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Dinosaur Slasher

21 February 2001 7:00 pm
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Number crunching. As the teeth of the upper jaw are subjected to force, colors ranging from yellow to dark blue show where the skull is compressed.

When it comes to dinosaurs, nothing seems to capture the attention of the public--and paleontologists--as much as the teeth of big predators. They have inspired speculation, detailed anatomical studies, and even hydraulic presses to study their strength. In the 22 February issue of Nature, a new technique borrowed from engineering backs up a theory about the hunting strategy of Allosaurus, a common Jurassic carnivore.

Engineers have used so-called finite-element analysis for decades to design objects, be they bridges or booster rockets. They recreate the structure with a virtual mesh of small, linked polygons, then designate its elasticity and other material properties at each tiny site. Force is applied, and as each element nudges its neighbors, the computer calculates the compression and tension. In the late 1970s, biomedical researchers began to use the technique to study, among other things, the strength of tooth implants. More recently, some biologists and paleontologists have begun to apply it to test ideas about anatomy, evolution, and ecology.

The subject of the new study is a remarkably complete Allosaurus found in Wyoming in 1991 and dubbed "Big Al." Like those of many other theropod dinosaurs, an Allosaurus skull is a lattice of small, thin bones that looks both light and strong. Emily Rayfield, a graduate student at Cambridge University, United Kingdom, wanted to understand how the 80-centimeter-long skull functioned as a tool and a weapon.

First Rayfield created a digital mesh from computed tomography scans of the skull. The highly detailed finite-element model contained nearly 250,000 elements. By applying force through six teeth in the virtual head, she found that the upper jaw and the rest of the skull could have withstood a load of up to 6 metric tons--26 times the maximum force that clenched teeth could produce. Why such drastic overengineering? Rayfield suspects that the skull had to absorb such large impacts when Allosaurus collided with its prey. She imagines Allosaurus running into a fleeing victim with jaws agape, slamming its upper teeth in like a hatchet and then using its strong neck muscles to rake out flesh with its teeth.

"At first glance, it seems like it would be a weird approach to biting," says theropod expert Tom Holtz of the University of Maryland, College Park. But it fits with the observation, published last year, that Allosaurus could open its jaws extremely wide. "It's appealing to see that the mechanical analysis is consistent," he says.

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More about Allosaurus

Links to information on finite-element analysis

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