| Named By: | Richard Owen in 1876 |
| Time Period: | Wuchiapingian, 260.4-253.8 Ma |
| Location: | South Africa |
| Size: | 1 meter long |
| Diet: | Carnivore |
| Fossil(s): | Skull |
| Classification: | | Chordata | Synapsida | Therapsida | Therocephalia | Whaitsiidae | |
Theriognathus (from Greek therion: beast, mammal, Greek, gnathos, "jaw," +us, pronounced THEH-ree-OG-nah-thuss) 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.