Meeting Abstract
Footprints, both modern and fossil, represent sedimentary distortions that provide anatomical, functional, and behavioural insight into trackmaker biology. Such interpretations can benefit from understanding the mechanisms of footprint formation. Yet the development of track morphology is obscured by both foot and sediment opacity, which conceals animal-substrate and substrate-substrate interactions. We used X-ray Reconstruction of Moving Morphology (XROMM) to image and animate the hind limb skeleton of guineafowl traversing a dry, granular material. The reconstructed 3-D foot motion was integrated with a validated substrate simulation employing the Discrete Element Method (DEM), resulting in a quantitative model of limb-induced substrate deformation. By defining sedimentary layers based on initial particle position, we were able to observe the track at multiple levels throughout its formation, and thus link morphological features of tracks with the motion of the foot, both at the surface and at depth. What was initially most striking was that even in loose, granular sediment, tracks with high definition were formed throughout the track volume beneath the sediment-air interface. Transmission played only a very minor role, with most observable deformation occurring close to the path of the foot. Despite the appearance of clear tracks on multiple surfaces, which could easily be misinterpreted as shallow tracks, none accurately represented the geometry of the foot due to its oblique interaction with the sediment. Linking the DEM and XROMM techniques has allowed for a direct correlation between track features and foot motions, and serves to illustrate the complexities inherent in interpreting fossil tracks in light of track maker, behaviour, or function.
