Mesozoic World

A Tyrannosaurus rex would have had great difficulty getting its jaws on fast, agile prey, according to a 2007 study. A US team used detailed computer models to work out the weight of a typical 'king of the dinosaurs', and to determine how it ran and turned.

The results indicated that a 6-8 tonne T rex was unlikely to have topped 40km/h (25mph) and would have taken a couple of seconds to swivel 45 degrees. The researchers reported their findings in the Journal of Theoretical Biology.

They built on previous work detailing the biomechanics of the famous dinosaur, but added in new refinements. The team found they had a pretty good estimate of its weight - over which there had previously been some controversy according to lead author Dr John Hutchinson. He and his colleagues were able to show that there was no way it could weigh 3-4 tonnes as some people had suggested. It had to have weighed between 6-8 tonnes.

Slowcoach dino

The team's computer modelling system estimated the centre of mass position and the inertia (resistance to turning), both of which had ramifications for how T rex would have stood and moved and what it would have looked like. As well as predicting the dinosaur's likely body mass and top speed (25-40km/h or 15-25mph), the computer calculations gave the team an idea of the turning ability of a T rex. This had never before been done.

The study indicated that the animal would have changed direction incredibly slowly due to its massive inertia, taking one or two seconds to make a quarter-turn. The species certainly could not have pirouetted rapidly on one leg, as popular illustrations have sometimes pictured it and other large dinosaurs doing. More agile prey would have given the slip to a marauding T rex quite easily, it seems.

The researchers believed that their work would help palaeontologists build up a more realistic picture of how the large dinosaurs lived. These were big, rather clunky things - T rex and also the animals it probably preyed on. The perceived view of that ecosystem needed to be slowed down. It wasn't like the Serengeti today, where everything is done at top speed.

Dr Paul Barrett, of London's Natural History Museum, commented that this was another finding which undermined the idea of T rex as a super-predator. The main reason for that is that it was a lot slower than we used to think it was; but it has this huge mouth filled with sixty-odd, 30cm-long teeth, so it was still a formidable animal.

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