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Encyclopedia > T. Rex
Tyrannosaurus rex
Conservation status: Fossil

T. rex skull, picture taken at
Field Museum of Natural History,
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Archosauria
Superorder: Dinosauria
Order: Theropoda
Family: Tyrannosauridae
Genus: Tyrannosaurus
Species: T. rex
Binomial name
Tyrannosaurus rex
Osborn, 1905
For the rock group Tyrannosaurus Rex, see T. Rex (band).

Tyrannosaurus rex was a predatory dinosaur. This is probably the most famous and most fearsome predator of all times (Cretaceous, 85-65 million years ago), its name derived from Greek and Latin words meaning 'tyrant lizard king'. Its remains are rare - as of 2001 only 20 specimens had been found, including only three complete skulls. This theropod dinosaur was first found by Barnum Brown (1873-1963), assistant curator of the American Museum of Natural History, in the early 1900s. His T. rex resides in New York City.



T. rex could reach a length of up to 15 metres (45 feet) and may have weighed 5-10 tonnes. Like other theropods, T. rex had recurved teeth that ensured that meat was pulled free when biting their victims. All food was swallowed whole, since these dinosaurs never developed any chewing mechanism. T. rex had only its teeth as a weapon (in contrast to for instance raptors, who also used their toe claws). The arms of T. rex were small, perhaps to make up for the weight of its enormous head, but were very sturdy. Paleontologists continue to argue about what role, if any, they played.

Compared to other carnivorous dinosaurs, the skull of Tyrannosaurus is heavily modified. Many of the bones are fused together, eliminating movement between them. The bones themselves are much more massive than is typical of a theropod, and the teeth, far from being bladelike, are massive and oval in cross-section. Heavy wear, and the bite marks found on bones of other dinosaurs, indicate that these teeth could bite into solid bone.

Relative to other carnivorous dinosaurs such as Allosaurus, Tyrannosaurus appears to have had a sizeable brain, but it was probably not particularly intelligent by mammalian standards. Much of Tyrannosaurus' biology - its lifespan, its breeding strategy, its color, etc. remains unknown. A site in Alberta has a large number of individuals of the related Albertosaurus preserved together, but whether these animals lived together, or formed any kind of social group, is open to argument.

Warm blood and feathers

The size of a Tyrannosaurus compared to a human.
The size of a Tyrannosaurus compared to a human.

There is active debate, with no irrefutable evidence on either side, about whether T. rex was warm or cold blooded. Perhaps the balance falls on the side of the creature being homeothermic (warm-blooded), although probably not as warm blooded as modern mammals. There is some speculation that the creature's homeothermic strategy might have changed at times in its life cycle.

The possibility that Tyrannosaurs were feathered has also been raised. Tyrannosaurs are members of Coelurosauria, a theropod group from which all of the recently discovered feathered dinosaur species also belong. Further positive evidence emerged in 2004 with the discovery of a primitive tyrannosaurid in China that had downy proto-feathers on its body. It is therefore quite possible that Tyrannosaurs may have had small feathers, although they would of course have functioned only for insulation and may have been more sparse as large adults, similar to the hair density of an elephant as it grows.

Behavior and feeding patterns

The discussion about the feeding patterns of T. rex, and other large predatory dinosaurs remains active. Some paleontologists have portrayed them as highly active predators, while others see them as scavengers. The available evidence of bite marks in other animals and even other T. rex, combined with the enormous serrated teeth and large jaw seem to speak in favour of a role as predator. Another theory is that their size and power allowed them to steal kills from smaller predators. Of course, few animals will pass up a chance for a free meal, so the T. rex probably did scavenge; the question is whether it hunted at all. Although not much is known about the vision of T. rex, the skulls clearly show that the eye sockets are positioned in such a way that they had binocular vision. Binocular vision is typically seen in active predators such as hawks, owls, cats, and humans. J. von Arrensdorff speculates that Tyrannosaurus may have used a similar strategy to that of the Komodo Dragon relying on one bite followed by steady pursuit of its stricken prey. A number of other giant carnivorous dinosaurs, including Carcharodontosaurus, Giganotosaurus, Acrocanthosaurus, and a giant specimen of Allosaurus are now known. Giganotosaurus actually appears to have been larger than Tyrannosaurus. There is still no clear scientific explanation for exactly why these animals grew to such tremendous sizes.

Other Tyrannosaurs

T. rex was not the only Tyrannosaurus. The following species have been identified:

A worker on scaffolding services the head of a full-size animatronic model of Tyrannosaurus rex

(measurements given are based on found fossils and estimates)

Skull length Total length Hip height Weight
T. torosus
(Russell, 1970)
1.1 m. 9 m. 2.5 m. 2.3 tonnes
T. bataar
in Mongolia)
1.35 m. 10 m. 2.9 m. 5 tonnes
T. rex
(Osborn, 1905)
1.75 m. 13.6 m. 4.4 m. 12 tonnes

The classification of these varies a little (for instance, T. bataar is sometimes called Tarbosaurus, and T. torosus is nearly always classified as a distinct genus Daspletosaurus). Other species included Gorgosaurus libratus, Albertosaurus sarcophagus, and Alectrosaurus olseni.

Barnum Brown's T. rex fossil is now on display at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.

T. rex, Field Museum, Chicago, showing the forearms. The wishbone is between the forearms

Susan Hendrickson, amateur paleontologist, discovered the most complete and largest Tyrannosaurus rex fossil skeleton (http://www.fieldmuseum.org/sue/default.htm) currently known, in South Dakota on August 12, 1990 . The T. rex, now named Sue, in her honor, is currently exhibited at the Field Museum of Natural History (illustration, left). Researchers report that a sub-adult and a juvenile skeleton were found in the same quarry as Sue; this lends evidence to the possibility that T. rex ran in packs or other groups.

The Tyrannosaurus rex is actually a member of the tyrannosaurids family of dinosaurs. The gigantic theropods are believed to have required extensive geographic feeding ranges - as large as a continent, and that theropods the size of T. rex arose in response to the retreat of the Western Interior Seaway of North America, 69 million years ago, which would have increased the size of the feeding range. (Scientific American, 290, no. 2, February 2004 pp. 23-24)


Paleontologist James Farlow calculated the number of lawyers a grown Tyrannosaurus had to eat (based on a scene from the movie Jurassic Park, in which a lawyer became T. rex fodder) to stay alive. Taken an average weight of 68 kilograms, 292 lawyers would be needed to keep one T. rex happy for a year!

External links

  • The secret of T rex's colossal size: a teenage growth spurt (The Guardian August 12, 2004) (http://www.guardian.co.uk/uk_news/story/0,3604,1281338,00.html)
  • Pictures of a replica of Sue the T. rex (http://www.mantyweb.com/dinosaur/sue_trex.htm)



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