Tyrannosaurus rex (Latin meaning 'tyrant lizard king') was a giant carnivorous theropod¹  dinosaur from the Upper Maastrichtian², between 65 and 66 million years ago. T. rex was the largest-known³ carnivorous dinosaur from the first discovery of fossilised bones.

Vital Statistics

T. rex measured up to 40 feet (12.4m) long, from its skull to the tip of its tail, and about 15 - 20 feet (4.6 to 6m) tall. In the enormous skull which was about five feet (1.6m) long, the eye sockets were four inches (10.2cm) wide, so the eyeballs would have been about three inches (7.6cm) in diameter. Its teeth measured a staggering six inches (15cm) and were the perfect shape for slicing through muscle and bone.

T. rex walked upright on its toes, with a stride length of 12 to 15 feet (3.7 to 4.6m), and may have had a running speed of 15mph (24kph). Its two tiny forearms were only about three feet (1m) long, with two fingers at the end of each forearm. Its feet were about three feet (1m) long. Adults weighed between five and seven tons.

No T. rex skin has been preserved so we can only guess at its colour (Hollywood film-makers seem to prefer grey); nor do we know for sure whether the creature had feathers or not. A major controversy still rages over whether dinosaurs were hot-blooded (endothermic - like humans and modern birds) or cold-blooded (ectothermic - like reptiles).

Fossils and Skeletons

T. rex fossil remains are rare finds indeed: as of 2005 only 30 specimens have been found, including only three intact skulls, and not one fully-intact skeleton. Hell Creek, Montana, is the world's most abundant area for finding T. rex fossils. Dr Jack Horner's team unearthed five almost-complete T. rex skeletons in the summer of 2000.

These fossils and skeletons are certainly worth detecting: one recent discovery netted the finders over a million pounds. The skeleton named 'Sue' on display at The Field Museum in Chicago, is the largest, most complete, and best-preserved T. rex fossil yet discovered.

Scavenger or Predator?

Some paleontologists⁴ have portrayed T. rex as highly active predators, while others see them as scavengers.

A clue to the scavenger hypothesis are their large [relative to their brain-size] olfactory bulbs and olfactory nerves, as wide as the spinal cord. These suggest a highly developed sense of smell, allegedly used to sniff out carcasses over great distances, like modern vultures. Their teeth could crack bone; a skill perhaps needed most when they were last to a kill and in need of extracting as much food (marrow) as possible. Modern hunters use their forelimbs to capture prey, while T. rex could hardly manipulate carcasses with its short and useless forelimbs.
- Dr Jack Horner from his book The Complete T. rex.

Dr Horner is the paleontology curator at the Museum of the Rockies in Bozeman, Montana, and he has studied more T. rex specimens than anyone else. Dr Horner was the paleontologist on whom it is thought Stephen Spielberg based the 'Dr Alan Grant' (Sam Neill) character in Jurassic Park; and he was the scientific advisor for the films.

We've presented all the evidence - we've compared them [T. rex] with modern animals and dinosaurs that we know were pack-hunting predators. We want people to do what scientists do, which is to take all that in, think about it, and then come to a conclusion. My own view is that the truth lies somewhere in the middle. We know it wasn't a fast-running creature like a cheetah, but I certainly think it would have been capable of killing a small, old or weak animal. Any animal, though, will choose the easy option first, so if it found another's kill, it would certainly eat it.
- Dr Angela Milner, Keeper of Paleontology at the Natural History Museum.

Realistic Museum Exhibit

A roaring life-size robot of a T. rex was installed at the Natural History Museum in London in 2001. It is scientifically accurate (although scaled down) and its roar can be heard all around the museum, delighting and scaring museum visitors. The exhibitors decided against piping in T. rex breath (a rotting-flesh smell) in case the visitors were turned off.

Unfortunately, we found the smell to be so terrible it would have put people off. So instead, we've gone for the smell of the swamp⁵ in which T. rex would have stood.
- Audrey O'Connell, the Natural History Museum's head of international business development.

Tyrannosaurus Rex - Film Star

Hollywood has made a superstar of the most well-known dinosaur of all, from the children's cartoon film series Land Before Time to the plasticine monster battle in the film One Million Years BC, which made a star of the fur bikini-clad Raquel Welch. More recently, we've been treated to the computer-generated special-effects-laden Spielberg thriller Jurassic Park, which was so popular it has spawned two sequels (with a third in the pipeline), and the 2005 blockbuster King Kong features a fight sequence between the giant gorilla and the dinosaur. T. rex continues to thrill audiences and fire the imaginations of new legions of fans with each subsequent generation.