The anatomy of Late Triassic drepanosauromorphs is re-examined, with a focus on the previously published surface models of the holotype of Avicranium renestoi from the Norian of North America. We comment on the cranial anatomy of this taxon and propose a new reconstruction of the skull and mandible. Contrary to previous interpretations, the entire rostrum and most of the palate are not preserved in this specimen. We also suggest that some proposed plesiomorphic characters may result from incomplete ossification due to immaturity. These new observations are compiled into a new morphological phylogenetic dataset designed to address the monophyly of ‘Avicephala’, the group comprising the Late Permian gliding reptiles Weigeltisauridae, and the Late Triassic chameleon-like Drepanosauromorpha. We recover Weigeltisauridae as stem-saurian diapsids and Drepanosauromorpha as sister-group to Trilophosauridae among archosauromorphs, thus implying the paraphyly of ‘Avicephala’. Drepanosauromorphs and trilophosaurids are recovered as sister-taxa for the first time, as supported by several cranial and postcranial synapomorphies. This new phylogenetic position of Drepanosauromorpha reduces the group’s ghost lineage that now does not necessarily cross the Permian–Triassic boundary. However, much remains unknown of the early history of trilophosaurids and drepanosauromorphs, and of the evolution of arboreality in Triassic archosauromorph reptiles.

中文翻译：

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两根羽毛的“鸟”：Avicranium renestoi 和鸟头爬行动物的并系动物（Diapsida：“Avicephala”）

重新研究了晚三叠世的drepanosauromorphs的解剖结构，重点是先前发表的来自北美诺里安人的Avicranium renesto正模模型的表面模型。我们评论了该分类单元的颅骨解剖结构，并提出了头骨和下颌骨的新重建。与之前的解释相反，整个喙部和大部分上颚都没有保存在这个标本中。我们还认为，一些拟议的拟形特征可能是由于不成熟导致的不完全骨化造成的。这些新的观察结果被编译成一个新的形态系统发育数据集，旨在解决“Avicephala”的单系性问题，该群体包括晚二叠世滑翔爬行动物 Weigeltisauridae 和晚三叠世变色龙状 Drepanosauromorpha。我们将 Weigeltisauridae 恢复为干蜥双孔类，并将 Drepanosauromorpha 恢复为主龙类中 Trilophosauridae 的姐妹群，因此暗示“Avicephala”的并系。角龙类和三叶龙类首次作为姊妹类群被发现，并得到了一些颅内和颅后联征性的支持。三角龙形目的这一新的系统发育位置减少了该类群的幽灵谱系，现在不一定跨越二叠纪-三叠纪边界。然而，对于三叶龙科和角龙类的早期历史，以及三叠纪主龙类爬行动物的树栖进化，人们仍然知之甚少。