Arctocyon

Arctocyon (from Ancient Greek ἄρκτος (árktos), meaning "bear", and κύων (kúon), meaning "dog", and thus, "bear-dog") is an extinct genus of large placental mammals, part of the possibly polyphyletic family Arctocyonidae. The type species is A. primaevus, though up to five other species may be known. Fossils of Arctocyon have been found in Europe and North America. Arctocyon was originally named as a subgenus of the bear-dog Amphicyon, though was subsequently found to belong to a genus and family of its own. The relationship between arctocyonids and other placentals is unclear, with early classification efforts placing them as carnivores or creodonts, and later ones classifying them under Condylarthra, a wastebasket taxon for various early ungulates. More recent phylogenetic analyses suggest that arctocyonids are an artificial assemblage of several distantly-related placental lineages, and Arctocyon may be closely related to Loxolophus (another arctocyonid) and to pantodonts.

Arctocyon was among the largest arctocyonids, if not the largest. A. primaevus measured at the shoulder, and weighed up to , while A. mumak was larger still. Like many other arctocyonids, Arctocyon had very large canine teeth. In the case of the lower canines, they were large enough that they had to be accommodated by a gap between the upper canines and the premolars. The occipital and sagittal crests were very large. The cheek teeth were fairly unspecialised, and resembled those of bears. Arctocyon's torso was rigid and well-muscled, and the tail was quite inflexible. The forelimbs were powerfully muscled, the claws were curved and laterally compressed, and the digits had a strong grasping ability, suggesting that at least some species, like A. primaevus, were capable of climbing. Other species, such as A. mumak, were more terrestrial, and may have occasionally burrowed.