Feet of the fierce (And not so Fierce): Pedal proportions in large theropods, other non-Avian Dinosaurs, and large ground birds

The extent to which the makers of tridactyl dinosaur footprints can be identifi ed depends on the extent to which their foot skeletons can be told apart. We examined this question for non-avian theropod dinosaurs (NATs) and large ground birds, making additional comparisons with functionally tridactyl, bipedal – or potentially bipedal – ornithischians. For birds we measured distances across the trochleae of the tarsometatarsus, and for NATs, the lengths of metatarsals II–IV. For birds, NATs, and ornithischians we measured the lengths and widths of individual phalanges and the aggregate lengths of digits II–IV. Metatarsal, digital, and phalangeal proportions distinguish some genera among dinosaurs (including birds). At higher taxonomic levels, pedal features are useful but not infallible proxies for the systematic affi nities of birds and non-avian dinosaurs. Our results suggest that the parameters commonly used to describe tridactyl dinosaur footprints can often be used to provide a minimum estimate of the number of trackmaker taxa within an ichnofauna and that similarity in footprint shape is useful but not always a trustworthy indicator of phylogenetic relationships of trackmakers.