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Clocking T. rex

Clocking T. rex Photo Credit: Steve Richmond (CC by 2.0)

Special effects can make moviegoers feel like they’re in another world—perhaps exploring another planet, swimming the ocean depths, or facing down a dinosaur. Those effects are meant to be entertaining, but not necessarily scientifically accurate. In this Science Update, you’ll hear how one of the most popular movies in history managed to achieve both—by accident.


Transcript

Was T. rex a slowpoke? I'm Bob Hirshon and this is Science Update.

In the movie ‘Jurassic Park,’ the Tyrannosaurus Rex gave pretty good chase. It seemed to run at least as fast as its human co-star could drive.

But a new study suggests that the real-life T. rex probably wasn’t that fleet of foot. John Hutchinson, a biomechanics researcher at Stanford University, and his Colleague Mariano Garcia analyzed T. rex’s running style.

Hutchinson:

What we did was build a really simple two-dimensional model of the legs and the body of a bipedal, or two-legged, animal running at a given speed and kind of constrain to a possible range of values for a Tyrannosaurus.

T. rex’s top speed came out between 10 and 25 miles an hour -- so it probably couldn’t have caught up to a Jeep.

But he says that, in a funny way, ‘Jurassic Park’ actually got things right.

Hutchinson:

If you go back and study the movie frame by frame, you can get an estimate of velocity. And actually the T. rex was only going about 10 or 15 miles an hour.

He says the animators tried to show T. rex going 45 or 50, but it looked unrealistic. So they slowed the dinosaur down and used quick edits to make the scene fast-paced and exciting.

For the American Association for the Advancement of Science, I'm Bob Hirshon.


Making Sense of the Research

In some areas, bigger isn’t necessarily better. Take running, for example. The bigger you are, the more leg muscle mass you need to run fast. But all that extra leg muscle can weigh you down, which in turn makes it harder to run. In other words, the math starts working against you.

That’s why gigantic animals like elephants usually aren’t the fastest runners on the block, at least compared to their size. Despite this, many scientists have estimated that the enormous T. rex could run at speeds up to 45 miles per hour. But those figures were just guesses based on eyeballing the dinosaur’s body. Hutchinson decided to look at the problem more closely.

He and Garcia designed a computer model that would predict whether an animal could run fast or not, based on its muscle and body structure. It’s not a fancy, full-color 3-D animation, like the kind you see in Jurassic Park, but it’s well suited for scientific purposes. To see if the model worked, they tested it with measurements from living animals, including chickens (surprisingly strong runners) and alligators (relatively weak runners). When it came up with the right answers, it was time to plug in the T. rex measurements—which were taken from four years of painstaking fossil studies!

The verdict, as you heard, was that T. rex was pretty pokey. 10 to 25 miles per hour isn’t slug-like, but it’s in the same ballpark as a top human runner (15 miles per hour) and nowhere near the fastest modern animals (cheetahs, for example, can run 70 miles per hour). And of course, it’s not as fast as a Jeep. Part of the reason it couldn’t have run very fast is because its legs were bent. Try running or walking with bent legs and you’ll see how tiring it is!

In fact, Hutchinson’s model suggests that in order to run at 45 miles per hour, a T. rex would need 86 percent of its weight to be concentrated in the muscles supporting its legs. That leaves just 14 percent for all the other muscles, plus skin, skeleton, organs, teeth, and so on. And that would be one funny-looking dinosaur.

Now try and answer these questions:

  1. Why are larger animals often slower runners?
  2. Besides leg muscle mass, what other factors might determine how fast an animal can run?
  3. Why do you think paleontologists would want to know this? What can we understand by knowing an animal’s approximate running speed?
  4. Can you think of other physical limitations that come from being very large?

For Educators

Learn more about the Stanford Neuromuscular Biomechanics Lab, where this research took place.

UC Berkeley Museum of Paleontology is a museum devoted to the history of life, including dinosaurs.

The Field Museum of Natural History’s Sue at the Field Museum contains detailed information about a significant T. rex fossil find.


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