Bonnan, M.F. 2005. Pes anatomy in sauropod dinosaurs: implications for functional morphology, evolution, and phylogeny; pp. 346-380 in K. Carpenter and V. Tidwell (eds.), Thunder-Lizards: The Sauropodomorph Dinosaurs. Bloomington, IN: Indiana University Press.
Abstract: The anatomy and evolutionary history of the sauropod tarsus and pes remain largely unexamined despite their manageable size. Sauropod pedes possess several unique features: an asymmetrical pes, the extreme reduction of the tarsus, large pedal claws, and expanded phalangeal articular surfaces. A review of tarsal and pedal anatomy in sauropods and their outgroups suggests that several characteristics of sauropod tarsi and pedes were acquired earlier than recent phylogenetic analyses suggest. These changes in pes morphology were not always directly correlated with graviportal constraints. The pedes of most sauropods assumed a semi-plantigrade configuration correlated with astragalus reorientation. This foot posture may have facilitated plantarflexion by changing the insertion angle through which plantarflexors acted on the pes and/or a plantar aponeurosis. Ossified distal tarsals have never been reported for any sauropod; they may have fused to the proximal surfaces of the metatarsals or remained as small cartilaginous elements. The metatarsals may have articulated directly with the astragalus and calcaneum in most sauropods. Proximally, eusauropod metatarsals form a broad arch, those of neosauropods form a more linear arrangement, and, based on outgroup comparison, the medial portion of the anterior face of metatarsal V probably articulated posteriorly with metatarsal IV. Diplodocids have low, lateral ridges on the anterior faces of metatarsals I-III. The broad articular surfaces, offset flexor tubercles, ventrolateral orientation of the pedal claws, and trackway evidence suggest flexion and rotation of the claws occurred during contact with the substrate. Overall, tarsus and pes morphology remained conservative during sauropod evolution, with anterolateral orientation of the pes and increased phalangeal mobility the only significant trends arising after basal sauropods.