism utilizing a mobile symphysis can be Webb and L. Barry Albright for thoughtful inferred. Therefore, the evident dental and reviews of the manuscript. osteological similarities of the jaws shared by canids and early Neogene amphicyonids, REFERENCES such as Y. americana and D. superbus, argue for a pattern of mandibular occlusion like Albright, L.B. 1996. Insectivores, rodents, and that described by Scapino for living canids. carnivores of the Toledo Bend local fauna: An This pattern is documented by tooth form Arikareean (earliest Miocene) assemblage from and number, mandibular morphology, includ- the Texas Coastal Plain. Journal of Vertebrate ing the anatomy of the mandibular symphy- Paleontology 16(3): 458±473. Barry, J.C. 1980. Occurrence of a hyaenodontine sis, and by the ontogeny of tooth wear di- creodont (Mammalia) in the late Miocene of rectly observable in rare population samples Pakistan. Journal of Paleontology 54(5): 1128± of beardogs such as D. superbus. 1131. Barry, J.C. 1988. Dissopsalis, a middle and late ACKNOWLEDGMENTS Miocene proviverrine creodont (Mammalia) from Pakistan and Kenya. Journal of Vertebrate I express my appreciation to the following Paleontology 8(1): 25±45. curators who permitted study of material in Barry, J.C., and L.J. Flynn. 1989. Key biostrati- their care: R.H. Tedford, M.C. McKenna, and graphic events in the Siwalik sequence. In E.H. N.B. Simmons, American Museum of Natu- Lindsay, V. Fahlbusch, and P. Mein (editors), European Neogene Mammal Chronology: 557± ral History, New York; M.R. Dawson, Car- 571. Plenum Press: New York. negie Museum of Natural History, Pitts- Barry, J.C., E.H. Lindsay, and L.L. Jacobs. 1982. burgh; M.C. Coombs, Pratt Museum, Am- A biostratigraphic zonation of the middle and herst College, and the University of Massa- upper Siwaliks of the Potwar Plateau of north- chusetts, Amherst; R.J. Emry, Smithsonian ern Pakistan. Palaeogeography, Palaeoclimatol- Institution, Washington, D.C.; J.A. 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APPENDIX 1 Letters from H.C. Clifford to O.C. Marsh in the to ship the fossils from Sydney, Nebraska, on Yale Peabody Museum establish the geographic April 2. A letter written by Yale paleontologist location of Clifford's explorations during 1875. R.S. Lull to W.J. Holland on November 6, 1908, Clifford made several trips between March 13 and establishes that the type material of Moropus ela- December 30, 1875, and on one of these must tus was collected on March 24, 1875, `èn route have collected the palate, an upper canine, and a from Crow Buttes to Sydney, presumably where calcaneum, later designated the holotype (YPM the trail crosses the Niobrara River'' (Holland and 10061) of `Àmphicyon'' americanus by Wortman Peterson, 1914: 225). (1901). The 1875 correspondence records only Although Lull and Holland believed that the two occasions when Clifford was likely to have trail to Sydney crossed the Niobrara River near collected the amphicyonid: in March during his the Agate fossil quarries, it in fact intersected the initial trip to the head of the White River, or on river much farther east, just a few miles west of a second visit in late May±early June. Other doc- Marsland, Nebraska. The discovery by Harold umentation in the YPM archives indicates that Cook of an early excavation and dump, over- YPM 10061 was collected during Clifford's ®rst grown by vegetation, not far from the river cross- trip in March 1875, very likely at the same time ing caused W.D. Matthew to accept the site as and at the same locality as Marsh's holotypes of Clifford's probable source for the types of M. ela- the chalicothere Moropus elatus. tus (Matthew, 1929: 520). In March 1875, Clifford reported the discovery The types of Moropus elatus are foot bones and and partial excavation of a brontothere skull a patella cataloged as YPM 13081, 24631, and (YPM 12048) and fossils of ``small animals'' in 24632. These elements also bear the YPM acces- the Chadron Formation along the White River sion number 704. This accession number appears near the Spotted Tail Agency (letter to O.C. at the head of the March 13, 1875, letter from Marsh, March 13, 1875, YPM archive). He even- Clifford to Marsh, indicating that the specimens tually traveled south from the White River bad- collected on the March trip were accessioned un- lands and the agency, crossing the Niobrara River, der 704. Signi®cantly, the holotype of `Àmphi- 2002 HUNT: NEOGENE AMPHICYONID YSENGRINIA 53 cyon'' americanus Wortman is included in