Bear dog

The Amphicyonidae is an extinct family of large terrestrial carnivores belonging to the suborder Caniformia (meaning "dog-like"), which inhabited North America, Europe, Asia, and Africa from the Middle Eocene subepoch to the Pleistocene epoch 46.2—1.8 Mya, existing for approximately 44.4 million years.

Taxonomy
Amphicyonidae were named by Haeckel (1886) [also attributed to Trouessart 1885]. It was assigned to Carnivora by Sach and Heizmann (2001); to Arctoidea by Hunt (2001), Hunt (2002) and Hunt (2002); affirmed as Arctoidea by Zhai et al. (2003); affirmed to Arctoidea by Carroll (1988), Hunt (1998) and Wang et al. (2005); and to Caniformia by Morlo et al. (2007).

Origins
Amphicyonids, often referred to as "bear dogs", crossed from Europe to North America during the Miocene epoch and are considered an Old World taxon. The earliest to appear is the (rather large) Ysengrinia (30—20 Mya), followed by Cynelos (24—7 Mya) and Amphicyon (23—5 Mya). These animals would have followed ungulates and other mammals to the New World for a period of about 7 million years. The New World amphicyonids of the subfamilies Daphoeninae (42-16 Mya) and Temnocyoninae (33-20 Mya) coexisted with the Old World counterparts.[5] Note that the (often similar looking) members of the family Hemicyonidae are also often called "bear-dogs" (although they are increasingly referred to as "dog-bears" to avoid confusion).

Amphicyonids were as small as 5 kg (11 lb) and as large as 100 to 600 kg (220 to 1,320 lb)[6] and evolved from wolf-like to bear-like.[7] Early amphicyonids, such as Daphoenodon, possessed a digitigrade posture and locomotion (walking on their toes), while many of the later and larger species were plantigrade or semiplantigrade.[8] The amphicyonids were obligate carnivores, unlike the Canidae, which are hypercarnivores or mesocarnivores.