Anatomy of a footprint: Bioturbation as a key to understanding dinosaur walk dynamics

Abstract

A series of polished slabs, cut vertically through a Grallator footprint, proved to be very useful in the reconstruction of the walking dynamics of theropod dinosaurs, and to an understanding of the animal‐substrate interactions. The trampled layer comprises a succession of plastic sediments and elastic cyanobacterial laminites, capped by semiliquid carbonate mud. The sections display records of the different pressures exerted onto the substrate by variable morphologic elements of the foot. Consequently it is possible to reconstruct the way the producing dinosaur walked. A progressive shift of the center of gravity is recorded by the different function of the digits in the different movement phases. The IV digit had a dominant function during the touch‐down and the beginning of the weight‐bearing phase. The II digit appears to have played an unexpected dominant function during the whole touch‐down and weight‐bearing phase, with a marked inward tangential translation and a diagonal penetration into the sediment. In the last phases of weight‐bearing and the kick‐off, the III digit had a functional dominance. In the propelling phase, it penetrated deeper than any other into the substrate. Such a study provides evidence for the correct interpretation, as dinosaur footprints, of deformation structures that crop out in the stratigraphic succession.

Key words:

• Dinosaur footprints
• sediment bioturbation
• walking dynamics