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2003 Intercontinental Migration of Large Mammalian : Earliest Occurrence of the Old World Beardog (, Amphicyonidae) in Robert M. Hunt Jr. University of Nebraska-Lincoln, [email protected]

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Hunt, Robert M. Jr., "Intercontinental Migration of Large Mammalian Carnivores: Earliest Occurrence of the Old World Beardog Amphicyon (Carnivora, Amphicyonidae) in North America" (2003). Papers in the Earth and Atmospheric Sciences. 545. https://digitalcommons.unl.edu/geosciencefacpub/545

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Intercontinental Migration of Large Mammalian Carnivores: Earliest Occurrence of the Old World Beardog Amphicyon (Carnivora, Amphicyonidae) in North America

ROBERT M. HUNT, JR.1

ABSTRACT North American amphicyonid carnivorans are prominent members of the mid-Cenozoic terres- trial community during the late to late (Duchesnean to Clarendonian). range in size from Ͻ5kgtoϾ200 kg. Among the largest amphicyonids are Old and New World species of the Amphicyon: A. giganteus in (18±ϳ15? Ma) and , A. ingens in North America (15.9±ϳ14.2 Ma). Amphicyon ®rst appears in the of western Europe, surviving there until the late Miocene. Migration to Africa and North America takes place in the . The genus occurs in the Arrisdrift fauna () of southwest Africa, indicating migration south through the length of the African continent by the mid-Miocene. Its occurrence in is problematical because of the tendency to place any moderately large Asian amphicyonid in the genus, and because of the fragmentary nature of many . Here I report the earliest North American occurrences of Amphicyon (18.8±ϳ17.5 Ma), assigning these individuals to a new and previously undescribed species, Amphicyon galushai, from early Hemingfordian sediments of western Nebraska and north-central Colorado. In the New World, small early Hemingfordian Amphicyon galushai is probably ancestral to larger late Hemingfordian A. frendens, and to the terminal and largest species of the genus, early to mid- A. ingens. Diagnostic basicranial and dental traits place these species in the Amphicyonidae, and demonstrate a close relationship of the North American lineage to the type species of the genus, A. major, from Sansan, . Amphicyon galushai is known from a complete adult skull, a partial juvenile skull, three mandibles, and the isolated teeth and postcranial elements of ϳ15 individuals, all from the early Miocene of western Nebraska. The species also is represented by a crushed rostrum from the Troublesome Formation, north-central Colorado. Basicranial, dental, and postcranial distinguish A. galushai from its contemporary in the Runningwater Formation, the large digitigrade beardog Daphoenodon. The Runningwater For- mation contains the last occurrence of Daphoenodon in North America and the ®rst occurrence of Amphicyon; the overlap in stratigraphic ranges of these two carnivores provides a useful early Miocene biostratigraphic datum. The two amphicyonids occur together in the same quarries, as- sociated with canid, mustelid, and rare procyonid carnivores, which are much smaller . The North American species of Amphicyon (A. galushai, A. frendens, A. ingens) most likely adopted ecological roles similar to the large living felids (in particular, the lion Panthera leo). Their robust skeleton with powerful forelimbs, massive clawed feet, heavily muscled jaws with large canines, and a composite crushing/shearing dentition suggest a mobile predator that most likely stalked and ambushed prey from cover, overpowering its victims through sheer size and strength.

INTRODUCTION toid carnivorans ranging in size from Ͻ5kg to Ͼ200 kg. Although known from , Amphicyonid carnivores are a geographi- North America, and Africa, most fossils have cally widespread family of mid-Cenozoic arc- come from Europe and the United States. The

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

77 78 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 oldest North American amphicyonids from though European haplocyonine amphicyonids the late Eocene and early Oligocene were rel- from this same time interval evidently shared atively small (Ͻ20 kg) carnivores, but by the a common ancestry with temnocyonines, and early to mid-Miocene, several lineages ex- the daphoenines are closely related to the Eu- ceeded 100 kg, and together with the large ropean stem amphicyonid Cynodictis (Petter, hemicyonine ursids, had become the domi- 1966). The North American amphicyonids of nant predators of the Holarctic continents Oligocene age are obviously different from (Ginsburg, 1961: 44±45, 178±179; Hunt and Old World Oligocene species, yet were related, Tedford, 1993: 68; Hunt, 1998). and were evolving in some cases in parallel The earliest North American amphicyonids (temnocyonines-haplocyonines). are Duchesnean (ϳ37±40 Ma, late Eocene) In the late Arikareean and early Heming- fossils referrable to Daphoenus, a small (2±4 fordian, in essence throughout the early Mio- kg) carnivore occurring from southern Canada cene, a number of large amphicyonids migrate to Texas (Hunt, 1996). Daphoenus ranges from Eurasia into North America. These taxa from the Duchesnean to the early Arikareean, belong to the Old World amphicyonid sub- and is the most common North American Pa- family Amphicyoninae (Hunt, 1998). The ear- leogene amphicyonid. Following the appear- liest to appear is the large beardog Ysengrinia ance of Daphoenus in the early Duchesnean, Ginsburg, followed by Jourdan, and Daphoenictis and Brachyrhynchocyon ®rst then by Amphicyon itself. This in¯ux of am- occur in the late Duchesnean and early Chad- phicyonines, accompanied by other Old ronian, respectively, coexisting with Da- World ungulates and small , indi- phoenus throughout the Chadronian: all of cates a prolonged interval (from 23 to ϳ16.5 these genera are small fox-sized carnivores Ma) of faunal exchange between Asia and (ϳ4±10 kg). Daphoenictis and Brachyrhyn- North America in the early Miocene, using chocyon become extinct at the end of the the trans-Beringian route. Chadronian, but Daphoenus (18±25 kg; Ra- INSTITUTIONAL ABBREVIATIONS: dinsky, 1980) persists into the Orellan (early Oligocene), and progressively increases in AMNH American Museum of Natural History, size during the Whitneyan. By the early Ari- New York, NY kareean (late Oligocene), Daphoenus ap- F:AM Frick Collection, American Museum of proaches the size (ϳ20±30 kg) of a small Natural History, NY MNHN MuseÂum National d'Histoire Naturelle, . These genera belong to the amphicyonid Paris, France subfamily Daphoeninae, considered endemic UNSM University of Nebraska State Museum, to North America (Hunt, 1996). Lincoln, NE A second subfamily of amphicyonids, the USGS U.S. Geological Survey, Federal Cen- Temnocyoninae, appears in North America in ter, Denver, CO the earliest Arikareean (ϳ29±30 Ma), and continues into the late Arikareean (Hunt, ARRIVAL OF AMPHICYON IN 1998). Temnocyonines are the ®rst New NORTH AMERICA World amphicyonids to attain large size fol- lowing the of creodonts (Hyaeno- North American early to mid-Miocene don) in North America in the early Arika- Amphicyon fossils are allocated here to three reean. The oldest species is a small carnivore species: A. galushai, new species, A. fren- (ϳ10±15 kg), dentally and postcranially sim- dens Matthew, and A. ingens Matthew. Al- ilar to early Oligocene Daphoenus. During the though other large amphicyonids from the Arikareean interval, the various temnocyonine Miocene of North America have been placed lineages rapidly increase in size, culminating in Amphicyon, many of these carnivores be- in late Arikareean species in several lineages long to other amphicyonid genera. The Am- that attained 80±90 kg, and were slightly larg- phicyon lineage in the New World is restrict- er than living (Canis lupus). ed here to these three species, ranging in time Daphoenines and temnocyonines are not from the early Hemingfordian to the mid- known outside of North America (Hunt, 1998). Barstovian (18.8±ϳ14.2 Ma). These species Nothing like them has been found in Asia, al- share the typical upper and lower dentition 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 79

Fig. 4.1. Geographic distribution of Amphicyon galushai in North America: all fossils from early Miocene sediments of northwestern Nebraska (1, Runningwater Formation) and north-central Colorado (2, Troublesome Formation), and represent ϳ16 individuals. and postcranial skeleton of the genus as ev- Nebraska (Skavdahl Dam section of Mac- idenced in the holotype skull, mandibles, and Fadden and Hunt, 1998: 160), indicated that postcranials of Amphicyon major from San- this part of the formation corresponds to san, France (Ginsburg, 1961). Chron C5En, the upper part of C5Er, and the The earliest occurrences in North America lower part of C5Dr of the Global Polarity are rare fossils from the lower part of the Time Scale (GPTS; Berggren et al., 1995). Runningwater Formation in Sioux County, This interval of the GPTS is dated to ϳ18.2± Nebraska, and from the lower part of the 18.8 Ma. Calibration of the paleomagnetic Troublesome Formation, Colorado (®g. 4.1). zones of the lower Runningwater Formation Each of these occurrences is represented by was based on a zircon ®ssion track date of a single specimen: a partial maxilla with M2 19.2 Ϯ 0.5 Ma on the Eagle Crag Ash (Hunt from the Runningwater Formation (UNSM et al., 1983) ϳ30 km north of the Skavdahl 26393, Foster Ranch), and a crushed rostrum Dam section. The maxilla of Amphicyon with fractured teeth (P3±M2) from the Trou- from the Foster Ranch (UNSM 26393) was blesome Formation (USGS D645 [65-G-6], found ϳ20 km southeast of the paleomag- U.S. Highway 40 roadcut; Izett, 1968: 42± netically zoned Skavdahl Dam section in ®ne 45). The remaining specimens of A. galushai, sandstone asssociated with typical cross- including all known postcranial remains, strati®ed sands and granitic gravel of the come from stratigraphically higher levels of lower Runningwater Formation in Sioux the Runningwater Formation in Box Butte County. The Foster Ranch site and Skavdahl and Dawes Counties, Nebraska. Dam section are both in the lower part of the These two ®rst occurrences of Amphicyon formation; however, the Foster site is within in North America are dated by radiometric the axial Runningwater paleovalley whereas calibration of paleomagnetic data supple- the Skavdahl Dam section is ϳ8 km north of mented by independent biostratigraphic evi- the paleovalley axis. dence. Paleomagnetic sampling of the lower Biostratigraphic evidence for the existence part of the Runningwater Formation north- of Amphicyon in the ϳ18.2±18.8 Ma interval east of Agate, Sioux County, northwestern comes from the joint occurrence of A. galu- 80 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 shai and the temporally restricted oreodont TABLE 4.1 in the lower part of the Trou- Minimum Number of Individuals (MNI) of blesome Formation in north-central Colora- Amphicyon galushai (North America) from the Runningwater Formation, Northwestern Nebraska do. Skulls of several individuals of the large early Hemingfordian oreodont Merycocho- erus magnus were collected from the same outcrop that produced the palate of A. galu- shai (USGS D645; Izett, 1968). This oreo- dont, restricted to the lower Runningwater Formation in Nebraska, is found exclusively in exposures of the formation northeast of Agate that include the Skavdahl Dam paleo- magnetic section of MacFadden and Hunt (1998). Merycochoerus magnus is succeeded in the upper Runningwater Formation by its more advanced descendant Merycochoerus proprius. The Skavdahl Dam paleomagnetic section and contiguous outcrops of the lower Runningwater Formation in Sioux County tributed to both Amphicyon and Cynelos. The are tentatively correlated with lower Run- maxilla contains deciduous teeth and also the ningwater exposures of the paleovalley axis adult P4 and M1. These teeth are most sim- that produced the Foster Ranch Amphicyon ilar to those of Cynelos idoneus from the maxilla 20 km to the southeast. Sheep Creek Formation, which is a smaller Teeth and postcranial bones of Amphicyon carnivore relative to contemporaneous Am- galushai also have been found in UNSM Hem- phicyon. Only one additional amphicyonid ingford Quarries 7B, 12B, and 12D in the up- has been found in the Box Butte Formation per part of the Runningwater Formation. Thus, in over half a century of collecting, a nearly on current stratigraphic evidence, A. galushai complete skeleton (UNSM 48413) lacking ranges throughout the vertical extent of the the skull and mandibles, found by Dr. Loren Runningwater Formation. The faunas Toohey in 1996 in the same drainage as Fol- from these upper Runningwater quarries in- ey Quarry. This amphicyonid skeleton ap- clude species of ungulates slightly more pears to be too small to belong to Amphi- evolved than their progenitors in the lower part cyon, and may represent the same species of of the formation, and are among the most ad- Cynelos as the maxilla. Unfortunately the vanced Runningwater faunas known. Current lack of associated teeth prevents con®rma- age estimates for a volcanic ash in the upper tion of this assignment. Runningwater Formation in stratigraphic prox- Particularly rich samples of the large North imity to the terminal paleosol (``Platy Bench'' American species of Amphicyon have been of Galusha, 1975) capping the formation are found in the Sheep Creek Formation (A. fren- ϳ17±17.5 Ma, suggesting that deposition of dens) and Olcott Formation (A. ingens) of cen- Runningwater sediments occurred over an in- tral Sioux County, northwest Nebraska. These terval of 1±1.5 million years. fossils occur in suf®cient quantity to demon- The Box Butte Formation disconformably strate dimorphism in skeletons and teeth of overlies the Runningwater beds in northwest both species, presumably representing large Nebraska, resting directly on the terminal males and much smaller females (Hunt, 1998). Runningwater paleosol at a number of local- ities. A maxilla of an amphicyonid (F:AM HISTORY OF COLLECTION 95276) was reported from Foley Quarry in the Box Butte Formation in association with The North American early Hemingfordian equids and other mammals (Galusha, hypodigm of Amphicyon (®g. 4.1) includes 1975: 57). Although Galusha suggested that the remains of ϳ15 individuals from 10 lo- the maxilla belonged to Amphicyon, his con- calities in northwest Nebraska (table 4.1) and cept of the genus included fossils today at- the single individual from north-central Col- 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 81

