An order of dominant, hoofed herbivores of the Cenozoic of South America that are abundantly represented in Paleocene through Pleistocene nonmarine sedimentary rocks of that continent. There are also isolated occurrences in the Paleocene of Central Asia and early Eocene of North America. Diverging from a primitive condylarth ancestry at an early date, they radiated into a wide diversity of forms, some of which were convergent with Northern Hemisphere ungulates.