Fish trails and imprints

The ichnotaxonomy, stratigraphic, geographic, and palaeoenvironmental distributions of fish trails and imprints are reviewed. A review of the key distinguishing characteristics of all included ichnotaxa of fish trails and imprints identifies that all currently named ichnogenera of fish locomotion trails (Undichna and Parundichna), resting imprints (Broomichnium, Pisquiesichnus, and Raederichnus), and feeding and nesting imprints (Piscichnus, Osculichnus, and Daandavichnus) are morphologically distinctive and should be considered valid. The key distinguishing characteristics of all included ichnospecies are summarized and simplified from the original and emended diagnoses to provide consistency and remove non-morphological criteria. Previous synonymyzation of ichnospecies within ichnogenera and reassignment of ichnospecies across ichnogenera are upheld. A comprehensive literature review of occurrences of fish swimming trails, resting imprints, and feeding and nesting imprints demonstrates that they range from the Silurian to Recent and they have a near global distribution, being reported from all present continents apart from Antarctica. Analysis of their palaeoenvironmental distribution demonstrates that fish trails and imprints, and particularly Undichna, are most common from lacustrine environments, followed by marginal marine, alluvial, and tidal settings; with few occurrences from marine environments through geological time. Comparison with the body fossil record of fish suggests that these observations are the result of taphonomic controls on the preservation of fish trace fossils, and agrees with previous predictions that they are most likely to be preserved in environments that were low energy but with relatively rapid burial, and had fine-grained sediment and limited infaunal bioturbation. Fish swimming trails have been attributed to jawless fish such as cephalaspids, as well as jawed fish such as acanthodians, cartilaginous fish, and bony fish, including members of the Actinopterygii (ray-finned fish) and Sarcopterygii (lobe-finned fish). The more complex fish swimming trails, with greater numbers of features, may be attributed to producers with higher degrees of precision and certainty. Neoichnological observations have provided many insights into the producers of fish resting imprints and feeding and nesting imprints.