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What evidence indicates that Orrorin tugenensis may have walked on two legs?
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human evolution
An artist's depiction of five species of the human lineage.
The evidence suggesting that Orrorin tugenensis practiced bipedalism is derived primarily from its fossilized femurs (thighbones).21
According to researchers, the specific anatomical features of these thighbones that imply an upright walking habit include:
- Overall proportions: The general size and shape of the femur resemble those of modern humans.2
- Internal structure: The internal architecture of the femoral neck—the column connecting the ball-shaped head of the bone to the shaft—shows characteristics associated with bipedal locomotion.2
- Muscle attachment: The presence of a specific groove on the bone, which served as an attachment site for the obturator externus muscle, indicates a mechanism used in upright walking.2
While O. tugenensis retains primitive, apelike traits in other areas of its anatomy, such as its canine and premolar teeth, these femoral features serve as the primary basis for its classification as a hominin by many experts.21