(2011) found that the maximum weight of Sue, the largest complete Tyrannosaurus specimen, was between 9.5 and 18.5 metric tons (9.3–18.2 long tons; 10.5–20.4 short tons), though the authors stated that their upper and lower estimates were based on models with wide error bars and that they "consider [them] to be too skinny, too fat, or too disproportionate" and provided a mean estimate at 14 metric tons (15.4 short tons) for this specimen. (2009) tested dinosaur mass estimation procedures on elephants and concluded that those of dinosaurs are flawed and produce over-estimations; thus, the weight of Tyrannosaurus, as well as other dinosaurs, could have been much less.
Due to the relatively small number of recovered specimens and the large population of individuals present at any given time when Tyrannosaurus was alive, there could have easily been larger specimens than those currently known including "Sue", though discovery of these largest individuals may be forever untenable due to the incomplete nature of the fossil record.
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.
Its taxonomy is also controversial, as some scientists consider Tarbosaurus bataar from Asia to be a second Tyrannosaurus species while others maintain Tarbosaurus is a separate genus.
Several other genera of North American tyrannosaurids have also been synonymized with Tyrannosaurus.
But in other respects Tyrannosaurus's skull was significantly different from those of large non-tyrannosauroid theropods.
It was extremely wide at the rear but had a narrow snout, allowing unusually good binocular vision.The D-shaped cross-section, reinforcing ridges and backwards curve reduced the risk that the teeth would snap when Tyrannosaurus bit and pulled.The remaining teeth were robust, like "lethal bananas" rather than daggers, more widely spaced and also had reinforcing ridges.Those in the upper jaw were larger than those in all but the rear of the lower jaw.The largest found so far is estimated to have been 30.5 centimeters (12 in) long including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur yet found. Mark Norell of the American Museum of Natural History summarized the balance of evidence by stating that: "we have as much evidence that T.More than 50 specimens of Tyrannosaurus rex have been identified, some of which are nearly complete skeletons.