Ediacaran pre-placozoan diploblasts in the Avalonian biota: the role of chemosynthesis in the evolution of early animal life
Suzanne C. Dufour, Duncan McIlroy, 2017. "Ediacaran pre-placozoan diploblasts in the Avalonian biota: the role of chemosynthesis in the evolution of early animal life", 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 large, enigmatic members of the Ediacaran biota have received much attention regarding their possible affinities and mode of life. Fossil evidence reveals that many Ediacaran animals, such as the rangeomorphs, were characterized by extensive surface areas, lived in close association with the seafloor and were non-motile. We argue for the presence of a simple, diploblastic body plan in these early animals and discuss the means by which they probably derived nutrients from chemosynthetic bacteria thriving at the sediment–water interface. We consider that the large surface area of some Ediacaran organisms in the Avalonian biota may have been an adaptation for maximizing a phagocytotic or chemosymbiotic surface. Ediacaran animals probably increased the availability of oxygen along their ventral surface either by diffusion or ciliary pumping. This increased supply of oxygen to the sediment is inferred to have simultaneously increased the productivity of their food source (chemosynthetic bacteria) and restricted the build-up of toxic sulphides in the pore waters below their bodies. This is an example of a very simple form of ecosystem engineering.
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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.