FLORIDA MARINE MICROMOLLUSKS FROM THE PINECREST BEDS, TAMIAMI FORMATION: HIGHER-LEVEL TAXA HITHERTO UNREPORTED THEREIN AND IN SUBSEQUENT WESTERN ATLANTIC PLIOCENE AND QUATERNARY FAUNAS

The well-known Pinecrest beds (Tamiami Fm.) of SW Florida contains one of the most species-rich malacofaunas in the world with an estimated 1,000 taxa (Allmon et al., 1993). However, the same authors commented on the markedly absent micromollusk component of that deposit. Accounts of Plio-Pleistocene Mollusca of the southeastern U.S.A., e.g., Campbell (1993), confirm this imbalance.

We investigated sediments exposed by sand and shell mining of SMR Aggregates of Sarasota County, Florida. The bulk of the material under study was collected since July, 2013 from Phase 10 of this operation and is now housed in the FLMNH collections. Collected in situ crude matrix and ex situ sediments were processed by standard methods of washing and serial sieving. Material was then dried and culled under stereomicroscopic surveillance. Our primary focus was micromollusks, here defined as <5.5 mm in average maximum adult shell dimension. Selected specimen(s) of each apparent species-level taxon in this general size range was imaged using a ZEBS EVO MA 10 scanning electron microscope (SEM). Linear dimensions were determined by the instrument’s software.

At present, we have recognized about 300 species in 157 micromollusk-dominated genus-level taxa. Of these genera, 64 (41%) have not been previously-reported from the Pinecrest beds. Bivalves contribute 30% (19 genera) and gastropods 70% (45 genera) to that numeric. Fifty-one (80%) of the taxa are new to the known Plio-Pleistocene of Florida, and 40 (63%) are unreported from the Plio-Pleistocene of the southeastern U.S.A. (Campbell, 1993). Furthermore, 26 of these genera have not been previously reported from the Plio-Pleistocene of the Western Atlantic, and eight, Basterotina (Sportellidae), Macromphalus (Vanikoridae), Clathropsis and Cerithiopsidella (Cerithiopsidae), Hypermastus (Eulimidae), Alora (Epitoniidae), Falsoebala (Ebalidae), and Agatha (Pyramidellidae), have never been recorded from the Recent or fossil faunas of that region. Only one of these genera, Basterotina, has been reported from the New World.

These new finding demonstrate the significance of this understudied faunal component. Implications in terms of biodiversity and the trajectory of origination and extinction in the Cenozoic Era, combined with images of critical species will be presented.