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Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order of fossil 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 configurat ...
era. The order is one of the five great orders of South American ungulates 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 la ...
brought new ungulate species. Like other endemic 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, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) ...
(odd-toed ungulates) including horses, rhinoceros, 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 inha ...
, and that litopterns are closely related to
notoungulates Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resem ...
, 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, and horses. 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 camelopardalis ...
, 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 you ...
'', ''
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'' was among the youngest genera of litopterns, and these two appear to have been the only members of the group to survive 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 la ...
. All four became extinct at the end of the Pleistocene. 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 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 contine ...
, however, possible remains belonging to a litoptern, likely a macraucheniid, have been found in Mexico. Litopterns, like the
notoungulates Notoungulata is an extinct order of mammalian ungulates that inhabited South America from the early Paleocene to the Holocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms resem ...
and pyrotheres, 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. During this period of isolation, unique mammals evolved to fill ecological niches 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 Pleistocene. Early forms were originally classified by European and North American paleontologists as closely related to
condylarth Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wast ...
s, 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 defined ...
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 Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) ...
and
artiodactyls The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
. 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 c ...
. 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 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, giraffes, c ...
s. The estimated divergence date is 66 million years ago. Analyses of collagen sequences obtained from ''Macrauchenia'' and the notoungulate '' Toxodon'' 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 kn ...
ns. It is consistent with some more recent morphological analyses which suggested they were basal
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, c ...
s.
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'' ** Family Protolipternidae *** '' Asmithwoodwardia'' *** '' Miguelsoria'' *** '' Protolipterna'' ** Family Indaleciidae *** '' Adiantoides'' *** '' Indalecia'' *** Family
Sparnotheriodontidae Sparnotheriodontidae is an enigmatic extinct family of litopterns known primarily from teeth. Sparnotheriodontids are one of two South American native ungulate clades known to have reached Antarctica, the other being astrapotheres. Description ...
**** '' Phoradiadius'' **** '' Notiolofos'' **** '' Sparnotheriodon'' **** '' Victorlemoinea'' *** 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'' ***** '' Tricoelodus'' *** Family
Macraucheniidae Macraucheniidae is a family in the extinct South American ungulate order Litopterna, that resembled various camelids. The reduced nasal bones of their skulls was originally suggested to have housed a small proboscis, similar to that of the saig ...
**** ''
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 "d ...
'' **** Subfamily Cramaucheniinae ***** '' Coniopternium'' ***** '' Caliphrium'' ***** ''
Cramauchenia ''Cramauchenia'' is an extinct genus of litoptern South American ungulate. ''Cramauchenia'' was named by Florentino Ameghino. The name has no literal translation. Instead, it is an anagram of the name of a related genus ''Macrauchenia''. This ge ...
'' ***** '' Phoenixauchenia'' ***** '' Polymorphis'' ***** ''
Pternoconius ''Pternoconius'' is an extinct genus of macraucheniid litoptern from the Late Oligocene and Early Miocene of Argentina. Fossils of this genus have been found in the Sarmiento Formation of Argentina. Etymology The genus name, ''Pternoconius'', ...
'' ***** ''
Theosodon ''Theosodon'' is an extinct genus of litoptern mammal from the Early to Middle Miocene of South America. Description ''Theosodon'' was long-legged with a long neck resembling modern llamas or guanacos. It was large for a litoptern, reaching ...
'' **** Subfamily Macraucheniinae ***** ''
Cullinia ''Cullinia'' is an extinct genus of litoptern, an order of South American native ungulates that included horse-like and camel-like animals such as ''Macrauchenia''. It is only known from fragmentary remains. ''Cullinia levis'' is known from Chasi ...
'' ***** ''
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 ...
'' ***** '' Macrauchenia'' ***** ''
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 you ...
'' ***** '' Oxyodontherium'' ***** '' Paranauchenia'' ***** ''
Promacrauchenia ''Promacrauchenia'' is an extinct genus of macraucheniids that lived during the Late Miocene to Late Pliocene epochs of what is now Argentina and Bolivia. It belongs to the subfamily Macraucheniinae, which also includes '' Huayqueriana'', ''Macra ...
'' ***** ''
Scalabrinitherium ''Scalabrinitherium'' is an extinct genus of mammals of the family Macraucheniidae. Fossils of this animal were found among the fossils of prehistoric xenarthrans in the Ituzaingó Formation of Argentina.Windhausenia ''Windhausenia'' is an extinct genus of mammals belonging to the family Macraucheniidae and the order Litopterna. While it reached the size of its better known relative ''Macrauchenia'', its constitution was lighter. Remains from the genus have b ...
'' ***** ''
Xenorhinotherium ''Xenorhinotherium'' is an extinct genus of macraucheniine macraucheniids, closely related to ''Macrauchenia'' of Patagonia. The type species is ''X. bahiense''.Proterotherioidea *** Family
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 American ...


References


Further reading

*


External links


An artist's rendition
of a Macrauchenia, 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