Comparison of Changes in Ocean Chemistry in the Early Triassic with Trends in Diversity and Ecology

The end-Permian mass extinction resulted in the demise of ~90% of marine genera. Recent work on the Early Triassic using carbon isotopes, ammonoids, conodonts, and some benthic fauna shows that this supposed recovery period was almost as turbulent as the extinction itself. Carbon isotope records from China, India, and Italy portray a global signal with major perturbations at stage boundaries in the Early Triassic most likely as a result of fluctuating environmental conditions. Comparison of global cycles of extinction and radiation of ammonoids and conodonts to the global carbon signal suggests that the two are related. In order to investigate the ubiquity of the connection between the carbon signal and biological changes, the benthic diversity and ecological structure of the western USA was examined. Instead of the fluctuating patterns that were expected, evidence for gradual increases in both taxonomic and guild diversity was found. The lack of evenness in the recovery suggests ecological stagnation; dominance of a few genera and a few life habits. The prolonged benthic recovery, and trends of pelagic boom and bust, both point to environmental instability in the Early Triassic as the probable cause for the protraction of the biotic crisis.