A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA
A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA
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DOI：
10.1080/14772019.2020.1748132
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发表时间：
2020-04-20
影响因子：
2.6
通讯作者：
Sander, P. Martin
中科院分区：
文献类型：
--
作者：
Klein, Nicole;Schmitz, Lars;Sander, P. Martin
报道了美国内华达州潘兴县奥古斯塔山脉Favret组化石山段晚期安尼期新分类群Cymbospondylus duelferi sp. nov.。全型和唯一的标本包括一个相当完整的颅骨，伴有关节和非关节的颅后材料。体长重建显示为中等体型个体，体长估计为4.3米。该标本的背椎骨以及左肱骨与三串铰接的尾巴和后背椎骨有关，其平均比中型个体的椎骨小68%。由于这些椎骨体积小，且位于躯干区域，它们很可能代表胎儿。Cymbospondylus duelferi sp. 11 .为鱼龙的胎生提供了第二古老的证据。在本研究的过程中，对C. petrinus和C. nichollsi的颅骨形态进行了回顾，并对两者的性状评分进行了修订。系统发育分析表明，新分类单元与C. petrinus具有姐妹分类单元关系，后者发现于同一地层单元，即化石山成员，也出现在洪堡山脉的经典化石山地区，该成员属于Prida组的一部分。Cymbospondylus duelferi sp. 11 .与C. petrinus和C. nichollsi有着非常相似的头骨形态，而肩带形态不同。由于在新标本中没有个体发育差异或性别二态性的证据，因此从化石山成员中识别出了第三种Cymbospondylus -忽略了仅从五个椎骨中已知的模式物种C. piscosus。该属在斯瓦尔巴群岛（北洋）和欧洲（特提斯）的下三叠纪和中三叠纪的进一步出现表明，在中三叠纪期间，cymbospondylids的辐射和扩散非常迅速。
A new taxon, Cymbospondylus duelferi sp. nov., is described from the late Anisian of the Fossil Hill Member of the Favret Formation of the Augusta Mountains, Pershing County, Nevada, USA. The holotype and only specimen consists of a fairly complete skull associated with articulated and disarticulated postcranial material. Body length reconstruction revealed a medium-sized individual with an estimated body length of 4.3 m. Dorsal vertebrae as well as the left humerus of this specimen are associated with three strings of articulated tail and posterior dorsal vertebrae, which are on average 68% smaller than the vertebrae of the medium-sized individual. Due to the small size of these vertebrae and their position within the trunk region, they most likely represent fetuses. Cymbospondylus duelferi sp. nov. provides the second-oldest evidence for viviparity in ichthyosaurs. In the course of this study, the skull morphology of C. petrinus and C. nichollsi was reviewed, resulting in revised character scorings for both. Phylogenetic analyses demonstrate a sister-taxon relationship of the new taxon with C. petrinus, which was found in the same stratigraphic unit, the Fossil Hill Member, that also crops out at the classical Fossil Hill locality in the Humboldt Range, where the member is part of the Prida Formation. Cymbospondylus duelferi sp. nov. shares a very similar skull morphology with C. petrinus and C. nichollsi, whereas the shoulder girdle morphology differs. Because there is no evidence for ontogenetic differences or sexual dimorphism in the new specimen, a third species of Cymbospondylus - neglecting the type species C. piscosus that is only known from five vertebrae - is recognized from the Fossil Hill Member. Further occurrences of the genus in the Lower and Middle Triassic of Svalbard (Boreal Ocean) and Europe (Tethys) point to a very fast radiation and dispersal of cymbospondylids during the Middle Triassic.