Ecology of the Ediacaran-Cambrian transition: The trace-fossil record

埃迪卡拉-寒武纪界线（541 Ma）是生物圈历史上的一个主要分界线。埃迪卡拉纪的生物群以软体生物为主，这些生物现在被认为在很大程度上与现代后生动物无关。另一方面，寒武纪见证了几乎所有现代动物群体的快速发展，这是一个被称为寒武纪大爆发的重大进化事件。大多数关于埃迪卡拉-寒武纪过渡的进化研究都是基于对身体化石和分子钟的分析。然而，痕迹化石记录（由动物留下的足迹、足迹和洞穴组成）为校准寒武纪大爆发提供了一条独立的证据线。尽管有几篇优秀的开创性论文考虑了这种转变的技术，但仍然缺乏定量和系统的分析来检验关于寒武纪大爆发的时间和意义的相互竞争的假设。综合沉积学、技术和地层学分析提供了对这些古老生态系统生态学的一瞥，并与了解埃迪卡拉-寒武纪过渡时期的底栖生物群落特别相关。该项目的目的是：(1)系统地评价生命历史上这一关键区间的痕迹化石记录；(2)在层序-地层框架内整合技术和沉积学信息，以评估寒武纪辐射在沉积剖面上的影响和程度。计划开展的活动包括：(1)对阿根廷、加拿大、南非、纳米比亚和伊朗的埃迪卡拉-寒武纪几个演替区进行野外考察；(2)对关键的化石标本进行修订；(3)分析埃迪卡拉-寒武纪的生物区系数据库。生态学理论的最新发展和对微量化石的行为学意义的日益了解，为我们对生物圈历史上这一关键时刻的看法取得重大突破铺平了道路。这项新的分析将为寒武纪辐射事件的年表以及这一重大事件的宏观进化和生态意义提供更全面的图景。

The Ediacaran-Cambrian boundary (541 Ma) represents a major divide in the history of the biosphere. Ediacaran biotas were dominated by soft-bodied organisms that are now considered for the most part to be unrelated with modern metazoans. On the other hand, the Cambrian witnessed the rapid development of almost all modern groups of animals, a major evolutionary event known as the Cambrian explosion. The majority of evolutionary studies on the Ediacaran-Cambrian transition have been based on the analysis of body fossils and molecular clocks. However, the trace-fossil record (that consisting of tracks, trails and burrows produced by animals) provides an independent line of evidence to calibrate the Cambrian explosion. Although several excellent pioneering papers have considered the ichnology of this transition, there is still a lack of quantitative and systematic analysis to test the competing hypotheses on the timing and significance of the Cambrian explosion. Integrated sedimentological, ichnological and stratigraphical analysis provides a glimpse into the ecology of these ancient ecosystems and is particularly relevant to understanding the benthic communities of the Ediacaran-Cambrian transition. The aims of this project are: (1) to systematically evaluate the trace-fossil record across this critical interval in the history of life, and (2) to integrate ichnologic and sedimentologic information within a sequence-stratigraphic framework, in order to evaluate the impact and extent of the Cambrian radiation across a depositional profile. Planned activities include: (1) fieldwork in several Ediacaran-Cambrian successions in Argentina, Canada, South Africa, Namibia and Iran, (2) revision of key trace-fossil collections, and (3) analysis of a database of Ediacaran-Cambrian ichnofaunas. Recent developments in ecology theory and a growing understanding of the ethologic significance of trace fossils is paving the way for a major breakthrough in our view of this critical time in the history of the biosphere. This new analysis will provide a more comprehensive picture of the chronology of events involved in the Cambrian radiation, and of the macroevolutionary and ecological significance of this major event.