In defence of an iconic ichnogenus – Oichnus Bromley, 1981

Abstract

By establishing the bioerosion ichnogenus Oichnus, Richard Bromley (1981) addressed ‘small round holes in shells’ and catalysed a series of still ongoing discussions on ichnotaxonomical principles. In a recent revision by Zonneveld and Gingras (2014), Oichnus was rejected, together with Tremichnus Brett, 1985 and Fossichnus Nielsen, Nielsen and Bromley, 2003, by means of subjective synonymisation with the presumed senior synonym Sedilichnus Müller, 1977. However, Sedilichnus is nomenclaturally unavailable, because it is an atelonym (conditionally proposed). In addition, reinvestigation of the type material of ‘Sedilichnus’ shows that it probably describes variably shaped oscula and thus is a genuine morphological character of the host sponge Prokaliapsisjanus, rather than a bioerosion trace fossil. The ichnogenera Oichnus and Tremichnus are re vised, leading to the synonymisation of Balticapunctum Rozhnov, 1989 with Tremichnus, and of Fossichnus with Oichnus. The refined ichnogeneric diagnoses return Oichnus to complete or incomplete bioerosive penetrations in calcareous skeletal substrates, commonly interpreted as praedichnia with or without signs of attachment, while Tremichnus (now including O. excavatus) exclusively refers to shallow pits passing into echinoderm skeletons that are interpreted as domichnia or fixichnia.