Sphenacodon ferox

Sphenacodon was a medium-large member of the Sphenacodontidae (to which it gives its name), an early group of carnivorous synapsids that also include the famous sail-backed Dimetrodon. Sphenacodon closely resembled its relative, sans the sail. Sphenacodon however, is known from even older rock dating to the Late Carboniferous, and survived into the Early Permian, living alongside Dimetrodon (generally however, in the early Permian, Dimetrodon was more common in the wetlands of the central and eastern US, while Sphenacodon was present in the drier regions of the west). S. ferox is the type species, named by O.C. Marsh, and is the smaller of the two known valid species.