Evolution of Giant Bears in the Americas

During the Pleistocene giant bears weighing over 1000 kg roamed both North and South America. These giants belonged to a now practically extinct subfamily of bears - Tremarctinae - which is today only represeeinted by the small, herbivorous Andean spectacled bear (Tremarctos omatus).

The giant North American bears (Arctodus) and South American bears (Arctotherium) have long been believed to be each others' closest relative. However, by comparing ancient DNA data obtained from representatives of the two extinct genera and comparing them with the living species, the scientists were able to show that Arctotherium is most closely related to Tremarctos and not Arctodus. 

This convergent evolution would have arisen in response to similar environmental conditions on both continents, most like it an abundance of large herbivore carcasses(killed by smaller predators), which Arctodus and Arctotherium could effectively dominate, and a lack of competing scavengers.