Paleobiological and paleoenvironmental control on the origin and diversification of Late Ordovician and early silurian epicontinental brachiopod faunas of North America

当今对全球变暖的一个主要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尺度。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环境和生物多样性的变化。在显生宙过去5.3亿年（myr）的地球历史中，全球变暖和海平面上升的两个最伟大的时期之一发生在晚奥陶世-早志留世（460-430 myr），当时北美古大陆被陆表海淹没，海洋生物繁盛，其中腕足类动物是主要的底栖动物。本文通过对北美洲丰富的腕足类化石记录的研究，探讨了陆表海洋壳类动物群的几个关键问题：1)陆表海洋壳类动物群在全球变暖和海洋海侵过程中是如何起源、分散和多样化的？2)陆表腕足动物群为何在晚奥陶世海侵期间分离，而在早志留世时期却没有分离？3)在晚奥陶世—早志留世，是什么样的环境和生物因素控制了同时期腕足动物区系的分化和生物多样性的时间波动？解决这些问题的方法是比较大陆边缘海（如Anticosti盆地、Mackenzie山脉、加拿大北极地区）和内陆盆地（Hudson Bay、Michigan和Williston盆地）的腕足动物区系，并利用分支分析和多变量分析追踪几种腕足动物谱系及其古生态环境的形态变化。研究结果可以帮助我们从百万年尺度的全球变暖和古代地球历史上发生的生物多样性变化的角度更好地理解现代全球变化。

A major concern about the 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. During the past 530 million years (myr) of the Phanerozoic Earth history, one of the two grandest episodes of global warming and sea-level rise occurred in Late Ordovician-Early Silurian time (460-430 myr ago), when the North American paleocontinent was flooded by epicontinental seas, in which marine life thrived, with brachiopods being the dominant benthic shelly organisms. In this proposal, the rich brachiopod fossil records of North America will be studied to address several key questions regarding the epicontinental marine shelly faunas: 1) How did the epicontinental brachiopod faunas originate, disperse, and diversify during the global warming and marine transgression? 2) Why did the epicontinental brachiopod faunas become isolated during the Late Ordovician marine transgression but not during the Early Silurian episode? and 3) What environmental and biological factors controlled the differentiation of contemporaneous brachiopod faunas and the temporal fluctuations in biodiversity during the Late Ordovician-Early Silurian? The approach to these questions is to compare the brachiopod faunas between continental-margin seas (e.g. Anticosti Basin, Mackenzie Mountains, Arctic Canada) and inland basins (Hudson Bay, Michigan, and Williston basins), and by tracing the morphological changes in several brachiopod lineages and their paleoecological settings, using cladistic and multivariate analyses. Results from the proposed research can help us better understand modern global change from the perspective of million year-scale global warming and biodiversity change that occurred in ancient Earth history.