Mesotheriidae - Geographic and Temporal Distribution

Geographic and Temporal Distribution

As with almost all other notoungulates, mesotheriids are known only from the Cenozoic of South America (McKenna and Bell, 1997). Unlike some other families, mesotheriid fossils are not found across the continent. Instead, mesotheriids are most abundant and diverse in faunas from middle latitudes in Bolivia and Chile, particularly the Altiplano (Flynn et al., 2005). Mesotheriid fossils are rare in high latitude Patagonian faunas and absent entirely from tropical faunas in northern South America.

The earliest potential record of a mesotheriid is ?Trachytherus mendocensis from the late Eocene or early Oligocene Divisadero Largo Formation of Mendoza Province, Argentina (Shockey et al., 2007), but Cerdeño et al. (2006) have suggested that this specimen may actually derive from early Miocene rocks that overlie the Divisadero Largo Formation. The earliest secure records of the family come from the late Oligocene, when the family is represented by the genera Anatrachytherus and Trachytherus from Argentina and Bolivia (Reguero and Castro, 2004). The family reached its greatest diversity in the Miocene (Flynn et al., 2005), and mesotheriids persisted into the middle Pleistocene, in the form of the type genus, Mesotherium (McKenna and Bell, 1997). Mesotheriidae was one of only three notoungulate families to persist into the Quaternary, the others being Hegetotheriidae and Toxodontidae.