Predatory behaviour on Ostracoda: spatial analysis of drill‐hole distribution in relation to shell size and ornamentation

Palaeobiological evidence of predation on ostracods derives primarily from drill-hole traces. However, this record is limited to sparse reports and rare quantitative analyses hinder understanding of influence of predator–prey interaction in the evolution of ostracods. Moreover, predation is rarely studied in deep-water settings. We analysed 242 drilled ostracod specimens from the relatively deep-water strata of the Miocene Navidad Formation of Chile to assess how predation varies with size and ornamentation. Specimens of Cytherella (smooth) and Apatihowella (ornamented) and drill hole distributions were analysed using the spatial point pattern analysis of traces (SPPAT) method. Among 3425 specimens, drilling intensity was 5.38% for Cytherella and 9.78% for Apatihowella. SPPAT (of all drilling traces) revealed significant concentrations of drill holes in the dorsal–median region of Cytherella and in the ventral region of Apatihowella. Moreover, drill holes located between the valves were observed only in Apatihowella for 30% of the traces. The predators selected primarily drilling sites close the soft tissue for the smooth shelled Cytherella. In contrast, the thick dorsal shell and the strongly ornamented median regions of Apatihowella may have displaced the preferred attack site, allowing continued access to its soft tissues but toward nutritionally poorer ventral and marginal regions. Thus, ornamentation did not deter predation of the ostracod but did influence predation behaviour. Our analysis highlights the importance of ostracod shell morphology in predator–prey interactions in the ostracod fossil record in deep water settings, and calls for further research to understand the role of evolutionary escalation in ostracods