In October of 2000, Brigette Senut and Martin Pickford found what may be the oldest known hominid in the Tugen Hills of Kenya. There, in the six million year old sediments, they found thirteen fossils, including a partial femur, bits of a lower jaw, and several teeth. There is no debate over the age of the find; the sediments were dated at 6.2 to 5.6 million years old by radiometric techniques. The confusion is in the question of whether or not the creature was bipedal, partially bipedal or entirely arboreal. The only clues come from limited post-cranial remains and a few teeth.

Nicknamed ‘Millennium Man’, Orrorin tugenensis was roughly the size of a modern chimpanzee. It has many ape-like features such as the humerus and finger bones which appear to be well-suited to climbing trees, and pronounced canines (though less pronounced than A. Afarensis). At the same time, the partial leg bones found seem to indicate bipedalism (through analysis of how the femur connects to the hip and the muscle attachments). These traits do not rule out bipedalism, nor do they support it. If Tugenensis did stand upright, it was most likely only partially bipedal, dividing its time between the trees and the ground.

The teeth are small when compared to other early hominids, except for the upper canine, which is relatively large (a primitive trait). There is thick enamel similar to australopithecine and Homo teeth. The molars are close in size to those of Ardipithecus ramidus but also resemble those of female chimpanzees.

What makes this find so interesting (besides the fact that it predates other hominids by almost two million years) is that the time period it is attributed to is very close to the time scientists believe hominids and apes diverged (between five and six million years ago). If this species was in fact a hominid, it could possibly represent one of two scenarios, or both. First, Tugenensis could be the missing link between hominids and apes. Second, it might be a more direct link to modern humans, which would push aside the australopithecines as being the precursors to the genus Homo. There is loose evidence for both sides, because of the mix of primitive and modern traits demonstrated in the small amount of fossil evidence.

No conclusion has yet been drawn as to whether Orrorin tugenensis was a hominid. Further fossil evidence would be needed, most notably a skull with the foramen magnum unwarped.