Toe function and dynamic pressure distribution in ostrich locomotion.

The ostrich is highly specialized in terrestrial locomotion and is the only extant bird that is both didactyl and exhibits a permanently elevated metatarsophalangeal joint. This extreme degree of digitigrady provides an excellent opportunity for the study of phalangeal adaptation towards fast, sustained bipedal locomotion. Data were gathered in a semi-natural setting with hand-raised, cooperative specimens. Dynamic pressure distribution, centre of pressure (CoP) trajectory and the positional inter-relationship of the toes during stance phase were investigated using pedobarography. Walking and running trials shared a J-shaped CoP trajectory with greater localization of CoP origin as speed increased. Slight variations of 4th toe position in walking affect CoP origin and modulation of 4th toe pressure on the substrate allows correction of balance, primarily at the beginning of stance phase at lower speeds. Load distribution patterns differed significantly between slow and fast trials. In walking, the 3rd and particularly the 4th toe exhibited notable variation in load distribution with minor claw participation only at push-off. Running trials yielded a distinctly triangular load distribution pattern defined by the 4th toe tip, the proximal part of the 3rd toe and the claw tip, with the sharp point of the claw providing an essential traction element at push-off. Consistency of CoP trajectory and load distribution at higher speeds arises from dynamic stability effects and may also reflect stringent limitations to degrees of freedom in hindlimb joint articulation that contribute to locomotor efficiency. This novel research could aid in the reconstruction of theropod locomotor modes and offers a systemic approach for future avian pedobarographic investigations.