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Could Tyrannosaurus rex run? Probably not

Improved computer modelling suggests that the leg bones of a T. rex would have snapped under the pressure of a sprint

Model showing the stresses on a T. rex skeleton while walking.
Model showing the stresses on a T. rex skeleton while walking.
University of Manchester

New discoveries never seem to be good news for Tyrannosaurus rex. In the early days of palaeontology it was described as “the most superb carnivorous mechanism among the terrestrial Vertebrata, in which raptorial destructive power and speed are combined”; it was an apex predator, sprinting across Cretaceous plains to ruthlessly tear through herds of meek herbivores.

But in 2011 a census of T. rex skeletons concluded that they were too numerous to be this kind of predator, and must instead have been opportunistic feeders. It was a demotion from the noble heights of the lion to the ignominious company of the hyena. Now, a new piece of sophisticated computer modelling suggests that the fearsome beasts couldn’t even run.

Simulation showing the stresses on a T. rex while walking.
Simulation showing the stresses on a T. rex while walking.
University of Manchester

In a paper published in PeerJ, William Sellers of the University of Manchester and colleagues demonstrate a model that shows that a true running gait would have placed intolerable stress on the T. rex frame and led to snapped leg-bones.

This reduces the range of possible speeds the dinosaur could have moved at, the authors write, and “essentially limits adults of this species to walking gaits”.

The new model combines two techniques – multibody dynamic analysis and skeletal stress analysis – to produce a single simulation that is more accurate than any previous one.

The result may make much previous research on the subject obsolete – Sellers himself, for example, published a paper in 2007 using robotic methods to estimate that T. rex had a top speed of around 29 km/h. (That’s less than a top human runner: Usain Bolt averages about 37 km/h over a 100-metre sprint.)

The authors say their result most likely applies to other large dinosaurs that walked on two legs, such as Giganotosaurus, Mapusaurus, and Acrocanthosaurus, but more detailed study will be necessary to check.

The modelling technique may also be applied to other dinosaur species. There is clearly a need for new methods in this area: in one 2014 study, researchers looking for a way to model the gait of smaller dinosaurs resorted to strapping artificial tails to chickens.

Michael Lucy is features editor of Cosmos.
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