PALEOECOLOGY OF EPIZOANS ON THE MIDDLE DEVONIAN BRACHIOPOD PARASPIRIFER BOWNOCKERI

The Silica Shale Formation (Middle Devonain) provides an abundant record of epibiont and host interactions in a shallow, tropical, marine environment. Specifically, the host brachiopod Paraspirifer bownockeri provides a window into the varied invertebrate epibionts that relied on this species as a source of substrate and food, and as a way to better position themselves in the water column. The preservation of community interaction preserved in these brachiopods is unusual in the fossil record, providing an opportunity to ask in-depth questions about the interactions between host and epibiont.

Through a combination of qualitative work, quantitative analysis, and 3D morphometrics, this study evaluates the epibiont-host relationships, and epibiont-epibiont relationships on P. bownockeri. More than 200 specimens of P. bownockeri from the University of Michigan Museum of Paleontology were evaluated to uncover epibiont patterns, life position of the host, and indicators of symbiosis. For each of the brachiopods, data on each epizoan was collected (e.g., number and types of epibionts, location on the host shell). Of the hundreds of specimens studied, 51 of them were selected for further analysis using 3D morphometrics. We created 3D models of these 51 brachiopods We placed fixed and semi-fixed landmarks on each of the specimens using the program 3D Slicer to capture shell surface differences caused by epibiont encrustation. We used multivariate ordination methods and visualization in R to examine preferential co-occurrence and placement tiering amongst epibionts.

The resulting patterns in epibiont placement data indicate preferential encrustation on the host, likely due to the feeding methods of each epibiont type. Locations that were preferentially encrusted or clear on the host were compared to brachiopod life position hypotheses to evaluate the life position of the host. Placement patterns on the host and other indicators (e.g., scarring of the host shell) provide evidence of symbiotic interaction between the epibiont and the host past the use of the host as a hard substrate. By using a combination of qualitative and quantitative analyses, we were able to create a more comprehensive analysis of the paleoecological interactions shown in these fossilized microcommunities.