A set of 21 fossilized footprints discovered along Kenya’s Lake Turkana reveals that eight adults—predominantly male—travelled together 1.4 million years ago. Dating from the Early Pleistocene, the tracks challenge long-held assumptions about the size and social behavior of Paranthropus boisei, an extinct human relative.
Twenty-one impressions pressed into a muddy lakeshore in northern Kenya offer scientists an unusually detailed look at the anatomy and social habits of a long-extinct branch of the human family tree. The trackway, designated GaJi10, was analyzed in a study published in the Proceedings of the National Academy of Sciences. The research brings fresh evidence to light about Paranthropus boisei, a hominin best known for its heavily buttressed skull, massive jaws, and oversized teeth.
Because most known fossils of the species consist only of skull fragments, researchers previously had little reliable evidence regarding body size below the neck. The newly studied trackway changes that equation entirely.
Excavating Lake Turkana: From a Hippo Print to a Major Trackway
The discovery has a long history rooted in the field work of Kay Behrensmeyer, who has worked in the region since 1969. In 1978, colleagues excavating a trench near Lake Turkana uncovered what Behrensmeyer initially recognized as a fossilized hippopotamus footprint. Clearing the surrounding rock revealed two ancient hominin tracks right beside it.
After the initial find, researchers protected the site by reburying it in sand. Teams returned in 2016 and 2023, uncovering a much larger extent of the preserved surface. Volcanic ash embedded in the surrounding rock strata allowed scientists to date the layer precisely to approximately 1.43 million years ago.
Behrensmeyer added that trackways allow people to relate to these fossils much more easily than an isolated piece of bone or jaw.
Rethinking Paranthropus boisei Size and Social Structure
Lead author Kevin Hatala, an associate professor of biology at Chatham University, worked alongside researchers in Kenya and the United States to map the impressions in two and three dimensions. By comparing the stride patterns and foot proportions with modern human data and other Early Pleistocene tracks, the team concluded the impressions belonged to Paranthropus boisei rather than contemporaries like Homo erectus.
Those dimensions suggest that some members of the species matched the stature of Homo erectus, a group previously assumed to be considerably larger. Furthermore, the alignment of the 21 tracks indicates that eight adult individuals—mostly males, with no apparent females or children—traversed the muddy lakeshore together. Co-author Neil Roach of Harvard University noted that a single-sex group hints at a complex social structure in this species, potentially involving male competition for mates or cooperative protection against shoreline predators like crocodiles.
Overlapping Landscapes at Lake Turkana
The muddy surface recorded a compressed window of activity. Hatala noted that the individuals probably weren’t all there at exactly the same time, but they’re definitely all moving through this space, maybe within hours of each other, or at least within a day or two, pointing to consistent directional movement and matching speeds among the track makers.
At a slightly older site nearby, researchers also identified Paranthropus boisei and Homo erectus footprints pressed into the same mudflat. While the overlapping evidence confirms that both lineages utilized the Lake Turkana shoreline for hundreds of thousands of years, current fossil and trackway data cannot tell whether they crossed paths or how they divided its resources.
With regional records now encompassing hundreds of hominin impressions across more than half a dozen sites spanning over 100,000 years, researchers plan to return to Kenya in 2026 to investigate how the trackways survived and what continuously drew ancient human relatives back to the water’s edge.
