Data from: An exceptionally preserved Jurassic skink suggests lizard diversification preceded fragmentation of Pangaea

The present distribution of lizards is usually explained as a result of relatively recent global events, i.e. faunal turnovers or exchanges within and between particular continents mostly connected with glaciations and land-bridges. However, today’s disjunct distribution of the North American Xantusiidae and African Cordyliformes (close relatives of skinks) does not fit generally accepted biogeographic patterns. A new exquisitely preserved specimen of the Late Jurassic lizard Ardeosaurus brevipes from the Solnhofen area, Germany sheds some light on the problem. A posterior projection of its parietal is known only in the Dibamidae, Gekkota, and Scincoidea, taxa representing first branches on the molecular tree of lizards. The projection of the parietal is proposed to be an apomorphy of the Squamata that was lost in the common ancestor of Lacertoidea and Toxicofera (snakes, anguimorphs and iguanians). This implies a basalmost position of A. brevipes on the Squamata tree. The location of the supratemporal such as in A. brevipes characterizes all the Scincoidea and some geckos, but most geckos lack osteoderms, which are common in Scincoidea. This makes A. brevipes the oldest known crown-member of this lineage. Moreover, this indicates that the main groups of modern lizards were present already in the Jurassic. Ancestors of Cordyliformes migrated to Gondwana in the Late Jurassic together with dinosaurs, prior to the Cretaceous separation of this ancient continent.

当前蜥蜴类的分布格局通常被归因于相对较近的全球性地质事件，即主要与冰期及陆桥相关的特定大陆内部及大陆间的动物群更替或物种交流。然而，现今北美夜蜥科（Xantusiidae）与非洲环尾蜥目（Cordyliformes，石龙子的近亲类群）的间断分布格局，并不符合学界公认的生物地理学模式。产自德国索伦霍芬地区的一件保存极为完好的晚侏罗世苍蜥（Ardeosaurus brevipes）新标本，为该问题提供了新的研究线索。该标本的顶骨存在后突结构，这种结构仅见于双足蜥科（Dibamidae）、壁虎下目（Gekkota）以及石龙子超科（Scincoidea）——这些类群均为蜥蜴分子系统发育树中的基部分支类群。研究认为，顶骨后突是有鳞目（Squamata）的一项特有衍征，该特征在蜥蜴超科（Lacertoidea）与有毒类群（Toxicofera，包含蛇类、蛇蜥亚目及鬣蜥亚目）的共同祖先中发生了丢失。这一特征表明短苍蜥（A. brevipes）在有鳞目系统发育树中处于最基部的位置。短苍蜥所具有的上颞骨位置特征，在所有石龙子超科类群以及部分壁虎类群中均存在，但多数壁虎类群不具备石龙子超科中常见的骨板结构。据此，短苍蜥成为该支系目前已知最古老的冠群成员。此外，该发现表明现代蜥蜴的主要类群在侏罗纪时期就已经出现。环尾蜥目的祖先类群在晚侏罗世便与恐龙一同迁徙至冈瓦纳大陆，早于该古老大陆在白垩纪时期的裂解事件。