Predation by boring gastropods on Late Cretaceous and Early Palaeocene ostracods

The predation by boring gastropods on ostracods can be thought of in terms of being a “truncated” system inasmuch as all adult prey individuals are accessible to all predators, but only attract juveniles of the latter. Material from the Santonian (Late Cretaceous) of Israel and the Palaeocene of Nigeria were studied. Hole-size is not correlated with prey-size for the Santonian material, whereas this relationship is highly significant in the Palaeocene samples. Holes made by juvenile naticids are larger, on the average, than those made by muricids. The dimensions of the boreholes for the two samples do not differ statistically at the bivariate level. Ostracods with strong surface ornament were less likely to be drilled than those with smoother shells. In neither the Santonian nor the Palaeocene could a case be made for a selective effect arising out of predational pressure (the predational level in the Santonian is 8% and in the Palaeocene, 2%). Partially completed holes made by muricids and naticids occur in both sets of material and there are several examples of multiple boreholes (i.e. two or more holes in the same shell). Examples of boreholes are figured and an early phase of drilling illustrated in which radula scratches and the effects of dissolution by the accessory boring organ (ABO) are visible. Estimates of muricid and naticid sizes, based on ABO dimensions, (reconstructed from borehole diameters) indicate a range in whorl-height running from 0.6–3.9 mm (mode at 1.8 mm).