DEVELOPING A KEY FOR IDENTIFYING TREPOSTOME BRYOZOANS FROM THE CINCINNATIAN SERIES OF THE CINCINNATI ARCH

Trepostome bryozoans constitute a large proportion of the fauna of Upper Ordovician rocks of the Cincinnati, Ohio area, but their identification is hampered by the need for thin-section or acetate peels of their internal structure. We are developing a key for trepostome identification for this region and our first efforts focus on ramose growth forms of the C5 sequence (Richmondian). Although growth form by itself is not sufficient to identify any Cincinnatian genus, it does narrow the range of likely options and serves as a useful starting point. Some ramose genera have distinctive traits that permit rapid identification. For example, Rhombotrypa has square zooecia in the endozone, which are visible in both transverse and oblique sections. Homotrypa and Gortanipora are the only ramose genera with abundant cystiphragms, which are readily visible in longitudinal section. Several genera lack such distinctive characters, and distinguishing among them is more difficult. Many of these can be quickly sorted based on the abundance of mesopores, which are visible in both tangential and longitudinal section. For example, Parvohallopora, Batostomella, Heterotrypa, and Batostoma have abundant tabulate mesopores. These genera can then be distinguished on other criteria, and a similar approach can be taken for genera in which mesopores are present to rare, such as Amplexopora, Dekayia, and Stigmatella. One challenge is determining those characteristics that hold true for all species of a genus, as the species of some genera display wide morphological variation. Our future work will focus on refining this key for the ramose trepostomes of the type Cincinnatian, then extending it to other growth forms. The key and updates to it will be posted to the UGA Stratigraphy Lab website at http://strata.uga.edu/cincy/fauna/trepostomatida/trepostomeGuide.html.