Earliest humans were bipedal, and could swing through trees

Becoming bipedal is considered to be a decisive step in the evolution of humans. However, for decades, there was no scientific consensus of the time period when this crucial adaptation emerged. Now, a research team led by the French National Center for Scientific Research (CNRS) and the University of Poitiers has examined three limb bones from the oldest representative of early humans currently identified – Sahelanthropus tchadensis – and found that bipedalism was most probably acquired very early in our history, in a period still associated with the ability to move on four limbs in trees.

Dating back seven million years old, Sahelanthropus tchadensis is considered to be the oldest representative species of humanity. This hominin was first described in 2001, when the Franco-Chadian Paleoanthropological Mission (MPFT) discovered the fossils of several individuals at Toros-Menalla in the Djurab Desert in Chad. The fossils included a well-preserved cranium which, together with the orientation and anterior position of the occipital foramen where the vertebral column is inserted, indicates that this ancestor was capable of bipedalism.

Now, experts discovered also two ulnae (forearm bones) and a femur (tight bone) that most likely belonged to Sahelanthropus. Data collected from a series of measurements and analyses of these bones – concerning both their external morphology and internal structures – was compared to already existing data of a large sample of extant and fossil apes, including chimpanzees, orangutans, gorillas, Miocene apes, as well as members of the human group, such as Orrorin, Ardipithecus, australopithecines, ancient Homo, and Homo sapiens.

The structure of the femur suggests that Sahelanthropus was bipedal on ground, and possibly also sometimes in trees. The analysis of the ulnae indicates that, in arboreal environments, this bipedalism coincided with a form of quadrupedalism characterized by arboreal clambering enabled by firm hand grips. These discoveries reinforce the idea of a very early emergence of bipedal locomotion in human history, even if at that stage other modes of locomotion were also employed.

“Taken together, these findings suggest that hominins were already bipeds at around seven million years ago, but also suggest that arboreal clambering was probably a significant part of their locomotor repertoire,” the authors concluded.

The study is published in the journal Nature.

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By Andrei Ionescu, Earth.com Staff Writer