Principles of ichnostratigraphy

Invertebrate trace fossils are usually considered as stratigraphically less useful than vertebrate footprints. This is because they commonly lack diagnostic "fingerprints", which are more closely related to the anatomy of the producer than to the biological purpose, or function, of the trace. Exceptions are trilobite burrows (Cruziana), arthrophycid burrows, ichnospecies of Oldhamia, and Treptichnus pedum. Even if their makers are unknown, they represent taxonomically coherent groups of animals, whose evolving behavior marks geologic time. Cruziana ichnospecies can also be used in paleogeography.