Mechanical significance of streptostyly in lizards

Abstract

The morphology of the lizard skull has been a subject of study for more than a century, particularly with respect to the morphology and function of the major jaw adducting muscles^1–5 and the mechanics of the moving parts^6–9. It is possible that controversies surrounding the extent and timing of bone movement, muscle contraction and force generation will be resolved by techniques such as electromyography, cineradiography and measurement of bone strain^3,10. I present here data that facilitate a reconsideration of the function of the pterygoideus muscle, one of the two major jaw adducting muscles, and the mechanical significance of movements of the quadrate around the quadrate-squamosal joint. This movement, known as streptostyly⁶ occurs in all living lizards¹¹ and also characterises the earliest members of the order^12–14. On the basis of my data I propose that streptostyly in lizards is a means by which the mechanical advantage of the pterygoideus muscle is increased, so that this muscle makes a major contribution to bite force.