Diversity patterns and biostratigraphy of Cenozoic echinoderms from Florida

Fossil echinoderms are an important faunal component in Cenozoic rocks of Florida and the southeastern Coastal Plain of the USA, that provide useful information regarding diversity patterns and paleoecology for the formations in which they were deposited. The research presented in this paper significantly improves what is known about the stratigraphic distribution and diversity patterns of echinoids, comatulid crinoids, asteroids, and ophiuroids from the Middle Eocene through Pleistocene strata of Florida. Biostratigraphic distribution of echinoderms, specifically the echinoids, has not been synthesized on a large scale for many years, and the first compilation of these taxa from the state is provided in this study. Echinoderms now are known from 25 formations that are exposed throughout the state. The echinoids are better documented and described than the other classes of echinoderms, yet even the echinoids were poorly known from some epochs, most notably the Miocene. Previously published information showed echinoid diversity decreasing significantly from the Eocene into the Oligocene, and continuing to decline into the Miocene. Our research shows the echinoid diversity does not drop from the Oligocene into the Miocene, but instead increases by at least five species. This marked change in alpha diversity during the Miocene is a result of careful examination of smaller size fractions of sediments, which contained fragmented components of echinoids such as test plates and spines, and the diligent collecting of moldic samples, which produced additional taxonomic and stratigraphic records. The record of other echinoderms is still poor, but fine-fraction sediments also have produced disarticulated ossicles of crinoids, asteroids, and ophiuroids from several formations that had no previous record of such echinoderms. The diversity pattern of echinoderms from Florida is a reflection of both intrinsic and extrinsic factors that affect (in varying degrees) the echinoderm-bearing formations from the Paleogene through the Neogene. One of the most influential appears to be collector bias against recovering incomplete echinoderms. Many of the new species or new records of taxa from stratigraphic units in the state are based on fossils that are poorly preserved or incomplete. Other biases include over-splitting of taxonomic groups, stratigraphic unit revisions, taphonomy, and preservation potential variation in carbonate versus siliciclastic environments. Significant r