Tremarctinae originate with their common ancestor,
Plionarctos, in the
Middle Hemphillian (
Late Miocene, ~7Ma) of North America;
Plionarctos is last recorded in the
early Blancan (Pliocene, ~3Ma).''''
and between Arctotherium
and Tremarctos'' at 4.1 Ma. An indeterminate
Arctotherium is first recorded from the late Pliocene of
El Salvador. In the Early Pleistocene, short-faced bears began to establish themselves more thoroughly in both North and South America. The medium sized
Arctodus pristinus inhabited a broad range in the North American continent, with
Tremarctos floridanus endemic to the Gulf Coast. 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. What the evolutionary history of
Arctotherium in the previous 1.5 million years, and their history in South America, is unclear. In the Middle Pleistocene, both
Arctodus and
Arctotherium gave way to new forms;
Arctodus pristinus gave way to the huge
Arctodus simus, which inhabited a pan-continental range, from
Alaska to
Mexico.
Arctotherium angustidens, on the other hand, was replaced by a series of smaller, medium-sized species-
Arctotherium vetustum, then shortly thereafter by
Arctotherium bonariense, and
Arctotherium tarijense. and to reinvade
Central America. By the terminal Pleistocene,
Arctodus simus,
Tremarctos floridanus,
Arctotherium tarijense and
Arctotherium wingei collectively occupied a range from Alaska to southernmost
Patagonia. All of these forms were extinct by the end of the early Holocene. Scholars suggest that the spectacled bear migrated into Central and South America upon the extinction of
Arctotherium wingei, if Pleistocene records of Andean
Arctotherium sp. aren't confirmed as the spectacled bear. == Paleobiology ==