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2002 New Amphicyonid Carnivorans (Mammalia, Daphoeninae) from the Early Miocene of Southeastern Wyoming Robert M. Hunt Jr. University of Nebraska-Lincoln, [email protected]

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Hunt, Robert M. Jr., "New Amphicyonid Carnivorans (Mammalia, Daphoeninae) from the Early Miocene of Southeastern Wyoming" (2002). Papers in the Earth and Atmospheric Sciences. 546. https://digitalcommons.unl.edu/geosciencefacpub/546

This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3385, 41 pp., 28 ®gures, 4 tables December 27, 2002

New Amphicyonid Carnivorans (Mammalia, Daphoeninae) from the Early Miocene of Southeastern Wyoming

ROBERT M. HUNT, JR.1

CONTENTS Abstract ...... 2 Introduction ...... 2 Abbreviations ...... 3 Geologic and Geographic Distribution ...... 3 Mammals of the Upper Harrison ...... 8 Systematic Paleontology ...... 9 Adilophontes brachykolos, new genus, new species ...... 10 Daphoenodon falkenbachi, new species ...... 21 Daphoenodon skinneri, new species ...... 29 Discussion ...... 31 Anderson Ranch Formation: A New Term for the Upper Harrison ...... 35 Acknowledgments ...... 39 References ...... 40 Appendix ...... 41

1 Research Associate, Division of Paleontology, American Museum of Natural History; Professor, Geological Sci- ences, and Curator, Vertebrate Paleontology, University of Nebraska, Lincoln, NE 68588-0549. e-mail: [email protected]

ABSTRACT

Latest Arikareean sediments of the upper Arikaree Group in southeastern Wyoming produced rare fossils of large, early Miocene amphicyonid carnivorans for ®eld parties of the Frick Laboratory, American Museum, from 1932 to 1940. Recent geologic ®eld investigations, including mapping, have discovered additional remains of these carnivorans, clarifying their geographic and stratigraphic distribution, and permitting a more informed description of the earlier collections. These carnivorans come from tuffaceous sandstones of the Upper Harrison beds, the terminal formation-rank unit of the Arikaree Group in southeastern Wyoming. A large species of the amphicyonid Daphoenodon (D. falkenbachi, n. sp.) occurs in northern Goshen and southeastern Platte Counties, Wyoming, and in the Niobrara Canyon, Sioux County, Nebraska. A smaller species of this genus (D. skinneri, n. sp.), probably ancestral to D. falkenbachi,is known from a single individual from southern Niobrara County, Wyoming. A third amphicyonid, Adilophontes brachykolos, n. gen., n. sp., is closely related to Daphoenodon, and is reported from northern Goshen County and east-central Platte County, Wyoming. The three species share a similar basicranial anatomy, including the form of the auditory bulla, and can be referred to the endemic North American amphicyonid subfamily Daphoeninae. They are found only in Upper Harrison strata in southeastern Wyoming and northwest Nebraska, and are presently unknown elsewhere in North America. Postcranial remains indicate that these large predators lacked the extreme digitigrade specializations of the feet and limbs encountered in living canids and large felids. They are characterized by relatively short lower-limb segments, and paraxonic feet with slightly spread- ing digits, which might be termed subdigitigrade. These skeletal traits and their carnassiform dentitions with prominent canines, premolars, and shearing carnassials indicate a carnivorous diet probably obtained by a rapid rush from cover and a short, powerful pursuit of ungulate prey in open grassland and riparian stream settings east of the Rocky Mountain uplifts. A new formal term, Anderson Ranch Formation, is proposed as a replacement for the Upper Harrison beds of Peterson (1909) that yielded the carnivores discussed in this study.

INTRODUCTION don falkenbachi, n. sp., based on previously unreported specimens collected from 1932 to Nonmarine tuffaceous sediments of the 1940 in Goshen and Platte Counties by ®eld Arikaree Group blanketed much of south- parties of the Frick Laboratory, American eastern Wyoming in the late Oligocene and Museum of Natural History (New York); and early Miocene, mantling the Precambrian D. skinneri, n. sp., a single individual from cores of the Hartville Uplift and the Laramie Niobrara County, Wyoming, collected in Mountains (®g. 1). For over a century these deposits have yielded collections of fossil 1957. mammals de®ning an important biochronol- The Upper Harrison beds are the terminal ogic interval in the early Miocene of North formation of the Arikaree Group in the cen- America. Most skeletal remains represent tral Great Plains, and contain a fauna of latest isolated individuals, buried on ancient land Arikareean age (ϳ18.8±19.2 Ma) in south- surfaces by ®ne-grained, ash-rich eolian sed- eastern Wyoming, western Nebraska, and iments. Ungulates (oreodonts, horses, cam- southwestern South Dakota. This rock unit els, rhinoceroses) are most common as fos- has produced the richest representation of sils, whereas predatory carnivorans at the latest Arikareean mammals in North Ameri- apex of the ecological pyramid are rare. The ca, including a remarkable diversity of large largest and most imposing carnivores were carnivores. The amphicyonids serve as reli- beardogs of the family Amphicyonidae. Here able biochronologic indicators of the con- I describe three species of early Miocene am- cluding interval of the Arikareean North phicyonids from the Upper Harrison beds of American Land Mammal Age in the Great southeastern Wyoming (®g. 2): Adilophontes Plains but at present are unknown elsewhere brachykolos, n. gen., n. sp., and Daphoeno- in North America. 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 3

Fig. 1. Fine-grained tuffaceous sandstones of the upper Arikaree Group mantling the granites and Paleozoic limestones of the Hartville Uplift in southeastern Wyoming (view to the southwest with Rawhide Butte at upper left and the Paleozoic carbonates of the Hartville Uplift on the far horizon). Arikaree outcrops east and north of Rawhide Butte include the Royal Valley district of C.H. Falkenbach.

ABBREVIATIONS Institutional AMNH American Museum of Natural History, Anatomical New York CM Carnegie Museum of Natural History, A alisphenoid Pittsburgh BO basioccipital FMNH Field Museum of Natural History, Chi- BS basisphenoid cago ex exoccipital F:AM Frick Laboratory, American Museum gf glenoid fossa of Natural History, New York h hypoglossal (condyloid) foramen LSUMG Louisiana State University Museum of ina bony tube for internal carotid artery Geoscience, Baton Rouge, LA m mastoid process UF Florida Museum of Natural History, me mastoid-exoccipital suture Gainesville, FL p petrosal promontorium UNSM University of Nebraska State Museum, pc posterior carotid foramen Lincoln, NE pg postglenoid foramen pl posterior lacerate foramen GEOLOGIC AND GEOGRAPHIC pp paroccipital process DISTRIBUTION R ?rostral entotympanic s basioccipital embayment for inferior The Upper Harrison beds were ®rst named petrosal venous sinus and described by O.A. Peterson (1907, SQ squamosal 1909a) from prominent exposures in the Ni- st styliform process of the auditory bulla obrara Canyon, Sioux County, northwest Ne- T ectotympanic braska (®g. 3). Hunt (1978, 1990) de®ned the tt tensor tympani fossa northern and southern limits of the Upper w posterior wall of the auditory bulla 4 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 2. Restorations of the skulls of amphicyonids from the Upper Harrison beds of southeastern Wyoming: top, Adilophontes brachykolos, n. gen., n. sp.; middle, Daphoenodon falkenbachi, n. sp.; bottom, Daphoenodon skinneri, n. sp. Scale bar, 5 cm. 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 5

Fig. 3. The Niobrara Canyon in northwest Nebraska was designated the stratotype area of the Upper Harrison beds by O.A. Peterson (1909a: 75); the canyon includes the thickest known exposures of the formation in Sioux County where siliceous paleosols form ¯at geomorphic surfaces (arrows) interpreted from their contained rhizoliths as regionally extensive grassland plains that extended westward to the Precambrian granite-cored Hartville Uplift.

Harrison in Sioux County, tracing the for- Harrison continue south of the river and east mation from Peterson's type area in the can- of the Laramie Mountains to the vicinity of yon north to the Pine Ridge and south to the Chugwater, Platte County, Wyoming. Al- Niobrara River valley at Agate Fossil Beds though the formation contains a variety of National Monument. Hunt's stratigraphic eolian, ¯uvial, and lacustrine lithofacies pro®le from the Pine Ridge escarpment to (Hunt, 1990), the ®ne-grained tuffaceous Agate in Sioux County indicated that the for- pale gray-brown to orange-brown eolian mation is thickest (ϳ50 m) in the vicinity of sandstones and siltstones predominate in the the Niobrara Canyon and thins both to the region, usually making up over 80% of out- north and south (Hunt, 1990: ®g. 4). Upper crop. These eolian strata are punctuated at Harrison beds extend eastward into Dawes intervals by grassland paleosols, character- and northern Sheridan Counties in Nebraska, ized by dense networks of ®ne (average di- where the sediments become noticeably ®ner ameter, 0.5 mm) anastomosed white silica grained. The beds continue to the northeast rootlets that weather to siliceous duricrusts along the Pine Ridge of southwestern South (®g. 4). The duricrusts form ¯at geomorphic Dakota where they had been identi®ed as the surfaces that are particularly prominent east Rosebud Formation by Macdonald (1963, of the Hartville Uplift in southeastern Wyo- 1970) and ``Upper Rosebud'' beds by Mat- ming and northwestern Nebraska (®g. 3). thew (1907). The formation can be traced in The regional extent of these duricrusts and outcrop from its type area in the Niobrara uniform expression of this lithofacies over Canyon nearly continuously westward to the several 1000 km2 indicate the prevalence of Hartville Uplift, and southward along the open grassland or savanna east of the prin- eastern margin of the uplift to the valley of cipal Precambrian-cored ranges in the early the North Platte River. Outcrops of the Upper Miocene. 6 AMERICAN MUSEUM NOVITATES NO. 3385 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 7

Fig. 5. Depositional environments of the early Miocene Upper Harrison beds in southeastern Wy- oming and northwest Nebraska (from Hunt, 1990). Amphicyonid carnivores occur in stream, waterhole, and grassland plains but have not been found in ephemeral lakes.

