Thursday, March 13, 2014

Dino Dining Versus Speed

Could you outrun a dinosaur? Well, it depends on the dinosaur. According to Scott Lee, a professor of physics at the University of Toledo in Ohio, herbivorous dinosaurs moved more slowly than predatory dinosaurs that often chased down their prey and could reach up to 30 miles per hour. Plant eaters, on the other hand, moseyed along at about 3 miles per hour.

This means you could easily outrun, and even out-walk, some herbivorous dinosaurs. But if you caught the attention of a ravenous raptor, chances are high that it would be the last race you ever ran.

It’s no surprise that predatory dinosaurs evolved to move faster than their prey. Otherwise, they would be hard pressed to find a decent meaty meal most days. But it would also make sense, from an evolutionary standpoint, if herbivorous dinosaurs at least gave predators a run for their money in the cat-and-mouse chase.

By studying 56 sets of distinctive fossilized footprints, or trackways, belonging to herbivorous dinosaurs that paleontologists have uncovered over the years, Lee determined that not a single set resulted from running. Lee calculated the ratio of the dinosaurs’ stride length to foot length and found that all of the footprints were likely made at a walking pace. So, how did the plant-eating dinosaurs protect themselves?

Two slides taken from a PowerPoint presentation Scott Lee offers to explain how he estimates the speed of dinosaurs based from their fossilized footprints. Credit: Scott Lee.

Some had body armor. Others were simply too large for a predator to take down alone or with a small group. Those who were smaller and armor-less likely sought protection in large numbers. From the samples he studied, Lee found that armored ankylosaurs and soropods – a group of dinosaurs that included the largest animals to have ever walked the planet – moseyed slower than unarmored ornithopods.

Ornithopods, unlike anklyosaurs or soropods, roamed on two legs instead of four. Although Lee’s sample did not include running ornithopods, scientists think these herbivorous dinosaurs had running capabilities. Whether they could have outrun a predator is unclear.

Lee also looked at 35 trackways belonging to types of predatory, two-legged theropods. Of the four groups of dinosaurs Lee studied, the carnivorous theropods showed the most variation in speed. About 25 percent of the tracks, Lee calculated, originated from running theropods, making them the fastest of the dinosaur types he analyzed.

 Fossilized dinosaur footprint, Clayton Lake State ParkNew Mexico, USA. Credit:  David Stapleton (Dsmdgold)

Lee said that his results compare to past studies on dinosaur locomotion and speed, but he is the first to compare the speed for the four groups: armored ankylosaurs, soropods, ornithopods and theropods.

“I’m trying to put together a bigger picture,” Lee said. “You’d expect that predator dinosaurs would have to move faster” and evidence suggests that is the case, at least for a small set of certain species of dinosaurs.

What about the over 700 other species of dinosaurs? Unfortunately, not all dinosaurs thoughtfully made muddy footprints that then fossilized for us to study tens and hundreds of millions of years later. So scientists like Lee must use other methods to interpret how fast most species, including T. rex, might have walked and possibly ran.

A 2002 study in Nature suggests that T. rex was simply too large to run. The scientists estimated the amount of leg muscle necessary for running in various-sized animals. Extrapolating their results from animals alive today, they argue that T. rex would have needed more than 80 percent of its total mass in its hind leg muscles in order to run, which they say is an unrealistic amount. Hollywood often ignores this, as shown in this highly amusing scene from the 2007 animated film Meet the Robinsons.


Instead of estimating muscle mass, Lee is looking at fossilized femur bones of types of theropod dinosaurs. So far, he’s studied 66 femora from over 30 different species of theropods.

“I was trying to find another way of getting running speeds by getting bone strength in dinosaur legs. I concentrated on the femur. That’s the bone up near your thigh,” Lee said.

When a human runs and their feet hit the ground, an impact shock wave propagated from the lower leg to the thigh, stressing the femur bone. There is a limit to the amount of stress the femur can take before it snaps in two. Lee calculated the force a femur bone feels for different-sized animals and from that estimated the maximum speed an animal could reach before the stress on the bone reached its breaking point.

Human femurs. Credit: Anatomography

Brachiosaurus femur, thigh bone of a large dinosaur, and geologist Metrinah Ruzvidzo in Zimbabwe. Credit:  Kevin Walsh

Larger animals alive today, like elephants, tend to be less athletic than smaller animals, like cheetahs, because their femur cannot handle the stress that would result if say an elephant were capable of reaching speeds up to 70 miles per hour.

Similarly, large theropods, like T. rex, were less capable of reaching high speeds than smaller theropods, like the Velociraptor, Lee reported in a poster session at last week’s APS March meeting in Denver, Colorado.

“If you scale up to T. rex, then they really could not be so athletic,” Lee said. “It looks like it could run eight meters per second,” which is about 18 miles per hour -- about half the speed that smaller predatory dinosaurs could reach, Lee said. That is, of course, if T. rex could have run at all, which can only ever be speculated from calculations since there are no known fossilized T. rex footprints.

Each year since 1993, Lee has offered a course at the University of Toledo on Jurassic physics.

1 comment:

  1. Interesting. I saw a T. Rex footprint in the Sugarite Canyon New Mexico State Park office/visitors center.