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Reliable quantification of bite-force performance requires use of appropriate biting substrate and standardization of bite out-lever

Bite-force performance is an ecologically important measure of whole-organism performance that shapes dietary breadth and feeding strategies and, in some taxa, determines reproductive success. It also is a metric that is crucial to testing and evaluating biomechanical models. We reviewed nearly 100 published studies of a range of taxa that incorporate direct in vivo measurements of bite force. Problematically, methods of data collection and processing vary considerably among studies. In particular, there is little consensus on the appropriate substrate to use on the biting surface of force transducers. In addition, the bite out-lever, defined as the distance from the fulcrum (i.e. jaw joint) to the position along the jawline at which the jaws engage the transducer, is rarely taken into account. We examined the effect of bite substrate and bite out-lever on bite-force estimates in a diverse sample of lizards. Results indicate that both variables have a significant impact on the accuracy of measurements. Maximum bite force is significantly greater using leather as the biting substrate compared with a metal substrate. Less-forceful bites on metal are likely due to inhibitory feedback from mechanoreceptors that prevent damage to the feeding apparatus. Standardization of bite out-lever affected which trial produced maximum performance for a given individual. Indeed, maximum bite force is usually underestimated without standardization because it is expected to be greatest at the minimum out-lever (i.e. back of the jaws), which in studies is rarely targeted with success. We assert that future studies should use a pliable substrate, such as leather, and use appropriate standardization for bite out-lever.