Cynodontia is a clade of 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.
Probainognathus meaning “progressive jaw” is an extinct genus of cynodonts that lived around 235 to 221.5 million years ago, during the Late Triassic in what is now Argentina. Together with the genus Bonacynodon from Brazil, Probainognathus forms the family Probainognathidae. Probainognathus was a relatively small, carnivorous or insectivorous cynodont. Like all cynodonts, it was a relative of mammals, and it possessed several mammal-like features. Like some other cynodonts, Probainognathus had a double jaw joint, which not only included the quadrate and articular bones like in more basal synapsids, but also the squamosal and surangular bones. A joint between the dentary and squamosal bones, as seen in modern mammals, was however absent in Probainognathus.
Chiniquodontidae is an extinct family of basal probainognathian cynodonts that lived in what is now Africa and South America during the Middle and Late Triassic. It is currently thought to include four valid genera: Aleodon, Chiniquodon, Cromptodon and Riojanodon. Two additional genera are usually regarded as junior synonyms of Chiniquodon.
Stahleckeria is an extinct genus of Middle Triassic (Ladinian) dicynodonts. It lived about 240 million years ago in what is now Brazil and Namibia. As a member of the group Kannemeyeriiformes, it was similar to the genus Kannemeyeria. The genus is known from the type species Stahleckeria potens, which was first collected from the Ladinian-age Santa Maria Formation in the Paleorrota fossil site of Brazil. Stahleckeria was named in honor of Rudolf Stahlecker, who discovered the first specimens during a 1935 expedition led by paleontologist Friedrich von Huene to the Chiniquá fossil site.
The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It is primarily Carnian in age, and is notable for its fossils of cynodonts, "rauisuchian" pseudosuchians, and early dinosaurs and other dinosauromorphs, including the herrerasaurid Staurikosaurus, the basal sauropodomorphs Buriolestes and Saturnalia, and the lagerpetid Ixalerpeton. The formation is named after the city of Santa Maria in the central region of Rio Grande do Sul, where outcrops were first studied.
Exaeretodon is an extinct genus of fairly large, low-slung traversodontid cynodonts from the southern parts of Pangea. Four species are known, from various formations. E. argentinus is from the Carnian-age Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina. E. major and E. riograndensis are from the Carnian-age portion of the Santa Maria Formation of the Paraná Basin in southeastern Brazil. E. statisticae is from the Carnian-age Lower Maleri Formation of India.
The Chañares Formation is a Carnian-age geologic formation of the Ischigualasto-Villa Unión Basin, located in La Rioja Province, Argentina. It is characterized by drab-colored fine-grained volcaniclastic claystones, siltstones, and sandstones which were deposited in a fluvial to lacustrine environment. The formation is most prominently exposed within Talampaya National Park, a UNESCO World Heritage Site within La Rioja Province.
Cromptodon is an extinct genus of cynodonts from the Triassic of Cerro Bayo de Portrerillos, Cerro de las Cabras Formation, Argentina, South America. It is known only from PVL 3858, a mandible.
Lumkuia is an extinct genus of cynodont, fossils of which have been found in the Cynognathus Assemblage Zone of the Beaufort Group in the South African Karoo Basin that date back to the early Middle Triassic. It contains a single species, Lumkuia fuzzi, which was named in 2001 on the basis of the holotype specimen BP/1/2669, which can now be found at the Bernard Price Institute in Johannesburg, South Africa. The genus has been placed in its own family, Lumkuiidae. Lumkuia is not as common as other cynodonts from the same locality such as Diademodon and Trirachodon.
The Tiki Formation is a Late Triassic geologic formation in Madhya Pradesh, northern India. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus. Phytosaur remains attributable to the genus Volcanosuchus have also been found in the Tiki Formation.
Trucidocynodon is an extinct genus of ecteniniid cynodonts from the Upper Triassic (Carnian) of Brazil. It contains a single species, Trucidocynodon riograndensis. Fossils of Trucidocynodon were discovered in outcrops of the Upper Santa Maria Formation in Paleorrota Geopark, Agudo. Trucidocynodon is one of the most completely known Triassic cynodonts, as its holotype is a nearly complete and fully articulated skeleton.
Menadon is an extinct genus of traversodontid cynodonts. The type and only species is Menadon besairiei.
Sanjuansaurus is a genus of herrerasaurid dinosaur from the Late Triassic (Carnian) Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.
Titanogomphodon is an extinct genus of diademodontid cynodonts from the Middle Triassic Omingonde Formation of Namibia. It is known from a single partial skull that was described in 1973 from the Omingonde Formation. The type and only species is Titanogomphodon crassus. At about 40 centimetres (16 in), the skull of Titanogomphodon was significantly larger than that of its closest relative, Diademodon. Its teeth are similar to those of another group of cynodonts called Traversodontidae, but the similarities are likely the result of convergent evolution. Aside from its larger size, Titanogomphodon differs from Diademodon in having a bony projection on the postorbital bar behind the eye socket.
Ixalerpeton is a genus of lagerpetid avemetatarsalian containing one species, I. polesinensis. It lived in the Late Triassic of Brazil alongside the sauropodomorph dinosaur Buriolestes.
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.
The Omingonde Formation is an Early to Middle Triassic geologic formation, part of the Karoo Supergroup, in the western Otjozondjupa Region and northeastern Erongo Region of north-central Namibia. The formation has a maximum thickness of about 600 metres (2,000 ft) and comprises sandstones, shales, siltstones and conglomerates, was deposited in a fluvial environment, alternating between a meandering and braided river setting.
The Río Seco de la Quebrada Formation is a Triassic geological formation in Mendoza Province, Argentina. Fossils of cynodonts such as Cynognathus, Diademodon, and Pascualgnathus have been found in this formation, along with dicynodonts such as Vinceria and Acratophorus. Based on biostratigraphy, the Río Seco de la Quebrada Formation is considered to have formed during the Anisian stage, as it shares fauna with the upper subzones of the Cynognathus Assemblage Zone in South Africa. However, radiometric dating controversially argues that it was deposited during the early Carnian stage, 10 million years younger than expected otherwise.
Oryctorhynchus is an extinct genus of rhynchosaur from the Late Triassic (Carnian-Norian)-aged Wolfville Formation of Nova Scotia, Canada that may have been the same animal as Beesiiwo. The type species, O. bairdi, was named and described in 2020. It was originally seen as a species of Hyperodapedon until 2020.
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).
