Cynodonts are eutheriodont therapsids that first appeared in the Late Permian, and extensively diversified after the Permian–Triassic extinction event. Mammals are cynodonts, as are their extinct ancestors and close relatives (Mammaliaformes), having evolved from advanced probainognathian cynodonts during the Late Triassic.
The theriodonts are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts.
Cynognathia is one of two major clades of cynodonts, the other being Probainognathia. Cynognathians included the large carnivorous genus Cynognathus and the herbivorous or omnivorous gomphodonts such as traversodontids. Cynognathians can be identified by several synapomorphies including a very deep zygomatic arch that extends above the middle of the orbit.
Massetognathus is an extinct genus of plant-eating traversodontid cynodonts. They lived during the Triassic Period about 235 million years ago, and are known from the Chañares Formation in Argentina and the Santa Maria Formation in Brazil.
Tritylodontidae is an extinct family of small to medium-sized, highly specialized mammal-like cynodonts, with several mammalian traits including erect limbs, endothermy and details of the skeleton. They were the last-known family of the non-mammaliaform synapsids, persisting into the Early Cretaceous.
Langbergia is an extinct genus of trirachodontid cynodont from the Early Triassic of South Africa. The type and only species L. modisei was named in 2006 after the farm where the holotype was found, Langberg 566. Langbergia was found in the Burgersdorp Formation in the Beaufort Group, a part of the Cynognathus Assemblage Zone. The closely related trirachodontids Trirachodon and Cricodon were found in the same area.
Trirachodontidae is an extinct, possibly paraphyletic family of cynognathian cynodonts from the Triassic of China and southern Africa. Trirachodontids appeared during the Early Triassic soon after the Permian-Triassic extinction event and quickly spread over a wide geographic area in a comparatively brief amount of time from 250 to 237 million years ago.
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.
Pascualgnathus is an extinct genus of traversodontid cynodonts from the Middle Triassic of Argentina. Fossils have been found from the Río Seco de la Quebrada Formation of the Puesto Viejo Group. The type species P. polanskii was named in 1966.
Boreogomphodon is an extinct genus of traversodontid cynodonts from the Late Triassic of the eastern United States. Fossils have been found from the Turkey Branch Formation in Virginia and the Pekin Formation of North Carolina.
Plinthogomphodon is an extinct genus of traversodontid cynodonts from the Late Triassic of the eastern United States. Fossils have been found from the Deep River basin of North Carolina, part of the larger Newark Supergroup. It is known from a single eroded snout. The type and only species is P. herpetairus.
Scalenodon is an extinct genus of traversodontid cynodonts from the Middle Triassic of Africa and possibly Russia. The type species S. angustifrons was named in 1946 and several other species were named in the following years. Most of the species from Africa are now thought to belong to different genera than Scalenodon.
Massetognathinae is an extinct subfamily of cynodonts in the family Traversodontidae. It includes four species from the Middle and Late Triassic: Massetognathus pascuali from Argentina, Massetognathus ochagaviae and Santacruzodon hopsoni from southern Brazil, and Dadadon isaloi from Madagascar. Massetognathines have several distinguishing characteristics, including flattened skulls, small canine teeth, and postcanine teeth with three cusps on their outer edges. Massetgognathinae was defined by Kammerer et al. (2012) as the clade containing all traversodontids more closely related to Massetognathus pascuali than to Gomphodontosuchus brasiliensis, and is the sister taxon of the traversodontid subfamily Gomphodontosuchinae, which was defined by Kammerer et al. (2008) as all traverodontids more closely related to G. brasiliensis than to M. pascuali.
Gomphodontia is a clade of cynognathian cynodonts that includes the families Diademodontidae, Trirachodontidae, and Traversodontidae. Gomphodonts are distinguished by wide and closely spaced molar-like postcanine teeth, which are convergent with those of mammals. Other distinguishing characteristics of gomphodonts include deep zygomatic arches, upper postcanines with three or more cusps spanning their widths and lower postcanines with two cusps spanning their widths. They are thought to have been herbivorous or omnivorous. Gomphodonts first appeared in the Early Triassic and became extinct at the end of the Late Triassic. Fossils are known from southern Africa, Argentina and southern Brazil, eastern North America, Europe, China, and Antarctica.
Aleodon is an extinct genus of cynodonts that lived from the Middle to the Late Triassic. Relatively few analyses have been conducted to identify the phylogenetic placement of Aleodon, however those that have place Aleodon as a sister taxon to Chiniquodon. Two species of Aleodon are recognized: A. brachyramphus which was discovered in Tanzania, and A. cromptoni which was discovered most recently in Brazil.
Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus, form the clade Charassognathidae. This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts.
Etjoia is an extinct genus of traversodontid cynodonts that lived during the Middle Triassic or Late Triassic period in southern Africa. This medium-sized omnivorous cynognathian provides important information on the dental evolution of early diverging gomphodonts and traversodontids.
Bonacynodon is an extinct genus of cynodonts that lived in what is now southern Brazil during the Triassic period. The genus is monotypic, containing only the type species Bonacynodon schultzi. B. schultzi is known from two specimens, consisting of two partial skulls and some badly preserved parts of the postcranium. Both specimens were recovered from the Pinheiros-Chiniquá Sequence, part of the Santa Maria Supersequence of the Paraná Basin. This sequence preserves a faunal association known as the Dinodontosaurus Assemblage Zone, which contains numerous other species of cynodonts, dicynodonts and reptiles. Bonacynodon was a small, likely insectivorous cynodont, whose length has been estimated at around 30 centimetres (12 in). It can be distinguished from other cynodonts by its large, serrated (saw-like) canine teeth. Together with the genus Probainognathus of Argentina, it made up the family Probainognathidae, one of the earliest-diverging lineages of the clade Probainognathia. It was a fairly close relative of mammals, the only group of cynodonts alive today.
Vetusodon is an extinct genus of cynodonts belonging to the clade Epicynodontia. It contains one species, Vetusodon elikhulu, which is known from four specimens found in the Late Permian Daptocephalus Assemblage Zone of South Africa. With a skull length of about 18 centimetres (7.1 in), Vetusodon is the largest known cynodont from the Permian. Through convergent evolution, it possessed several unusual features reminiscent of the contemporary therocephalian Moschorhinus, including broad, robust jaws, large incisors and canines, and small, single-cusped postcanine teeth.
Scalenodontoides is an extinct genus of Traversodontidae, a family of herbivorous cynodonts. It lived during the Late Triassic in what is now South Africa. Its type species is Scalenodontoides macrodontes. It was named in 1957 by A. W. Crompton and F. Ellenberger. Arctotraversodon plemmyrodon was originally classified as a species of Scalenodontoides, but was given its own genus in 1992. It is found in the Scalenodontoides Assemblage Zone of the Elliot Formation, which is named for it. It is one of the geologically youngest traversodontids, alongside the putative traversodontid Boreogomphodon. It is closely related to Exaeretodon and Siriusgnathus, but is distinguished by the presence of a shelf-like expansion of its parietal called the nuchal table. Though the largest known complete skull is only 248 millimetres (9.8 in) long, it may have been the largest non-mammalian cynodont, as an incomplete snout would have belonged to a specimen with an estimated skull length of 617 millimetres (24.3 in).
