''Tetragonostylops'' 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 Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

, related to

Astrapotheria Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, ."The uruguaytheriine Astrapotheriidae from the rich middle Miocene Honda Group of the upper Magdalena ...

. It lived during the Late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

, and its fossils were discovered in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

Description

This genus is only known from incomplete remains, notably a well-preserved

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

and a fragmentary skull. Like other astrapotheres, ''Tetragonostylops'' may have had a strong elongated body, and a long, flat skull. The skull was 20 centimeters long, and the entire body was supposedly one meter long. Its mandible was strong, and endowed with an elongated cylindrical

symphysis A symphysis (, pl. symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together ...

. The mandibular condyle was elevated, and the coronoid process was high, but lower than in its relative ''

Trigonostylops ''Trigonostylops'' is an extinct genus of South American meridiungulatan ungulate, from the Late Paleocene to Late Eocene (Itaboraian to Tinguirirican in the SALMA classification) of South America (Argentina and Peru) and Antarctica (Seymour Isla ...

''. The shape of their molars was different, with ''Tetragonostylops'' having more squared molars (hence his name, ''Tetragon-'' meaning "four corners"), and had an infraorbital canal, which does not appear in ''Trigonostylops''. The molars were brachyodont, like those of ''Trigonostylops'', and the canines were strong and large. There was a large diastema between the canines and the

premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...

Classification

The first fossils from the genus were discovered in the

Itaboraí Formation The Itaboraí Formation ( pt, Formação Itaboraí) is a highly list of fossiliferous stratigraphic units in Brazil, fossiliferous geologic Formation (geology), formation and LagerstätteKellner & Campos, 1999, p.399 of the Itaboraí Basin in Rio ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, and were ascribed to the genus ''Trigonostylops'' by

Carlos de Paula Couto Carlos de Paula Couto, (Porto Alegre, August 30, 1910 – November 15, 1982) was a Brazilian paleontologist. Biography Paula Couto was a researcher at the National Museum of Brazil in Rio de Janeiro, specialized in paleontology of mammals. ...

, as ''T. apthomasi''. Subsequently, the same scholar recognized fundamental differences with the Eocene species of ''Trigonostylops'', and therefore created a new genus, ''Tetragonostylops'', for the Brazilian Paleocene species. Despite its antiquity, ''Tetragonostylops'' may have been more derived than its relative, and may have been ancestral to other genera of astrapotheres such as ''

Albertogaudrya ''Albertogaudrya'' is an extinct genus of astrapotherian mammal that lived in present-day Salta, Argentina (, paleocoordinates ) during the Eocene (Casamayoran SALMA The South American land mammal ages (SALMA) establish a geologic timescale f ...

'' and '' Scaglia''. ''Tetragonostylops'' and ''Trigonostylops'' are considered members of

Trigonostylopidae ''Trigonostylops'' is an extinct genus of South American meridiungulatan ungulate, from the Late Paleocene to Late Eocene (Itaboraian to Tinguirirican in the SALMA classification) of South America (Argentina and Peru) and Antarctica (Seymour Isla ...

, a possibly paraphyletic family of astrapotheres, including more derived forms such as ''

Shecenia ''Shecenia'' is an extinct genus of mammal, probably belonging to the order Astrapotheria. It lived between the Late Paleocene and the Early Eocene, and its fossilized remains were found in South America. Description This animal is known from v ...

''.

Bibliography

*C. de Paula Couto. 1952. Fossil mammals from the beginning of the Cenozoic in Brazil. Condylarthra, Litopterna, Xenungulata, and Astrapotheria. Bulletin of the American Museum of Natural History 99(6):355-394 *C. de Paula Couto. 1963. Um Trigonostylopidae do Paleoceno do Brasil. Anais da Academia Brasileira de Ciências 35(3):339-351 *Soria, M. F. (1982). "Tetragonostylops apthomasi (Price y Paula Couto, 1950): su asignación a Astrapotheriidae (Mammalia; Astrapotheria)". Ameghiniana. 19 (3–4): 234–238. *Vallejo-Pareja, M. C.; Carrillo, J. D.; Moreno-Bernal, J. W.; Pardo-Jaramillo, M.; Rodriguez-Gonzalez, D. F.; Muñoz-Duran, J. (2015). "Hilarcotherium castanedaii, gen. et sp. nov., a new Miocene astrapothere (Mammalia, Astrapotheriidae) from the Upper Magdalena Valley, Colombia". Journal of Vertebrate Paleontology. 35 (2): e903960. doi:10.1080/02724634.2014.903960. {{Taxonbar, from=Q63522402 Meridiungulata Paleocene mammals Paleocene mammals of South America Paleogene Brazil Fossils of Brazil Fossil taxa described in 1952 Prehistoric placental genera Itaboraí Formation Golfo San Jorge Basin Sarmiento Formation