Biogeography and dietary ecomorphology of squamate reptiles: exploring modern patterns and the Paleogene fossil record in continental North America

Abstract

Squamate reptiles (lizards and snakes) are a taxonomically diverse (> 11,000 extant species), morphologically disparate, and ecologically varied clade of tetrapod vertebrates, with an extensive fossil record spanning at least the last 240 million years of Earth history. Most squamates are (and were) ectothermic and poikilothermic, or reliant on heat from their external environments to power their metabolisms and aid in thermoregulation. Therefore, squamates are closely linked with their immediate habitats and broader environments, making them useful as (paleo)climatic proxies. However, not all squamate groups respond similarly to the same climatic parameters across different geographic scales. Squamates also have diverse diets, ranging from herbivory to hypercarnivory. These diets appear to be qualitatively reflected by tooth morphology, but quantitative studies of squamate dietary ecomorphology are limited. New applications of high-resolution computed tomography (CT) scanning and three-dimensional (3D) dental topographic methods, previously developed with and applied to mammals, could help quantify and elucidate trends in extant squamate dietary ecomorphology. The logical extension of these methods to the fossil record could provide novel insights into extinct squamate diets and the possible paleoecological responses (or lack thereof) of ancient squamates to past episodes of global climate change and/or environmental perturbations. One such episode, the Paleocene–Eocene thermal maximum (PETM) ~56 Ma, is uniquely positioned as perhaps the closest past geologic analog to our modern anthropogenic climate change experiment. Studying fossil squamates from the PETM could expand our understanding of the possible impacts that rapid climatic and environmental changes may have had on ancient squamate faunas, and also provide insights into the potential ecological responses of modern squamates to continued anthropogenic climate change. My dissertation research addresses these major themes and more using GIS techniques, high-resolution CT scanning, 3D dental topographic analysis, and myriad quantitative statistical methods and analyses. Herein, I deconstruct the latitudinal and environmental gradients of extant squamate diversity across continental North America, explore the dietary ecomorphology of extant squamates using 3D dental topographic analysis, and then apply those same 3D dental topographic methods to fossil lizards from the Bighorn Basin of Wyoming to investigate their possible paleoecological responses to the PETM.