A POTENTIAL TWO-PHASED EXTINCTION EVENT AT THE EDIACARAN-CAMBRIAN BOUNDARY, AND LESSONS FOR THE CURRENT BIODIVERSITY CRISIS (Invited Presentation)

The Ediacaran-Cambrian transition captures one of the most fundamental changes in the history of life, and yet very little is known about the cause(s) of the apparent end Ediacaran extinction event. Two hypotheses have been put forth to explain this extinction: 1) a more gradual ‘biotic replacement’ hypothesis precipitated by metazoan ecosystem engineering; and, 2) a more sudden, exogenic and environmentally-driven ‘catastrophe’ hypothesis. The Nama Group of southern Namibia preserves a depauperate community of Ediacaran fossils together with a diversifying suite of metazoan body- and trace fossils that provides strong evidence for the ‘biotic replacement’ model. However, evidence from elsewhere in the world also points to large-scale perturbations to global geochemical cycles at the Ediacaran-Cambrian boundary coincident with global faunal turnover, supporting the ‘catastrophe’ model. Here I discuss the evidence for a combined scenario and two-phased end-Ediacaran extinction event, and highlight several areas where these data may have relevance to the current biodiversity crisis and present-day patterns of global change.