Theriognathus: The animals in the therocephalian family, such as Theriognuthtis^ resembled the gorgonopsians and had a similar lifestyle. They flourished at the end of the Permian and continued on into the IViassic. It was once thought that the mammals themselves evolved from the therocephalians, hut this idea is not now generally held. However, they had developed several mammal-type features. dinosaur model
Features: Thenognathus has a flat |aw with a wide muzzle. In life it must have resembled a modern rodent or small carnivore, and it is quite possible that the mammal-like features of a high metabolic rate backed up by an insulating layer of fur first appeared. Turbinals (coiled bones in the nose that help temperature regulation) were present, as were a palate and a complex ear structure, all mammalian features. However, it still retains the reptilian jaw structure made up of several bones, rather than the single bone we find in the lower jaw of mammals.
DICYNODONTS AND CYNODONTS
Probably the most abundant of the mammal-like reptiles, in both Permian and Triassic periods, were the dicynodonts. The name ktwo dog-like teeth ” derives from the pair of long canines that were such a prominent feature of these mammals. The front of the mouth became toothless and armed with a beak. The whole of the jaw structure seems to have been adapted to nuikiftg these features function.
Cistecephalus: The fossils of Cistecepbalus are so common that it has given its name to a zone of stratification in the Permian rocks of South Africa. It was also one of the first of the dicynodonts to he described, back in the 1870s. It was a burrowing animal (possibly explaining the abundance of fossils), living underground like a modern mole, devouring insects, worms and probably roots and rhizomes as well. It is the oldest-known burrowing synapsid.
Features: The skeleton of Cistecephalus is compact and streamlined, and the skull is wedge-shaped and flattened, with broad muscle attachments at the rear for strong neck muscles. These are just the features for a burrowing mode of life. The humerus is short and the front legs very muscular as shown by the big muscle scars. The front feet have broad toes. These would have been used for digging.