A seven-million-year-old fossil may mark the moment our ancestors first stood up and walked.
For years, scientists have argued over whether a fossil dating back about seven million years was capable of walking upright. That question matters because bipedal movement would place the fossil among the very earliest human ancestors. A new study by a team of anthropologists now presents strong evidence that Sahelanthropus tchadensis, a species first identified in the early 2000s, did in fact move on two legs. The conclusion is based on the discovery of a specific anatomical feature that until now has only been seen in bipedal hominins.
Key Bone Feature Linked to Upright Walking
By combining 3D imaging with other analytical tools, the researchers identified a femoral tubercle in Sahelanthropus. This structure marks the attachment point for the iliofemoral ligament, the largest and strongest ligament in the human body and a crucial component for maintaining an upright posture while walking. The study also confirmed several additional skeletal traits in Sahelanthropus that are commonly associated with bipedal movement.
“Sahelanthropus tchadensis was essentially a bipedal ape that possessed a chimpanzee-sized brain and likely spent a significant portion of its time in trees, foraging and seeking safety,” says Scott Williams, an associate professor in New York University’s Department of Anthropology who led the research. “Despite its superficial appearance, Sahelanthropus was adapted to using bipedal posture and movement on the ground.”
The research team included scientists from the University of Washington, Chaffey College, and the University of Chicago. Their findings were published in the journal Science Advances.
From Skull Discovery to Ongoing Questions
Sahelanthropus was first uncovered in the Djurab desert of Chad by palaeontologists from the University of Poitiers in the early 2000s. Early studies focused mainly on the skull, which offered limited insight into how the species moved. Roughly twenty years later, researchers reported analyses of additional bones from the same discovery, including the forearms, known as ulnae, and a thigh bone, or femur. Those later findings reignited debate over whether Sahelanthropus truly walked upright, leaving its classification unresolved: Was Sahelanthropus a hominin (a human ancestor)?
Comparing Fossil Bones Across Species
In the Science Advances study, the scientists reexamined the ulnae and femur using two main approaches. One involved comparing multiple traits in these bones with those of living species and other fossil specimens. The second method used 3D geometric morphometrics, a standard technique that allows researchers to study bone shapes in fine detail and highlight subtle but important differences. Among the fossils included for comparison was Australopithecus, an early human ancestor best known from the discovery of the “Lucy” skeleton in the early 1970s and dated to roughly four to two million years ago.
Three Anatomical Signs of Bipedalism
The analysis identified three specific characteristics in Sahelanthropus that support upright walking:
- The presence of a femoral tubercle, which anchors the iliofemoral ligament connecting the pelvis to the femur and has so far been observed only in hominins
- A natural rotational twist in the femur, known as femoral antetorsion, that falls within the hominin range and helps orient the legs forward during walking
- Evidence from 3D analysis of gluteal, or butt, muscles resembling those of early hominins, which stabilize the hips and support standing, walking, and running
The last two traits, femoral antetorsion and the gluteal complex, had been reported in earlier research, and the new study confirmed their presence.
Limb Proportions Add More Evidence
The researchers also found that Sahelanthropus had a relatively long femur compared to its ulna, offering further support for bipedal movement. Apes typically have long arms and short legs, while hominins show the opposite pattern. Although Sahelanthropus had much shorter legs than modern humans, its proportions differed from those of apes and more closely resembled Australopithecus in relative femur length. This pattern points to another anatomical adaptation linked to upright walking.
“Our analysis of these fossils offers direct evident that Sahelanthropus tchadensis could walk on two legs, demonstrating that bipedalism evolved early in our lineage and from an ancestor that looked most similar to today’s chimpanzees and bonobos,” Williams concludes.
Reference: “Earliest evidence of hominin bipedalism in Sahelanthropus tchadensis” by Scott A. Williams, Xue Wang, Isabella Araiza, Jordan S. Guerra, Marc R. Meyer and Jeffrey K. Spear, 2 January 2026, Science Advances.
DOI: 10.1126/sciadv.adv0130
The study’s coauthors include Xue Wang and Jordan Guerra, both doctoral students at NYU; Isabella Araiza, an NYU graduate student at the time of the research and now a doctoral candidate at the University of Washington; Marc Meyer, an anthropology professor at Chaffey College; and Jeffery Spear, an NYU graduate student during the study who is now a researcher at the University of Chicago.
The research was supported by a grant from the National Science Foundation (BCS-2041700).
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.
7 Comments
That should have been named Sahelpithicus instead of Sahelanthropus.
Those skulls don’t even look as similar to human skulls as any of the present-day non-human primates. Get a real job.
It’s all in the legs!
Well, you certainly demonstrated that you can’t work with this. Humans are ordinarily recognized on teeth, which are less deformed than the crushed skull seen here. It is in the paper: “S. tchadensis was announced in 2002 as a very early (6.7 to 7.2 Ma)(19) hominin based on derived craniodental morphologies, including a reduced, nonhoning canine and an anteriorly positioned, inferiorly angled foramen magnum (20, 21).”
A shared ancestor would look like something in between and the skull is very deformed. Between us and chimps there is 12 million years of evolution along both branches, why do you expect to see close similarity?
Well, you just proved why condoms were invented.
As one could assume, the paper conclusions are controversial and the only fact everyone agree on is that more evidence is needed.
“But the case is far from closed. Dr Marine Cazenave, of the Max Planck Institute for Evolutionary Anthropology, in Germany, said most of the results pointed to similarities with African great apes or extinct apes, and called the evidence for upright walking “weak”. She found the femoral tubercle unconvincing too, adding that it is not directly related to upright walking and was “very faint” in a “highly damaged” region of the thigh bone.
Dr Rhianna Drummond-Clarke, at the same institute, found some of the evidence convincing, but still had questions. “More work is needed to clarify whether walking on two feet was used to walk in the trees, or to move on the ground, the latter of which is a defining feature of the human lineage,” she said. The results could equally suggest Sahelanthropus was an early chimpanzee that became less upright, and a knuckle-walker, as it evolved, she said.”
– Nature
If you expect there to be very close similarities in bone structure, you’re the reason we have Special Education Classes.