Tyrannosaurus

Tyrannosaurus is the general name of a group of large, two-legged, meat-eating dinosaurs that lived in the late Cretaceous Period, about 65 million years ago. The name Tyrannosaurus is derived from the Greek words tyrannos, “tyrant,” and sauros, “lizard.” Instantly recognizable by their size, upright posture, jagged teeth, and small, two-fingered forelimbs, Tyrannosaurus were some of the largest meat-eating land animals that ever existed. Scientists know more about Tyrannosaurus than they do about any other predatory dinosaur. They have found dozens of skeletons of these giant saurischians (“lizard-hipped” dinosaurs) in Mongolia and throughout the western United States and Canada.

Tyrannosaurus are members of the family Tyrannosauridae, in the suborder Theropoda. Although scientists disagree about the number of species in the genus Tyrannosaurus, some scientists recognize four species, of which Tyrannosaurus rex is the best known.

Tyrannosaurus were among the largest flesh-eating terrestrial animals, exceeded in size only by the Giganotosaurus and Carcharodontosaurus. They reached 41 feet in length and 16 feet in height, and they weighed over 5 metric tons. The skull of a Tyrannosaurus was large and flexible and contained a brain comparable in size to those of modern reptiles. Its bone-crushing bite was probably more powerful than that of any other flesh-eating dinosaur. The bridge of the nose contained wartlike knobs and pits. The animals had a broad field of vision but could focus their eyes directly to the front. A Tyrannosaurus had short arms with few nerves running through them. This limited nerve development suggests that the arm movements must have been unwieldy and clumsy. The barrel-shaped chest of these dinosaurs indicates that the lungs were very large. A latticework of bones protected the stomach and other internal organs. The legs were long and slender.

Tyrannosaurus probably preferred open terrain, such as broad game trails and open forests, where it could move its large body and see unimpeded by brush. Scientists estimate that Tyrannosaurus could walk rapidly and may have been able to run at speeds up to 25 miles per hour when chasing prey. They also could lie in ambush upon a strong pelvic extension, with chin on the ground, watching for prey with their high-placed eyes.

A uniform body temperature suggests that Tyrannosaurus had a metabolic rate higher than that of other reptiles. Therefore, these dinosaurs would have had to eat more often than other reptiles. Their stomach could hold more than half a metric ton of flesh, which it would consume every few weeks. Scientists have found a 2.1-quart lump of fossilized dung that contains direct evidence of the prey of Tyrannosaurus: partly digested bone fragments of young plant-eating dinosaurs. Further evidence of their diet includes a Triceratops pelvis that exhibits deep punctures and grooves made by Tyrannosaurus teeth. Like most active carnivores, Tyrannosaurus probably also fed on the decaying bodies of dinosaurs killed by starvation and floods. Tooth marks on some Tyrannosaurus skulls indicate that the animals fought with one another by biting on the face. In the skull to the right, the eye sockets are deceptively high. Other orifices are the bone surrounding the nasal cavities.

Contributed By: Dale Alan Russell