Jaw and hyolingual muscle activity patterns and bite forces in the herbivorous lizard Uromastyx acanthinurus

Uromastyx lizards are basal agamid lizards that are characterized by an herbivorous diet and a robust akinetic skull. Recently, lizards in general, and Uromastyx lizards in particular, have become a model system for mechanical analyses of skull function. However, quantitative models of skull function are hampered by a lack of knowledge on the activation patterns of jaw and hyolingual muscles. Moreover, in vivo bite force or strain data, essential to test the validity of these modelling efforts, are lacking. Here we provide data on the muscle activation patterns and bite forces in the lizard Uromastyx acanthinurus. Our results show that muscle recruitment patterns during intra-oral transport and swallowing, are qualitatively similar to those observed for other lizards. Whereas during the slow opening phase the hyolingual muscles show a pronounced activity, the fast opening phase is characterised by strong activity in the jaw opener and the tongue and hyoid retractors. During fast closing the jaw closers become active and at the end of this phase, the jaw closers become silent momentarily before showing a renewed and strong activity during the slow closing/power stroke phase. Measurements of bite forces indicate bite force levels similar to those of agamid lizards of similar size, and similar to those predicted based on recent modelling efforts. These data should allow further refinement and validation of recently published models of biting in lizards of the genus Uromastyx.