The trace fossil Circulichnis as a record of feeding exploration: New data from deep-sea Oligocene–Miocene deposits of northern Italy

Circulichnis is a puzzling, ring-like trace fossil preserved on bedding planes. It is represented mostly by its type ichnospecies C. montanus, which is characterized by an evenly circular or elliptical course. A new ichnospecies, C. ligusticus, is distinguished based on material from deep-sea Oligocene–Miocene deposits of the Tertiary Piemonte Basin, NW Italy. It shows a winding or irregular course. A new model of Circulichnis is proposed as an exploration burrow produced mostly by the trace makers of Helminthoidichnites, Gordia, or Helminthopsis, as it moved to a different sediment layer to checking its feeding utility. This type of behaviour occurred already by the Ediacaran and is common in marine, mostly deep-sea bedded sediments. The trace makers belong mostly to polychaetes in marine sediments and to oligochaetes in continental sediments.