Amphicyonidae is an extinct family of terrestrial carnivorans belonging to the suborder Caniformia. They first appeared in North America in the middle Eocene (around 45 Ma), spread to Europe by the late Eocene (35 Ma), and further spread to Asia and Africa by the early Miocene (23 Ma). Amphicyonids were among the first lineages of carnivorans to reach large body sizes. The family had largely disappeared worldwide by the late Miocene (9-7 Ma), with the latest recorded species at the end of the Miocene in Africa. Amphicyonids are colloquially referred to as "bear-dogs".

Taxonomy

thumb|left|Restoration of Amphicyon ingens

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

thumb|Skull diagram of [[Daphoenus|Daphoenus vetus]]

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. 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.

! Subfamily Daphoeninae<br/>(North America)

! Subfamily Temnocyoninae<br/>(North America)

! Subfamily Thaumastocyoninae

|- style="vertical-align: top;"

|<!--Not assigned-->

  • Amphicyanis
  • Angelarctocyon
  • A. australis (formerly Miacis australis)
  • Brachycyon
  • B. reyi
  • B. palaeolycos
  • B. gaudryi
  • Gustafsonia
  • G. cognita (formerly Miacis cognitus)
  • Guangxicyon
  • G. sinoamericanus
  • Harpagocyon
  • H. inusitatus
  • Harpagophagus
  • Meiniogale
  • S. ferox
  • Storchictis
  • S. miacinus
  • Symplectocyon
  • V. chinjiensis

|<!--Amphicyoninae-->

  • Afrocyon
  • A. burolleti
  • Amphicyon
  • A. astrei
  • A. carnutense?
  • A. cooperi
  • A. frendens
  • A. galushai
  • A. giganteus?
  • A. gutmanni
  • A. ingens
  • A. lactorensis
  • A. laugnacensis
  • A. longiramus
  • A. lyddekeri?
  • A. major (type)
  • A. palaeindicus?
  • A. pannonicus
  • A. shahbazi
  • A. ulungurensis
  • A. zhanxiangi
  • Askazansoria
  • A. mavrini
  • Bonisicyon
  • M. dojambir
  • M. kiptalami
  • M. peignei
  • Mogharacyon
  • M. anubisi
  • Namibiocyon
  • P. bohemicus
  • Pliocyon
  • P. medius
  • P. ossifragus
  • P. robustus
  • Pseudocyon
  • P. sansaniensis
  • P. steinheimensis?
  • P. styriacus
  • Pseudarctos
  • P. bavaricus
  • Pseudocyonopsis
  • T. grivense
  • Ysengrinia
  • Y. americanus
  • Y. depereti
  • Y. geraniana
  • Y. tolosana
  • Y. valentiana

|}

References

  • Whence the beardogs? Reappraisal of the Middle to Late Eocene 'Miacis' from Texas, US, and the origin of Amphicyonidae