Quantitative analyses of Ediacaran Ecosystems

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Organisms have occupied the planet for at least the past 3.5 billion years, but only relatively recently have their fossil remains been large enough to see with the naked eye. The first properly macroscopic fossils turn up around 580 million years ago, in the middle of the Ediacaran Period, less than 50 million years before the appearance of recognizable animals and the conventional fossil record of shells, bones and burrows. The significance of the Ediacaran fossil record is that is provides a direct account of the transition from the exclusively microbial world of the first three billion years, to the conspicuously belated establishment of a recognizably modern biosphere. Unfortunately, the Ediacaran record is also profoundly problematic. Not only do we not know what these earliest large life-forms were related to, it is not even clear what kinds of things they were, or how they made a living. The aim of this research proposed here is to reconstruct the original community ecology of these fossils - how they interacted with one another and with their environment - with an eye to understanding their role in bringing about the modern world.One of the advantages of studying Ediacaran macrofossils is that none of them moved during life, so their fossilized positions provide an exact account of their original spatial inter-relationships. By analysing these spatial data, it is possible extract a surprising amount of original ecological detail. Like trees in a forest, the distribution of Ediacaran fossils on bedding surfaces reflects the interplay of numerous effects including organism life-history, inter-specific competition and facilitation, and the physical environment. As such, these ecological processes can be reverse engineered using many of the sophisticated statistical and modelling techniques developed by modern forest ecologists. We have already demonstrated the potential of this approach with a recent paper in Nature, and now plan to apply it systematically to the earliest known Ediacaran macrofossils, the "Avalonian assemblage" - known almost exclusively from iconic occurrences in Charnwood Forest, Leicestershire and SE Newfoundland. The research programme is divided into two main parts. The first is data collection. Here we plan to assemble a comprehensive database of high-resolution, digitized 3D images of all known Avalonian bedding surfaces preserving large populations (> 100 specimens) of macrofossils. Made possible by recent advances in laser-scanning technology, this will yield the precise size, position and orientation of ~20,000 fossils comprising 44 separate bedding-surface communities. The second, and primary, focus of this project is to analyse these data for their primary ecological content. Using a range of complementary quantitative techniques, we plan to address three main issues in early Ediacaran ecology:1) How did these organisms interact with their environment, and how much did these environmental interactions matter compared to organism reproduction? This is the subject of a longstanding debate in modern community ecology, and the Ediacaran record offers a unique view of the balance among the first large organisms.2) What was the distribution of body-sizes in Ediacaran ecosystems and what ecological processes were responsible for their particular size-structure? In modern aquatic systems, body-size is directly related to predation and the feeding relationships of animals, but there is no evidence of predatory animals in any of these early macroscopic communities. 3) Did competition for resources within the overlying water-column dominate interactions between Avalonian organisms? This has often been promoted as a significant factor in Ediacaran ecology, but has never been quantitatively tested. Our analytical approach to this and other questions of Ediacaran ecology promise to shed significant new light on the origin of the modern biosphere.