ANALYSIS OF CHONDRICHTHYAN GENERIC RICHNESS, MORPHOLOGICAL DIVERSIFICATION, AND ECOSPACE DIVERSITY ACROSS THE PERMIAN-TRIASSIC BOUNDARY

Chondrichthyans were one of the key taxonomic groups that survived the End-Permian Mass Extinction. Not only did the group managed to survive the largest cataclysm in the last 545 million years, they did so nearly unchanged. While chondrichthyan diversity decreased slightly, morphological diversity was little altered, with many Paleozoic forms surviving well into the Early Mesozoic. As with many other taxonomic groups, changes in morphological diversification was delayed well into the Mesozoic.

The first component of our analysis focused on the pattern of extinction and recovery after the Permian Mass Extinction. Because of the general lack of preservation of the cartilaginous elements composing the chondrichthyan skeleton, we centered our attention on fossil dentition. We chose to concentrate on familial and generic taxonomic ranks because of intraspecies variation of tooth morphology. All data and faunal lists were acquired through an analysis of the literature.

In order to determine the pattern and processes of the Chondrichthyan response to the End-Permian Mass Extinction we performed two primary types of analyses. First, we examined the extinction and origination rates and standing diversity at the family and genus taxonomic levels. We also investigated how these rates vary when the analysis is performed at the geological epoch versus stage increment.

The second component of this project was to determine how tooth morphology, and hence, nutritional guilds and paleoecology, changed after the End-Permian Mass extinction and through the subsequent recovery and diversification. This was accomplished by examining chondrichthyan teeth from 14 localities worldwide, that spanned the Mississippian – Neogene periods. Once obtained, teeth were assigned to distinct morphological categories. In order to compare tooth types and numbers at each locality, the data was statistically analyzed using the Monte Carlo method of bootstrapping.

The preliminary results from this study indicate that the evolution of new tooth types enabled chondrichthyans to inhabit new feeding niches. Chondrichthyan species became more specialized in these feeding niches during Late the Mesozoic. Thus, it is possible that new tooth types lead to greater diversity amongst chondrichthyans throughout the post-Paleozoic Eras.