Arctocyonidae

Arctocyonidae (from Ancient Greek ἄρκτος (árktos), meaning "bear", and κύων (kúon), meaning "dog", and thus, "bear-dog") is an extinct, possibly polyphyletic family of placental mammals which lived from the late Cretaceous to the early Eocene. They were initially regarded as creodonts, though have since been reassigned to an order of their own, the Arctocyonia. Some have suggested that arctocyonids are ancestral to modern-day artiodactyls, or that they form a sister group. However, more recent phylogenetic analyses suggest that arctocyonids may represent an artificial grouping of extinct ungulates, or that they might be an assemblage of unrelated placentals related to pangolins, pantodonts, and periptychids.

Members of Arctocyonidae are characterised by long skulls, with large sagittal crests and very large canines. In the case of Arctocyon proper, the lower canines especially were large enough to require a diastema on the upper jaw to accommodate them. Arctocyonids varied considerably in size and morphology. Smaller genera, like Chriacus, were about the size of a coati, while larger ones, such as Arctocyon, weighed up to and stood at the shoulder. Many arctocyonids have climbing adaptations, suggesting that they were either descended from arboreal taxa, or were arboreal themselves. The North American Anacodon was more robust than other genera, and had adaptations for burrowing as well as climbing. Most genera appear to have been omnivorous, though Anacodon showed signs of an increase in herbivory.