Litopterna (from "smooth heel") 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 ...

order of

South American native ungulates South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals that were indigenous to South America from the Paleocene (from at least 63 million years ago) until the end of the Late Pleistocene (~12,000 years a ...

that lived from the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

to the

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 ...

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

around 62.5 million to 12,000 years ago (or possibly as late as 3,500 years ago), and were also present in Antarctica during 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 ...

. They represent the second most diverse group of South American ungulates after

Notoungulata Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms re ...

. It is divided into nine families, with

Proterotheriidae Proterotheriidae is an extinction, extinct family of Litopterna, litoptern ungulates known from the Eocene-Late Pleistocene of South America. Members of the group were small-medium sized cursorial Herbivore, herbivores with brachydont Tooth, teet ...

and Macraucheniidae being the most diverse and last surviving families.

Diversity

The body forms of many litopterns, notably in the limb and skull structure, are broadly similar to those of living

ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...

s, unlike other

South American native ungulate South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals that were indigenous to South America from the Paleocene (from at least 63 million years ago) until the end of the Late Pleistocene (~12,000 years a ...

groups, which are often strongly divergent from living ungulates. Paleocene and Eocene litopterns generally had small body masses, with '' Protolipterna'' ( Protolipternidae) estimated to have had a body mass of , though the Eocene sparnotheriodontids were considerably larger, with estimated body masses of around . Most proterotheriids had body masses of around while many macraucheniids had body masses of around . Some of the last macraucheniids like ''

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 ...

'' were considerably larger, with body masses around a ton. Adianthidae generally had small body masses, with members of the genus '' Adianthus'' estimated to weigh . Members of the proterotheriid subfamily Megadolodinae are noted for having bunodont (rounded cusp) molar teeth, which is largely unique to litopterns among South American native ungulates. Litopterns of the mid-late Cenozoic had hinge-like limb joints and hooves similar to those of modern ungulates, with the weight being supported on three toes in macraucheniids and one in proterotheriids, with the protherotheriid '' Thoatherium'' developing greater toe reduction than that present in living horses. Macraucheniids had long necks and limbs. Members of the macraucheniid subfamily Macraucheniinae saw the progressive migration of the nasal opening to the top of the skull, which was often historically suggested to indicate the presence of a trunk, though other authors have suggested that a

moose The moose (: 'moose'; used in North America) or elk (: 'elk' or 'elks'; used in Eurasia) (''Alces alces'') is the world's tallest, largest and heaviest extant species of deer and the only species in the genus ''Alces''. It is also the tal ...

-like prehensile lip, or a saiga-like nose to filter dust are more likely.

Ecology

Litopterns were likely hindgut fermenters. At least some macraucheniids like ''Macrauchenia'' are suggested to have been mixed feeders feeding on both browse and grass. Sparnotheriodontids are suggested to have been browsers. Some proterotheriids are suggested to have been browsers, while some members proterotheriid subfamily Megadolodinae like '' Megadolodus'' have been suggested to have been

omnivorous An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...

with at least part of their diet consisting of hard fruit.

Evolutionary history

Litopterna, like other "South American native ungulates" is thought to have originated from groups of archaic "

condylarth Condylarthra is an informal group – previously considered an Order (biology), order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates and is now largely consid ...

s" that migrated from North America. Sequencing of the

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

proteome A proteome is the entire set of proteins that is, or can be, expressed by a genome, cell, tissue, or organism at a certain time. It is the set of expressed proteins in a given type of cell or organism, at a given time, under defined conditions. P ...

and mitochondrial genome of ''Macrauchenia'' has revealed that litopterns are true ungulates, sharing a common ancestor with

, and with their closest living relatives being

Perissodactyla Perissodactyla (, ), or odd-toed ungulates, is an order of ungulates. The order includes about 17 living species divided into three families: Equidae (horses, asses, and zebras), Rhinocerotidae (rhinoceroses), and Tapiridae (tapirs). They t ...

(the group containing living

equines ''Equus'' () is a genus of mammals in the perissodactyl family (biology), family Equidae, which includes wild horse, horses, Asinus, asses, and zebras. Within the Equidae, ''Equus'' is the only recognized Extant taxon, extant genus, comprising s ...

rhinoceros A rhinoceros ( ; ; ; : rhinoceros or rhinoceroses), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates (perissodactyls) in the family (biology), famil ...

and

tapirs Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...

) as part of the clade Panperissodactyla, with the split from Perissodactyla being estimated at around 66 million years ago. The relationship of Litopterna to other South American native ungulate groups is uncertain, though it may be closely related to the "condylarth" group Didolodontidae. The earliest litopterns appeared during the early

, around 62.5 million years ago. Aside from South America, sparnotheriodontids are also known from the

aged La Meseta Formation in the Antarctic Peninsula, representing the only record of litopterns on the Antarctic continent. Litopterns declined during the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene 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 ...

, likely as a result of climatic change and competition with recently immigrated North American ungulates who arrived as part of the

Great American interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which land ...

, following the connection of the previously isolated North and South America via the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

. ''Macrauchenia,'' '' Xenorhinotherium'' (Macraucheniidae) and '' Neolicaphrium'' (Proterotheriidae) were the last surviving genera of litopterns. All became extinct at the end of the

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 ...

around 12,000 years ago as part of the end-Pleistocene extinction event, along with most other large mammals in the Americas, co-inciding with the arrival of the first humans to the continent. A study in 2025 suggested that ''Xenorhinotherium'' may have survived until the late Holocene based on a specimen radiocarbon dated to 3,493–4,217 years cal.

Before Present Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because ...

(BP). It is possible that hunting had a causal role in their extinction.

Classification

* Order Litopterna ** '' Proacrodon'' ** Family Protolipternidae *** '' Asmithwoodwardia'' *** '' Miguelsoria'' *** '' Protolipterna'' ** Family Indaleciidae *** Adiantoides leali

'' Adiantoides'' *** '' Indalecia'' ** Family Sparnotheriodontidae *** '' Phoradiadius'' *** '' Notiolofos'' *** '' Sparnotheriodon'' *** '' Victorlemoinea'' ** Family Amilnedwardsiidae *** '' Amilnedwardsia'' *** '' Ernestohaeckelia'' *** '' Rutimeyeria'' ** Family Notonychopidae *** '' Notonychops'' *** '' Requisia'' ** Superfamily Macrauchenioidea *** Family Adianthidae **** '' Proectocion'' **** Adianthinae ***** '' Adianthus'' ***** '' Proadiantus'' ***** '' Proheptaconus'' ***** '' Thadanius'' ***** '' Tricoelodus'' *** Family Macraucheniidae **** '' Llullataruca'' **** Subfamily Cramaucheniinae ***** '' Coniopternium'' ***** '' Caliphrium'' ***** '' Cramauchenia'' ***** '' Phoenixauchenia'' ***** '' Polymorphis'' ***** '' Pternoconius'' ***** '' Theosodon'' ****

Subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...

Macraucheniinae ***** '' Cullinia'' ***** ''

Huayqueriana ''Huayqueriana'' is an extinct genus of South American litoptern, related to ''Macrauchenia'', and belonging to the same family, Macraucheniidae. It was formerly known as ''Macrauchenidia latidens'', described in 1939 by Cabrera, but redefined as ...

'' ***** ''

'' ***** '' Macraucheniopsis'' ***** '' Oxyodontherium'' ***** '' Paranauchenia'' ***** '' Promacrauchenia'' ***** '' Scalabrinitherium'' ***** '' Windhausenia'' ***** '' Xenorhinotherium'' ** Superfamily Proterotherioidea *** Family

****

'' 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''

References

External links

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