It was a medium-sized animal, smaller than the extant vicuña. The lower incisors, unlike those of more derived proterotheriids such as Diadiaphorus, were relatively small and unspecialized. The lower dentition was complete and there was no trace of diastema. The upper teeth were similar to those of Anisolambda and Polymorphis. The mandible had a very high vertical branch. Its leg bones, firstly attributed to a notoungulate, are incompletely known.
Classification
Outdated reconstruction of Protheosodon by Frederic Loomis, combining its scarce remains with a now outdated assumed affinity with the macraucheniid Theosodon.
Protheosodon coniferus was first described in 1897 by Florentino Ameghino, based on fossils found in Deseadan deposits from Chubut Province, Argentina. Other fossils attributed to the genus have been found in slightly older deposits in Colombia.
Protheosodon was initially thought to be a member of Macraucheniidae, mainly based on characteristics from its lower teeth. Subsequent researches has indicated that it was more probably nested within Proterotheriidae, a group of litopterns which, in the course of their evolution, developed horse-like forms, well adapted for running. It may have been a member of Anisolambdinae, the most basal subfamily of proterotheriids. Protheosodon seems to have been part of a collateral branch, contemporary to other, more derived, proterotheriids.[2]
F. Ameghino. 1897. Mamiferos Cretaceos de la Argentina. Segunda contribucion al conocimiento de la fauna mastologica de las capas con restos de Pyrotherium. Boletin Instituto Geografico Argentino 18:406-521
Hapalops is an extinct genus of ground sloth from the Early to Late Miocene of Brazil, Bolivia, Colombia, and Argentina in South America.
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.
Victorlemoinea is an extinct litoptern genus of the family Sparnotheriodontidae, that lived from the Early to Middle Eocene. Fossils of Victorlemoinea have been found in the Las Flores, Sarmiento and Koluel Kaike Formations of Argentina, the Itaboraí Formation of Brazil and La Meseta Formation, Antarctica.
Proterotherium is an extinct genus of litoptern mammal of the family Proterotheriidae that lived during the Late Miocene of Argentina and Chile. Fossils of this genus have been found in the Ituzaingó Formation of Argentina, and the Galera Formation of Chile.
Megadolodus is an extinct genus of proterotheriid litopterns.
Astrapothericulus is an extinct genus of mammals, belonging to the order Astrapotheria. It lived during the Lower Miocene in what is now South America.
Neodolodus is a genus of extinct litoptern from the late middle Miocene of southern Colombia. It was named in 1986 by Hoffstetter and Soria, for the species Neodolodus colombianus from the Castilletes Formation and the La Victoria and Villavieja Formations of the Honda Group. The type species N. colombianus is known from a right mandibular ramus, teeth, and part of the fore- and hindlimbs. Neodolodus has been classified as a species of Prothoatherium or Lambdaconus, but was recognized as a distinct genus by McGrath and colleagues in 2020. The taxon was recovered in a phylogenetic analysis as the sister taxon of Protheosodon, between other proterotheriid genera like Picturotherium and Anisolophus.
Adianthus is an extinct genus of litoptern that lived during the Early Miocene to the Middle Miocene in what is now Argentina and Chile.
Proadiantus(Ameghino, 1897) is an extinct genus of adianthid litoptern. It lived during the Late Oligocene, in what is today South America. It consists of only 1 species, Proadiantus excavatus.
Anisolambda is an extinct genus of litoptern. It lived from the Late Paleocene to the Middle Eocene in what is now Argentina.
Proectocion is an extinct genus of adianthid litoptern. It lived during the Early Eocene, in what is now South America.
Prolicaphrium is an extinct genus of proterotheriid litoptern that lived during the Early Miocene, in what is now Argentina. Fossils have been found in the Sarmiento Formation of Argentina.
Tetramerorhinus is an extinct genus of proterotheriid litoptern that lived during the Early and Middle Miocene in what is now Argentina and Peru.
Proadinotherium is an extinct genus of toxodontid. It lived between the Late Oligocene and the Early Miocene in what is now South America.
Henricosbornia is an extinct genus of henricosborniid notoungulate that lived from the Late Paleocene to the Middle Eocene of what is now Argentina and Brazil.
Paramacrauchenia is an extinct genus of proterotheriid litopterns from the Early Miocene of what is now Argentina and Chile. Its fossils have been found in the Sarmiento and Santa Cruz Formations of Argentina and Chile.
Archaeopithecus is an extinct genus of Notoungulate, belonging to the suborder Typotheria. It lived during the Middle Eocene, in what is today Argentina.
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.
Glyptatelus is an extinct genus of glyptodont. It lived from the Late Eocene to the Middle Oligocene in what is now Argentina and Bolivia.
Guilielmofloweria is an extinct genus of proterotheriid litoptern that lived from the Middle to Late Eocene of what is now Argentina. Fossils have been found in the Sarmiento Formation of Argentina.
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