AS GOOD AS IT GETS: QUANTITATIVE LESSONS FROM TRACE FOSSILS PRODUCED BY DRILLING PREDATORS

Quantitative paleoecological research on predator-prey interactions in marine ecosystems has been dominated by studies that focus on drilling predation. In fact, more than 90% of paleontological publications that report quantitative data on predator-prey interactions (e.g., frequency of attacks, attack site selectivity, prey size selectivity) center on drill hole data. This narrow focus is not myopic but pragmatic: paleontologists have long recognized that distinct trace fossils left by drilling organisms represent an unrivalled source of quantitative paleoecological data. Arguably, the drill holes are as good as it gets when it comes to quantitative studies of predation in the marine fossil record.

Seemingly, drill holes offer us diverse opportunities to gain quantitative insights into prey-predator interactions and predatory behaviors. The most common quantitative themes include (1) relative drilling frequency; (2) relative frequency of failed attacks (incomplete/multiple drill holes); (3) frequency of edge drilling; (4) variation in drilling frequency across prey species; (5) distribution of drill holes across prey size classes; (6) spatial distribution of drill holes on prey skeleton; (7) drill hole size; (8) correlatives between drill hole size and prey size/type; and (9) drill hole distribution across taphonomic grades of prey specimens. All these themes involve numerous assumptions that are rarely verifiable but often ignored tacitly. However, some of the quantitative themes require relatively fewer assumptions than others. In addition, comparative analyses, across space or through time, can often minimize some of those assumptions or make them more sensible. Nevertheless, multiple interpretations are usually viable for quantitative patterns recorded by drill holes and unambiguous conclusions are rarely irrefutable. Drill holes are a potent illustration of both, the cognitive limits of quantitative paleoecology as well as our scholarly optimism in tackling research questions that are unlikely to be fully solvable.