15 feet long
Permian Era, 300 million years ago
Western North America, Texas
Dimetrodon was a meat-eating ancestor of both mammals and dinosaurs. But itwas built more like a modern reptile with bent legs. What Dimetrodon's big sailwas good for is a mystery. Perhaps it helped to give off heat for the animal since itlived in a hot time for the Earth. Or it was simply a display to show off to mates orscare rivals.