Amphicyonids have been found not only ofacies re¯ects their ability to range widely, in the grasslands but in all depositional en- occupying whatever settings offered suitable vironments of the Upper Harrison beds with prey. the exception of a few shallow ephemeral Two species of amphicyonids discussed lakes isolated on the open plains (®g. 5). No here are among the largest predators of their mammals have been found in these lacustrine time, approached in size by a carnivorous limestones, which are sparsely populated by Upper Harrison mustelid Megalictis ferox fossils of pulmonate gastropods, ostracods, (Hunt and Skolnick, 1996) and surpassed aquatic plants, but are without ®sh or other only by the large immigrant amphicyonine aquatic vertebrates. Presumably the distribu- Ysengrinia americana (Hunt, in press a). tion of the amphicyonids in a variety of lith- The geographic distribution of these am-

← Fig. 4. A well-developed siliceous paleosol of the Upper Harrison beds, Agate Fossil Beds National Monument, Sioux County, Nebraska: A, tuffaceous ®ne-grained silty sandstone with siliceous paleosol (ps) at top of section forming duricrust; zone (br) of rhizoliths and invertebrate burrows gradually diminishes downward below duricrust (cliff height ϳ4.5 m). B, SEM photomicrograph showing sediment fabric of very ®ne sand and silt grains cemented by authigenic silica derived from pedogenic dissolution of volcanic glass shards and unstable mineral grains. Dense anastomosing networks of ®ne-diameter siliceous rhizoliths (rz, 0.5 mm) in these paleosols are interpreted as evidence of extensive grassland plains. C, Photomicrograph showing very ®ne tuffaceous sand and silt of Upper Harrison eolian lithofacies with abundant angular grains and volcanic glass shards. This lithofacies has produced large numbers of fossil mammals. 8 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 6. Geographic distribution of Adilophontes brachykolos, Daphoenodon falkenbachi, and D. skinneri in the early Miocene Upper Harrison beds of southeastern Wyoming and western Nebraska. A. brachykolos: 1, F:AM 27568, 18 Mile District, Goshen Co., Wyoming; 2, F:AM 54140±54141, southwest of Spoon Butte, Goshen Co., Wyoming; 3, F:AM 54148, Roll Quarry, Platte Co., Wyoming. D. falkenbachi: 4, F:AM 54144, 18 Mile District, Goshen Co., Wyoming; 5, UNSM 99420, Lay Ranch beds west of Spoon Butte, Goshen Co., Wyoming; 6, CM 3719, Niobrara Canyon, Sioux Co., Nebraska; 7, 8, F:AM 54145±54150, 54146, 5±7 (ϳ8±11.3 km) miles southeast of Chugwater, Platte Co., Wyo- ming. D. skinneri: 9, F:AM 70801, ϳ9 miles (14.5 km) southeast of Lusk, Niobrara Co., Wyoming. These amphicyonids are not known from Arikaree rocks in Colorado or South Dakota. phicyonids in southeastern Wyoming and by three individuals; D. falkenbachi by re- western Nebraska (®g. 6) is limited to the mains of ®ve individuals; and D. skinneri by geographic extent of outcrops of the Upper one individual, re¯ecting how rarely these Harrison and is essentially random within the animals are discovered relative to the more outcrop area of the formation. The northern- commonly encountered fossil ungulates. most occurrences are in the Niobrara Can- yon, Sioux County, Nebraska, and ϳ9 miles MAMMALS OF THE UPPER (14.5 km) southeast of Lusk, Niobrara Coun- HARRISON BEDS ty, Wyoming, and the southernmost ϳ5 miles (8 km) southeast of Chugwater, Platte Coun- All but one specimen of the three species ty, Wyoming; they have not been found in of amphicyonids described in this report younger rock units in the immediate area or come from Goshen, Platte, and Niobrara elsewhere in North America. Counties, Wyoming. Unfortunately, the exact Adilophontes brachykolos is represented location where each was found remains un- 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 9 certain. Most were collected from 1932 to oceras and the small oreodont Merychyus 1940 by personnel of the Frick Laboratory, have been found in beardog dens in the re- American Museum of Natural History, New gion (Hunt et al., 1983). York, under the direction of Charles H. Fal- kenbach. Falkenbach's ®eld parties were re- SYSTEMATIC PALEONTOLOGY sponsible for extensive collections of late Ol- ORDER CARNIVORA BOWDICH, 1821 igocene and early Miocene mammals from Arikaree strata in the vicinity of the Hartville DIVISION ARCTOIDEA FLOWER, 1869 Uplift in southeastern Wyoming during the FAMILY AMPHICYONIDAE TROUESSART, 1885 decade prior to World War II (Galusha, 1975: SUBFAMILY DAPHOENINAE HOUGH, 1948a 10f.). Frick's collectors brought together a rich Adilophontes, new genus mammalian fauna from the Upper Harrison TYPE SPECIES: Adilophontes brachykolos, beds east of the Hartville Uplift in northern new genus and species. Goshen County, extending south and west ETYMOLOGY: adeilos, fearless; phontes, into eastern Platte County. This fauna in- slayer, Greek; in reference to its carnivorous cludes a homogeneous assemblage of early habit. Miocene taxa: the oreodonts Merychyus and INCLUDED SPECIES: Only the type species. Merycochoerus matthewi; equids Parahippus KNOWN DISTRIBUTION: Latest Arikareean, nebrascensis, P. wyomingensis, and an an- Goshen County and Platte County, Wyo- chithere; camels Tanymykter, Oxydactylus, ming. and Stenomylus; rhinoceroses Menoceras and DIAGNOSIS: As for the monotypic species. Diceratherium; the large entelodont Dinoh- DISCUSSION: The genus is based upon rare yus; and the chalicothere Moropus. Among occurrences of a large carnivorous amphi- the small and mid-sized carnivorans were ca- cyonid from the Upper Harrison beds of nids (Desmocyon thomsoni, Osbornodon southeastern Wyoming, at present recognized brachypus, Cynarctoides luskensis), the mus- nowhere else in North America. Each of the telid Promartes, and the hemicyonine ursid three known individuals includes a well-pre- Cephalogale. The large carnivorans were pri- served skull with mandible, and some asso- marily amphicyonids: the immigrant amphi- ciated postcranial elements. Limb bones and cyonine Ysengrinia; several species of the metapodials demonstrate lower forelimbs endemic daphoenines Daphoenodon and Ad- and feet that were short relative to the size ilophontes, described here; at least two spe- of the skull. Males have large skulls accom- cies of temnocyonines; and the predatory pa- panied by a radius with a distal exostosis; a leomustelid Megalictis. Adilophontes, Ysen- small skull associated with a radius without grinia, and one of the temnocyonines were an exostosis is considered female. The radial the largest of these carnivores, the males exostosis is not a pathologic feature but is a probably attaining a body mass of ϳ60± normal osteological characteristic of several Ͼ100 kg. daphoenine species (e.g., Daphoenus vetus, The notable absence of highly cursorial Daphoenodon superbus, Daphoenodon no- ungulates of large size in the Upper Harrison tionastes). fauna ®nds a parallel in the lack of large digitigrade carnivores. Ruminant artiodactyls Adilophontes brachykolos, and oreodonts were mostly small, and were new species probably frequent prey of the beardogs. Figures 2A, 7±17, 25B Horses and camels were larger on average and would have presented a greater challenge HOLOTYPE: F:AM 27568, complete uncru- to these carnivores. Adult entelodonts, chal- shed skull and mandibles, left humerus, ulna icotheres, and dicerathere rhinoceros should and radius (without exostosis), proximal left have been to some degree immune to pre- femur, distal right tibia, both astragali, left dation by amphicyonids because of their size, navicular and ectocuneiform, four lumbar with the exception of their vulnerable young. vertebrae and numerous fragments (®gs. 7, Bones of calves of the small rhinoceros Men- 8B, 10A, C). 10 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 7. Holotype skull of Adilophontes brachykolos, F:AM 27568, Upper Harrison beds, 18 Mile District, Goshen Co., Wyoming: A, dorsal view; B, palatal view. Scale bar, 5 cm.

ETYMOLOGY: brachykolos, Greek, short- TYPE HORIZON: Upper Harrison beds, up- legged, in reference to the short forelimb of per Arikaree Group (early Miocene). the species, based on the radii associated REFERRED SPECIMENS: (1) F:AM 54140, with two of the skulls (F:AM 27568, F:AM complete skull, slightly crushed, associated 54140). with distal femur, left radius (with distal ex- TYPE LOCALITY: Approximately 18 miles ostosis), left calcaneum, three articulated cer- (29 km) southeast of Lusk, Goshen County, vical vertebrae, vertebral fragments, left Wyoming (18 Mile District of C.H. Falken- metatarsal 3, left metatarsal 4, proximal bach). metatarsal 5, from southwest of Spoon Butte, 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 11

Fig. 8. Adilophontes brachykolos: A, male cranium, F:AM 54140, Upper Harrison beds, southwest of Spoon Butte, Goshen Co., Wyoming; B, female cranium, F:AM 27568, holotype, Upper Harrison beds, 18 Mile District, Goshen Co., Wyoming. Scale bars, 5 cm.

Goshen Co., Wyoming (®gs. 8A, 9, 10B, 11); sal 4), from Roll Quarry, about 3 miles (4.8 F:AM 54141, a damaged right mandible with km) south of Guernsey, Platte County, Wy- m1±3 and p4 fragment, from the same lo- oming (®gs. 12, 13). cality as F:AM 54140 and probably the same KNOWN DISTRIBUTION: Latest Arikareean, individual; (2) F:AM 54148, complete skull Goshen County and Platte County, Wyo- and associated mandibles, atlas vertebra, left ming. femur, and a distal metapodial (?left metatar- DIAGNOSIS: Mid-sized to large amphicyon- 12 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 9. Adilophontes brachykolos, F:AM 54140, upper dentition and palate of adult male, Upper Harrison beds, southwest of Spoon Butte, Goshen Co., Wyoming. Adilophontes retains fully developed premolars in contrast to the reduced premolars of the amphicyonine Ysengrinia, which also occurs in Upper Harrison beds at Spoon Butte. Scale bar, 1 cm. ids with long, narrow dolichocephalic skulls, from west of Spoon Butte, and probably be- dorsoventrally deep (in contrast to Daphoen- longs to the same individual as F:AM odon superbus, in which the skull is low and 54140); (2) F:AM 54148, an aged male skull broad); rostrum deep; epipodial limb seg- (basilar length, 30.5 cm), both mandibles, ments short, not elongated as in some am- and femur, from Roll Quarry, Platte County, phicyonid species; distal radius with promi- Wyoming, associated with a number of other nent exostosis in males (the exostosis does mammals (rhinoceros Menoceras, equid Par- not occur in Ysengrinia and Amphicyon); me- ahippus), apparently in a local bonebed; (3) tapodials short, not elongated as they are in F:AM 27568, the holotype, a mature female temnocyonines; premolars well-developed, skull (basilar length, 24.3 cm), two heavily not reduced as in Ysengrinia; dental formula damaged mandibles, associated with a partial 3-1-4-3/3-1-4-3; M2 not enlarged relative to forelimb including the radius, and a partial M1; p2 and p3 longer (also p1±4 length) than hindfoot (astragalus, navicular, ectocunei- the corresponding premolars of Daphoeno- form) from the 18 Mile District of Falken- don superbus and Ysengrinia. bach, Goshen County, Wyoming. The skull DISCUSSION: The three individuals assigned of F:AM 54140 is associated with a radius to this species are interpreted as two large that has a prominent bony distal exostosis males and a smaller female: (1) F:AM (®g. 10B). The smaller skull of F:AM 27568 54140, a mature male, represented by a skull is accompanied by a radius without an ex- (basilar length, ϳ30 cm), radius, distal femur, ostosis (®g. 10A). F:AM 27568 and 54148 partial hindfoot, and several vertebrae, from both retain the basicranium and remnants of west of Spoon Butte, Goshen County, Wyo- the auditory bulla, which are useful in deter- ming (F:AM 54141, a partial mandible mining phylogenetic relationships of carni- which shows the same preservation as the vorans. skull and corresponds in size also comes Although the precise localities at which 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 13

