7-Million-Year-Old Sahelanthropus Fossils Bolster Case for Earliest Upright Walking

For more than two decades, Sahelanthropus chadensis — a very ancient species of hominids (6.7 to 7.2 million years old) discovered in Chad in 2001 — is at the center of a controversial question: did one of humanity’s first parents walk upright? New research by paleoanthropologists at New York University provides the strongest evidence yet. Their findings suggest that Sahelanthropus chadensis was an early African ape-like hominid with the first known adaptations to terrestrial bipedalism.

Reconstruction of Sahelanthropus chadensis. Image credit: University of Silesia.

“Sahelanthropus chadensis was essentially a bipedal ape that had a brain the size of a chimpanzee and probably spent a significant portion of its time in trees, foraging for food and seeking safety,” said Dr. Scott Williams of New York University.

“Despite its superficial appearance, Sahelanthropus chadensis has been adapted to the use of bipedal posture and ground movements.

In the study, Dr. Williams and his colleagues focused on a femur and two partial forearm bones of Sahelanthropus chadensis recovered from the Toros-Menalla site in Chad.

While previous work claimed the bones were too ape-like to allow vertical walking, their new analysis combines 3D shape modeling with anatomical traits linked specifically to human-like locomotion.

“Together, these features suggest hip and knee function similar to that of hominids. Sahelanthropus chadensis and may represent some of the earliest adaptations to bipedalism in the hominid lineage,” they said.

Researchers found that although the external shape of the limb bones most closely resembles those of chimpanzees, their proportions tell a different story.

The relationship between arm and leg length is described as more hominid-like, falling between modern bonobos and early members of the human lineage.

Most strikingly, they identified a small bony structure on the femur – a femoral tubercle – that serves as an attachment point for the iliofemoral ligament, a key stabilizer of the human hip.

According to the team, this characteristic has so far only been identified in hominids.

The femur also exhibits pronounced internal twisting, known as antetorsion (medial twisting of the femoral shaft), a trait associated with the knees coming together below the body’s center of mass during walking.

This twist concerns exclusively hominids versus living apes and extinct Miocene species.

Taken together, the results challenge long-held assumptions about how and when upright walking evolved.

Rather than appearing suddenly, scientists say, bipedalism developed gradually.

“We view the evolution of bipedalism as a process rather than an event,” they said.

“Sahelanthropus chadensis may represent an early form of habitual bipedalism, but not obligatory.

“In addition to terrestrial bipedalism, Sahelanthropus chadensis likely engaged in a diverse set of arboreal stance behaviors not limited to vertical climbing, suspension of the forelimbs under the branch, arboreal quadrupedalism and bipedalism, and various forms of climbing.

The authors interpret the fossil as evidence that early hominids evolved from a “Stove-like the ancestor of Miocene apes,” 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 bipedalism evolved very early in our lineage and from an ancestor that most closely resembled today’s chimpanzees and bonobos,” Dr Williams said.

The study was published this month in the journal Scientific advances.

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Scott A. Williams and others. 2026. First evidence of hominin bipedalism in Sahelanthropus chadensis. Scientific advances 12 (1); doi: 10.1126/sciadv.adv0130