Taxonomic reappraisal of Nihilichnus from taphonomic perspectives of crocodile predatory ecology

The ichnogenus Nihilichnus has been broadly applied to penetrative feeding traces (bite marks) generated by vertebrates. The type ichnospecies Nihilichnus nihilicus encompasses all pit and puncture traces on vertebrate bone. This definition belies the diversity of pit and puncture morphologies found in the palaeontological and archaeological record and has led to inconsistency in the application and interpretation of these trace fossils. We resolve this ambiguity by splitting previously included morphologies that are too morphologically disparate to include within one ichnospecies. Using a sample of fossil, modern, and experimentally obtained crocodile modified bones, we describe three new ichnospecies under this ichnogenus: rounded pits N. clavus n. isp., bisected pits N. sicarius n. isp., and bisected punctures N. hastarius n. isp.; all of which we contend are morphologically distinct. Using these new ichnospecies, we provide a review, and reclassification when appropriate, of feeding traces previously published under Nihilichnus. We find that N. mortalis, lacking any official documentation, is nomen nudum and thus taxonomically unavailable. This article highlights how the usage of more specific ichnotaxonomic descriptions improves the utility of praedichnia in making palaeoecological inferences.