Fig. 1. Experimental setup. (A) Plan view schematic of experimental arena. Ostriches ran along a narrow trackway until encountering a barrier placed directly beyond a force platform. Turns where ostriches stepped on the force platform were recorded and analyzed. Three-dimensional positions of 13 points on the body and legs were measured with a camera-based motion analysis system. (B) Points placed on the left side of an ostrich (with the exception of Spine, equivalent points were placed on the right side). Points were placed near joint centers for the hip, knee, ankle and MTP. (C) Angle convention used to analyze kinematic data. The X-axis was aligned axially along the fore–aft axis of the body and along leg segments. The Y-axis was approximately normal to the plane of motion of the joint. The Z-axis was normal to the X and Y axes. The two ground points identified the force platform in the tracking system but were not used for analysis.