Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order 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 ...

hoofed mammals 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 configu ...

era. The order is one of the five great orders of

South American ungulates South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþaz ...

that were endemic to the continent, until the

Great American Biotic 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 lan ...

brought new ungulate species. Like other

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

South American mammals, their relationship to other mammal groups had long been unclear, but recent genetic and proteomic evidence indicates that their closest living relatives are Perissodactyls (odd-toed ungulates) including

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 million ...

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant taxon, extant species (or numerous extinct species) of odd-toed ungulates in the family (biology), family Rhinocerotidae. (It can also refer to a member ...

, and

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

, and that litopterns are closely related to notoungulates, another widespread group of South American ungulates. There were two major groups of litopterns: Proterotheriidae and Macraucheniidae. Proterotheriids were medium to large animals that evolved adaptations for fast running, and occupied a variety of niches that elsewhere were filled by animals such as goats and antelopes,

mouse deer Chevrotains, or mouse-deer, are small even-toed ungulates that make up the family Tragulidae, the only extant members of the infraorder Tragulina. The 10 extant species are placed in three genera, but several species also are known only ...

, and

. Macraucheniids were large to very large animals with long necks; they evolved retracted nasal openings, indicating that a number of their species likely had a muscular upper lip or short trunk. They likely filled roles in the environment similar to

camels A camel (from: la, camelus and grc-gre, κάμηλος (''kamēlos'') from Hebrew or Phoenician: גָמָל ''gāmāl''.) is an even-toed ungulate in the genus ''Camelus'' that bears distinctive fatty deposits known as "humps" on its back. C ...

giraffes The giraffe is a large African hoofed mammal belonging to the genus ''Giraffa''. It is the tallest living terrestrial animal and the largest ruminant on Earth. Traditionally, giraffes were thought to be one species, '' Giraffa camelopardali ...

, sivatheres, and browsing rhinoceroses on other continents. Many types of litopterns were abundant in South American faunas, almost all ate plants, and the group reached its maximum diversity in the late Miocene. All litopterns displayed toe reduction – three-toed forms developed, and some proterotheriids had a single hoof on each foot. Together with ''

Macraucheniopsis ''Macraucheniopsis'' is an extinct genus of litoptern mammal belonging to the family Macraucheniidae from the Middle to Late Pleistocene of Argentina. It, along with ''Macrauchenia'', ''Neolicaphrium'', and ''Xenorhinotherium'' were among the y ...

'', ''

Neolicaphrium ''Neolicaphrium'' is an extinct genus of ungulate mammal belonging to the extinct order Litopterna. This animal lived from the Late Pliocene (Chapadmalalan) to the Late Pleistocene ( Lujanian) in southern South America, being the last survivor of ...

'', and ''

Xenorhinotherium ''Xenorhinotherium'' is an extinct genus of macraucheniine macraucheniids, closely related to ''Macrauchenia'' of Patagonia. The type species is ''X. bahiense''.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 ...

'' was among the youngest genera of litopterns, and these two appear to have been the only members of the group to survive the

. All four became extinct at the end of the

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 ...

. The genera that died out during this faunal exchange are presumed to have been driven to extinction at least in part by competition with invading North American ungulates.

Evolutionary background

This order is known only from fossils in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the souther ...

and

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...

, however, possible remains belonging to a litoptern, likely a macraucheniid, have been found in

Mexico Mexico ( Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guate ...

. Litopterns, like the notoungulates and

pyrotheres Pyrotheria is an order of extinct meridiungulate mammals. These mastodon-like ungulates include the genera ''Baguatherium'', ''Carolozittelia'', ''Colombitherium'', ''Griphodon'', ''Propyrotherium'', ''Proticia'', and ''Pyrotherium''. They had ...

, are examples of ungulate mammals that evolved independently in "splendid isolation" on the island continent of South America. Like Australia, South America was isolated from all other continents following the breakup of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final st ...

. During this period of isolation, unique mammals evolved to fill

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (fo ...

s similar to other mammals elsewhere. The Litopterna occupied ecological roles as browsers and grazers similar to perissodactyl and artiodactyl hoofed mammals in

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

. Litopterns were common and varied in early faunas and persisted, in decreasing variety, into the

. Early forms were originally classified by European and North American paleontologists as closely related to condylarths, believed to be the order that gave rise to modern hoofed mammals. Litopterns were seen as persisting condylarths, primitive mammals that survived in isolation. "Condylarth" is now recognized as a

wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. They are typically define ...

for any generalized early mammal that wasn't obviously a predator, making this theory outdated. The modern version of the idea is that litopterns are a sister group of one of the ungulate taxa whose early fossils are found in Eurasia, meaning that all hoofed mammals share distant common ancestors. However, an opposing view has been that litopterns (together with other South-American ungulates) originated independently from ungulates on other continents, and thus are unrelated to all the groups once called condylarths, including the early perissodactyls and artiodactyls. In the independent-origin theory, litopterns are classified with other endemic South American ungulates as the clade

Meridiungulata South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups ...

. Sequencing of mitochondrial DNA in 2017, extracted from a ''Macrauchenia patachonica'' fossil from a cave in southern Chile, indicates that Litopterna is the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to Perissodactyla, making litopterns true

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, giraff ...

s. The estimated divergence date is 66 million years ago. Analyses of collagen sequences obtained from ''Macrauchenia'' and the notoungulate ''

Toxodon ''Toxodon'' (meaning "bow tooth" in reference to the curvature of the teeth) is an extinct genus of South American mammals from the Late Miocene to early Holocene epochs ( Mayoan to Lujanian in the SALMA classification) (about 11.6 million to ...

