Proterotheriidae is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family of litoptern ungulates known from the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

. Members of the group were small-medium sized

cursorial A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often ...

herbivores A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

with brachydont

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

, with their toes showing progressive reduction, with later members of the group bearing weight on a single large toe similar to living

horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 milli ...

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 ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. Better known genera of the family include '' Diadiaphorus'' and '' Thoatherium'' from the Miocene. Thoatheriumknight

Taxonomy

* Proterotheriidae ** '' Anisolambda'' ** '' Anisolophus'' ** '' Brachytherium'' ** '' Diadiaphorus'' ** '' Diplasiotherium'' ** '' Eoauchenia'' ** '' Eolicaphrium'' ** '' Epecuenia'' ** '' Epitherium'' ** '' Guilielmofloweria'' ** '' Heteroglyphis'' ** '' Lambdaconus'' ** '' Lambdaconops'' ** '' Mesolicaphrium'' ** '' Neobrachytherium'' ** '' Neodolodus'' ** '' Neolicaphrium'' ** '' Olisanophus'' ** '' Paramacrauchenia'' ** '' Paranisolambda'' ** '' Picturotherium'' ** '' Prolicaphrium'' ** '' Promylophis'' ** '' 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 that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

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") is an extinct genus of large ungulate native to South America from the Pliocene or Middle Pleistocene to the end of the Late Pleistocene. I ...

'', '' 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