Drilling predation presents a rare opportunity to quantify ecological interactions in the fossil record. Most large-scale studies have focused on temporal rather than spatial patterns. However, spatial variability patterns may both mask secular trends and provide important insights into geographic and environmental gradients in predation. To explore spatial patterns in predation, bulk samples of mollusks were collected from middle Miocene (Burdigalian and Langhian) marine deposits of Europe, including multiple sites from two adjacent bioprovinces: the Boreal Province and Paratethys. Two facies were sampled: fine-grained and coarse-grained siliciclastics. The sampling scheme allows for a comparison of drilling predation at the local scale (within provinces), regional scale (between provinces), and between facies (within and between provinces).
In the Miocene of Europe, statistically significant spatial variations in drilling-predation patterns occur locally, regionally, and among facies (these variations can be either masked or exaggerated when the samples are pooled into coarser analytical groupings). Regardless of the taxonomic resolution of the analysis, inter-regional and facies variation between samples is significant and on occasions exceeds 20%. The sample-level pattern of variation in drilling intensity is notably consistent for pooled data and for each mollusk class, but major differences exist at finer taxonomic scales of families and genera. Escalation parameters (proportion of failed and multiple predatory attacks) also vary significantly between the provinces. In contrast, drill-hole size and site distributions display remarkably consistent patterns across samples regardless of the region, environment, composition of potential prey and predator, observed drilling intensity, and levels of escalation parameters. This suggests that stereotypy in predatory behavior can be displayed by higher taxa and may be independent of the environment, geography, and prey type. The dramatic differences between intensity patterns and stereotypy patterns indicate that the scale and nature of spatial variability may vary notably among different predation parameters. Thus, whereas behavioral stereotypy appears to be stable, the drilling intensity and escalation parameters display variability levels that are comparable to the temporal variations observed among samples collected over evolutionary time scales. The spatial variation in the fossil record of all relevant predation parameters should be evaluated independently, and controlled for, before any large-scale temporal trends are inferred.