Fig. 10. Forelimb bones of Adilophontes brachykolos associated with female and male skulls of ®gure 8: A, female radius lacking distal exostosis, F:AM 27568, holotype; B, male radius with distal exostosis, F:AM 54140; C, female humerus, F:AM 27568, associated with holotype radius. Scale bar, 5 cm. the three individuals of Adilophontes were F:AM 54140 was collected from an area found were not recorded by the Frick Labo- ``southwest of Spoon Butte'' in Goshen ratory ®eld collectors, identi®cation of the County. Spoon Butte is a commanding approximate locations can be based on recent north±south-oriented topographic feature in ®eld studies of the same geographic areas. northeastern Goshen County, 3.4 miles (5.7 Two of the three individuals (F:AM 27568, km) in length and 0.6 miles (1 km) in width F:AM 54140±54141) from the Upper Harri- at several points; it is intersected by the Wy- son beds in northern Goshen County can be oming±Nebraska state boundary. Rising 400 placed fairly accurately in a modern strati- ft above the surrounding terrain, the ¯at- graphic context. topped butte is held up by a thick (ϳ20 ft) 14 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 11. Partial hindfoot of Adilophontes brachykolos associated with the male cranium, F:AM 54140, from left to right: calcaneum, metatarsals 3, 4, and proximal part of 5, all of the left side, and a proximal phalanx. Scale bar, 1 cm. caprock of mid-Miocene ¯uvial sandstone and Survey Division, Lincoln, NE) discov- representing a linear remnant of a major ¯u- ered an early Miocene paleovalley ®ll, 2 vial system in reversed topographic mode. miles (3.2 km) in width, passing through the Our geologic mapping of the butte and the butte from west to east, and extending for a surrounding region (R.M. Hunt, Jr., Open- considerable distance beyond the butte itself. File Map, Spoon Butte 7.5-minute quadran- These early Miocene strata yielded a latest gle, University of Nebraska Conservation Arikareean mammal fauna to UNSM ®eld

Fig. 12. Cranium of an aged adult male Adilophontes brachykolos with heavily worn teeth, F:AM 54148, Upper Harrison beds, Roll Quarry, Platte Co., Wyoming. Scale bar, 5 cm. 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 15

Fig. 13. Left mandible of Adilophontes brachykolos associated with cranium in ®gure 12, F:AM 54148; note worn premolars, molars, and blunted canine. Similar toothwear has been observed in aged North American wolves (Canis lupus). Scale bar, 1 cm. workers and comprise ¯uvial channel and ofacies (Hunt, 1990: 75f.). Sediment samples ¯oodplain units of ®ne-grained tuffaceous taken from this lithofacies and from F:AM sandstones, siltstones, and lithic pebble grav- 27568 are comparable: a ®ne brownish-gray el, age-equivalent to the Upper Harrison tuffaceous sand with dark minerals scattered beds. Because this paleovalley ®ll is geo- through the rock matrix. graphically isolated from the main body of Mammalian fossils found in the 18 Mile the Upper Harrison beds to the north in District and in the Lay Ranch paleovalley northern Goshen County (Lone Sand Hill commonly occur as partial skeletons of sin- 7.5-minute quadrangle), the strata have been gle individuals, with some bones still artic- informally named the Lay Ranch beds (Hunt, ulated. The skeletons accumulated on land 1985a; Skolnick, 1985). The Lay Ranch beds surfaces of semiarid grassland plains (18 are the only fossiliferous formation likely to Mile District) and in shallow channels and have produced this amphicyonid carnivore the ¯oodplain of a broad ephemeral stream (F:AM 54140±54141). A sediment sample (Lay Ranch paleovalley), where they were removed from the skull, a ®ne-grained scavenged and scattered prior to burial by brownish-gray tuffaceous sand with abun- gradually accumulating ®ne-grained tuffa- dant dark minerals scattered through the ma- ceous sediments. The partial skeletons of F: trix, is comparable to similar samples taken AM 27568 and F:AM 54140±54141 conform from Lay Ranch outcrops west and south- to this taphonomic mode. west of Spoon Butte. The burial environment of the Roll Quarry F:AM 27568 came from Upper Harrison individual (F:AM 54148) from Platte County outcrops approximately 18 miles (29 km) south of Guernsey, Wyoming, is more dif®- southeast of Lusk, Wyoming, that Falken- cult to interpret because the exact quarry lo- bach designated the ``18-Mile District''. This cation is lost. American Museum ®eld re- district lies east of Route 85 in northern Go- cords do not establish its geographic loca- shen County. Most of the exposures are ®ne- tion, only that the quarry was sited ``3 miles grained eolian tuffaceous sandstones over- south of Guernsey, Wyoming''. Fortunately, printed at various levels by siliceous paleo- a plaster-jacketed block of fossils in the orig- sols, referrable to a volcaniclastic loess lith- inal sediment matrix from the quarry sur- 16 AMERICAN MUSEUM NOVITATES NO. 3385 vives at the American Museum. It includes and associated radius (199 mm) of the ho- the mixed skeletal remains of horse and rhi- lotype of A. brachykolos indicate a humero- noceros, evidently part of a mass accumula- radial index of 89.6 (®g. 10A, C), similar to tion buried either in a waterhole or local ¯u- that of the amphicyonines Ysengrinia amer- vial channel. A stratigraphic section made by icana (ϳ89.3) and Cynelos lemanensis C.H. Falkenbach in the AMNH archives, as (ϳ89.5). This ratio in D. superbus is 86.7. In well as the associated fauna from Roll Quar- living lions (Panthera leo, 90±94, N ϭ 11) ry, suggests that the quarry was either in the and digitigrade canids (Canis lupus, C. la- Upper Harrison beds or an unidenti®ed over- trans, 97±104, N ϭ 7) this ratio consistently lying stratigraphic unit. A personal recon- is Ͼ90, indicating a more elongate forelimb. naissance in October 2001 of Arikaree rocks The degree of elongation of the manus rel- south of Guernsey demonstrated the presence ative to the radius is not known in Adilo- of Upper Harrison lithologies that conform phontes because of the absence of metacar- to Falkenbach's stratigraphic section and lith- pals. However, in amphicyonids the forefoot ic descriptions but failed to locate the quarry. is usually shorter than the hindfoot, and a However, examination of sediment samples short hindfoot is evident in A. brachykolos from the Roll Quarry skull, and sediment re- (F:AM 54140) based on the length of MT3± moved from the other skulls of Adilophontes 4 (73.2, 78.6 mm) relative to the length of (F:AM 27568, 54140), shows a uniform min- its associated calcaneum (80.9 mm) and ra- eralogy: a ®ne, brownish-gray, silty tuffa- dius (218 mm). Associated hindfeet of the ceous sandstone of similar petrographic com- smaller D. superbus (CM 1589c: MT3±4, position, typical of the Upper Harrison beds 73.1, 77.2 mm; calcaneum, 63.3 mm; CM of southeastern Wyoming. All of these sam- 1589, holotype: MT3±4, 70, 73 mm; calca- ples, including one removed from the Roll neum, 59.1 mm) from the Agate Monument Quarry skull, contain unusual elongated an- carnivore dens have metatarsals of almost the gular laths of glassy black obsidian that have same lengths, but much less robust, and a not been observed in overlying rock units, much smaller calcaneum, indicating a rela- and therefore suggest that Roll Quarry does tively larger but quite short hindfoot in A. occur in the Upper Harrison beds. brachykolos (®g. 11). When these three individuals were col- Although the two large skulls of Adilo- lected in the period 1932±1940, they were phontes (F:AM 54148, 54140) differ con- informally referred to Daphoenodon by the spicuously in size (basilar lengths, 30.5 cm, Frick Laboratory. However, the laterally ϳ30 cm) from the smaller skull of the ho- compressed skulls of Adilophontes, with lotype (ϳ24 cm, F:AM 27568), the upper their deep rostra and more rounded dorsal toothrows of these three individuals are pro®le, differ markedly from the low, broad much more similar in size (C±M2 length: skulls of Daphoenodon (®g. 2). These dif- 13.2, 12.1, 11.4 cm, respectively). The ferences in skull form, together with the marked size difference in the skulls is prob- short forelimb and a dentition with well-de- ably attributable to sexual dimorphism, an in- veloped premolars, distinguish A. brachyko- ference supported by the osteology of the ra- los from other Arikareean amphicyonids: all dius. The smaller skull of the holotype (F: temnocyonine amphicyonids have elongated AM 27568) is accompanied by a short radius lower limbs and feet; the daphoenines D. su- without an exostosis (®g. 10A); one of the perbus and D. falkenbachi differ in their low, larger skulls (F:AM 54140) is also associated broad skulls; and the amphicyonines Ysen- with a short radius but with a prominent ex- grinia and Amphicyon have much reduced ostosis (®g. 10B). Males of daphoenine am- anterior premolars. phicyonids are known to have such exostoses Postcranial bones associated with two of on the distal radius that are lacking in fe- the skulls of Adilophontes demonstrate that, males (Hatcher, 1902; Hunt, 1996: 483). De- despite their large size, these carnivores were spite the ϳ6 cm difference in basilar length short-legged, evidenced by the proportions of between F:AM 27568 and F:AM 54140, the radius and metapodials relative to the hu- lengths of their radii are similar (F:AM merus. The lengths of humerus (222 mm) 27568, 19.9 cm; F:AM 54140, 21.8 cm). The 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 17 ratio of radius length/basilar length of skull relative to D. superbus, and a visual inspec- in F:AM 27568 is 82.5, and in F:AM 54140 tion of the skulls of A. brachykolos con®rms is 72, indicating the relatively larger size of this impression: the elongate, narrow skull the head in the male. Here these specimens (®g. 7) includes a small basicranium coupled are considered a single species, and A. bra- to a large rostrum with a particularly robust chykolos is identi®ed as a short-legged car- dentition. nivorous amphicyonid with large, robust The auditory bulla is largely intact in the males and smaller-skulled females (®g. 14). holotype except for the loss of the ventral The basicranium of the holotype (F:AM ¯oor (®gs. 15, 16). As in other early Miocene 27568) is well-preserved (®g. 15), and al- amphicyonids, the bulla was a rudimentary though crushed, a comparable basicranial ¯ask-shaped bony capsule. Formed mostly or anatomy occurs in one of the referred male entirely by the ectotympanic bone, its walls skulls (F:AM 54148). The basioccipital is are thin and very delicate. The bulla protrud- broad, 30.4 mm in the holotype; width across ed below the level of the basicranial axis and the mastoid processes is 78.3 mm. The pro- so was susceptible to breakage. The large portions in F:AM 54148, the large male, are male (F:AM 54148, ®g. 17) retains more of similar, but crushing precludes accurate mea- the ventral ¯oor of the bulla than the holo- surements. The form of the basicranial bones type female; its shape and modest degree of surrounding the auditory region in both male in¯ation are similar to the bulla of the D. and female is the same: the glenoid fossae superbus holotype (®g. 18, CM 1589). The lie on the same plane as the basicranial axis; anterior part of the bulla is strongly extended and the basicranial axis forms an angle of into the anteromedial corner of the auditory ϳ30Њ with the palate, demonstrating that the region and includes a lathlike styliform pro- face of this carnivore was somewhat de- cess. As in D. superbus, the anterior part of pressed (®g. 2A), allowing the orbits to be the bulla is prolonged ϳ2 to 8 mm in front more forwardly directed (this angle is ϳ15Њ of a transverse line drawn through the post- in D. superbus). The roof of the external au- glenoid processes. In contrast to the evident ditory meatus formed by the squamosal is anterior extension of the bulla, the posterior 17.6 mm in width, and internal to this, the wall is quite thin and unin¯ated; it does not petrosal is deeply inset in the auditory area; extend behind the mastoid processes, an in- the mastoid processes are well-developed but dication that the bulla remains in a rudimen- small relative to the size of the skull, and the tary form typical of early arctoid carnivor- paroccipital processes are very small. The ans. This bulla form is closely approximated lateral margin of the basioccipital is deeply by living ursids which, however, have an embayed for an enlarged inferior petrosal ve- even more strongly ossi®ed posterior wall nous sinus, presumably containing a loop of than seen in these beardogs (Hunt, 1974: pl. the internal carotid artery as in living ursids 4). (Hunt, 1974). The postglenoid foramen is The internal structure of the bulla can also moderately developed for internal jugular be seen in the holotype female (®g. 16). The drainage; the hypoglossal foramen lies rela- interior of the right auditory region is essen- tively close to the posterior lacerate foramen. tially intact. Here, and in F:AM 54148, a Perhaps the most striking aspect of the ba- short bony external auditory meatus ϳ8mm sicranium in this species is that it is so small in length was probably continued laterad by relative to the overall dimensions of the skull cartilage in the living animal. The middle ear (®g. 7B). In the holotype female (F:AM cavity is rather long and narrow, 5.5±7.5 mm 27568) the ratio of basicranial width (mea- in width in the holotype, and possibly as sured across the mastoid processes) to basilar much as 1 cm in the large male. The length length of skull is 78.3/243 mm, or 0.32; for of the middle ear cavity in the holotype is the large male of A. brachykolos this ratio is ϳ20 mm and in F:AM 54148 is ϳ24 mm; ϳ92/305 mm, or 0.30; in the female holotype the cavity is a single chamber. The crista of D. superbus this ratio is 80.4/215 mm, or tympanica is nearly vertical, with the plane 0.37. In overall dimensions, the basicranium of the tympanum tilted inward ϳ15Њ and roof A. brachykolos is short and rather narrow tated slightly mesad. Ventral to the crista the 18 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 14. Restoration of male and female crania of Adilophontes brachykolos from the Upper Harrison beds, Goshen Co., Wyoming: top, male, F:AM 54140; bottom, female, F:AM 27568. Scale bar, 5 cm. 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 19

