''Andescynodon'' is a

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 traversodontid

cynodont Cynodontia () is a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 Megaannum, mya), and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extin ...

s from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epoch (geology), epochs of the Triassic period (geology), period or the middle of three series (stratigraphy), series in which the Triassic system (stratigraphy), system is di ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. Fossils are known from the Cerro de las Cabras and Cacheutá Formations. ''Andescynodon'' is one of the most basal traversodontids. Another traversodontid called ''Rusconiodon'' has also been identified from the Cerro de las Cabras Formation but is now considered a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''Andescynodon''.

Description and history

The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''Andescynodon mendozensis'' was named in 1967 and reported from the Rio Mendoza Formation. The location where remains have been found was later shown to be part of the Cerro de las Cabras Formation. Like all traversodontids, ''Andescynodon'' has wide postcanine teeth at the back of its jaws. These wide teeth are seen as evidence of a herbivorous diet and give traversodontids their name (their teeth are transversely wide). One distinguishing feature of ''Andescynodon'' is the forward position of a ridge on these postcanine teeth. The temporal region behind the skull is large, but smaller than those of related traversodontids. The snout is much narrower, but widens toward its tip. The skull of ''Andescynodon'' is also flatter than most traversodontids. ''Rusconiodon mignonei'' was named in 1970 from the same locality as ''Andescynodon mendozensis''. ''Rusconiodon'' was distinguished from ''Andescynodon'' because it had larger canine teeth. Between the nostril openings and the canines, ''Rusconiodon'' skulls had a hole called the paracanine fossa. This fossa was also present in ''Andescynodon'' skulls, but did not emerge as a hole on the upper surface of the snout. The paracanine fossa provides room for the canine teeth of the lower jaw, which were especially large in ''Rusconiodon'' specimens. The variation in size of the teeth were considered to be the result of natural intraspecific variation by Liu and Powell (2009). The skulls of ''A. mendozensis'' and ''R. mignonei'' represented one species, and because ''Andescynodon'' was named first, its name takes priority. ''Rusconiodon'' individuals have larger upper canine teeth because their overall body size is larger. Therefore, the two types represent a growth series, with ''Andescynodon'' representing smaller individuals and ''Rusconiodon'' representing larger ones.

Classification

''Andescynodon'' is one of the most basal members of Traversodontidae, a group of cynodonts that was common 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 ...

during the Triassic. '' Pascualgnathus'' is a very close relative of ''Andescynodon'' but can be distinguished by the greater amount of incisor and postcanine teeth. While ''Pascualgnathus'' has three incisors on each side of the upper jaw, while ''Andescynodon'' has four (a primitive feature for a traversodontid). ''Andescynodon'' also has more postcanine teeth than ''Pascualgnathus''. Its skull is lower and its temporal fenestrae, a pair of holes at the back of the skull, are shorter and narrower. The postcranial bones of ''Andescynodon'' are similar to those of the more basal gomphodont ''

Diademodon ''Diademodon'' is an extinct genus of cynodonts. It was about long. Discovery Harry Seeley had found his fossil in the Burgersdorp Formation of the Beaufort Group in the Karoo Basin of South Africa. As late as 1988, ''Diademodon'' had ...

'', suggesting that it had a relatively primitive morphology.

References

{{Taxonbar, from=Q4754290 Traversodontidae Middle Triassic synapsids of South America Triassic Argentina Fossils of Argentina Fossil taxa described in 1969 Taxa named by José Bonaparte