The ichnogenus Teichichnus Seilacher, 1955

The ichnotaxonomy of the Phanerozoic trace fossil Teichichnus Seilacher, 1955 is revised and its ethology, producers and environmental affiliation are re-evaluated. Newly studied material reveals that Teichichnus is a sub-vertical spreite burrow with an arcuate shape, containing stacked laminae and a passively filled terminal causative burrow. Funnel-like extension of the terminal causative burrow and wall ornamentation may occur. High variation of burrow morphology is common and has resulted in the erection of 18 ichnospecies, of which only four are herein regarded as valid: Teichichnus rectus, T. zigzag, T. patens and T. duplex. These ichnospecies are characterised by their overall burrow shape, spreite morphology and, more subordinate, occurrence of branching and sculpture as recommended ichnotaxobases. Combined modes of feeding become evident, including deposit- and suspension-feeding, suggesting that Teichichnus is a dwelling trace rather than a feeding trace. Aside from the classical interpretation of polychaetes as producers, many features accord with an interpretation of dwelling echiurans and holothurians. This interpretation may apply for many post-Palaeozoic T. rectus and T. zigzag, whereas T. duplex and partly T. patens are likely produced by arthropods (i.e. trilobites and crustaceans). Bivalves are also considered for producing Teichichnus-like traces. Teichichnus is a marine trace fossil with predominance in shallow-marine environments. Low-diversity and high-density occurrences of Teichichnus characterise marginal-marine (paralic) environments with reduced salinity (i.e. brackish water) and oxygen (i.e. dysoxia), whereas in shoreface and offshore settings Teichichnus occurs in association with many other ichnotaxa and in low density. Deep-marine occurrences of Teichichnus are comparably sparse, and isolated records may indicate dysoxic bottom conditions.