Amphicyonidae

The family was erected by Haeckel in 1866 (also attributed to Trouessart 1885). Their exact position has long been disputed. Early paleontologists usually defined them as members of Canidae (the dog family) or Ursidae (the bear family), but the modern consensus is that they form their own family. Some researchers have defined it as the sister clade to ursids, based on morphological analysis of the ear region. Amphicyonids should not be confused with the similar looking (and similarly nicknamed) "dog-bears", a more derived group of caniforms that is sometimes classified as a family (Hemicyonidae), but is more often considered a primitive subfamily of ursids (Hemicyoninae). They should also not be confused with Amphicynodontidae (another family of extinct caniforms which were related to bears or pinnipeds) or Arctocyonidae (a family of "condylarths" which literally translates to "bear-dogs"). ==Description==

Amphicyonids ranged in size from as small as and as large as and evolved from wolf-like to bear-like body forms. Skull '' Amphicyonids tended to have relatively large skulls, with the snout shorter than the rear portion of the cranium. In some large members of the family, such as Amphicyon, the back of the skull develops a sharp sagittal crest which defines attachment points for large jaw muscles. Amphicyonids had a relatively rudimentary form of auditory bulla, a bony sheath which encases the middle ear cavity. The bulla is small, mostly formed by the crescent-shaped ectotympanic bone below the middle ear. The entotympanics only make a minor contribution whenever they are ossified, which only becomes commonplace in Miocene amphicyonids. In these regards, amphicyonids are similar to living bears, otters, walruses, eared seals, and the red panda. At the start of their evolution, amphicyonids retained the typical placental dental formula of , but each subfamily follows their own trend in modifying their teeth. This period is suggested to be short and would have left the animal somewhat vulnerable. and some species of the large daphoenine Daphoenodon. ==Evolution==

It has long been uncertain where amphicyonids originated. It was thought that they may have crossed from Europe to North America during the Miocene epoch, but recent research suggests a possible North American origin from the miacids Miacis cognitus and M. australis (now renamed as the genera Gustafsonia and Angelarctocyon, respectively). As these are of North American origin, but appear to be early amphicyonids, it may be that the Amphicyonidae actually originates in North America. New World amphicyonids include the oldest known amphicyonid, Daphoenus (40–27 Ma). During the Arikareean in North America, amphicyonids had a competitive advantage over nimravids as the Oligocene progressed due to their greater cursoriality compared to the latter, helping them to persist as the latter disappeared from the continent as terrestrial habitats became more open. Extinction Amphicyonids began to decline in the late Miocene, The extinction of amphicyonids have been hypothesized by experts. Werdelin and Simpson (2009) suggested the extinction of Bonisicyon may have been the result of the inability to compete with Eucyon. == Ecology ==

Amphicyonids are suggested to have ranged in ecology from omnivores to hypercarnivores, with some amphicyonids suggested to have engaged in bone-crushing like some modern hyenas. However, in the case of Daphoenodon, five adults and one juvenile were found in three adjacent burrows, suggesting this species were gregarious predators. == Classification ==

Family Amphicyonidae ==References==