An Animated Excursion into Dino Locomotion

Museum of Natural History calls upon Paleontologist Steve Gatesy's Expertise

by Wendy Y. Lawton

For a creature that lived 85 million to 65 million years ago, we know a lot about Tyrannosaurus rex. This "tyrant lizard king" measured up to 20 feet tall and 40 feet long. It had slim legs, a stiff tail, a muscular neck, tiny hands, and a huge skull. Some of its teeth were as big as butcher knives. Some scientists also believe that Tyrannosaurus was a formidable hunter, with powerful jaws, binocular vision, and an intelligent brain - a creature able to eat as much as 500 pounds of flesh and bone in a single bite.

But how did T rex move? Waddle or stride? Walk or run? Did they hold their thighs relatively upright like humans, or more horizontally, like birds?

Motion is one mystery surrounding this storied dinosaur. Steve Gatesy says it's a mystery that can't be solved completely. Muscles - their size and weight - would tell scientists a good deal about how Tyrannosaurus walked through the steamy forests of North America. Muscles, however, don't make it into the fossil record.

Yet Gatesy (left), an associate professor in the Department of Ecology and Evolutionary Biology, and colleague John Hutchinson, a biomechanics expert at the Royal Veterinary College, argue that when it comes to dinosaur locomotion, science can be brought to bear on imagination. The pair say fossils hold important clues, but so do basic principles of biomechanics derived from the movements of living animals.

Their argument for authenticity was laid out this spring in the journal Nature. In their article, titled "Dinosaur Locomotion: Beyond the Bones," Gatesy and Hutchinson say that to get a better grasp on dinosaur locomotion, scientists and animators alike need to look beyond skeletal remains and focus on entire limbs and the physical forces that acted upon them. This would allow for scientifically rigorous inferences about the movement of individual dinosaurs, such as T rex, as well as patterns of evolution across dinosaur species.

In short, Gatesy and Hutchinson say, Hollywood can get real.

"Animation doesn't necessarily mean accuracy," Gatesy says. "While we can't say for certain how Tyrannosaurus or any dinosaur moved, we can at least make educated guesses."

The Nature article spun out of the pair's own animation experience. The American Museum of Natural History invited them to act as consultants to "Dinosaurs: Ancient Fossils, New Discoveries," a major exhibit on dinosaur behavior, movement, and morphology. The exhibit would include a mechanical, skeletal T rex, as well as animations of the flesh-and-blood beast. Could they advise museum animator Scott Michael Harris?

The pair was an obvious choice. Gatesy is an expert on the movement of crocodiles and birds, descendants of dinosaurs. He has also studied tracks left by other dinosaurs that walked upright on hind legs, noting important similarities and differences compared to modern turkeys. Hutchinson is a biomechanics expert specializing in large animals such as elephants. Four years ago, he published a study showing that it would be physically impossible for a T rex to run fast - as one did in the famous Jeep-chasing scene in Jurassic Park. Instead, by estimating muscle mass on 2D models, Hutchinson found that Tyrannosaurus moved anywhere from 10 to 25 miles per hour. That's a brisk walk or a slow jog - not an outright run.

Advising Harris proved a humbling experience. Joint position, body posture, stride length and frequency, muscle mass, and the animal's center of gravity - the pair was faced with multiple variables, many unknowns, and thousands of possibilities.

So Gatesy and Hutchinson started a grueling weeks-long process of elimination to best determine how T rex moved. Fossils were helpful in understanding joints and muscle position. The rules of biomechanics came in handy, too. One example: As the body passes over the foot, hips sit behind knees, knees are in front of ankles.

Observing the movement of living animals was also a boon. With their large tails and heads, alligators inform where Tyrannosaurus' center of gravity may have sat. Elephants inform how an animal the size of T rex might have made strides. Birds were the biggest help. Like turkeys and chickens,T rex walked on its toes, and like barnyard fowl, its toes fold together when its feet are off the ground and spread wide when they hit.

After working with the scientists and making twenty-two revisions to his original animation, Harris called the transformation "extreme." At first, T rex sat low to the ground and made flat-footed lumbering strides. Its tailed flicked and its jaws were open. In the end, the animals' hips sat higher and it walked with a smoother, more rolling gait. Its tail was stiffer. Its jaw was closed.

"My first attempt made T rex looked pretty menacing, crouched and creepy, like something out of a movie or video game," Harris said. "In the end, we got something much closer to reality. This would've been impossible without Steve and John."

The American Museum of Natural History exhibit is now heading from New York City to Houston, then moving on to San Francisco, Chicago, and Raleigh. Gatesy and Hutchinson are moving on, too. In April, the pair met in London to talk about continuing their quest to more accurately animate the past.