The Jurassic rise of squamates as supported by lepidosaur disparity and evolutionary rates

The squamates (lizards, snakes, and relatives) today comprise more than 10,000 species, and yet their sister group, the Rhynchocephalia, is represented by a single species today, the tuatara. The explosion in squamate diversity has been tracked back to the Cretaceous Terrestrial Revolution, 100 million years ago (Ma), the time when flowering plants began their takeover of terrestrial ecosystems, associated with diversification of coevolving insects and insect-eating predators such as lizards, birds, and mammals. Squamates arose much earlier, but their long pre-Cretaceous history of some 150 million years (Myr) is documented by sparse fossils. Here, we provide evidence for an initial radiation of squamate morphology in the Middle and Late Jurassic (174–145 Ma), and show that they established their key ecological roles much earlier than had been assumed, and they have not changed them much since.

Methods
Landmarking

Geometric morphometrics

现存有鳞目（squamates，涵盖蜥蜴、蛇类及其近缘类群）的物种数量已逾10000种，而其姊妹群喙头蜥目（Rhynchocephalia）如今仅存1个物种，即喙头蜥（tuatara）。有鳞类的多样性爆发事件可追溯至1亿年前（100 Ma）的白垩纪陆地革命（Cretaceous Terrestrial Revolution），该时期被子植物开始主导陆地生态系统，与之协同演化的昆虫以及以昆虫为食的捕食类群（如蜥蜴、鸟类与哺乳类）也同步发生辐射分化。有鳞类的起源时间远早于此，但其长达约1.5亿年的白垩纪前演化历史仅依靠零星化石记录得以佐证。本研究首次提供了有鳞类形态在中侏罗世至晚侏罗世（174–145 Ma，即1.74亿至1.45亿年前）发生初始辐射演化的证据，并证实它们早在学界此前所推定的时间之前就已确立了核心生态角色，且此后其生态角色并未发生显著改变。
研究方法
地标标注（Landmarking）
几何形态测量学（Geometric morphometrics）