COLLABORATIVE RESEARCH: The Ecology of the Ordovician Radiation: Evidence From the Basin and Range Province of the Western U.S.A.

9706021 Droser T‘he奥陶纪辐射是生命史上最大的辐射之一。目前对奥陶系辐射的理解主要是基于对个体群体的分类研究和综合文献汇编。该项目将是对奥陶系辐射生态的首次实地考察。在奥陶纪辐射期间，寒武纪演化动物群被古生代演化动物群取代。腕足类、苔藓虫类、皱纹珊瑚和扁平珊瑚、棘皮动物、基质孔虫和头足类等类群占优势。海洋物种多样性增加了两倍，反映了海洋形态多样性的极大增加。随着许多新的行会的建立，社区的复杂性显著增加。在这项研究中，将解决四个基本问题：1)社区如何发展？社区层面的变化是渐进的、突然的(地质学上的)、阶梯式的还是某种组合的？2)不同的分支在社区内是一致扩展的，还是它们只是在大时间尺度上的汇编中看起来是相关的？3)寒武纪动物群在社区发展过程中实际上是移位的吗？或者它仍然存在于社区中，只是被冲淡了(Westrop等人，1995)？4)社区复杂性是如何增加的？例如，是将新的社区添加到生态系统中，还是仅仅将分支添加到现有社区？该项目将研究保存在大盆地中的碳酸盐台地沉积。该地区拥有世界上奥陶系中最好的浅海动物记录之一，使其成为进行这项研究的理想地点。PLS已经为这项提案进行了前期工作，并对该地区的奥陶系岩石和动物群进行了广泛的研究经验。实地工作将在内华达州的樱桃溪山脉、伊根山脉南部和热溪山脉南部以及犹他州的熊河山脉和伊贝克斯地区进行。重点将放在保存在怪石和石灰岩相中的浅海软基岩群落上。选择这种环境有几个原因。在这些相中，贝壳的返修微乎其微。通过将这项研究限制在一个一般的环境中，而不是一个完整的水深断面，可以避免辐射期间发生的陆上-近海变化所导致的复杂情况。初步工作表明，在奥陶纪，群落至少进行了5次重组。伊贝克期下部、中部和上部、怀特罗克期下部和中部以及莫霍基期-辛辛那提期六个地层段似乎具有独特的群落类型，这些群落类型日益多样化和复杂。初步证据还表明，社区的重组可能在每个间隔开始时发生得很快。如果重组是快速的，社区可能一直是稳定的，在这五个间隔的大部分时间里几乎没有发生变化。

9706021 Droser T'he Ordovician radiation was one of the largest radiations in the history of life. Current understanding of the Ordovician radiation is based largely on taxonomic studies of 'individual groups and on synthetic literature compilations. This project will be the first field-based examination of the ecology of the Ordovician radiation. During the Ordovician radiation the Cambrian Evolutionary Fauna was replaced by the Paleozoic Evolutionary Fauna. Groups, such as brachiopods, bryozoans, rugose and tabulate corals, echinoderms, stromatoporaids, and cephalopods rose to dominance. Marine family diversity tripled, reflecting vastly increased morphological diversity in the oceans. Community complexity increased significantly as many new guilds were established. In this study, four basic questions will be addressed: 1) How do the communities develop? Are community level changes gradual, sudden (geologically), stepped, or some combination? 2) Do different clades expand in concert within communities or do they just appear to be related when viewed in compilations on large-time scales? 3 ) Is the Cambrian fauna actually displaced during community development? Or is it still present m the communities and simply diluted (Westrop et al., 1995)? 4) How did community complexity increase? For example, are new communities added to the ecosystem or are clades simply added to existing communities? This project will examine carbonate platform deposits preserved in the Great Basin. This region has one of the finest records of shallow marine faunas in the Ordovician anywhere in the world, making it an ideal locale to conduct this study. The Pls have conducted preliminary work for this proposal and also have extensive experience studying Ordovician rocks and faunas of this region Field work will be conducted in the Cherry Creek Range, the southern Egan Range, and the southern Hot Creek Range in Nevada and 'm the Bear River Range and the Ibex region in Utah. T'he focus wi ll be on shallow-marine soft-substrate communities preserved in wackestone and limemudstone facies. This environment has been chosen for several reasons. Reworking of shells is minimal in these facies. By confining the study to one general environment, rather than a complete bathymetric transect, the complications that would result from onshore-offshore changes that took place during the radiation can be avoided. Preliminary work suggests that communities were reorganized at least 5 times during the Ordovician. Six stratigraphic intervals, lower, middle and upper Ibexian, lower and middle Whiterockian, and Mohawkian-Cincinnatian appear to have distinctive community-types that are increasingly diverse and complex. Preliminary evidence also suggests that the reorganizations of communities may have occurred quickly at the beginning of each interval. If reorganizations were rapid, communities may have been stable with little change occurring during the bulk of these five intervals.