Late Ordovician brachiopod faunal endemism and mass extinction during drastic climate change, ocean anoxia and sea-level fluctuations

我们今天对全球变暖的担忧是它对海平面上升和生物多样性变化的影响。对现代全球气候和生物多样性变化的研究仅限于十年到千年的范围。古生物学家根据保存在沉积岩中的化石记录，在百万年的尺度上研究地球历史上的环境和生物多样性变化，从而提供独特和有价值的数据和解释，以补充对现代和最近全球变化的研究。在显生界地球历史的过去5.3亿年(MYR)中，全球海平面上升最盛大的两次事件之一发生在晚奥陶世(460-443MYR前)，当时北美大部分地区被陆表海淹没，海洋生物在其中繁衍生息，腕足类是占主导地位的底栖壳生物。紧随其后的是奥陶纪末期冰川和大灭绝事件。在这项建议中，将研究北美丰富的腕足类化石记录，以确定晚奥陶世海洋底栖贝壳动物对海平面剧烈变化的响应。特别是以下问题：1)陆缘腕足动物群是如何在晚奥陶世海平面高位期间产生陆缘-海动物群并随后被陆缘-海相动物群取代的？2)为什么陆缘腕足动物群在晚奥陶世海侵期间变得高度特有，而在其他类似的高海平面期间却没有？3)为什么奥陶纪末期冰川导致了大规模灭绝，而其他主要冰川没有？解决这些问题的途径是利用分支学、多元和其他数值分析方法，从大陆边缘(如安提科里盆地、辛辛那提拱门、麦肯齐山脉)到内陆盆地(密歇根哈德逊湾和威利斯顿盆地)，通过晚奥陶世海平面波动，在物种、属、群落和动物群水平上追踪腕足类的演化。建议的研究成果可以帮助我们从地球历史上百万年尺度的全球气候-生物多样性变化的角度更好地理解现代全球变化。

Our concern about global warming today is its effect on sea level rise and biodiversity change. The study of modern global change in climate and biodiversity is confined to the scale of decade to millennium. Paleontologists investigate environmental and biodiversity changes in Earth history at a million-year scale based on fossil record preserved in sedimentary rocks and thus provide unique and valuable data and interpretations to complement studies on modern and recent global change. During the past 530 million years (myr) of the Phanerozoic Earth history, one of the two grandest episodes of global sea-level rises occurred in the Late Ordovician (460–443 myr ago), when much of North America was flooded by epicontinental seas, in which marine life thrived, with brachiopods being the dominant benthic shelly organisms. This was followed by a terminal Ordovician glaciation and mass extinction event. In this proposal, the rich brachiopod fossil record of North America will be studied to determine the responses of Late Ordovician marine benthic shelly faunas to drastic sea level changes. In particular, the following questions will be addressed: 1) How did the continental-margin brachiopod faunas give rise to, and was subsequently replaced by, the epicontinental-sea faunas during the Late Ordovician sea level highstand? 2) Why did the epicontinental brachiopod faunas become highly endemic during the Late Ordovician marine transgression but not during some other similarly high sea-level? and 3) Why did the terminal Ordovician glaciation cause a mass extinction, whereas other major glaciations did not? The approach to these questions is to trace the brachiopod evolution at the species, genus, community, and faunal levels from both continental-margin (e.g. Anticosti Basin, Cincinnati Arch, Mackenzie Mountains) to inland-basin (Hudson Bay, Michigan, and Williston basins) depositional environments through the Late Ordovician sea-level fluctuations, using cladistics, multivariate and other numerical analyses. Results from the proposed research can help us better understand modern global change from the perspective of million year-scale global climate-biodiversity changes in Earth history.