Paleocommunities of the Fort Thompson Formation (Pleistocene) of Florida
Weeks Post-Doctoral Research Project of G.M. Daley, Department of Geology and Geophysics, University of Wisconsin, 1215 West Dayton, Madison, Wisconsin 53706
In January of 1999, I took a field trip to the Tampa, Florida region with a colleague of mine to collect samples from the Caloosa Shell pit in Ruskin, Florida. The locality is an active quarry working several clastic-carbonate mix shallow water marine facies of the Pleistocene Fort Thompson Formation. The most famous fossils from this locality came from the "Bone Layer" which contains a diverse assemblage of terrestrial vertebrates and is beneath the strata that we studied. We collected from the "Upper Shell Bed" which is composed of a quartz sand with a plethora of mostly molluscan fossils forming a rather dense shell bed.
My colleague, Andy Bush, and I decided that this exposure would be an ideal place to combine his expertise in the analysis of morphologic variation with my expertise in paleoecology. I took replicate samples at one foot intervals for four sections along the outcrop, for a total of 72 bulk samples each weighing 2-4 kilograms.
Andy collected hundreds of Mercenaria campechiensis to analyze shell shape, and thus determine the short term rates of evolution in this lineage. He based his collection scheme on the grid formed by my paleoecologic collections, so we have a contemporaneous sampling scheme - his clams lived at the same time in the same place as the bivalves and gastropods in my samples.
Since the two sampling schemes are contemporaneous, any simultaneous changes in the paleocommunity structure and the morphology of the M. campechiensis can be correlated in order to nail down what morphologic changes may be ecophenotypic. Any changes in the morphology of M. campechiensis that do not correlate with paleoecologic change should be due to evolutionary change. Other Fort Thompson Formation taxa can also be analyzed in this way,
A number of research projects are currently ongoing:
- Paleocommunity Analysis - A detailed analysis of the species present in the Fort Thompson Formation samples. The research has two components:
- Molluscan Databases - Ecological information about modern representatives of fossil species. There are several databases including an online picture gallery of Fort Thompson mollusks and a very large compilation of geologically-interesting environmental tolerances and preferences of several hundred modern mollusks.
- Multivariate Analysis of Samples - Factor, cluster, and guild analysis of the paleoecological structure of the outcrop. This research forms the conceptual framework on which the rest of the research projects below depend.
- Morphometric Analysis of Mercenaria campechiensis - Analysis of morphological variation among M. campechiensis collected from different paleoenvironmental settings. (Andrew Bush)
- Morphometric Analysis of Chione cancellata - Analysis of morphological variation among C. cancellata collected from different paleoenvironmental settings. We are especially interested to see if these patterns match those seen in the analysis of Andy's clams. (Christine Pagelsdorf)
- Predation and Epibiont Patterns on Chione cancellata - Analysis of differences in both the distribution of predatory bore holes and coral and barnacle epibionts on C. cancellata from different paleoenvironmental settings. (Summer Ostrowski)
- Geochemistry - Several large clam shells from different paleoenvironmental settings. have been drilled and are being analyzed for both trace elements and stable isotope geochemistry. (Martha Kutter)
- Taphonomy - An analysis to determine whether or not there are different taphofacies associated with the different paleoenvironments defined in the paleoecological analysis. (Holly Schultz)
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