'' have led to the same conclusion, and add notoungulates to the sister group clade to litopterns. This idea contrasts with the results of some past morphological analyses which favoured them as

afrotheria Afrotheria ( from Latin ''Afro-'' "of Africa" + ''theria'' "wild beast") is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also ...

ns. It is consistent with some more recent morphological analyses which suggested they were basal

Panperissodactyla Mesaxonia (near-synonymous with Panperissodactyla) is a clade of ungulates whose weight is distributed on the third toe on all legs through the plane symmetry of their feet. For a while it was often seen to only contain the order Perissodactyla ...

has been proposed as the name of an unranked clade to include perissodactyls and their extinct South American ungulate relatives.

Taxonomy

* Order Litopterna ** ''

Proacrodon ''Proacrodon'' is a dubious genus of extinct mammal from South America. Its type species is ''Proacrodon transformatus''. The only known specimen, a lower premolar or molar, is now lost, and its affinities are unknown. In 1899, Santiago Roth nam ...

'' ** Family Protolipternidae *** '' Asmithwoodwardia'' *** '' Miguelsoria'' *** ''

Protolipterna ''Protolipterna'' is an extinct genus of mammal, belonging to the order Litopterna. It lived during the Late Paleocene and the Early Eocene, in what is now South America. Description It was a small-sized animal, not exceeding 35 centimeter ...

'' ** Family Indaleciidae *** '' Adiantoides'' *** '' Indalecia'' *** Family Sparnotheriodontidae **** '' Phoradiadius'' **** ''

Notiolofos ''Notiolofos'' is an extinct genus of sparnotheriodontid ungulate from the order Litopterna. The animal lived during the Eocene, in modern-day Antarctica. The genus contains two species, ''N. arquinotiensis'', the type species, and ''N. regueroi ...

'' **** ''

Sparnotheriodon ''Sparnotheriodon'' is an extinct genus of sparnotheriodontid litoptern that lived during the Middle Eocene of what is now Argentina, leaving fossils in the Sarmiento Formation. Description ''Sparnotheriodon'' was a medium-sized litoptern. ''Sp ...

'' **** ''

Victorlemoinea ''Victorlemoinea'' is an extinct litoptern genus of the family Sparnotheriodontidae, that lived from the Early to Middle Eocene. Fossils of ''Victorlemoinea'' have been found in the Las Flores, Sarmiento and Koluel Kaike Formations of Argenti ...

'' *** Family Amilnedwardsiidae **** '' Amilnedwardsia'' **** '' Ernestohaeckelia'' **** '' Rutimeyeria'' *** Family Notonychopidae **** '' Notonychops'' **** '' Requisia'' ** Superfamily Macrauchenioidea *** Family

Adianthidae Adianthidae is an extinct family of litopterns that existed from the Middle Eocene ( Mustersan) to the Early Miocene (Santacrucian). Description These scansorial, viviparous animals were actively mobile and were herbivores. They were small in s ...

**** '' Proectocion'' **** Adianthinae ***** '' Adianthus'' ***** '' Proadiantus'' ***** '' Proheptaconus'' ***** ''

Thadanius ''Thadanius'' is an extinct genus of Litoptern, belonging to the family Adianthidae. It lived during the Late Oligocene, in what is today Bolivia. Description Only known from the fossilized remains of its mandible and teeth, this animal may hav ...

'' ***** '' Tricoelodus'' *** Family Macraucheniidae **** ''

Llullataruca ''Llullataruca'' is an extinct genus of macraucheniid litoptern. It lived during the Middle Miocene of what is now Bolivia. Etymology The genus name, ''Llullataruca,'' is derived from the Quechua words ''llulla'' meaning "false", "lie" or " ...

'' **** Subfamily Cramaucheniinae ***** '' Coniopternium'' ***** '' Caliphrium'' ***** '' Cramauchenia'' ***** '' Phoenixauchenia'' ***** ''

Polymorphis ''Polymorphis'' is an extinct genus of litopterns belonging to the family Macraucheniidae. It lived during the Middle Eocene of Argentina. Taxonomy The type species of ''Polymorphis'' is ''Polymorphis lechei''. Both the genus and the species ...

'' ***** '' Pternoconius'' ***** '' Theosodon'' **** Subfamily Macraucheniinae ***** '' Cullinia'' ***** '' Huayqueriana'' ***** ''

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 ...

'' ***** ''

'' ***** '' Oxyodontherium'' ***** '' Paranauchenia'' ***** '' Promacrauchenia'' ***** '' Scalabrinitherium'' ***** '' Windhausenia'' ***** ''

Proterotheriidae Proterotheriidae is an extinct family of fossil ungulates 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 America ...

References

External links

An artist's rendition
of a

, a representative genus of the Litopterna. Retrieved from the Red Académica Uruguayabr>megafauna page
{{Taxonbar, from=Q132153 Danian first appearances Holocene extinctions Fossil taxa described in 1889 Taxa named by Florentino Ameghino

Evolutionary background

Taxonomy

References

Further reading

External links