DIMETRODON
Dimetrodon means two sizes of teeth. He was a fierce, sharp-toothed meat eater. The Dimetrodon had a huge fin, like a sail, growing right up out of its back. His sail was probably used as a radiator. It kept him cool in the hot sun allowing him more time to look for food.
Dimetrodon used his sharp teeth to kill and eat smaller dinosaurs. He was about 10 feet long.
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http://www.enchantedlearning.com/subjects/dinosaurs/dinos/Dimetrodon.shtml
Dinosaur Land Meat Eaters