Guineafowl hind limb function. I: Cineradiographic analysis and speed effects.

Avian striding bipedalism was studied in the helmeted guineafowl, Numida meleagris. High-speed cineradiographs, light films, and videos were used to record hind limb movements across a wide range of speeds. In particular, direct visualization of the skeleton in X-ray images allowed changes in pelvic and femoral position to be quantified with great accuracy for the first time. With the exception of limb protraction angle, all stride parameters are speed-dependent. During the stance phase, guineafowl primarily employ knee flexion at very low speeds. At higher speeds, the magnitudes of hip and knee extension in the second half of stance progressively increase. Pelvic rotations are relatively small, but birds gradually pitch further forward with speed. An aerial phase is not present at speeds less than 2.0 m/sec, but discontinuities in the relationship of some parameters to speed indicate a gait transition near 0.9 m/sec. Birds are considered to be flying theropod dinosaurs, making characterization of bipedalism in living birds essential to understanding the evolution of theropod locomotion. Data from guineafowl, including the kinematic effects of speed, are informative about several aspects of locomotion in extinct theropods. However, many details of avian bipedalism evolved only within a subset of Theropoda, and are therefore not directly applicable to all members of the clade. J. Morphol. 240:115-125, 1999. © 1999 Wiley-Liss, Inc.