 Before these discoveries , a theory existed that a <unk> seaway separated what is now Texas and Oklahoma from more western lands during the Early Permian , isolating Dimetrodon to a small region of North America while a smaller <unk> called Sphenacodon dominated the western area . While this seaway probably did exist , the discovery of fossils outside Texas and Oklahoma show that its extent was limited and that it was not an effective barrier to the distribution of Dimetrodon . 
