Theriodonts[1] are a major group of therapsids.[2] They are a clade which include not only the traditional theriodonts, but also their descendants the mammals as well (in the same way that theropod dinosaurs include the birds as a sub-clade).
They can be defined in traditional terms as a suborder of Synapsida that lived from the Middle Permian to the Middle Cretaceous. Theriodonts appeared about 265 million years ago, in the Middle Permian. Even these early theriodonts were more mammal-like than their relatives.
Theriodont jaws were more mammal-like than was the case of other therapsids, because their dentary (lower jaw) was larger, which gave them more efficient chewing. Several other bones that were previously on the lower jaw, moved into the ears, allowing the theriodonts to hear better and their mouths to open wider. This made the theriodonts the most successful group of synapsids.
Eutheriodonts refer to all theriodonts except the gorgonopsians (the most primitive group). They included the therocephalians, cynodonts and their descendants – the mammals. The name means "true beast tooth". The eutheriodonts have larger skulls, accommodating larger brains and improved jaw muscles.
The remaining theriodonts, the cynodonts, also included carrnivores such as Cynognathus, as well as newly evolved herbivorous Traversodonts. While Traversodonts for the most part remained medium-sized to reasonably large (length of largest species up to 2 meters), the carnivorous forms became progressively smaller as the Triassic progressed.