orado. The UNSM sample of A. galushai INCLUDED SPECIES: Amphicyon major was collected from 1934 to 1941 (and a skull (Blainville), Amphicyon giganteus (Schinz), in 1959) by ®eld parties of the Division of Amphicyon laugnacensis Ginsburg, Amphi- Vertebrate Paleontology, working in fossil- cyon ingens Matthew, Amphicyon frendens rich early Miocene outcrops designated the Matthew, Amphicyon galushai, new species. ``upper Marsland Formation'' by UNSM pa- DISTRIBUTION: Amphicyon galushai-fren- leontologists. In 1965, Harold Cook, in a dens-ingens group: early Hemingfordian to posthumous publication, recognized that early Barstovian of northwestern Nebraska; these ¯uvial sediments ®lled an early Mio- early Hemingfordian of north-central Colo- cene paleovalley that extended across north- rado; early to mid-Barstovian of northeastern west Nebraska from west to east for more Colorado; early Barstovian, Barstow Syn- than 150 km (Cook, 1965; Skinner et al., cline, , and EspanÄola Basin, New 1977). These sediments represented a dis- Mexico. crete lithostratigraphic unit that Cook named Reported temporal range of Old World the Runningwater Formation; the rock unit Amphicyon (s.s.): Europe, MN zone 1 to MN included granitic gravels derived from the zone 11 (Ginsburg, 1999), 23.8±ϳ9Ma Rocky Mountains to the west, and contained (Steininger et al., 1996), early Miocene to abundant early Hemingfordian mammals. early late Miocene; early mid-Miocene of The efforts of UNSM paleontologists re- southern Africa (Hendey, 1978: 12, ®g. 4; sulted in the discovery of large numbers of Morales et al., 1998); early Miocene of ungulates (primarily camels, the dromomery- northern Vietnam (Ginsburg et al., 1992). cid , several species of equids, and DIAGNOSIS (NEW WORLD SPECIES): Mid- the oreodonts and Merycochoerus) sized to very large (ϳ40±Ͼ200 kg) North from the Hemingford Quarries of the Univer- American amphicyonid carnivorans with sity of Nebraska. Canids were the most fre- skull lengths of 27±31 cm (early Hemingfor- quently encountered carnivores; mustelids, ur- dian), 37±39 cm (late Hemingfordian), and sids, and amphicyonids were much less com- about 42±52 cm (early to mid-Barstovian). mon. Over time a small sample of Amphicyon Lower carnassial (m1) lengths: Amphicyon was brought together; many of these fossils galushai (early Hemingfordian, Nebraska), initially went unrecognized, simply labeled as 30.2±32.2 mm (N ϭ 3); A. frendens (late ``large carnivore.'' Hemingfordian, Nebraska), ϳ33.5±39.8 mm Similarly, the ®eld collectors of the Frick (N ϭ 11); A. ingens (early to mid-Barstovian, Laboratory, American Museum of Natural Nebraska, Colorado, New Mexico, and Cal- History, New York, also working in the Run- ifornia, 36.0±44.9 mm (N ϭ 20). Rudimen- ningwater Formation of northwest Nebraska tary ¯ask-shaped auditory bulla formed by a from 1937 to 1965, discovered specimens of slightly in¯ated ossi®ed ectotympanic that A. galushai in quarries north of the Niobrara fully encloses the middle ear; participation of River. This sample included the most complete entotympanics in the auditory bulla uncer- and best preserved cranial material of the spe- tain. Hypotympanic sinus of the middle ear cies, the holotype mandible and paratype cra- invades the ¯oor of the bony external audi- nium of A. galushai, which was collected by tory meatus even in the oldest North Amer- Ted Galusha from Dunlap Camel Quarry in ican (early Hemingfordian) crania. Dental 1939. formula 3-1-4-3/3-1-4-3: reduction of pre- molar (p1±3, P1±3) size and height (relative SYSTEMATICS to Daphoenodon) but without loss of pre- ORDER CARNIVORA BOWDICH, 1821 molars. There is no premolar crowding as seen in Pliocyon. There is marked hypertro- DIVISION ARCTOIDEA FLOWER, 1869 phy of posterior molars (m2±3, M2±3), pro- FAMILY AMPHICYONIDAE TROUESSART, 1885 ducing the largest such teeth evolved within Amphicyon Lartet, 1836 the family. M1±3 length commonly greater than twice the length of P4 as a result of TYPE SPECIES: Amphicyon major (Blain- molar expansion, in contrast to Daphoeno- ville, 1841). don, Ysengrinia, and temnocyonines, which 82 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

all lack this degree of molar expansion (in A. TYPE LOCALITY AND HORIZON: Dunlap galushai, M1±3 length is approximately Camel Quarry, Runningwater Formation, twice the length of P4). Enlarged M2 some- Dawes Co., NE. The holotype and paratype what wider transversely than M1; M2 sub- were collected in the same quarry, and are triangular in early species, rapidly becoming similar in size but represent different individ- subrectangular in later larger forms, and pro- uals, based on toothwear. jecting lingually farther than the inner edge ETYMOLOGY: The species is named for the of M1. M2 protocone connected to paracon- late Ted Galusha, Frick Curator Emeritus, ule, but metaconule isolated as in European ®eld geologist and paleontologist for the Amphicyon. P4 short, wide, robust with small Frick Laboratory (AMNH), whose dedicated parastylar cusp and weak to moderate devel- efforts resulted in important collections of opment of the protocone. The m1 has a swol- Miocene mammals from western Nebraska. len in¯ated appearance, always retains a REFERRED SPECIMENS: (A) From the Run- metaconid (lost or vestigial in Ysengrinia), ningwater Formation, Hemingford Group, and has a wide talonid with prominent, northwest Nebraska (year of collection at end somewhat laterally placed, ridgelike hypo- of each entry): conid. The m2 is rectangular, with trigonid Dental: (1) F:AM 25407, right mandible elevated above talonid, protoconid much with p2±m2, Dunlap Camel Quarry, Dawes larger than metaconid, and a small vestigial Co., NE, 1937; (2) F:AM 95013, left m2 paraconid (the arcuate crest at the anterior (worn), Dunlap Camel Quarry, Dawes Co., end of the m2 trigonid in Cynelos is absent). NE, 1939; (3) F:AM 25401, left P4, Dunlap A laterally placed, low hypoconid dominates Camel Quarry, Dawes Co., NE, ?1937; (4) F: the m2 talonid. M3/m3 are ¯at, massive teeth AM 25436, right mandible with p2±m2, Cot- with subdued occlusal topography. tonwood Creek Quarry, Dawes Co., NE, is present, particularly 1965; (5) F:AM 25437, left M2, Cottonwood evident in the teeth and limb bones of the Creek Quarry, Dawes Co., NE, 1965; (6) latest and largest species. Postcranial skeletal UNSM 25687, right maxilla with P3±M1, traits can be combined with dental characters Marsland Quarry (UNSM Loc. Bx-22), Box to identify the genus: the limb skeleton is Butte Co., NE, 1934; (7) UNSM 25579, left massive and robust, and the radius, ulna, and M1, Hemingford Quarry 7B (UNSM Loc. tibia are short relative to the upper limb Bx-7), Box Butte Co., NE, 1938; (8) UNSM bones, as in large living ursids. Metapodials 25575, left P4, Hemingford Quarry 7B are short, not elongate, and the digits spread (UNSM Loc. Bx-7), Box Butte Co., NE, more widely than in living canids. Speciali- 1939; (9) UNSM 25762, right M3, Heming- zations for cursoriality such as lengthened ford Quarry 7B (UNSM Loc. Bx-7), Box lower limb segments and elongate, appressed Butte Co., NE, 1938; (10) UNSM 25929, left metapodials (as in living canids) are absent. P4, Hemingford Quarry 12B (UNSM Loc. The feet, however, are paraxonic (principal Bx-28), Box Butte Co., NE, 1938; (11) weight-bearing axis passing between meta- UNSM 26392, left p4, Hemingford Quarry podials 3 and 4), unlike those of living ur- 12D (UNSM Loc. Bx-12), Box Butte Co., sids, and are more similar to those of large NE, 1938; (12) UNSM 25578, left M2 (large), living felids such as Panthera. Hemingford Quarry 12D (UNSM Loc. Bx- 12), Box Butte Co., NE, 1937; (13) UNSM Amphicyon galushai, new species 26393 (a cast), right partial maxilla with M2, broken alveoli for M1, alveoli for M3, Foster TYPE SPECIMEN: F:AM 25406, complete Ranch, sect. 5, T.27N., R.53W., Sioux Co., left mandible with p2±m2, with single alveoli NE (from a ®ne sandstone above Fe-stained for the canine, p1, and m3; the holotype and crossbedded sandstone and granitic gravel), paratype were both collected in 1939. collected 1985; (14) UNSM 1570±59, crani- PARATYPE: F:AM 25400, nearly complete um, slightly crushed, lacking posterior brain- cranium (lacking the nasals and parts of the case, with right P2±M2, left broken canine, zygomatic arches) with left and right P4±M1, partial M1, M2, Hovorka's Quarry (UNSM and alveoli for all other teeth (d.f. 3-1-4-3). Loc. Bx-21), Box Butte Co., NE, 1959. 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 83

