Proterotheriidae is an extinct

Extinction

In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 family of fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 ungulate

Ungulate

Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...

s from the Tertiary

Tertiary

The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

 period that displays toe reduction. Despite resembling primitive, small horses, they were not related to them, but belonged to the order Litopterna

Litopterna

Litopterna is an extinct order of fossil hoofed mammals from the Tertiary period that displays toe reduction. Three-toed, and even a one-toed horselike form developed....

.
Two subfamilies and 18 genera of Proterotheriidae are known. All forms were small or medium-sized. Typical is a reduction of the number of toes and brachydont or mesodont teeth. The family is recorded since the late Palaeocene. Various fossils are known from many parts of the South American continent. The diversity decreased in the Miocene to Pliocene and it has been assumed for a long time that they entirely disappeared in the late Pliocene. However, fossils found in Argentina and Uruguay show that one member of the group, Neolicaphrium recens survived into the Lujanian

Lujanian

The Lujanian age is a period of geologic time within the Pleistocene and Holocene epochs of the Neogene used more specifically with South American Land Mammal Ages...

. Better known genera of the family include Diadiaphorus

Diadiaphorus

Diadiaphorus is an extinct genus of litoptern mammal from the Miocene of South America.Diadiaphorus closely resembled a horse, but was only around in body length, similar to a modern sheep. It had three toes, only one of which touched the ground. This toe had a large hoof; the two outer toes were...

or Thoatherium

Thoatherium

Thoatherium is an extinct genus of litoptern mammal.With a length of , the gazelle-like Thoatherium was the smallest 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...

from the Miocene

Genera

• Proterotheriidae
  • Anisolambdinae
    • Anisolambda
    • Paranisolambda
    • Protheosodon
    • Richardolydekkeria
    • Wainka
    • Xesmodon
  • Proterotheriinae
    • Brachytherium
    • Deuterotherium
    • Diadiaphorus
      Diadiaphorus
      Diadiaphorus is an extinct genus of litoptern mammal from the Miocene of South America.Diadiaphorus closely resembled a horse, but was only around in body length, similar to a modern sheep. It had three toes, only one of which touched the ground. This toe had a large hoof; the two outer toes were...
      
      
    • Diplasiotherium
    • Eoproterotherium
    • Epecuenia
    • Licaphrium
    • Neolicaphrium
    • Prolicaphrium
    • Proterotherium
    • Prothoatherium
    • Thoatherium
      Thoatherium
      Thoatherium is an extinct genus of litoptern mammal.With a length of , the gazelle-like Thoatherium was the smallest 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...
      
      
    • Villarroelia
  • Megadolodinae
    • Bounodus
    • Megadolodus