Proterotheriidae is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually 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 ...

family of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, cam ...

s from the

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

era that displays toe reduction. Despite resembling primitive, small horses, they were only distantly related to them, and instead belonged to the native South American ungulate order Litopterna.

Description

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, Brazil and Uruguay show that one member of the group, ''Neolicaphrium recens'' survived into the Late Lujanian, Pleistocene. Better known genera of the family include ''Diadiaphorus'' and ''Thoatherium'' from the Miocene.

Taxonomy

* Proterotheriidae ** ''Anisolambda'' ** ''Anisolophus'' ** ''Brachytherium'' ** ''Diadiaphorus'' ** ''Diplasiotherium'' ** ''Eoauchenia'' ** ''Eolicaphrium'' ** ''Epecuenia'' ** ''Epitherium'' ** ''Guilielmofloweria'' ** ''Heteroglyphis'' ** ''Lambdaconus'' ** ''Lambdaconops'' ** ''Mesolicaphrium'' ** ''Neobrachytherium'' ** ''Neodolodus'' ** ''Neolicaphrium'' ** ''Olisanophus'' ** ''Paramacrauchenia'' ** ''Paranisolambda'' ** ''Picturotherium'' ** ''Prolicaphrium'' ** ''Proterotherium'' ** ''Protheosodon'' ** ''Pseudobrachytherium'' ** ''Tetramerorhinus'' ** ''Thoatherium'' ** ''Thoatheriopsis'' ** ''Villarroelia'' ** ''Uruguayodon'' ** ''Wainka'' ** ''Xesmodon'' ** Megadolodinae *** ''Bounodus'' *** ''Megadolodus'' ** Indaleciidae *** ''Adiantoides'' *** ''Indalecia'' Proterotheriidae is traditionally considered to include two subfamilies, Anisolambdinae and Proterotheriinae. Anisolambdinae (also called Anisolambdidae in some studies) was proposed to unite the primitive and earlier forms ''Anisolambda'', ''Eolicaphrium'', ''Paranisolambda'', ''Protheosodon'', ''Guilielmofloweria'', ''Heteroglyphis'', ''Lambdaconops'', ''Wainka'' and ''Xesmodon''. However, the phylogenetic analysis of McGrath and colleagues recovered the included genera to neither form their own clade, or to universally represent basal taxa outside the genera of Proterotheriinae per Soria, making Anisolambdinae a polyphyletic group of unrelated organisms. Proterotheriidae was redefined by McGrath and colleagues in 2019 to be all taxa closer to ''Tetramerorhinus'' than ''Macrauchenia'', ''Tricoelodus'' or ''Protolipterna''. The cladogram below shows the modified results of their phylogenetic analysis, where incomplete taxa were placed based on morphology. The unrelated genera of the polyphyletic taxon Anisolambdinae or Anisolambdidae is highlighted in pink.

References

{{Taxonbar, from=Q138661 Proterotheriids, Litopterns Prehistoric mammal families Paleocene first appearances Holocene extinctions Pleistocene mammals of South America Neogene mammals of South America Paleogene mammals of South America Taxa named by Florentino Ameghino