VARIATION IN SKELETOBIONT-HOST RELATIONSHIPS ACROSS THE FRASNIAN-FAMENNIAN EXTINCTION EVENT ALONG AN ENVIRONMENTAL GRADIENT

During mass extinctions, both the abiotic and biotic components of the Earth system are in a state of dramatic change, and extinctions may result directly from changes in the physical environment or secondarily from ecological disruption. Brachiopods and organisms that attach to or bore into their shells (skeletobionts) provide a useful system in which to observe biotic interactions across a mass extinction event at the regional spatial scale. This is because brachiopod shells readily preserve as fossils, often exhibit evidence of boring or encrusting organisms, and are found in facies representing a range of depths. A series of bulk assemblages containing brachiopods were examined from multiple sites in the Upper Devonian of western New York State and northern Pennsylvania to examine (1) gradients in assemblage composition associated with water depth among both brachiopods and skeletobionts and (2) changes in these gradients across the Frasnian-Famennian extinction. Non-metric multidimensional scaling (NMDS) of the brachiopod data was used to reconstruct the depth gradient before and after the first pulse of extinction (Lower Kellwasser event). Preliminary data indicate that skeletobionts living on the brachiopod shells had limited paleoenvironmental distributions, and that the greatest variation in skeletobionts assemblage composition is found at intermediate depths. Additional analysis will be used to determine if and how the skeletobiont-host relationship varies with depth. When combined with data relating the skeletobionts to their hosts, the paleoenvironmental results will provide a case in which we can measure the relative degree of control that both biotic and abiotic factors have on the distribution, abundance, and success of organisms over the course of a mass extinction.