"Sphenacodon" and "Dimetrodon" typically have been found in different geographical areas that were separated by the ancient Hueco Seaway that penetrated equatorial Pangaea during the Early Permian and "covered much of southern New Mexico and parts of West Texas". "Sphenacodon" is known from the west in New Mexico, Arizona, and Utah, and "Dimetrodon" is known mainly from the east in Texas and Oklahoma in more deltaic environments. However, the species "Dimetrodon occidentalis" is found in New Mexico. Each genus would have been an apex land predator in its region and likely preyed on amphibians, diadectids, and early synapsids and diapsids. "Sphenacodon" appears to have died out before about 280 million years ago during the Wolfcampian. The genus "Dimetrodon" survived until about 270 million years ago. Such large sphenacodontid predators were later replaced by therapsids, the group of synapsids that includes the direct ancestors of mammals.