The role of skull flexibility in feeding - an investigation using advanced computer modelling techniques

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The project examines the role of skull flexibility in lizard feeding, using an advanced computer modelling approach. In a newborn human baby, areas of soft tissue remain between skull bones, allowing flexibility and continued growth. In an adult, the sutures close and the brain is enclosed in a rigid bony shell to which the facial bones are immovably attached. Gape is limited. However, in the skulls of adult lizards, snakes and birds some sutures remain open, allowing movement of the skull parts on one another. This flexibility (=kinesis) can be spectacular, e.g. in a large snake swallowing prey with a body diameter several times that of its own head. Such skulls clearly operate in a very different way to the rigid skulls of mammals, and reflect major differences in biology and lifestyle. Comparative studies between skull types are important in shedding light on normal, pathological and aging skull functions generally. Mammals need a regular supply of food to maintain a constant high body temperature. Their skulls have evolved to maximise the efficiency of oral food processing (chewing) (e.g. differentiated teeth, precise occlusion, hard palate, precise muscle control). Lizards and snakes, in contrast, warm themselves from external sources and can feed opportunistically. A large meal can last a snake for months), and there is usually little oral food processing. Instead, the skull of advanced snakes allows increased gape and aids both food transport through the mouth and swallowing. In lizards, from which snakes evolved, the situation is less clear-cut. Skull movements are more subtle and many of the joints through which they act, or potentially act, are not well understood. Many questions remain unanswered, notably: a) which lizards are really kinetic and to what degree? b) how do the different skull parts move in relation to one another, and by how much (passive adjustments or active linked movements)? c) what is the role of the membrane-cartilage braincase in the adult? Does it aid or limit kinesis? Does observed anatomical variation match the pattern of kinesis? d) what are the consequences of kinesis for skull function and stability, and how does this relate to diet? e) can kinetic ability be predicted by skull shape? To date, most discussion of lizard kinesis has been based on dissection, manipulation of dead or anaesthetised animals, theoretical analyses, and a few experimental studies. As a result, there is a lack of agreement on many points. Advanced computer modelling offers an alternative approach. Our research group is cross-disciplinary (reptile anatomy/evolution; biomechanical engineering; analysis of shape in relation to function). We have a strong track-record and have pioneered an approach that combines the use of 3-D computer simulations (multibody dynamics analysis) and stress analysis (finite element analysis). This yields detailed, anatomically accurate working computer models of animal skulls, including joints and muscles (jaw, neck). Sophisticated software then allows us to relate changing skull shape to skull performance during feeding. Comparisons with living animals (bite force data, records of muscle action and feeding) have shown our models to be biologically realistic, but our U.S collaborators (Ross, Lappin) will collect further comparative data in the new project. Beneficiaries of our work include the academic community (evolutionary biologists, palaeontologists, functional anatomists - data and new methodological approaches), the UK science base in general (through training of young scientists in an interdisciplinary framework, attraction of overseas students and collaborators, engaging young people in science), the wider public (public engagement, media interest) and, potentially, clinicians (perspectives on normal, aging and pathological skull, jaw and tooth function).