Fig. 15. Basicranium of Adilophontes brachykolos, holotype, F:AM 27568, Upper Harrison beds, Goshen Co., Wyoming. Stereophotographs. Scale bar, 1 cm. For abbreviations in this and all subsequent anatomical ®gures, see p. 3. middle ear cavity has been extended laterad both Adilophontes and Daphoenodon. The a short distance into the bony external audi- pocketing is also present in the earliest North tory meatus; this space is con¯uent with an American Amphicyon, in which it is much extension of the middle ear cavity into the more extensively developed. We now know anterolateral bulla wall that produces a small that this type of middle ear extension evolved pocket (®gs. 15, 16). This pocketing also oc- in parallel in several lineages of early Mio- curs in Daphoenodon falkenbachi (®g. 23A) cene amphicyonids. and is a shared derived trait characteristic of The internal carotid artery traveled the en-

Fig. 16. Stereophotographs of the right auditory region of Adilophontes brachykolos (anterior to left), F:AM 27568, female holotype, Upper Harrison beds, Goshen Co., Wyoming. Scale bar, 1 cm. 20 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 17. Stereophotographs of left auditory region of aged male Adilophontes brachykolos (anterior at top), F:AM 54148, showing auditory bulla in place. White dashed line indicates the location of the posterior bulla wall which has been lost to breakage in this individual. Note that the bulla does not extend behind the mastoid process. Scale bar, 1 cm. tire length of the medial wall of the bulla as a shallow depression situated between the enclosed in a thin-walled bony tube. This mastoid and paroccipital processes. It is bi- bony tube rested directly on the medial mar- sected by the mastoid-exoccipital suture, gin of the petrosal promontorium (®gs. 15, which remains prominent in adults. The me- 16). The artery entered the tube at the pos- dial portion of this depressed surface is ru- teromedial corner of the bulla, as in many gose and was the site of origin of the digas- living ursids (Hunt, 1974: pl. 4, ®g. 16), and tric muscle. not farther forward along the medial wall, as Several features of the basicranium indi- in most living mustelids and procyonids. It cate that A. brachykolos retained a relatively continued within the tube to the anteromedial primitive arctoid auditory region: (1) the ba- corner of the auditory region, where it trav- sicranium occupies only a small area of the eled the ventral margin of a small triangular skull in ventral view and lacks any evident ossi®cation situated on the anterior slope of anatomical specializations; (2) the bulla is a the promontorium (?rostral entotympanic, rudimentary arctoid type, formed chie¯y by ®g. 16, R). It then turned abruptly to enter an ectotympanic bone, either entirely lack- the basioccipital embayment that presumably ing, or with only a minor caudal entotym- contained the enlarged inferior petrosal si- panic contribution; (3) the thin-walled, deli- nus. cate construction of the bulla and the absence The area occupied by the auditory region of bulla expansion posterior to the mastoid posterior to the bulla is very small; the dis- processes of the skull; and (4) the very small tance from the posterior bulla wall to the area occupied by the posterior auditory re- base of the paraoccipital process is only ϳ5± gion behind the bulla anterior to the paroc- 6 mm in the holotype skull. The posterior cipital processes. The bulla of A. brachykolos wall of the auditory region formed by the closely corresponds in structure and form to mastoid and exoccipital bones is excavated the auditory bulla and basicranium of Da- 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 21

(``High Brown Sand'' of Falkenbach), upper Arikaree Group (early Miocene). REFERRED SPECIMENS: Referred material is from the Upper Harrison beds in Sioux County, Nebraska, and Niobrara, Goshen, and Platte Counties, southeastern Wyoming: (1) F:AM 54146, partial left mandible with p4±m3, partial right mandible with m2, from 5 miles southeast of Chugwater, Platte Coun- ty, Wyoming; (2) F:AM 54145, left partial mandible with c±m1 that makes a reliable contact with a fragment with m2 (F:AM 54150), indicating the same individual, from 5 miles southeast of Chugwater, Platte Coun- ty, Wyoming; (3) CM 3719, left mandible of a young individual with m1±2, partial p4, Ni- obrara Canyon, Sioux County, Nebraska; (5) UNSM 99420, partial rostrum with left P1± M2, right I3, and partial postcranial skeleton, from the Lay Ranch paleovalley, west of Spoon Butte, Goshen County, Wyoming. KNOWN DISTRIBUTION: Latest Arikareean of Sioux County, Nebraska, and Niobrara, Goshen, and Platte Counties, Wyoming. DIAGNOSIS: Mid-sized species of the genus Fig. 18. Drawing of right auditory region of in the North American midcontinent; distin- Daphoenodon superbus (anterior at top), CM 1589, holotype female, from the carnivore dens at guished by larger size from Daphoenodon Agate National Monument, Carnegie Quarry 3, notionastes (ϳ34±38%) and D. superbus basal Upper Harrison beds, Sioux Co., Nebraska. (ϳ10±23%), demonstrated by cranial (table The auditory bullae of D. superbus and A. bra- 1) and dental measurements (tables 2, 3). The chykolos (®g. 17) are similar in form and indicate posterior border of p4 in D. falkenbachi is a relationship between the two species. more rounded than in D. superbus and D. notionastes in which the posterior p4 margin is usually straight, with squared corners. phoenodon superbus (CM 1589), providing Length of m2 relative to m1 length (table 4) evidence of the close relationship of the two in D. superbus (54.5±63.1%, N ϭ 5) is genera within the New World amphicyonid slightly greater than in D. falkenbachi (51.3± subfamily Daphoeninae. 54.3%, N ϭ 3), indicating a shorter m2 in D. falkenbachi. Distinguished from A. brachy- Daphoenodon falkenbachi, kolos by a lower, wider skull with less down- new species ward rotation of the facial region on the posterior cranium and by short, broader anterior Figures 19, 20, 21A, 23, 25A premolars. Dental formula: 3-1-4-3/3-1-4-3. HOLOTYPE: F:AM 54144, complete skull The postcranial skeleton of D. falkenbachi and associated mandibles (®gs. 19, 20, 21A). is poorly known, represented only by the par- ETYMOLOGY: Named for the late C.H. Fal- tial skeleton of a single individual (UNSM kenbach, Frick Laboratory (AMNH), who 99420) collected in 1983 from the Lay led ®eld parties south of Lusk, Wyoming, Ranch beds west of Spoon Butte: included that discovered the holotype in 1939. are the tibia (without distal end), distal ®bula, TYPE LOCALITY: 18 Mile District of C.H. calcaneum, proximal ulna, carpal cuneiform, Falkenbach, Goshen County, Wyoming. scapholunar, a proximal phalanx, and a few TYPE HORIZON: Upper Harrison beds ribs and vertebrae, which do not provide suf- 22 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 19. Holotype cranium and mandible of Daphoenodon falkenbachi, F:AM 54144, Upper Har- rison beds, 18 Mile District, Goshen Co., Wyoming. Scale bar, 5 cm.

®cient information to determine the degree come from southeastern Wyoming, whereas of elongation of the lower limbs. the entire sample of D. superbus is from DISCUSSION: In the lowest stratigraphic lev- northwest Nebraska. However, the two spe- el of the Upper Harrison beds in northwestern cies occur together in superposed stratigraph- Nebraska, waterholes and carnivore dens have ic relationship in the Niobrara Canyon as de- produced most of the the known sample of scribed below. On September 4, 1901, a Daphoenodon superbus, the holotype species mandible of D. falkenbachi (CM 3719), ini- of the genus. The species was discovered and tially identi®ed as ?Aelurodon, was found by named by O.A. Peterson (1907, 1909b, 1910) O.A. Peterson along the Niobrara River in for specimens from the carnivore dens of Car- Sioux County. We know from ®eld records negie Quarry 3 at Agate National Monument of the Carnegie Museum that Peterson col- in Sioux County. In the higher stratigraphic lected the mandible in the Niobrara Canyon, levels of the Upper Harrison beds in north- southwest of Harrison, Nebraska, in outcrops western Nebraska and southeastern Wyoming, he later designated as the type area for the Daphoenodon is represented by a species Upper Harrison beds (Peterson, 1909a). Sed- larger and more robust than D. superbus. This iment adhering to the mandible con®rms that species is herein named D. falkenbachi for it was collected in the Upper Harrison beds Charles Falkenbach of the Frick Laboratory from the pale brownish-gray volcaniclastic whose ®eld crews collected the holotype cra- loess lithofacies. In the Niobrara Canyon this nium and mandibles in 1939 from the 18 Mile lithofacies always occurs stratigraphically District, northern Goshen County, Wyoming. above the waterhole bonebeds (Harper Quar- A few additional mandibular fragments with ry and equivalent sites) that yielded D. su- teeth of D. falkenbachi were found by Frick perbus in the lowest part of the formation. ®eld parties in 1939±1940 near Chugwater, Thus, in the canyon the two species occur in Platte County, Wyoming. superpositional relationship: D. superbus in Almost all specimens of D. falkenbachi a bonebed (Harper Quarry local fauna) in the 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 23

Fig. 20. Holotype left mandible of Daphoenodon falkenbachi, F:AM 54144, Upper Harrison beds, 18 Mile District, Goshen Co., Nebraska. A, lateral view; B, medial view. Scale bars, 1 cm.

lowest part of the formation (Hunt, 1978), tal region. The D. falkenbachi skull differs and D. falkenbachi from a higher level within these features from the high, laterally in the pale brown volcaniclastic loess (Nio- compressed cranium of Adilophontes from brara Canyon local fauna, Hunt, 1990). the same locality and stratigraphic unit (the Identi®cation as Daphoenodon is support- holotype crania of D. falkenbachi and A. bra- ed by the distinctive skull form of the D. chykolos are both from Falkenbach's 18 Mile falkenbachi holotype (FAM 54144, ®g. 2B), District). In its dentition, D. falkenbachi which is identical to the skull of D. superbus. lacks the characterictic squared posterior bor- Both the holotype of D. falkenbachi and the der of p4 seen in D. superbus (which occurs holotype skull of D. superbus (CM 1589, Pe- in all known mandibles of the species); D. terson, 1910) are low and broad crania, with falkenbachi also lacks the long, rectangular a short rostrum and moderately in¯ated fron- m2 of the D. superbus hypodigm. In other 24 AMERICAN MUSEUM NOVITATES NO. 3385 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 25

