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

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.     

Upper Katian (Upper Ordovician) trans-Atlantic δ13C chemostratigraphy: the geochronological equivalence of the ELKHORN and PAROVEJA excursions and its implications

Since 2010 when the North American ELKHORN and Baltoscandic PAROVEJA isotope excursions were first described and named, their mutual age relations have remained uncertain, if not controversial. This was at least partly due to the incompleteness of the ELKHORN excursion in its reference section in western Ohio. The unexpected discovery of an apparently complete ELKHORN excursion in a drill core from St Marys in western Ohio has led to the conclusion that in terms of stratigraphical position and δ¹³C curve correspondence, the ELKHORN and PAROVEJA excursions are so similar that they apparently represent the same isotopic curve perturbation. The ELKHORN/PAROVEJA excursion occurs in the D. pacificus Graptolite Zone and uppermost A. ordovicicus Conodont Zone in the uppermost Katian Stage (Stage Slice Ka4 of Bergström et al. Lethaia 42, 97–197, 2009). Because the designation PAROVEJA was published two months before that of ELKHORN, it has priority as excursion designation. This excursion is particularly well represented in the carbonate successions in the Great Basin of western United States. Chemostratigraphy and biostratigraphy in that region show that the Richmondian transgression was contemporaneous with the beginning of the middle Katian WHITEWATER/MOE excursion. The onset of the Richmondian transgression has long been controversial but now available evidence suggests that it is of essentially the same age across large regions of the southern, western and central United States.