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T. rex tail was built for speed

A new study of Tyrannosaurus rex's muscular tail suggests that the dinosaur was one of the world's fastest-moving hunters.
Image: T.rex
Without rib bones to limit the size of the caudofemoralis muscles, they became a robust power plant enabling T.rex to run.Nobu Tamura
/ Source: Discovery Channel

A new study of Tyrannosaurus rex's muscular tail suggests that the dinosaur was one of the world's fastest-moving hunters.

The study, published in The Anatomical Record, shows that T. rex's long tail didn't just serve to counterbalance the up-front weight of the massive carnivore's extremely large head. Paleontologists had previously suspected that was the tail's primary function.

Instead, the new research led by University of Alberta researcher Scott Persons reveals that T. rex's powerful tail muscles helped to give this dinosaur super speed.

Persons came to this conclusion after comparing the tails of modern-day reptiles, like crocodiles and Komodo dragons, to T.rex's tail. He found that for all of the animals in his study, the biggest muscles in the tail are attached to upper leg bones. These caudofemoralis muscles provide the power stroke allowing fast forward movement.

But T. rex's tail was unique.

The tails of both T. rex and modern animals are given their shape and strength by rib bones attached to the vertebrae. Persons found that the ribs in the tail of T. rex are located much higher on the tail. That leaves much more room along the lower end of the tail for the caudofemoralis muscles to bulk-up and expand.

Without rib bones to limit the size of the caudofemoralis muscles, they became a robust power plant enabling T.rex to run.

He now believes that previous estimates of the muscle mass in this dinosaur's tail were underestimated by up to 45 percent. This explains why earlier researchers thought T. rex was more of a plodding animal that couldn't run very fast.

As Persons said, "contrary to earlier theories, T. rex had more than just junk in its trunk."

There's even been some debate over whether or not T. rex was an active hunter or just a scavenger. The new research tips the scales over to active hunter.

It's unclear at present what T. rex's exact sprinting speed was, but Persons believes this fleet footed dinosaur could run down all other animals in its ecosystem.