ABSTRACT

Our understanding of South American megatheriine ground sloths was traditionally based largely on abundant material from Brazil and Argentina, mainly because megatheriine remains from elsewhere in South America were scant and poorly preserved. In recent years, however, the recovery and description of remains from northwestern South America has led to the recognition of several new taxa and the validation of species originally based on sparse remains. Falling in the latter group is Megatherium (Pseudomegatherium) tarijense Gervais and Ameghino, 1880, which is based on a complete but eroded calcaneum from Pleistocene deposits of the Tarija Valley of southern Bolivia. Most authors of the past century viewed this species as poorly defined and probably synonymous with Megatherium (Megatherium) americanum. This uncertainty is attributable to both the poor nature of the remains of M. (P.) tarijense and the presence of M. (M.) americanum in the Bolivian Pleistocene. Well preserved and nearly complete remains of several individuals indicate that M. (P.) tarijense is indeed valid. This material includes abundant remains from the Tarija Basin (Bolivia) housed in the Field Museum of Natural History (USA) and the Museo Nacional de Paleontología y Arqueología de Tarija (Bolivia) and also from the Peruvian Andes (Yantac), housed in the Universidad Nacional de Ingeniería de Lima. M. (P.) tarijense differs from M. (M.) americanum mainly in its smaller size; shorter, less robust premaxillae; shallower mandibular ramus; reduced size of the humeral deltopectoral crest; less torsion of the femoral diaphysis; unreduced patellar trochlea; and relatively shorter, stockier calcaneum.