TAPHONOMIC INFERENCES DRAWN FROM EPIBIONTS ON LATE OLIGOCENE CRABS OF THE KEASEY FORMATION, COLUMBIA COUNTY, OREGON

Epibionts tend to foul the lightly calcified epicuticle of crabs. Evidence of epibionts is often lost on specimens preserved within concretions due to weakness between this layer and the underlying exocuticle. As a result, they are seldom preserved on fossil decapod crustaceans. Three species of well-preserved crabs from the late Oligocene Keasey Formation of Oregon have been colonized by epibionts across the dorsal carapace, the anterolateral margins, on the joints between leg segments, and across the orbit. Epibionts can significantly interfer with the host, and the animal to which they attach may spend more energy carrying them as a result of colonization. Some decapods possess antifouling mechanisms that include grooming with setal brushes located at the tips of pereiopods; others, including members of the Brachyura, exhibit only limited grooming behaviors. While grooming of sensory and respiratory surfaces is common among brachyurans, general body grooming is not well-developed. The bodies of brachyurans typically are not streamlined for swimming, and they are unable to manipulate their appendages in a way that might aid grooming most of the carapace surface. Portunids, however, have swimming appendages with setae lining the margins of the fifth pereiopod dactyl. In order to determine the regions of the carapace the late Oligocene crabs of the Keasey Formation could have effectively groomed, epibiont locations have been plotted on maps of the dorsal and ventral surfaces of modern portunid and non-portunid crabs to identify the regions of the carapace that can be efficiently groomed. The mapping strategy permits distinguishing in-vivo and post-mortem colonization. The paleoecology and taphonomy are interpreted for barnacles and serpulid worms based on their living positions and degree of interference on specimens belonging to three fossilized crab species. Research supported by a grant from Sigma Gamma Epsilon at Kent State University.