Mesozoic squamate mandible ecomorphospaces

Among modern vertebrates, squamates (lizards and snakes) are one of the most successful groups, with over 10,000 species and a broad range of ecological adaptations. Molecular phylogenetic studies point to the end-Cretaceous mass extinction, 66 million years ago (Ma) as the trigger for massive expansion of diversity in the Paleogene, and yet squamates had had a long fossil record dating back to the Triassic, over 240 Ma. Here we show that this diversity expansion was preceded by an expansion of morphological disparity and ecological function in the mid-Cretaceous, 120–100 Ma. We explore traits of the jaws and teeth as indicators of diet, and show that whereas all major modern clades had emerged by the Middle Jurassic (170 Ma), they had a limited range of dentitions, jaw shapes and sizes; ecomorphological diversity, range of body sizes, and overall trophic disparity all expanded substantially in the mid-Cretaceous, 120–100 Ma. This corresponds to the Cretaceous Terrestrial Explosion, when angiosperms began to take over terrestrial ecosystems, providing new roles for plant-eating and pollinating insects, which were in turn new sources of food for herbivorous and insectivorous squamates. The second, larger diversification of squamates happened in the Paleogene as angiosperms diversified further forming the first tropical rainforests.,Landmarking Geometric morphometrics,