 Dimetrodon ( / daɪˈmiːtrədɒn / ; meaning " two measures of teeth " ) is an extinct genus of synapsid that lived during the Early Permian period , around 295 – 272 million years ago ( Ma ) . It is a member of the family Sphenacodontidae . The most prominent feature of Dimetrodon is the large sail on its back formed by elongated spines extending from the vertebrae . It walked on four legs and had a tall , curved skull with large teeth of different sizes set along the jaws . Most fossils have been found in the southwestern United States , the majority coming from a geological deposit called the Red Beds in Texas and Oklahoma . More recently , fossils have been found in Germany . Over a dozen species have been named since the genus was first described in 1878 . 
