Therapsida is a major group of eupelycosaurian synapsids that includes mammals and their ancestors. 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. The earliest fossil attributed to Therapsida used to be Tetraceratops insignis from the Lower Permian. However in 2020, a new study has found that Tetraceratops is not actually a true Therapsid, but should be considered to be a member of the more ancient Sphenacodontia from which the therapsids evolved.
The cynodonts are therapsids that first appeared in the Late Permian. Mammals are cynodonts, as are their extinct ancestors and close relatives. All other cynodont lines went extinct, with the last known non-mammalian cynodont group, the Tritylodontidae having its last records in the Early Cretaceous.
Anomodontia is an extinct group of non-mammalian therapsids containing many species from the Permian and Triassic periods, most of which were toothless, possibly endothermic herbivores. Anomodonts were very diverse during the Middle Permian, including primitive forms like Anomocephalus and Patranomodon and groups like Venyukovioidea, Dromasauria, and Dicynodontia. Of these, only the dicynodonts survived beyond the Middle Permian. Dicynodonts became the most successful and abundant of all herbivores in the Late Permian and Triassic, filling ecological niches ranging from large browsers down to small burrowers. Few dicynodont families survived the Permian–Triassic extinction event, but one lineage evolved into large, stocky forms that remained the dominant terrestrial herbivores right until the Late Triassic, when changing conditions caused them to decline.
"Rauisuchia" is a group of mostly large Triassic archosaurs. It belongs to a larger clade called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs. "Rauisuchia" is currently considered an evolutionary grade, or even a wastebin taxon. It includes most of the large, carnivorous pseudosuchians that lived during the Triassic Period. Since crocodylomorphs likely originated from an ancestor that would have been a "rauisuchian", Rauisuchia in its traditional sense is considered paraphyletic as it excludes crocodylomorphs. To designate it as an informal group in scientific literature, the name in its traditional sense is often enclosed in quotation marks. The monophyletic equivalent of the group Rauisuchia is the clade Paracrocodylomorpha. Paracrocodylomorpha consists of two branches: Poposauroidea, which includes a variety of strange archosaurs, and Loricata, which includes traditional "rauisuchians" and their crocodylomorph descendants.
Therocephalia is an extinct suborder of eutheriodont therapsids from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their teeth, suggest that they were carnivores. Like other non-mammalian synapsids, therocephalians were once described as "mammal-like reptiles". Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals. This relationship takes evidence in a variety of skeletal features. The phylogeny of therocephalians has been disputed, as the monophyly of the group and the relationships of its members are unclear.
Euchambersia is a genus of therocephalian therapsid that lived during the Late Permian, approximately 255 million years ago, in what is now South Africa. The genus contains a single species, Euchambersia mirabilis, named by paleontologist Robert Broom in 1931 from a skull missing the lower jaws; a second skull, belonging to an immature individual, was later described. It is a member of the family Akidnognathidae, which historically has also been referred by as the synonymous Euchambersiidae.
Moschorhinus is an extinct genus of therocephalian in the family Akidnognathidae, with only one species: M. kitchingi. It was a carnivorous, lion-sized synapsid which has been found in the Late Permian to Early Triassic of the South African Karoo Supergroup. It had a broad, blunt snout which bore long, straight canines. It appears to have replaced the gorgonopsids ecologically, and hunted much like a big cat. While most abundant in the Late Permian, it survived a little after the Permian Extinction, though these Triassic individuals had stunted growth.
Regisaurus is an extinct genus of small carnivorous therocephalian. It is known from a single described species, the type species Regisaurus jacobi, from the Early Triassic Lystrosaurus Assemblage Zone of South Africa, although at least one undescribed species is also known.
Tetracynodon is an extinct genus of therocephalian. Fossils of Tetracynodon have been found in the Karoo Basin of South Africa. Two species are known: the type species T. tenuis from the Late Permian and the species T. darti from the Early Triassic. Both species were small-bodied and probably fed on insects and small vertebrates. Although Tetracynodon is more closely related to mammals than it is to reptiles, its braincase is very primitive and shares more in common with modern amphibians and reptiles than it does with mammals.
