The human ancestors split up from the chimpanzee line some 6-7 million years before present, however, this date may extend earlier than that but not later in any case. Around the time of split between human and chimpanzee ancestors, a new bipedal hominid appeared on the scene. It was Orroron tugenensis and can be considered the earliest bipedal hominid. But the first hominin fossil which probably walked on two legs was Sahelanthropus tchadensis dated between 6 and 7 million years before present. Although earlier it was thought that this creature couldn’t walk on two legs. But with the collection of more specimens of this fossil, Franck Guy, a scientists from the University of Poitiers inferred that this creature did walk on two legs.
A detailed analysis of thigh and forearm bones of humans, great apes and Sahelanthropus tchadensis, revealed that this specimen did spend time on trees but usually walked on two legs on the ground. The structure of the femur of this creature was anatomically more close to humans than to great apes. The foramen magnum of the skull is situated forward than that of the great apes indicating erect posture in this creature and a tendency to bipedal walking. The cortex of the femur of this animal was quite thick and there was rough surface on the top of the femur where gluteus muscles attach pointing to the possibility of bipedal walking. If this is true then the history of bipedal walking is extended on the time scale up to about 7 million years before present. If we look at the locomotion of primates who are quadrupedal, we find bipedal walking for some distance in these animals. Whether Sahelanthropus tchadensis was a true bipedal or not is a bone of contention among the scientists as there are divergent views about it. Therefore the fossils of this creature though a mystery on its locomotion, still holds potential for future research on human evolution and bipedalism.
Professor S. P. Singh, Ph.D.
Editor-in-Chief, Human Biology Review
Former Dean, Faculty of Life Sciences,
Punjabi University, Patiala, India