the first, clearly primitive pre-mammalian reptiles (300 mya). Best known as the sailbacks of the late Paleozoic (360 mya) and the best known pelycosaur is probably Dimetrodon, an animal which is very often mislabelled as a dinosaur in the toy industry. Ancestor of mammals. Slimmer than average stem-reptile and teeth showed early evidence of mammalian hetrodont condition. Clearly synapsida. Evolved int the Therapsida.