Allosaurus as a Jurassic headbanger.

Being referred to as thickheaded isn't exactly a compliment. Depending on your lifestyle, however, you just might need a skull that can occasionally take a good smack.

Consider a carnivorous dinosaur such as Allosaurus fragilis attacking and feeding on its prey. New research shows that the predator's skull can resist stress many times higher than that expected merely from the dinosaur's chewing on its victims. The finding provides insight into Allosaurus' method of subduing its prey, says Emily J. Rayfield, a doctoral student at the University of Cambridge in England, who performed the analysis.

To study the skull and jaw of Allosaurus, Rayfield took advantage of the same techniques that engineers use to calculate the stresses in bridges and aircraft wings.

First, she used computerized tomography scans of a fossil skull to construct a detailed mathematical model of the dinosaur's head. Then, she calculated the forces that the jaw muscles would have produced on the upper teeth during chewing, and she plugged those results into the model to estimate the resulting stresses.

The analysis showed that Allosaurus had a weak bite force and a relatively flexible lower jaw. In particular, Rayfield found that the dinosaur's lower jaw had a small margin of safety; that is, it couldn't withstand a load much larger than the chewing force.

So, Allosaurus probably wasn't capable of delivering bone-crushing bites on large prey. However, Rayfield showed that the predator's skull could absorb forces directed against the upper jaw that were many times larger than those that could be produced by the jaw muscles alone.

Rayfield says this mismatch between upper and lower jaw suggests another purpose for the thick skull. She contends that Allosaurus used what she terms a high-impact attack strategy against larger prey. In such an assault, the dinosaur would ambush its victim, slam into it at high speed with jaws agape to drive in its upper teeth, and then use its strong neck muscles and sharp teeth to rip out a mouthful of flesh.