Putative crayfish burrows from the Upper Triassic Grabowa Formation of southern Poland

Abstract

The present paper provides the first description of natural casts of arthropod- made burrows recovered from the continental Upper Triassic Grabowa Formation in the southern Poland. Casts' general morphologies and nature of cast- forming sediments – all corroborate the conclusion that the casts are of open tubular burrows once communicated with the surface and subsequently passively infilled with sediments. Despite their fragmentary and ex situ preservation, some of the casts represent branched structures and horizontal components of the original burrows. The surficial morphology is smooth or displays features like: scrap marks, scratches, knobby textures, metameric body parts' impressions, nodes and elongated coiled imprints. Branching, horizontal components and most of the surficial features (excluding nodes and elongated coiled imprints) are assignable to activity of arthropods, possibly crayfish. One specimen displays features known from lungfish burrows. The observed smooth to sculptured variation of surface morphology is likely a function of substrate water saturation – burrowers lived in a phreatic and vadose zones of the groundwater profile and dug within softground and firmground substrates, respectively.