Geometric morphometrics as a tool to support taxonomic identification in palaeontology: a comparison with traditional morphometrics in the study of isolated fossil shark teeth

Isolated teeth of elasmobranch fishes are extremely abundant in the fossil record. However, taxonomic identification solely based on qualitative characters might lead to erroneous results because several taxa might exhibit similar morphologies, making it difficult to detect significant morphological differences. As a valid support for qualitative taxonomic identification, an increasing number of studies have proposed supplementing qualitative features with quantitative approaches, including both traditional and geometric morphometrics. These methods are particularly effective in detecting minimal morphological differences that are often overlooked by purely qualitative analyses. To evaluate whether traditional and geometric morphometric approaches can reliably support the qualitative taxonomic identifications, using geometric morphometrics we examined a sample of isolated teeth of living and fossil lamniform sharks that had been previously investigated using traditional morphometric approaches. The goal of the present study is to understand whether geometric morphometrics and traditional morphometrics, when applied on the same dataset of isolated shark teeth, are equally reliable in supporting a priori qualitative taxonomic identifications and, if so, which approach is more effective. Our results show that geometric morphometrics recovers the same taxonomic separation identified by traditional morphometrics while also capturing additional shape variables that traditional methods did not consider. Consequently, geometric morphometrics provides a larger amount of information about tooth morphology, representing a powerful tool for supporting taxonomic identification of isolated fossil shark teeth.