Ctenospondylus was a sail-backed pelycosaur (a mammal-like reptile) that was about 10 ft (3 m) long. This carnivore (meat-eater) walked on four legs, had a long tail, short back spines, and a deep but narrow skull with massive jaws that contained many sharp teeth. This advanced sphenacodontid lived from the Late Pennsylvanian through the Early Perm...