Bioerosion on Megacardita jouanetti (Bivalvia) from the Miocene of Foz do Rego (Costa de Caparica, Portugal)

This work focuses on the study of bioerosion structures associated with Megacardita jouanetti shells from the Miocene of Foz do Rego, Costa de Caparica (Portugal), revealing 18 different speciic icnotaxa. Besides the considerable ichnodiversity, the percentage of bioeroded shells in the analysed samples is extremely high (99%). The dominant bioerosion structure is Umbichnus inopinatus, followed by structures linked to the boring activity of non-predatory organisms, including annelid borings (Caulostrepsis and Meandropolydora), algal microborings (Semidendrina - form) and ctenostome bryozoans (Pinaceocladiochnus and Pennatichnus). Spatial distribution analysis of bioerosion structures show that there is a predominance of structures produced in a clearly post-mortem stage of the biosubstrate, rather than produced during the life of the bivalve or immediately post-mortem