There’s always more to be learned from fossils. Case in point, Scott Persons and Philip Currie of the University of Alberta have determined that Tyrannosaurus rex was much faster than previously thought. The source of its newfound speed: the animal’s massive tail muscles.
Persons, a graduate student, compared T. rex tails to the tails of modern reptiles such as crocodiles and Komodo dragons. In each case, large muscles within the tail, called caudofemoralis muscles, are attached to the upper leg bones. These caudofemoralis muscles provide much of the power to move the animal forward.
There was one crucial difference between the T. rex tails and the modern tails, however. The rib bones which give the tails their structure were positioned much higher up along the T. rex tails. Whereas the caudofemoralis muscles of modern reptiles are confined within their tail ribs, T. rex tail muscles suffered no such restraint. As a result, the dinosaurs were able to grow enormous propulsion muscles in their tails.
Far from being a lumbering giant, Persons thinks that T. rex would have been one of the fastest creatures in its territory.