Measured axes and angles in the pitch plane. Measured axes and angles in the pitch plane. Head axis was a line passing through the external auditory meatus and the apex of the prognathous mouth. Trunk axis was a line passing through the hip and shoulder joints. Head angle relative to space (θ) and trunk angle relative to space (β) were measured in reference to earth horizontal. Head-to-trunk angle (α) was calculated from the head-to-space and trunk-to-space angles. Donald C. Dunbar et al. J Exp Biol 2004;207:1027-1042 © The Company of Biologists Limited 2004