RESTRUCTURING OF PHANEROZOIC SHALLOW MARINE COMMUNITIES DURING THE AFTERMATH OF THE END-PERMIAN MASS EXTINCTION

Taxonomic approaches, in which the numbers of different taxa within temporal or geographical contexts are tallied, and paleoecologic approaches, in which organisms and their interactions with each other and the environment are evaluated, are the two methodological paradigms that govern how evolutionary patterns and processes are deciphered from the fossil record. Mass extinctions and their aftermaths typically have been examined within a taxonomic framework because profound taxonomic changes are their hallmark. Increasingly, however, taxonomic approaches alone are considered insufficient for elucidating a complete picture of the course of evolution because organisms are not placed in an ecological context. Despite many recent studies, the ecological effects of the end-Permian mass extinction and the environmental perturbations that persisted through the Early Triassic aftermath are still crudely understood. The purpose of this study was to re-examine the end-Permian mass extinction and the Early Triassic aftermath within a paleoecological framework to determine if these events were ecologically, as well as taxonomically, significant.

Using skeletonized fossil accumulations as a proxy, relative abundance data gathered through literature- and field-based studies provided the framework for determining the ecological significance of these events. Results reveal broadly that rhynchonelliform brachiopods were the most abundant skeletonized groups in shallow level-bottom benthic marine communities during the Ordovician through the Permian and that during the post-Paleozoic, bivalves numerically dominate the same paleocommunities. A fine-scale study of Lower Triassic strata revealed the numerical dominance of bivalves throughout the entire stage, indicating that the end-Permian mass extinction and its aftermath facilitated the restructuring of shallow level-bottom benthic marine communities. This paleocommunity restructuring represents a second-level paleoecological change (sensu Droser et al., 1997) and was likely aided by environmental perturbations that lingered during the Early Triassic. Arguably, the end-Permian mass extinction was the most important macroevolutionary event of the Phanerozoic, and was largely responsible for the development of modern ecosystems.