MORPHOMETRIC ANALYSIS OF THEROPOD (DINOSAURIA: THEROPODA) UNGUALS FROM THE LOWER CRETACEOUS ARUNDEL CLAY OF MARYLAND

The Arundel Clay, part of the larger Potomac Group, represents one of the few Lower Cretaceous terrestrial fossil-bearing units on the East Coast of North America. Despite its paleontological significance, theropod biodiversity in this formation remains poorly understood, with most identifications based on isolated and fragmentary skeletal elements. Yet among these elements, several distinctive theropod unguals suggest the presence of multiple different species. The classification of isolated theropod unguals has historically been challenging due to morphological variability within and between clades. This study aims to refine the understanding of theropod diversity in the Arundel Clay by conducting a morphometric analysis of four theropod ungual specimens (USNM 4973, 8505, 535490, and 617417), all recovered from the Arundel and housed at the Smithsonian Institution’s National Museum of Natural History (USNM). The measurements of the USNM specimens were compared to a dataset of theropod ungual measurements gathered from several major museum collections. A Principal Component Analysis (PCA) was conducted in R to identify taxonomic patterns and morphological variations. The PCA results reveal that some aspects of the Arundel Clay specimens are consistent with known theropod clades, whereas others exhibit significant overlap between groups. Despite this, PCA results indicate that the specimens align most closely with specific theropod taxa, chiefly Carnosauria, Dromaeosauridae, and Ornithomimosauria. Variations in curvature, robustness, and articular proportions suggest potential ecological implications, consistent with the known anatomy of more complete examples from these clades. These findings contribute to a broader understanding of theropod diversity in the Early Cretaceous of eastern North America. Additionally, this study provides a foundation for future research on theropod morphology within the Potomac Group and other fossil assemblages.