Tritylodon

Tritylodon (Greek for 3 cusped tooth) was a genus of tritylodont, one of the most advanced group of cynodont therapsids. They lived in the Early Jurassic and possibly Late Triassic periods along with dinosaurs. They also shared a lot of characteristics with mammals, and were once considered mammals because of overall skeleton construction. That was changed due to them retaining the vestigial reptilian jawbones and a different skull structure. Tritylodons are now regarded as synapsids (often called "mammal-like reptiles").

Characteristics
If a living Tritylodon were to be seen today, it would look a lot like a large rodent. They were about 30 centimetres (12 in) long but there is no certainty about the exact weight. Also the way they ate was much like a rodent, doing a grinding motion with the bottom teeth sliding against the top teeth. The bottom teeth were much like a set of cusps and the top teeth were a set of matching grooves that matched perfectly allowing this motion. There were large incisors at the very front of their mouth separated by a gap from the rest of the teeth. Even with their mouth closed the incisors would still stick out slightly visible. The legs were directly beneath the body like mammals, unlike the earlier therapsids with sprawling limbs.

These animals were burrowers; the structure of the shoulder and front limbs show this. Also the large front incisors worked very well with helping digging and getting buried plant parts. Tritylodons were strictly herbivores based on the way they ate and shape of teeth are proof. Any of the Tritylodonts including Tritylodon were warm-blooded or endothermic. Another interesting thing about them was that they were oviviparous.

Intermediate species
With partial reptile characteristics and mammal characteristics, the Tritylodon part of the Tritylodont family could be part of the link between reptiles and mammals. Some argue[citation needed] that Tritylodonts were too specialized, and were outcompeted by carnivorous archosaurs and other newly evolving early mammals, to become such a link. There is some possible evidence of a link to the group multituberculata.[citation needed] The features of the multituberculata group do match a lot of characteristics of the order Monotremata which includes the egg laying mammals: the duck-billed platypus and echidna.