Carnivorous dinosaurs evolved for speed, U of A researcher finds

A new study published out of the University of Alberta has found that carnivorous dinosaurs evolved to become faster and faster over time and the proof is in the leg length.

• READ:An approach to scoring cursorial limb proportions in carnivorous dinosaurs and an attempt to account for allometry

As part of his doctoral research, lead authorScott Persons travelled the world measuring the limb lengths for 53 different species of carnivorous bipedal dinosaurs, including theVelociraptor, Allosaurus and Tyrannosaurus rex.

In particular, Personslookedat the length of the dinosaurs' legs below the knee. As a rule, he said, the longer the lower leg is in comparison to the upper leg, the faster the animal is.

Modern-day cheetahs have proportionately longer legs than hyenas. That relationship is mirrored in the animals' speeds, Persons said.

"That's true for modern carnivores, and must have been true for dinosaurs," Persons said in a statement released Wednesday.

Looking at each fossil carnivore's "cursoriallimb proportion score" in other words, a measure of how much each was built for speed Persons determined that theyevolved to be faster and faster over time.

And leading the pack: theNanotyrannus, a five-metre talldinosaur similar in appearance to a young Tyrannosaurus. In fact, the resemblance between the two is so close that it wasn't until leg lengths were compared that it wasconclusively determined they were not, in fact, the same species.

"In terms of Cretaceous ecology, T. rex was the lion andNanotyrannuswas the cheetah," Persons said of his findings.

"As far as I'm concerned, it was the scariest dinosaur. Sure, it might take it four to five bites to eat you, while T. rex could do it in just one or two. But eaten is eatenand no dinosaur was better adapted to chase you down."

That burst in speed comes at a cost, however, as longer legs are less-suited to carrying heavy weights and are weaker.

"Speed determines what prey you can catch, how you hunt it, and the sort of environment that you are most successful in," Persons said.

"Over evolution, you have these two conflicting forces: the need for speed and the need for weight support."