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

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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.