EDIACARAN DISTRIBUTIONS IN SPACE AND TIME


Oceanographic factors such as temperature, nutrient availability, and biologically relevant periods of oxygenation have profound impacts on the distribution of animals in modern marine environments that certainly translate into the stratigraphic record. These factors will undoubtedly require attention in the future as novel geochemical proxies are applied to the rock record.


Conclusions The Ediacaran Period spans a unique and


dynamic interval in the paleontological record, providing insight into both early metazoan origins at the end of the Proterozoic and emergence of profound biological and environ- mental drivers that would facilitate the subse- quentCambrian radiation of animal complexity. Ultimately, these mechanisms rely on well- defined chronostratigraphic constraints to illus- trate any temporal interrelationships between biology and the environment on evolutionary patterns. The lack of a clear biostratigraphic record for the Ediacaran Period is a significant barrier that hinders such correlation. Our updated paleontological database sup-


ports the taxonomic integrity of the traditional Avalon, White Sea, and Nama assemblages as coherent, distinct faunal associations as origin- ally proposed in Waggoner (2003). However, not reflected in earlier studies is the high level of taxonomic disparity that exists in new localities such as in China when compared to the classic assemblages in Newfoundland, Russia, Australia, and Namibia. This suggests that the emerging taxonomic heterogeneities that presently exist are likely to grow as worker effort increases the known diversity in both novel and present localities. With time, this trend could potentially challenge current Ediacaran assemblage concepts and will require continued revision of the global Ediacaran data set. Taphonomic results expand on previous


studies and demonstrate that lithology (and paleoenvironment) is largely decoupled from the pervasive moldic preservation, occurring in both siliciclastic and carbonate lithofacies and at depths ranging from deep-water slope/basinal to upper shoreface. This ubiquity is reflected


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within ordination plots, as convex hulls for each lithology show limited separation toward any of the traditional assemblages. Some styles of moldic preservation such as Fermeuse and to a lesser degree Flinders appear to select against complete preservation of epifaunal frondose taxa. However, shallower-water localities such as Nilpena, Australia, are an exception to this trend, preserving a low diversity of frondose-specifictaxainotherwise


highly


diverse communities. This may therefore point to other mechanisms controlling the absence of diverse frondose communities in shallow-water environments. The Ediacaran carbonaceous compression record meanwhile displays mark- edly different taxonomic trends, and is highly correlated with shale and mudstone lithologies. The current carbonaceous compressionwindow appears to select against many Ediacara-type taxa; however, due to the highly underrepre- sented nature of this taphonomic mode, carbo- naceous compression settings are likely to be a productive facies for paleontological research moving forward. Beyond taphonomy, both geologic time and


bathymetry play an important role in under- standing the Avalon, White Sea, and Nama assemblages, at least in a stratigraphic context. Despite the early first appearance of Ediacara biota in the ~579Ma deep-water Drook Forma- tion, Newfoundland, new geochronological data now demonstrate that the taxonomically and geographically distinct Avalonian and White Sea assemblages were likely temporally coeval at least during the Avalon–White Sea transition ca. 560–557Ma (Noble et al. 2014). Furthermore, both these assemblages are tightly constrained to narrow bathymetric ranges and are therefore likely to be disparate paleoenvir- onmental–ecological biotopes that were spa- tially restricted in marine settings. This patchy paleoenvironmental distribution could account for significant stratigraphic gaps in the fossil record, since bathymetrically restricted taxawill be strongly affected by gradual changes in paleoenvironmental settings. This is likely to be the case in the youngest sections of both New- foundland and Charnwood Forest, where shal- lowing upward successions do not preserve the diversefrondoseassemblagesthatoccur older, deep-water sections. Conversely, this can


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