Palaeobiological and palaeoenvironmental significance of the Pliocene trace fossil Dactyloidites peniculus

The radial trace fossil Dactyloidites peniculus occurs in a deep tier in totally bioturbated shoreface sediments of Pliocene age in the Stirone Valley, N Italy, together with Thalassinoides isp. and Ophiomorpha nodosa. Long, narrow shafts running from centre of the radiating structure and abundant faecal pellets in the radial structure were discovered. The trace maker of D. peniculus, probably a polychaete, deposited the pellets deeply in the sediment, probably for reinforcement of the tubes and a gardening of microbes for feeding. This trace fossil exclusively occurs within a narrow horizon at the top of a shallowing−up section interpreted as a high−stand system tract, below a discontinuity surface capped by finer sediments. D. peniculus was formed in soft sandy sediments under stable conditions related to the latest phases of the highstand system tract. Therefore, it is a candidate for indication of similar environmental situations having a soft sandy, but stable sea floor.