Stock Photo - Tyrannosaurus Rex. Artwork of a Tyrannosaurus rex dinosaur hunting in a forest ... . Tyrannosaurus (tyrant reptile') was a large carnivore, being about 14 metres (m) long, 5m tall and weighing about 7 tonnes. Its mouth contained sharp, doubly- serrated teeth up to 15 centimetres long. Tyrannosaurus rex's front legs were tiny in comparison to its body. It walked on its two hind legs, the weight of its body being counterbalanced by a heavy tail. Tyrannosaurus rex was one of the last dinosaurs to evolve, first appearing about 70 million years ago before becoming extinct at the end of the Cretaceous period (65 million years ago) along with the other dinosaurs.'