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Keywords:

  • Orangutan;
  • Pongo;
  • Knuckle-walking;
  • Hands;
  • Hominoid evolution

Abstract

An adult male orangutan at the Chicago Zoological Park utilizes various knuckle-walking hand postures in terrestrial bipedal-squatting and quadrupedal diagonal-sequence, diagonal-couplet gaits. A study was conducted in order to discern the circumstances surrounding the subject's terrestrial locomotor modes. It was found that various locomotor behaviors correlate with specific conditions of the substrate and the subject's motivation. Biomechanical properties of orangutan knuckle-walking are discussed in terms of their relevance for modelling hominoid phylogeny.