Andescynodon
Encyclopedia
Andescynodon is a genus
of traversodontid cynodont
from the Middle Triassic
of Argentina
. Fossils are known from the Cerro de las Cabras Formation. 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.
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.
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of traversodontid cynodont
Cynodont
Cynodontia or cynodonts are a taxon of therapsids which first appeared in the Late Permian and were eventually distributed throughout all seven continents by the Early Triassic . This clade includes modern mammals and their extinct close relatives. They were one of the most diverse groups of...
from the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
of Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. Fossils are known from the Cerro de las Cabras Formation. Andescynodon is one of the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
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 speciesType species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the 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 basalBasal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
members of Traversodontidae, a group of cynodonts that was common in South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
during the Triassic. Pascualgnathus
Pascualgnathus
Pascualgnathus is a genus of traversodontid cynodont from the Middle Triassic of Argentina. Fossils have been found from the Río Seco de la Quebrada Formation. The type species P. polanskii was named in 1966.-Description:...
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
Diademodon is an vegetarian extinct genus of therapsid. It was about the size of a small cow. Fossils of the Diademodon tetragonus were found in levels of the Rio Seco de la Quebrada geological formation in Mendoza Province, Argentina....
, suggesting that it had a relatively primitive morphology.