TYRANNOSAUR

any member of a genus (Tyrannosaurus) of very large carnivorous dinosaurs found as fossils in Late Cretaceous deposits of North America and eastern Asia (66.4 to 97.5 million years old). Tyrannosaurs were the largest land carnivores of the Cretaceous Period. A fully grown tyrannosaur was more than 14 m (47 feet) long; the skull alone was more than 1.3 m long. The tyrannosaur was a biped, walking about on its powerfully developed hind limbs. If the animal stood upright, it was more than 6.5 m tall, but the ordinary pose was stooped with the body carried forward and the tail held off the ground. It has been estimated that in life a tyrannosaur weighed almost 8 tons. The body was massive, and the neck was short and thick. The skull was very large in relation to the body and was equipped with large, pointed teeth up to 15 cm (6 inches) long; the teeth had serrated edges and were effective for cutting and slicing. The forelimbs were small but robust; each forelimb had only two claws, which the animal may have used as hooks to hold struggling prey. The long tail served as a counterbalance to the body. The musculature was very well developed, especially those muscles used for biting and chewing and for support and mobility. Tyrannosaur remains are often found in the same deposits as those of the giant horned dinosaurs (ceratopsians), upon which tyrannosaurs probably preyed. The tyrannosaur probably was a rather rare animal, with perhaps only a single individual present for every 260 square km (100 square miles). Best known is the species Tyrannosaurus rex.