IDENTIFYING PREDATORY FRAGMENTATION IN THE FOSSIL RECORD: A PALEOZOIC BRACHIOPOD EXAMPLE

Predation is a crucial aspect of ecosystems and a driver of evolutionary adaptation (Vermeij, 1987). It is difficult to gauge predation intensity in the fossil record because ambiguity exists in the interpretation of commonly used data. Most studies use injury scars to infer predation, but healed scars are failed attacks, and could have multiple interpretations. This study aims to use Vermeij Crushing Analysis (VCA) (Vermeij,1982; Stafford and Leighton, 2011) to identify successful predation using the Devonian brachiopod Douvillina. VCA estimates the amount of crushing predation in a system by using drilling predation to infer a taphonomic baseline: because prey killed by drilling would not subsequently be attacked by crushing predators, any crushing damage incurred to a drilled shell is due to taphonomic processes. If the crushing damage to undrilled shells is greater than that of drilled shells, that additional damage to undrilled shells may be attributed to crushing predation.Some fragments of Douvillina consist of a characteristic thickened muscle platform on the pedicle valve, which we hypothesize are the result of crushing predation. Material for this study was collected from the Lime Creek Formation at the Rockford Fossil and Prairie Park in Rockford, Iowa, USA. Whole and fragmentary material was examined (N = 532), and the muscle platform fragments were never drilled, even though this region of the shell is a stereotyped drilling site. The drilling frequencies of whole specimens and platform fragments are significantly different (Fisher’s exact test, p<0.03). The expectation, in the case of purely taphonomic damage, would be that there would be equal rates of drilling regardless of damage type, as all shells would be equally likely to be taphonomically fragmented. Had taphonomy played a role in the genesis of the fragments in this study, then we would have expected to observe at least a few drill-holes as there is no obvious taphonomic explanation for why fragments without holes would be more likely to fracture. Thus, the evidence is indicative of successful crushing predation as the primary cause for these commonly found fragments. By using the characteristic fragments as evidence of successful kills,it is possible to determine the mortality rate of the prey, in this case 23.7%.