PHYLOGENY, DIVERSITY, AND EVOLUTIONARY TEMPO AND MODE IN MIOCENE-RECENT TURRITELLINE GASTROPODS FROM FLORIDA

Turritelline gastropods are conspicuous, diverse, and abundant in the extremely shell-rich Plio-Pleistocene deposits of Florida, which span approximately the last 3.5 million years. Yet the patterns and processes of their evolution are almost unknown. Analysis of these forms reveals at least 15 distinguishable fossil and two Recent morphospecies. A phylogeny of these species based on both “traditional” shell characters and a relatively new approach using continuous variables shows two major clades.

Ten of the 15 fossil species are known only from the mid-late Pliocene Pinecrest Sand, making the diverse Pinecrest fauna of more than 300 species one of the most species-rich turritelline assemblages known. At the end of Pinecrest time, a major extinction occurs among all marine mollusks in Florida, including most of the turritellines, and especially the very largest species. The origins of this high local diversity appear to lie in speciation events that occurred across several million years during the Miocene, both in Florida and the northern Caribbean. The Pinecrest itself is thus not a turritelline “cradle” but rather – perhaps because of conditions of high primary productivity -- a turritelline “museum” of species.