ASSESSING BIODIVERSITY TRENDS USING THE TYPE CINCINNATIAN AS A MICROCOSM: TESTING SAMPLING EFFECTS IN A CLOSED SYSTEM

The ability to assess trends in Phanerozoic global marine biodiversity has a broad impact on paleontology. However, since the global fossil record represents an integrated system of parameters such as lithological variation, taphonomic disparity, differential amounts of fossiliferous rock volume, and variability in population structure, definitively assessing the biological meaning of biodiversity trends is not a straightforward endeavor.

Since the global system is complex, it is difficult to test how these parameters influence each other as well as their effect on biodiversity measures. To resolve this problem, variables including rock volume, taphonomic disparity, population structure, sample size, taxonomic resolution and choice of data treatments are investigated here within a geographically, stratigraphically, and temporally constrained microcosm: the type Cincinnatian of Kentucky. By using a closed system, the relationships of the variables to one another are known definitively, making it possible to directly assess their effects on aggregate regional diversity trends.

As part of this ongoing study, a collection-level faunal database is being compiled from the literature for the Kope, Fairview, and Bellevue formations which comprise the lower third of the type Cincinnatian. Preliminary assessments using faunal occurrences and abundances illustrate differences in taxonomic composition and magnitude of measured diversity both in aggregate and among the three formations comprising the study interval. Upon initial examination, these differences appear to be influenced by variations in sample size and population structure. In addition to using literature-based data, later stages of this project will incorporate field derived faunal data and censuses from museum collections, as well as estimates of the amount of rock actually sampled for diversity analyses conducted here.

Although initial analyses illustrate qualitatively the extent to which parameters of the rock record or methods of sampling affect biodiversity trends, it remains to be seen how these effects are manifested quantitatively. Results of this study should help to identify relationships among variables that affect estimates of biodiversity at the local, regional, and global levels.