A View from the Other Side of the World: Middle Triassic Ichthyosaurs of Nevada and Their Implications for the Initial Phase of the Mesozoic Marine Revolution in the Eastern Pacific Realm

早三叠纪和中三叠纪是我们理解生态系统组织和进化的关键时期，因为它代表了地球历史上最具破坏性的灭绝事件（二叠纪末）之后现代生态系统结构建立的时间。在海洋领域，次级水生爬行动物，特别是鱼龙和翼龙，迅速发展，被认为是所谓的中生代海洋革命（MMR）的关键因素，在此期间，海洋营养网向现代结构的重组发生了。虽然在特提斯王国的浅水环境中收集了大量数据，但对太平洋王国的开放水域动物群的了解相对较少，这使得我们对脊椎动物进化的这一关键阶段的认识存在重大空白。在这里，我们试图解决这一问题和差距，以便全面了解特提斯和太平洋领域之间的动物差异。这为真正理解P/T灭绝事件后海洋生态系统的恢复和结构以及相关的生物地理模式奠定了基础。我们的工作包括几种方法，实地和收集为基础。我们建议系统地勘探内华达州中部奥古斯塔山脉未勘探的中三叠世化石山成员露头，这有望进一步发现与太平洋地区开放水域环境高度相关的海洋爬行动物。之前的野外季节已经发现了保存完好的中型怀孕鱼龙骨架，以及巨型鱼龙骨架的前三分之一（头骨长度1.95米）。这个壮观的标本不同于Thalattoarchon，二级水生四足动物中的第一个大型捕食者，在更大的尺寸上，特别是鱼食性牙齿。结合对洪堡山脉和奥古斯塔山脉的混合鱼龙和棘骨鱼龙的重新评价，这些新标本的解剖描述将为了解早期鱼龙的形态差异和繁殖策略提供重要的数据。系统发育分析将为详细讨论早期鱼龙的进化以及进一步分析生物地理和生态系统结构提供基础。系统工作之后将对营养关系进行分析，因为这些关系在建立生态系统和海洋爬行动物的辐射中起着不可或缺的作用。该项目将与DFG已经资助的另一个项目密切结合，即对化石山成员的氨气动物群和生物地层学的调查。

The Early and Middle Triassic represent crucial time periods for our understanding of the organization and evolution of ecosystem because it represents the time the modern ecosystem structure was established after the most devastating extinction event in Earth history at the end of the Permian. In the marine realm, secondarily aquatic reptiles, in particular ichthyosaurs and sauropterygians, radiated quickly and are considered key elements of the so called Mesozoic Marine Revolution (MMR) during which a reorganization of marine trophic webs towards their modern structure took place. While much data has been gathered on the shallow-water environments of the Tethys realm, comparatively little is known on the open water fauna of the Pacific realm, leaving a significant gap in our knowledge of this crucial phase of vertebrate evolution. Here we seek to address this and gap in order to gain a comprehensive picture of the faunal differences between the Tethys and Pacific realms. This forms the foundation for a true understanding of the recovery and structuring of marine ecosystems after the P/T extinction events and the associated biogeographic patterns. Our work involves several approaches, field- and collections-based. We propose to systematically prospect the unexplored fossiliferous Middle Triassic Fossil Hill Member outcrops in the Augusta Mountains in Central Nevada which promise to yield further highly relevant finds of marine reptiles of the open water environment in the Pacific realm. Previous field seasons have yielded well-preserved skeletons of a medium-sized pregnant ichthyosaur as well as the anterior third of the skeleton of a giant ichthyosaur (skull length 1.95 m). This spectacular specimen differs from Thalattoarchon, the first macropredator among secondarily aquatic tetrapods, in the even larger size and particularly the piscivorous dentition. In combination with a reevaluation of mixosaurid and cymbospondylid ichthyosaurs from the Fossil Hill Member of both the classical Humboldt Range and the Augusta Mountains, anatomical description of these new specimens will provide important data for understanding morphological disparity and reproductive strategies in early ichthyosaurians. A phylogenetic analysis will provide the foundation for a detailed discussion of early ichthyosaurian evolution as well as further analyses of the biogeography and ecosystem structures. Systematic work will be followed by an analysis of trophic relationships because these play an integral role in the establishment of the ecosystem and the radiation of marine reptiles. The project will integrate closely with another project already funded by the DFG, the investigation of the ammonoid fauna and biostratigraphy of the Fossil Hill Member.