''Theosodon'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

litoptern Litopterna (from "smooth heel") is an extinct order of South American native ungulates that lived from the Paleocene to the Pleistocene-Holocene around 62.5 million to 12,000 years ago (or possibly as late as 3,500 years ago), and were also pres ...

mammal from the Early to Middle Miocene of South America.

Description

''Theosodon'' was long-legged with a long neck resembling modern

llama The llama (; or ) (''Lama glama'') is a domesticated South American camelid, widely used as a List of meat animals, meat and pack animal by Inca empire, Andean cultures since the pre-Columbian era. Llamas are social animals and live with ...

s or

guanaco The guanaco ( ; ''Lama guanicoe'') is a camelid native to South America, closely related to the llama. Guanacos are one of two wild South American camelids; the other species is the vicuña, which lives at higher elevations. Etymology The gua ...

s. It was large for a litoptern, reaching up to in length and weighing up to . It had a long neck and

tapir 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 ...

-like, three-toed feet, and like other litopterns and modern horses, tapirs and rhinos, it bore its weight on its middle toes. Extraordinarily, rather than having nostrils at the front of its head, ''Theosodon'' had its nostrils on the top of its snout, halfway between the forehead and the tip of the snout, and its nostrils pointed upwards rather than forwards, possibly as an adaptation for browsing on prickly vegetation.

History and species

''Theosodon'' has been known since the 19th century, and by 1910 seven species had been described within the genus, all from the early

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

Santa Cruz Formation The Santa Cruz Formation is a geological formation in the Magallanes Basin, Magallanes/Austral Basin in southern Patagonia in Argentina and adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with the eponym ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. The name ''Theosodon'' means "god tooth". The first fossils were only dental remains, but it is unknown why this name was given. Though seven species had originally been described, the exact number of discovered species remains uncertain as it varies between different authors. There are either ten or seven species, and in 2014 Schmidt and Ferrero put forward that the genus needed a full taxonomic revision due to this issue.

''"Theosodon" hystatus''

In 1931, fossils found in the late Miocene

Arroyo Chasicó Formation Arroyo often refers to: * Arroyo (watercourse), an intermittently dry creek Arroyo may also refer to: Places United States * Arroyo, Pennsylvania * Arroyo, Puerto Rico, a municipality * Arroyo, West Virginia Spain * Arroyo (Santillana del Mar), ...

were assigned to the genus under the name ''Theosodon hystatus''. This was questioned in 1995, and in 2014 it was moved to the genus '' Paranauchenia'' due to similarities to the species ''Paranauchenia denticulata''. This move was supported by phylogenetic analysis that showed the two species formed

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

clade.

''"Theosodon" arozquetai''

In 2018 a new species of macraucheniid litoptern was described based on the partial remains of a skull and two metapodials. A phylogenetic analysis tentatively linked the species to ''Theosodon'' as a sister clade and it was named ''Theosodon arozquetai'' pending revision. Its body mass was estimated to be somewhere from . It dated to the middle Miocene, about 13 million years ago, somewhat later than most other ''Theosodon'' species.

Classification

''Theosodon'' is in the subfamily Cramaucheniinae within the family

Macraucheniidae Macraucheniidae is a family in the extinct South American ungulate order Litopterna, that resembled camelids. They had three functional digits on the fore and hind feet, as well as elongate necks. The family is generally divided up into two sub ...

. A phylogenetic analysis of the family in 2014 found that Cramaucheniinae is a paraphyletic group, and that ''Theosodon'' is a sister clade to the subfamily Macraucheniinae, the least primitive of the members of Cramaucheniinae.

Paleobiology

''Theosodon'' was a terrestrial and

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 ...

animal that may have lived in both forests and more open environments. Due to its size and its long neck, ''Theosodon'' was likely a high browser, stripping leaves off of trees and shrubs high off the ground. ''Theosodon'' had a slender jaw compared to many other

s, indicating its food was softer, such as

dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...

s. As its nostrils are upward-facing and at the centre of its head rather than the front, ''Theosodon'' may have used this adaptation to feed on thorny plants. Some modern animals such as

giraffe The giraffe is a large Fauna of Africa, African even-toed ungulate, hoofed mammal belonging to the genus ''Giraffa.'' It is the Largest mammals#Even-toed Ungulates (Artiodactyla), tallest living terrestrial animal and the largest ruminant on ...

s feed on thorny plants, and their nostrils are also further back and face more upwards than forwards. Other fossils were found in the

Sarmiento Formation The Sarmiento Formation (Spanish language, Spanish: ''Formación Sarmiento''), in older literature described as the Casamayor Formation, is a geological formation in Chubut Province, Argentina, in central Patagonia, which spans around 30 million y ...

of Argentina, the Yecua Formation of Bolivia, the Honda Group of Colombia, the Chucal and

Río Frías Formation Río Frías Formation () is a Miocene, Middle Miocene geologic formation made up sedimentary rock located in Aysén Region, western Patagonia. The formation crops out along the upper course of Cisnes River ().Marshall & Salinas, 1990 Marsupial fos ...

s of Chile and the Ipururo Formation of Peru.''Theosodon''
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org

References

{{Taxonbar, from=Q2708140 Macraucheniids Miocene mammals of South America Laventan Colloncuran Friasian Santacrucian Colhuehuapian Neogene Argentina Fossils of Argentina Neogene Bolivia Fossils of Bolivia Neogene Chile Fossils of Chile Neogene Colombia Fossils of Colombia Honda Group, Colombia Neogene Peru Fossils of Peru Fossil taxa described in 1887 Taxa named by Florentino Ameghino Prehistoric placental genera Golfo San Jorge Basin Sarmiento Formation Austral or Magallanes Basin Santa Cruz Formation