Paranthropus boisei footprints in Kenya, published in the Proceedings of the National Academy of Sciences, are challenging long-held assumptions about how large and socially complex this extinct human relative could be, with eight individuals apparently travelling together near an ancient lakeshore 1.4 million years ago.
The tracks, preserved in ancient lakeshore sediments in northern Kenya, appear to record all eight individuals occupying the same surface at roughly the same time. The international research team, made up of scientists from the US and Kenya, concluded that all eight trackmakers were likely adults. Several appear to have been considerably larger than earlier estimates of Paranthropus boisei body size derived from the limited skeletal remains previously available.
What the tracks say about body size
The size of the prints was unexpected. ‘The sizes of the footprints indicate human-like body sizes, up to 1.8 metres tall and around 75 kilograms,’ said lead author Kevin Hatala, of Chatham University and an associated researcher of the Department of Human Origins at the Max Planck Institute for Evolutionary Anthropology in Leipzig.
For decades, most known fossils of Paranthropus boisei consisted of skulls, including specimens with exceptionally large jaws and teeth. Much less has been known about what the species looked like below the neck because fossils from the rest of the skeleton are far rarer. The new tracks now challenge earlier research suggesting that Paranthropus boisei was substantially smaller than Homo erectus, another hominin that lived during the same general period and is considered a possible direct ancestor of modern humans.
The researchers used analytical techniques first developed by their team in 2024 to identify the footprints as belonging to Paranthropus boisei. The classification was based on clues in foot anatomy as well as the apparent gait of the individuals. That methodological groundwork matters: without a reliable way of telling one hominin’s prints from another’s, the body-size inferences would rest on shaky foundations. On that point, the team at least has a prior publication to point to.
Paranthropus boisei footprints Kenya and what they suggest about group behaviour
Footprints can reveal more than anatomy. Because a walking surface may be formed and preserved over a very short span of time, fossil tracks can capture a brief moment rather than a long accumulation. The team describes the discovery as a snapshot of ‘fossil behavior’.
In this case, most of the eight individuals were likely adult males, with no obvious evidence of females or children among them. ‘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.’
The species shared its world with early members of the genus Homo but followed a very different evolutionary path. According to Stony Brook Medicine News, Paranthropus boisei went extinct within a few hundred thousand years after 1.5 million years ago. The footprints, dated to approximately 1.4 million years ago, therefore represent the species relatively late in its existence, which adds some weight to the question of whether its social arrangements and body size varied across that timespan in ways the fossil record has not yet captured.
The same source reports that the footprints were found in 2021 during excavation of overlying sediments, a detail that places the discovery some years before the analysis now appearing in print. Fossil footprint research tends to move slowly: careful excavation, 3D documentation, and cross-comparison with anatomical references all take time before any conclusions can be offered with confidence.
The Lake Turkana lakeshore as a repeated destination
The new discovery is part of a much larger collection of hominin footprints found in ancient lakeshore environments around Lake Turkana. Researchers have now documented hundreds of hominin footprints at more than half a dozen sites across the region. That pattern suggests these areas were important habitats that offered resources valuable enough to draw extinct human relatives back repeatedly.
‘To me, it is amazing that we have the same kind of lake margin deposits in two areas of East Turkana that are 40 kilometres apart, at about the same age,’ said co-author Kay Behrensmeyer of the Smithsonian Institution. Understanding why the tracks survived could also help explain why ancient hominins kept returning. Behrensmeyer predicts that ‘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 lake shore environment over more than 100,000 years.’
Co-author Purity Kiura of the National Museums of Kenya stressed the broader significance: ‘The discovery of these fossil footprints along the margins of Lake Turkana reinforces the region’s global importance in understanding human evolution, preserving remarkable evidence of how our ancient relatives lived 1.4 million years ago.’
What comes next
The research team plans to return to Kenya this year to continue investigating the fossil footprint sites. Hatala frames the cumulative work as building a ‘photo album’ of snapshots from the Early Pleistocene: ‘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.’
Each newly documented surface can preserve a different moment from the distant past. The combination of body-size data, apparent group composition, and repeated site use around Lake Turkana is the kind of multi-signal evidence that bones alone rarely provide. Whether the team’s return this year yields further trackways from the same period will determine how far these initial conclusions can be extended.
