A 480-million-year-old parasitic spionid annelid

The Paleozoic fossil record can provide unique insights into the evolution of life history traits through the direct preservation of interspecific interactions in deep time. However, evidence of direct interactions between different species is relatively rare, even among localities with exceptional soft-tissue preservation, with most examples being known from Cambrian marine deposits. Here we provide the first evidence of parasitic organisms from the Fezouata Shale biota of Morocco, the most diverse and abundant Ordovician site with exceptional preservation, but that has heretofore shown no evidence for parasitism. Seven specimens of the bivalve mollusc Babinka show highly characteristic, question mark-shaped shell borings consistent with those produced by modern and fossil parasitic spionid polychaetes. Our results include anatomical and quantitative comparisons with modern and fossil spionid borings and underscore two major conclusions. The first is that the spionid polychaetes were present in the Early Ordovician, which evidences a significant biostratigraphic shift in their temporal origins from their accepted Devonian occurrence. The second is that many unique life history strategies, which were significant components of the Fezouata Shale biota, remain undiscovered, despite the high concentration of taxonomic attention the site has received.