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Tyrannosaurus rex was a giant meat-eating dinosaur in the family Tyrannosauridae. Known from scores of fossils (including a number of skeletons) found in western North America, from Alberta and Saskatchewan in the north to New Mexico in the south, this species lived near the end of the Cretaceous Period (66-68 million years before present).

One of largest land-living carnivores of all time, Tyrannosaurus rex attained a length of more than 12 meters (40 feet) and stood up to 4 meters (13 feet) tall at the hip. Weight estimates for adults range from 5,400 kg (11,904 pounds) to 6,800 kg (14,991 pounds). The known skeletons of Tyrannosaurus rex include larger, more robust and smaller, more lightly built individuals, which are thought to represent females and males, respectively.

The jaws of the robust, up to 1.5 meters (59 inches) long skull of T. rex bear large teeth with banana-shaped crowns with serrated cutting edges that indicate that this dinosaur was capable of delivering strong crushing bites. The largest known tooth has a length of nearly 30 centimeters (12 inches) including the long root. A large coprolite (fossil feces) assigned to T. rex contains many pieces of bone and traces of soft tissue. This giant carnivore was the top predator in its ecosystem and fed on plant-eating dinosaurs, especially duck-billed and horned dinosaurs. It probably hunted live prey and fed on carcasses. Based on the structure of its reconstructed brain, T. rex had a strong sense of smell and keen hearing. Its partly forward-directed eyes gave it binocular vision. The arms of T. rex are proportionately very short but strongly muscled and end in only two clawed fingers. Their function has been the subject of much speculation. By contrast, the hind legs are pillar-like and end in three sturdy toes. T. rex moved only on its hind legs, counterbalancing the head and body with a long, massive tail. There has been much debate about how fast T. rex could move. Recent studies suggest that it probably attained top speeds of no more than 25 miles per hour (40.23 km).

Some remains of smaller tyrannosaurs found in the same rocks as the fossils of Tyrannosaurus rex were given separate scientific names but probably just represent younger individuals of T. rex.


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