AN ARTICULATED HINDLIMB OF DROMOMERON ROMERI (LAGERPETIDAE) AND ITS IMPLICATIONS FOR INTERPRETING DINOSAUROMORPH FOOTPRINTS

The Triassic Period was a time of evolutionary diversification and faunal turnover. During the Late Triassic, early dinosaurs and pterosaurs co-existed with their close relatives. Because early representatives of these lineages have a patchy and fragmentary body fossil record, footprints may provide important data for documenting the early evolution of this group. Unfortunately, this potential is often limited by the difficulty in identifying specific trackmakers. Some authors have hypothesized that the footprint ichnogenera Prorotodactylus and Rotodactylus were made by early dinosauromorphs, potentially members of the Lagerpetidae. Lagerpetids have recently been recognized as the sister group to pterosaurs and include Dromomeron romeri from the Chinle Formation of northern New Mexico. Previously, complete hindlimb material for comparison with footprints was only known from a single species of lagerpetid, Lagerpeton chanarensis. We describe new articulated hindlimb material of D. romeri that reveals new anatomical details about the pes of lagerpetids, and reconstruct the pes using segmented µCT scans. Our 3D kinematic analyses using this reconstruction indicate that the pes of D.romeri could not make the tracks of Prorotodactylus or Rotodactylus, and that Lagerpeton is unlikely to be a trackmaker as well, though this does not rule out the possibility of a different lagerpetid or dinosauromorph trackmaker. Our study not only provides new insights into lagerpetid hindlimb anatomy, but also highlights the importance of detailed anatomical comparisons in identifying putative trackmakers in the fossil record.