Therapsida is a 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 is Tetraceratops insignis from the Lower Permian.
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.
Procynosuchidae is an extinct family of therapsids which, along with Dviniidae, were the earliest cynodonts. They appeared around 260 million years ago, and were most abundant during the latest Permian time, shortly before the Permian-Triassic extinction event. Despite being the basal member of the cynodont clade, they already showed some of the advanced mammalian characteristics, but Procynosuchids bore resemblance to the Therocephalians.
Eutherocephalia is an infraorder of therocephalian therapsids. Eutherocephalians are distinguished from the lycosuchids and scylacosaurids, two early therocephalian families. While lycosuchids and scyalosaurids became extinct by the end of the Permian period, eutherocephalians survived the Permian–Triassic extinction event. The group eventually became extinct in the Middle Triassic.
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.
Theriognathus is an extinct genus of therocephalian therapsid belonging to the family Whaitsiidae, from South Africa and Tanzania. Theriognathus has been dated as existing during the Late Permian. Although Theriognathus means mammal jaw, the lower jaw is actually made up of several bones as seen in modern reptiles, in contrast to mammals. Theriognathus displayed many different reptilian and mammalian characteristics. For example, Theriognathus had canine teeth like mammals, and a secondary palate, multiple bones in the mandible, and a typical reptilian jaw joint, all characteristics of reptiles. It is speculated that Theriognathus was either carnivorous or omnivorous based on its teeth, and was suited to hunting small prey in undergrowth. This synapsid adopted a sleek profile of a mammalian predator, with a narrow snout and around 1 meter long. Theriognathus is represented by 56 specimens in the fossil record.
Moschowhaitsia is an extinct genus of therocephalian theriodonts. It was among the larger carnivores in the faunal assemblages it occurred in.
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.
Ictidosuchoides is an extinct genus of ictidosuchid therocephalians. Fossils have been found from the Karoo Basin in South Africa. The genus is known to have been one of the few therocephalians to have survived the Permian-Triassic extinction event in this area, although its numbers were quite low after the extinction.
Chlynovia is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The type species is C. serridentatus, named in 2000. Chlynovia was originally classified within Scaloposauria, a group of therocephalians characterized by their small size and lightly built skulls. Scaloposaurians are no longer recognized as a true grouping, but instead represent the juvenile forms of many types of therocephalians. Chlynovia was placed in the family Perplexisauridae along with Perplexisaurus, but both therocephalians are now placed in the family Ictidosuchidae.
Lycosuchidae is an extinct family of therocephalian therapsids from the Middle Permian Beaufort Group of South Africa. It currently contains two monotypic genera, Lycosuchus, represented by L. vanderrieti, which was named by paleontologist Robert Broom in 1903, and Simorhinella, represented by S. baini, which was named by Broom in 1915. Both species are characterized by their large body sizes and short, deep snouts. Two sets of enlarged canine teeth were once regarded as a defining feature of lycosuchids, but recent studies have proposed that the front-most pair are replacements for the ones behind them, which would have eventually fallen out as individuals aged. Lycosuchids are the earliest known therocephalians and are also thought to be the most basal.
Muchia is an extinct genus of therocephalian therapsids from the Late Permian of Russia. Fossils have been found in the Kotelnichsky District of Kirov Oblast. The type species M. microdenta was named in 2011. Muchia is known only from a fragment of the lower jaw, making its classification among therocephalians uncertain. It is thought to be within the subfamily Tetracynodontinae, part of the larger group Baurioidea. Other members of the group such as Tetracynodon and Malasaurus are known from more complete material, and have small elongated skulls. Muchia probably had a similar appearance to these therocephalians.
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.
Icticephalus is an extinct genus of therocephalian therapsids from the Middle and Late Permian of South Africa. The type species Icticephalus polycynodon was named from the Tapinocephalus Assemblage Zone by South African paleontologist Robert Broom in 1915. Specimens of Icticephalus have also been described from the Cistecephalus Assemblage Zone. Broom originally placed Icticephalus in the Scaloposauridae, a group of very small therocephalians. Most scaloposaurids are now thought to be juvenile forms of other therocephalians, and Scaloposauridae is no longer recognized as a valid grouping. Icticephalus and other former scaloposaurids are now classified as basal members of Baurioidea.
Ictidodon is an extinct genus of therocephalian therapsids from the Late Permian of South Africa. The type species Ictidodon agilis was named by South African paleontologist Robert Broom in 1925. Broom classified Ictidodon in the Scaloposauridae, a group of small-bodied therocephalians that are now thought to be juvenile forms of larger therocephalians. Ictidodon and many other scaloposaurids are now classified as basal members of the clade Baurioidea.
Scalopodon is an extinct genus of therocephalian therapsids from the Late Permian of Russia. The type species Scalopodon tenuisfrons was named in 1999 from the Kotelnichsky District of Kirov Oblast. Scalopodon is known from a single fragmentary holotype specimen including the back of the skull, the left side of the lower jaw and isolated postorbital and prefrontal bones. The skull was found in the Deltavjatia Assemblage Zone, which dates back to the early Wuchiapingian about 260 million years ago. Distinguishing features of Scalopodon include narrow frontal bones and a distinctive sagittal crest along the parietal region at the back of the skull. Scalopodon was originally classified in the family Scaloposauridae, and was the first scaloposaurid found in Russia. More recent studies of therocephalians have found scaloposaurids like Scalopodon to be juvenile forms of larger therocephalians and do not consider Scaloposauridae to be a valid group. Scalopodon and most other scaloposaurids are now classified as basal members of Baurioidea.
Simorhinella is an extinct genus of therocephalian therapsids from the Late Permian of South Africa. It is known from a single species, Simorhinella baini, named by South African paleontologist Robert Broom in 1915. Broom named it on the basis of a single fossil collected by the British Museum of Natural History in 1878 that included the skull and jaws forward from the eye sockets. The skull is unusual in that it has an extremely short and deep snout, unlike the longer and lower snouts of most other therocephalians. Because of the skull's distinctiveness, the classification of Simorhinella within Therocephalia is uncertain. However, a 2014 study proposed that it was closely related to the basal therocephalian Lycosuchus, placing it in the family Lycosuchidae.
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.
Gorynychus is a genus of therocephalian from the mid-Permian from Kotelnich, Russia. The genus contains two species, G. masyutinae and G. sundyrensis. It was named after the three-headed dragon Zmey Gorynych from Russian mythology.
