Evolutionary ecomorphology of the feeding biology of crotaphytid lizards

Ecomorphology is an integrative discipline that focuses on the relationship between organismal morphology and ecology and behavior. Its principal tenet is the use of whole-animal performance measures to link morphology to ecology and behavior. Done in a comparative phylogenetic framework, patterns of ecomorphological evolution can be identified. The feeding ecomorphology of a clade of lizards, the Crotaphytidae, is a contribution to such research. Trophic apparatus morphology, dietary ecology, feeding behavior, and bite-force performance are examined; ecomorphological links are identified.;Interspecific comparison of the trophic apparatus morphology of crotaphytid lizards shows that derived taxa in the genera examined exhibit a pattern of reduced cranial and rostral robustness as well as elongation of the rostrum. Analysis of the dietary ecology of crotaphytids reveals that saurophagous specialization is a derived characteristic positively correlated with reduced cranial robustness and rostral elongation. Also, durophagous specialization, i.e., consumption of hard-integumented insect taxa, is ancestral for Crotaphytus and positively correlated with great cranial robustness and rostral truncation. Examination of crotaphytids dispatching prey lizards reveals that C. collaris, with a robust cranium and short rostrum, uses head-crushing bites during saurophagy. Gambelia wislizenii , with a relatively lightly built cranium and elongate rostrum, uses holding compressive bites to the torso to incapacitate prey lizards. Crotaphytus bicinctores, a morphological intermediate, exhibits a composite of the behaviors observed for the other species.;Quantification of bite-force performance shows that reduced cranial robustness, rostral elongation, and increased saurophagy are correlated with reduced peak bite-force performance and increased holding bite-force performance. The phylogenetic perspective reveals that this is a general derived pattern for both genera. Great cranial robustness, rostral truncation, and elevated durophagous habits are correlated with higher peak bite-force performance. Additional data on the dietary ecology of G. sila, a basal species of Gambelia, are required to evaluate whether or not this pattern is similarly derived for both genera. Among crotaphytid taxa, an ability to generate great peak bite forces is associated with head-crushing behavior. In contrast, low peak bite-force performance and high holding bite-force performance is correlated with torso-compression behavior, a pattern that may be convergent between Crotaphytus and Gambelia.