Tyrannosaurus rex tooth found in the USA from the Maastrichtian age of the Cretaceous period, 65 million years ago. The T-Rex was one of the most well-represented of the large theropods. It was a huge carnivore and primarily ate herbivorous dinosaurs, including Triceratops. Tyrannosaurus rex may not have been a lone operator and may have hunted in packs. Collection Jean-Philippe et Francois-Xavier Blouet, paleontologists.