Why is it important to understand how skulls deal with stress generated from bite force

Dr Marc Jones writes a guest post on his latest paper on bite force in reptiles

Among animals there is great variation in skull shape, and this is related to a variety of environmental factors such as diet and life style.

The shape of an animal’s skull is closely linked to its function: the skull supports soft tissue such as muscles and other connective tissue which allow movement and support.
Lizards, despite looking superficially similar on the outside have large variation in skull shape. We set out to show how the differences in skull shape are related to stresses distributed through the skull during biting.

Our work, published today in Royal Society Interface studies how soft tissue and bone interact during biting motion, and the bite force. Our paper, is the first to include the front part of the lizard braincase. It also includes the soft tissue joints between bones. This study takes us a step closer to understanding why skulls are the shape that they are.

We used the skull of the South American tegu lizard as our model species as it’s a very charismatic creature with a varied diet. We used CT scans to model the soft tissue structures and bone construction and analyse bite force.
The technology we used for this “whole picture” approach is the same engineering software used to design bridge and aeroplanes, as it is able to track the motion and strain on many complicated pieces.  For the analyses, we developed a computer model made up of many individual bones held together by flexible material – just like the real skull. The muscles were represented by contracting struts and based on detailed anatomical dissections.

To enable calculations the model was divided into a large number of very simple tetrahedrons (finite elements). Results comprised images of the skull colour coded according to strain as well as plots of strain along the length of the skull and braincase.

Our results were surprising – we found the flexible material between the individual bones doesn’t act like a “stress absorber” as previously thought; instead it increases overall strain but spreads it more evenly throughout the skull. This event strain is important for normal growth.
These results are also of interest to the field of human biomedicine despite differences in skull shape and species.  Humans can experience premature fusion of skull bones, result in skull deformities, in infant children.

In lizards, the part of the skull that houses the front of the brain (the chondrocranium) is made from cartilage and varies among species as to its shape and mineralisation. Our study  finds that this structure had little effect on skull function and contradicts previous suggestions that it might serve as a vertical support structure.

In the future we hope to study the structure and loading of many more species of lizards including species from Australia which we’ve been measuring bite force in wild populations.

He talks further on this topic in a video produced for Australia’s Science Media Centre,


The paper was by Dr Marc Jones and an international team from University College London, University of Aberdeen, and University of Hull. It was funded by the UK Biotechnology and Biological Sciences Research Council and the Australian Research Council.

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