The longstanding debate over whether the earliest known hominin, Sahelanthropus tchadensis, walked upright or used a knuckle-walking gait similar to modern chimpanzees may have found a resolution. A team led by Scott Williams at New York University has reexamined fossil remains, suggesting that this ancient species exhibited key anatomical traits indicative of bipedalism.
The 7-million-year-old fossils, discovered in the Chad desert region in 2002, include a skull, teeth, and jawbone of Sahelanthropus. Initial studies highlighted its distinct brow ridge and small canines, setting it apart from great apes. Notably, the skull’s structure suggested it likely sat directly atop the spine, a characteristic associated with upright walking.
The fossil narrative continued to evolve when in 2004, French scientists identified a femur and ulna associated with the skull, attributing them to Sahelanthropus. In 2020, conflicting interpretations emerged, with some researchers arguing that the femur’s curvature resembled that of non-bipedal great apes, reigniting the debate on its locomotion.
Recent findings reported by Williams and his team focus on the femur’s gluteus maximus attachment point, which they argue aligns more closely with hominin anatomical structures. In addition, they analyzed the femur and ulna’s size and shape. While similar in dimensions to chimpanzee bones, their proportions suggested a connection to bipedal hominins. Furthermore, the discovery of a “femoral tubercle”—a small prominence on the femur—was considered pivotal.
Williams stated, “I actually initially identified it by touch, then confirmed it visually using 3D scans of the fossil. It serves as the attachment point of the iliofemoral ligament, the largest and most powerful ligament in the human body.” This ligament plays a crucial role in stabilizing the body during upright movement.
Despite the compelling evidence, Williams expressed caution regarding the conclusion of the debate. “We’re fairly convinced that Sahelanthropus was an early bipedal hominin at this point, but I’d be foolish to think we ended the debate.”
In response, researchers Franck Guy and Guillaume Daver, who previously argued for the species’ bipedality, stated that the new study supports their interpretations. They emphasized that it provides new insights into the adaptations of the earliest known hominin, even as they acknowledged that further fossil discoveries would be necessary for definitive conclusions.
Adding to the discourse, John Hawks from the University of Wisconsin-Madison expressed agreement with the new findings. He remarked that these insights reveal a complex evolutionary trajectory for the hominin lineage. “I think it may be misleading to imagine that Sahelanthropus are all hominin or all ape,” Hawks said.
Conversely, Clément Zanolli from the University of Bordeaux, who has previously contended that Sahelanthropus was not bipedal, criticized the new analysis. He asserted that the skeletal features primarily align with those of African great apes and suggested that the locomotion of Sahelanthropus might have been varied, ranging from behaviors seen in chimpanzees to gorillas.
As research continues, the implications of these findings on our understanding of human evolution remain significant. The question of whether Sahelanthropus tchadensis walked upright or not continues to provoke discussion among scientists, with both new evidence and differing interpretations shaping the ongoing exploration of our ancient ancestors.
