New insights on the osteology of istiodactyliforms from the Jehol Biota: new material of <i>Hongshanopterus lacustris</i> Wang et al., 2008 and restudy of <i>Nurhachius ignaciobritoi</i> Wang et al., 2005

The Istiodactyliformes, a group of short-toothed Cretaceous pterosaurs including istiodactylids and their relatives, have mostly been reported from the Jehol Biota of Northeastern China. Recently, a new specimen of <i>Hongshanopterus lacustris</i>, an istiodactyliform from the Lower Cretaceous Jiufotang Formation, has been unveiled. Here we present a detailed description of a new specimen, which comprises most of the skull, the mandible, several cervical vertebrae, and plenty of isolated teeth, providing additional anatomical information of this taxon. We also present the comprehensive redescription of the holotype of <i>Nurhachius ignaciobritoi</i>, the first reported istiodactylid from China. Most of the previously suggested variances between <i>Nurhachius</i> specimens are here found invalid to separate different taxa, but the holotype has a shorter rostrum compared with others. Additional morphological information revealed by the new specimen and redescription further supports the affinity between <i>Hongshanopterus</i> and istiodactylids, and between istiodactylids and other pteranodontoids, but istiodactylids possess narrower cervical vertebrae compared with anhanguerians.短齿翼龙形类（Istiodactyliformes）是一类具有短齿特征的白垩纪翼龙类群，涵盖梳颌翼龙科（Istiodactylidae）及其近缘类群，其化石记录绝大多数发现于中国东北地区的热河生物群（Jehol Biota）。近日，一件产自下白垩统九佛堂组（Lower Cretaceous Jiufotang Formation）的新标本被正式发表，该标本隶属于梳颌翼龙形类的湖生红山翼龙（Hongshanopterus lacustris）。本文详细记述了这件新标本的形态特征：其保存了大部分头骨、下颌骨、多节颈椎以及大量孤立牙齿，为该分类单元（taxon）提供了更多解剖学信息。同时，我们对中国首件被报道的梳颌翼龙科物种——伊格纳西奥诺氏翼龙（Nurhachius ignaciobritoi）的正模标本（holotype）进行了全面的重新描述。本次研究发现，此前被认为可区分不同类群的诺氏翼龙（Nurhachius）标本间的多数形态差异均为无效特征，不过该属正模标本的吻部（rostrum）确实较其他标本更短。通过新标本与正模重新描述所揭示的额外形态学信息，进一步支持了红山翼龙与梳颌翼龙科、以及梳颌翼龙科与其他无齿翼龙超科（Pteranodontoidea）类群的亲缘关系；但相较于安汉格翼龙类（anhanguerians），梳颌翼龙科的颈椎更为狭窄。