Tuesday, 13 March 2012

More than just a Bone-crunching Bite

Tyrannosaurus rex had the most powerful bite of any land animal that ever lived, but recent research shows that their was more to it's bite than brute force alone.

Image via Paleoblog

That T. rex had a powerful bite had long been known, a mechanical test of it's biting strength done by Paleontologist G.M. Erickson and engineers from Stanford University built a mechanical rig to replicate the teeth marks found on fossilized T. rex victims. They found a minimum bite strength of 3.300 pounds (~16.000 Newtons).
A recent computer analysis put the bite force even higher, with a minimum bite force of 20.000N and a maximum estimated  at an astonishing 57 thousand Newtons. And it should be noted that because of the differently sized teeth of Tyrannosaurs the bite force would initially be applied only to the tallest teeth, which would punch their way into the flesh (and any bones they happened to meet) ahead of the rest.

There is however evidence that T. rex wasn't optimized for brute force alone, and it comes from yet another computer analysis of the T. rex skull.

For a paper published in 2004 Emily J. Rayfield created a computer-model of a T. rex skull to test how strong the skull really was. The research was based on the observation that the skull of T. rex, like that of most vertebrates, does not consist only of completely fused bones. Instead many of the bones in the skull are connected to each other by 'sutures', joints that allow limited movement and give the skull a measure of flexibility.
It had long been hypothesised that these sutures would act as "shock-absorbers" taking up some of the stress caused the force of the bite.
Stress distribution in a fused (l) and partly fused (r) skull (adapted from Rayfield)
What Rayfield found was different however, the model of the skull that was not completely fused (as it would have been in reality) could take less force, and thus a weaker bite. The stress caused by the bite however was differently distributed because of the sutures, with more of the load going to the rear of the skull and the tip of the snout. These areas are where the T. rex skulls is reinforced by ridges, hornlets and in the case of the snout fused nasal bones (fused nasals are in fact a defining characteristic of Tyrannosaurs).
The skull of Tyrannosaurus is clearly optimized for large bite forces, but it's not perfectly optimised. This means that in life it wouldn't have achieved the maximum theoretically possible bite force.

Perhaps even more significant was another find from this study, which also looked at the capability of the T. rex skull to withstand shear forces. That is, the forces that would be caused by pulling the head backwards while the teeth were embedded in a victim, tearing the through the flesh.
Stress distribution caused by biting (l) and tearing (r) (adapted from Rayfield)
The results showed that the skull of a Tyrannosaurus was equally adapted to tearing as it was to biting, lending support to the idea that T. rex used a unique form of feeding that has been termed 'puncture-pull'.
Puncture-pull is pretty self-explanatory, T. rex would have used it's powerful bite to create a row of puncture and than pulling back with it's strong neck muscles to separate a large chunk  of flesh from it's victim. Much like tearing perforated paper.


Rayfield, E.J. (2004) Cranial mechanics and feeding in Tyrannosaurus rex Proc. R. Soc. Lond.
Bates, K. T., Falkingham, P.L. (2012) Estimating maximum bite performance in Tyrannosaurus rex using multi-body dynamics Biology letters (quoted on Paleoblog)

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