Vermeij Crushing Analysis: A new old technique for estimating crushing predation in gastropod assemblages

Vermeij Crushing Analysis allows researchers to estimate frequencies of fragmentation due to crushing predation by establishing a taphonomic fragmentation baseline using shells bearing predatory drillholes. We calculated the frequencies of several types of shell damage on groups of drilled and undrilled shells. Shells of the modern species Olivella biplicata, O. baetica, Nassarius perpinguis, and Euspira lewisii were collected at Torrey Pines State Beach, Del Mar, California. The shells were divided into drilled and undrilled groups and examined for multiple types of damage. The frequencies of damage in the drilled groups represent taphonomic damage, as the cause of death of these shells is known to be naticid gastropod predation. In cases where the damage frequencies were higher for the undrilled shells (cause of death unknown, possibly crushing), the differences in fragmentation between the two categories is attributed to crushing predation. The frequencies of damage due to crushing predation are used to estimate a minimum frequency of mortality due to crushing predation in the shell assemblage. Potential confounding factors were also examined, such as potential differences in taphonomic susceptibility and hermit crab habitation between drilled and undrilled shells. This technique bypasses the logistical difficulties of field predation studies and the problems of interpretation of shell repair frequencies, two common methods of assessing crushing predation in shelled prey. Most significantly, Vermeij Crushing Analysis can be performed on both modern and fossil shell assemblages, allowing the study of trends in crushing predation over both space and time. (C) 2011 Elsevier B.V. All rights reserved.