Tyrannosaurus (/tɨˌrænəˈsɔrəs/ or /taɪˌrænəˈsɔrəs/ ("tyrant lizard", from the Ancient Greek tyrannos (τύραννος), "tyrant", and sauros (σαῦρος), "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex (rex meaning "king" in Latin), commonly abbreviated to T.rex, is one of the most well-represented of the large theropods. Tyrannosaurus lived throughout what is now western North America, which then was an island continent named 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 Cretaceous Period, 68 to 66 million years ago. It was among the last non-avian dinosaurs to exist before the Cretaceous–Paleogene extinction event.Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to its large and powerful hind limbs, Tyrannosaurus fore limbs were short but unusually powerful for their size and had two clawed digits. Although other theropods rivaled or exceeded Tyrannosaurus rex in size, it was the largest known tyrannosaurid and one of the largest known land predators. In fact, the most complete specimen measures up to 12.3 m (40 ft) in length, up to 4 metres (13 ft) tall at the hips, and up to 6.8 metric tons (7.5 short tons) in weight. By far the largest carnivore in its environment, Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods, although some experts have suggested the dinosaur was primarily a scavenger. The debate about whether Tyrannosaurus was an apex predator or scavenger was among the longest ongoing feud in paleontology; however, most scientists now agree that Tyrannosaurus rex was an opportunistic carnivore, acting as both a predator and a scavenger. It is estimated to be capable of exerting one of the largest bite forces among all terrestrial animals.More than 50 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons. Soft tissue and proteins have been reported in at least one of these specimens. The abundance of fossil material has allowed significant research into many aspects of its biology, including its life history and biomechanics. The feeding habits, physiology and potential speed of Tyrannosaurus rex are a few subjects of debate. Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second species of the Tyrannosaurus and others maintaining the Tarbosaurus is a separate genus of dinosaur. Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.