THE HISTORY OF DRILLING PREDATION AND/OR PARASITISM THROUGHOUT THE PALEOZOIC

Despite numerous reports documenting predation in the Paleozoic, we lack secular estimates for the entire Paleozoic history of predator-prey interactions. Consequently, we surveyed museum and research collections to assemble a database of drilling predation/parasitism in Paleozoic marine benthic assemblages (with a primary focus on brachiopods). The database includes 473 drilled fossils (out of 66,000 total) and offers several important insights into the Paleozoic history of predation. Drillings were extremely rare (~0.3%; n=9,624) in the Early Paleozoic (Cambrian-Silurian). The average drilling frequencies were still low in the Late Paleozoic (from ~0.9% in the Devonian to ~1.5% in the Permian), but are nevertheless 3 to 5 times higher than in the Early Paleozoic. However, in the Late Paleozoic, drilled specimens were documented form nearly every stratigraphic stage, including specimens from many continents. In addition, many collections yielded high frequencies of drilled fossils (both for single genera or entire assemblages), occasionally attaining frequencies comparable to those reported for Cenozoic mollusks (>>10%). Also, drillings in Late Paleozoic appear to have been significantly more frequent in bivalves than in brachiopods from the same sites. Finally, the drill holes found in our survey varied widely in size (from less than 0.2mm to more than 4 mm) and shape (from cylindrical to parabolic profiles, sometimes with a beveled edge). The results suggest that the Late Paleozoic record of drilling predation/parasitism is globally widespread and stratigraphically continuous. The results also confirm that the Paleozoic frequencies of drilling (mostly estimated for brachiopods) were much lower than Cenozoic ones (primarily known for mollusks). Whereas drillings appear to have been extremely rare in the Early Paleozoic, the previously postulated mid-Paleozoic (Devonian) phase of higher drilling frequencies may have extended throughout the entire Late Paleozoic. The sporadic instances of high frequencies suggest that high drilling intensity is not exclusively restricted to Late Mesozoic and Cenozoic mollusks. The dramatic variation in morphology and frequency of drillings is suggestive of behavioral, and perhaps also taxonomic, diversity of drillers.