Palaeoenvironmental trends in the history of trace fossils

Tracks, trails and burrows made by organisms are commonly preserved in Phanerozoic sedimentary rocks. These biogenic sedimentary structures, or trace fossils, have been most intensively studied from rocks deposited in marine environments, and have proven to be extremely useful in palaeoenvironmental reconstruc-tions. Our systematic analysis of occurrences in the stratigraphic record of two of the most common trace fossils, Zoophycos and Ophiomorpha, indicates that occurrences for each show an environmentally linked directional pattern through time. Zoophycos is commonly reported from Palaeozoic strata deposited from nearshore to deep-sea environments, whereas in post-Palaeozoic stratait is generally reported only from rocks deposited in deeper-water environments. Ophiomorpha first appeared in Permian shallowwater environments and was common in deep-sea fan environments by the Cretaceous, and has been distributed from nearshore to deep-sea environments since then. These onshore-offshore trends, which are similar to those previously reported for Phanerozoic benthic macroinvertebrate assemblages and individual higher taxa, require integration into future palaeoenvironmental reconstructions that use trace fossils.