Emily S. Stafford

Categorization of shell fragments provides a proxy for environmental energy and predation intensity

Shell fragments are extremely abundant in many marine environments; the origins of these fragments can largely be attributed to either crushing by predators or post-mortem processes such as transport. We present and test a new approach to identifying the origin of shell fragments in marine environments by examining modern mollusc assemblages from three wave-exposed, low-predation and three wave-sheltered, high-predation intertidal localities in Bamfield, British Columbia. We hypothesized that fragments with all-rounded edges (AR) or a combination of rounded and sharp edges (R&S) are indicative of taphonomic processes such as transport and so should occur more often in wave-exposed, low-predation localities whereas fragments with all sharp edges (AS) or a combination of intact and sharp edges (I&S), indicative of predation, should be more common in wave-sheltered, high-predation settings. In keeping with the prediction, All-Rounded (AR) and Rounded and Sharp (R&S) fragments are more abundant at the wave-exposed localities than at wave-sheltered localities whereas Intact and Sharp (I&S) and All-Sharp (AS) fragments are more abundant at high-predation localities than at low-predation localities. The two types of localities were statistically distinguishable for either gastropod or bivalve fragments. This supports the hypothesis that I&S and AS result from predation, whereas AR and R&S have a taphonomic genesis.

Brachiopod morphology, life mode, and crushing predation in the Ordovician Arnheim Formation, Kentucky, USA

Abstract Predation on ancient shelled prey is an often-studied topic in paleoecology, but the early Paleozoic and the brachiopods that dominated the seafloor at that time are relatively underrepresented in the predation literature. We assessed predatory repair scar frequencies among the brachiopod genera from the Early Richmondian (Late Ordovician) Oregonia Member (Arnheim Formation) near Flemingsburg, Kentucky. We found higher repair frequencies on the concavo-convex Rafinesquina and Leptaena relative to the bi-convex genera. There were no trends in repair frequency through the stratigraphic section and no relationships between repair frequency and community diversity metrics. It is possible that concavo-convex brachiopods’ flat shape, thin shell profile, and free-lying (no pedicle attachment) lifestyle made them more likely or appealing targets of Ordovician crushing predators. It is also possible that concavo-convex brachiopods were better suited to survive crushing attacks than biconvex taxa. We also found differences in shell ornament that may influence the visibility of repair scars.