Abstract & Overview
A model of static bite force during the power phase is used to investigate the relationship between the feeding ecology (herbivorous vs. animalivorous) and biomechanics of the jaw system in four species of lizards. For the analysis the bite model of Herrel et al. (1998) is used. The model calculates both the bite and joint forces and the moments at the quadratosquamosal joint for a range of orientations of food reaction forces. No relative jaw movements during the power phase of biting are observed (based on cineradiography) in any of the examined species, thus excluding grinding mechanisms as an adaptation to a herbivorous diet. However, trends in magnitude and orientation of the joint forces and required and remaining moments at the quadratosquamosal joint are similar in species with similar food preferences. Herbivorous lizards bite harder and show lower joint forces for a given bite force than non-herbivorous species do. It is argued that this difference might be a more general characteristic of herbivorous lizards and that a high bite force has an adaptive value for these species. Whereas, in lizards, dental grinding mechanisms are presumably not a prerequisite for a herbivorous diet, adaptations of the digestive apparatus and the development of a relatively high bite force probably are. Additionally it is argued that the shift of the insertion site of the temporal ligament can be considered as a preadaptation for herbivory in lizards. A hypothetical transformation series of the bauplann of the skull departing from a basic lepidosaurian stock and leading to the skull system in extant herbivorous lizards is proposed.