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The fastest gait and speed of large theropod dinosaurs such as T. rex is controversial. Some studies said that T. rex was limited to walking, or at best an 11 m s-1 top speed, whereas others argue for at least 20 m s-1 running speeds. Hutchinson and Garcia who conducted their research while at the University of California at Berkeley, demonstrate in Nature Tyrannosaurus was not a fast runner and could only walk at a respectable five 5 m s-1 just half the top speed clocked for an elephant or a top human sprinter. This means that T. rex would still have been able to catch its ambling herbivorous prey.

They demonstrate a method of gauging running ability by estimating the minimum mass of extensor (supportive) muscle needed for fast running. The model\\\\\\\'s predictions are validated for living alligators and chickens. Applying the method to small dinosaurs corroborates other studies by showing that they could have been competent runners. However, models show that in order to run quickly, an adult Tyrannosaurus would have needed an unreasonably large mass of extensor muscle, even with generous assumptions. Therefore, it is doubtful that Tyrannosaurus and other huge dinosaurs ( 6,000 kg) were capable runners or could reach high speeds\\\\\\\".

In their model a running chicken would need at least 4.7 per cent of its body mass in muscle in each leg; an actual chicken has 8.8 per cent. In contrast, a full-size T. rex would have needed muscle weighing 43 per cent of its body mass in each leg to get up a bit of speed - a practical impossibility. Its Hutchinson opinion that this model is going to hold for large dinosaurs in general. For fast running giants like T. rex a fall could have been lethal.

Hutchinson, J.R. and Garcia, M. (2002).
Tyrannosaurus was not a fast runner. Nature 415: 1018 - 1021

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