|Quantitative studies of drilling predation on Cenozoic and Recent marine molluscs from Europe|
Sawyer, J.A. (2010). Quantitative studies of drilling predation on Cenozoic and Recent marine molluscs from Europe. PhD Thesis. Universität Wien: Wien. 229 pp.
Direct evidence of ecological interactions between fossil organisms is generally rare, but one exception is predatory drill holes on hard-shelled prey. Few studies have accounted for spatial variation in drilling predation when exploring trends through time, data on predation from European molluscs are scarce and predation intensities have rarely been studied for ecological guilds. Natural variation through space, however, may confound temporal trends. To address these issues, four studies involving drilling predation on Cenozoic and Recent molluscs from Central Europe are presented. Examination of >85,000 molluscs from 134 bulk samples suggests that variation in drilling predation can be drastic within and between environments. Drill frequency of Miocene storm bed samples at the locality Immendorf varied between 0 and 57.5%, and values from the modern Northern Adriatic ranged from 1.4% to 27.4% from intertidal to sublittoral deposits, suggesting careful environmental determinations are necessary to ensure sampling protocols account for spatial variation in predation intensities. Overall drilling predation from Miocene deposits of the Central Paratethys is lower than that from contemporary deposits from North America, suggesting large-scale differences in predation pressure. Comparison of Eocene samples from the Paris Basin and Miocene samples from the Central Paratethys revealed assemblage-level drilling frequencies were sensitive to the sieve-size used for sample processing, highlighting potential problems when comparing studies using different methodologies. In the Northern Adriatic Sea, highest drilling intensities were seen in suspension feeding, epifaunal and cementing taxa, supporting long-held paleoecological theories relating predation to changes in ecological guilds through the Phanerozoic. A case-study of predation on Mytilus galloprovincialis by the muricid Hexaplex trunculus on a sublittoral mussel bed in the Gulf of Trieste indicates facultative feeding activity, with the gastropod often chipping rather than drilling its prey, suggesting that multiple modes of predation should be considered whenever possible.