T-Rex was a huge, ferocious predator that had a thick, heavy skull and a massive 4-foot-long jaw with 50-60 serrated blade-like teeth–some of which were 9 inches long! Scientists believe that its jaw was so big and powerful that it could eat up to 500 pounds of meat and bones in one bite! T-Rex was believed to be a very fast runner, reaching speeds of up to 20 miles per hour and covering up to 15 feet in one step! T-Rex is one of the best known dinosaurs even though it was only in existence for a relatively short period of time. T-Rex roamed the earth just before the dinosaurs became extinct, at the end of the Cretaceous Period.