Fossils of Tyrannosaurus rex are found in rocks from the last three million years of the Cretaceous period. It was among the last dinosaurs to exist before the Cretaceous-Tertiary Extinction event, 65 million years ago.Tyrannosaurus was a carnivore that walked on two legs with a masssive skull balanced by a long, heavy tail. Tyrannosaurus had large, powerful hindlimbs with three toes, each of which would have ended in a claw like this one.