ENVIRONMENTAL LIMITATIONS ON SETTLING LOCATION OF LATE DEVONIAN SKELETOBIONTS IN THE APPALACHIAN BASIN

Many factors may influence the suitability of a site for the settlement of hard-substrate marine fauna. Here, we examine some of these factors for fossil skeletobionts, organisms that live attached to or bored into the skeletal material of other organisms. Specifically, we examined the distribution of skeletobionts on fossil brachiopod shells from the Upper Devonian of the Appalachian Basin. Factors we evaluated as potential influences on skeletobiont settlement include onshore-offshore location, frequency of disturbance, body size of host brachiopods, sculpture of hosts, and location on the hosts’ shells (interior vs. exterior, dorsal vs. ventral valve). Multivariable logistic regressions indicate that onshore-offshore position and host body size consistently predict skeletobiosis and that sculpture predicts skeletobiosis to a lesser degree. Skeletobiosis was more common in more onshore settings and on larger shells. In cases for which skeletobiosis was significantly predicted by sculpture, skeletobiosis was most common on ribbed shells. Susceptibility to disturbance was only found to be significant for the ichnogenus Canaliparva. Binomial tests indicate that skeletobionts are preferentially found on the exteriors of shells and on the ventral valves of their hosts. These results may indicate that skeletobiont settlement was most strongly limited by depth or proximity to shoreline and the area (and possibly exposure time) of the shell substrate. Results are consistent with settlement occurring on both disarticulated brachiopod shells and articulated brachiopod shells (including live hosts). Settlement may also have been more likely on surfaces exposed upward into the water column. These results add detail to our understanding of the environmental limitations of Devonian skeletobionts which may be used in future for paleoenvironmental interpretation.