The dimetrodon was a large reptilian, not technically a dinosaur, having lived thousands of years before they existed. They lived in the North American Northeast, mainly Texas and Oklahoma in the Early Permian period. The dimetrodon was much taller than a human with its sail. It reached about 10 feet long, and the sail on its back were used to regulate its body tempurature. If the dimetrodon turned its sail towards the sun, the sun would have heated the creatures blood. When it wanted to cool off, it would keep the sail in the shade, and the wind would strike it, so the creature's blood was cooled.