Sphenacodon ferox

Sphenacodon was, not surprisingly, a sphenacodontid synapsid, making it related to the ancestors of mammals, but not dinosaurs. It also lived long before the dinosaurs, from the Late Carboniferous through the Early Permian, in what is today the southwestern United States. It was a close relative of Dimetrodon, and though Sphenacodon had a low ridge of neural spines, the absence of a Dimetrodon-like sail makes the function of that sail in its relative all the more perplexing. Regardless, both taxa were big-headed carnivores that would have been apex predators in their respective environments, although notably Sphenacodon is found in sediments that were better drained than the swampy environments Dimetrodon is found in.