There are 13 fossils from at least 5 Orrorinindividuals. Two well-preserved thigh bones (femora), BAR 1002’00 and BAR 1003’00, show evidence of bipedal walking. Other parts of the skeleton show apelike features: long, curved finger bones and apelike canine and premolar teeth. The type specimen, BAR 1000’00, is a jaw fragment with three lower molars.
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Living around 6 million years ago, Orrorin tugenensis is the one of the oldest early humans on our family tree. Individuals of this species were approximately the size of a chimpanzee and had small teeth with thick enamel, similar to modern humans. The most important fossil of this species is an upper femur, showing evidence of bone buildup typical of a biped - so Orrorin tugenensis individuals climbed trees but also probably walked upright with two legs on the ground.
A research team led by French paleontologist Brigitte Senut and French geologist Martin Pickford discovered this species in the Tugen Hills region of central Kenya. They found more than a dozen early human fossils dating between about 6.2 million and 6.0 million years old. Because of its novel combination of ape and human traits, the researchers gave a new genus and species name to these fossils, Orrorin tugenensis, which in the local language means “original man in the Tugen region.” So far, Orrorin tugenensis is the only species in the genus Orrorin.
We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.
Below are some of the still unanswered questions about Orrorin tugenensis that may be answered with future discoveries:
- Is Orrorin a direct human ancestor to Homo sapiens? If so, does this make Au. afarensis a side branch of our of hominin family tree that eventually hit a dead-end?
- Did Orrorin routinely walk on two legs? Orrorin’s fossil evidence indicates that Orrorin was possibly capable of bipedalism, but not necessarily that Orrorin routinely walked bipedal.
- How did bipedalism originate? One hypothesis suggests early apes walked on branches while using their arms for balance and this technique eventually made its way to the ground.
- What is the relationship between this species and Sahelanthropus tchadensis, the other current contender for the title of earliest human?
Pickford, M., Senut, B., 2001. 'Millennium Ancestor', a 6-million-year-old bipedal hominid from Kenya - Recent discoveries push back human origins by 1.5 million years. South African Journal of Science 97, 22-22.
Other suggested reading:
Pickford, M., Senut, B., Gommery, D., Triel, J., 2002. Bipedalism in Orrorin tugenensis revealed by its femora. Comptes Rendus Palevol 1, 191-203.
Richmond, B.G., Jungers, W.L., 2008. Orrorin tugenensis femoral morphology and the evolution of hominin bipedalism. Science 319, 1662-1665.
Senut, B., Pickford, M., Gommery, D., Mein, P., Cheboi, K., Coppens, Y., 2001. First hominid from the Miocene (Lukeino Formation, Kenya). Comptes Rendus De L Academie Des Sciences Serie Ii Fascicule a-Sciences De La Terre Et Des Planetes 332, 137-144.
Thorpe, S.K.S., Holder, R.L., Crompton, R.H., 2007. Origin of human bipedalism as an adaptation for locomotion on flexible branches. Science 316, 1328-1331.
From Orrorin's low, rounded molars and small canine teeth, paleoanthropologists can infer that this species ate mainly a plant-based diet. This probably included leaves, fruit, seeds, roots, nuts, and insects.
Orrorin is at the base of the human family tree, and has more ape-like features than human-like ones -- except that it walked upright on two legs.