EXPLORING EPIBIONT ENCRUSTATION PATTERNS: A CASE STUDY WITH PARASPIRIFER BOWKNOCKERI

The preservation of symbiotic relationships in the fossil record can provide a wealth of information regarding the paleoecology of microcommunities. The Middle Devonian Silica Shale Formation (Ohio and Michigan, USA), a sedimentary formation that represents a once shallow, tropical marine environment, preserves a unique window into studying symbiotic relationships in the fossil record. A large population of spiriferid brachiopods (Paraspirifer bowknockeri) hosted a diverse array of epibionts, including corals, bryozoans, brachiopods, annelids, and others.

This study examines hundreds of specimens of the spiriferid brachiopod P. bownockeri and the preserved epibionts on their shells to evaluate relationships between the encrusting organisms, their host, and their environmental and ecological conditions. All the encrusting organisms were identified and their locations on the brachiopod (i.e., commissure, hinge, pedicle valve, brachial valve) were recorded.

Using previously generated 3D models of a subset of the studied Paraspirifer samples along with the newly collected data (i.e., location data and epibiont identification) allows us to test a number of hypotheses. Specifically, we examine whether or not the epibionts encrusted while the brachiopod was alive, and, if alive, examine possible life position of the host brachiopods based on the presence or absence of epibionts on each valve. We also examine the co-occurence of certain epibionts on each valve and patterns of epibionts layering on top of one another. Principal Components Analyses (PCA) and cluster analysis were performed to determine if the epibionts displayed preferential tiering on certain valves and preferential co-occurrence with other epibionts. Using 3D models, we also consider the percentage of surface area occupied by the epibionts.

Results indicate that certain epibionts preferentially encrust in particular locations on the host, likely due to preferences for location in feeding in the water column; these patterns also allow for interpretation of the life stage in which the brachiopod became encrusted. These data can be used to build a better picture of how fossil microcommunities interacted with one another, their hosts, and their environment.