Postcranial: From Hemingford Quarry 31 cm; basicranium of amphicyonid type 12D, UNSM Loc. Bx-12: (1) UNSM 25561, (Hunt, 1998), auditory bulla formed primarily partial left scapula, 1937; (2) UNSM 26383, if not entirely by the ectotympanic, with an left humerus, 1941; (3) UNSM 25559, left accessory hypotympanic sinus invading the ulna, 1937; (4) UNSM 25557, right radius, osseous ¯oor of the external auditory meatus. 1938; (5) UNSM 26384, left calcaneum, Dental formula 3/3±1/1±4/4±3/3; I1±2 small, 1941; (6) UNSM 26385, right calcaneum, I3 enlarged, based on size of incisor alveoli 1941; (7) UNSM 26386, left calcaneum, (incisors and canines not preserved in jaws); 1941; (8) UNSM 25581, right calcaneum, lower incisors probably not enlarged but size 1939; (9) UNSM 26387, right astragalus, dif®cult to determine from poorly preserved 1937; (10) UNSM 26388, right astragalus, i1±3 alveoli; P1±3/ p1±3 reduced, short, with- 1941; (11) UNSM 26389, right astragalus, out posterior accessory cusps (p4 with pos- 1937; (12) UNSM 26390, right cuboid, terior accessory cusp, occasionally present on 1937; (13) UNSM 25582, right metatarsal 1, p3), with strong cingula, and separated by 1939; (14) UNSM 26391, left metatarsal 2, short diastemata. P4 more or less in the form 1938; (15) UNSM 25565, left metatarsal 4, of an isosceles triangle in occlusal view 1938; (16) UNSM 25568, right metacarpal 2, (somewhat longer than M1, table 4.2), with 1938; (17) UNSM 25573, left metacarpal 3, reduced protocone, in contrast to Daphoeno- 1939; (18) UNSM 25560, right femur, 1941; don, in which the P4 protocone is prominent. (19) UNSM 26394, right cuboid, 1939. A relatively low m1 trigonid (in contrast to From Hemingford Quarry 7B, UNSM tall m1 trigonid of North American late Ari- Loc. Bx-7: (20) UNSM 26376, proximal kareean Ysengrinia), paraconid shortened and right ulna, 1939; (21) UNSM 26377, right positioned almost directly anterior to proto- metatarsal 2, 1939; (22) UNSM 26378, left conid, entoconid present but weak (no ento- metatarsal 3, 1937; (23) UNSM 26379, left conid in Daphoenodon and Ysengrinia), pos- metatarsal 3, 1937; (24) UNSM 25569, left terior part of m1 trigonid and anterior talonid metacarpal 2, 1939; (25) UNSM 26380, right slightly swollen. M1 triangular in occlusal metacarpal 5, 1939. view, anterior border convex, posterior border From Hemingford Quarry 12B (UNSM convex or straight, but not concave; lingual Loc. Bx-28): (26) UNSM 26375, left distal cingulum developed almost entirely posterior humerus, large, 1938. to protocone, and separated from it by a short From Hemingford Quarry 11B (UNSM curvilinear groove; M1 paraconule indistinct, Loc. Bx-26): (27) UNSM 26381, right distal but small, distinct metaconule present, as in humerus, heavily water-worn, 1940. European species; protocone close to the an- From SE 1/4, NE 1/4, sect. 23, T.30N., terior border. M2/m2 enlarged relative to M1/ R.49W., Dawes Co., NE: (28) UNSM 26382, m1. The m1/m2 length ratio is 1.5±1.6. M2 left calcaneum, 1940. subrectangular and slightly smaller than M1 From Cottonwood Creek Quarry, Dawes (the marked enlargement of M2 in A. frendens Co., NE: (29) F:AM 25458, astragalus; (30) and A. ingens is not evident); M2 projects lin- F:AM 25447, metacarpal 1; (31) F:AM guad somewhat farther than M1, anterior bor- 25448, metacarpal 2; (32) F:AM 25452, der of M2 slightly convex, posterior border metacarpal 4; (33) F:AM 25438, metatarsal somewhat concave; M2 lingual cingulum 3; (34) F:AM 25446, metatarsal 4, all col- wide, thick, rounded, separated from proto- lected in 1965. cone by wide groove; protocone only slightly (B): From the Troublesome Formation, displaced toward anterior border of tooth. NW4, SW4, sect. 9, T.1N, R.79W, base of More or less rectangular m2; talonid shorter U.S. Highway 40 roadcut, Grand County, than trigonid. The m3 single-rooted or with north-central Colorado, USGS D645 (65-G- fused double-roots. 6), crushed rostrum including left maxilla Postcranial skeleton re¯ecting ambulatory with P3±M2, broken canine and P1, alveoli life mode (a walking gait interspersed with for M3, collected by G. A. Izett, July 1962. short bursts of speed): upper limb bones ro- DIAGNOSIS: Smallest North American spe- bust, massive; lower limb bones robust, not cies of Amphicyon, basilar length of skull 27± elongated; retained primitive ability to supi- 84 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 4.2 Dental Measurements (in millimeters) of Amphicyon galushai (North America)

nate/pronate the manus on the lower fore- Quarry, Hovorka's Quarry) within the Run- limb; metapodials relatively short when com- ningwater Formation indicate a mid-sized pared to elongated metapodials of contem- amphicyonid about the size of arctos. porary Daphoenodon; astragalus short, with The holotype mandible (®g. 4.2) is similar to distal condyle not shifted underneath the a mandible initially referred to Amphicyon proximal trochlea (in contemporary Da- major by Roman and Viret (1934, pl. 1, ®g. phoenodon the astragalus is elongate, with 1) from the late of La Romieu, distal condyle shifted underneath the proxi- southern France. The La Romieu Amphicyon mal trochlea); calcaneum ursid-like, distally was later referred to A. giganteus by Gins- broad, robust, generally wider and not as burg and Telles-Antunes (1968). deeply grooved on the posterior surface of The paratype skull (F:AM 25400, basilar the sustentaculum for the ¯exor tendons of length, 31 cm) is an adult from Dunlap Cam- the hindfoot, in contrast to Daphoenodon in el Quarry (®g. 4.2). The size of the canines the same quarries in which the groove on the suggests it is a female. It is uncrushed, al- sustentaculum is pronounced and the calca- lowing its proportions to be accurately com- neum is taller and narrower. pared with those of other contemporary am- phicyonids. The form and proportions of the DESCRIPTION skull are similar to the only known European CRANIUM AND MANDIBLES: Two skulls and skull of the genus (A. major, Sansan, basilar three mandibles from separate localities length, ϳ33.6 cm; Bergounioux and Crouzel, (Dunlap Camel Quarry, Cottonwood Creek 1973). Although the Sansan skull is crushed, 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 85

Fig. 4.2. Amphicyon galushai, new species: (A) P4±M1, paratype (F:AM 25400), occlusal view; (B) paratype cranium with P4±M1 (F:AM 25400), lateral view; (C) holotype mandible with p2±m2 (F: AM 25406), lateral view; (D) p2±m2 (F:AM 25407), occlusal view, all from Dunlap Camel Quarry, Runningwater Formation, Hemingford Group, NE. its snout was probably somewhat longer than ushai is smaller, and is not as enlarged as in the North American species. However, be- A. major (compare M2 in tables 4.2, 4.3). cause the North American skull is probably The second skull (UNSM 1570±59, ®g. a female, the snout can be expected to be 4.3), a juvenile from Hovorka's Quarry, is more gracile than in the larger males. With- not as well preserved as the paratype. It has out additional European crania, we cannot be been dorsoventrally crushed, and the greater certain of the signi®cance of what may be part of the basicranium is missing. The snout minor proportional differences. The only is short with a broad palate. On the right, P2± teeth in place in the paratype are P4±M1, but M2 are present, including alveoli for M3, P1, the alveoli for the remaining upper teeth in- C, and I1±3. Most of the teeth on the left dicate their size. P4±M1 are like those of A. side are lost or damaged. This skull is im- major from Sansan; however, M2 in A. gal- portant in retaining P4±M2 in place, dem- 86 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 4.3 Dental Measurements (in millimeters) of Amphicyon major (Sansan, France)a

Fig. 4.3. Cranium (in palatal view) of juvenile Amphicyon galushai (UNSM 1570±59), Hovorka's Quarry (UNSM Loc. Bx-21), Runningwater Formation, NE. 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 87

Fig. 4.4. Crushed rostrum (in lateral view) of Amphicyon galushai (USGS D645), Troublesome Formation, U.S. Highway 40 roadcut, Grand County, CO. onstrating the small size of M2 relative to blesome Formation Amphicyon (®g. 4.4) was M1, which is diagnostic of A. galushai,in also short, with a wide palate, and a slight contrast to the enlarged M2 of A. major, A. constriction of the snout posterior to the ca- frendens, and A. ingens. Both skulls of A. nines, features also seen in F:AM 25400 and galushai show alveoli for M3 in contrast to UNSM 1570±59. Runningwater Formation Daphoenodon Basilar lengths for A. galushai (ϳ310 mm) skulls, which have lost this tooth. are similar to those of the larger living ursids Despite the distortion produced by post- (table 4.4)ÐUrsus arctos (basilar lengths of mortem crushing, the rostrum of the Trou- 284±310 mm, N ϭ 4), Ursus americanus

TABLE 4.4 Basilar Skull Length and Length of Basicranial Axis in Living Ursids and in Amphicyon galushai from the Runningwater Formation, Northwestern Nebraska (in millimeters) 88 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

(232±276, N ϭ 7), Ursus arctos (Kodiak Is- phicyon in North America are crania of late land, 386 mm, N ϭ 1), and Thalarctos mar- Arikareean amphicyonids from the Upper itimus (360 mm, N ϭ 1). Harrison beds of northwest Nebraska and Because the paratype skull is uncrushed, southeastern Wyoming. Nearly complete details of basicranial anatomy and general skulls are known for Daphoenodon, Ysengri- anatomical proportions of the cranium can be nia, and an unnamed genus. All of these gen- established with greater con®dence than in era differ in their dentitions, and more con- the case of the crushed skull of Amphicyon spicuously in skull form, from early Heming- major from Sansan described by Bergou- fordian Amphicyon: (a) the skulls of Da- nioux and Crouzel (1973). The postorbital phoenodon are short-faced, low crania, much length is nearly two times the preorbital, in- smaller than the paratype skull of Amphicyon; dicating cranial proportions as in most am- (b) the skull of Ysengrinia, a probable male, phicyonids and living and extinct ursids has a robust snout but narrows behind the or- (similar proportions are plesiomorphic for bits, and has a low forehead and very small early arctoids). The form of the cranium ap- braincase; (c) the undescribed genus is the proaches that of some large living ursids only one of these amphicyonids to attain the such as Ursus arctos, but is most similar to skull size of Amphicyon; however, its brain- the fossil skulls of its probable descendants, case is smaller than Amphicyon, its skull more A. frendens and A. ingens. Skulls of A. fren- elongate, and its dentition more primitive, dens and A. ingens in the AMNH collections lacking expanded posterior molars. No late show variation in length of snout and in the Arikareean amphicyonids enlarge M2±3 and development of the sagittal crest that are at- m2±3, in contrast to Amphicyon, which does. tributable to sexual dimorphism. Large males Somewhat similar in skull form to Amphi- have slightly longer, more robust snouts, cyon is its contemporary in the Runningwa- larger canine teeth, and, in some cases, enor- ter quarries, the terminal species of Da- mous sagittal crests for attachment of mas- phoenodon. Runningwater Daphoenodon re- sive temporal musculature. tains the short snout and broad skull char- An attempt to obtain an endocast from the acteristic of the genus, but the skull in this, cranial cavity of the paratype was made by the largest species of the genus, equals the Radinsky (1980) but was not completed; he dimensions of Amphicyon. This huge Da- did describe a damaged endocast of A. fren- phoenodon can be most readily distinguished dens, suggesting that the lineage retains a from Amphicyon by its teeth, but certain cra- number of primitive featuresÐunexpanded nial features also differ between the two gen- sigmoid gyri, narrow lateral gyri, absence of era: in Runningwater Amphicyon, the frontal an entolateral sulcus, and much of the cere- region is not as expanded or in¯ated; the bellum not yet covered by the occipital lobe braincase seems to be slightly greater in vol- of the cerebrum. Radinsky was careful to ume; the occiput is broader; and the mastoid point out that the greater amount of infolding process is more developed. Male and female of the amphicyonid neocortex observed in the skulls of the Runningwater Daphoenodon are family over time might not be due to actual known; hence these distinctions are not in- increase in relative amount of neocortex. Be- ¯uenced by sexual dimorphism. cause the neocortex is a sheet, it can increase Thus, at its ®rst appearance on this conti- only by areal expansion; as the volume of the nent, Amphicyon is distinct in its skull form brain below the neocortex increases, the neo- from other genera of early Miocene amphi- cortex must compensate by complex infold- cyonids. When the form of the cranium is ing. Although he could demonstrate a de®nite combined with the dentition and basicranial increase in relative brain size over time in the anatomy, the genus can be readily identi®ed. amphicyonids that he studied, it was not pos- BASICRANIUM: Only the paratype skull of sible to show a gain in neocortical volume, Amphicyon galushai (F:AM 25400) pre- despite the suspicion that it occurred. serves the basicranium, including the audi- At present, the principal source of infor- tory region and part of the right bulla (®g. mation on skull form in amphicyonids that 4.5). This is the only remnant of the bulla immediately precede the appearance of Am- known in this species. The juvenile skull 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 89

