A tiny new Middle Triassic stem-lepidosauromorph from Germany: implications for the early evolution of lepidosauromorphs and the Vellberg fauna

The Middle Triassic was a time of major changes in tetrapod faunas worldwide, but the fossil record for this interval is largely obscure for terrestrial faunas. This poses a severe limitation to our understanding on the earliest stages of the diversification of lineages representing some of the most diverse faunas in the world today, such as lepidosauromorphs (e.g., lizards and tuataras). Here, we report a tiny new lepidosauromorph from the Middle Triassic from Vellberg (Germany), which combines a mosaic of features from both early evolving squamates and rhynchocephalians, such as the simultaneous occurrence of a splenial bone and partial development of acrodonty. Phylogenetic analyses applying different optimality criteria, and combined morphological and molecular data, consistently recover the new taxon as a stem-lepidosauromorph, implying stem-lepidosauromorph species coinhabited areas comprising today’s central Europe at the same time as the earliest known rhynchocephalians and squa...中三叠世（Middle Triassic）是全球四足动物群发生重大演化变革的时期，但该时段的陆生动物群化石记录整体较为模糊。这极大限制了我们对现今全球多样性最高的动物群之一的代表支系——鳞龙形类（lepidosauromorphs，如蜥蜴与喙头蜥）——早期辐射演化阶段的认知。本文报道了一件产自德国韦尔贝格（Vellberg）中三叠世地层的小型新鳞龙形类化石，其兼具早期演化的有鳞目（squamates）与喙头目（rhynchocephalians）的镶嵌演化特征，例如同时保留夹板骨（splenial bone）与部分端生齿（acrodonty）的发育特征。采用不同最优准则、结合形态学与分子数据开展的系统发育分析，均一致将该新分类群恢复为基干鳞龙形类（stem-lepidosauromorph），这表明基干鳞龙形类物种与已知最早的喙头目和squa……类群同期共存于现今中欧区域。