Arctotherium

Arctotherium is an extinct genus of Central and South American short-faced bears within Ursidae of the Pleistocene. Their ancestors migrated from North America to South America during the Great American Interchange, following the formation of the Isthmus of Panama during the late Pliocene. The oldest confirmed remains are those of A. angustidens from Buenos Aires, Argentina, dating to the Ensenadan epoch, 0.98 to 1.76 Ma old, within the Early to Middle Pleistocene, with a tooth possibly belonging to Arctotherium dating about 2.588 Mya. Their closest known relative is the spectacled bear (Tremarctos ornatus). Arctotherium was named by Hermann Burmeister in 1879. A specimen of A. angustidens from Buenos Aires shows an individual estimated, using the humerus, to weigh between 983 and 2,042 kg (2,167 and 4,502 lb), though the authors consider the upper limit as improbable and say that 1,588 to 1,749 kg (3,501 to 3,856 lb) is more likely. It would still make the genus the largest bear ever found and contender for the largest carnivorous land mammal known. Its large size has been attributed to increased competition from other, later-arriving or evolving carnivorans, such as jaguars, or Smilodon, following the early dispersal of short-faced bears to South America. The North American carnivorans that invaded South America, including short-faced bears and Smilodon, probably quickly dominated the predatory niches formerly occupied by the native typical South American groups as metatherian sparassodont and avian phorusrhacid carnivores. There is evidence to suggest that Arctotherium had dens. Fossils of Arctotherium have been found in: