Proterotheriids

Thoatherium (meaning "active swift-beast") is an extinct genus of litoptern mammals from the Early Miocene of Argentina. Fossils of the genus have been found in the Santa Cruz Formation in Argentina. With a length of , the gazelle-like Thoatherium was a small representative of the order Litopterna. Judging from its long legs, it was a fast runner. Thoatherium had remarkably reduced toes; only one horse-like hoof remained. Thoatherium even lacked splint bones, which are remnants of the second and fourth toe found in modern horses. Judging from its generalised, brachydont teeth, Thoatherium fed

Proterotheriidae is an extinct family of litoptern ungulates known from the Eocene-Late Pleistocene of South America. Members of the group were small to medium-sized cursorial herbivores with brachydont teeth, with their toes showing progressive reduction, with later members of the group bearing weight on a single large toe similar to living horses.

Diadiaphorus is an extinct genus of litoptern mammal from the Miocene of Argentina (Ituzaingó, Pinturas, Chiquimil and Santa Cruz Formations) and Bolivia (Nazareno Formation), South America.

Neolicaphrium is an extinct genus of ungulate mammal belonging to the extinct order Litopterna. This animal lived from the Late Pliocene (Chapadmalalan) to the Late Pleistocene (Lujanian) in southern South America, being the last survivor of the family Proterotheriidae.

Tetramerorhinus is an extinct genus of proterotheriid litoptern that lived during the Early and Middle Miocene in what is now Argentina and Peru.

Diplasiotherium is an extinct genus of litoptern belonging to the family Proterotheriidae, that lived between the late Miocene and the early Pliocene (in the SALMAs Huayquerian and Montehermosan). The fossils of this animal have been found in Argentina, in the Monte Hermoso Formation.