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What evidence shows that Australopithecus walked on two legs?
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Australopithecus
Artist's rendering of Australopithecus afarensis, which lived from 3.8 to 2.9 million years ago.
Evidence for bipedalism in the genus Australopithecus is derived from both fossilized skeletal remains and preserved footprints. Key indicators include:
- Footprints: The Laetoli trackway in Tanzania, dated to approximately 3.5 million years ago, provides direct evidence of three individuals walking on two legs. The footprints exhibit featuresāsuch as a robust heel and aligned toesāthat are remarkably similar to those of modern, habitually barefoot humans.12
- Pelvic Structure: The pelvis of Australopithecus underwent significant evolutionary changes to support upright posture. Fossils show short, broad ilia and a stout sacrum, which allowed for the transfer of upper-body mass to the lower limbs and provided attachment sites for muscles that stabilize the pelvis during bipedal walking.13
- Lower Limb Anatomy: The femur (thighbone) in Australopithecus species exhibits a characteristic inward angle toward the knee, which positions the feet closer to the body's center of gravity. This anatomical feature is a hallmark of bipedal locomotion.13
- Skeletal Remains: Discoveries at sites like Hadar have yielded locomotor skeletons, including those of Au. afarensis, that confirm a bipedal habit while retaining some features for arboreal climbing.12