Andescynodon

Andescynodon is a genus of traversodontid cynodonts from the Middle Triassic of Argentina. 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 of "Andescynodon".
Description and history.
The type species "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 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", suggesting that it had a relatively primitive morphology.