New Fossil of an Ancient Human Relative Shows it Had Strong Grip, Human-Like Dexterity

Louise and Meave Leakey out at the excavation site with members of the Koobi Fora Research team.

For more than half a century, scientists have debated whether Paranthropus boisei, an extinct human relative known for its extremely powerful jaws and massive teeth, could make and use stone tools. Now, researchers report in the journal Nature the first hand and foot bones unambiguously associated with this species. Their work shows that P. boisei had human-like dexterity with gorilla-like gripping strength.

"This is the first time we can confidently link Paranthropus boisei to specific hand and foot bones," said Carrie S. Mongle, a paleoanthropologist and assistant professor of anthropology at Stony Brook University, who led the study. "The hand shows it could form precision grips similar to ours, while also retaining powerful grasping capabilities more like those of gorillas, and the foot is unquestionably adapted to walking upright on two legs."

Carrie Mongle (left) and Meave Leakey discussing the new Paranthropus boisei hand fossils at the Turkana Basin Institute research station in Ileret, Kenya. Photo Louise Leakey.

Paranthropus is an evolutionary cousin of Homo sapiens, likely diverging from a common australopith ancestor more than 3 million years ago. Previously, P. boisei was known to scientists almost exclusively from fossil skulls and teeth, without much from the rest of the skeleton, especially the hands and feet. Because of that, it has been difficult for researchers to confidently infer details about their locomotor repertoire or ability to make and use stone tools.

Homo and Paranthropus fossils are sometimes found at the same fossil sites, but it has been generally assumed that any recovered stone tools at these sites should be attributed to Homo rather than Paranthropus.

The partial skeleton - designated KNM-ER 101000 - was discovered and excavated between 2019 and 2021 at Koobi Fora, on the eastern side of Lake Turkana in Kenya, from deposits dated to just over 1.5 million years ago.

"It took a huge amount of time to carefully remove the sediments that ultimately revealed these amazing fossils," said Cyprian Nyete, field director of the excavations. These samples included cranial fragments, teeth, and a remarkably preserved set of hand and foot bones.

"There has been a long controversy about whether or not this species made and used stone tools," said Matt Tocheri, a co-author of the study from Lakehead University in Canada. "This fossil evidence effectively ends that debate."

This team's analysis shows that although P. boisei clearly had human-like hand proportions, which would have enabled it to manipulate stone tools just as well as species of early Homo, they still lacked the specialized wrist anatomy seen in later humans and Neanderthals.

The new discovery also sharpens debate over the ecological roles of different early hominin species. While species of early Homo appear to have evolved to be more reliant on tool use, Paranthropus likely had a very specialized diet of plant foods, based on distinctive adaptations in its face, teeth, jaws, and now, hands.

"This discovery helps us understand a lot more about Paranthropus boisei, especially how its hand shared similarities with members of our own genus Homo while evolving its own capabilities," said Caley Orr, a co-author from the University of Colorado School of Medicine. "It has converged on gorilla morphology in ways that are consistent with obtaining and processing tougher plant foods with its hands," he explains, "and these powerful grasping abilities would also have been quite useful for climbing."

An image of the reconstructed fossil hand of Paranthropus boisei. Credit: Matt Tocheri.

A rich history of Paranthropus fossil finds

"Overall, this discovery is a great example of how much we can achieve when we undertake long-term fieldwork that involves strong collaborations between researchers from around the world and the local communities that live in the places where hominin fossils are preserved," stated Louise Leakey, director of the Koobi Fora Research Project, whose team recovered the new fossils.

"None of this would be possible if it weren't for the dedication and commitment of our local community partners, who spend seven to eight months a year exploring, surveying, and excavating this area. It is definitely an exciting new era in paleoanthropology, which has changed and grown so much since my grandparents [Louis and Mary Leakey] discovered the first skull of Paranthropus boisei at Olduvai and my parents [Richard and Meave Leakey] first began to focus their research on the fossil-rich Turkana Basin in Kenya," Leakey added.

The research leading to the finding was supported by funding from the National Geographic Society and the Stony Brook Research Foundation.

This study was carried out by an international team of researchers from the Turkana Basin Institute, National Museums of Kenya, Koobi Fora Research Project, Stony Brook University, University of Colorado, Lakehead University, Washington University in St. Louis, Rutgers, University of Southern California, and the American Museum of Natural History.