extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
, 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 R ...
. 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), ...
, 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 considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
.
Description
This genus is only known from incomplete remains, notably a well-preserved
mandible
In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla).
The jawbone i ...
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 (, : 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 o ...
. The mandibular condyle was elevated, and the coronoid process was high, but lower than in its relative '' Trigonostylops''. 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 Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...
s.
Classification
The first fossils from the genus were discovered in the
Itaboraí Formation
The Itaboraí Formation () 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 de Janeiro (state), Rio d ...
of
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, and were ascribed to the genus ''Trigonostylops'' by Carlos de Paula Couto, 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 Patagonia and Salta, Argentina (, paleocoordinates ) during the Eocene (Casamayoran SALMA) .Scaglia''. ''Tetragonostylops'' and ''Trigonostylops'' are considered members of Trigonostylopidae, a possibly paraphyletic family of astrapotheres, including more derived forms such as '' Shecenia''.
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
AstrapotheriaPaleocene mammalsPaleocene mammals of South AmericaPaleogene BrazilFossils of BrazilFossil taxa described in 1952Prehistoric placental generaItaboraí FormationGolfo San Jorge BasinSarmiento FormationPaleogene Argentina