acces- palate and teeth are similar to fossils from the sion 704, demonstrating that it too was collected Harrison Formation and lower part of the Upper by Clifford during the March trip. Harrison beds, the principal upper Arikaree rock Both Ted Galusha of the Frick Laboratory and units in Sioux and Dawes Counties, Nebraska. Al- Margery Coombs of the University of Massachu- though the Yale drawer label states that the ho- setts have suggested that Clifford's excavation, as lotype was found by Clifford in ``L. Miocene identi®ed by Cook, corresponds to the site of the (Arikaree), White River, Neb.'', this appears to be Morava Ranch Quarry of the American Museum, in error. The Yale catalogue records most speci- located ϳ6 miles (ϳ9.6 km) west of Marsland, mens of accession 704 as ``White River, Nebras- Nebraska. Galusha worked the site in 1940, as did ka'' because most of the fossils came from the Coombs in 1975 (Coombs and Coombs, 1997). White River badlands near the agencies. However, Their excavations produced the remains of both accession 704 also lists a few fossils collected in Moropus elatus and Ysengrinia americana, in- the Niobrara valley and supports Wortman's cluding an edentulous mandible of the amphi- (1901) published statement that YPM 10061 came cyonid (F:AM 25423) which corresponds in size from the ``Loup Fork beds, Niobrara River, Ne- to Wortman's holotype palate. In addition, an M1 braska''. Wortman's ``Niobrara River'' attribution (F:AM 25420, Hunt, 1972: ®g. 10A) collected by suggests that he had some knowledge that YPM Galusha is virtually identical to the M1 of YPM 10061 actually was found in the Niobrara valley 10061. These discoveries strengthen the assertion where the Harrison Formation and Upper Harri- that Morava Ranch Quarry was a likely source of son beds are fossiliferous. Although Clifford YPM 10061. could have collected the amphicyonid as he tra- Is Morava Ranch Quarry the only site where versed the Pine Ridge during his departure from YPM 10061 could have been collected? South of the White River country, these upper Arikaree the Red Cloud and Spotted Tail agencies, the Pine strata are not particularly fossiliferous, hence it is Ridge escarpment is formed by Arikaree Group more likely that he found it a few miles farther strata that Clifford would have traversed on his south in the Niobrara valley. The term `Àrikaree'' route to Sidney. The palate must have been col- was not applied to these strata until 1898±1899 lected from either upper Arikaree rocks of the es- when N.H. Darton of the United States Geological carpment or from upper Arikaree rocks in the val- Survey mapped these rocks; prior to that time ley of the Niobrara River immediately south of they would have been considered the ``Loup the escarpment. The preservation and color of the Fork'' beds as reported by Wortman.

APPENDIX 2 Viret's (1929) hypodigm of gerandianus in- and the rostrum are correctly placed in the same cluded, in addition to the holotype mandibular species, then this smaller amphicyonid is un- fragment with p2±m1 (FSL 213828), a second known in North America; North American Ysen- nearly edentulous mandible with only m2 (MGL grinia shows closest af®nity to Y. tolosana from St.-G. 2848) and a tentatively referred rostrum Paulhiac (NMB Pa 951). In addition, there re- with partial upper dentition (MuseÂum National mains some uncertainty with regard to the m2 of d'Histoire Naturelle, Paris). Bonis (1973) noted Y. gerandiana because the holotype lacks this that these three specimens are from different in- tooth, which is only retained in the referred man- dividuals. The teeth of FSL 213828 occlude rea- dible (MGL St.-G. 2848). The eventual discovery sonably well with the teeth of the rostrum, and of a Y. gerandiana mandible that includes the thus assembled, the composite dentition indicates complete premolar-molar toothrow with m2 is es- a carnivore somewhat smaller than Y. americana. sential to con®rm the identity of the lower denti- If the holotype lower dentition of Y. gerandiana tion of the genus. Recent issues of the Novitates may be purchased from the Museum. Lists of back issues of the Novitates and Bulletin published during the last ®ve years are available at World Wide Web site http://library.amnh.org. Or address mail orders to: American Museum of Natural History Library, Central Park West at 79th St., New York, NY 10024. TEL: (212) 769-5545. FAX: (212) 769- 5009. E-MAIL: [email protected]

a This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper).