That size doesn’t fit the species everyone assumed made the tracks. The researchers say so themselves, and they don’t pretend the question is settled.
On a single bedding plane at a site called GaJi10, on the eastern shore of Kenya’s Lake Turkana, twenty-one ancient footprints sit preserved in what was once soft lakeshore mud.
A team led by Kevin Hatala of Chatham University and the Max Planck Institute for Evolutionary Anthropology, working with colleagues across the United States and Kenya, reported the find this year in the Proceedings of the National Academy of Sciences.
The tracks record eight individuals crossing the same patch of shoreline roughly 1.43 million years ago, and the largest of them, by the team’s own estimate, stood close to 1.8 meters tall and weighed around 75 kilograms, considerably bigger than most previous reconstructions of the species researchers believe made the prints.
That’s the genuinely useful thing about a find like this. Skeletal fossils accumulate slowly and separately, one bone at a time, almost never preserving evidence of individuals interacting.
A trackway does something bones structurally can’t: it captures several individuals in the same place at the same moment, walking together across ground that held their weight for only as long as it took the mud to dry and get buried.
Twenty-one prints, eight individuals, one shore
GaJi10 sits within Area 103 of the Koobi Fora Formation, in a geological layer called the Okote Member, roughly 40 centimeters below a volcanic ash layer that correlates with the Akait Tuff, independently dated to about 1.43 million years old.
The site’s history stretches back decades: Smithsonian paleontologist Kay Behrensmeyer and colleague Léo Laporte first spotted signs of it in 1978, when a geological survey trench happened to cut through a hippo footprint and exposed a pair of hominin tracks alongside it.
The site was subsequently buried in sand and left largely undisturbed until renewed excavations in 2016 and again in 2023 reopened the same layer and revealed far more tracks than the original 1978-79 dig had found.
The 2023 mapping effort documented 21 hominin footprints in total, 14 of them newly exposed since the original discovery. Two of the tracks recorded in the 1970s have since been lost to ongoing erosion, though they survive in archival photographs and in a physical cast held at the National Museums of Kenya.
The research team provisionally grouped the 21 individual prints into eight separate trackways, representing eight distinct individuals. One trackway heads east; every other one heads west.
The researchers note it’s possible the single east-bound walker also appears somewhere among the west-bound tracks, but they say there isn’t enough evidence in the prints themselves to confirm or rule that out.
The same preserved surface wasn’t exclusively hominin. It also holds 146 other animal tracks, including 67 attributed to hippos, 64 to bovids, 13 to birds, and two to equids. The hippo prints alone range from 15.5 to 42 centimeters wide, likely representing two different hippo species of noticeably different sizes.
Researchers describe the sediment conditions as consistent with a shallow, freshly wet surface, covered by only a few centimeters of water and then sealed under fine sand relatively quickly, with no desiccation cracks and no root traces disturbing the layer.
It reads less like an accumulated graveyard of remains built up over time and more like a single preserved snapshot of one ordinary day.
Which species actually made these tracks
The paper’s preferred identification is Paranthropus boisei, a heavily built, small-brained hominin known mostly from a limited number of skulls and teeth. Hatala’s group applied kinematic analysis methods they’d previously published in 2024, measuring relative arch volume against footprint depth alongside the angle at which the big toe splays outward from the rest of the foot.
On those specific measures, the GaJi10 tracks cluster together with other East Turkana footprints already attributed to P. boisei, and even with the much older Laetoli footprints in Tanzania generally attributed to Australopithecus afarensis.
All of these tracks share flatter arches and a more outward-angled big toe than anything found in the normal range of modern human feet, and they clearly don’t match a separate set of more human-like East Turkana tracks that researchers attribute to Homo erectus.
Size is where the identification runs into a genuine complication. Assuming the GaJi10 individuals had body proportions similar to Australopithecus, the researchers calculated stature estimates for the measurable trackmakers ranging from 130.6 to 180.9 centimeters.
Published skeletal-based estimates for P. boisei, by comparison, average around 131.1 centimeters, with a previously reported maximum of 161.3 centimeters. Four of the GaJi10 individuals exceed that previously recorded maximum.
Using the same scaling approach for body mass, estimates for the group ranged from 39.8 to 74.6 kilograms, and two of the individuals exceed the largest mass previously estimated for the species from skeletal remains alone.
As Hatala put it in comments accompanying the publication, the footprints point to up to 1.8 metres tall and around 75 kilograms, sizes well beyond what the existing skeletal record for P. boisei had suggested was possible.
The researchers themselves are careful not to treat the species question as fully resolved. If the tracks really do belong to P. boisei, it would mean the species was considerably larger and more physically variable than the existing bone record has shown.
If they instead belong to Homo erectus, it would mean that species’ foot anatomy and walking mechanics varied far more than anything observed in living humans today. The paper’s authors describe the current weight of evidence as favoring the P. boisei identification while explicitly declining to rule out Homo erectus.
They also raise, and largely dismiss, a third possibility: an entirely unidentified hominin species, a scenario they consider unlikely mainly because every other Okote Member hominin fossil identified to species level so far has turned out to be either P. boisei or H. erectus.
What the “all-male group” headline actually overstates
Coverage of the study has, in places, hardened a much more careful original claim into something more dramatic than the data supports. Harvard researcher Neil Roach, commenting on the find, described the group as mostly adult males that appeared to travel together without females or children, a detail that made it into multiple headlines framing the discovery as evidence of “all-male hominin gangs.”
The actual underlying claim in the paper is narrower than that framing suggests. If these footprints do belong to P. boisei, and if the existing skeletal fossil record for the species represents a roughly even mix of sexes, then individuals whose estimated body size falls above the species’ average are statistically more likely, though not confirmed, to have been adult males.
Five of the larger individuals happened to be walking west, roughly perpendicular to the inferred north-south shoreline, moving from shallower water toward deeper water, and none of the preserved hominin tracks overlap or cross each other, which the researchers read as evidence of at least mutual tolerance among individuals moving across the same surface, possibly as a single group.
That’s meaningfully different from a confirmed headcount of an all-male social unit, and it’s not evidence that females or juveniles were generally absent from P. boisei social groups as a species.
The three trackways detailed enough to calculate a walking speed came out slow, ranging from about 0.32 to 0.50 meters per second.
The researchers don’t believe this reflects the species’ typical walking pace, since other East Turkana sites with comparable footprints preserved in comparable mud conditions show substantially longer strides, suggesting the GaJi10 individuals may simply have been moving cautiously or carefully across that particular stretch of ground at that particular moment.
Why researchers keep finding tracks at Turkana
Purity Kiura of the National Museums of Kenya has emphasized what finds like this mean for the region’s broader scientific standing, noting that discoveries like the GaJi10 tracks reinforce the region’s global importance in understanding human evolution.
Behrensmeyer, who has worked this same lakeshore since 1969, points out that similar lake-margin sediment deposits of roughly the same age exist at sites roughly 40 kilometers away, and that hundreds of hominin footprints have now turned up across more than half a dozen locations in the broader area.
Why early hominins kept returning to walk across the same kind of muddy lakeshore repeatedly over such a long span of time is, in her framing, as much a question about the region’s geology and hydrology as it is a question about hominin behavior itself.
What remains, in the end, is a genuinely small and specific find: 21 footprints, provisionally sorted into eight individuals, on one muddy shoreline at one site called GaJi10, with the largest trackmaker estimated at up to 1.8 meters tall and around 75 kilograms.
It’s a rare kind of fossil evidence, capturing a group of individuals together at a single moment in a way bone fragments almost never can, and the researchers who found it have been notably careful not to claim it proves more than it actually shows.