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.

[2] 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.

This division is further broken down into assemblage zones, intervals of geological strata that are defined based on the distributions of previously found tetrapod taxa.

Diversification was shown by an increase in richness of eutherocephalian groups in the Cistecephalus and Dicynodon assemblage zones.

[3] Theriognathus was first described by Sir Richard Owen in 1876 based on specimens that were discovered and donated by A.G. Bain from South Africa.

The specimens (consisting of therocephalians, including Theriognathus) were described and illustrated in “Catalogue of the Fossil Reptiles of South Africa in the Collections of the British Museum,” by Owen.

[2] Results from the analysis of a basal cynodont, Charassognathus gracilis, from the Late Permian Tropidostoma Assemblage Zone, South Africa, supported an original hypothesis of T. S. Kemp’s concept of Therocephalia being paraphyletic, placing Cynodontia as the sister taxon to Theriognathus.

A few authors have supported this phylogenetic hypothesis, based on the existence of an enlarged epiterygoid and a quadrate notch in the squamosal.

[9] It extends from the jugal onto the posterior end of the maxillary facial plate, creating orbital convergence and appearing more triangular than circular in dorsal view.

A portion of the vomer separates the choanae, and bears specialized transverse processes just anterior to the contact with the premaxilla.

The pterygoid flange expansion is severe, and looks like posteriorly protruding wings with a slight posterolateral tilt, a character shared with most therocephalians.

According to Ricqlès, Theriognathus’ radius midshaft bone wall is extremely thick and has a reduced central cavity without cancellous structures.

Ricqlès suggested that therocephalians might have exhibited accelerated growth rates later in their evolutionary history due to the comparatively more vascularized cortical bone in the radius of the whaitsiid.

[15] In 2009, another phylogenetic analysis of therocephalians found that the group was monophyletic and placed Theriognathus in a deeply nested position within the clade.