notoungulates

Notoungulata is an extinct order of placental mammals that were endemic to South America. They were a highly diverse group, appearing in the Paleocene epoch and surviving until the end of the Pleistocene. Their fossil record is extensive, particularly in Argentina and Patagonia, providing significant insights into mammalian evolution in isolation.

The group displayed a wide range of body sizes and lifestyles. Some, like the toxodonts, were large, bulky herbivores resembling rhinoceroses or hippopotamuses. Others, such as the typotheres, were smaller and more cursorial, with some adaptations for digging. Astrapotheres were another subgroup, characterized by their robust build and often a short trunk-like proboscis. The earliest notoungulates were relatively small, but they diversified significantly over millions of years, occupying various herbivorous niches.

Their evolutionary relationships have been a subject of debate, but they are generally considered part of a larger superorder called Meridiungulata, which includes other South American endemic ungulates. The extinction of notoungulates likely occurred due to the arrival of North American fauna after the formation of the Isthmus of Panama, leading to increased competition and predation. Their disappearance marked the end of a unique evolutionary experiment in South American mammalian history.