Data from: Shape variability in tridactyl dinosaur footprints: the significance of size and function

The functional anatomy of the hindlimb of bipedal dinosaurs has been
intensively studied. Yet, surprisingly little work has been done
concerning functional adaptations in the digits for terrestrial
locomotion. While complete and articulated pes skeletons are scarce, pes
shape is abundantly recorded by fossil footprints. Here we aim to
elucidate the significance of footprint shape and size for locomotion
using a large sample (n = 303) of tridactyl dinosaur footprints from a
broad range of geographic localities and time slots. Size and shape
variation is characterised separately for theropods and ornithischians,
the two principal trackmaker taxa. At smaller sizes, theropod footprints
are best discriminated from ornithischian footprints based on their
smaller interdigital angle and larger projection of digit III, while at
larger sizes digital widths are effective discriminants. Ornithischian
footprints are shown to increase in size from the Early Jurassic to the
Late Cretaceous, a trend not observed in theropod footprints. Size and
function are argued to be important determinants of footprint shape, and
an attempt made to infer function from shape. Digit III projection and
length-to-width ratio of the footprints are negatively correlated with
size in both trackmaker groups, while digit impression widths are
positively correlated with size only in ornithischians. Digit III
projection is proposed to be positively correlated with cursorial ability.
Increased interdigital angles are associated with a decrease in digital
widths, possibly representing an adaptation for stability. Footprints are
found to yield great unrecognised potential for the understanding of the
functional morphology of dinosaur feet.