The Dimetrodon is often referred to as a dinosaur. However, it is a primeval reptile, a so-called Pelycosaurus.The Dimetrodon is often referred to as a dinosaur. However, it is a primeval reptile, a so-called Pelycosaurus. The sail on its back was made of skin and bones, helping it to warm itself quicker in the sun. If it wanted to cool down, it positioned the sail parallel to the sun's rays.