The notoungulates are an extinct order of hoofed mammals (ungulates) that were native to South America. The order includes the huge Toxodon. Due to the isolated nature of South America, many notoungulates evolved along the lines of convergent evolution into forms that resembled mammals on other continents. Examples of this are Pachyrukhos, a notoungulate that evolved to fill the role of rabbits and hares and Homalodotherium, which evolved to resemble chalicotheres. During the Pleistocene, Toxodon was the largest common notoungulate. Most of the group (Toxodon being an exception) became extinct after the landbridge between North and South America was formed, allowing North American ungulates to enter South America in the Great American Interchange and out-compete the native fauna. This order is united with other South-American ungulates in the super-order Meridiungulata.
Following McKenna and Bell (1997)
Cifelli (1993) has argued that Notioprogonia is paraphyletic, as it would include the ancestors of the remaining suborders. Similarly, Cifelli indicated that Typotheria would be paraphyletic if it excluded Hegetotheria and he advocated inclusion of Archaeohyracidae and Hegetotheriidae in Typotheria.