University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Papers in the Earth and Atmospheric Sciences Earth and Atmospheric Sciences, Department of 2009 LONG-LEGGED PURSUIT CARNIVORANS (AMPHICYONIDAE, DAPHOENINAE) FROM THE EARLYMIOCENE OF NORTH AMERICA Robert M. Hunt Jr. University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences Commons Hunt, Robert M. Jr., "LONG-LEGGED PURSUIT CARNIVORANS (AMPHICYONIDAE, DAPHOENINAE) FROM THE EARLYMIOCENE OF NORTH AMERICA" (2009). Papers in the Earth and Atmospheric Sciences. 543. https://digitalcommons.unl.edu/geosciencefacpub/543 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. LONG-LEGGED PURSUIT CARNIVORANS (AMPHICYONIDAE, DAPHOENINAE) FROM THE EARLY MIOCENE OF NORTH AMERICA ROBERT M. HUNT, JR. Department of Geosciences University of Nebraska Lincoln, NE 68588-0514 ([email protected]) BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 318, 95 pp., 39 figures, 7 tables Issued March 17, 2009 Copyright E American Museum of Natural History 2009 ISSN 0003-0090 The amphicyonid carnivoran Daphoenodon (Borocyon) robustum from the early Miocene Runningwater Formation, northwestern Nebraska (paratype cranium, UNSM 25686, Marsland Quarry; mandible, UNSM 25684, Hemingford Quarry 7A). CONTENTS Abstract.......................................................... 4 Introduction....................................................... 4 Abbreviations..................................................... 5 Late Paleogene and Early Neogene Amphicyonids of North America ............... 5 Early Miocene Daphoenines ............................................ 7 Discovery of North American Borocyon .................................... 9 Geographic and Stratigraphic Distribution of North American Borocyon ........... 11 Systematics....................................................... 14 Daphoenodon (Daphoenodon) Peterson, 1909 . ........................... 14 Daphoenodon (Borocyon) Peterson, 1910............................... 14 Daphoenodon (Borocyon) robustum Peterson, 1910 ...................... 14 Daphoenodon (Borocyon) niobrarensis Loomis, 1936 ..................... 21 Daphoenodon (Borocyon) neomexicanus,newspecies..................... 23 Craniodental Osteology. ............................................. 31 PostcranialOsteology................................................ 36 GaitandStance.................................................... 71 DentitionandFeeding............................................... 75 Conclusions....................................................... 82 Acknowledgments.................................................. 83 References........................................................ 84 Appendix 1. Limb Bone Lengths and Proportions (Carnivoran) .................. 88 Appendix 2. Metapodial Lengths (Amphicyonidae) ........................... 91 Appendix 3. Metapodial Lengths (Canidae, Felidae, Ursidae, Hyaenidae) . .......... 93 Appendix 4. Comparative Lengths of Carnivoran Paraxonic Metapodials . ........ 95 3 ABSTRACT In the early Miocene, endemic North American amphicyonids of the subfamily Daphoeninae evolved a lineage of large beardogs adapted for prey pursuit over open terrain. Three species comprise this lineage, here placed in the genus Daphoenodon, subgenus Borocyon Peterson, 1910, the sister subgenus to the daphoenine beardog Daphoenodon (Daphoenodon). These species (Borocyon robustum, B. niobrarensis, B. neomexicanus, n. sp.) are distinguished by limbs modified for fore–aft motion and parasagittal alignment contributing to a lengthened stride. These adaptive features are most evident in the terminal species, B. robustum, where the forelimb is conspicuously elongated. The species of Borocyon increase in body size from small B. neomexicanus, known only from the latest Arikareean of northern New Mexico, through earliest Hemingfordian B. niobrarensis from western Nebraska and southeast Wyoming, to B. robustum, likely the keystone predator of its guild. Borocyon robustum (,100–150 kg) was the most widely distributed, occurring during the early Hemingfordian from the Pacific Northwest through the Great Plains to the Florida Gulf Coast. Regional aridity prevalent in the North American midcontinent during the Arikareean may have contributed to the emergence of Borocyon by providing an appropriate niche for a long-legged, open-country predator. The skeleton of Borocyon robustum, based on composite elements acquired over many decades, reveals a carnivoran unlike any living pursuit predator. The species displays a mosaic of