The influence of environmental setting on the community ecology of Ediacaran organisms.

The broad-scale environment plays a substantial role in shaping modern marine ecosystems, but the degree to which palaeocommunities were influenced by their environment is unclear. To investigate how broad-scale environment influenced the community ecology of early animal ecosystems, we employed spatial point process analyses (SPPA) to examine the community structure of seven late Ediacaran (558-550 Ma) bedding-plane assemblages drawn from a range of environmental settings and global localities. The studied palaeocommunities exhibit marked differences in the response of their component taxa to sub-metre-scale habitat heterogeneities on the seafloor. Shallow-marine (nearshore) palaeocommunities were heavily influenced by local habitat heterogeneities, in contrast to their deeper-water counterparts. The local patchiness within shallow-water communities may have been further accentuated by the presence of grazers and detritivores, whose behaviours potentially initiated a propagation of increasing habitat heterogeneity of benthic communities from shallow to deep-marine depositional environments. Higher species richness in shallow-water Ediacaran assemblages compared to deep-water counterparts across the studied time-interval could have been driven by this environmental patchiness, because habitat heterogeneities increase species richness in modern marine environments. Our results provide quantitative support for the 'Savannah' hypothesis for early animal diversification-whereby Ediacaran diversification was driven by patchiness in the local benthic environment.This work has been supported by the Natural Environment Research Council [grant numbers NE/P002412/1 and Independent Research Fellowship NE/S014756/1 to EGM, and Independent Research Fellowship NE/L011409/2 to AGL], a Gibbs Travelling Fellowship (2016-2017) from Newnham College, Cambridge, and a Henslow Research Fellowship from Cambridge Philosophical Society to EGM (2016–-2019). Field research in the White Sea Region, Arctic Siberia and Central Urals has been supported by the Russian Science Foundation [grant number 17-17-01241 to DG]. SX acknowledges funding from the NASA Exobiology and Evolutionary Biology Program [80NSSC18K1086]. Large image processing and interpretation of photomontages of the Dickinsonia Surface was supported by the Russian Foundation for Basic Research [grant number 19-05-00828 to AVK]