Taphonomy and the Mesozoic marine revolution; preservation state masks the importance of boring predator

Exceptionally neomorphosed bivalves from a range of Jurassic sediments from England and North Ireland have been discovered to bear neat, circular, straight-sided boreholes over a millimeter in diameter. These boreholes appear to have been predatory in origin and are highly reminiscent of those produced by muricid gastropods. Although none of the known gastropod borers have stratigraphic ranges that extend into the Jurassic, it seems likely that other taxa, perhaps other gastropods, also possessed the ability to feed in this manner, thus extending the record of this type of predation by at least 90 million years. The frequency of boreholes recorded in Liassic bivalves from Blockley is as great as has been recorded in Tertiary and Recent malacofaunas that are assailed by predatory gastropods, thus indicating that these unknown predators were capable of exerting a substantial selection pressure on their prey. Recognition of Mesozoic predatory boreholes occurs only where shell preservation is particularly good. More usual moldic and castic preservation is incapable of recording borehole morphology and, thus, the presence of boreholes is overlooked in most faunas of this age. Consequently, the timing of the onset of this type of predation may be underestimated. The boreholes described in this paper probably do not represent the actions of the very earliest large, gastropod-like predators but they do have implications for further studies that seek to document the appearance of adaptations in prey taxa in response to this threat, and also indicate that taphonomy may affect evolutionary interpretations.