Ancient mitochondrial DNA reveals convergent evolution of giant short-faced bears (Tremarctinae) in North and South America

Abstract

The Tremarctinae are a subfamily of bears endemic to the New World,including two of the largest terrestrial mammalian carnivores that haveever lived: the giant, short-faced bears Arctodus simus from North Americaand Arctotherium angustidens from South America (greater than or equal to1000 kg). Arctotherium angustidens became extinct during the EarlyPleistocene, whereas Arctodus simus went extinct at the very end of thePleistocene. The only living tremarctine is the spectacled bear (Tremarctosornatus), a largely herbivorous bear that is today only found in SouthAmerica. The relationships among the spectacled bears (Tremarctos), SouthAmerican short-faced bears (Arctotherium) and North American shortfacedbears (Arctodus) remain uncertain. In this study, we sequenced amitochondrial genome from an Arctotherium femur preserved in a Chileancave. Our molecular phylogenetic analyses revealed that the SouthAmerican short-faced bears were more closely related to the extant SouthAmerican spectacled bear than to the North American short-faced bears.This result suggests striking convergent evolution of giant forms in thetwo groups of short-faced bears (Arctodus and Arctotherium), potentially asan adaptation to dominate competition for megafaunal carcasses.