Long-Legged Pursuit Carnivorans (Amphicyonidae, Daphoeninae) from the Early Miocene of North America

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 d...