The first records of Arctotherium in South America come in the form of the gigantic Arctotherium angustidens, possibly the largest carnivorous land mammal ever, in Argentina circa 1 Ma. The medium sized Arctodus pristinus inhabited a broad range in the North American continent, with Tremarctos floridanus endemic to the Gulf Coast. In the Early Pleistocene, short-faced bears began to establish themselves more thoroughly in both North and South America. Interestingly, all three genera are first recorded from the Blancan (Pliocene) of North America. A further study calculated the divergence date between Arctodus and Tremarctos at 5.5 Ma. Correspondingly, a 2008 study suggested that the mean divergence dates for Arctotherium, Arctodus and Tremarctos were 4.8 Ma, and between Arctotherium and Tremarctos at 4.1 Ma. Around the Miocene- Pliocene boundary (~5 Ma), tremarctines, along with other ursids, experienced an explosive radiation in diversity, as C4 vegetation ( grasses) and open habitats dominated, the world experienced a major temperature drop and increased seasonality, and a faunal turnover which extinguished 60–70% of all Eurasian faunal genera, and 70–80% of North American genera. Tremarctinae originate with their common ancestor, Plionarctos, in the Middle Hemphillian (earliest Late Miocene, ~10Ma) of North America Plionarctos is last recorded in the early Blancan (Early Pliocene, ~3.3Ma). Life restoration of Arctotherium bonariense. Most short-faced bears became extinct at the end of the Pleistocene. The group is thought to have originated in eastern North America, and then invaded South America as part of the Great American Interchange. Of these, the giant short-faced bears ( Arctodus simus and Arctotherium angustidens) may have been the largest ever carnivorans in the Americas. harroldorum), which is thought to be ancestral to the other three genera. simus), the South American giant short-faced bear Arctotherium (including A. The Tremarctinae or short-faced bears is a subfamily of Ursidae that contains one living representative, the spectacled bear ( Tremarctos ornatus) of South America, and several extinct species from four genera: the Florida spectacled bear ( Tremarctos floridanus), the North American giant short-faced bears Arctodus ( A.

Bear vs skeleton