Reconciling the Ediacaran and Cambrian fossil records of early animal evolution

Establishing the timing and trajectory of early animal evolution is vital to efforts to determine the evolutionary processes responsible for generating Earth’s incredible diversity of animals. However, the early evolutionary history of animals is poorly constrained. This project will gather fossil and geological data from spectacular new localities in southern Namibia to illuminate the early stages of animal diversification, and to ascertain the extent to which animals both caused, and responded to, major environmental shifts at the dawn of animal life. Recognisable members of most major living groups of animals appear ‘explosively’ in the fossil record ~538–510 million years ago (Mya) in the Cambrian Period, but older fossils of large and complex soft-bodied organisms in late Ediacaran rocks (~574–538 Mya) demonstrate that animal evolution commenced considerably earlier. However, many Ediacaran fossils lack the recognisable anatomical features that characterise the main animal groups, making it difficult to precisely determine how closely related Cambrian animals were to the earlier Ediacaran forms. To unify these disparate records, we require new, high-quality fossil assemblages that bridge the transitional interval of time between the Ediacaran and Cambrian periods. We have discovered remarkable new fossil sites in southern Namibia that span the final ten million years of the Ediacaran Period, and which offer an unprecedented opportunity to reveal the progress of animal evolution during this critical interval. The sites contain an astonishing array of new fossil species and include unexpected forms alongside candidate members of ‘modern’ animal groups, in addition to clear evidence for behavioural innovations such as movement and burrowing. These new assemblages hold the potential to fundamentally reshape our knowledge of early animal ecosystems and their role in setting the stage for the ‘Cambrian explosion’ of animal diversity. We will employ detailed palaeontological, sedimentological, stratigraphic and cutting-edge geochemical techniques to these new fossil assemblages to achieve the following objectives: Objective 1: Describe and interpret new latest Ediacaran fossil taxa from in-situ fossil assemblages, and utilise their anatomical features to inform the evolutionary timing and trajectory of animal diversification. Objective 2: Document the ecosystem structure of terminal Ediacaran fossil communities, and the nature of organism interactions and behaviours in early animal ecosystems. Objective 3: Constrain the physical depositional environments of in-situ early animal ecosystems and component organisms. Objective 4: Reconstruct the terminal Ediacaran ocean chemical conditions these organisms lived in. Successfully achieving these objectives will allow us to resolve key questions about how early animal ecosystems emerged, diversified, and adapted in response to local and global shifts in ocean chemistry and climate. Our findings will directly advance knowledge of links between early animal evolution and environmental change, for example identifying the extent to which physical and chemical conditions influenced the distribution of early animals in marine habitats, or addressing how animals themselves shaped the biosphere through their evolutionary and behavioural innovations. Our palaeobiological results will inform the pattern and timing of early animal diversification, and contribute key datapoints for discussions regarding the precise biological relationships between basal animal clades. We will track evolutionary innovations such as burrowing and shell-building to determine how they altered sediment structure and ocean chemistry, and we will provide essential chemical and environmental context to enable robust testing of hypotheses regarding the causes and consequences of the ‘explosive’ radiation of animal life.