Ichnotaxonomic and morphological differentiation in pterosaur tracks using Geometric Morphometric analysis: A case study on Pteraichnus manus tracks from Cretaceous East Asia

Pteraichnus is the most reported pterosaur ichnotaxa and the taxon with the largest number of reported ichnospecies. However, most ichnospecies of Pteraichnus are restricted to the type locality and type specimens and have not been expanded. This study employs two-dimensional landmark-based Geometric Morphometric analyses (GMA) to investigate the manus tracks of four ichnotaxa of Pteraichnus (P. koreanensis, P. nipponensis, P. wuerhoensis, and P. gracilis) from the Early Cretaceous of East Asia. These analyses are the first attempt to perform GMA on pterosaur ichnofossil and reveal that the morphological characteristics of these ichnotaxa are significantly distinguishable. In addition to traditional descriptive criteria, features such as the width of the digits and the metacarpal-phalangeal joint area were identified as valid criteria for numerical comparison. The results suggest that GMA can enhance the ichnotaxonomic classification of invalid or questionable ichnotaxa and provide taxonomic estimation for manus-only tracks. This approach highlights the potential for spatiotemporal comparisons between disparate pterosaur footprints. The distinct morphological features observed in tracks from relatively close localities suggest the presence of diverse pterosaur faunas across East Asia. Further research with an expanded dataset of pterosaurian ichnotaxa is recommended to refine ichnotaxonomic classifications and enhance our knowledge of pterosaur paleogeography.