The size of Allosaurus's skull had been something of a conundrum for palaeontologists because -- compared with skulls of other Cretaceous carnivores such as Tyrannosaurus rex -- it seemed too robust considering the relative weakness of its bite. But after testing an Allosaurus skull using the engineering apparatus, Emily Rayfield of Britain's University of Cambridge and colleagues find that Allosaurus probably used its skull in a completely different way from its fellow predators.

The researchers used finite-element analysis (FEA), which is normally deployed to work out how stresses are distributed around a structure under various loads. For example, FEA might be used to see how a bridge design reacts to trucks of a certain weight moving across it.

In a similar way, Rayfield's team used FEA to study how the strong, lightly built skull of Allosaurus responded to stresses such as biting and shearing. It soon became apparent that the skull itself was immensely strong and would have been able to withstand very powerful impacts. But the teeth would not survived the very large compressive loads borne, for example, by the teeth of a much larger dinosaur such as T. rex.

Rayfield and colleagues think that the skull of Allosaurus wasn't over-engineered but designed with a different purpose in mind. Allosaurus was a pursuit predator that head-butted its prey (large, herbivorous dinosaurs) with great force. An analogy, the researchers say, is a man hitting a block of wood with a hatchet. Once impacted, the dinosaur would not bite straight down into its prey, but slash, slice and tear pieces of flesh before withdrawing. This kind of behaviour would put a premium on skull strength without requiring individual teeth to bite with comparable force.

This work makes for especially interesting reading when compared with earlier studies of T. rex bite forces. Palaeontologist Gregory Erickson and colleagues2 showed, using real bones and models of dinosaur teeth, that the bite of T. rex delivered a compressive load strong enough to bite through the bones of its adversary Triceratops. This could mean that T. rex had become a specialist in dismembering carcasses of large and perhaps heavily armoured dinosaurs.

Taken together, the work shows the kind of range in hunting strategies that one might have expected in a group of animals as large, diverse and successful as the dinosaurs.