Dimetrodons are an extinct species of reptiles of the order Pelycosauria known for their mammal-like characteristics and ability to regulate their body temperature. The most prominent feature of dimetrodons are the large neural spine sail on its back, formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Over a dozen species have been named since the genus was first discovered in Germany in 1878.
The dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the first appearance of dinosaurs.