Fig. 4.5. Above: Stereophotographs of the basicranium of Amphicyon galushai (F:AM 25400, para- type), Dunlap Camel Quarry, Runningwater Formation, NE (ventral view, anterior to right). Below: Stereophotographs of the right auditory region (ventral view) of Amphicyon galushai (F:AM 25400, paratype). The ectotympanic bulla shows the specialized hypotympanic sinus (S) that invades the bony ¯oor of the external auditory meatus in North American species of Amphicyon. BO, basioccipital; GF, glenoid fossa; M, mastoid process. Note the petrosal deeply recessed within the auditory region.

(UNSM 1570±59) is slightly crushed dorso- gle individual of A. major at Sansan (Bergou- ventrally and has lost the posterior cranium, nioux and Crouzel, 1966, 1973) yielded an including the entire occiput, but retains an intact skull. Unfortunately it was crushed, pre- intact left petrosal. The petrosal description venting a detailed description of the basicra- is taken from UNSM 1570±59. nium (its basilar length of 33.6 cm is similar Basilar length of the paratype cranium is to the paratype skull of A. galushai). Conse- 31 cm, and the length of the basicranium from quently, the paratype skull of A. galushai pro- the base of the foramen magnum to a trans- vides the ®rst record of an undistorted basi- verse line joining the oval foramina is ϳ7.5 cranium in an early species of the genus, and cm; thus, the basicranial length is ϳ25% of establishes that the basicranial anatomical pat- the length of the skull. The basicranial width tern typical of large mid-Miocene North measured between the mastoid processes is American species of Amphicyon was already 11.2 cm. Only a few pieces of the anterior in existence in the early Miocene. cranium of A. major from Sansan were avail- As in living ursids, the basicranium dis- able to Ginsburg (1961), but in 1965, the dis- plays a broad basioccipital (38.6 mm in width covery of a nearly complete skeleton of a sin- in the paratype, 34.5 mm in the juvenile), 90 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

¯anked by deeply recessed auditory regions depressions found in the tegmen (epitympan- on either side. The lateral margin of the ba- ic recess, tensor tympani fossa, stapedius fos- sioccipital is not ventrally extended as a sa, facial canal) of Amphicyon galushai are downturned ¯ange as in living ursids (U. arc- in the plesiomorphic carnivoran state. The tos, U. americanus), but turns dorsad to form tensor and stapedius fossae are both shallow, a thin lateral wall for the recessed inferior pe- narrow cavities, and the epitympanic recess trosal venous sinus that travels the basioccip- is only a modestly developed depression of ital margin (Hunt, 1977). The squamosal is small volume, not penetrating deeply into the characterized by a weakly concave glenoid squamosal. In living ursids, the epitympanic fossa that lies in the same horizontal plane as recess and tensor and stapedius fossae are the basicranial axis. The posterior margin of found in the same rudimentary state as in the fossa is delimited by a postglenoid process Amphicyon galushai, and re¯ect the relative- of moderate height (20 mm at medial border ly unspecialized condition of the tegmen and in the paratype) that gradually decreases in adjacent cranial bones. height laterally. At the base of the inner mar- The mastoid bone and exoccipital together gin of the process is a well-de®ned circular form a broad, massive, blocky process char- postglenoid foramen 3±4 mm in diameter, acteristic of all North American species of present in both skulls, indicating a viable ex- Amphicyon (®g. 4.5). The mastoid process is ternal jugular venous drainage from the cra- thick, wide (27.8 mm in width in the para- nium. Immediately medial to this foramen is type, not preserved in juvenile) but does not a shallowly incised Glaserian ®ssure adjacent descend ventrally, remaining at the level of to the squamosal-alisphenoid suture. the basioccipital. A nearly vertical groove for The alisphenoid contains the foramen ovale the exit of the facial nerve is present in the placed at the posterior end of a common de- medial side of the mastoid bone. Its vertical pression (12 mm in length in the paratype, 9.6 orientation is due to the deeply recessed po- mm in juvenile) that also houses at its anterior sition of the petrosal that requires the nerve end the posterior opening of the alisphenoid to descend almost directly ventrad to exit the canal. The posterior part of the alisphenoid auditory region. Appended to the mastoid (tympanic wing) descends into the deeply re- process is a very short (10 mm) paroccipital cessed middle ear cavity roofed by the petro- process that seems inordinately small for the sal. The petrosal can be observed in both A. large skull, but which is similar in size to the galushai skulls (®gs. 4.3, 4.5). It is deeply set short paroccipital process of living ursids. In- into the auditory region, its ventral surface re- ternal to the paroccipital process is the pos- cessed 13 mm dorsal to the surface of the terior lacerate foramen for the internal jug- basioccipital in the paratype cranium. Its form ular vein and associated cranial nerves, is best preserved in UNSM 1570±59, where which has a transverse diameter of 7±8 mm; it measures 19.9 mm in length, 16.3 mm in its anterior margin is ill de®ned because the width. In UNSM 1570±59, the bulla has been posterior part of the auditory bulla that forms lost from the left auditory region, providing this margin is lost in the paratype skull. an unobstructed view of the middle ear (this The remnant of the bulla preserved in the area is partly covered by the bulla in F:AM paratype skull is of particular importance 25400). The petrosals of the two Running- (®g. 4.5). This is the oldest known auditory water skulls are extremely similar, although bulla preserved in any species of North UNSM 1570±59 was smaller in body size, American Amphicyon. The auditory bulla probably a young female. and its relationship to surrounding basicra- The petrosal promontorium in ventral nial elements distinguishes Amphicyon from view is elliptical, low and rounded, quite other contemporary amphicyonids (the bulla small (anteroposterior diameter 12.8 mm in of species of Daphoenodon is of entirely dif- paratype, 11.4 mm in juvenile), and without ferent shape). The bulla in A. galushai is a ventral process (®g. 4.5). A broad tegmen formed primarily by an ectotympanic ele- tympani (width, 7.3 mm in juvenile) extends ment as in other North American species of laterad from the promontorium to contact the the genus. Its length was ϳ23 mm and width squamosal. The form and placement of the ϳ30 mm. Although the medial and posterior 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 91 parts of the bulla have been broken and lost, cyonid bulla: If one or more caudal entotym- the remaining anterior and lateral parts reveal panics existed as small bony elements, form- that the bulla was ¯ask-shaped in ventral ing part or all of the medial wall of the bulla view. A short osseous external auditory me- as in living ursids, they were not utilized to atus was present in the paratype, as in many expand the volume of the middle ear. Instead, arctoid carnivorans; but in Amphicyon galu- Amphicyon used an alternative strategy to in- shai the middle ear space enclosed by the crease middle ear volume by invading the bulla extended laterad into the ventral ¯oor ¯oor of the bony external auditory meatus. of the meatal tube, creating an accessory hy- In the skulls of Amphicyon, the medial potympanic sinus. In F:AM 25400, the bony margin of the petrosal contacts the edge of meatus is deeply invaded by this sinus, the basioccipital, but there is no suturing of which penetrates nearly to its lateral termi- petrosal to basioccipital as occurs in canids. nus. The roof of the sinus is smooth bone, The margin of the basioccipital is deeply ex- traversed by two thin ridges, and was evi- cavated for the inferior petrosal venous sinus dently covered by the mucosa lining the mid- (Hunt, 1977; Hunt and Barnes, 1994); this dle ear space. This sinus is a derived trait, excavation is evident in the paratype skull of and has been observed in the other species A. galushai (®g. 4.5). of North American Amphicyon (A. frendens, The form of the ectotympanic bulla, the F:AM 54415, Long Quarry; A. ingens, F:AM penetration of the hypotympanic sinus into 28307, Horse & Mastodon Quarry). Its oc- the bony meatal ¯oor of the bulla, the rela- currence in the paratype skull of A. galushai tionship of the bulla to the deeply recessed and also in A. ingens from Horse & Masto- petrosal promontorium, the embayed lateral don Quarry demonstrates that the sinus was margin of the basioccipital, and the lack of a present during the entire time span of the lin- sutural contact between petrosal and basioc- eage in the New World. The sinus also oc- cipital distinguish Amphicyon galushai from curs in North American skulls of Pliocyon contemporary carnivorans, and ally the spe- and Ischyrocyon, but is only incipient in ear- cies with the Amphicyonidae. ly species of Cynelos (Hunt, 1977, pl. 1). DENTITION: In contrast to Daphoenodon The auditory bulla was apparently fully from the Runningwater Formation, the upper ossi®ed and completely enclosed the audi- dentition of Amphicyon galushai is character- tory region, including the petrosal promon- torium. However, if the plane of the posterior ized by short premolars and a triangular M1 wall of the bulla is projected medially, it (nearly equilateral) with a large, rather ¯at, passes close to the posterior border of the subrectangular M2 (®gs. 4.2, 4.6, table 4.2). promontorium, indicating little or no back- The form of these teeth is as in the Sansan ward extension of the bulla, hence no pos- species, Amphicyon major, and unlike the terior expansion of the middle ear space. elongate upper premolars and transversely It is not possible to determine if entotym- elongate, anteroposteriorly narrow M1±M2 of panic elements contributed to the ectotym- Runningwater Daphoenodon. Upper incisors panic bulla of A. galushai. If they were pre- are not known, but from the alveoli it is clear sent, they were in a rudimentary state, not that I3 was much enlarged, whereas I1±2 expanded or encroaching to any degree on were small and narrow. The canines were of adjacent basicranial bones, and probably average size, the root present in UNSM making only a minor contribution to the me- 1570±59 measuring 19 ϫ 13 mm near the dial wall and posterointernal corner of the base, and the alveolus of the upper canine in bulla, as in a living ursid (Hunt, 1974, pl. 4). the paratype measuring 22.3 ϫ 15.0 mm. It is evident from the form of the occipital P1 has a single root and was probably a and mastoid bones that a caudal entotympan- small peglike tooth, judging from the form ic was not closely applied to their surfaces, of P1 in other species of the genus. in contrast to the situation in canids where P2 is preserved in UNSM 1570±59 as a this occurs. The presence of the accessory double-rooted tooth, with low central cusp, hypotympanic sinus on the question of no accessory cusps, a weak posterior ridge an entotympanic contribution to the amphi- running directly down the posterior slope; 92 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.6. A: Stereophotographs of upper dentition of Amphicyon galushai, UNSM 1570±59, Ho- vorka's Quarry, Runningwater Formation, NE. B: Restoration of upper dentition of UNSM 1570±59, showing relative size of M1 and M2 (reversed for comparison with paratype P4±M1, ®g. 4.2). the posterior part of the tooth is narrower border of the tooth is convex, and the pos- than the anterior part. terior border is straight to convex because of P3 is diagnostic: short in Amphicyon and a swelling midway along this edge. The tooth long in Runningwater Daphoenodon. In both is nearly an equilateral triangle in occlusal UNSM 1570±59 and in a referred maxilla view, thus differing from the much more (UNSM 25687), this tooth is extremely short, transversely extended M1 of Runningwater almost round, and peglike, and it lacks any Daphoenodon. There is no notch in the an- accessory cusps. The main cusp is centrally terior margin of the tooth as exists in Da- placed, the lateral part of the tooth slightly phoenodon. The protocone is placed more to- convex, the medial concave, but not to the ward the anterior border of M1. From the extent seen in Runningwater Daphoenodon. protocone to the base of the paracone there Most notably, there is little posterior widen- extends an unbroken ridge (preprotocrista of ing of the tooth, which does occur in Da- Van Valen, 1966) without cusps that termi- phoenodon. nates in unworn specimens in a small, low P4 is also diagnostic, especially its short- vestigial paraconule. The postprotocrista ex- ness relative to width, lack of a prominent tending from the protocone toward the meta- cusp on the protocone, and the presence of a cone ends at a low, distinct swelling, the parastylar cusp at the base of the anterior metaconule, much larger and more promi- face of the paracone. This short, wide P4 is nent than the paraconule, and placed farther also seen in Sansan Amphicyon.InA. major, linguad. The distinct metaconule has been A. galushai, A. frendens, and A. ingens,P4 noted as a characteristic feature of Old World length is slightly greater than M1 length (ta- Amphicyon major by Ginsburg (1961). The bles 4.2, 4.3, 4.5). cingulum is swollen and thickened at its pos- M1 has a tall, well-developed paracone, terolingual corner, just as in Daphoenodon, and a slightly shorter metacone. The anterior but there is no development of a cusp or 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 93 ridge that could be called a well-de®ned hy- ternal projection; posterolingual to the para- poconeÐthe thickened cingulum does little cone is a low metacone. Internal to the para- to alter the triangular form of M1. cone-metacone is a shallow ¯at protocone M2 occurs in place in the smaller skull basin entirely surrounded by a thick lingual (UNSM 1570±59), and in the Foster Ranch cingulum. M3 is represented only by alveoli maxilla (UNSM 26393) from the lower part in the paratype skull (F:AM 25400), in of the Runningwater Formation, Sioux Co., UNSM 1570±59, and in the Troublesome NE. It also is present in the rostrum (USGS Formation rostrum (USGS D645). D645) from the Troublesome Formation, CO. The lower dentition is known from three In UNSM 1570±59 and USGS D645, the M2 mandibles; the holotype (F:AM 25406) is is seen in relationship to M1 and the remain- the best preserved and most complete (®g. der of the upper teeth (®g. 4.6). There are 4.2). The lower premolars are separated by also two isolated M2s, a smaller one from short diastemata, are reduced in size, and Cottonwood Creek Quarry, and a much larg- are very low and of variable form. The p1 er M2 from Hemingford Quarry 12D, both is not preserved, but represented by a sin- in the Runningwater Formation. These ®ve gle alveolus or by two alveoliÐtheir shape M2s are all subrectangular in occlusal view, suggests that p1 was slightly elongate. It is but differ among themselves in shape and separated from p2 by a long or short dia- size (®g. 4.7). Because M2s of UNSM 1570± stema, and is always separated by a diaste- 59 and USGS D645 are in partial skulls of ma from the canine. A. galushai, there is no doubt that they be- The p2 is a low tooth, oval in occlusal long to that species. Although the variation view, with a low central cusp, narrower be- in M2 size and form is greater than in any hind the cusp than anterior to it (but in one other tooth in A. galushai, I infer that they individual wider behind), and with weak an- belong to a single species. Variation in M2 terointernal and posteroexternal ridges run- is likely the result of sexual dimorphism and ning downward from the central cusp to the also slight differences in geologic age among respective corners. the various Runningwater quarries. The p3 is slightly larger than p2 but is still M2 of Amphicyon is easily distinguished low, considerably more so than p4, and with from M2 of Runningwater Daphoenodon be- a low central cusp. However, in p3, the an- cause the latter has a transversely terior and posterior ridges run directly to the elongate, anteroposteriorly short M2 which is anterior and posterior basal borders, not to ``bent'' or folded around an anteroposterior the corners. The rear of the tooth is often axis through the protocone basin, causing the elevated as a small cingulum cusp, and to paracone-metacone to appear to be rotated this point runs the ridge in the Dunlap Camel inward toward the lingual half of the tooth. Quarry mandibles (F:AM 25407, F:AM In contrast, the occlusal surface of M2 of 25406). In the Cottonwood Quarry mandible, Amphicyon is quite ¯at, nearly a horizontal the ridge includes a posterior accessory cusp plane. The entire perimeter of the A. galushai not present in the other two jaws. M2 is bordered by a heavy cingulum thick- The p4 is considerably taller than p1±3 as ened to over 6 mm in width around the lin- in Amphicyon major from Sansan. It has a gual face of the protocone (®g. 4.7; UNSM posterior accessory cusp, no distinct anterior 25578), yet separated from that cusp by a accessory cusp, is slightly wider posteriorly, shallow groove. The M2 paracone is the larg- and has a rounded posterior basal border, in est cusp, taller than the metacone, the meta- contrast to the truncated or ``squared'' border cone is reduced, and the protocone low. of Runningwater Daphoenodon. The p4 There is a distinct and prominent paraconule; abuts the anterior face of m1. the metaconule is low, more subdued. The m1 is similar to m1 of Runningwater M3 is known only from an isolated tooth Daphoenodon, and it can be dif®cult to dis- (UNSM 25762) much smaller than M2. It tinguish isolated teeth. The paraconid is ad- has a large lingual and a small labial root. vanced anteriorly, the larger protoconid The occlusal surface is essentially ¯at; a low placed directly behind it. These two trigonid paracone is placed far labiad, forming an ex- cusps are rather tall, swollen, and become 94 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 4.5 Dental Measurements (in millimeters) of Amphicyon frendens and A. ingens (North America)

