[2] Theriodonts appeared at the same time as their sister group within the Neotherapsida, the Anomodontia, about 270 million years ago, in the Middle Permian.

Theriodont jaws were more mammal-like than was the case of other therapsids, because their dentary was larger, which gave them more efficient chewing ability.

Furthermore, several other bones that were on the lower jaw (found in reptiles), moved into the ears, allowing the theriodonts to hear better and their mouths to open wider.

The remaining theriodonts, the cynodonts, also included carnivores, such as Cynognathus, as well as newly evolved herbivores (Traversodontidae).

The tritheledontids died out during the Jurassic, and the tritylodontids survived into the Cretaceous, but their relatives, the mammals, continued to evolve.