Tyrannosaurus, tih ran uh SAWR uhs or ty ran uh SAWR uhs, was a large, meat-eating dinosaur that lived about 68 million to 65 million years ago in what is now western North America. The name Tyrannosaurus means tyrant lizard. A tyrant is a cruel, powerful ruler. Tyrannosaurus got its name because scientists thought that such a huge beast must have ruled over all other animals, killing whatever and whenever it chose. The scientific name for this species is Tyrannosaurus rex.