The origin of paleontology as a science, as well as its traditional affiliation with earth sciences, derives from the use of fossils as stratigraphic markers. Index species define biozones and stages, while series are marked by the appearance or disappearance of higher taxa and era boundaries by mass extinctions. Although biostratigraphy is not implicitly based on evolutionary theory, the taxa used should be short-ranged and phyletically coherent. As we have seen, most trace fossils fail to meet these requirements, because different organisms may produce similar traces. Nor does current ichnotaxonomy capitalize makership: similar trace fossils, it is claimed, should bear the same name, no matter what kinds of animals made them. As such an attitude is unacceptable for a paleobiologist, I have tried throughout this book to focus on the biological identity of the trace maker as far as possible. Where this could not be done (e.g., in arthrophycids, Chap. IX), biologically coherent “ichnofamilies” have nevertheless been singled out as more or less coherent higher units. On the level below ichnogenera (which have practically become the fundamental units) it would be desirable to take the ichnospecies level more seriously. As this would have required a much more profound review of all the literature (papers that are otherwise irrelevant in this context may still contain new names!) and since many ichnogenera simply do not have enough diagnostic features to justify subdivision, weeding at the ichnospecies level has not been attempted.
Cruziana Stratigraphy. (2007). In Trace Fossil Analysis (pp. 187–200). Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-540-47226-1_14