see trace fossil

A trace fossil, evidence of an organism or of its activities (e.g.: burrows or tracks) but with no remnant of the original organism remaining. Sometimes it is impossible to determine which organism was responsible for a particular ichnofossil. In other cases several organisms may create the same ichnofossil. Distinctive ichnofossils may be given scientific names (referred to as form genera) for purposes of identification. ( Tracks and trails)