For more than two decades, Sahelanthropus chadensis – a very early (6.7 to 7.2 million years old) species of hominin. discovered in Chad in 2001 – found himself at the center of a controversial question: was man one of the first relatives of mankind walking upright? A new study by New York University paleoanthropologists provides compelling evidence that this is the case. Their results show that Sahelanthropus chadensis was an African ape-like early hominin with the earliest known adaptation to terrestrial upright walking.
“Sahelanthropus chadensis “was essentially a bipedal ape that had a brain the size of a chimpanzee and likely spent much of its time in the trees foraging for food and seeking safety,” the New York University researchers said. Dr. Scott Williams.
“Despite the superficial appearance, Sahelanthropus chadensis “has been adapted to use a bipedal posture and locomotion on land.”
In their study, Dr. Williams and his colleagues focused on the femur and two partial forearm bones. Sahelanthropus chadensis discovered at the Toros Menalla site in Chad.
While earlier work argued that the bones were too ape-like to support upright walking, their new analysis combines 3D modeling of the shape with anatomical features related specifically to human-style locomotion.
“Taken together, these features suggest that humans have ape-like hip and knee functions. Sahelanthropus chadensis and may represent one of the earliest adaptations to upright walking in the hominin lineage,” they said.
The researchers found that while the external shape of the limb bones most closely resembles that of chimpanzees, their proportions tell a different story.
The relationship between arm and leg lengths has been described as more human-like, between modern bonobos and early members of the human species.
Most strikingly, they discovered a small bony structure on the femur—the femoral tubercle—that serves as the attachment point for the iliofemoral ligament, a key stabilizer of the human hip.
According to the team, this feature has so far only been identified in hominins.
The femur also exhibits pronounced internal torsion, known as antetorsion (medial femoral torsion), a sign associated with bringing the knees under the body's center of mass while walking.
This twisting is unique to hominins, compared to both living apes and extinct Miocene species.
Taken together, the findings challenge long-held assumptions about how and when bipedalism emerged.
Scientists argue that upright walking developed gradually and did not arise suddenly.
“We view the evolution of bipedalism as a process rather than an event,” they said.
“Sahelanthropus chadensis may represent an early form of habitual, but not obligatory, upright walking.”
“In addition to earthly upright walking, Sahelanthropus chadensis likely engages in a diverse set of arboreal positional behaviors not limited to vertical climbing, forelimb suspension under branches, arboreal quadrupedalism and bipedalism, and various forms of climbing.”
The authors interpret the fossil as evidence that early hominins evolved fromPot-like the Miocene ancestor of the ape,” reinforcing models that place chimpanzee-like creatures near the root of the human family tree.
“Our analysis of these fossils provides direct evidence that Sahelanthropus chadensis could walk on two legs, demonstrating that upright walking evolved early in our lineage and from an ancestor that was most similar to today's chimpanzees and bonobos,” Dr Williams said.
study was published this month in the magazine Achievements of science.
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Scott A. Williams etc.. 2026. Earliest evidence of hominin walking upright in Sahelanthropus chadensis. Achievements of science 12 (1); two: 10.1126/sciadv.adv0130
