END PERMIAN ANOMALY: HOW DID CHONDRICHTHYANS ESCAPE HISTORY'S LARGEST DEVASTATION?

Throughout the Phanerozoic the earth has experienced five major biotic extinctions. However, the extinction that occurred 251 million years ago (mya) brought the Paleozoic to a close and was the most severe with regard to loss of taxonomic richness and morphological diversity. Informally known as the ‘mother of mass extinctions’ (Erwin, 1994) this extinction produced the largest devastation to both marine and terrestrial organisms throughout the entire Phanerozoic: 70% of terrestrial vertebrate families were obliterated, 53% of marine families, 84% of marine genera and 95% of marine species (Erwin, 1994). Numerous faunal groups were affected by this catastrophic event; ironically, chondrichthyans experienced, relatively, little impact.

During the Paleozoic, chondrichthyans peaked both taxonomically and morphologically in the Late Mississippian to Early Pennsylvanian, with a subsequent decrease in diversity much earlier than the End Permian. From the fossil record, it appears that the largest negative biotic event to impact the chondrichthyans happened well before the End Permian mass extinction. Is the decrease in diversity real or an artifact of a poorly sampled or non-existent rock record for the interval in question?

The fact that 95% of all marine species were impacted by the End Permian extinction yet chondrichthyans were scarcely affected, begs yet another important question: What characteristic or morphological traits allowed sharks to remain unscathed, or is this just a misinterpretation of the Permian rock record?

The purpose of this research is to “decouple” the inconsistencies of the rock record from the fossil record, and explore possible reasons why this major faunal group showed such a drastically differential pattern of survival compared to other marine faunas. If, indeed the pattern of differential survival is real, what characteristics or morphologies may have enhanced survivorship of most major taxonomic groups into the Early Triassic?