| Trachytherus | |
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| Skull and mandible of Trachytherus | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | † Notoungulata |
| Family: | † Mesotheriidae |
| Subfamily: | † Trachytheriinae |
| Genus: | † Trachytherus Ameghino, 1889 |
| Type species | |
| †Trachytherus spegazzinianus | |
| Species | |
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| Synonyms | |
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Trachytherus is an extinct genus of mesotheriid notoungulate that lived from the Late Oligocene to the Early Miocene in what is now South America.
Trachytherus had a relatively low, compact skull with an elongated snout, longer than in Mesotherium 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 and Cochilius , but did not possess the three-lobed internal structure characteristic of Mesotheriinae. [1]
The genus Trachytherus was first described in 1889 by Florentino Ameghino, [2] based on fossil remains found in the Sarmiento Formation, a Late Oligocene 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 moved the genus back to Typotheriidae, regarding it as the taxon that evolutionarily connected Nesodon and Typotherium . [3] In 1895, Ameghino refuted these affinities, although considering that Trachytherus and Typotherium were related, although not closely enough to belong to the same family. [4] In 1897, for unknown reasons, Ameghino changed the genus name to Eutrachytherus, with its own family, Eutrachytheridae. [5] 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. [6] In 1913, William Berryman Scott placed Trachytherus back in the Typotheriidae, and from there there was a consensus from the researchers. [7] [1] Typotheriidae was the name Lydekker assigned to the family containing the genus Typotherium. This genus was later synonymized with Mesotherium , meaning the name "Typotheriidae" lost its validity and is now synonymous with Mesotheriidae.
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, 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. [8]
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Several species of Trachytherus are known from the mid latitudes of western South America, in an area called the Bolivian Orocline. 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. [1]
Pyrotherium is an extinct genus of South American ungulate, of the order Pyrotheria, that lived in what is now Argentina and Bolivia, during the Late Oligocene. It was named Pyrotherium because the first specimens were excavated from an ancient volcanic ash deposit. Fossils of the genus have been found in the Deseado and Sarmiento Formations of Argentina and the Salla Formation of Bolivia.
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, 59 to 11.8 million years ago. Astrapotheres were large, rhinoceros-like animals and have been called one of the most bizarre orders of mammals with an enigmatic evolutionary history.
Mesotheriidae 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.
Mesotherium 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. It was first named by Étienne Serres in 1867, and through further finds now contains four species, M. cristatum, M. hystatum, M. maendrum, and M. pachygnathum. Fossils have been found in Argentina, dating to the Early-Middle Pleistocene.
Astrapotheriidae is an extinct family of herbivorous South American land mammals that lived from the Late Eocene to the Middle Miocene 37.71 to 15.97 million years ago. The most derived of the astrapotherians, they were also the largest and most specialized mammals in the Tertiary of South America. There are two sister taxa: Eoastrapostylopidae and Trigonostylopidae.
Parastrapotherium is an extinct genus of South American land mammal that existed from the Late Oligocene to the Early Miocene. The genus includes some of the largest and smallest known astrapotherian, but at present no generally recognized description can adequately characterize it.
Prosotherium is an extinct genus of hegetotheriid notoungulate. It lived during the Late Oligocene, and its fossilized remains were found in South America.
Astrapothericulus is an extinct genus of mammals, belonging to the order Astrapotheria. It lived during the Lower Miocene in what is now South America.
Pseudhyrax is an extinct genus of archaeohyracid notoungulate. It lived from the Late Eocene to the Early Oligocene, of what is now South America.
Argyrohippus is an extinct genus of notoungulate, belonging to the family Notohippidae. It lived from the Late Oligocene to the Early Miocene, and its fossilized remains were found in South America.
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.
Pleurostylodon is an extinct genus of notoungulate belonging to the family Isotemnidae. It lived during the Middle Eocene, in what is now Argentina.
Eomorphippus is an extinct genus of notohippid notoungulate that lived from the Late Eocene to the Early Oligocene in what is today South America.
Eurygenium is an extinct genus of notoungulate belonging to the family Notohippidae. It lived during the Late Oligocene in what is today South America.
Morphippus is an extinct genus of notohippid notoungulate that lived during the Middle to Late Oligocene in what is now South America.
Ancylocoelus is an extinct genus of mammal, belonging to the order Notoungulata. It lived during the Late Oligocene, in what is today Argentina, in South America.
Colpodon is an extinct genus of herbivorous mammal, belonging to the order Notoungulata. It lived during the Early Miocene, in what is today Argentina and Chile, in South America.
Oldfieldthomasia is an extinct genus of Notoungulate, probably related to the suborder Typotheria. It lived during the Middle Eocene, in what is today South America.
Patriarchus is an extinct genus of interatheriid notoungulates that lived during the Early Miocene in what is now Argentina. Fossils of this genus have been found in the Santa Cruz Formation of Argentina.
Notopithecus is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived from the Middle to the Late Eocene and its fossilized remains were discovered in South America.
