ECOMORPHOLOGY OF THE LIZARD FEEDING APPARATUS - A MODELING APPROACH

A model of static bite force during the power phase is used to investi gate the relationship between the feeding ecology (herbivorous vs. ani malivorous) and biomechanics of the jaw system in four species of liza rds. 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 react ion forces. No relative jaw movements during the power phase of biting are observed (based on cineradiography) in any of the examined specie s, thus excluding grinding mechanisms as an adaptation to a herbivorou s diet. However, trends in magnitude and orientation of the joint forc es and required and remaining moments at the quadratosquamosal joint a re similar in species with similar food preferences. Herbivorous lizar ds bite harder and show lower joint forces for a given bite force than non-herbivorous species do. It is argued that this difference might b e a more general characteristic of herbivorous lizards and that a high bite force has an adaptive value for these species. Whereas, in lizar ds, dental grinding mechanisms are presumably not a prerequisite for a herbivorous diet, adaptations of the digestive apparatus and the deve lopment of a relatively high bite force probably are. Additionally it is argued that the shift of the insertion site of the temporal ligamen t can be considered as a preadaptation for herbivory in lizards. A hyp othetical transformation series of the bauplann of the skull departing from a basic lepidosaurian stock and leading to the skull system in e xtant herbivorous lizards is proposed.