STAYTON, C. Tristan; The University of Chicago: On the road to herbivory: patterns of morphological and functional evolution in herbivorous lizard lineages

Lizards provide an excellent opportunity for investigating the origin and evolution of herbivory, as plant-eating has evolved many times in this group. Although patterns of convergence in body size, skull shape, and jaw function have been documented among herbivorous lizards, no quantitative investigations of morphological or functional evolution have been performed for these taxa. Additionally, many hypothetical scenarios for the evolution of herbivory predict a specific order of character change. Thus a study of character evolution can also be used to test these hypotheses in lizards. This study combines a geometric morphometric analysis of skull shape, a functional analysis of lower jaws, and phylogenies of herbivorous lizards in eight lineages to determine if there are any common patterns of evolution of these groups. Character states of herbivore ancestors were reconstructed using Generalized Least-Squares (GLS) methods and examined to determine if trait evolution was correlated or if traits evolved in a consistent order. Independent contrasts and GLS were used to assess evolutionary correlations between variables, to determine if the patterns of character evolution discovered in herbivorous lineages were the result of broader correlations within all lizards. No single pattern characterizes the evolution of herbivory in lizards. Even with herbivores partitioned into more specific subcategories, such as frugivores or folivores, no common patterns emerge. In some cases, traits typically associated with herbivory appear before the evolution of herbivory, raising the possibility of exaptation as a mechanism for herbivore evolution. No current hypothesis for the evolution of herbivory can explain the order of trait evolution in all herbivorous lizard clades.