Evolution Bear

plithocyon armagnacensis skull, member of extinct subfamily hemicyoninae miocene

the earliest members of ursidae belong extinct subfamily amphicynodontinae, including parictis (late eocene middle miocene, 38–18 mya) , younger allocyon (early oligocene, 34–30 mya), both north america. these animals looked different today s bears, being small , raccoon-like in overall appearance, , diets perhaps more similar of badger. parictis not appear in eurasia , africa until miocene. unclear whether late-eocene ursids present in eurasia, although faunal exchange across bering land bridge may have been possible during major sea level low stand late eocene (about 37 mya) , continuing oligocene. european genera morphologically similar allocyon, , younger american kolponomos (about 18 mya), known oligocene, including amphicticeps , amphicynodon.

the raccoon-sized, dog-like cephalogale oldest-known member of subfamily hemicyoninae, first appeared during middle oligocene in eurasia 30 mya. subfamily includes younger genera phoberocyon (20–15 mya), , plithocyon (15–7 mya). cephalogale-like species gave rise genus ursavus during oligocene (30–28 mya); genus proliferated many species in asia , ancestral living bears. species of ursavus subsequently entered north america, amphicynodon , cephalogale, during miocene (21–18 mya). members of living lineages of bears diverged ursavus between 15 , 20 mya, via species ursavus elmensis. based on genetic , morphological data, ailuropodinae (pandas) first diverge other living bears 19 mya, although no fossils of group have been found before 5 mya.

the new world short-faced bears (tremarctinae) differentiated ursinae following dispersal event north america during mid-miocene (about 13 mya). invaded south america (≈1 ma) following formation of isthmus of panama. earliest fossil representative plionarctos in north america (~ 10–2 ma). genus direct ancestor north american short-faced bears (genus arctodus), south american short-faced bears (arctotherium), , spectacled bears, tremarctos, represented both extinct north american species (t. floridanus), , lone surviving representative of tremarctinae, south american spectacled bear (t. ornatus).

fossil of cave bear (ursus spelaeus), relative of brown bear , polar bear pleistocene of europe

the subfamily ursinae experienced dramatic proliferation of taxa 5.3–4.5 mya, coincident major environmental changes; first members of genus ursus appeared around time. sloth bear modern survivor of 1 of earliest lineages diverge during radiation event (5.3 mya); took on peculiar morphology, related diet of termites , ants, no later pleistocene. 3–4 mya, species ursus minimus appears in fossil record of europe; apart size, identical today s asian black bear. ancestral bears within ursinae, perhaps aside sloth bear. 2 lineages evolved u. minimus: black bears (including sun bear, asian black bear, , american black bear); , brown bears (which includes polar bear). modern brown bears evolved u. minimus via ursus etruscus, ancestral extinct pleistocene cave bear. species of ursinae have migrated repeatedly north america eurasia 4 mya during pliocene. polar bear evolved species , descended brown bear around 400,000 years ago.