TAXONOMIC REAPPRAISAL OF THE ICHNOGENUS NIHILICHNUS

The ichnogenus Nihilichnus describes pit and puncture traces occurring on skeletal material. This ichnogenus is distinct from other forms of bioerosion, presenting singular or multiple depressions or holes in a skeletal substrate, produced by the action of a vertebrate agent. These traces are thus extremely important in making inferences on the trophic relationships of vertebrates in the fossil record. The ichnospecies defined under Nihilichnus, however, are overly broad and belie the diversity of pit and puncture traces found in the paleontological and archaeological record. This problem inhibits the ecological and ethological interpretation of vertebrate feeding traces. Using a sample of bones modified by Nile Crocodiles (Crocodylus niloticus), we observe various morphologies of Nihilichnus. We observe unique morphological indices which warrant the usage of a multispecific definition of Nihilichnus. We emend the taxonomic diagnosis of the type species N. nihilichnus and split previously included morphologies which are too disparate to include within one ichnospecies. We then describe two new ichnospecies under this genus which are morphologically and behaviorally distinct. This new taxonomy should help to clarify the behavioral implications of different morphologies of Nihilichnus and constrain the ichnospecies applied to this ichnogenus to definite, constrained, and translatable definitions.