''Trachytherus'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus of mesotheriid notoungulate that lived from the Late Oligocene to the Early Miocene in what is now South America.

Description

''Trachytherus'' had a relatively low, compact skull with an elongated snout, longer than in ''

Mesotherium ''Mesotherium'' ("Middle Beast") is an extinct genus of mesotheriid, a long-lasting family of superficially rodent-like, burrowing notoungulates from South America. It one of the youngest notoungulates, and the last known member of Typotheria. I ...

'' but very similar. The postorbital process was also smaller and the nasal bones did not extend as far as in ''Mesotherium''. The most notable difference between the two genera was in the zygomatic arch ; in the anterior region, the insertion surface of the lateral masseter was highly developed, but not as large than in ''Mesotherium''. The first upper incisor was highly developed, continuously growing (hypsodont) and arched, with an enamel band only on the labial side. The following incisors, canines and premolars were greatly reduced or vestigial. The last three premolars were molar-like, with a very complex pattern rapidly disappearing with wear. The molars were similar to those of ''

Pseudotypotherium ''Pseudotypotherium'' is an extinct genus of Notoungulates, belonging to the suborder Typotheria. It lived from the Late Miocene to the Late Pliocene, and its fossilized remains were discovered in South America. Description This animal, like a ...

'' and ''

Cochilius ''Cochilius'' is an extinct genus of interatheriid notoungulate that lived between the Late Oligocene and the lower Miocene in what is now Argentina. Description The skull and skeleton show features also found in other similar contemporary o ...

'', but did not possess the three-lobed internal structure characteristic of

Mesotheriinae Mesotheriidae ("Middle Beasts") is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging. Characteristics M ...

Classification

The genus ''Trachytherus'' was first described in 1889 by Florentino Ameghino, based on fossil remains 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- ...

, a Late

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

geological formation in Patagonia. The type species ''Trachytherus spegazzinianus'', was also found in several other Oligocene deposits across South America. It was originally assigned to the family Typotheriidae, but Ameghino moved it in 1892 to its own family, Trachytheriidae. In 1894

Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...

moved the genus back to Typotheriidae, regarding it as the taxon that evolutionarily connected ''

Nesodon ''Nesodon'' ("island tooth")Palmer (1904) p. 457. is a genus of Miocene mammal belonging to the extinct order Notoungulata which inhabited southern South America during the Late Oligocene to Miocene living from 29.0 to 16.3 Ma and existed fo ...

'' and '' Typotherium''. In 1895, Ameghino refuted these affinities, although considering that ''Trachytherus'' and ''Typotherium'' were related, although not closely enough to belong to the same family. In 1897, for unknown reasons, Ameghino changed the genus name to ''Eutrachytherus'', with its own family, Eutrachytheridae. Later, working on its astragalus, he admitted that the similarities between the bones of Eutrachytheriidae and Typotheriidae were so important that their differences were insignificant to him. In 1913,

William Berryman Scott William Berryman Scott (February 12, 1858 – March 29, 1947) was an American vertebrate paleontologist, authority on mammals, and principal author of the White River Oligocene monographs. He was a professor of geology and paleontology at P ...

placed ''Trachytherus'' back in the Typotheriidae, and from there there was a consensus from the researchers. Typotheriidae was the name Lydekker assigned to the family containing the genus ''Typotherium''. This genus was later synonymized with ''

'', meaning the name "Typotheriidae" lost its validity and is now synonymous with

Mesotheriidae Mesotheriidae ("Middle Beasts") is an extinct family of notoungulate mammals known from the Oligocene through the Pleistocene of South America. Mesotheriids were small to medium-sized herbivorous mammals adapted for digging. Characteristics Meso ...

. Several other species have been assigned to ''Trachytherus'', such as ''T. medocensis'', ''T. ramirezi'', ''T. alloxus'', ''T. subandinus'', ''T. modestus'', ''T. grandis'', found in

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

, Peru, and Argentina. However, several studies indicates that the genus ''Trachytherus'' is paraphyletic and represents a series of derived and basal forms of other typotheres.

Paleoecology

Several species of ''Trachytherus'' are known from the mid latitudes of western South America, in an area called the

Bolivian Orocline An orocline — from the Greek words for "mountain" and "to bend" — is a bend or curvature of an orogenic (mountain building) belt imposed after it was formed. The term was introduced by S. Warren Carey in 1955 in a paper setting forth how comp ...

. A paleobiogeographical reconstruction indicate that this region is the possible ancestral area of the Mesotheriidae, and therefore an important region for the diversification of these animals. Later, the mesotheriids, including Trachytherus'', dispersed to more southern areas.

References

{{Taxonbar, from=Q56217117 Typotheres Prehistoric placental genera Miocene mammals of South America Fossils of Argentina Paleogene Argentina Neogene Argentina Fossils of Bolivia Paleogene Bolivia Fossils of Peru Paleogene Peru Fossil taxa described in 1889 Golfo San Jorge Basin Sarmiento Formation