MARINE BIODIVERSITY AND ECOSYSTEM FUNCTIONING DURING TWO CRITICAL INTERVALS OF ANIMAL EVOLUTION: THE EDIACARAN-CAMBRIAN RADIATION AND THE END-PERMIAN MASS EXTINCTION AND ITS AFTERMATH

The study of modern marine biodiversity and its relationship with ecosystem-level emergent processes such as productivity, biogeochemical cycling, and stability has been fruitful in assessing the impact of the modern biodiversity crisis on ecosystem structure and functioning. The relationship between biodiversity and ecosystem functioning is a complex set of feedback interactions operating in both directions, so that not only do such factors as ecosystem productivity and stability impact biodiversity, but biodiversity itself can also affect such ecosystem-wide functions. The extension of this perspective into the animal fossil record should likewise be important in understanding the modern biodiversity crisis because the fossil record has recorded the outcomes of several previous natural experiments in drastic biodiversity changes and ecosystem disruptions on a global scale. The animal fossil record offers a unique temporal perspective on how ecosystems and their denizens have evolved, and how these systems have coped with global disturbances similar to those that threaten our modern ecosystems. Although limited by preservational and collection bias difficulties associated with fossil collections, marine biodiversity and ecosystem functioning can be thoroughly examined by comparing the outcomes of these large-scale natural experiments recorded in the fossil record. Two case studies, each a critical event in the history of life, are the focus of this study: the Ediacaran-Cambrian radiation of complex animals and the end-Permian mass extinction and its aftermath. These events were quite different, but alike in the sense that they represent large changes in biodiversity that affected ecosystem functioning in dramatic ways. For each of these events, changes in body fossil and trace fossil biodiversity, bioturbation levels, and nutrient levels are examined and considered in the context of their impact on ecosystem functioning. This study displays the utility of the fossil record in understanding not only the outcomes of natural experiments in the interaction of biodiversity and ecosystem functioning that took place on geologic time scales, but also the modern biodiversity crisis.