Theriodontia ("Beast Tooth, referring to more mammal-like teeth), are therapsids. This group is the third main group of therapsids. Theriodonts appeared almost the same time as the anomodonts, about 265 million years ago, in the Middle Permian. Most theriodonts are more mammal-like than the Anomodonts and Dinocephalians. Early Theriodonts may have been warm-blooded, but they resembled more like the earlier therapsids, such as the biarmosuchians, or they might have resembled primitive anomodonts. They were mostly carnivorous, but they have developed herbivorous traits during the Jurassic and the Cretaceous. Their jaws were more advanced, because their was dentary growing, which gave them a more effecient bite. Furthermore, the rest of the 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. This made the theriodonts one most successful synapsids. Theriodonts fall into three great groups - Gorgonopsia, Therocephalia and Cynodontia. Theriodonts evolved from Neotherapsids, which in turn evolved from Eutherapsids.

The Eutheriodontia

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This branch is the most advanced of therapsids. Its name means "true beast tooth". Eutheriodonts appeared Middle Permian (probably a little later after the first theriodonts appeared). The Eutheriodonts evolved from a Gorgonopsian-like theriodont. Most Eutheriodonts are warm-blooded, because respiratory turbinal bones were present. Both therocephalia and cynodonts are Eutheriodontia, excluding the Gorgonopsians. The eutheriodonts were almost decimated by the Permian-Triassic extinction event, both the therocephalians and the cynodonts made it to the Triassic. Unfortunately, their cousins, the Gorgonopsians weren't so lucky and they didn't make it to the Triassic, leaving no descendants. The Therocephalians becoming endagered after the event, until the end of Early Triassic epoch, they went extinct. They were probably outcompeted by their relatives, the cynodonts - which were the dominant predators of their time. The remaining theriodonts, the cynodonts continued to remain abundant for the rest of the Triassic. But they became smaller as the Triassic Period went on. By the Late Triassic, from one of these small cynodonts, the first mammals came, and the long-lived Tritylodontids came. But because the cynodonts and the other therapsids (and the mammals) were losing ground to the dinosaurs, the mammals remained small and other non-mammalian therapsids were becoming extinct and became rare during the rest of the Mesozoic Era until the Middle Cretaceous, where the non-mammalian therapsids truly went extinct. The Cretaceous-Tertiary extinction event wiped out all non-avian dinosaurs. The mammals started to dominate, now that there are no large dinosaurs. There are over 4,500 species of mammals alive today, though reptile and bird species outnumber them.

External links

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• Theriodontia - at Paleos

Theriodonts