blunted with age; they wear in mature indi- Ysengrinia, where the entoconid ridge is not viduals to relatively ¯at surfaces, not to ver- developed). The tooth is widest between the tical shear planes. The metaconid is some- trigonid and talonid, and in occlusal view has what reduced and is placed on the postero- an elliptical outline. In contrast, m1 in Run- internal slope of the protoconid. The talonid ningwater Daphoenodon is somewhat nar- is shorter than the massive trigonid, a huge rower in occlusal view, but to reliably distin- hypoconid dominates the labial margin of the guish the two genera, p4±m2 in place in the talonid, and there is an entoconid ridge, well mandible is required. developed in the holotype (in contrast to The m2 is similar to m2 in Runningwater 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 95

TABLE 4.5 (Continued) 96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.7. Comparison of M2 in Amphicyon galushai illustrating variation in size and form: Left, UNSM 26393 (cast); center, UNSM 25578; right, F:AM 25437 (cast), all Runningwater Formation, NE. Note alveoli for M3 in UNSM 26393.

Daphoenodon, but is wider and more ellipti- teeth are similar in size, but much different in cal in occlusal view. The protoconid is quite form, from those of Amphicyon. Other than large, the small metaconid is a discrete, low by its teeth, Amphicyon galushai is most eas- cusp placed directly internal to the posterior ily distinguished from contemporary Da- part of the protoconid, but the paraconid is phoenodon by the bones of the feet and lower not evident as a distinct cusp, its position be- limbs. Daphoenodon has considerably more ing occupied by a low curved ridge. In old elongated lower limb bones and metapodials individuals, the m2 trigonid is worn to a ¯at relative to the short, stout lower limb elements surface without relief. The trigonid is larger and metapodials of Amphicyon. than the talonid, the latter with a prominent In addition to the two crania, three man- hypoconid and a very small entoconid. The dibles, and a number of isolated teeth from m3 is evidenced by a single, large, oval al- the Runningwater Formation, a scapula, hu- veolus. merus, ulna, radius, femur, astragalus, cal- The middle and posterior mental foramina caneum, cuboid, metacarpals 1±5, and meta- are placed below the anterior roots of p2 and tarsals 1±4 can be attributed to A. galushai p3, respectively. There are no demonstrable (®gs. 4.8±4.13). The sample lacks the ver- differences from Runningwater Daphoenodon tebrae, pelvis, sacrum, tibia and ®bula, and in location of the angular process, articular the smaller bones of the carpus and tarsus. condyle, or ascending ramus, except that the Based on comparison with other species of articular condyle itself appears to have been the genus, A. galushai must have had a long more transversely elongate in Daphoenodon. tail, but there are no certainly attributable POSTCRANIAL SKELETON: Almost all postcra- caudal vertebrae. Postcranial bones of A. gal- nial elements of Amphicyon galushai come ushai are extremely similar to postcrania of from only a few quarries: Hemingford Quar- European A. major described by Ginsburg ries 7B and 12D, and from Cottonwood Creek (1961). Quarry. Hemingford Quarries 7B and 12D are The forelimb of A. galushai is represented located at the surface of the Hartville Table in by the scapula, humerus, radius, ulna, and all northwestern Nebraska (Hunt, 1990), at a metacarpals. The proportions of scapula, hu- high topographic elevation, also considered merus, lower limb, and foot bones are essen- stratigraphically high in the Runningwater tially as in A. major. The scapula is massive, Formation. Isolated teeth of Amphicyon ac- robust, with broad surfaces of origin for the company the postcranial remains at these rotator cuff muscles that stabilize the scapu- sites. The only other large amphicyonid car- lohumeral joint. A large infraspinous fossa, nivore in these quarries in the upper Run- 16 cm in length and 2.5 cm in width, com- ningwater Formation is the large beardog Da- mon to amphicyonids and ursids, occupies phoenodon, whose postcranial remains and the ventral border of the scapula. The hu- 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 97

