Bioerosion structures and their distribution on shells of the Lower Pleistocene terebratulid brachiopod Gryphus minor

Abstract

We present an analysis of bioerosion structures occurring on the shells of a Gryphus minor fossil population from Reggio Calabria (S. Italy), Early Pleistocene (Calabrian) in age. This population belongs to a palaeobiocoenosis that can be compared with present-day detritic terrigenous mud outer circalittoral environment. The assemblage includes 5 different brachiopod species, but it is dominated by Gryphus minor. We analyzed all of the 4069 Gryphus individuals in search of shell damage due to biological activity (bioerosion). About 12% of the specimens were affected to some extent. Bioerosion traces were identified down to the ichnospecies level and ascribed to potential biological agents (predators, epibionts or endobionts). Evidence for predation (Praedichnia) is limited, whereas etchings for attachments (Fixichnia) are more common. In particular, 453 traces belong to Podichnus obliquus, an ichnotaxon that describes a distinctive etching scar due to the pedicle attachment of other brachiopods on the shell. In the case of Gryphus minor, Podichnus were caused by conspecifics. Podichnus distribution on the shells, and its shape, suggest that Gryphus minor had a somewhat short pedicle, and lived with the umbo close to the substrate.