TAPHONOMY AND THE MESOZOIC MARINE REVOLUTION - PRESERVATION STATE MASKS THE IMPORTANCE OF BORING PREDATORS

Exceptionally neomorphosed bivalves from a range of Jurassic sediments from England and North Ireland have been discovered to bear neat, cir cular, straight-sided boreholes over a millimeter in diameter. These b oreholes appear to have been predatory in origin and are highly remini scent of those produced by muricid gastropods. Although none of the kn own gastropod borers have stratigraphic ranges that extend into the Ju rassic, it seems likely that other taxa, perhaps other gastropods, als o possessed the ability to feed in this manner, thus extending the rec ord of this type of prediction. by at least 90 million years. The freq uency of boreholes recorded in Liassic bivalves from Blockley is as gr eat 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 w here shell preservation is particularly good. More usual moldic and ca stic preservation is incapable of recording borehole morphology and th us, 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 n ot represent the actions of the very earliest large, gastropod-like pr edators but they do have implications for further studies that seek to document the appearance of adaptations in prey taxa in response to th is threat, and also indicate that taphonomy may affect evolutionary in terpretations.