Sauropedia

A tribute to the 1993-1998 'Dinosaurs!' collection by Orbis Publishing Ltd.

Tyrannosaurus May 12, 2011

Filed under: Theropoda — muzillu @ 9:39 am

Perhaps the best-known of all dinosaurs, Tyrannosaurus held the record for the biggest and most powerful land-living predator of all time for a century, until the discovery of the big carnosaurs, such as Carcharodontosaurus and Giganotosaurus, in the 1990s. About 20 skeletons of Tyrannosaurus are known, some articulated and some scattered, and so the appearance of this dinosaur is known with confidence.

Tyrannosaurus was about as long as four cars, as tall as the tallest giraffe, and weighed about the same as an African elephant. The head of a tall man would have come half way up its thigh. No-one knows exactly the sort of noises Tyrannosaurus made, but it may have roared or squealed to call its young and to keep in touch with other members of its group.

Factbox

NameTyrannosaurus, meaning ‘tyrant reptile’

Size: 12-14m long and 5.6m high

Food: meat, especially other dinosaurs

Lived: about 67 million years ago, in the Cretaceous Period in North America, China and possibly South America and India

The skull is short and deep, and solid compared with that of other carnivores. The teeth are 8-16cm long and about 2.5cm wide. Those at the front are D-shaped, built for gripping, while the back teeth are thin blades, evolved for shearing meat. The eyes are positioned so that they give a stereoscopic view forward. The ear structure is like that of crocodiles, which have good hearing.

Each of its back feet had three long claws at the front and one at the back. Its front legs were quite small and high up on its body. They ended in what looked like small ‘hands’ with two thin, clawed fingers. No one knows for certain what these front legs were used for, but they may have been used to grip prey. They were not even long enough to reach its mouth to push food in. Some experts though, have suggested that Tyrannosaurus used its front legs to heave itself up on to its back legs after it had been resting or sleeping on the ground.

Its heavy head was about 1.2m long, held up by a short, strong neck. Tyrannosaurus also had huge jaws, big enough to swallow a human being whole. Its rows of sharp teeth were slightly curved to get a better grip on its prey. Like a shark, once Tyrannosaurus had bitten into its prey, the victim had no chance of sliding out of its mouth and getting away. If any teeth were broken off in a fight, they may have grown again.

A long-running debate among scientists concerns the lifestyle of the tyrannosaurids, and Tyrannosaurus in particular. Was it the fearsome hunter, the terror of the Cretaceous plains and forests, as it has always been portrayed? Or was it a slow-moving animal, eking out a living as a scavenger, subsisting only on the corpses of animals that had already died or been killed by more active hunters?

Evidence for the former includes the position of the eyes. These pointed forwards, giving stereoscopic vision, essential for a hunter of swift prey. The nostrils contained turbinal bones, thin sheets of bone that would have carried moist, sensitive tissue. This would have enhanced the sense of smell, which would be useful for either a hunter or a scavenger.

On the other hand, a Tyrannosaurus was a very big animal, perhaps too big to be capable of much sustained speed or activity. Once up to speed, the slightest stumble would have resulted in a crash that might have been fatal. The Tyrannosaurus tooth marks found on ceratopsian bones show signs of flesh being scraped off a dead animal, rather than chunks bitten off a live one, but this is not to say that the ceratopsian had not been killed by the Tyrannosaurus in the first place. A bite mark in the backbone of a duckbill was made by a Tyrannosaurus on a living animal. It is, in fact, very likely that both lines of evidence are valid, and that Tyrannosaurus and its relatives were active hunters, but did not pass up the chance of devouring any corpse that they came across.

In 1902, part of a huge skeleton was uncovered in Montana, USA. Later, another was found in Wyoming, also in the USA. From these bones the American paleontologist Henry Fairfield Osborn drew up the first picture of this giant creature. He named it Tyrannosaurus rex (meaning ‘king of the tyrant reptiles’) because it was the biggest carnivorous dinosaur then known to have lived on Earth.

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