Toxodonta

Toxodonta is a suborder of the extinct mammalian order Notoungulata. The group is named after Toxodon, the first example of the group to be discovered. The suborder includes the largest known notoungulates, members of the family Toxodontidae. Toxodontids first appeared during the Oligocene in the form of Proadinotherium. Another well-known toxodontid is Nesodon, a medium-sized Miocene toxodontid descended from Proadinotherium which had converted its second upper incisors into tusks. Toxodon itself evolved during the Pliocene alongside the related Trigodon, an equally large mammal which possessed a horn projecting from its forehead, in the same way as a modern rhinoceros. Toxodon was a huge herbivore (about the size of a modern black rhinoceros) with four toes on each hoof.

Closely related to the toxodontids are two additional families: the Leontiniidae of the Eocene through Miocene and the Notohippidae. The last surviving notohippid was Colpodon from the late Oligocene, which was medium-sized but heavily built. Notohippids possessed molars that were superficially like those of modern horses.