Erratum

In [1], the legend for Figure 4 should have read:

Figure 4 – Illustration of some vertical ground reaction forces for orangutan (A, B, E) and chimpanzee (D) bipedalism. While most orangutan bipedalism produces a single peak (A) – ignoring the heel-strike transient, seen also in chimpanzee bipedalism (D), and produced by contact of the calcaneal tuberosity with the ground (see picture C) as in humans – the highly extended hip and knee in voluntary bipedalism of orangutans (C) produce clearly double-humped curves in 25% of cases (B). This gives ca. 50% energy transformation (depending on method of calculation, see, e.g. Wang et al. 2003), resembling curves in human slow walking and some cases (e.g. E, an incomplete record) even human ‘comfortable’ walking.

The references to ‘Fig. 4D’ on pages 506 and 507 should read ‘Fig. 4B’.