We calculated the incidence of drilling on bivalve genera from the Neogene fossil record of Panama and Costa Rica to determine differences in predation intensity among groups based on shell architecture, life habit, mobility, and taxonomic affinity. Bulk samples from 28 localities yielded
>106,000 bivalve specimens, which were examined for characteristic drilling traces of muricid and naticid gastropods. We calculated the drilling intensity for the 90 most common genera, and characterized the size, ornament, life habit, and mobility for each genus. Large size confers considerable
protection from drilling, but shell ornamentation does not. Life habit is strongly linked with drilling intensity. Epifaunal bivalves experience higher predation than infaunal bivalves and shallow burrowers experience higher drilling than deep burrowers. Mobility is also important for epifaunal
bivalves; cemented taxa are twice as likely to be drilled as their uncemented counterparts. Our results suggest that bivalve behavior and life habits are more important than shell architecture for defense against drilling predators.
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