Illustration of the early mammal-like reptile dimetrodon at the shore of a body of water. Frequently mistaken for a dinosaur, this animal was a synapsid, and died out 40 million years before the first dinosaurs appeared. It lived 295 to 272 million years ago, during the Early Permian. Most of the known fossils have been found in Texas, USA. Around 3 metres in length, it was one of the dominant land predators at the time. The neural spine sail may have been for thermoregulation, but is also thought to have been used for mating displays