Tritylodon was a species of tritylodont, one of the most advanced group of cynodonts. They lived in the Early Jurassic period along with dinosaurs, and had many features of modern mammals, but were egg-laying. Some scientists think that mammals descended from the tritylodonts, others believe that mammals arose from the Trithelodontidae, another group of specialized cynodonts.
Tritylodon was a small herbivorous cynodont. Most cynodonts were carnivorous, but it seems that Tritylodon and its close kin had evolved to eat plants because its carnivorous ancestors were outcompeted by carnivorous archosaurs and other reptiles, and the newly evolved mammals.