Arctotherium

Arctotherium ("bear beast") is an extinct genus of the Pleistocene South American short-faced bears within Ursidae. 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 dated confirmed remains are those of "A. angustidens" from Buenos Aires, Argentina, dating to the Ensenadan epoch, 1.76 to 0.98 Ma old, within the Early to Middle Pleistocene, with a tooth possibly belonging to "Arctotherium" dating about 2.588 Mya. They are genetically closer to the spectacled bear ("Tremarctos ornatus"), than to "Arctodus" of North America, implying the two extinct forms evolved large size in a convergent manner, perhaps to facilitate dominating other carnivores in the competition for the biggest carcasses. The northernmost species, "A. wingei", known from Venezuela in South America, apparently invaded Central America and reached as far north as the Yucatán.
Description.
"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 , though the authors consider the upper limit as improbable and say that is more likely. An estimated standing height for "Arctotherium" is . 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, Protocyon 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 such as metatherian sparassodont and avian phorusrhacid carnivores.
Ecology.
There is evidence to suggest that "Arctotherium" had dens.
Distribution.
Fossils of "Arctotherium" have been found in: