CHONDRICHTHYAN DIVERSITY ACROSS THE EOCENE-OLIGOCENE TRANSITION OF FLORIDA

Chondrichthyan taxa are poorly documented from Florida, despite their popularity, abundance, and utility for interpreting paleoecology. The Florida Museum of Natural History (FLMNH) has a curated collection of over 100,000 chondrichthyan specimens spanning from the Eocene through the Pleistocene, and yet less than 1% of these have been documented in published literature. This presentation will focus on a small portion of the FLMNH collection by examining chondrichthyan diversity across the Eocene-Oligocene Transition (EOT), which marks the largest cooling event of the Cenozoic. Previous research analyzing Mg/Ca ratios in shallow-water foraminifera reported ~2.5 ⁰C drop in tropical sea surface temperatures. While chondrichthyans have been described from Eocene and Oligocene deposits, no study has focused on the impact of this major cooling event on chondrichthyan diversity in the Atlantic and Gulf Coastal Plains. The FLMNH collection consists of 224 Eocene chondrichthyan specimens representing at least 17 taxa and 865 Oligocene chondrichthyan specimens representing at least 15 taxa. At least 10 Eocene taxa are extinct post-EOT and at least eight taxa first appear in the Oligocene. Based on Sepkoski’s diversity metrics, this reflects an extinction rate of 0.0478 in the Eocene and an origination rate of 0.0489 in the Oligocene. These nearly equivalent rates of extinction and origination reflect a rapid recovery to this significant cooling effect. Despite at least 59% of taxa going extinct across the EOT, there is little change in the functional types represented. However, there is a change in the dominant taxonomic group, with a shift from the lamniform dominated Eocene to the carcharhiniform dominated Oligocene.