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

[9706021]奥陶纪的辐射是生命史上最大的辐射之一。目前对奥陶纪辐射的认识主要是基于对单个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学的第一次实地考察。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所取代。诸如腕足类、苔藓虫、皱珊瑚和板状珊瑚、棘皮类、叠层孔虫和头足类等群体上升到优势地位。海洋科的多样性增加了两倍，反映了海洋中形态多样性的大大增加。随着许多新公会的建立，社区的复杂性显著增加。在本研究中，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（地质上的），阶梯式的，还是某种组合？2)不同的进化支是在群体内一致扩展，还是在大时间尺度上综合起来看，它们只是看起来有联系？3)寒武纪动物群是否在社区发展过程中发生了迁移？或者它仍然存在于社区中，只是被稀释了（Westrop et al., 1995）？4)社区复杂性是如何增加的？例如，是新的群落被添加到生态系统中，还是进化枝只是被添加到现有的群落中？该项目将检查保存在大盆地的碳酸盐台地矿床。这个地区拥有世界上最优秀的奥陶纪浅海动物记录，是开展这项研究的理想场所。野外工作将在内华达州的Cherry Creek Range、Egan Range南部、Hot Creek Range南部以及犹他州的Bear River Range和Ibex地区进行。重点将放在保存在尾岩和灰岩相中的浅海软基质群落上。选择这种环境有几个原因。在这些相中，壳类的再加工很少。通过将研究限制在一个一般环境中，而不是一个完整的水深样带，可以避免辐射期间发生的陆上和海上变化所导致的并发症。初步研究表明，这些群落在奥陶纪至少重组了5次。下、中、上伊贝县、下、中怀特洛克和莫霍克—辛辛那提6个地层层段的群落类型各具特色，且日益多样化和复杂化。初步证据还表明，在每个间歇期开始时，群落的重组可能发生得很快。如果重组是快速的，群落可能是稳定的，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.