Meeting Abstract
Large-scale evolutionary studies typically have invoked extrinsic factors (e.g. environment), but intrinsic factors, such as developmental constraint, ultimately shape the variation available to natural selection. While comprehensive studies on cranial evolution in birds and mammals have analyzed how patterns of trait covariation have influenced their diversification, parallel investigations into other major vertebrate clades remain elusive. With >10,000 known extant species, squamates (lizards, snakes) exhibit remarkable variation in cranial morphology and ecological modes. To identify the integrated structures that underpin their cranial disparity, we present the first squamate-wide analysis of cranial shape harnessing a new, high-dimensional geometric morphometric dataset comprising ~1,000 3D landmarks and ~200 modern and extinct species. With this rich phenotypic dataset, we identify a shared set of highly integrated regions in lizards and snakes despite their fundamental differences in form. Meanwhile, we find no evidence that the magnitude of trait integration within those regions has constrained or promoted phenotypic evolution across squamates. In fact, our analyses demonstrate highly mosaic patterns across these cranial regions that dictate morphological novelty and disparity, particularly those associated with fossoriality, major changes in diet, and elaborate cranial ornamentations. Our results also suggest that earlier ossifying regions exhibit weaker trait integration. Collectively, this study highlights the incredible potential of an emerging class of comparative studies that combines high-density morphological data with modern evolutionary analyses.
