BENTHIC RECOVERY FROM THE END-PERMIAN MASS EXTINCTION: NEW INSIGHTS FROM AN EXCEPTIONAL LAGERSTÄTTE OF SOUTH CHINA

Poor preservation of fossils is a major obstacle for the identification of ecological and evolutionary processes in the immediate aftermath of the end-Permian mass extinction. Here we report the notable exception of an unusually well-preserved benthic fauna from the base of the Early Triassic Luolou Formation in the Nanpanjiang Basin, which occurs in shell accumulations trapped in-between microbialitic dome structures. The newly reported fauna is Griesbachian in age, extraordinarily rich (30 benthic macroinvertebrate species), and thrived in an environmentally stable setting according to microfacies and carbon isotope data. The duration of these regionally stable conditions is within the magnitude order of 100 ka as indicated by preliminary U-Pb ages. Whereas changes in the taxonomic structure are negligible over this time interval, three ecological stages are identified that document a successive decline of disaster taxa and a corresponding increase of taxa that were ecologically important in background times. In absence of both environmental and taxonomic changes, the observed pattern is fully attributable to the effects of interactions between species. The trends can be described by a standard Lotka-Volterra model, but they occur in a timescale that is orders of magnitude longer than processes of competitive replacement in background times. We suggest that this long duration is due to a non-actualistic low level of competition as a consequence of the extraordinary high extinction magnitude, combined with a limited pool of taxa from which the community could recruit immigrants.