Cranial and post-cranial remains and phylogenetic relationships of the Gondwanan meiolaniform turtle Peligrochelys walshae from the Paleocene of Chubut, Argentina

Peligrochelys walshae is a meiolaniform turtle originally described based on one specimen represented by cranial remains found in the classic locality of Punta Peligro (Chubut, Argentina) in outcrops of the Salamanca Formation (Danian). Recent field works in the vicinity of Punta Peligro resulted in the discovery of almost 30 new specimens, represented by cranial and postcranial remains that can be assigned to P. walshae. In this contribution we provide a detailed anatomical description of the new specimens, provide an emended diagnosis for the species, and explore its phylogenetic relationships based on all anatomical data available for the species. The new specimens bring valuable information about the anatomy of the skull and postcranium of P. walshae as well as for meiolaniforms in general. The 3D preservation of the skull bones allows us to provide a 3D reconstruction using novel techniques. The updated phylogenetic analysis confirms that P. walshae is part of the clade Meiolaniformes, which spans from the Early Cretaceous until the Holocene and contains the giant, horned turtles (Meiolaniidae). This phylogenetic analysis reinforces the previously hypothesis that the clade Meiolaniformes is dominated by Gondwanan taxa, but also includes some Laurasian representatives. Alternate phylogenetic positions of taxa included in Meiolaniformes in this analysis were tested using the Templeton test. The lineage leading to Peligrochelys walshae is the only meiolaniform non-meiolaniid lineage to have survived the K-Pg mass extinction; its study provides valuable information to evaluate the effects of the K-Pg extinction in turtles.

瓦尔沙佩利龟（Peligrochelys walshae）是一种美兰类龟类（Meiolaniformes），其最初的正式描述基于一件产自阿根廷丘布特省佩利格罗角（Punta Peligro）经典产地萨拉曼卡组（Salamanca Formation，达宁期（Danian））露头中的颅部化石标本。近期在佩利格罗角周边开展的野外考察中，研究团队发现了近30件新标本，这些标本带有可归属于瓦尔沙佩利龟的颅部及颅后骨骼遗骸。本研究对这批新标本开展了详细的解剖学描述，对该物种的鉴定特征进行了修订，并基于该物种已有的全部解剖学数据探讨了其系统发育关系。这批新标本为瓦尔沙佩利龟以及美兰类龟类整体的颅骨与颅后骨骼解剖学特征提供了宝贵的研究资料。颅骨骨骼的三维保存状态使得研究团队能够借助新兴技术完成三维重建。更新后的系统发育分析证实，瓦尔沙佩利龟隶属于美兰类龟演化支（Meiolaniformes）；该演化支的地质时限从早白垩世一直延续至全新世，包含巨型带角的梅兰尼龟科（Meiolaniidae）类群。本次系统发育分析进一步验证了此前的假说：美兰类龟演化支以冈瓦纳类群（Gondwanan taxa）为主，但也包含部分劳亚类群（Laurasian taxa）成员。本研究借助坦普尔顿检验（Templeton test），对本次系统发育分析中纳入的美兰类龟类各成员的不同系统发育位置进行了验证。指向瓦尔沙佩利龟的演化支是唯一幸存白垩纪-古近纪灭绝事件（K-Pg mass extinction）的非梅兰尼龟科美兰类龟演化支，对该类群的研究可为评估白垩纪-古近纪灭绝事件对龟类类群的影响提供珍贵的参考资料。