Staatliches Museum für Naturkunde Stuttgart, Rosenstein 1, D-70191, Stuttgart, Germany.
Department of Organismic and Evolutionary Biology, Museum of Comparative Zoology, Harvard University, Cambridge, MA, 02138, USA.
Sci Rep. 2020 Feb 20;10(1):2273. doi: 10.1038/s41598-020-58883-x.
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 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 squamates. It further demonstrates a more complex evolutionary scenario for dental evolution in early lepidosauromorphs, with independent acquisitions of acrodonty early in their evolutionary history. The small size of most terrestrial vertebrates from Vellberg is conspicuous, contrasting to younger Triassic deposits worldwide, but comparable to Early Triassic faunas, suggesting a potential long-lasting Lilliput effect in this fauna.
中三叠世是全球四足动物群发生重大变化的时期，但这一时期的陆生动物群化石记录在很大程度上不为人知。这严重限制了我们对当今世界上一些最多样化的动物群（如蜥蜴类和楔齿蜥类）的代表谱系最早多样化阶段的理解。在这里，我们报道了来自德国韦尔堡（Vellberg）的一个新的中三叠世微小的蜥蜴形类，它结合了早期演化的有鳞目和喙头目（例如，同时出现的间蝶骨和部分发展的前齿型）的特征镶嵌体。应用不同最优性标准的系统发育分析，以及结合形态和分子数据，一致将新分类群恢复为基干蜥蜴形类，这意味着基干蜥蜴形类物种与最早的已知喙头目和有鳞目同时共同生活在今天的中欧地区。它进一步证明了早期蜥蜴形类牙齿进化的更复杂的进化场景，在前齿型的进化历史早期独立获得了前齿型。与全球年轻的三叠纪沉积物相比，韦尔堡大多数陆生脊椎动物的体型较小，引人注目，但与早三叠世的动物群相当，这表明该动物群可能存在长期的利立浦特效应。
