Therapsida is a clade composing of a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more underneath the body, as opposed to the sprawling posture of many reptiles and salamanders.
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.
Eucynodontia is a clade of cynodont therapsids including mammals and most non-mammalian cynodonts. The oldest eucynodonts are known from the Early Triassic and possibly Late Permian. Eucynodontia includes two major subgroups, Cynognathia and Probainognathia.
Cynognathus is an extinct genus of large-bodied cynodontian therapsids that lived in the Middle Triassic. It is known from a single species, Cynognathus crateronotus. Cynognathus was a predator closely related to mammals and had a southern hemispheric distribution. Fossils have so far been recovered from South Africa, Argentina, Antarctica, and Namibia.
Probainognathidae is an extinct family of insectivorous cynodonts which lived in what is now South America during the Middle to Late Triassic. The family was established by Alfred Romer in 1973 and includes two genera, Probainognathus from the Chañares Formation of Argentina and Bonacynodon from the Dinodontosaurus Assemblage Zone of Brazil. Probainognathids were closely related to the clade Prozostrodontia, which includes mammals and their close relatives.
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.
Ecteninion is an extinct genus of meat-eating cynodonts that lived during the Late Triassic (Carnian) in South America. The type species Ecteninion lunensis was named by R.N. Martinez, C.L. May, and C.A. Forster in 1996. E. lunensis is known from a nearly complete skull of about 11 centimetres (4.3 in) in length. It was found in the Cancha de Bochas Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin in northwestern Argentina. It has been interpreted as a basal eucynodont. The holotype is in the collection of the Universidad Nacional de San Juan.
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.
Probainognathia is one of the two major subgroups of the clade Eucynodontia, the other being Cynognathia. The earliest forms were carnivorous and insectivorous, though some groups eventually also evolved herbivorous diets. The earliest and most basal probainognathian is the Middle Triassic (Anisian) aged Lumkuia, from South Africa, though probainognathians would not become prominent until the mid Norian stage of the Late Triassic. Three groups survived the extinction at the end of Triassic: Tritheledontidae and Tritylodontidae, which both survived until the Jurassic—the latter even into the Cretaceous —and Mammaliaformes, which includes the mammals.
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.
Prozostrodon is an extinct genus of probainognathian cynodonts that was closely related to mammals. The remains were found in Brazil and are dated to the Carnian age of the Late Triassic. The holotype has an estimated skull length of 6.7 centimetres (2.6 in), indicating that the whole animal may have been the size of a cat. The teeth were typical of advanced cynodonts, and the animal was probably a carnivore hunting reptiles and other small prey.
Luangwa is an extinct genus of traversodontid cynodonts. The species Luangwa drysdalli was discovered 1963 in the valley of the Luangwa river in Zambia, Africa. Luangwa lived in the Triassic period 240 Million years ago.
Brasilodon is an extinct genus of small, mammal-like cynodonts that lived in what is now Brazil during the Norian age of the Late Triassic epoch, about 225.42 million years ago. While no complete skeletons have been found, the length of Brasilodon has been estimated at 12 centimetres (4.7 in). Its dentition shows that it was most likely an insectivore. The genus is monotypic, containing only the species B. quadrangularis. Brasilodon belongs to the family Brasilodontidae, whose members were some of the closest relatives of mammals, the only cynodonts alive today. Two other brasilodontid genera, Brasilitherium and Minicynodon, are now considered to be junior synonyms of Brasilodon.
Riograndia is an extinct genus of prozostrodontian cynodonts from the Late Triassic of Brazil. The type and only species is Riograndia guaibensis, named after the State of Rio Grande do Sul and Guaíba Basin, where it was discovered. Remains have been found in the Caturrita Formation of the geopark of Paleorrota. It was a small non-mammalian cynodont, with several advanced features also present in mammals. Several specimens of Riograndia guaibensis have been found in the towns of Candelária and Faxinal do Soturno in the Caturrita Formation. The genus defines the Riograndia Assemblage Zone.
Pachygenelus is an extinct genus of tritheledontid cynodonts. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic.
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.
Botucaraitherium is an extinct genus of prozostrodontian cynodonts from the early Norian Riograndia Assemblage Zone in the Candelária Formation of the Paraná Basin in southeastern Brazil. It is known from a single type species, Botucaraitherium belarminoi. The genus name is derived from the Botucaraí Hill, which dominates the landscape of Candelária, Rio Grande do Sul. The species epithet honors Belarmino Stefanello, a volunteer at the Museu Municipal Aristides Carlos Rodrigues, who found the fossil.
Pseudotherium is an extinct genus of prozostrodontian cynodonts from the Late Triassic of Argentina. It contains one species, P. argentinus, which was first described in 2019 from remains found in the La Peña Member of the Ischigualasto Formation in the Ischigualasto-Villa Unión Basin.
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.
