A recently analyzed set of 1.5-million-year-old Kenyan fossils has provided the most complete view yet of the anatomy of Paranthropus boisei, an ancient hominin known for its mᴀssive jaw and teeth. The fossils, discovered near Lake Turkana between 2019 and 2021, include hand, wrist, and foot bones, and fragments of a skull and teeth. They suggest that this now-extinct species, previously thought to be a plant-crunching specialist, would have been capable of walking and tool use in a distinctly human-like way.

A reconstructed left hand of a P. boisei partial skeleton. Cicero Moraes; CC BY-SA 4.0

The partial skeleton, designated KNM-ER 101000, is the most complete P. boisei individual to have been discovered. The dental and skull features, including the large molars, thick enamel, and prominent crest on the skull, confirm the identification of the species. However, what really makes this find remarkable are the hand and foot elements, which had not previously been definitively ᴀssociated with P. boisei.

The hand fossils show that P. boisei possessed a thumb and finger arrangement very close to humans. The thumb was comparably long, allowing a precision grip—pinching objects between fingers and thumb—that would allow controlled tool or food manipulation. However, the overall wrist and palm structure was still primitive and gorilla-like, so that its grip, though strong, lacked the precision of early Homo. This suggests that P. boisei may have carried out powerful manual tasks such as stripping plants or pounding food, even though it probably did not use stone tools routinely.

Researchers found that the bones were particularly robust, indicating exceptional strength in the hands and arms. The second phalanx, for instance, was as thick as that of a large male gorilla, implying an ability to exert very high force with the fingers and palms. Such a grip would have served not only in food processing but also in manipulating natural materials in its environment.

Paranthropus boisei forensic facial reconstruction. Credit: C.S. Mongle et al., Nature (2025); (This image is used under the terms of the CC BY-NC-ND license for non-commercial, educational, and informational purposes. If you are the copyright holder and have any concerns regarding its use, please contact us for prompt removal.)

Fossils of the feet also tell us more about how P. boisei walked. The species was obviously a committed biped, walking upright with a relatively human-like gait. Its foot bones also display a developed arch and a big toe with the ability to bend during walking, both essential for balance and propulsion. But its shorter big toe would have made its stride less powerful and efficient than that of modern humans. This set of features suggests an adaptation for mostly terrestrial movement, but with differences in the manner in which force was applied in each step.

These findings contradict the long-standing ᴀssumption that advanced tool use was unique to the Homo lineage. The anatomy of P. boisei suggests that even individuals from species outside our genus might have possessed the manual abilities required for simple tool use. While less sophisticated than Homo habilis or Homo erectus, P. boisei could perhaps have had enough control to use simple cutting or pounding tools, which may have aided its plant-based diet.

The discovery also fills a significant gap in the early human relatives’ fossil record. By placing hand and foot bones directly with those of P. boisei, researchers can gain a better understanding of the evolutionary paths that shaped different hominin behaviors during the Pleistocene. The combination of advanced and primitive traits is characteristic of an animal that combined strength and dexterity, walking on the ground, and perhaps engaging in occasional tool-related activities.

Ultimately, the fossils demonstrate that Paranthropus boisei was far more than a robust vegetarian with oversized jaws. It was a complex, adaptable hominin—one that shared more with early humans than was previously thought, blurring the distinctions of what we consider uniquely “human.”

More information: Mongle, C.S., Orr, C.M., Tocheri, M.W. et al. (2025). New fossils reveal the hand of Paranthropus boisei. Nature. doi:10.1038/s41586-025-09594-8