Bioturbation structures of polychaetes in modern shallow marine environments and their analogues to Chondrites group traces

The present interdisciplinary study comprising actuopalaeontology, marine biology and marine chemistry reveals particular polychaete species as trace-makers of distinct branched burrow systems in modern intertidal and shallow subtidal deposits. In this way, the study concerns one of the most enigmatic trace fossils in earth history, the cosmopolitan ichnogenus Chondrites. Bioturbate structures of this type are frequently found and described in the fossil record, as well as in deep sea cores from modern environments. So far, they have generally been ascribed to unknown producers living as endobenthic, chemosymbiontic organisms in anoxic sediments, mostly in deep sea environments.Scoloplos armiger, occurring in the German Wadden Sea in the lower parts of tidal flats, produces burrow structures that conform with numerous trace fossils of the ichnogenus Chondrites. Heteromastus filiformis, typical of the upper parts of tidal flats, produces burrows resembling trace fossils of the extended Chondrites group, namely the ichnogenus Pilichnus. Burrows of this trace fossil type were also found in subtidal muddy sediments near a barrier island at the coast of Georgia, U.S.A., originating from Capitella cf. aciculata.Pathways for detection of the modern traces, chemical properties of the sediments, life modes of the respective organisms and their environmental implications are briefly discussed. The results contribute to a more precise and differentiated interpretation of palaeoecologic and palaeooceanographic data.