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Stanford engineers help measure the force of T-rex's bite

STANFORD -- Was Tyrannosaurus rex a fearsome predator who preyed on fellow dinosaurs? Or was the king of the thunder lizards a lowly carrion-eater?

This question has been the subject of a recent scientific debate among paleontologists. Now the first measurements of how hard T-rex could bite, published in the Aug. 22 issue of the British journal Nature, appear to support the popular view of the dinosaur as one of the most awesome predators to have walked the Earth.

The authors report that the ferocious beast 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.

"Their teeth were as strong as those of the alligator, a predator that frequently has to deal with struggling prey. We contend that if T-rex could consistently engage prey with its teeth, it could have exploited a predatory niche," says the paper's first author, Gregory Erickson, a graduate student in biology at the University of California-Berkeley. Collaborating on the study were Dennis R. Carter, Stanford professor of biomechanical engineering and an expert on bone mechanics, and two of his graduate students, Samuel D. Van Kirk and Jinntung Su.

Erickson and Carter met through the Society of Vertebrate Paleontology at a time when Erickson was a graduate student at Montana State University studying the gnawed bone of a 70-million-year-old victim of Tyrannosaurus rex ­ a vegetarian dinosaur called Triceratops. The bone was found by amateur fossil hunter Kenneth H. Olson in 1991 in the Hell Creek Formation in Montana, which has yielded many T-rex and Triceratops fossils. Erickson had determined that the bite marks in the fossil had been made by a Tyrannosaurus rex and proposed a collaboration with Carter to measure the forces required to make such marks.

Erickson, who later moved to the University of California-Berkeley, joined forces with the Stanford team to determine the force that T-rex had to apply to create the bite marks seen in the fossil.

Consulting with Veterans Affairs engineer William E. Caler in Menlo Park and Stanford teaching assistant Marc E. Levenston, the team found a cow pelvis that matched the Triceratops bone in both growth form and microstructure. They then made precise measurements of the amount of force required to make an 11.5 mm (half-inch) deep puncture in the cow bone, duplicating the marks found in the Triceratops bone. The role of the tooth was played by a bronze and aluminum cast of a real Tyrannosaurus maxillary tooth, placed in a hydraulic loading machine.

Breaking only one bronze tooth in the process, the team determined that the T-rex would have exerted the most force at maximum penetration ­ about 1,440 pounds for the tooth that produced the 11.5 mm deep puncture. This tooth was from the front half of the Tyrannosaurus jaw.

Greater forces would have been exerted simultaneously by teeth further back in the mouth nearer the jaw hinge. From the data the researchers calculated this force to be 3,011 pounds. By comparison, a human exerts a maximum force of about 175 pounds with the rear teeth, an African lion about 937 pounds, and an alligator slightly less than 3,000 pounds.

"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.

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