PALEOENVIRONMENTAL DISTRIBUTION OF SKELETOBIOSIS ACROSS A LATE DEVONIAN MASS EXTINCTION EVENT IN THE APPALACHIAN BASIN

During mass extinction events, both biotic and abiotic conditions change dramatically, and the relative effects of these two types of change on fauna are often uncertain. Here, we examine the dynamics of a mass extinction from the points of view of both interactions between organisms and the changing abiotic environment. Specifically, we examine changes in patterns of skeletobiosis (encrustation and boring of shells) on brachiopods in the Catskill delta complex (Appalachian foreland basin) during the Frasnian-Famennian (F-F) mass extinction. Skeletobionts preserve an unambiguous record of interaction, in that host shells are required for settling, and there is turnover of brachiopod host taxa in the extinction. This work focuses on the first pulse of the F-F extinction, the Lower Kellwasser (LK) event, because it is well represented in the surveyed locations in western New York State and northern Pennsylvania. Previous work with this system has shown that skeletobionts of the Catskill delta complex experienced a change in relative abundance across the LK event. It is possible that changes in the host communities influenced skeletobiont communities, but the relative effect of abiotic factors is not yet known. Paleonvironmental gradients have been identified using non-metric multidimensional scaling (NMDS) analysis of the brachiopod assemblages. The environmental distribution of skeletobionts living on the brachiopods can be examined along the same NMDS gradients. Preliminary results indicate that skeletobionts were located throughout the range of their hosts prior to the LK event, whereas skeletobionts were more sparsely distributed in deep environments following the LK event. We will examine several potential explanations for this pattern, including extinction in the host community and changes in the physical environment.