Meeting Abstract
When a typical vertebrate bites, bite out-lever (i.e., distance from jaw joint to location of the bite on the tooth row) and gape angle are two variables influenced by its behavior that are expected to affect bite-force performance. As bite out-lever increases, the law of the lever indicates that bite force should decrease following a linear relationship with a predictable slope. For gape angle, existing theoretical models and empirical data from mammals generally indicate that bite force is expected to increase with decreasing gape angle. To examine the effects of bite out-lever and gape angle on bite force in lizards, we conducted in situ experiments in which the jaw-adductor muscles of euthanized brown anoles (Anolis sagrei) were stimulated directly while bite force was simultaneously measured with a double-cantilever beam force transducer. Comparing our empirical results with a model we developed, we found that bite force in the brown anole largely follows the law of the lever. With respect to gape angle, the results of a separate set of experiments show that bite force is greatest at small gape angles, though brown anoles are capable of generating relatively strong bites across a range of gape angles. The generality of these results is uncertain, given that many lizards exhibit various forms of cranial kinesis. Cranial kinesis, including streptostyly observed in anoles, may affect jaw muscle levers, lines-of-action, and length-tension properties during biting, such that basic lever mechanics are not entirely predictive of how bite force is affected by bite out-lever or gape angle.
