Meridiungulata

Meridiungulata is an extinct order of South American ungulates. The name refers to their geographic origin, with "meridi" meaning southern and "ungulata" referring to hooved mammals. These animals were part of the South American fauna that evolved in isolation after the breakup of the supercontinent Gondwana. Meridiungulates were a diverse group, encompassing a range of herbivores, from small browsers to large grazers.

The fossil record indicates that meridiungulates were present from the Paleocene or Eocene epochs up to the Pleistocene epoch. Their evolutionary history is complex, and their relationships to other ungulate groups have been a subject of much debate. Early classifications placed them as artiodactyls (even-toed ungulates), but later phylogenetic analyses, particularly those incorporating molecular data, suggested they might be more distantly related. Some studies have proposed relationships with Afrotheria, a superorder of mammals that includes elephants and manatees.

Key characteristics of meridiungulates often included fused navicular and cuboid bones in their ankle, a feature that distinguishes them from other ungulates. They occupied a variety of ecological niches, filling roles similar to those of horses, deer, and rhinoceroses in other continents. Despite their long evolutionary history and diversity, all meridiungulate lineages eventually went extinct. The precise causes of their extinction are not fully understood but likely involved a combination of factors, including climate change and competition from newly arrived invasive species after the formation of the Isthmus of Panama. Prominent families within Meridiungulata include Toxodontidae, Macraucheniidae, and Notoungulata.