A 1.4-million-year-old trail of footprints reveals that a powerful human relative grew nearly as large as us and may have traveled in all-male groups.
Eight individuals walked across the wet ground beside an ancient Kenyan lake. Within a short time, sediment buried their footprints and preserved a scene that would remain hidden for roughly 1.4 million years.
The tracks offer something bones rarely can: evidence of several extinct human relatives moving through the same place at nearly the same moment. Researchers believe the footprints were left by a group of Paranthropus boisei, a powerful-jawed hominin that lived alongside early members of the human genus but ultimately disappeared without leaving descendants.
All eight individuals appear to have been adults, and most may have been males. Their apparent decision to travel together raises the possibility that Paranthropus boisei had a more complex social life than its fragmentary fossil record has revealed.
A Surprisingly Large Human Relative
The footprints also overturn a long-standing assumption about the species. Some were made by individuals approaching 1.8 meters (5 feet 11 inches) tall and 75 kilograms (165 pounds), dimensions comparable to those of many people today.
“The sizes of the footprints indicate human-like body sizes, up to 1.8 meters (5 feet 11 inches) tall and around 75 kilograms (165 pounds),” said lead author Kevin Hatala of Chatham University, who is also associated with the Department of Human Origins at the Max Planck Institute for Evolutionary Anthropology in Leipzig.
That size was unexpected because Paranthropus boisei has long been reconstructed largely from skulls rather than complete skeletons. Its most recognizable features include a broad face, enormous molars, and powerful chewing muscles, adaptations that once earned it the nickname “Nutcracker Man.”
Far less is known about the animal below the neck. Earlier estimates based on scarce limb bones suggested that Paranthropus boisei was substantially smaller than Homo erectus, another hominin living in East Africa at the time. Homo erectus had more human-like body proportions and may lie directly along the evolutionary path that eventually produced our species.
Footprints Reveal Two Hominin Species
The new tracks complicate that comparison. At least some Paranthropus boisei individuals may have rivaled Homo erectus in height and body mass, even though the two species had very different skulls, diets, and evolutionary histories.
Researchers assigned the footprints to Paranthropus boisei using analytical methods the team introduced in 2024. The approach compares details of foot shape and walking motion preserved in the tracks, allowing scientists to distinguish prints made by different hominin species.
Earlier work in the same region identified footprints from both Paranthropus boisei and Homo erectus on one ancient surface. That discovery provided direct evidence that the two species used the same lakeshore environment and may have encountered one another.
The newly studied tracks reveal a different kind of scene. Instead of two species crossing the same ground, they appear to record a group of Paranthropus boisei moving together.
Clues to a Complex Social Life
The absence of obvious juveniles or females is particularly intriguing. Although footprints cannot reveal the exact relationships among their makers, the apparent group of mostly adult males may point to social arrangements involving both competition and cooperation.
“The fact that eight, mostly adult male, Paranthropus boisei individuals seemingly traveled together as a group, without females or children, hints at a complex social structure in this species,” said co-author Neil Roach of Harvard University.
“They may have lived in large groups, where males competed for mates, but also tolerated each other at times for safety in a dangerous environment.”
Reconstructing an Extinct Hominin Group
Footprints record only a brief event, and researchers cannot determine whether the individuals regularly traveled together, had gathered temporarily, or were moving independently through the same area over a short period.
Even so, the scene expands Paranthropus boisei beyond the familiar image of a heavily built skull in a museum case. It presents the species as a living animal that walked upright, navigated a shared landscape, and may have formed organized groups.
The location of the tracks also matters. Scientists have now documented hundreds of hominin footprints at more than six sites around East Turkana, suggesting that lakeshores repeatedly attracted ancient human relatives for more than 100,000 years.
These environments would have offered water and food, but they may also have brought danger. Large predators and competing hominins could have gathered near the same limited resources, possibly making group travel advantageous.
“To me, it is amazing that we have the same kind of lake margin deposits in two areas of East Turkana that are 40 kilometers (25 miles) apart, at about the same age,” said co-author Kay Behrensmeyer of the Smithsonian Institution.
How Ancient Footprints Were Preserved
The footprints survived because a rare sequence of events protected them. Hominins first crossed soft, impressionable sediment near the water. New layers then covered the surface before wind, waves or other animals could destroy the tracks. Over immense spans of time, the sediment hardened and preserved their shapes.
Understanding that process could help researchers locate additional footprint surfaces and reconstruct why several hominin species returned so often to the lake.
“If we can understand what geological conditions allowed these tracks to be preserved, we should know more about why hominins continued to return to the lakeshore environment over more than 100,000 years,” Behrensmeyer said.
A Record of Prehistoric Daily Life
Each new surface captures only a few moments, but together they are beginning to form a record of movement, body size, habitat use, and social behavior that fossilized bones alone could never provide.
“Each site represents a snapshot of our past, and we are quickly building a photo album with several different windows to hominin anatomy, locomotion, behavior, and environments during the Early Pleistocene,” Hatala said.
That growing collection is transforming the ancient shores of Lake Turkana into something close to a prehistoric record of daily life. Instead of showing only who existed, the footprints reveal where extinct human relatives went, how they moved, and, occasionally, who walked beside them.
Reference: “Insights into hominin body size, locomotion, and behavior from Early Pleistocene trackways in northern Kenya” by Kevin G. Hatala, Neil T. Roach, John W. K. Harris, Purity Kiura, Emmanuel K. Ndiema, Ben Sila, David Kipkebut, Joyce Waweru, Philiphine Kisale, Apolo Alkoro Longaye, Hilary Sale and Anna K. Behrensmeyer, 27 July 2026, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2530996123
This study was supported by the U.S. National Science Foundation, Turkana Basin Institute Ape and Human Evolution Research Fund.
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