Abstract We describe the detailed cranial osteology of Sapeornis chaoyangensis based on information from previously described specimens and IVPP V19058, a specimen that was recently reported with regards to the palatal elements but not fully described. The skull in this specimen is entirely preserved in disarticulation, providing the most comprehensive glimpse into the morphology of the cranial bones and their articulations for this taxon. Based on the new information extracted from this specimen, we revise some interpretations of cranial elements in previously published Sapeornis specimens and provide a comprehensive description of the cranial osteology for this basal pygostylian. The results of this study demonstrate that the postorbital bar, jugal bar, nasal, quadrate, and palate in Sapeornis show the plesiomorphic rigid articulations among birds. The comparison of cranial features across Paraves suggests that major cranial modifications evolved at the base of Ornithothoraces, and primarily in the ornithuromorph lineage.

中文翻译：

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早白垩世 Sapeornis chaoyangensis (Aves: Pygostylia) 的颅骨骨学

摘要 我们根据先前描述的标本和 IVPP V19058 的信息描述了 Sapeornis chaoyangensis 的详细颅骨骨学，IVPP V19058 是最近报道的关于腭部元素但未完全描述的标本。该标本中的头骨完全保留在脱节状态，提供了对该类群颅骨形态及其关节的最全面了解。根据从该标本中提取的新信息，我们修改了先前发表的 Sapeornis 标本中颅骨元素的一些解释，并提供了对这种基底后尾骨的颅骨骨学的全面描述。本研究的结果表明，眶后杆、颈后杆、鼻、方形、Sapeornis 的上颚和上颚显示了鸟类之间的拟形刚性关节。Paraves 颅骨特征的比较表明，主要的颅骨修饰是在鸟胸科的基部进化的，主要是在鸟形谱系中。