postcranial features that parallel limb elements of both highly evolved cursors (Canis lupus, Acinonyx jubatus) and large, ambush felids (Panthera leo, P. tigris). Skeletal traits contributing to its efficient locomotion include: proportionately lengthened forelimbs, the parasagittal radioulnar articulation with the humerus, an elongate radius and ulna, a modified carpal structure, and paraxonic elongate metapodials of the fore- and hindfoot, as well as details of the anatomy of femur, tibia, and proximal tarsals. These postcranial features indicate a large digitigrade predator with a number of anatomical parallels in the forelimb to running pursuit predators such as the wolf, but there are also musculoskeletal adaptations of the shoulder and hindlimb that compare with those of large, living felids. Skull, dentition, and mandibular anatomy are similar to those of living wolves. However, Borocyon robustum, on average a much larger carnivore, placed even greater emphasis on a pattern of dental occlusion and toothwear suggesting both carnivory and durophagous habits. Physiological attributes of Borocyon that may have contributed significantly to its adaptive program as a pursuit predator remain unknown. INTRODUCTION long-legged carnivorans. The development of widespread grasslands east of the Rocky Long-legged pursuit carnivorans are not Mountains favored larger carnivores adapted represented among Paleocene and Eocene for open-country predation. Following the species of the Order Carnivora. In North extinction of temnocyonines in latest Arika- America it is not until the late Oligocene/ reean time, Eurasian digitigrade hemicyonine early Miocene that carnivorans evolve mul- ursids (Cephalogale and its contemporary tiple lineages with elongated fore- and Phoberocyon) made a brief appearance in hindlimbs. Presumably limb elongation in- the early Hemingfordian of North America. creased stride length, contributing to a more However, the most spectacular response to energy-efficient gait. This initial experiment these environmental conditions arguably attained a climax in the early Miocene when took place among endemic daphoenine am- Arikareean temnocyonines and early Hem- phicyonids, a group characterized for most of ingfordian daphoenines developed striking its history by ‘‘normal’’ limb proportions. By anatomical parallels in limbs and feet relative the end of the early Miocene the daphoenines to long-legged carnivorans common in late produced an enormous long-legged predator, Cenozoic and Recent faunas. Daphoenodon (Borocyon) robustum, the larg- A seasonally arid climate in the North est New World pursuit carnivoran evolved up American mid-continent in the early Miocene to that time. This species and its lineage are apparently contributed to the emergence of the subject of this report. 4 2009 HUNT: NEOGENE AMPHICYONID BOROCYON 5 ABBREVIATIONS in which amphicyonids play a prominent role (fig. 1). ACM Amherst College Museum of Oligocene amphicyonids of North Amer- Natural History, Amherst, Mas- ica include only species belonging to the sachusetts endemic subfamily Daphoeninae and to the AM Division of Mammalogy, Amer- dentally and postcranially specialized Tem- ican Museum of Natural Histo- nocyoninae. No Oligocene daphoenine at- ry, New York tains large size—all are ,20 kg in Orellan AMNH Division of Paleontology, Amer- and Whitneyan faunas and are assigned to ican Museum of Natural Histo- the genera Daphoenus and Paradaphoenus ry, New York (Hunt, 1996, 2001). Their lower limb seg- CM Division of Vertebrate Fossils, ments and feet are normally proportioned Carnegie Museum of Natural and lack elongation. A terminal and largest History, Pittsburgh species of Oligocene Daphoenus (,20–25 kg, CNHM Department of Geology, Field basilar skull length 24 cm, lacking a postcra- Museum of Natural History, nial skeleton) co-occurs with the first appear- Chicago ance of temnocyonines in earliest Arikareean interval Ar1. Temnocyonines of moderate F:AM Frick Collection, American Mu- size (,20–30 kg, basilar lengths of 24–28 cm) seum of Natural History, New are known in the early Arikareean (Ar1–Ar2 York intervals fide Tedford et al., 2004), but FMNH Field Museum of Natural Histo- pronounced specialization of the limbs and ry, Chicago feet is not seen until the temnocyonine KU Vertebrate Paleontology, Uni- Mammacyon obtusidens appears in Ar2. versity of Kansas, Lawrence By the late Arikareean (Ar3–Ar4, early UCMP University of California Muse- Miocene), all temnocyonine genera included um of Paleontology, Berkeley at least