Haptodus was a small sphenacodont, a lineage that includes therapsids. It was at least 1.5 meteres (5 ft) in length. It lived from Latest Carboniferous to Early Permian, in the equatorial Pangea. It was a medium-sized predator, feeding on insects and small vertebrates. It is one of the most primitive sphenacodontid and it is related to other sphenacodontids (or it may have been ancestral to them), such as Dimetrodon. It shares many structural features of the skull and skeleton with the more specialized sphenacodontids. Unlike Dimetrodon, it lacked the "sail".