Evaluating evidence from the Torridonian Supergroup (Scotland, UK) for eukaryotic life on land in the Proterozoic
A. T. Brasier, T. Culwick, L. Battison, R. H. T. Callow, M. D. Brasier, 2017. "Evaluating evidence from the Torridonian Supergroup (Scotland, UK) for eukaryotic life on land in the Proterozoic", Earth System Evolution and Early Life: A Celebration of the Work of Martin Brasier, A. T. Brasier, D. McIlroy, N. McLoughlin
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The Stoer, Sleat and Torridon groups lie unconformably on Palaeoproterozoic Lewisian metamorphic rocks. They contain organic carbon microfossils claimed to be non-marine and to include eukaryotes. We consider the evidence for terrestrial interpretations from each formation of the Torridonian Supergroup. The range of sedimentary structures and the boron content of illite led us to the overall conclusion that, based on the currently available evidence, the Torridonian Supergroup was probably entirely non-marine. Evidence for terrestrial life in these rocks comes from microbially induced sedimentary structures, including wrinkle structures with reticulate and elephant skin fabrics. Organic remains and microscopic carbonaceous compressions mostly reported from phosphates in the grey shales of the Stoer, Aultbea and Applecross formations are dominated by sphaeromorph acritarchs. The Diabaig phosphatic lagerstätte includes three-dimensional preservation of eukaryotic and prokaryotic organisms, providing remarkable insights into non-marine life around 1 billion years ago.
Supplementary material: Taxonomy of Torridon Group microfossils from thin sections of phosphatic material (adapted from Battison 2012) is available at https://doi.org/10.6084/m9.figshare.c.3522753
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This volume in memory of Professor Martin Brasier, which has many of his unfinished works, summarizes recent progress in some of the hottest topics in palaeobiology including cellular preservation of early microbial life and early evolution of macroscopic animal life, encompassing the Ediacara biota. The papers focus on how to decipher evidence for early life, which requires exceptional preservation, employment of state-of-the-art techniques and also an understanding gleaned from Phanerozoic lagerstätte and modern analogues. The papers also apply Martin’s MOFAOTYOF principle (my oldest fossils are older than your oldest fossils), requiring an integrated approach to understanding fossils. The adoption of the null-hypothesis that all putative traces of life are abiotic until proven otherwise, and the consideration of putative fossils within their spatial context, characterized the work of Martin Brasier, as is well demonstrated by the papers in this volume.