A dimetrodon is a quadrupedal reptile similar in shape to a crocodile, but with a blunter snout filled with jagged, sharp teeth. Its most distinguishing feature is the massive sail that runs the length of its back. By extending or contracting the fin, the cold-blooded reptile can control its body temperature with ease. While they are not technically dinosaurs, dimetrodons are still often found dwelling in regions inhabited by such creatures. A fully grown adult dimetrodon can reach a length of up to 15 feet and weigh upward of 2,000 pounds.