''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 up to in length and weighing up to . It had a long neck and tapir-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 Santa Cruz Formation in Argentina. 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 (creek), an intermittently dry creek Arroyo may also refer to: People * Arroyo (surname) Places United States ;California * Arroyo Burro Beach, a public beach park in Santa Barbara County, California * Arroyo ...

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 cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

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. 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 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 litopterns, 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, t ...

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 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 ...

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: ''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 years from the mid- ...

of Argentina, the Yecua Formation of Bolivia, the

Honda Group is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan. Honda has been the world's largest motorcycle manufacturer since 1959, reaching a product ...

of Colombia, the Chucal and Río Frías Formations of Chile and the Ipururo Formation of Peru.''Theosodon''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.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