Illustration of a Tyrannosaurus rex near a nest with eggs. Often called T. rex or colloquially T-Rex, it 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. It lived 68 million years ago during the Cretaceous Period throughout what is now western North America.