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24 September 2014
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Tyrannosaurus rex
BBC Two, Thursday 11 March 2004, 9pm
T.rex - Warrior or Wimp?
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T.rex - Warrior or Wimp? - questions and answers

How did T. rex end up with a reputation as a ferocious killer?

Tyrannosaurus rex was first found by Barnum Brown in 1902 in Montana’s Hell Creek Formation. Brown initially came across a hip girdle, hind limbs, and a few backbones of a huge animal. The significance of his discovery wasn’t immediately known, as large predatory dinosaurs were mostly unknown to science. When he returned to the site in 1905, the animal was so huge that it took two summers to excavate, using dynamite to unveil large stretches of bone.

Henry Fairfield Osborn, Director of the American Museum of Natural History, named this enormous dinosaur with massive teeth Tyrannosaurus rex – 'the tyrant king of the lizards.' And it was his initial description of the dinosaur – ferocious, upright, and tail-dragging – that inspired the appearance of the creature that was embraced by generations.

How many T. rex fossils have now been unearthed?

There are around 20 specimens in existence, and eight of these have been discovered by Jack Horner and his team in the last five years. Of all these specimens, only 3 near-complete skulls exist.

Why do scientists study crocodilians to discover more about how T. rex fed?

In order to find out more about dinosaur behaviour, scientists must study living animals. Birds are the closest living relatives to theropods, the group to which T. rex belongs, but birds don’t have teeth. So when working on feeding behaviour, it is appropriate to study the next closest relatives with teeth, which are crocodilians (alligators and crocodiles).

We know a bit about T. rex’s eyesight, but how good were its other senses?

T. rex’s sense of smell was probably very good. CT scans of the skull have revealed that T. rex’s olfactory bulbs, areas of the brain associated with smell, were very large in proportion to their brain. Modern scavengers, such as vultures, also have relatively large olfactory lobes, as a heightened sense of smell enables them to find carrion at a distance. While this might seem to support the idea that T. rex was a scavenger, in the absence of knowing about its behaviours, all that can be said is that sense of smell was important to it. A good sense of smell might also benefit a predator.

Scientists don’t know anything about T. rex’s hearing or other senses.

T. rex had a very high bite-force strength and robust teeth, but how much could it eat?

Scientists have worked out that the maximum amount a T. rex the size of Sue could bite in one go is 150kg, but it’s unlikely that it actually took mouthfuls that big. It is very hard to chew and swallow a large amount of food, so you tend to take smaller mouthfuls. It’s likely that T. rex did the same.

How fast was T. rex?

In 'Jurassic Park', T. rex was a sprinting behemoth, running down cars at speeds of up to 45mph, but scientists now know that this is unlikely to be true. Biomechanical studies by Dr John Hutchinson of the Royal Veterinary College have shown that in order to run at this speed in a crouched position, T. rex would have needed over 43% of its muscle mass in each leg. That would mean 86% of its muscle mass would be in its legs, leaving little room for anything else in its body: a physical impossibility. To put this in perspective, even good runners such as the ostrich only have between 5 and 10% of their muscle mass in their legs.

So how fast could T. rex run?

Dr Hutchinson’s work suggests that an upper speed limit for T. rex would fall in the 10-25mph range. That’s about the same speed as the best human sprinters. In terms of what this means for the scavenger versus predator issue, the important question to ask is not whether T. rex could run quickly, but whether it could outrun its potential prey. Unfortunately, studies have not been carried out on hadrosaur and triceratops running speeds, but as they were so large, it is unlikely they moved very fast.

Are there any other aspects of T. rex biology that give clues to its feeding behaviour?

Scientists believe they have found fossilised faecal matter, or coprolites, from T. rex. Dr Karen Chin has been working on what might be the world’s largest poo. It’s possible to look inside these 6-7 litre remains, and learn something of what they were eating. Dr Chin found evidence of crushed bone inside a coprolite that appears to have come from an ornithiscian dinosaur. This confirms that T. rex was definitely a meat eater, and seems to have eaten bone, but it doesn’t tell us whether this bone was either part of a living dinosaur, or carrion.

How do scientists calculate the metabolic rate of a T. rex?

Scientists do not know whether T. rex was warm- or cold-blooded. There are arguments on both sides, but no irrefutable evidence. In the case of Professors Ruxton and Houston’s work on scavenging, they made calculations based on both scenarios. When calculating a metabolic rate for cold-bloodedness they used reptiles as a guide, and when calculating a rate for warm-blooded animals, mammals were used as a guide.

Do the majority of scientists now agree that T. rex was both a predator and a scavenger?

Scientists don’t know what T. rex did for a living but most now accept that it was like modern meat-eating animals that might favour a certain strategy, but are capable of both predation and scavenging. It is hard to imagine that a predatory T. rex would turn down a free meal of carrion, or that a scavenging T. rex wouldn’t hunt when the opportunity arose.

Weblinks and bibliography
The Field Museum
Chicago T. rex 'Sue'
St Augustine Alligator Farm
Reptiles, birds and mammals
American Museum of Natural History
History of Barnum Brown
The Complete T. rex. How Stunning New Discoveries Are Changing Our Understanding of the World's Most Famous Dinosaur
John R. Horner & Don Lessem
Tyrannosaurus Sue: The Extraordinary Saga of the Largest, Most Fought over T. rex Ever Found
Steve Fiffer & Robert T. Bakker
Rex Appeal: The Amazing Story of Sue, the Dinosaur That Changed Science, the Law, and My Life
Peter L. Larson & Kristin Donnan
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