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Feature - Answering a truly big question: How did dinosaurs move

Answering a truly big question: how did dinosaurs move?

Dinosaurs such as this therapod ("beast-foot") are believed to be the ancestors of modern birds. Image courtesy LDAustinArt.com

In a memorable scene from Steven Spielberg's Jurassic Park, a Tyrannosaurus rex gallops behind a jeep, close to overtaking it, lunging to take a bite out of Jeff Goldblum - to the horrorified delight of millions of thrill-seeking movie-goers.

Assuming dinosaurs could be resurrected, how realistic would this situation be?

Not very, according to Karl Bates, a researcher in dinosaur locomotion. In fact, our scrawny-armed, prehistoric friend would probably have trouble outrunning a bicyclist. Depending on how fast you run, you may or may not be in trouble if you were on foot.

How does Bates know this?

Because he is a member of the Animal Simulation Laboratory at the University of Manchester, UK, which for over five years has made computer models of prehistoric animals to solve questions about how they moved and what they were capable of doing. This work helps answer how novel structures could help or affect animals, how different walking styles evolved, and how you get from a T-Rex to a modern bird.

Large predatory dinosaurs are his forte, especially the therapods ("beast-foot" dinosaurs believed to be in the lineage of modern birds). For his doctoral thesis, he chose to look into Acrocanthosaurus atokensis. "It is essentially the same size as a T-Rex and looks superficially similar but with big spines along its back," he said.

It lived 110 million years ago in North America; its fossils have been found in Texas and Oklahoma.

"I picked this dinosaur because it is big, and there are fossil tracks and foot prints that are supposed to be from this dinosaur," says Bates. "The proportions of its limbs are some of those most different from modern birds: very long thigh and short ankle bones compared with the short thigh and long ankle bones of birds. With these differences, how they would move is a very interesting question."

Image courtesy Animal Simulation Laboratory

A mixture of science and best guesses

Bates sought to answer this question by creating a grid-enabled computer model of this 'T-Rex with big spines' on a stroll, using NGS resources. The first step is to digitize the dinosaur's skeleton. Using laser scanners, a museum's near-complete skeleton of Acrocanthosaurus is captured as a three-dimensional frame.

"That gives us a 3-D skeleton on the computer that we can spin around and look at," explained Bates. Then skin and muscle is added to the model using the same software animators use for cartoons. "This part is completely subjective," says Bates.

This also makes it the most tricky, because setting body mass determines center of mass. His best guess for Acrocantusosaurus is about six tons, with a possible range of five to seven. Heavier than that and the dino is obese to the point of immobility; thinner than that and it is just skin-covered bones.

This model is then split into sections since - due to the computational load - it isn't feasible to move every joint in the animal individually. Tail-trunk-neck and head are grouped into one theme, and joints are added in the legs, between thighs, shanks, ankles and feet. Bates then adds muscles to this model: another very subjective area. Muscle size is the biggest determinant of the dinosaurs' speed.

"We then put the model in a physics environment - and computer representation of the real world's properties - which allows us to simulate gravity and begin working on the animals' movements."

By his best guess, this dinosaur ran at about an average running speed of 15 miles per hour (24.5 kph) and would have walked at about 5.5 mph (9 kph), faster than the average humans - but not the fastest ones.

Capturing the minds of the public

Bates is also very involved in sharing his science with the public, working with museums and speaking to the media. He believes this not only draws young people to the field, but also helps the public understand the scientific process and contemporary science issues.

"Public engagement is very rewarding," he says, "and very important. Especially in a field like paleontology, where there is little direct economic benefits emerging from the science. In the majority of cases you get a fairly quiet or modest response from parents and kids but every now and again you strike up a really enthusiastic discussion or get an excited response, and it really feels worthwhile.

It's actually amazing how often you speak to scientists in other fields who tell you that fossils were their first big scientific interest."

-Danielle Venton, EGEE

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