TABLE 1 Basilar Lengths of Skulls of North American Arikareean Daphoenine and Amphicyonine Amphicyonids and the European Aquitanian Amphicyonine Cynelos

respects, the teeth of D. falkenbachi are sim- length of the forelimb and feet, thus allowing ilar in form yet larger than the teeth of D. a comparison with the short forelimb of A. bra- superbus (tables 2, 3). D. falkenbachi is char- chykolos. Despite these limitations, the post- acterized by short yet unreduced premolars, crania of UNSM 99420 indicate a larger car- short m2 relative to m1 length (table 4), and nivore than any known individual of D. su- an m1 with a tall trigonid and a talonid with perbus. The limbs of D. superbus are not elon- a robust, ridgelike hypoconid (®g. 20). The gated in the epipodial segments, indicating a shorter p2 of D. falkenbachi differs from the short-legged carnivore (Peterson, 1910). longer p2 of D. superbus. Additional information on forelimb length The absence of postcranial material for all of D. falkenbachi is provided by the scapho- but one individual of D. falkenbachi prevents lunar. Both D. superbus and D. falkenbachi a more thorough description of the skeleton. (UNSM 99420) have a scapholunar of simi- The only individual with dentition and asso- lar dorsoventral thickness. Undescribed am- ciated postcranials is UNSM 99420 from the phicyonids closely related to Daphoenodon Lay Ranch paleovalley west of Spoon Butte, from younger Miocene rock units in the Wyoming (®g. 22). The Lay Ranch beds are UNSM collection have elongate forelimbs equivalent in age to the Upper Harrison beds associated with much thicker scapholunars, of northwest Nebraska and contain a fauna cor- suggesting that the elongation of the forelimb relative with the Niobrara Canyon local fauna is correlated with an increase in thickness of (Hunt, 1985a, 1990). The UNSM ®eld party this carpal bone. The scapholunar of UNSM realized at the time of its discovery in 1983 99420 does not show this increase in thick- that UNSM 99420 represented the only known ness, suggesting that the forelimb was not instance of postcranial material in association signi®cantly lengthened. with a dentition of this species. Consequently, The basicranium is preserved only in the the outcrop was thoroughly searched but very holotype (®g. 23), and its structure is like few limb elements were preserved: a partial that of the basicranium of D. superbus (CM tibia lacking the distal end, a ®bula without its 1589). Although damaged by crushing, the proximal end, a calcaneum, scapholunar, carpal right petrosal and left auditory bulla are pre- cuneiform, proximal ulna, a phalanx, and a served. The bulla (®g. 23A) has the charac- badly weathered scapula. The skeleton lacked teristic asymmetric ¯ask-shaped form of the complete limb elements (radius, ulna, meta- bullae of D. superbus and A. brachykolos in podials) that would conclusively establish the which the anterior part has been extended or

← Fig. 21. A, upper dentition of holotype cranium, Daphoenodon falkenbachi, F:AM 54144, 18 Mile District, Goshen Co., Wyoming; B, upper dentition of holotype cranium, D. skinneri, F:AM 70801, ϳ9 miles (14.5 km) southeast of Lusk, Niobrara Co., Wyoming. Stereophotographs. Scale bars, 1 cm. 26 AMERICAN MUSEUM NOVITATES NO. 3385

TABLE 2 Dental Measurements (length ؋ width in mm) of Lower Teeth of North American Arikareean Species of Adilophontes and Daphoenodon

in¯ated, entirely ®lling the anteromedial au- versely oriented, and unin¯ated; its position ditory region. A short bony external auditory shows that the bulla did not extend behind meatus of 6±7 mm length was present. The the mastoid processes. posterior wall of the bulla was thin, trans- The middle ear cavity was ϳ19.5 cm in 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 27

TABLE 3 Dental Measurements (length ؋ width in mm) of Upper Teeth of North American Arikareean Species of Adilophontes and Daphoenodon

length and perhaps ϳ13 mm in maximum parently took the same path as in A. brachy- width. The cavity extended ventral to the kolos. The lateral margin of the basioccipital tympanum a short distance into the ¯oor of was embayed for the enlarged inferior petro- the bony external auditory meatus, creating sal venous sinus. a bony shelf 5.5 mm in width ventral to the A low, rounded promontorium is typical crista tympani; anterior to this shelf is a small of the petrosals of D. falkenbachi, D. super- pocket in the anterolateral wall of the bulla bus, and A. brachykolos. However, in Adi- similar to this same feature in the holotype lophontes the promontorium is somewhat of A. brachykolos. The paroccipital process- longer and wider than in Daphoenodon, rel- es, although damaged, were relatively larger ative to overall skull size. The characteristic and more posteriorly directed than in A. bra- depressions (tensor tympani fossa, epitym- chykolos and were similar in these respects panic recess, stapedius fossa) in the ventral to D. superbus. surface of the tegmen tympani in both genera A bony tube for the internal carotid artery are simple and without specializations, and is present within the medial bulla wall which the tensor fossa and epitympanic recess are is applied to the medial margin of the right con¯uent without a ridge separating them. petrosal promontorium. The tube begins at The similarities in bulla and petrosal mor- the posteromedial corner of the bulla and ap- phology support a relationship between Da- 28 AMERICAN MUSEUM NOVITATES NO. 3385

TABLE 4 Ratio of m2/m1 Length in Species of North American Daphoenodon and Adilophontes

phoenodon and Adilophontes within the subfamily Daphoeninae. A skull with associated mandibles (F:AM 70801) from 9 miles (14.5 km) southeast of Lusk, Wyoming, represents a stratigraphically older member of the D. falkenbachi line- Fig. 22. Fluvial lithofacies of the Lay Ranch age (®gs. 21B, 24). This is a smaller carni- beds, a latest Arikareean paleovalley at Spoon vore than D. falkenbachi; in all aspects of the Butte, Goshen Co., Wyoming, that produced the skull, mandibles, and teeth it is clearly the amphicyonids A. brachykolos, D. falkenbachi, and predecessor to that species. Ysengrinia: A, channel (cs) and ¯oodplain (fp) facies within the Lay Ranch paleovalley (D. falken- Daphoenodon skinneri, bachi, UNSM 99420, was found in interbedded new species ¯oodplain silts and ®ne sands ϳ100 m northeast Figures 21B, 24 of this outcrop)Ðhammer on outcrop, 30 cm HOLOTYPE: F:AM 70801, a crushed skull length; B, photomicrograph of tuffaceous very with complete dentition (left I1±3, C, P1± ®ne sand (glass shards, 41%) from the Lay Ranch paleovalley ¯oodplain that includes both reworked airfall ash and a minor epiclastic fraction ← derived from the Hartville Uplift to the west; C, photomicrograph of cross-strati®ed epiclastic within the Lay Ranch paleovalley which is almost sandstone derived from the Precambrian core of entirely ®lled by ¯uvially reworked tuffaceous eo- the Hartville Uplift; this lithofacies rarely occurs lian sediments in channels and ¯oodplain. 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 29

Fig. 23. Basicranium of Daphoenodon falkenbachi, holotype (F:AM 54144): A, ventral view of right auditory region showing the ectotympanic bulla; B, ventral view of crushed left auditory region showing the form of the petrosal. Stereophotographs. Scale bars, 1 cm.

M3, right I1±3, C, P1±M2) and associated TYPE LOCALITY: About 9 miles (14.5 km) mandibles (right and left i1±3, c, p1±m3). southeast of Lusk, Royal Valley District of ETYMOLOGY: Named for the late Morris F. the Frick Laboratory (AMNH), collected Skinner, Frick Laboratory (AMNH), in rec- somewhere within sections 25±28, 33±36, ognition of his extensive contributions to the T31N, R63W, east of U.S. Highway 85, Ni- study of the geology and paleontology of obrara County, Wyoming. western Nebraska and southeastern Wyo- TYPE HORIZON: Upper Harrison beds, up- ming. per Arikaree Group (early Miocene). 30 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 24. Holotype right mandible of Daphoenodon skinneri, F:AM 70801, from ϳ9 miles (14.5 km) southeast of Lusk, Niobrara County, Wyoming: A, lateral view; B, medial view. Scale bars, 1 cm.

