ANALYSIS OF PATTERNS AND PROCESSES OF CHONDRICHTHYES ACROSS THE PERMIAN-TRIASSIC BOUNDARY

One of the key taxonomic groups that survived the End-Permian Mass Extinction was the Chondrichthyans. While the group managed to survive the largest cataclysm in the last 545 million years, they did not escape unscathed. Not only did chondrichthyan diversity decrease, but disparity, or morphological diversity, also was affected. As with many other taxonomic groups, full recovery from the End-Permian Mass Extinction was delayed well into the Triassic.

Our primary analysis focused on the pattern of extinction and recovery within the Chondrichtyes, and the possible processes that were responsible for said patterns. 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, Sepkoski's (1992, 2002 ) Compendia, and Benton's (1994), The Fossil Record 2.

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. By analyzing Chondrichthyan extinction and origination rates, and standing diversity at varying time and taxonomic levels, we hope to isolate extinction and origination patterns and processes that may not have been previously apparent.

The second component of this project is to determine how body and tooth morphology, and hence, nutritional guilds and paleoecology, affected standing chondrichthyan diversity directly after the End-Permian Mass extinction and through the subsequent recovery and diversification. This was accomplished by examining: the differences among rates of origination and extinction, and the standing diversity between fresh, marine, and brackish taxa, and major taxonomic groups within the elasmobranchs and holocephalans; and the dental morphologies and structures that were found in the surviving taxa.