EVOLUTIONARY HISTORY OF PLIO-PLEISTOCENE CONUS FROM THE SOUTHEASTERN UNITED STATES

Conus (Neogastropoda) is the most species-rich extant genus of marine animal, but its Eocene-to-Pleistocene fossil record is underutilized for exploring the history and causes of this unparalleled diversity. Cone fossils are common in Plio-Pleistocene deposits in the southeastern U. S. Coastal Plain, but taxonomic problems have thus far prevented analyses of diversity patterns within Conus across space and time in this region. A complete systematic revision of these cones was recently completed based on examination of about 20,000 Conus specimens and treatment of nearly 80 available species names that have been applied to members of this fauna. Morphospecies were circumscribed primarily using combinations of discrete shell characters. This revision resulted in the recognition of a total of 23 distinctive morphospecies of Conus occurring in the Plio-Pleistocene of Florida, North and South Carolina, and Virginia. Only one new species was discovered during this revision.

Temporal patterns of species diversity were assessed across four temporal intervals using a newly constructed database containing stratigraphic and locality information from over 2,300 museum specimen lots. The highest observed diversity occurs in the Pliocene Pinecrest Beds (Tamiami Formation) of southern Florida. Conus species diversity then decreases through the Plio-Pleistocene. This pattern is in contrast to previous studies that show relatively constant diversity through time in this area for gastropods as a whole.

Based on protoconch morphology, a majority of the recognized fossil Conus species with preserved larval shells appear to have had lecithotrophic development. Alternatively, previously published data suggest that many more cone species had planktotrophic development during the Miocene in Florida, implying a shift in developmental mode regimes through time. Finally, as evidenced by new combined cladistic analyses of published molecular sequence data and a new shell character matrix, the studied Plio-Pleistocene fauna contains members of both the Indo-Pacific (IP) and eastern Pacific and western Atlantic (EP+WA) Conus clades sensu Duda and Kohn.