Pioneer colonization, evidenced by Rhizocorallium in the Middle Triassic of Poland

Abstract

Rhizocorallium is a common ichnogenus of the trace fossils of invertebrates that occurs throughout the Phanerozoic. It is also one of the earliest recognized and most cited trace fossils (Knaust, 2013). Many older papers interpret this trace fossil as a structure, formed by crustaceans or bivalves, but according to Knaust (2013), the most likely producers of marine Rhizocorallium are polychaetes. Reviews on this ichnogenus by Fürsich (1974) and Knaust (2013), in addition to many other ichnotaxonomic papers, illustrate and describe diverse forms of Rhizocorallium in different areas. Several ichnospecies of Rhizocorallium were described by Fürsich (1974), but only two ichnospecies, R. jenense Zenker, 1836 and R. commune Schmid, 1876, with several ichnosubspecies and variants, are accepted in the recent classification by Knaust (2013). Nevertheless, the junior synonym R. irregulare Mayer, 1954 of the latter ichnospecies has been widely used in the literature; recently, some workers (e.g., Feng et al., 2018) suggested several new ichnospecies that seem to be morphological or taphonomic variants of known ichnotaxa.The ichnogenus Rhizocorallium is typical of shallow-marine environments and its ichnospecies and variants usually reflect some parameters of sedimentation, especially substrate consistency. In fact, this trace fossil, or more precisely its ichnospecies, ichnosubspecies or variants, demarcates the Cruziana and Glossifungites ichnofacies, depending on the presence or absence of scratches (