THE INFLUENCE OF ENVIRONMENTAL CHANGE: THE BRACHIOPOD SOWERBYELLA RUGOSA IN THE UPPER ORDOVICIAN KOPE FORMATION OF THE CINCINNATI OHIO AREA

In microevolutionary studies, stratigraphic changes in fossil morphology are commonly interpreted directly as the evolution of morphology. However, given the ubiquity of ecophenotypy as well as changes in facies related to sequence stratigraphic architecture, an equally plausible interpretation of such stratigraphic changes is that they solely reflect the sampling of morphologies from different sedimentary environments with no evolutionary change. The combination of ecophenotypy and sequence architecture may underlie some reported patterns of punctuated equilibrium, phyletic gradualism, and iterative evolution.

These issues are addressed in this study of the sowerbyellid brachiopods from the Upper Ordovician of the Cincinnati, Ohio area. Samples of Sowerbyella rugosa were collected from the C1 sequence (Kope Formation) and samples of the closely related Thaerodonta clarksvillensis were collected from the C4 sequence (Waynesville and Liberty Formations). The Kope and Waynesville record offshore deposition, whereas the Liberty records deposition in a slightly shallower transition zone environment. Three questions will be addressed: (1) Does S. rugosa show any facies-related morphologic change within the Kope Formation? (2) Is S. rugosa morphologically distinguishable from C4 occurrences of T. clarksvillensis from offshore facies similar to that found in the C1? (3) Is S. rugosa morphologically distinguishable from C4 occurrences of T. clarksvillensis from shallower, transition zone facies?

Landmark analysis was used to analyze the morphology of these brachiopods. Eight landmarks were selected on the brachial valve interior, based on morphologic significance (cf. Haney, Mitchell, and Kim, 2001). Each individual was digitally photographed and then the coordinates of each landmark were measured and analyzed using the relative warp method. Multivariate statistical analyses will be used to test for differences in morphology among beds and among sequences.