Fig. 4.8. Humerus, A. galushai, UNSM 26383, Hemingford Quarry 12D, Runningwater Formation, NE: anterior (left) and lateral (right) views. merus (length, 298 mm) is remarkable for the width and ventral extent of the broad surface for insertion of the deltopectoral muscles (®g. 4.8). This surface forms a prominent V- shaped plateau on the anterior surface of the diaphysis; this is more developed and ex- tends further ventrad than in living large ur- Fig. 4.9. Radius, A. galushai, UNSM 25557, sids and felids. Attachment areas for the or- Hemingford Quarry 12D, Runningwater Forma- igin of extensor and ¯exor muscles of the tion, NE: anterior (left) and posterior (right) carpus are prominent on the lateral and me- views. dial condylar areas of the distal humerus. Both radius (272 mm, ®g. 4.9) and ulna (321 mm, ®g. 4.10) are short relative to the more articulate satisfactorily, and indicate a radius elongated radius and ulna of the large Run- shorter than the humerus. Lengths of the ra- ningwater Daphoenodon (5 radii, mean ϭ dius (272 mm) and ulna (321 mm) of A. gal- 303.6 mm). A radius, ulna, and humerus of ushai fall within the range of the radius Amphicyon from the same quarry (Heming- (239±280 mm) and ulna (295±336 mm) of ford Quarry 12D), although not associated, A. major (data from Ginsburg, 1961; Ber- 98 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.10. Ulna, A. galushai, UNSM 25559, Hemingford Quarry 12D, Runningwater Formation, NE: lateral (left) and medial (right) views. gounioux and Crouzel, 1973). The diaphyses the lower forelimb bones which function of the radius and ulna exhibit elliptical ru- both in locomotion and as weight-bearing gose tracts for the anchoring of strong inter- columns. The metacarpals are short, robust osseous ligaments binding these bones to- bones (®g. 4.11); when articulated, they are gether; the con®guration of the proximal and not tightly appressed along their shafts as in distal articulations of the radius with the ulna living canids, but diverge distad. Although indicate a relatively unrestricted ability to there is no associated metacarpus to deter- pronate/supinate the forefoot on the lower mine the relative lengths of these bones, limb (more so than in living canids, where measurements of metacarpals 1±5 (table 4.6) this motion is restricted). Of interest is that suggest that they are proportionately similar the ulna in A. ingens no longer maintains the to those of A. major from Sansan, described slight curvature of the diaphysis seen in the by Ginsburg (1961). These measurements smaller species A. galushai. The enormous from unassociated metacarpals at ®rst seem size of A. ingens has modi®ed the form of to indicate that the forefoot was paraxonic, 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 99

Fig. 4.11. Metapodials, A. galushai, Runningwater Formation, NE. Above (left to right): MC 2, right, female, UNSM 25568; cuboid, UNSM 26394; MC2, left, male, UNSM 25569; MC 3, left, male, UNSM 25573. Below (left to right): MT 1, right, UNSM 25582; MT 2, left, UNSM 26391; MT 3, left, UNSM 26378; MT 4, left, UNSM 25565. with the central axis between metacarpals 3 sals 1±4. The femur (®g. 4.12, length 363 and 4 (MC1, 48; MC2, ϳ68±76; MC3, 82.8; mm) takes the same form as that bone in MC4, 85; MC5, 66.7 mm; table 4.6). How- Sansan A. major but is somewhat shorter, and ever, the associated metacarpals of A. major more robust. As in that carnivore, it is likely from Sansan described by Bergounioux and that the tibia and ®bula were short, much Crouzel (1973) reveal a forefoot more like more so than the tibia-®bula of Runningwa- that of living bears, but with greater empha- ter Daphoenodon. The cuboid (®g. 4.11) is sis on digits 3 and 4 and less emphasis of dorsoventrally short, lacking the elongation digits 1, 2, and 5. The sum of these anatom- seen in cursorial carnivorans such as living ical traits indicates a powerful but short fore- canids, felids, and Runningwater Daphoen- limb, capable of bearing considerable weight, odon. Its dorsal articular surface for the cal- and tolerant of signi®cant stresses during lo- caneum slopes laterad as in large ursines, and comotion and prey capture, yet permitting a it lacks the ¯at, horizontal dorsal surface of reasonable amount of manipulation with the living cursors. The calcaneum (®g. 4.12) is manus. most similar to that of large living ursids, and The hindlimb is represented by the femur, is distinct from the more elongate calcaneum cuboid, calcaneum, astragalus, and metatar- of large living felids; the lack of elongation 100 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.12. Femur, UNSM 25560, and calcaneum, UNSM 26386, of A. galushai from Hemingford Quarry 12D, Runningwater Formation, NE. Anterior (left) and posterior (right) views of femur, anterior view of calcaneum. 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 101

Fig. 4.13. Dimorphism in A. galushai:(A) female astragalus, UNSM 26389; (B) male astragalus, UNSM 26387; (C) female distal humerus, UNSM 26383; (D) male distal humerus, UNSM 26375. (A), (B), and (C) are from Hemingford Quarry 12D; (D) is from Hemingford Quarry 12B, Runningwater Formation, NE. of the distal calcaneum, the distal placement This is supported by the metatarsals (®g. of the sustentaculum, and the modest groov- 4.11), which are longer than the metacarpals; ing of the posterior surface of the sustentac- the metatarsals diverged distad and were not ulum for ¯exor tendons of the hindfoot all closely appressed, but the hindfoot was in- demonstrate less vertical orientation of the A. cipiently paraxonic. The lack of an associ- galushai hindfoot than seen in large felids. ated metatarsus of A. galushai prevents the However, the form of the astragalus (®g. determination of exact proportional relations 4.13) is intermediate between that of large among the metatarsals; however, table 4.6 living ursids and felids, and in its totality, the shows that metatarsals 3 and 4 were the lon- hindfoot was probably placed in an inter- gest; in fact, the metatarsals are similar in mediate position between the fully planti- length to those of A. major at Sansan (Gins- grade stance of living bears and the more burg, 1961). The skeleton of A. major de- vertically oriented hindfoot of large felids. scribed by Bergounioux and Crouzel, prob- 102 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 4.6 Comparison of Metapodial Lengths of Amphicyon galushai (North America) and Amphicyon major (France) in millimeters

ably a female on the basis of size (table 4.6), dicate that the long axis of the hindfoot of also has metatarsals 3±4 as the longest. As A. galushai was not as vertically oriented as remarked by Ginsburg, the slight elongation in the hindfoot of Daphoenodon. The meta- of the hindfoot coupled with the hindlimb tarsals and digits were somewhat more di- anatomy suggests the capability for powerful vergent in Amphicyon, but more closely ap- forward propulsion in keeping with a sudden, posed in Daphoenodon. In the hindfoot, Am- explosive rush from cover, similar to that ob- phicyon could be termed subdigitigrade and served for living lions (Panthera leo). Daphoenodon digitigrade. The calcaneum, astragalus, and cuboid of DIMORPHISM IN THE POSTCRANIAL SKELETON A. galushai are much different from those AND TEETH: Ginsburg (1961) and Ginsburg bones in Runningwater Daphoenodon. These and Telles-Antunes (1968) noted the pro- elements are elongated in Daphoenodon and nounced dimorphism in teeth and postcrania are indicative of the more vertical orientation of European Amphicyon. There is no doubt of the fore- and hindfoot in that genus. In that this also occurs in the species of North Daphoenodon, the calcaneum is narrow, with American Amphicyon, and is ®rst evident in a more dorsally placed sustentaculum deeply A. galushai (®g. 4.13), but also is present in grooved on its posterior surface for the ¯exor the larger A. frendens and A. ingens. Dimor- tendons of the hindfoot; the distal process of the astragalus is elongated, and more directly phism in A. galushai is based on signi®cant beneath the proximal trochlea; the cuboid is size differences in the following teeth and taller, with a nearly horizontal articular sur- postcranials: P4, M1, M2, humerus, astraga- face with the calcaneum. In Amphicyon, the lus, metacarpal 2, and metatarsal 2. This di- calcaneum is wider, with a more ventrally morphism has been considered sexual, the placed sustentaculum that is not as deeply larger morph the huge males, suggesting that grooved on its posterior surface; the distal these species are polygynous. In polygynous process of the astragalus is shorter, not carnivoran species, the males are usually moved beneath the proximal trochlea; the cu- highly territorial and solitary, and compete boid is short, robust, and retains a sloping among themselves for females during the dorsal surface (described as a ``surface breeding season. This is probably true of oblique'' by Ginsburg, 1961: 37) for articu- both Old and New World species of Amphi- lation with the calcaneum. These features in- cyon, and contributed to the large size at- 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 103 tained by these animals in Europe and North cranial remains of Amphicyon galushai, and America during the Miocene. retain the most plesiomorphic dentition at- tributable to Amphicyon in North America. DISCUSSION Although the paratype cranium lacks many teeth, the referred cranium (UNSM 1570±59) The fossils of early Hemingfordian Am- from Hovorka's Quarry has most of the up- phicyon come from two principal geographic per dentition in place. Only three mandibles areas: (1) the Runningwater Formation of of the species are known, two from Dunlap northwest Nebraska, comprising (a) speci- Camel Quarry and one from Cottonwood mens from the Hemingford Quarries of Creek Quarry, and these show considerable UNSM in Box Butte County, (b) from quar- wear on the molars, slight wear on the main ries of the Frick Laboratory (AMNH) in cusp of p4, and no wear on p1±3. These Dawes County; and (c) the isolated maxilla mandibles demonstrate that over time the from Foster Ranch, Sioux County, which molars become blunted with wear, lose their comes from the lower part of the Running- shear surfaces, and in later life must be pri- water Formation and represents the oldest marily limited to crushing. This toothwear occurrence of the genus in the Great Plains; pattern, however, does not preclude active (2) the U.S. Highway 40 roadcut in tuffa- carnivory because this type of molar wear ceous siltstones of the Troublesome Forma- also develops during the lifetime of living tion, Grand County, north-central Colorado, carnivorous canids such as North American deposited in the Middle Park intermontane wolves (Canis lupus). basin, west of the Rocky Mountain Front Amphicyon galushai may be ancestral to Range (Izett, 1968). A. frendens of the Sheep Creek Formation Fossils from the lower part of the Running- and A. ingens of the Olcott Formation, both water Formation, Nebraska (the Foster Ranch Nebraska. Premolars and molars of these maxilla), and from the Troublesome Forma- three species are similar in form but differ in tion, Colorado (the crushed rostrum), mark size (compare tables 4.2, 4.5): All have a re- the ®rst appearance of Amphicyon in the New duced P1±3/p1±3, p4 is prominent and con- World. These are the westernmost occurrenc- spicuously larger than p3, and the molars are es of North American Amphicyon in the early adapted for crushing. P4 in these three spe- Hemingfordian, and belong to the smallest cies is a robust, rectangular, massive carnas- species of the genus yet identi®ed in North sial with a low, reduced protocone and small America, here placed in the new species, A. parastylar cusp. However, these species differ galushai. With the exception of these two in the degree of enlargement of the molars. specimens, all other fossils come from quar- Figure 4.14 shows that M1 progressively in- ries or isolated outcrops of the Runningwater creases in size from A. galushai through A. Formation farther east in Dawes County and frendens to A. ingens. Similarly, M2 is rela- Box Butte County, Nebraska. Most A. galu- tively small in A. galushai, but in A. frendens shai specimens were discovered from 1934 to and A. ingens, this tooth has considerably in- 1941 by American Museum and UNSM ®eld creased surface area (®g. 4.15), as does M3. parties in northwest Nebraska; the two oldest In these large species of North American records, however, were found in 1965 and Amphicyon, the rear molars form broad 1982, and the smaller of the two known skulls crushing platforms, and the carnassials be- in 1959. The species is rare, and no complete come blunted by wear in older individuals as skeleton or even an associated skull and man- the result of a mortar/pestle action that drives dible has been found despite extensive quar- the m1 trigonid into the embrasure between rying in ¯uvial channel ®lls of the Running- P4 and M1 in the upper jaw. The anterior water Formation, sediments that have pro- premolars do not take part in this crushing duced large population samples of early Mio- occlusion, and remain greatly reduced, essen- cene ungulates. tially nonfunctional teeth. The paratype skull and the holotype man- COMPARISON WITH OLD WORLD AMPHICYON: dible from Dunlap Camel Quarry in the Run- Teeth and mandibles of Amphicyon galushai ningwater Formation are the best preserved most closely resemble those of Burdigalian 104 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.14. Comparison of M1 dimensions among North American species of Amphicyon.

