T. rex's tail made it speedy

Tyrannosaurus rex was likely one of the fastest predators of the Cretaceous era, thanks to a massively muscular tail, Alberta researchers have found.

The findings published in the journal The Anatomical Record contradict earlier theories that suggested the dinosaur was a slow-moving scavenger whose tail served mainly to counterbalance the weight of its massive head.

"T. rex had more than just junk in its trunk," said Scott Persons, lead author of the study, in a statement.

Persons, a master's student in paleontology at the University of Alberta in Edmonton, found the dinosaur's tail had a unique feature that would have allowed it to grow proportionately much larger tail muscles than modern-day reptiles such as crocodiles and Komodo dragons — something overlooked by previous studies.

Tail muscles attached to the upper leg bones in both dinosaurs and modern-day reptiles provide power when they run.

But when Persons compared the location of the lowest rib bones in modern-day reptiles and T. rex, he found the dinosaur's ribs were much higher on the tail, leaving room for the tail muscles to grow to a massive size.

Based on the tail-bone examinations and computer modeling, the researchers concluded that previous studies underestimated the amount of muscle mass in T. rex 's tail by up to 45 per cent.

That means the predator could likely outrun any other animal in its ecosystem, Persons said.

The study was co-authored by Philip Currie, a University of Alberta professor.