- North America
The Eothyrididae are a family of synapsids from the group of Pelycosaurier. So you're after classic view " reptiles ", but related to those animals that make up the " mammal-like reptiles " and finally the mammals have evolved.
So far, only the skulls of the two species are known, and Eothyris Oedaleops that were each about 6 inches long, which suggests that, the total length of the animals under 1 meter. The skulls are characterized by a remarkably broad, flat shape and a large cranial window. In the upper jaw were at Eothyris per hemimandible two enlarged, eckzahnartige teeth in the lower jaw without correspondence - at Oedaleops these teeth were much weaker. The remaining teeth are uniformly small and pointed, suggesting meat or insects as food of Eothyrididae. From the rest of the body so far no fossils were found.
Both genera are known from the Upper Carboniferous and the Mittelperm from North America. Systematically form the Eothyrididae with the Caseidae the group of Caseasauria standing at the base of the synapsids and which forms the sister group of the Eupelycosauria, from which have developed the therapsids (the ' mammal-like reptiles ").