The evolution of large body size has often been considered a key trait allowing the evolution of herbivory in lizards. Although many omnivorous lizards appear unspecialized, they typically show high bite forces, allowing them to reduce tough and fibrous plant matter. In contrast, true herbivores often show a suite of morphological and physiological specializations, allowing them to efficiently process and assimilate plant material. Moreover, many specialized herbivores have a large body size, thus likely relaxing constraints on bite-force generation given that bite force increases with increasing body mass. In this study, we test whether large herbivorous lizards of the genus Uromastyx have relatively lower bite forces for their body size compared with a medium-sized congener. No differences in bite force or head dimensions were observed between the two species or between both sexes in our sample. Moreover, bite force scaled with positive allometry relative to jaw length, suggesting that larger animals have disproportionately large bite forces. This suggests that even in the largest species, constraints on bite-force generation are still strong, possibly due to the demands imposed on the jaw system by the mechanical properties of the diet.
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