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Murray Edwards College
University of Cambridge

Science issue: Detecting interactions at the start of complex macroscopic life

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    23 Nov

    For me, the most important transition in the evolution of life on Earth is the one that occurred over half a billion years ago during the Ediacaran time period. Prior to the Ediacaran, there had been 3 billion years of just microbial life, and just after the Ediacaran, most modern animal groups first appear.  This Ediacaran – Cambrian transition describes the evolutionary changes from simple, microbial life, to complex, macroscopic life – that is fossils appear for the first time that are visible to the naked eye.  The anatomy of these Ediacaran organisms differs fundamentally from those found in any other time periods, making it difficult to resolve their basic biology such as their phylogenetic relationships or their ecology.  However, the preservation of these Ediacaran organisms is exceptional: Thousands of fossils are preserved under volcano ash, so rather like Pompeii, entire communities are preserved where they lived.

    The oldest group of Ediacaran macro-fossils, the Avalon assemblage, contains almost exclusively non-mobile species, so that they could not escape these volcanic ash falls.  As such, the positions of the fossils on the rock surface encapsulate their life-history.  Therefore, analyses of these spatial patterns can determine the biological and ecological processes that affected Ediacaran organisms during their lives. 

    Ediacaran palaeontology is particularly appealing to me because of the large quantity of data-rich fossil surfaces which provide an amazing opportunity to use spatial statistics to extract previously unknown information about Ediacaran organisms.  Spatial analyses can be used to resolve biological or ecological traits by comparing the fossil patterns to spatial patterns with known underlying processes.  For example, comparison of the type of spatial patterns saplings make when clustering around their parent plant can be used to deduce the mode of Ediacaran reproduction.  Similarly, comparison of the spatial patterns plants make when they preferentially grow in good quality soil can be used to deduce the presence of local habitat variations on Ediacaran organisms.  Therefore, by using spatial analyses we can test hypotheses made about Ediacaran life, and work out what the key processes that governed these organisms were.

    Spatial analyses require mapping out the positions, sizes and taxonomic identity of all the specimens on a fossilerferous surface.  But mapping out Ediacaran fossil surfaces is tricky because the fossils are hard to see due to their low-relief – often they are only visible with light angled in a very specific direction. So instead of photographing them, I use high-resolution laser-line probes to laser scan these large rock surfaces in Charnwood Forest, UK and Newfoundland, Canada to a 40 micron resolution. These laser scans capture the entire surface enabling the spatial and anatomical data to be extracted, back in the lab in Cambridge.  The combination of laser scanning and spatial analyses enables me to detect, describe and understand what interactions were happening right at the start of complex macroscopic life on Earth, and the evolution of the first animals in the Ediacaran. 

    Dr Emily Mitchell
    Henslow Junior Research Fellow