Taphonomy and possible tracemakers of Psammichnites from the lower Cambrianof the Holy Cross Mountains, Poland

The sandstones of the upper part of the Ociesęki Formation (Cambrian Stage 4) contain numerous Psammichnites gigas arcuatus specimens that dominate lithologies characteristic of the high-energy Skolithos ichnofacies. The burrows are represented by four morphotypes being in fact taphonomic variants. These include horizontal sections displaying meniscate backfill composed of a series of arcuate ridges (“Arcuatichnus wimani” Kowalski, 1978), concave furrows with a U-shaped pattern (“Plagiogmus arcuatus” Roedel 1929), resembling Climactichnites isp., positive hypichnial reliefs visible as bilobate ridges with a median furrow and, occasionally, a V-shaped pattern (“Cruziana sp.” of Orłowski, 1975b), and complex structures that are combinations of these variants. The differences observed result from stratinomic effects and substrate grain size and consistency. Observations of striae on P. gigas arcuatus suggest that these may have been produced by halkieriids or other animals with hard skeletal elements. In the literature, similar ichnofossils were interpreted as traces of “worms”, gastropods or other molluscs, and rarely halkieriids and arthropods including trilobites. The different morphology of the examples of P. gigas arcuatus studied compared to other common Cambrian specimens may represent evolutionary change, as it reflects a relatively late occurrence of this trace fossil in the Cambrian of the Holy Cross Mountains