Fig. 3. Ranges and mean positions of the head and trunk during treadmill walks and gallops (N=10 cycles/gait). Vervet head range is plotted against trunk range (A). The circles depict walks and the crosses depict gallops. A comparable head range-trunk range plot (B) based on overground locomotor data for two other species (Macaca radiata or bonnet macaque, Semnopithecus entellus or hanuman langur) is provided for comparison (Dunbar et al., 2004). The circles depict walks and the crosses depict gallops by bonnet macaques, whereas the squares depict walks and the inverted triangles depict gallops by hanuman langurs. In A and B, the horizontal and vertical dashed lines indicate the 20° threshold for stabilization of the head and trunk, respectively. Mean head (C) and trunk (D) positions are plotted against locomotor velocity. In A and C, the clusters of symbols to the left (lower velocities) are for walks, whereas the clusters to the right (higher velocities) are for gallops.