Landmarking data for mandible specimens from Ecomorphological diversification of squamates in the Cretaceous

Squamates (lizards and snakes) are highly successful modern vertebrates, with over 10 000 species. Squamates have a long history, dating back to at least 240 million years ago (Ma), and showing increasing species richness in the Late Cretaceous (84 Ma) and Early Paleogene (66–55 Ma). We confirm that the major expansion of dietary functional morphology happened before these diversifications, in the Mid-Cretaceous, 110–90 Ma. Until that time, squamates had relatively uniform tooth types, which then diversified substantially and ecomorphospace expanded to modern levels. This coincides with the Cretaceous Terrestrial Revolution, 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. There was also an early Late Cretaceous (95–90 Ma) rise in jaw size disparity, driven by the diversification of marine squamates, particularly early mosasaurs. These events established modern levels of squamate feeding ecomorphology before the major steps in species diversification, confirming decoupling of diversity and disparity. In fact, squamate feeding ecomorphospace had been partially explored in the Late Jurassic and Early Cretaceous, and jaw innovation in Late Cretaceous squamates involved expansions at the extremes of morphospace.

有鳞目（Squamates）涵盖蜥蜴与蛇类，是现生最为成功的脊椎动物类群之一，现存物种数量超过10000种。该类群的演化历史可追溯至至少2.4亿年前（Ma），并在晚白垩世（Late Cretaceous，84 Ma）与古近纪早期（Early Paleogene，66–55 Ma）呈现出物种丰富度持续增长的趋势。本研究证实，有鳞类摄食功能形态学（dietary functional morphology）的重大扩张发生于上述物种辐射演化之前，即白垩纪中期（Mid-Cretaceous，110–90 Ma）。在此之前，有鳞类的牙齿类型相对统一；此后其牙齿类型发生显著的辐射分化，生态形态空间（ecomorphospace）也扩张至现代水平。这一演化节点与白垩纪陆地革命（Cretaceous Terrestrial Revolution）高度吻合：彼时被子植物开始主导陆地生态系统，为植食性与传粉昆虫提供了全新的生态位，而这些昆虫又成为植食性与食虫性有鳞类的全新食物来源。晚白垩世早期（95–90 Ma）还出现了颌骨大小差异度（jaw size disparity）的上升，这一现象由海洋有鳞类（尤其是早期沧龙类（mosasaurs））的辐射分化所驱动。上述事件在物种大规模辐射演化之前，就已奠定了现生有鳞类摄食生态形态的基本格局，证实了物种多样性与形态差异度的解耦（decoupling of diversity and disparity）关系。事实上，有鳞类的摄食生态形态空间在侏罗纪晚期（Late Jurassic）与白垩纪早期（Early Cretaceous）就已得到部分探索，而晚白垩世有鳞类的颌骨革新则表现为生态形态空间极端区域的进一步扩张。