Dimetrodon
Lived mainly in the swamps of Pangaea, and grew up to 11 feet and 500 pounds, a carnivore and thrived until the mass extinction of the population of earth. The most noticeable feature of this reptile is its large sail like adaptation which was large extensions of its spine, which was probably used for drawing in and releasing heat as well as the theory for attracting mates and making other predators feel intimidated when faced by this predator. Walked on four legs, a tall curved skull with many different teeth, and was one of the top predators, mainly eating fish, tetrapods, even other reptiles. This animal went extinct during the mass extinction from either lack of food or could simply not survive the constant climate change.