Corkscrew-like horizontal trace fossils with a focus on a new ichnospecies of Helicodromites from the Oligocene Molare Formation of NW Italy

Horizontal helical trace fossils constitute a characteristic burrow architectural design, but their ichnotaxonomy requires some clarification. In this paper, we review and revise this taxonomy on the basis of collections and data from the literature. Helicorhaphe is included in Helicodromites because its type ichnospecies displays the same morphological principles. A new ichnospecies of Helicodromites is distinguished from Oligocene offshore fan delta deposits in NW Italy. All ichnospecies of Helicodromites display a characteristic set of morphometric parameters that allow their distinction. All were probably produced by capitellid polychaetes in a deep tier within the sediment. They were generally stationary burrows, whose tracemakers benefited from feeding on microbes without significant sediment reworking.