Amphicyon in Europe. Ginsburg and Telles- smaller, narrower, and more plesiomorphic Antunes (1968) at ®rst placed most fossils of carnassials and molars. Recently, Ginsburg Burdigalian Amphicyon in the species A. gi- (1999) has restricted Amphicyon giganteus to ganteus. They divided A. giganteus into three specimens from MN zones 4±5, and now types that correspond to the increasing age places the late Aquitanian-Burdigalian spec- of the samples (table 4.7): (a) ``un type prim- imens from MN zones 2b±3 in a new species, itif'' of early Burdigalian age, (b) ``une A. laugnacensis (Ginsburg, 1989: 104). forme typique'' of mid- to late Burdigalian The form of the A. galushai mandible and and early Helvetian age, and (c) the early the cusp pattern of m1±m2 are very much Helvetian sample from the locality of Pon- like those of the late Burdigalian Amphicyon tlevoy, France. A. galushai is most similar in fossils from La Romieu, France (MN4a), ®rst dental traits to ``un type primitif, d'age bur- assigned to A. major by Roman and Viret digalien infeÂrieur.'' Both A. galushai and the (1934) and later placed in A. giganteus by early Burdigalian fossils of A. giganteus Ginsburg and Telles-Antunes (1968). The La share several primitive traits: the m1 talonid Romieu specimens include a small mandible, is slightly basined with a wide internal shelf, probably female, and a large mandible, prob- and m2 narrows posteriorly in width and re- ably male (Roman and Viret, 1934, pl. I, ®gs. tains a distinct paraconid. Nevertheless, A. 1±2). The molars in these mandibles are larg- galushai is clearly distinct from these early er than the molars of the A. galushai sample Burdigalian fossils of Amphicyon in its (®gs. 4.16, 4.17, tables 4.2, 4.7), and repre- 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 105

Fig. 4.15. Comparison of M2 dimensions among North American species of Amphicyon. sent a species more dentally advanced than mous teeth (Dehm, 1950, ®gs. 55, 56), much the Runningwater Amphicyon, yet apparently larger than M3/m3 in A. galushai (table 4.2). closely related. Early Burdigalian sites at Consequently, if these terminal molars be- Neuville and Chilleurs in France also have long to the same species of Amphicyon as the produced Amphicyon that measures some- Wintershof m1, then the Bavarian Amphi- what larger in m1±2 dimensions than A. gal- cyon differs from A. galushai in its more en- ushai, consequently suggesting that A. galu- larged posterior molars, and the New World shai displays more plesiomorphic molars A. galushai seems more primitive in its mo- than European Amphicyon of the Burdigalian lar battery than any of the Burdigalian or A. giganteus-A. laugnacensis group. Helvetian Old World species of the genus. An m1 and two terminal molars (M3, m3) Another Burdigalian amphicyonid often from the early Burdigalian locality of Win- placed in Amphicyon is found at several sites tershof-West, Germany (Dehm, 1950, ®g. 54, in Europe, and can be compared with A. gal- Munich 12297; ®gs. 55, 56, Munich 13565, ushai. This species, Amphicyon bohemicus, 13570) were attributed to A. giganteus by has been variously called Amphicyon stein- Ginsburg and Telles-Antunes (1968); m1 is heimensis bohemicus by Kuss (1965) or A. similar in size to lower carnassials of A. gal- dietrichi by Dehm (1950). Specimens from ushai, but no other similarly sized material the Burdigalian of Wintershof-West, Tuchori- was reported from these ®ssures. The termi- ce, and Feisternitz are said to belong to this nal molars of this Wintershof-West Amphi- taxon (see Kuss, 1965: 46). I have been able cyon, if they are correctly allocated, are enor- to study casts of the material described by 106 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

TABLE 4.7 Dental Measurements (in millimeters) of Amphicyon giganteus from Europea 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 107

Fig. 4.16. Comparison of m1 dimensions of North American Amphicyon galushai and European Amphicyon.

Dehm from Wintershof-West: This carnivore Bonis (1973, pl. 8) and by Kuss (1965, ®g. is not as large as A. galushai, and has a more 72), this is a conservative species in which compressed snout with smaller carnassials and the posterior molars have not yet enlarged. A molars, and more narrow m1±m2 (table 4.8). maxilla with P4±M2 (MuseÂum de Toulouse) Ginsburg (1999: 116) regarded Amphicyon from Hauterive (Haute-Garonne) ®gured by bohemicus-A. steinheimensis as a European Kuss (1965, ®g. 56) is similar in proportions Miocene lineage, and has placed these two to these teeth in A. galushai, indicating that species in the subgenus Heizmannocyon.It the Old and New World species are at a sim- may be more closely related to the amphi- ilar stage of molar evolution; however, the cyonine Cynelos than to Amphicyon. MN1 fossils are much older (22.8±23.8 Ma; Before the Hemingfordian North American Steininger et al., 1996) than early Hemingfor- Land Mammal Age (NALMA), there is no dian A. galushai. record of Amphicyon in the New World. How- Ginsburg's (1999) recent summary of Eu- ever, prior to the late Aquitanian and Burdi- ropean Amphicyon identi®es A. astrei in galian in Europe ( mammal zones MN1 as the earliest species in western Eu- MN2b-MN3), Amphicyon has been reported rope; later in MN2b, A. laugnacensis appears at several early Aquitanian (MN1) sites in at Laugnac, and continues into MN3; in southern France (Kuss, 1962; Ginsburg and MN4±5, large A. giganteus is the commonly Telles-Antunes, 1968; Bonis, 1973). These encountered representative of the genus; in fossils, placed in Amphicyon astrei or A. cf. MN6, this large species is no longer present, astrei, were found at Garrouch, Hauterive, and is replaced by the smaller A. major at and Paulhiac. This species is acknowledged Sansan and correlative sites. Ginsburg and as the oldest representative of the genus in Telles-Antunes (1968), however, noted a Europe (Ginsburg, 1999). Based on mandibles number of isolated teeth in the Burdigalian from Paulhiac and Garrouch, illustrated by and early Helvetian that they believed could 108 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279

Fig. 4.17. Comparison of m2 dimensions of North American Amphicyon galushai and European Amphicyon. represent A. major, coexisting with the larger cestor of the great European amphicyons of A. giganteus. Were the two European species the Burdigalian and Helvetian. Amphicyon evolved in situ from European Oligocene astrei in turn is said to have evolved from a amphicyonids, or were A. major and A. gi- Stampian species of the amphicyonid Pseu- ganteus immigrants that entered Europe in docyonopsis (Ginsburg, 1966). Thus, these the Burdigalian, accompanying the equid An- European species of Amphicyon are seen as chitherium and proboscideans? Ginsburg endemic forms, evolved in place in the re- concluded that Amphicyon astrei was the an- gion.

TABLE 4.8 Dental Measurements (in millimeters) of Amphicyon bohemicus from Europea 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 109

