Los Ursidae (Mammalia: Carnivora) Fósiles de la República Argentina.

LEOPOLDO HECTOR SOIBELZON; BOND, M.

Buenos Aires

Congreso; X CONGRESO LATINOAMERICANO DE GEOLOGIA Y VI CONGRESO NACIONAL DE GEOLOGIA ECONOMICA; 1998

The Ursidae (Mammalia, Carnivora) from Argentina. A general review of the fossil short-faced  bears (Ursidae, Tremarctinae) of Argentina is reported here. These bears, related to the extant south american species Tremarctos ornatus, are all included in the extinct and  exclusively south-american genus Arctotherium, under two distinct  groups recognizable as  subgenera, Arctotherium (Arctotherium), the large to giant-sized forms, and Arctotherium (Pararctotherium), the smaller forms. The larger forms Arctotherium (Arctotherium) have occurred some what earlier than the other forms, probably since the Marplatan (Upper Pliocene), and have been very abundant during the Ensenadan (Upper Pliocene?-Early Pleistocene). These forms are less abundant in the Early Lujanian (Upper Pleistocene) and are not recorded  in the Late Lujanian  (Uppermost Pleistocene). Instead,Arctotherium (Pararctotherium), first recorded in the Ensenadan, is relatively frequent in the Early Lujanian, probably lasting until the Late Lujanian. It is suggested here, that the different success of survival of these bears has been related to environmental changes ocurring since the Ensenadan. The larger forms, Arctotherium (Arctotherium), are thougt to be more frequent in Ensenadan wich, when compared into the Lujanian, represents warmer and more humid conditions. The decrease in the abundance during the Lujanian is limbed with the cooler and more arid conditions. On the contrary, the smaller forms, Arctotherium (Pararctotherium) were not so profoundly affected by the changing habitats, and were more abundant in the Lujanian apparently lasting longer than its larger relatives. In addition,  other fossils under study suggest the presence, at least in the Lujanian, of a group of bears which have a more definite cranial resemblance to the living genus Tremarctos, than the other known species of  argentinian fossil bears.