The trace-fossil record of the Cambrian explosion

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The Cambrian explosion represents one of the most dramatic episodes in the history of life. Following a period known as Ediacaran, when biotas were dominated by soft-bodied*organisms, the fossil record changed rapidly as revealed by the appearance of fossilized representatives of almost all the basic animal body plans in lower Cambrian rocks. There are two opposed views on the early evolution of animals. One view considers the fossil record at face value, favoring a scenario of rapid origination of modern phyla (the Cambrian explosion). The other view stresses the imperfect nature of the fossil record, stressing the notion of deep Precambrian roots in metazoan evolutionary history. According to this*second perspective, the sudden appearance of fossils near the beginning of the Phanerozoic is just an artifact resulting from an increase in preservability of body fossils related to the acquisition of mineralized skeletons. Ichnology comprises the study of biogenic structures (known as trace fossils) that result from the interactions between organisms and the substrate. Because trace fossils are commonly produced by soft-bodied animals, they are not subjected to the same preservational constrains than body fossils. Accordingly, trace fossils may offer an independent line of evidence to calibrate the Cambrian explosion. The objectives of this project are: (1) to document ichnofaunas associated with the*Cambrian explosion and its Fortunian prelude, (2) to explore the potential of trace fossils to improve our understanding of Cambrian ecosystem construction at a critical time in the history of the biosphere; and (3) to explore how ichnologic information provides insights into the timing and environmental constrains of this breaktrough, revealing potential diachronism in evolutionary innovations.******