Limnarchia is a clade of temnospondyls. It includes the mostly Carboniferous-Permian age Dvinosauria and the mostly Permian-Triassic age Stereospondylomorpha. The clade was named in a 2000 phylogenetic analysis of stereospondyls and their relatives. Limnarchia means "lake rulers" in Greek, in reference to their aquatic lifestyles and long existence over a span of approximately 200 million years from the Late Carboniferous to the Early Cretaceous. In phylogenetic terms, Limnarchia is a stem-based taxon including all temnospondyls more closely related to Parotosuchus than to Eryops. It is the sister group of the clade Euskelia, which is all temnospondyls more closely related to Eryops than to Parotosuchus. Limnarchians represent an evolutionary radiation of temnospondyls into aquatic environments, while euskelians represent a radiation into terrestrial environments. While many euskelians were adapted to life on land with strong limbs and bony scutes, most limnarchians were better adapted for the water with poorly developed limbs and lateral line sensory systems in their skulls.
Promoschorhynchus is a genus of akidnognathid therocephalians from the Late Permian and Early Triassic of South Africa. Unlike many other therapsids, Promoschorhynchus survived the Permian-Triassic extinction event.
Raranimus is an extinct genus of therapsids of the Middle Permian. It was described in 2009 from a partial skull found in 1998 from the Dashankou locality of the Xidagou Formation, outcropping in the Qilian Mountains of Gansu, China. The genus is the most basal known member of the clade Therapsida, to which the later Mammalia belong.
Christian Alfred Sidor is an American vertebrate paleontologist. He is currently a Professor in the Department of Biology, University of Washington in Seattle, as well as Curator of Vertebrate Paleontology and Associate Director for Research and Collections at the Burke Museum of Natural History and Culture. His research focuses on Permian and Triassic tetrapod evolution, especially on therapsids.
Baurioidea is a superfamily of therocephalian therapsids. It includes advanced therocephalians such as Regisaurus and Bauria. The superfamily was named by South African paleontologist Robert Broom in 1911. Bauriamorpha, named by D. M. S. Watson and Alfred Romer in 1956, is a junior synonym of Bauriodea.
Bauriidae is an extinct family of therocephalian therapsids. Bauriids were the latest-surviving group of therocephalians after the Permian–Triassic extinction event, going extinct in the Middle Triassic. They are among the most advanced eutherocephalians and possess several mammal-like features such as a secondary palate and wide postcanine teeth at the back of the jaws. Unlike other therocephalians, bauriids were herbivorous. They were also smaller than earlier members of the group. Two subfamilies are classified within Bauriidae: Nothogomphodontinae and Bauriinae.
Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae and probably also the Doswelliidae. Nesbitt (2011) defines Proterochampsia as a stem-based taxon that includes Proterochampsa and all forms more closely related to it than Euparkeria, Erythrosuchus, Passer domesticus, or Crocodylus niloticus. Therefore, the inclusion of Doswelliidae in it is dependent upon whether Doswellia and Proterochampsa form a monophyletic group to the exclusion of Archosauria and other related groups.
Choerosaurus is an extinct genus of therocephalian therapsids from the Late Permian of South Africa. The type species Choerosaurus dejageri was named by South African paleontologist Sidney H. Haughton from the Tropidostoma Assemblage Zone in 1929.
Blattoidealestes is an extinct genus of therocephalian therapsid from the Middle Permian of South Africa. The type species Blattoidealestes gracilis was named by South African paleontologist Lieuwe Dirk Boonstra from the Tapinocephalus Assemblage Zone in 1954. Dating back to the Middle Permian, Blattoidealestes is one of the oldest therocephalians. It is similar in appearance to the small therocephalian Perplexisaurus from Russia, and may be closely related.
Lycideopidae is an extinct family of therocephalians from the Late Permian and Early Triassic of South Africa.
Ichibengops is an extinct genus of therocephalian therapsids known from the type species Ichibengops munyamadziensis, which lived in what is now Zambia during the Late Permian. Ichibengops was named in 2015 on the basis of fossils found in the Wuchiapingian-age Madumabisa Mudstone Formation in the Luangwa Basin. Therocephalians have been known from the Luangwa Basin for decades, yet Ichibengops was the first endemic Zambian therocephalian to have been described in detail. Phylogenetic analysis indicates that it is a basal member of the clade Eutherocephalia, lying just outside a clade containing hofmeyriids, whaitsiids, and baurioids. Ichibengops is the sister taxon of the Russian therocephalian Chthonosaurus; together they form one of several known African-Russian sister taxon pairs of eutherocephalians, which indicate that eutherocephalians could freely disperse across most of Pangea during the Late Permian. Like the fellow therocephalian Euchambersia, Ichibengops might have been venomous, as evidenced by grooves above its teeth.
