Almost everyone is familiar with the Stegosaurus, a four-legged herbivore from the Mid-Jurassic to the Late Cretaceous time. Its two rows of bony plates and tail spikes probably provided it much protection against large predators like Tyrannosaurus rex. Some people have guessed another purpose for the plates. A closer look at the fossilized plates reveals small grooves which may have held blood vessels which the Stegosaurus may have used to rid itself of excess body heat. In this sense, the plates were probably a form of heat-exchanger, giving off or taking on heat as the dinosaur needed. This dinosaur grew to about 30 feet, and it may have stood on two legs to reach high vegetation. Fossils of Stegosaurus have been found in western United States, in Europe, in eastern, southern Africa, and in Asia, particularly in southern India and in China.