The Dimetrodon was a dreaded apex predator which lived about 300270 million years ago thus 4070 million years before the first prehistoric saurian. It was not a real dinosaur but rather a prehistoric reptile which was surprisingly closely related to mammals. It preyed upon reptiles amphibians and fish which it tore into pieces with its many razorsharp teeth. Its scientific name essentially means two measures of teeth because its teeth were of different sizes.