The “Plastotype Problem” in Ichnological Taxonomy

Abstract When naming ichnotaxa based on uncollectable trace fossils, the holotype is the actual ichnofossil in the outcrop, though some ichnologists identify the holotype as a replica (cast) held in a museum collection, and refer to it as a “plastotype,” although not all such replicas are made from plaster. Nevertheless, through its Code, the International Commission on Zoological Nomenclature (ICZN) makes it clear that an artificial, human-made replica (plaster cast or otherwise) is not eligible to be the holotype of an ichnotaxon. This directive is potentially destabilizing to much ichnological taxonomy, which is based on holotypes left in the field that have disappeared or will disappear. One possible solution for ichnologists will be to petition the ICZN to recognize that artificial, human-made replicas of ichnofossils can serve as name-bearing types. These may best be called “axiotypes” (from the Greek axios, meaning “of equal value”).