A FULL AND VARIED EDIACARA SEAFOOD PLATTER WITH A SLIPPERY DIP FOR CHIPS: COMPLEXITY OF EDIACARA ECOSYSTEMS

With notable exceptions, studies of Ediacaran fossils are typically focused on individual specimens with paleoecological studies most often aimed at understanding the autecology of fossils largely in the context of determinging their systematic affinities.

Ediacaran-aged strata in the vicinity of the Flinders Ranges, South Australia, offer the opportunity to study bedding plane surfaces, many of which are sequential, exposing Ediacaran fossils. Body fossil genera include Dickinsonia, Spriggina, Aspidella, Parvancorina, Conomedusites, Charniodiscus, Tribrachidium, Eoporpita, Rugoconites and forms typical of the White Sea assemblage. Extensive bedding plane exposures of 12 discrete beds revealing over 100 square meters, demonstrate a strikingly significant level of heterogeneity between beds in terms of composition, evenness and relative abundance. Only some of the heterpgenity can be attributed to taphonomic differences, the rest is likely a result of varying communitites across small-scale environmental gradients within this shallow marine setting. Even in the case where several beds are dominated by the disk Aspidella, the size and spatial distribution of fossils between beds varies considerably.

Although it is not possible to evaluate biomass, fossils are not rare and many beds are covered with densely packed non-transported body fossils, in particular tubular forms. Equally striking is the presence of abundant bioclastic sandstones reflecting a biomass otherwise unrecorded in standard body fossil preservation. Bioclasts, which superficially resemble mud chips, are present most commonly on the tops of beds, where they are formed either in situ as broken-up microbial mats or as transported peices of sand-filled body fossils preserved in 3-D. These structures are distinct from surrounding rock because they have sharp continuous boundaries and the sand grains do not exhibit the overgrowth present in the surounding matrix.

These data suggest that the Ediacara biota formed complex ecosystems with considerable biomass.