REDEFINING PHYLOGENETIC RELATIONSHIPS IN FLORIDA'S PLIO-PLEISTOCENE TURRITELLINE GASTROPODS USING PROTOCONCH MORPHOLOGY AND GENETIC INVESTIGATION

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.

Analysis of these forms reveals at least sixteen distinguishable fossil and two Recent morphospecies. Reconstructing phylogenetic histories of Turritella has been fraught with difficulties for decades. Previous phylogenies of these species based on both “traditional” shell characters and a relatively new approach using continuous variables showed two major clades.

Unfortunately, newer genetic-based phylogenies do not match cladograms created using only morphological traits. However, protoconch morphology and early ontogenetic stages revealed two potential higher clades that are supported by genes. In this study we use a previous phylogeny to test this hypothetical division in sixteen Plio-Pleistocene Turritella from Florida. The first clade to be investigated includes T. pontoni, subannulata, fluxionalis, and alticostata. The second clade includes T. etiwanensis, mansfieldi, magnasulcus, gladeensis, perattentuata, wagneriana, and alumensis. These results give us greater insight into the macroevolutionary history of Neogene western Atlantic turritellines.

Ten of the sixteen 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 and Pliocene, both in Florida and the northern Caribbean.