Therocephalia is the group most closely related to the cynodonts, which gave rise to the mammals, and this relationship takes evidence in a variety of skeletal features.

The fossils of therocephalians are numerous in the Karoo of South Africa, but have also been found in Russia, China, Tanzania, Zambia, and Antarctica.

Early therocephalian fossils discovered in Middle Permian deposits of South Africa support a Gondwanan origin for the group, which seems to have spread quickly across Earth.

Although almost every therocephalian lineage ended during the great Permian–Triassic extinction event, a few representatives of the subgroup called Eutherocephalia survived into the Early Triassic.

However, the last therocephalians became extinct by the early Middle Triassic, possibly due to climate change, along with competition with cynodonts and various groups of reptiles — mostly archosaurs and their close relatives, including archosauromorphs and archosauriforms.

For instance, small baurioids and the herbivorous Bauria did not have an ossified postorbital bar separating the orbit from the temporal opening—a condition typical of primitive mammals.

These and other advanced features led to the long-held opinion, now rejected, that the ictidosaurs and even some early mammals arose from a baurioid therocephalian stem.

[2] The genera Euchambersia and Ichibengops, dating from the Lopingian, particularly attract the attention of paleontologists, because the fossil skulls attributed to them have some structures which suggests that these two animals had organs for distributing venom.

[6] The oldest known therocephalians first appear in the fossil record at the same time as other major therapsid groups, including the Gorgonopsia, which they resemble in many primitive features.

[9] Therocephalia was first named and conceived of by Robert Broom in 1903 as an order to include what he regarded as primitive theriodonts, based primarily on Scylacosaurus and Ictidosaurus.

The latter's inclusion highlighted Broom's view of therocephalians as 'primitive' and ancestral to other therapsids, believing anomodonts to be descended from a therocephalian-like ancestor such as Galechirus.

[14] However, subsequent analysis has exposed additional synapomorphies supporting the monophyly of this group (including delayed caniniform replacement), and Lycosuchidae is currently considered a valid basal clade within Therocephalia.

[23][24][17] An example of the lability of these relationships is demonstrated by Liu and Abdala (2023), who recovered an alternative topology with Chthonosauridae nested deeply within Akidnognathidae.

[25] Biarmosuchus tener Titanophoneus potens Gorgonopsia Anomodontia Charassognathus Dvinia Procynosuchus Lycosuchus Scylacosauridae Scylacosuchus Perplexisaurus Chthonosauridae Akidnognathidae Ophidostoma Hofmeyriidae Whaitsiidae Ictidosuchus Ictidosuchoides Ictidosuchops Regisaurus Urumchia Karenitidae Lycideops Choerosaurus Tetracynodon Scaloposaurus Ericiolacertidae Notictoides Nothogomphodon danilovi Ordosiodon Hazhenia Bauriidae Below is a cladogram modified from Pusch et al. (2024) analysing the relationships of therocephalians and early cynodonts.

This differs from previous proposals of a paraphyletic Therocephalia which typically regarded cynodonts as being closest to derived whaitsiid therocephalians.

[6] Cynariops Lycosuchus Alopecognathus Olivierosuchus Theriognathus Charassognathus Abdalodon Dvinia Procynosuchus Galesaurus Progalesaurus Vetusodon Cynosaurus Nanictosaurus Platycraniellus Thrinaxodon Probainognathus Lumkuia Boreogomphodon Trirachodon