1. Department of Anthropology, University of Massachusetts at Amherst, Amherst, MA 01003, USA
2. Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
3. Department of Anthropology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
4. Animal Care Sciences, National Zoological Park, Smithsonian Institution, Washington, DC 20008, USA
5. Department of Psychology, University of Stirling, Stirling, FK9 4LA, UK