University of California at Berkeley

Nibbling Triceratops

T-Rex Chomps: A Toothful Tale of a Long-Ago Lunch

 by Robert Sanders

The gnawed remains of a 70 million-year-old victim of Tyrannosaurus rex have provided the key to how powerful the dinosaur's bite really was.

Gregory M. Erickson, a graduate student in biology, teamed up with engineers at Stanford to estimate the force that created the punctures and tears in the fossilized pelvis of a hapless Triceratops discovered in Montana a few years ago.

They found that the ferocious T-rex could exert between 1,440 and 3,011 pounds of force, greater than the crushing force of any known creature, though close to the maximum force exerted by the American alligator, a dinosaur relative.

"This is like the weight of a pickup truck behind each tooth," Erickson says.

The estimate is for a bite during feeding, which typically is less forceful than higher velocity snapping bites such as those used by alligators to seize prey.

The new evidence refutes an argument made by some scientists that Tyrannosaurus rex was primarily a scavenger because its teeth were too weak to attack live prey.

"Their teeth were as strong as those of the alligator, a predator that frequently has to deal with struggling prey," Erickson says.

"From a comparative standpoint it appears that T-rex was equipped to struggle with its prey too."

While this is not proof that T-rex was primarily a predator, he says, it does show that when confronted with prey the dinosaur could have held a death grip with its powerful teeth.

"We contend that if T-rex could consistently engage prey with its teeth, it could have exploited a predatory niche," Erickson says.

Erickson and his colleagues, including Dennis R. Carter, professor of biomechanical engineering and director of the Biomechanical Engineering Program at Stanford University and an expert on bone mechanics, published their findings in the Aug. 22 issue of the British journal Nature.

The 4 1/2-foot-long Triceratops pelvis had 58 definite bite marks and 22 probable bite marks that could only have been made by a T-rex, Erickson says.

A cast of one of the punctures was an exact replica of the canine-like tooth of an adult Tyrannosaurus, and distinctive serrations like those on the cutting edges of T-rex teeth could be seen where the teeth had scraped the bone surface. Many of the bites were furrows produced by what Erickson calls "puncture and pull" biting. Living Komodo monitors use a similar feeding strategy to deflesh their victims.

Erickson, who recently completed his MS at Montana State University with paleontologist Jack Horner and amateur fossil hunter Kenneth H. Olson of Lewiston, Mont., described the specimen earlier this year in a paper in the Journal of Vertebrate Paleontology.

Olson discovered the lone pelvis in 1991 in the famous Hell Creek Formation, which has yielded many T-rex and Triceratops fossils.

Erickson does not believe there is enough evidence in the fossil record at this point to definitely say T-rex was predominantly a predator or scavenger.

"It's very difficult to find evidence of behavior in the fossil record."


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