REFERRED SPECIMENS: None. m2, which is proportionately shorter, relative KNOWN DISTRIBUTION: Latest Arikareean, to m1 length, than in D. superbus from Niobrara County, Wyoming. northwest Nebraska (table 4). The ratio of DIAGNOSIS: A species of the Daphoenodon m2 length/m1 length for D. skinneri is 0.54 group, closely similar in cranial and dental (N ϭ 1); for D. superbus, 0.57±0.63 (N ϭ morphology to D. falkenbachi, but markedly 8); for D. falkenbachi, 0.51±0.56 (N ϭ 3); smaller. The species is distinguished from D. and for A. brachykolos, 0.57±0.58 (N ϭ 3). falkenbachi by smaller size (tables 1±3), and DISCUSSION: Although the skull of the ho- from D. superbus by smaller M1±2 and m2 lotype is crushed, it is apparent that the skull relative to the size of the carnassials (P4, form is like that of D. falkenbachi and D. m1). D. skinneri differs in the length of its superbus. Its skull form differs conspicuous- 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 31 ly, however, from the deeper, more laterally western facies of the Upper Harrison beds compressed skull of A. brachykolos. When developed in southern Niobrara County. The compared with the skull and mandible of the sediment remaining on the skull is a light D. superbus holotype (CM 1589), the holo- gray very ®ne sandstone typical of Upper type of D. skinneri has proportionately small- Harrison sediments exposed today at Royal er M1±2 and m2 but slightly larger incisors, Valley and 9 miles (14.5 km) southeast of canines, premolars, and m1. Lusk. These exposures apparently carry a The skull of D. skinneri (basilar length, fauna somewhat older than the Upper Har- 24.5 cm) is also noticeably larger than the D. rison beds to the south in the 18 Mile District superbus holotype (basilar length, 21.5 cm) of C.H. Falkenbach that yielded fossils of the from the Carnegie Quarry 3 carnivore dens, larger and more advanced D. falkenbachi. but this latter skull is undoubtedly female (Hunt et al., 1983); males of D. superbus DISCUSSION from Quarry 3 attained the size of D. skinneri (table 1). However, a male D. superbus Dental dimensions and tooth morphology, (UNSM 700±82) from the same den system but particularly the distinctive form of the as the D. superbus holotype female has ca- skull, most clearly distinguish these species nines, premolars, and molars of larger size of amphicyonids. The shorter premolars of than D. skinneri, and the premolars (p2±4) Daphoenodon falkenbachi and D. skinneri of UNSM 700±82 are much longer and nar- contrast with the more elongate and narrow rower than those of D. skinneri (table 2), premolars of A. brachykolos (®g. 25). Simi- demonstrating that D. skinneri is not simply larly, a bivariate plot of the dimensions of a male of D. superbus. D. superbus and its the lower carnassial and the m2 of these close relative, D. notionastes, are character- beardogs differentiates D. falkenbachi, D. ized by longer and more slender premolars skinneri, D. superbus, and D. notionastes relative to the shorter, wider premolars of D. from Adilophontes (®g. 26). Dimensions of skinneri and its descendant D. falkenbachi. the upper carnassial and molars also contrib- No postcranials were found with the ho- ute to discrimination among these species lotype of D. skinneri. (®g. 27). These bivariate plots show that A. The site where the holotype of D. skinneri brachykolos and D. falkenbachi display the was collected can be approximately located largest carnassials and molars. However, (®g. 1). Records of the Frick Laboratory while these two species have consistently (AMNH) state that the specimen was ob- larger carnassials and upper molars (M1±2) tained in 1957 from the private collection of relative to D. superbus and D. notionastes, N.Z. Ward, a member of Falkenbach's ®eld their m2 dimensions are much closer to D. crew. Falkenbach and Ward worked together superbus, re¯ecting a failure to signi®cantly in Upper Harrison beds south of Lusk in lengthen m2 in D. falkenbachi and A. bra- southern Niobrara County in 1961±1962, but chykolos. Based on dental measurements, the not in 1957. Apparently Ward found the skull series Daphoenodon notionastes-superbus- in 1957 during his own exploration of Upper skinneri-falkenbachi shows a progressive in- Harrison exposures in southern Niobrara crease in tooth size that accompanies larger County. The locality marked on F:AM 70801 body size in this genus. reads ``about 9 mi S.E. of Lusk'' which was Amphicyonids from the Upper Harrison included in the Royal Valley District (letter beds of southeastern Wyoming and contigu- from C.H. Falkenbach to Childs Frick, June ous outcrops in northwest Nebraska comprise 18, 1942). The Royal Valley District includes a unique assemblage of large carnivorans Upper Harrison outcrops at Royal Valley that is restricted to the formation and does (west of Highway 85) that are situated 3±4 not occur in younger faunas of the central miles (4.8±6.4 km) west of similar outcrops Great Plains (®g. 28). Amphicyonids from ϳ9 miles (14.5 km) southeast of Lusk (east the lowest levels of the Upper Harrison in of Highway 85). Outcrops in these two lo- northwest Nebraska include Daphoenodon calities occur in the S½, T31N, R63W, and superbus (the common indicator taxon, con- appear to represent the same lithic unit, a ®ned to this stratigraphic level) and the am- 32 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 25. Comparison of upper and lower dentitions of Daphoenodon falkenbachi (above), holotype, F:AM 54144, and Adilophontes brachykolos (below), holotype, F:AM 27568, both from the Upper Harrison beds, 18 Mile District, Goshen County, Wyoming. Note the difference in form of the premolars. Scale bar 1 cm. phicyonines Ysengrinia americana (Hunt, in Wyoming, and from the Lay Ranch beds at press a) and rare remains of Cynelos. These Spoon Butte; a time-equivalent fauna is de- carnivorans come from stream and waterhole rived from outcrops along the western mar- deposits of the basal Upper Harrison at Agate gin of Goshen Hole in southeastern Platte National Monument and in the Niobrara County, Wyoming. Canyon (Hunt, 1990). Higher stratigraphic The stratigraphically superposed faunas of levels of the Upper Harrison have produced the early Hemingfordian Runningwater For- the more advanced D. falkenbachi, as well as mation in northwest Nebraska lack these ear- Y. americana and A. brachykolos. However, lier species of Daphoenodon, Ysengrinia, outcrops in southernmost Niobrara County and Cynelos, and instead contain the ®rst that yielded D. skinneri appear to carry a New World appearances of the immigrant slightly older fauna than typical Upper Har- Eurasian amphicyonine Amphicyon (Hunt, in rison exposures with D. falkenbachi in Go- press b), a new larger species of Cynelos, and shen County. In Goshen County an appar- a very large digitigrade species of daphoen- ently homogeneous Upper Harrison mam- ine amphicyonid with elongate limbs and malian fauna comes from the collecting dis- feet, Borocyon Peterson 1910 (Hunt, in tricts of Falkenbach south of Lusk, prep.). The shift in the amphicyonid taxa 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 33

Fig. 26. Dimensions (in mm) of the lower molars (m1, m2) of the amphicyonids Adilophontes and Daphoenodon. A. brachykolos and D. falkenbachi have a short m2 relative to m1 length when compared to D. superbus. The sample of Daphoenodon superbus (N ϭ 13) demonstrates the extent of variation in these measurements in a single species from a limited stratigraphic interval. from the Upper Harrison into the Running- prius; and several lineages of small moschid water is part of a highly selective faunal and dromomerycid deer persisted as well transformation at the beginning of the Hem- (Webb, 1998). Stenomyline camels, Oxydac- ingfordian NALMA in the Great Plains of tylus, and the protolabines Michenia, Proto- North America. labis, and Tanymykter also survived the Up- Among the large carnivorans that have per Harrison±Runningwater faunal transition their last appearances in the Upper Harrison (Honey et al., 1998), as did dicerathere rhi- fauna of southeastern Wyoming and north- noceroses, the long-footed rhinoceros Men- west Nebraska are the amphicyonids Y. oceras, tapirs, and chalicotheres. The hyper- americana, D. skinneri, D. falkenbachi, D. tragulids made their last appearance in the superbus, and the giant mustelid Megalictis Upper Harrison as the genus Nanotragulus, ferox. Several lineages of temnocyonine am- possibly replaced by the ®rst occurrence of phicyonids that persisted throughout the Ari- merycodont antilocaprids in the Running- kareean also did not extend into the early water Formation. Hemingfordian. Upper Harrison horses par- The last occurrences of a number of mam- alleled the carnivorans in last appearances of mal species in the Upper Harrison and the Parahippus wyomingensis and the very large appearance of new mammals in the Run- P. nebrascensis. These equids were replaced ningwater fauna are in part explained by the in the early Hemingfordian by Parahippus depositional environments represented in tyleri, P. pawniensis, and Archaeohippus.On each of these formations (Hunt, 1985b). the other hand, a number of oreodonts, cam- Most Upper Harrison rocks belong to the els, peccaries, the entelodont Dinohyus, and volcaniclastic loess lithofacies (®g. 4), and ruminant artiodactyls ranged from the Upper represent episodic accumulations of ®ne- Harrison into the Runningwater fauna: Mer- grained eolian tuffaceous sediment settling ychyus evolved from a smaller into a larger on open semiarid grassland plains east of the species; the large Merycochoerus matthewi Hartville and Laramie uplifts (Hunt, 1990). evolved directly into M. magnus and M. pro- On the other hand, a signi®cant proportion 34 AMERICAN MUSEUM NOVITATES NO. 3385

Fig. 27. Dimensions (in mm) of the upper cheek teeth (P4, M1, M2) of the amphicyonids Adilo- phontes and Daphoenodon. A. brachykolos and D. falkenbachi are larger carnivores relative to D. superbus and D. notionastes, re¯ected in their larger carnassials and upper molars. of Runningwater exposures represent ¯uvial Arikaree air-fall sedimentÐlenses of granitic facies deposited in channels and ¯oodplains sands derived locally from the Hartville Up- of a major throughgoing river system drain- lift to the west are extremely rare and found ing the northern Laramie Mountains and in only a few localities (Hunt, 1990). Hartville Uplift and carrying granitic pebble Thus, mammals restricted to, or commonly gravels derived from Precambrian rocks of frequenting riparian settings near, a master the Laramie Mountains (Skinner et al., 1977; stream of Runningwater type are absent from Yatkola, 1978; Hunt, 1985a). Such a major the Upper Harrison faunas. The ``sudden'' drainage has not been discovered in the Up- appearance in the Runningwater faunas of per Harrison beds of southeastern Wyoming numerous small carnivores (leptarctine and or the western panhandle of Nebraska. The musteline mustelids, the lutrine mustelid most prominent Upper Harrison paleovalley Mionictis, paleomustelid Brachypsalis, the occurs in the vicinity of Spoon Butte in Go- semiaquatic Potamotherium, and procyonid shen County (®g. 22); there the Lay Ranch Edaphocyon) previously unknown in the beds comprise ®ne-grained tuffaceous silts Great Plains, together with the advent of new and sands representing ¯uvially reworked insectivores and rodents, and the frequent oc- 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 35

Fig. 28. Stratigraphic distribution of daphoenine and amphicyonine amphicyonids in southeastern Wyoming and western Nebraska in the early Miocene. *Amphicyon galushai: Hunt, in press b, Bulletin of the American Museum of Natural History.

