Bioerosion and bioincrustation in body fossils from the coastal plain of Rio Grande do Sul State, southern Brazil

The Coastal Plain of Rio Grande do Sul State (CPRS), in southern Brazil, is known for the presence of fossil accumulations containing remains of both marine and terrestrial Pleistocene organisms as large biodetrital concentrations on the continental shelf and also in continental outcrops in the Chuí Creek and Mangueira Lake. Many invertebrate remains exhibit bioerosion traces caused by endoskeletozoan organisms, while surface colonization by episkeletozoans is scarce. The trace fossils Entobia and Caulostrepsis are the most common, followed by Pennatichnus, Gastrochaenolites and Maeandropolydora. Gastrochaenolites is found mostly in ostreids and Oichnus is mostly absent among fossils from the continental shelf and Mangueira Lake, but it is found in many bivalves from the Chuí Creek. Trace fossils identified as cf. Clionoides isp. are recorded for the first time among fossils from the CPRS. Bioincrustation on invertebrates is very scarce, represented by cheilostomate bryozoans, ostreids and cirripeds. Among vertebrate remains found in the continental shelf, bioerosion has been recorded, so far, on three specimens, and remains collected at greater depths are mostly covered by fouling organisms, including serpulid polychaetes and corals. While fossils from shallower areas are affected by bioerosion, bioincrustation affects mostly remains found in deeper areas of the shelf. Ichnological differences among invertebrate fossils found in the continental shelf and those from outcrops in terrestrial environments seem to be related to marine transgressions and regressions that affected the area during the Late Quaternary.