Rocky Shorelines

Modern rocky coasts bear diverse and complex organism communities constituted by a variety of epi- and endolithic taxa. Among borers, the most important are sponges, bivalves, polychaete and sipunculan worms, regular echinoids, and cirripedes. The types of bioerosion trace fossils are fundamental to recognize rocky shores in the geologic record, where they occur linked to transgressive events flooding rocky substrates. Trace-fossil assemblages are less diverse in noncarbonate than in carbonate rockgrounds, as chemical borers are not able to colonize the first. There is a marked increase in rocky shore trace-fossil diversity throughout the Phanerozoic. Paleozoic assemblages are generally poorly diverse with great dominance of worm borings (Trypanites). Ichnodiversity increases in the Mesozoic, and particularly in the Cretaceous, when assemblages take on a more modern aspect dominated by bivalve (Gastrochaenolites) and sponge (Entobia) borings.