Since the transition to bipedal locomotion was a watershed event in our species’ development, researchers have been eager to pin down its precise timing. A recent study suggests that the change occurred some 7 million years ago.
This is what researchers have concluded after carefully examining the fossilized bones of the thigh (femur) and forearm (ulna) of Sahelanthropus tchadensis, the earliest known human ancestor. In 2001, these fossils were uncovered for the first time in Toros-Menalla, Chad.
It’s also plausible that before they shifted to bipedalism, early hominins spent a lot of time in trees utilizing all four limbs. The researchers were able to piece together the mechanics of this species’ movement by comparing the fossilized thigh and forearm bones to their modern-day counterparts from humans, chimps, and gorillas.
S. tchadensis’ bipedalism was determined by analyzing 20 separate features of the fossilized bones, such as the external shape of the remains and the internal architecture, evaluated using microtomography.
The most plausible scenario, they determined, involved “habitual bipedality” along with some tree climbing.
The group also argues that the species differed from modern gorillas and chimpanzees in how they climbed trees, using a technique that relied more on firm hand grips than on leaning back on finger and toe bones.
This investigation expands on previous work done on a fossilized skull believed to be from S. tchadensis and discovered in the same location. There was some evidence from the study of their skulls that these ape-like species were bipedal, but now we have more concrete proof.
The fossils were created between 6 and 8 million years ago, which is right around the time when humans genetically diverged from our closest living cousins, the chimpanzee and the bonobo. This is an extremely important moment in human evolution, and it has already sparked much scholarly controversy.
These early hominins likely encountered food and water by walking on two legs and climbing trees in a landscape that also included palm groves and grasslands.