Other Phanerozoic Extinctions
The end-Triassic mass extinction event, one of the five biggest in the Phanerozoic, is clearly marked in the marine realm by the almost total extinction of the ammonites, final disappearance of the conodonts, collapse of the reef ecosystem, and substantial changes in other groups. In the terrestrial realm a contemporary mass extinction event among the tetrapods is clearly recorded in eastern North America, the site of the best stratigraphic record, and there was also a major floral turnover that has probably been hitherto underestimated. With regard to possible causes, there is no evidence in the stratigraphic sequence supporting bolide impact, such as shocked quartz or iridium anomalies, although such evidence has been sought, and no evidence of a significant climatic change across the Triassic/Jurassic boundary. There is, however, strong evidence of a sea-level change at the boundary in the form of a regressive-transgressive complet that appears to be associated with the inception of tensional tectonics and volcanicity in the central part of Pangaea. In the western Americas there is evidence of transgression–sea-level rise at or close to the Triassic-Jurassic boundary but no evidence of preceding regression. Both in Europe and the Americas, transgressive deposits are characteristically anoxic or hypoxic. The underlying control is likely to be bound up with events in the mantle.