The chondrichthyan fossil record of the Florida Platform (Eocene–Pleistocene)

Abstract.— As of September 2019, the Florida Museum of Natural History (FLMNH) had a curated collection of 117,449 chondrichthyan specimens from Florida, spanning the Eocene through the Pleistocene. Herein, I evaluate the completeness of the chondrichthyan fossil record from Florida based on the FLMNH collection, while analyzing patterns in taxonomic and ecomorphological diversity. At least 70 chondrichthyan taxa were recognized, representing 10 orders, 26 families, and 42 genera; of which, 20 taxa represent first occurrences from Florida. A sample of 107,698 specimens was organized into 12 time bins to analyze taxonomic and ecomorphological diversity, with an expectation that diversity patterns would correspond with global climate events (e.g., the Eocene–Oligocene transition and the middle Miocene climatic optimum). However, diversity patterns were obscured by pervasive sampling bias, attributable to variable collection methods, research prioritizations, and regional lithologic controls. Sampling is particularly poor for smaller specimens and older geologic units (e.g., the Paleogene). Despite incomplete sampling of the Florida chondrichthyan fossil record, there was an apparent turnover along the Atlantic and Gulf Coastal Plains from a lamniform- to carcharhiniform-dominated chondrichthyan fauna that occurred during the Eocene. This turnover corresponded with the extinction of many lamniform taxa with grasping-dominated dentition types (e.g., Brachycarcharias, Jaekelotodus, and Macrorhizodus). Selachian taxa that survived the late Eocene extinctions were predominantly represented by cutting-dominant dentition types. As cutting aids in the dismemberment of prey, this may reflect a macroevolutionary trend toward active predation and scavenging on larger prey, such as marine mammals, teleost fish, and other sharks.