Orrorin tugenensis
Thigh bones about 6 million years old from Kenya's Tugen Hills show bone buildup typical of a biped, suggesting this early hominin walked upright as well as climbed.
The story
Orrorin tugenensis, whose name means 'original man in the Tugen region', is an early hominin known from fossils about 6 million years old found in the Tugen Hills of Kenya. In 2000, Brigitte Senut and Martin Pickford announced about 20 fossils from at least five individuals, including thigh bones, jaw fragments, teeth and finger bones. The animal was about the size of a chimpanzee. Its small teeth with thick enamel point to a diet of fruit and other plants.
The key evidence is in the thigh bone. A hip joint that carries weight on two legs leaves a distinct pattern: a long neck of the femur with thick bone on the underside, which stands up to the stress of upright walking. Orrorin's femur shows this feature, and researchers argue that it was a biped when on the ground, while its curved finger bones show it still climbed trees. Not everyone agrees; some scientists think the femur resembles those of apes and say the species is not a human ancestor. It lived in woodland, supporting the picture that early bipedalism arose in forested settings.
Why it mattered
- It suggested that upright walking began at least 6 million years ago, much earlier than the first stone tools.
- It added a second contender, after Sahelanthropus, to the search for the earliest members of the human line.
- Its woodland setting challenged the idea that bipedalism evolved only on open grassland.
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