notoungulate

The notoungulates were an extinct order of placental mammals that were endemic to South America. They first appeared in the Early Paleocene epoch and survived until the Late Pleistocene, making them one of the longest-lived South American mammal groups. Their diversity was remarkable, encompassing a wide range of sizes and forms, from small, rodent-like creatures to large, hippopotamus-sized herbivores.

These animals are characterized by a number of shared traits, particularly in their cranial and dental anatomy. Notoungulates generally possessed a relatively short skull, a tendency towards hypsodonty (high-crowned teeth), and often had distinctively shaped incisors. Their taxonomic relationships have been a subject of debate, but they are now generally considered to be related to other South American ungulate orders, such as litopterns, and possibly to Afrotheria.

The fossil record of notoungulates is extensive, particularly in Argentina and other parts of South America. Their ecological roles varied greatly throughout their evolutionary history, with many being grazers or browsers, adapted to the diverse South American landscapes. Some groups, like the toxodonts, were formidable herbivores. The extinction of the notoungulates coincided with the Great American Biotic Interchange, when North American mammals invaded South America, possibly leading to increased competition and predation that contributed to their demise.