 When referring to trace fossils, the terms "ichnogenus" and "ichnospecies" parallel genus and species respectively.The most promising cases of phylogenetic classification are those in which similar trace fossils show details complex enough to deduce the makers, such as bryozoan borings, large trilobite trace fossils such as "Cruziana", and vertebrate footprints.However, most trace fossils lack sufficiently complex details to allow such classification.