currences of anthracotheres, tapirs, alligators, ANDERSON RANCH FORMATION: and ®sh, coincides with the arrival of signif- A NEW TERM FOR THE icant ¯uvial environments of the Running- UPPER HARRISON water Formation in the region. Sediments of large throughgoing ¯uvial systems are infre- The Anderson Ranch Formation is herein quently represented by surface exposures of proposed as a formal formation-rank term Arikaree rocks in the region. The contrasting based on the stratotype of O.A. Peterson's styles of sedimentation indicated by Upper Upper Harrison beds in Sioux County, north- Harrison and Runningwater rocks suggest west Nebraska (Peterson, 1909a). Peterson that a number of ®rst and last appearances (1909a: 75) designated prominent exposures are probably correlated with environmental along the Niobrara River immediately east of preferences of these mammals, and do not the Wyoming-Nebraska state boundary as the actually re¯ect their `èxtinction'' or ``sud- type area of the Upper Harrison beds (®g. 3). den'' origin in the North American midcon- Here the river cuts a deep canyon through tinent. As such, the evident turnover in am- rocks of the upper Arikaree Group. The phicyonid species at the Arikareean±Hem- south wall of the Niobrara Canyon comprises ingfordian boundary may be at least in¯u- laterally continuous cliff-forming outcrops enced, and possibly determined, by the shift that extend from the state line ϳ4 miles (6.4 in depositional environments taking place at km) to the east (Hunt, 1985b: ®gs. 3, 9, 10, this time in the central Great Plains. S½, T31N, R57W). Whereas these laterally 36 AMERICAN MUSEUM NOVITATES NO. 3385 continuous exposures could serve as the type yon or farther north in Sioux County where section, it is useful to designate the thickest rocks above the Anderson Ranch Formation interval of these beds along the south wall of have been removed by erosion. However, to the canyon as the stratotype (S½, SE4, sec. the southeast of the canyon on the divide be- 28, continuing into N½, NE4, sec. 33, T31N, tween the Niobrara and White Rivers (S½, R57W, Sioux County, Nebraska). The stra- T30N, R55W and T29N, R55W), and along totype section has been previously illustrated and to the south of the Niobrara River at Ag- and described, and a paleomagnetic transect ate postof®ce (N½ of T28N, R55W; N½, sampled (MacFadden and Hunt, 1998: 155, T28N, R56W), the Anderson Ranch Forma- ®g. 10). A composite stratigraphic section of tion is disconformably overlain by the low- the stratotype area that includes all lithofa- ermost strata of the Runningwater Formation cies of the formation on both south and north of Cook (1965). The lithostratigraphic rela- walls of the Niobrara Canyon has also been tionship of the Anderson Ranch Formation published (Hunt, 1985: ®g. 3; 1990: ®g. 7). and the lowermost Runningwater beds is par- The Geologic Names Committee of the ticularly evident along the valley of the Ni- U.S. Geological Survey has reserved the obrara River at Agate Fossil Beds National term Anderson Ranch Formation for the Monument where the contact between the above-mentioned formation-rank lithostrati- two formations is well-exposed both north graphic unit (W.A. Bryant, written commun., and south of the river. MacFadden and Hunt May 22, 1995). Here it is my intent to re- (1998: 157±159, ®g. 14, Skavdahl Dam) place the lithostratigraphic formation-rank published a reference section northeast of term `Ùpper Harrison'' beds used in this re- Agate postof®ce showing the upper contact port with the new term Anderson Ranch For- of the Anderson Ranch Formation (ϭ Upper mation (see appendix). Harrison beds) with the Runningwater For- BOUNDARIES: The lower contact of the formation. mation in the type area and throughout Sioux The Anderson Ranch Formation in the Ni- County in northwestern Nebraska is a readily obrara Canyon and to the north along the recognized erosional disconformity that has Pine Ridge in Sioux County conforms to Pe- been mapped and illustrated in earlier pub- terson's initial Upper Harrison concept. Un- lications (Hunt, 1978: ®g. 17; 1985b: ®g. 3; fortunately, Peterson (e.g., 1910: 263) also 1990: ®gs. 4, 7). The subjacent unit is almost included in his Upper Harrison the lower- invariably the Harrison Formation (Hatcher, most Runningwater beds northeast of Agate 1902). However, the Upper Harrison beds are on the Niobrara-White River divide and in lithically distinct from the Harrison Forma- the vicinity of Agate National Monument. tion, cannot be considered its upper part, and Although the lower Runningwater beds ap- are separated from the Harrison beds by a pear similar in their pale orange-brown color regional unconformity. At Agate Fossil Beds to the Anderson Ranch Formation, on closer National Monument a broad paleovalley has inspection the Runningwater strata contain been incised into the Harrison Formation and on average a lesser percentage of volcanic ®lled by Anderson Ranch ¯uvial sediments glass shards, are distinguished by thin sheet- that contain the celebrated Carnegie Hill ¯ood units interbedded with air-fall sedi- mammalian bonebed (Hunt, 1990). ment, lack the siliceous paleosols of the An- In much of Sioux County and in Niobrara derson Ranch, are invariably superposed on and Goshen Counties in southeastern Wyo- the older unit, and contain a younger mam- ming, erosion has removed strata that may malian fauna. have once been present above the Anderson As suggested by the North American Ranch beds. However, in central Sioux Stratigraphic Code (1983: 858), boundaries County and in Platte County, Wyoming, of lithostratigraphic units should be selected younger Miocene units are disconformable on the basis of lithologic properties that, on and locally incise the Anderson Ranch where possible, coincide with the boundaries Formation. of genetic units. The lower and upper bound- An upper contact with younger beds does ing contacts of the Anderson Ranch Forma- not occur in the type area at Niobrara Can- tion in Sioux County, Nebraska, enclose a 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 37 lithofacies association de®ning a genetic rock volcaniclastic sand and silt; epiclastic debris unit (Hunt, 1990). Anderson Ranch outcrops is limited to rare, local lenses of arkosic in Niobrara, Goshen, and Platte Counties are sandstones derived from the Hartville Uplift in lateral continuity with those in Sioux to the west (®g. 22). County, demonstrating the regional extent of Waterholes that accumulated volcanic ash, the formation from its type area in northwest limy mud, and ®ne volcaniclastic sand com- Nebraska into southeastern Wyoming. prise a ®nal lithofacies (®g. 5). These water- LITHIC CONTENT: The formation comprises hole deposits are often the locus of major characteristic lithofacies that are present mammalian bonebeds. Diatomites also ®lled throughout the type area in Nebarska and local ephemeral depressions within the pa- also occur in southeastern Wyoming. The leovalleys. principal lithofacies and their lithologic char- MAPPABILITY AND THICKNESS: The forma- acteristics have been previously described tion was not mapped by Peterson and has not (Hunt, 1985b: 164±177, ®gs. 4±11; 1990: been mapped throughout its regional extent. 74±94, ®gs. 5±7). These include: (1) eolian A representative part of the type area in the volcaniclastic loess with siliceous paleosols; Niobrara Canyon is mapped (Hunt, 1978: ®g. (2) lacustrine calcareous mudstone; (3) ¯u- 2, symbol Tm). The formation has also been vial volcaniclastic sands and intraformational mapped at Agate Fossil Beds National Mon- gravels; (4) calcareous tuff and ¯uvial silty ument where its lower and upper bounding sandstone accumulated in shallow waterho- contacts are well-de®ned (Hunt, 1984). The les. formation has also recently been mapped in Approximately 87% of outcrop of the for- the Spoon Butte and Lone Sand Hill 7.5-mi- mation is eolian volcaniclastic loess. Volca- nute topographic quadrangles, along the Wy- nic glass shards comprise 30±54% of the oming-Nebraska state boundary (R.M. Hunt, rock, and additional pyroclastic grains indi- Open-File Maps, Nebraska Conservation and cate a total pyrogenic fraction of 50±75%. Survey Division). The sediment is predominantly silty ®ne to The formation has been traced from the very ®ne sandstone, massive, homogeneous type section throughout Sioux County, Ne- in texture and fabric, and pale brown to light braska, demonstrated by a north-south pro®le gray in color. This lithofacies includes nu- from the Pine Ridge southward to Agate Fos- merous siliceous paleosols of great lateral ex- sil Beds National Monument (Hunt, 1978: tent, rich in dense, small diameter (0.5 mm) rhizolith networks, suggestive of grasslands ®g. 17; 1985b: ®g. 3; 1990, ®gs. 4, 7). Both (®gs. 3, 4). These paleosols are characteristic south and north of the Niobrara Canyon in of the formation and do not occur in the sub- Sioux County the formation thins (Hunt, jacent Harrison Formation, except for a sili- 1990, ®g. 7), so that at Agate National Mon- ceous paleosol developed on the terminal ument the thickest section is ϳ50 ft (15.2 m) Harrison surface marking the initiation of the and along the Pine Ridge north of the town Anderson Ranch climatic regime. of Harrison is ϳ55 ft (16.8 m). The type sec- Lacustrine calcareous mudstones consti- tion is representative of the thickest expo- tute only about 2% of the formation but are sures of the formation in Sioux County, conspicuously visible as widespread, thin, which in the Niobrara Canyon attain a thick- white micritic limestones that often are silic- ness of as much as 160 ft (ϳ50 m). i®ed. Calcareous mudstone grades laterally The formation can be traced to the west into ®ne volcaniclastic shoreline sands at the into Niobrara County and southward to Go- margins of these shallow lakes (®g. 5). shen County where outcrop thickness is less Fluvial cross- and horizontally strati®ed than 200 ft (ϳ60 m); however, over much of sandstones, siltstones, and intraformational this area the unit continues into the subsur- gravels make up about 10% of formation face and the lower contact is not exposed. outcrop, occupying broad shallow paleoval- The southernmost exposures of the formation leys, local ephemeral channels, and tributary in Platte County, Wyoming, near Wheatland gullies. In Sioux County the sandstones are and Chugwater, are of similar thickness and almost entirely made up of reworked, ®ne represent the youngest sediments attributed 38 AMERICAN MUSEUM NOVITATES NO. 3385 to the Anderson Ranch Formation, identi®ed Marsland . . . are not the Ùpper Harrison' by a latest Arikareean mammal fauna. beds, but later and distinct from them'' ABANDONMENT OF THE TERM ``MARSLAND (Cook and Gregory, 1941: 549). He was the FORMATION'': According to the North Amer- ®rst to express what is believed today to be ican Stratigraphic Code (1983, Article 20, p. the actual relation of these units when he 855), a formally de®ned unit may be aban- stated that: ``The Marsland Formation as de- doned due to ``widespread misuse in diverse ®ned by Schultz includes . . . two separable ways which compound confusion''. Here I formations, the Ùpper Harrison' beds and demonstrate a concern for nomenclatural sta- the [stratigraphically] higher, previously un- bility should this term be retained, and rec- named deposits exposed east of Marsland.'' ommend an alternative nomenclature to take Despite these statements, the lithic distinc- its place as required by the Code. tions between these units remained unclear. The Marsland Formation was ®rst pro- It was evident that Schultz's (1938) proposed by Schultz (1938) who said it was posal to apply the term Marsland Formation ``best exposed in Nebraska in the region as a replacement name for the Upper Harri- about [the town of] Marsland along the Ni- son beds was inappropriate, for it failed to obrara River where it includes some 150 feet recognize that at least two distinct formation- of buff and gray, soft sandstones.'' No map- rank units were included, and the type area ping, type section, or reference sections were of Peterson's Upper Harrison beds and most presented. Later, a type section was indicated of its contiguous outcrop had been excluded. in an abstract (Schultz, 1941: secs. 23±27, Although Cook and Gregory (1941: 549) had T28N, R52W, and secs. 19 and 30, T28N, suggested that the term Marsland Formation R51W) but was not described. The formation be restricted to the rocks in the vicinity of was ®rst mapped by Lugn (1939: pl. 1), but Marsland, this usage was not accepted by in combination with another formation so Schultz and his associates who continued to that its geographic extent remained indeter- apply the term to a much wider geographic minate. A type section or reference sections area. were not described nor were upper or lower Eventually Cook (1960) began to apply a bounding contacts explicitly designated. The new formation-rank term, Runningwater For- formation was said to extend from Nebraska mation, to the beds in the vicinity of Mars- into Wyoming, Colorado, and South Dakota land, while retaining the term `Ùpper Har- but no geographic determinants or lithologic rison'' for the lower unit. However, Cook's descriptions were provided. death prevented an adequate de®nition of the The Marsland Formation bears on the re- Runningwater Formation. This was accom- naming of the Upper Harrison because plished by McKenna (1965) who thoroughly Schultz (1941) explicitly stated that `Ìn Ne- reviewed the Marsland problem, and simul- braska and Wyoming, the Marsland [For- taneously published a posthumous manu- mation] includes all the deposits formerly script by Cook (1965) that provided a type called Ùpper Harrison'.'' However, Lugn's section, lithic description, and map of the (1939) map of the Marsland Formation (and type area of Cook's Runningwater Forma- the second unit, the Sheep Creek Formation, tion. Unfortunately, Cook (1965: 6) further that was combined with it) does not include complicated the issue when he suggested that the type area of the Upper Harrison of Pe- the term Marsland not designate the beds in terson (1909) nor most of its contiguous out- the vicinity of the town of Marsland but rath- crop, thus inaugurating the confused usage of er replace Peterson's term Upper Harrison, the term. thus a proposal similar to Schultz's use of the Shortly after the publications of Schultz term as a replacement name. McKenna and Lugn appeared, Cook and Gregory (1965), Hunt (1978), and others followed this (1941) noted that it was unclear what was to suggestion, designating two formation-rank be included in the Marsland Formation, and units, a Marsland Formation (Peterson's Up- argued that the relationship of the Upper per Harrison) overlain by Cook's Running- Harrison of Peterson to the Marsland was water Formation. However, this amounted to vague. Cook was aware that the ``beds near a division of a unit (Marsland Formation of 2002 HUNT: EARLY MIOCENE AMPHICYONIDS 39

