Bipedalism: A Step In The Upright Direction Matthew Clare Au. sediba   , Lee R. Berger University of the Witwatersrand   This poster shows the evolution of the anatomical features that led to bipedalism in humans. Bipedalism is one of several features used to identify species as hominin and on a separate lineage from chimpanzees and other apes. Features indicative of bidepalism include: A forward foramen magnum – the hole through which the spinal cord passes is close to the base of the skull rather than at the back so that the head can be held in an upright position[1], as seen in S. tchadenis. The femur of Orrinin tugenensis has a long neck to form a strong bridge with the hip to support the body weight[2]. In Au. anamensis the tibia is thickened[2] to absorb the extra stress of walking upright and the femur angles in towards the knees, which themselves later evolve to allow full extension as seen in Au. sediba[3]. Pelvis – although the lower pelvis allowed fixation of the huge leg muscles needed for climbing, Ardipithecus ramidus adaptations show the upper blades are shorter and broader than in other primates and allow bipedal movement without a side to side gait[4,5]. It becomes more “bowl-shaped” [6] with time as seen in Au. Afarensis, accommodating the lower centre of gravity needed to support bipedal movement. The spine, almost horizontal in the quadruped, becomes more vertical and develops a S-shape[2] in the lower back to keep the head and chest position over the hips. This was identified in Au. africanus , dating to c.3 – 2mya. Chip Clark: Smithsonian Institution [10] [12] Homo habilis, claimed by some to be Australopithecine   Australopithecus, c.4.5 - 2mya . c.2.4mya 1.9mya The foot becomes more rigid to allow “push-off”[5], as seen in “Ardi”. The foot later loses the divergent big toe and the Laetoli footprints suggest a heel-to-toe action[1] was used in walking . Features evolved to be more human-like so that Homo habilis could cover greater distances bipedally[7]. This supports the paleoenvironmental evidence for its more open grassland habitat[8]. Its ability to use tools led to the “Handy Man” nickname and the adaptations suggests that arms and hands were no longer habitually used for locomotion. [5] AAAS Ardi 3.2mya Au. anamensis Lovejoy, Johansen and Coppens (1982) 4.2mya Ardipithecus ramidus  3.7mya 4.4mya Laetoli Footprints Au.afarensis Sahelanthropus tchadensis © MPFT 6.5mya Orronin tugenensis 6mya http://www.ecotao.com/holism/hu_austral.htm [9] [8] [1] [10] References 1. Fossil Evidence of Bipedalism, http://efossils.org/book/fossil-evidence-bipedalism; 2. http://humanorigins.si.edu/human-characteristics/walking; 3. Walk this way: New research suggests human ancestors may have used different forms of bipedalism during the plio-pleistocene - http://www.sciencedaily.com/releases/2013/04/130411142710.htm; 4. http://news.nationalgeographic.com/news/2009/10/091001-oldest-human-skeleton-ardi-missing-link-chimps-ardipithecus-ramidus.html; 5. Ardipithecus ramidus and the Paleobiology of Early Hominids Science 2 October 2009: Vol. 326 no. 5949 pp. 64, 75-86 DOI: 10.1126/science.1175802 6. Analysis of Early Hominins:http://anthro.palomar.edu/hominid/australo_2.htm 7. Functional Morphology of Homo habilis, Susman, Randall L.,Stern, Jack T. Science,1982, Vol.217(4563), pp.931-934; 8. http://www.nhm.ac.uk/nature-online/life/human-origins/modern-human-evolution/when/index.html 9. Lovejoy, Johanson, and Coppens, (1982) Hominid Lower Limb Bones Recovered From the Hadar Formation: 1974-1977 Collections. AJPA 57:679-700; http://www.sciencemag.org.ezproxy.lancs.ac.uk/content/326/5949/64.full; 10. http://humanorigins.si.edu/evidence/human-fossils/fossils/al-288-1 11. http://www.bbc.co.uk/sn/prehistoric_life/human/human_evolution/mother_of_man1.shtml (banner) 12. http://www.sciencedaily.com/releases/2013/04/130411142942.htm; Lectures of Ian Hartley, Jane Foster, Kevin Moffat, Georgy Koentges. Assistance provided by Philippa Barlin, Rebecca Slavin, and Adam Stewart.