Proterotheriidae is an extinct 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, ...

s from the Cenozoic 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

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

. 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 A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

group of unrelated organisms. Proterotheriidae was redefined by McGrath and colleagues in 2019 to be all taxa closer to '' Tetramerorhinus'' than ''

Macrauchenia ''Macrauchenia'' ("long llama", based on the now-invalid llama genus, ''Auchenia'', from Greek "big neck") was a large, long-necked and long-limbed, three-toed native South American mammal in the order Litopterna. The genus gives its name to its ...

'', '' 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 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