Schultz) into subunits while using the name type area and section are to be included in Marsland for one of the subdivisons, a prac- the formation. In this area the Anderson tice discouraged by the North American Ranch Formation rests directly on the Har- Code (1983: Article 19g). The principal ob- rison Formation. The formation-rank unit su- jection to this proposal that has emerged perposed on the Anderson Ranch Formation, from recent study of these rocks is that no most evident northeast of Agate postof®ce Upper Harrison beds occur in the immediate and south of the Agate National Monument vicinity of Marsland or in the Marsland on the Niobrara-Whistle Creek divide, is the ``type section'' of Schultz (1941). Runningwater Formation of Cook (1965). An alternative solution was proposed by The term ``Marsland Formation'' is aban- Yatkola (1978) who mapped the rocks in the doned. As de®ned herein, the Anderson vicinity of Marsland that Schultz had regard- Ranch and Runningwater Formations are un- ed as the type area of his Marsland Forma- conformity-bounded lithogenetic units of the tion. He continued the use of the term Mars- type endorsed by the North American Strati- land at the rank of formation to include all graphic Code (1983: Article 23d, e). rocks between the Harrison Formation and Box Butte Formation in this area, and des- ACKNOWLEDGMENTS ignated lower (unnamed) and upper (Run- ningwater) members. A type section of the For permission to study the Frick collec- unnamed lower member was measured in the tion of amphicyonids I express my appreci- same approximate location as our type sec- ation to R.H. Tedford and M.C. McKenna, tion for the Anderson Ranch Formation, and who provided much useful information dur- it is evident that he intended his lower mem- ing the early years of my work on these car- ber to correspond to Peterson's Upper Har- nivores. For access to the collections of the rison unit. Also, Yatkola (1978: 25) correctly Department of Geology and Geophysics, recognized that reddish-brown sediments University of Wyoming, I thank M. Cassili- forming the Miocene outcrops northeast of ano and J.A. Lillegraven. My thanks to Mary Agate postof®ce and continuing southward Dawson, Carnegie Museum of Natural His- on the Niobrara-Whistle Creek divide that tory, Pittsburgh, for the loan of Peterson's were considered Upper Harrison beds by Pe- specimen of Daphoenodon falkenbachi from terson (1910: 263) and Cook and Gregory the Niobrara Canyon, Sioux County, Nebras- (1941: 549) are in fact directly traceable into ka. For good companionship and assistance the Runningwater Formation. Although he in the ®eld in southeastern Wyoming and noted that his lower member could not be western Nebraska, I acknowledge my UNSM mapped into the type area of Peterson's Up- colleagues R.I. Skolnick and Ellen Stepleton, per Harrison beds, his lower and upper mem- who also ably prepared key material for this bers closely correspond to the concept ad- study. UNSM 99420 was discovered by Dan vocated here of two formation-rank units: Miller and Rob Skolnick in the Lay Ranch Anderson Ranch Formation and Running- beds in 1983, a specimen that contributed water Formation. important information to the study of Da- It is evident that the term ``Marsland For- phoenodon falkenbachi. Rob Skolnick and mation'' has been applied at various times to the author also collaborated in mapping of almost all early Miocene formation-rank the Lay Ranch beds at Spoon Butte, Goshen units within the area, both as separate entities County, Wyoming, where a number of am- and taken together. This degree of uncertain- phicyonids were discovered. UNSM illustra- ty and misuse would seem to satisfy the cri- tor Angie Fox prepared ®gures 6, 18, 26±28; terion stated in the Code as grounds for aban- the late Raymond Gooris, artist for the Frick donment. Laboratory, originally prepared ®gures 2, 14, Accordingly, I employ the term Anderson and 25, which were modi®ed by Angie Fox Ranch Formation for the formation-rank unit for this report. I appreciate the useful reviews de®ned in the Niobrara Canyon by Peterson of the manuscript provided by J.A. Lille- (1909) as the Upper Harrison beds. Only graven and B.J. MacFadden. rocks that can be traced outward from the This study could not have been success- 40 AMERICAN MUSEUM NOVITATES NO. 3385 fully completed without the friendly coop- lian, and lacustrine paleoenvironments, Nebras- eration of ranchers Gene Lay, George and ka and Wyoming. In M.J. Lockley and A. Rice Chuck Oberg, Martin Marshall, the late (editors), Volcanism and fossil biotas. Geolog- Frank Boggs and Verna Boggs, Jim Phipps, ical Society of America Special Paper 244: 69± and the Desenfants family, all of whom gra- 111. ciously permitted our ®eld parties to work on Hunt, R.M., Jr. 1996. Amphicyonidae (Chapter 23). In D. Prothero and R. J. Emry (editors), their lands. The terrestrial Eocene-Oligocene transition in North America: 476±485. London: Cambridge REFERENCES University Press. Cook, H.C. 1960. New concepts of late Tertiary Hunt, R.M., Jr. In press a. Intercontinental migra- crustal deformation in the Rocky Mountain re- tion of Neogene amphicyonids (Mammalia, gion of North America and Eurasia. Report of Carnivora): Appearance of the Eurasian bear- the International Geological Congress, XXI dog Ysengrinia in North America. American Session, Norden, 1960, part 12: 198±212. Museum Novitates. Cook, H.C. 1965. Runningwater Formation, mid- Hunt, R.M., Jr. In press b. Intercontinental migra- dle Miocene of Nebraska. American Museum tion of large mammalian carnivores: Earliest Novitates 2227: 1±8. occurrence of the Old World beardog Amphi- Cook, H.C., and J.T. Gregory, 1941. Mesogaulus cyon (Carnivora, Amphicyonidae) in North praecursor, a new rodent from the Miocene of America. Bullletin of the American Museum of Nebraska. Journal of Paleontology 15(5): 549± Natural History. 552. Hunt, R.M., Jr., and R.I. Skolnick. 1996. The gi- Galusha, T. 1975. Childs Frick and the Frick Col- ant mustelid Megalictis from the Early Miocene lection of Fossil Mammals. Curator 18(1): 10± carnivore dens at Agate National Monument, 15. Nebraska: earliest evidence of dimorphism in Hatcher, J.B. 1902. Oligocene Canidae. Memoirs New World Mustelidae (Carnivora, Mamma- of the Carnegie Museum 1(2): 65±108. lia). Contributions to Geology, University of Honey, J.G., J.A. Harrison, D.R. Prothero, and Wyoming 31(1): 35±48. M.S. Stevens. 1998. Camelidae. In C.M. Janis, Hunt, R.M. Jr., X.-X. Xue, and J. Kaufman. 1983. K.M. Scott, and L.L. Jacobs (editors), Evolu- Miocene burrows of extinct beardogs: indica- tion of Tertiary Mammals of North America, tion of early denning behavior of large mam- Vol. 1: Terrestrial carnivores, ungulates, and malian carnivores. Science 221: 364±366. ungulatelike mammals: 439±462. London: Lugn, A.L. 1939. Classi®cation of the Tertiary Cambridge University Press. System in Nebraska. Bulletin of the Geological Hunt, R.M., Jr. 1974. The auditory bulla in Car- Society of America 50: 1245±1276. nivora: an anatomical basis for reappraisal of Macdonald, J.R. 1963. The Miocene faunas from carnivore evolution. Journal of Morphology the Wounded Knee area of western South Da- 143(1): 21±76. kota. Bulletin of the American Museum of Nat- Hunt, R.M., Jr. 1978. Depositional setting of a ural History 125(3): 139±238. Miocene mammal assemblage, Sioux County, Macdonald, J.R. 1970. Review of the Miocene Nebraska (U.S.A.). Palaeogeography, Palaeo- Wounded Knee faunas of southwestern South climatology, Palaeoecology 24: 1±52. Hunt, R.M., Jr. 1984. The Agate hills: History of Dakota. Bulletin of the Los Angeles County paleontological excavations. National Park Ser- Museum of Natural History 8: 1±82. vice, Midwest Region, Omaha, 179 pp. MacFadden, B., and Hunt, R.M., Jr. 1998. Mag- Hunt, R.M., Jr. 1985a. Geology and paleontology netic polarity stratigraphy and correlation of the of the Patrick Buttes, Wyoming-Nebraska. Na- Arikaree Group, Arikareean (late Oligocene- tional Geographic Society Research Reports 20: early Miocene) of northwestern Nebraska. Geo- 399±416. logical Society of America Special Paper 325: Hunt, R.M., Jr. 1985b. Faunal succession, litho- 143±165. facies, and depositional environments in Ari- Matthew, W.D. 1907. A lower Miocene fauna karee rocks (Lower Miocene) of the Hartville from South Dakota. Bulletin of the American Table, Nebraska and Wyoming. In J.E. 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menclature. Bulletin of the American Associa- of the Geological Society of America 52(10): tion of Petroleum Geologists 67(5): 841±875. 1990±1991 (abstract). Peterson, O.A. 1907. The Miocene beds of west- Skinner, M.F., S.M. Skinner, and R.J. Gooris. ern Nebraska and eastern Wyoming and their 1977. Stratigraphy and biostratigraphy of late vertebrate faunae. Annals of the Carnegie Mu- Cenozoic deposits in central Sioux County, seum 4(1): 21±72. western Nebraska. Bulletin of the American Peterson, O.A. 1909a. A revision of the Entelo- Museum of Natural History 158(5): 263±370. dontidae. Memoirs of the Carnegie Museum Skolnick, R.I. 1985. Geology and paleontology of 4(3): 41±158. the Lay Ranch beds, Sioux County, Nebraska, Peterson, O.A. 1909b. A new genus of carnivores and Goshen County, Wyoming. Master's thesis, from the Miocene of western Nebraska. Sci- University of Nebraska, Lincoln, 156 pp. Webb, S.D. 1998. Hornless ruminants. In C.M. ence 29: 620±621. Janis, K.M. Scott, and L.L. Jacobs (editors), Peterson, O.A. 1910. Description of new carni- Evolution of Tertiary mammals of North Amer- vores from the Miocene of western Nebraska. ica, Vol. 1: Terrestrial carnivores, ungulates, Memoirs of the Carnegie Museum 4(5): 205± and ungulatelike mammals: 463±476. London: 278. Cambridge University Press. Schultz, C.B. 1938. The Miocene of western Ne- Yatkola, D. 1978. Tertiary stratigraphy of the Ni- braska. American Journal of Science 35(10): obrara River valley, Marsland quadrangle, 441±444. western Nebraska. Nebraska Geological Survey Schultz, C.B. 1941. Marsland Formation. Bulletin Paper 19: 1±66.

APPENDIX The John Anderson ranch, for which the for- the canyon from August 10 to September 28, mation is named, was one of the earliest cattle 1901, where he made a rich collection of oreo- ranches in the vicinity of the Niobrara Canyon in donts, horses, camels, and carnivores. In 1901 he Sioux County. When O.A. Peterson ®rst explored considered these Niobrara Canyon outcrops the the canyon in 1901, he made frequent references upper part of the Loup Fork beds, a term used by to the Andersons, occasionally lodged at the him as an equivalent of today's Arikaree Group. ranch, and repaired equipment there; his ®eld out- In 1904 he mistakenly applied the name ``Ne- braska beds'' to the Upper Harrison unit, but later, ®t was cared for by them during the winter of realizing that this was in error, selected the term 1901±1902 after his departure for the Carnegie Upper Harrison beds for these fossiliferous de- Museum. Peterson's ®eldnotes (Memorandum for posits (Peterson, 1907, 1909a). The John Ander- Field Expedition, 1901, Section of Vertebrate Pa- son ranch included the greater part of the Upper leontology, Carnegie Museum of Natural History, 33, one of the ®rst large ranches in northwest Ne- Pittsburgh) document his work in the type area of braska, originally owned by the cattleman Bartlett the Upper Harrison beds along the south rim of Richards from 1883 to 1897. Recent issues of the Novitates may be purchased from the Museum. Lists of back issues of the Novitates and Bulletin published during the last ®ve years are available at World Wide Web site http://library.amnh.org. Or address mail orders to: American Museum of Natural History Library, Central Park West at 79th St., New York, NY 10024. TEL: (212) 769-5545. FAX: (212) 769- 5009. E-MAIL: [email protected]

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