Tyrannosaurus is a genus of coelurosaurian theropod dinosaur. The speciesTyrannosaurus rex (rex meaning "king" in Latin), often colloquially called simply T. rex or T-Rex, is one of the most well-represented of the large theropods. Tyrannosaurus lived throughout what is now western North America, on what was then an island continent known as Laramidia. Tyrannosaurus had a much wider range than other tyrannosaurids. Fossils are found in a variety of rock formations dating to the Maastrichtian age of the upper CretaceousPeriod, 68 to 66 million years ago.It was the last known member of the tyrannosaurids,and among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.