AMPHICYONÐSUMMARY AND CONCLUSIONS: genus could extend from as early as ϳ18.8 This report summarizes all known fossil ma- Ma to ϳ14.2 Ma. The upper range limit is terial of the earliest North American occur- somewhat uncertain; however, the last occur- rences of the Old World amphicyonid carni- rence of Amphicyon in North America is be- vore Amphicyon. These fossils constitute the lieved to be at Horse and Mastodon Quarry, earliest North American record of this line- northern Colorado, of Barstovian age, where age of large predatory amphicyonids (ϳ40± A. ingens is found together with probosci- 200 kg) that ranged from the eastern sea- deans above a tuff dated at 14.3 Ϯ 0.02 Ma board to the Paci®c coast, and from southern (Tedford, 1999: 43, ®g. 18A). The genus is Canada to Texas, but whose remains are best last recorded along the Paci®c coast at ϳ14.8 represented in the central Great Plains. The Ma (Skyline Quarry) in the Barstow syn- genus includes at least three species: early cline, California. Although some Barstovian Hemingfordian A. galushai, new species, late occurrences cannot be reliably dated, there is Hemingfordian A. frendens Matthew, and little probability that Amphicyon survived be- early and mid-Barstovian A. ingens Matthew. yond 14 Ma in the New World. Cranium, dentition, and postcrania of the The paratype skull of A. galushai from a oldest New World species, A. galushai, are ¯uvial channel ®ll in northwest Nebraska be- similar to these same elements found in the longed to a mature adult; it is uncrushed and Old World Amphicyon major and A. gigan- adequately preserves the undistorted skull teus, but demonstrate the existence of a dis- form, including the basicranium. The basi- tinct New World lineage of Amphicyon that cranium is typical of amphicyonids in having evolved in isolation, spatially disjunct from a relatively small ectotympanic bulla and a the European species. deep embayment of the basioccipital for the Amphicyon is known for its tendency to inferior petrosal venous sinus; the basicrani- enlarge the molars in both upper and lower um of A. galushai is similar in these features jaws, and reduce in size yet retain the pre- to basicrania of the New World A. frendens molars. The enlarged molars, particularly and A. ingens. The paratype of A. galushai M2/m2 and M3/m3, become the hallmark of also retains an anatomically signi®cant part the younger species. By the mid-Miocene in of the auditory bulla that shows the highly both the Old and New World, these carni- specialized penetration of the middle ear cav- vores evolved massive crushing molars, re- ity into the bony external auditory meatus. duced premolars, enormous body size, and a This is found in all North American species postcranial skeleton indicative of powerful of the genus. It remains to be determined if musculature, employed in short bursts of this accessory hypotympanic sinus occurs in speed to overtake and kill their smaller prey, European Amphicyon. using their great strength. Despite similarities in skull form, skeleton, Amphicyon galushai is remarkable in and dentition, the Old and New World spe- showing the initial stage in the broadening of cies of Amphicyon appear to have evolved M2±3/m2±3 that preceded the marked molar independently in isolation. The scarcity of hypertrophy seen in the later species of North adequately preserved Asian fossils de®nitely American Amphicyon. Its posterior molars attributable to Amphicyon prevents insight are the smallest on record for any species of into the possibility that Asian Amphicyon New World Amphicyon. populations connect the New and Old World The discovery of A. galushai in early lineages. Only isolated teeth and a few frag- Hemingfordian sediments in northwest Ne- mentary jaws of Neogene amphicyonids braska and north-central Colorado establish- have been described from the Siwaliks of es a temporal datum for the earliest appear- southern Asia (Matthew, 1929; Pilgrim, ance of the genus in the New World, a min- 1932; Colbert, 1935) and from Viet Nam imum age of ϳ18.2 Ma, based upon the pa- (Ginsburg et al., 1992). Additional teeth and leomagnetic determination of Chron C5En partial maxillae and mandibles are known (ϳ18.2±18.8 Ma) within the lower Running- from and , but most are in- water Formation, northeast of Agate, Sioux adequate for con®dent referral to Amphicyon County, Nebraska. The temporal range of the (s.s.). East Asian fossils that may be correctly 110 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 referred to Amphicyon include the holotype gapredator role with large hemicyonine ur- mandibles of Amphicyon confucianus sids and a few relict creodonts. (Young, 1937, Shanwang) and A. ulungur- ensis (Qi, 1989, Xinjiang); a maxilla referred PALEOECOLOGY OF NORTH to A. cf. major from the Tongxin basin; and AMERICAN AMPHICYON isolated teeth of A. palaeindicus from the Si- A functional interpretation of the teeth, waliks (Colbert, 1935, ®gs. 38, 39). skull, and postcranial skeleton demonstrates A continuously maintained geographic con- that North American Amphicyon was a mid- nection between Old and New World lineages to large-sized terrestrial lacking cur- seems unlikely, however, because of the size sorial specializations like those seen in the discrepancy between New and Old World limbs and feet of living canids; its postcranial Amphicyon species at various times in the ear- skeleton shares a number of features with large ly and mid-Miocene. In Europe, a large spe- living ursids and felids. Ginsburg (1961: 44± cies of Amphicyon already occurs in the early 45) earlier remarked on this postcranial mo- and mid-Burdigalian (MN3b±MN4) when saic. However, these skeletal similarities do not only the smaller A. galushai occurs in North indicate close relationship to either ursids or America. An enormous A. giganteus is pre- felids. The postcranial skeletons of large ur- sent in Europe in the late Burdigalian±early sids, felids, and amphicyonids are now recog- Helvetian (MN5) when, in North America, A. nized as independently evolved solutions to the frendens appears in the late Hemingfordian, common problems of weight-bearing and ef- preceding the huge A. ingens of the early to ®cient locomotion in large carnivores. Slightly mid-Barstovian. The more modestly built A. different postcranial skeletal patterns devel- major probably occurs in Europe at ϳ15.2 Ma oped in these lineages as species within each in MN6 (Steininger et al., 1996: 13) at a time family attained large body size during the mid- in North America when only the very large to late Cenozoic. A. ingens is known. Amphicyon ingens exists The skeletal characteristics of North Amer- in North America from ϳ15.9 Ma to at least ican Amphicyon would be compatible with a 14.2 Ma. These populations of A. ingens are wooded habitat, whether savanna or riverine the ®nal representatives of Amphicyon in the gallery forest, and it seems likely that these New World. We see, then, that the species of large carnivores ambushed prey from cover, Amphicyon in North America increase in size overpowering them with their size and from their ®rst arrival in the early Heming- strength. European species of Amphicyon have fordian to their last appearance in the mid- been similarly portrayed as stalking predators, Barstovian. But in Europe, a smaller species, leaping suddenly on prey from cover, much in A. major, succeeds A. giganteus, the largest the manner of the living lions (Ginsburg and species of the genus to evolve in the Old Telles-Antunes, 1968; Bergounioux and World, and additional species of Amphicyon Crouzel, 1973; Ginsburg, 1999). not recognized in the New World are also pre- sent in the Miocene of Europe (Ginsburg, NEOGENE MIGRATION OF LARGE 1999), indicating a more diverse and complex CARNIVORANS FROM EURASIA TO amphicyonid radiation than is evident at this NORTH AMERICA time in North America. On the northern continents during the ear- The ®rst appearances in the geologic re- ly and mid-Miocene, a niche existed for large cord of a number of large mammalian car- predatory carnivorans, following the extinc- nivores have been employed as datum points tion of large creodonts in Eurasia and North in Cenozoic biochronology (Tedford et al., America. Amphicyonids were the ®rst car- 1987, ®g. 6.3; Webb, 1989; Webb and Op- nivorans to respond to this ecological oppor- dyke, 1995; Woodburne and Swisher, 1995, tunity, rapidly deploying a variety of lineages ®gs. 3±5). Such occurrences have been used (amphicyonines, temnocyonines, haplocyon- to clarify the boundaries and temporal spans ines, daphoenines) to exploit these niches. In of the North America Land Mammal Ages the early and mid-Miocene of Eurasia and (NALMAs). Recent research into the phylo- North America, amphicyonids share this me- genetic relationships of major groups of Car- 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 111 nivora, and new information as to the geo- can provide reliable evidence for biochronol- logic and geographic distribution of the larg- ogic datum events. er mammalian carnivores, both in North Figure 4.18 presents ®rst and last appear- America and Eurasia, have resulted in revi- ance data for selected mid-sized and large sion of these earlier data. Figure 4.18 sum- carnivorans for the North American late Ol- marizes ®rst and last appearances of selected igocene to early . The initial appear- carnivorans during the Miocene and early ance of Amphicyon, revised in this study, Pliocene in North America (relevant late Ol- now occurs with the earliest Hemingfordian igocene data are also included). faunas in North America. The extinction of First appearances of fossil carnivorans are the genus takes place between 14 and 14.2 usually indicated as migrant genera, and are Ma; the last Amphicyon (A. ingens) is coeval recorded as a ®rst occurrence when present with the earliest records of Proboscidea in in the rock record at one or more localities. the interior of North America. An acknowledged problem with this ap- The late Eocene to early Pliocene of North proach is that carnivores are often among the America can be subdivided into temporal in- rarest fossils in collected assemblages of fos- tervals, each characterized by a particular sil mammals. Because of their place at or large carnivoran association (Hunt and Ted- near the top of the ecological pyramid, they ford, 1993). Four associations are recognized are commonly represented by smaller popu- here: (1) hyaenodont creodonts±nimravid lations relative to ungulates and other pri- carnivores (ϳ40±24 Ma); (2) temnocyonine mary consumers. Thus, their poorer repre- amphicyonids±large entelodonts (ϳ29±18.8 sentation in the living fauna may result in Ma); (3) amphicyonine amphicyonids±hem- less frequent incorporation into thanatocoe- icyonine ursids (ϳ18.8±9 Ma); (4) large fe- noses. A number of ®rst occurrences of Car- lids±ursids±borophagine canids (9±ϳ4 Ma). nivora are based on single fossils. Hyaenodonts and nimravids de®ne the late Eocene through late Oligocene interval in An equally important factor in assessing im- North America. Creodonts and nimravid cat- migration±extinction patterns in the fossil re- like carnivores, together with less diverse cord is the pattern of sedimentation in time and amphicyonids, are the common large carni- space. If sedimentation in local basins is absent vores of White River Group deposits in the from extensive geographic areas within a con- North American interior during the late Eo- tinent over prolonged temporal intervals, the cene and Oligocene. Hyaenodonts are extinct probability of preserving an immigration by ϳ29.5 Ma, whereas nimravids continue to event, particularly with regard to rare Carniv- ϳ24 Ma and are not certainly recorded in ora, is low. Consequently, a ``®rst appearance'' any early Miocene sites. may occur in the rock record long after the With the extinction of creodonts in the carnivore enters the area. Similarly, an animal New World, there is an almost simultaneous may occupy a habitat geographically removed appearance of temnocyonine amphicyonids, from active areas of sedimentation on a con- accompanied by large durophagous entelo- tinent well before its presence is recorded by donts. Although artiodactyls, entelodonts eventual migration into an active sedimentary were scavenger± that ®lled a niche basin. Despite these dif®culties, the pattern of later occupied by durophagous hyaenids in ®rst and last occurrences (®g. 4.18), whether the Old World and by ``hyaenoid'' canids in interpreted as immigration and extinction North America. Temnocyonines initially are events or simply as the currently identi®able small carnivores (ϳ10±15 kg), rapidly in- limits of taxon ranges, directs attention to sig- creasing in size in several lineages during the ni®cant turnover episodes in the carnivoran late Oligoene and early Miocene. From fauna during the North American Neogene. ϳ29±30 Ma to 24 Ma, temnocyonines co- Particularly useful are well-documented pres- exist with nimravids, but after ϳ24 Ma, nim- ence/absence data for major groups over con- ravids are extinct. The date of 24 Ma (ap- tinent-wide regions, where numerous fossil proximating the Oligocene±Miocene bound- samples have been collected in a variety of ary) marks the beginning of the North Amer- depositional settings over many years; these ican early Miocene ``,'' the interval 112 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 279 2003 HUNT: MIGRATION OF MAMMALIAN CARNIVORES 113 from ϳ24 Ma to ϳ17 ma when no nimravids the large felids and Nimravi- or true felids are known in North American des, joining late Miocene endemic lineages Miocene faunas, despite extensive sampling of hyaenoid canids (, ). of numerous localities of appropriate age. These carnivorans mark the ascendance of a Late Arikareean temnocyonines are now rec- canid±felid±ursid assemblage that continues ognized as the ®rst North American amphi- to the present. In the Pliocene (Blancan cyonids to attain large body size, developed NALMA) and early (Irvingtoni- in at least three separate lineages. an NALMA), important changes in this as- From ϳ18.8 Ma to 9 Ma, the large carni- semblage occur: (a) the Hemphillian ursids voran fauna differs entirely from earlier ones. are replaced by Ursus and tremarctine bears Large amphicyonine amphicyonids (includ- (, Arctodus); (b) the sabertoothed ing Amphicyon) and hemicyonine ursids now felids are gradually replaced by numerous dominate the carnivore assemblages at early species of Felinae; and (c) the borophagine and mid-Miocene localities in North Ameri- canids become extinct and are replaced by ca. Almost all genera are immigrants from the radiation of modern Caninae. Eurasia at this time. Amphicyonines (Ysen- grinia, Cynelos) and endemic daphoenine amphicyonids (Daphoenodon and a related ACKNOWLEDGMENTS genus) replace the temnocyonines (last re- Permission to describe the American Mu- corded in the Upper Harrison beds, Arikaree seum fossils was given by R. H. Tedford and Group, central Great Plains), and eventually, M. C. McKenna. The Troublesome Formation the large entelodonts, which become extinct Amphicyon, collected in 1962 by Glenn Izett, at about ϳ17.5 Ma. U.S. Geological Survey (USGS), was loaned During the ϳ18.8 Ma to 9 Ma interval, certain important changes occur in the large by James Honey and the USGS, Denver, CO. carnivoran assemblage. Early in the interval, The Foster Ranch maxilla from the lower Run- Amphicyon coexists with smaller - ningwater Formation in Sioux County, Ne- ines such as and . braska, was found by Grayson Meade, who Later, following the extinction of Amphicyon kindly allowed the casting and study of the at ϳ14±14.2 Ma, the large amphicyonids specimen, and who took the author to the site Pseudocyon and Ischyrocyon are accompa- of collection. The original is kept at the Agate nied by and a new large hemi- Ranch headquarters, Agate, Nebraska, in the cyonine genus (Hunt, 1998). At ϳ9Ma collection of the late Grayson and Dorothy (Clarendonian±Hemphillian boundary), these Meade. Figures 4.1, 4.8±4.10, and 4.12±4.18 large amphicyonids and hemicyonines be- were ably prepared by University of Nebraska come extinct, leaving the large carnivore State Museum (UNSM) illustrator Angie Fox. niche open to lineages of felids, endemic ca- Preparation of the Amphicyon skulls was ca- nids, and migrant ursids that rapidly increase pably undertaken by Ellen Stepleton, and in body size to occupy that role. many of the postcranials were prepared by Rob In the North American Hemphillian, a va- Skolnick, who also located undescribed post- riety of Old World Carnivora make their ap- cranial elements in unopened ®eld jackets at pearance as immigrants (Tedford et al., UNSM. For helpful reviews of the manuscript, 1987). Conspicuous in these faunas are the I appreciate the comments of Bruce J. Mac- large ursids and , the Fadden and Margery C. Coombs. My interest smaller tremarctine ursid , and in the biogeography of the Carnivora stems

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