Croc strength all in the snout, study says

By Alice McRae 23 January 2013
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Crocodile jaw strength can be measured by length, new research has revealed – and shorter is better.

IN THE WORLD OF crocodiles, not all individuals are equal, new research suggests.

A recent study into crocodile jaw mechanics has found that those with shorter snouts are able to take down large prey, while longer-snouted species are restricted to feeding upon smaller animals, such as fish.

The study, led by Dr Colin McHenry at Monash University in Melbourne, found that the strength of a crocodile’s lower jaw can be accurately predicted by measuring the length of the region where the two halves of the jaw join, known as the mandibular symphysis.

The results, published this month in the journal PLOS One, found that crocodiles with a longer mandibular symphysis cannot withstand the loads associated with taking down large prey.

The long and short of crocodile jaw mechanics

The study was conducted using high resolution 3D models of seven different species of crocodiles, ranging from the very long-snouted (those bearing a long mandibular symphysis) to the short-snouted (those bearing a shorter mandibular symphysis).

Analysis of the models determined how the different jaws would respond to the various loads required to take down large prey. The loads were divided into three groups: biting; shaking, which is necessary when prey is too large to swallow; and twisting, for ripping chunks off very large prey.

The results showed that during twisting and shaking, the jaw was weaker when there was a longer symphysis, and that the length of the symphysis could be used to predict the strength of the jaw.

Colin says the study is interesting because shaking and twisting are behaviours required for crocodiles to feed on large prey. “It suggests that those crocs that do feed on large prey have to have a short symphysis to make the jaw strong enough to undertake those behaviours,” he says.

Reason for long snouts on crocs unknown

Professor Gordon Grigg at the University of Queensland in Brisbane says the study confirms the idea that a long, thin snout is more fragile, and hence more suited to feeding on smaller prey.

“It is a very interesting study, it confirms ideas researchers have had for some time that the feeding habits of crocodilians have had a big influence on the way the shape of their skull has evolved.”

However, Gordon says the benefits of a longer snout still remain unclear. “It’s probably something to do with the capacity to rapidly swing their heads through the water,” he says, adding that more work using similar engineering techniques may shed further light on the topic.

Colin says the fact that jaw strength may be predicted based on a simple measurement shows that this finding is not particular to crocodiles – rather it is likely to be a basic function of jaw shape in general.

“This suggests that these results are applicable to other groups, such as dolphins,” says Colin. “It also allows us to be a lot more confident when establishing the strength and feeding patterns of fossil marine reptiles.”

3D image of the skull of a slender-snouted croc (Mecistops cataphractus). (Credit: Image produced by FABLab)