HOW SUDDEN WAS THE GREAT DYING AT THE END OF THE PALEOZOIC ERA?

The Great Dying at the end of the Paleozoic Era was the most catastrophic event in Phanerozoic history. Eliminating perhaps 95% of marine species, it ended the two hundred million year reign of the epifaunal suspension feeding Paleozoic Fauna and allowed the rapid post-Paleozoic radiation of the mobile, predatory, and actively burrowing Modern Fauna. An initial mass extinction occurred late in the Guadalupian Age of Middle Permian Epoch, followed by an even larger one during the Tatarian Age at the close of the Permian Period. While these biotic crises undoubtedly resulted in massive reductions in marine diversity, the incompleteness of the fossil record may obscure the true pattern and timing of the extinctions (i.e., the Signor-Lipps effect). To assess the extent of preservational artifact, a mathematical model of taxonomic evolution and fossil preservation was used to estimate stratigraphic range extensions (intervals of complete non-preservation) in fourteen major marine invertebrate taxa that became extinct during the Guadalupian and Tatarian ages. At the 50% confidence level, range extensions of taxa whose fossil records terminate during the Guadalupian Age span between 1.87 to 6.28 × 10⁶ years. While the Guadalupian demise of rostroconchs, modiomorphoid bivalves, disparid crinoids, and fissiculate blastoids appears to represent a true extinction event, only the flexible crinoids and spiraculate blastoids are calculated to have become extinct in the ensuing Tatarian Age. Preservational ‘backsmearing’ of Tatarian extinctions therefore contributed relatively little to the Guadalupian crisis. Despite range extensions of between 0.99 to 3.74 × 10⁶ years at the 50% confidence level, tabulate corals, hyoliths, fenestrate bryozoans, and camerate crinoids all likely died out during the end-Permian mass extinction. Rugose corals, goniatite ammonoids, proetid trilobites, and orthid brachiopods, on the other hand, are estimated to have persisted slightly (<10⁶ years) into the Induan Age of the Triassic Period.