Dimetrodon Permian Synapsid

Dimetrodon, meaning "two-measures tooth," was a reptile that lived in the Permian Period, living between 280 and 265 million years ago. It is believed to be more closely related to mammals than to reptiles (Sauropsida) such as dinosaurs, lizards and birds. Dimetrodon fossils have been found in North America and Europe. Growing up to 10 feet in length, and possessing a large head with large canine-like teeth, it was a top carnivore during part of Permian time. Dimetrodon had a large sail on its back that was probably used to regulate body temperature much like the radiator in a car. The sail may have also provided camoflague when it lurked in bamboo-like Calamite plants.

Importantly, the synapsids were the first tetrapods to evolve differentiated (or heterodont) teeth used to chew food prior to swallowing, enabling more rapid digestion. As a synapsid, Dimetrodon is a closer ancestor to modern mammals, including humans, than the sauropsids. Dimetrodon is placed in order Pelycosauria, a group of synapsids with direct ancestral linkage to Mammalia, based on the differentiated teeth and a developing hard palate.