Concepts in ichnology illustrated by small round holes in shells

Trace fossil classificationrequires a double system ofnomenclature. The trace fossil name (ichnotaxon) is based on the morphology of the structure whereas the biological taxon represents the interpreted phylogenetic position of the causative organism. The two nomenclatural systems are in no way interchangeable, and both are required for the complete classification of the trace fossil. Many trace fossils have not yet been designated a descriptive ichnotaxon, but since trace fossils require names if they are to be treated systematicauy, an interpretative biotaxon is commonly offered in such cases in place of the lacking ichnotaxon This procedure tends to deflect attention from the true nature of the trace fossil and implies a spurious accuracy in phylogenetic determination, which leads to unreliable palaeobiological conclusions. Small, round drill-holes in shells illustrate these points well. They are abundant trace fossils anc/having no ichnotaxon, tend to be referred to as the work of shell-drilling muricid and naticid gastropods. However, several other groups of gastropods, as well as the octopodid cephalopods, turbellarians, nematodes and articulate brachiopods also produce round holes, although their work is little understood. Prior to embarking on such speculation as to causative organisms, an ichnotaxon is required in order to draw attention to these trace fossils and increase the rigour of their treatment When their morphology and distribution are more fully understood we shall be in a better position to discuss their phylogenetic attributions.