STAYTON, C.T.; The University of Chicago: Functional and Morphological Evolution of Herbivory in Lizards

Multiple, independent origins of herbivory within lizards (Sauria, Lacertilia) have repeatedly produced similar morphological and mechanical changes in the skull. Herbivory has evolved multiple times in lizards, but the morphological consequences of the evolution of this dietary strategy have never been quantitatively studied in the Lacertilia. Geometric morphometrics were used to study the independent evolution of herbivory in eight lizard families. Seventeen functionally relevant landmarks were digitized on 1105 lizard crania and lower jaws, and the data examined using shape-based analyses. Thin-plate spline visualizations of relative warps reveal that, although herbivores from different families do not occupy the same area of shape space, all herbivores vary in the same direction away from their carnivorous sister groups. Specifically, herbivores possess higher skulls, shorter jaws, and larger areas for adductor muscle attachment than their carnivores. These differences are significant under MANOVAs of relative warps scores, permutation tests, and phylogenetically independent contrasts. The use of functional landmarks allows these shape differences to be interpreted mechanically: herbivore lower jaws are characterized by higher mechanical advantages (higher potential closing force) but lower potential closing speeds as compared to their carnivorous relatives. Overall, lizard MAs for jaw closing range between 0.21 and 0.51. The results of this study indicate that there is a strong ecomorphological relationship between skull shape and diet, but that this relationship is only discernible when phylogeny has been taken into account. Because many functional characteristics of organisms are influenced by shape, geometric morphometrics show great promise for functional and mechanical studies.