Arctocyonidae (from Greek arktos and kyôn, "bear/dog-like") is an extinct, possibly polyphyletic family of placental mammals which lived from the late Cretaceous to the early Eocene.

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.

In the case of Arctocyon proper, the lower canines especially were large enough to require a diastema on the upper jaw to accommodate them.

Smaller genera, like Chriacus, were about the size of a coati, while larger ones, such as Arctocyon, weighed up to 44 kg (97 lb) and stood 45 cm (18 in) at the shoulder.

The family Arctocyonidae was named by Christoph Gottfried Andreas Giebel in 1855, as a carnivoran subfamily that included Arctocyon, the amphicyonid Amphicyon, and the ursid Agriotherium.

William Diller Matthew, in 1937, divided it into four subfamilies (Arctocyoninae, Chriacinae, Oxyclaeninae, and Triisodontinae);[6] the latter is now regarded as a family of its own.

In 2012, a phylogenetic analysis of Prolatidens waudrae, a traditional arctocyonid, recovered it as a more basal ungulate; Arctocyon, Landenodon and Thryptacodon were recovered as part of a clade sister to triisodonts and mesonychids; and the reminder of tested arctocyonids formed a polytomy basal to that clade and Diacodexis.

[12] That same year, a larger analysis by Thomas J. D. Halliday, Paul Upchurch and Anjali Goswami recovered arctocyonids as several entirely unrelated placental lineages.

By their constrained strict consensus tree, Arctocyon and Loxolophus form a clade related to pantodonts and periptychids, and the rest of Arctocyonidae is recovered close to pangolins.

[16] The skulls of arctocyonids were fairly long, with a small braincase and very large sagittal and occipital crests,[6] combined traits of herbivorous and carnivorous mammals.

[15] In Chriacus, the ankle joints were flexible and allowed the hind feet to rotate, enabling them to climb downward.