Biodiversity in the Precambrian Fossil Record: Constructing a Digital Database of the Ediacara Biota and Closing the Precambrian-Cambrian Evolutionary Gap.

English Abstract:

Large, complex life first appears in the latest Ediacaran (579-541 Ma), characterized by globally distributed marine soft-bodied organisms colloquially called the Ediacara biota. Although it is well documented that these organisms went extinct prior to the Cambrian explosion of bilaterian animals, the ultimate cause is still unclear. Three hypotheses are proposed: 1) gradual and evolutionarily mediated biotic turnover in response to the appearance of metazoan ‘ecosystem engineers’; 2) a taphonomic artifact produced by the disappearance of conditions required for preservation; and 3) a sudden, coeval mass extinction driven by perturbations to global geochemical cycles. Critical testing of these hypotheses requires a detailed understanding of Ediacaran biodiversity in both paleogeographic space and stratigraphic time. Here, I present preliminary results from an exhaustive integrated paleontological database that summarizes the known distributions of Ediacaran taxa, combined with geological characterization of Ediacaran depositional and taphonomic settings as compiled from both literature research and recent fieldwork. I include additional data on chronostratigraphy, lithostratigraphy, preservational mode, and mineralogy of local-scale diagenetic alteration. I find that the Ediacaran fossil record displays a distinct bias towards moldic-style preservation in coarse-grained siliciclastic lithologies – with comparatively little preserved in carbonate facies or as compressions in shales. I also find strong correlation between worker effort and genus richness among major localities worldwide. These data illustrate that accurately quantifying changes in Ediacaran biodiversity through time requires a variety of sample standardizing techniques. Ultimately, these findings will guide future fieldwork in targeting under-studied strata, paleoenvironments, and preservational windows, helping to resolve the tempo and mode of early animal evolution preluding the Cambrian explosion.