Doctor Claude Guérin dedicated many years of his research to fossil rhinoceroses, but also to some of the interesting mammals that evolved in South America. This is why I contribute to this volume in his memory with a synthesis on one of the families that are known as South American Native Ungulates. The order Notoungulata was the most diverse and abundant of these native ungulates throughout the Cenozoic, and is mainly gathered in two suborders, Toxodontia and Typotheria, which in turn include up to 11-12 families, not all presently considered as monophyletic groups. The family Mesotheriidae includes the largest-sized typotheres and is recorded from Early Oligocene to Early Pleistocene. Mesotheriids are mainly known from Argentina, but are also present in Chile, Bolivia, and Peru. The record of Argentinean mesotheriids has increased in recent years, both from Paleogene and Neogene levels, and some emphasis is made in the new records from west-central areas such as Mendoza Province. The systematics of mesotheriids is far from being well resolved. Recent studies have evidenced a marked change in tooth morphology, size, and proportions along the ontogeny within mesotheriines, which have led to questioning some assumed diagnostic features. Research in progress on new findings from several localities in Mendoza could help elucidate some taxonomic issues, especially among Miocene taxa.

Fil: Cerdeño Serrano, Maria Esperanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina