Hyloidichnus trackways with digit and tail drag traces from the Permian of Gonfaron (Var, France): New insights on the locomotion of captorhinomorph eureptiles

摘要

Newly discovered tetrapod footprints from the middle Permian Pelitic Formation of Gonfaron (Le Luc Basin, Var, France) are described in detail and assigned to the ichnogenus Hyloidichnus. These specimens are very well-preserved, with detailed trackways showing anatomical features, digit drag traces and continuous tail impressions. Together with other Hyloidichnus specimens from the same locality and from the University of Burgundy collections, they allow the identification of the possible trackmakers of Hyloidichnus: small Hyloidichnus footprints are correlated with captorhinomorphs with autopodia similar to Captorhinus whereas large Hyloidichnus footprints might be correlated with larger captorhinomorphs or other 'basal' (eventually stem-) moradisaurines. A detailed comparative analysis is proposed to better understand the locomotion style of the trackmakers. Starting from the reconstruction of the stance phase of Captorhinus, we document the swing phase of the fore- and hind-limbs of captorhinomorphs thanks to the continuous digit drag traces associated with Hyloidichnus. A link between gait and track preservation have been highlighted through the analysis of tail impressions and high-resolution 3D models. In all, this study increases our understanding of captorhinomorph locomotion and enhances the integration of both tracks and skeletal remains to highlight the biomechanics of Permian tetrapods.