THE FŒTID GARDEN OF EDIACARA: RE-EVALUATING THE PALEOECOLOGY OF THE EDIACARAN SEAFLOOR

Studies that take the population densities of Ediacaran siliciclastic bedding planes at face value consider them to preserve census populations of living organisms at the time of burial. Based on this assumption, several authors have come to interesting paleoecological conclusions, most notably that they preserve communities dominated by suspension feeding animals.

Study of bedding planes from the Avalon biotic assemblage of Newfoundland and the United Kingdom leads us to believe that these beds preserve not only living organisms, but also numerous taphomorphs, formed by autolytic and microbial breakdown of deceased organisms on the seafloor over periods of weeks to months prior to burial by the casting medium. Such decay has created a spectrum of preservational fidelity on Avalonian bedding planes, from the exceptional preservation of many rangeomorph organisms, to effaced preservation of degraded forms. Our hypothesis that microbial decay is responsible for this spectrum is also supported by experimental evidence.

We consider that the ecological database preserved on Ediacaran bedding planes is compromised by the lack of ecological contemporaneity of the fossil assemblage. The assemblages do not represent ecological communities (i.e. living census populations of Ediacaran biota), but rather comprise a time-averaged assemblage of both living and deceased organisms. Reconsideration of previous paleoecological studies to account for these findings is therefore required. Our study of the E surface at Mistaken Point in Newfoundland suggests that incorporation of taphonomic data may have important consequences for our interpretations of Ediacaran taxonomic affinities. The abundance of decaying carcasses on the Ediacaran seafloor therefore means that the idyllic scene of a lush ‘Garden of Ediacara’ populated by peaceful communities of waving Ediacaran fronds takes on an altogether more fœtid appearance.