A trackway of fossilized footprints pressed into ancient lakeshore mud 1.43 million years ago is rewriting a basic assumption about one of our extinct evolutionary relatives: that Paranthropus boisei, a heavily built hominin usually reconstructed as short and largely solitary, could grow considerably taller than previously thought — and that individuals of the species moved through the landscape together, as a group.
The findings, published in the Proceedings of the National Academy of Sciences (PNAS 123(31): e2530996123), come from 21 hominin footprints uncovered at the GaJi10 site within the Koobi Fora Formation, on the eastern shore of Kenya’s Turkana Basin — one of the most productive hominin fossil landscapes in the world. Unlike bones, which capture an isolated moment of anatomy, a trackway is a record of behavior: who was walking, how they were built, which direction they were headed, and whether they were moving alone or as part of a group.
What a footprint can tell you that a bone can’t
Body size in the fossil record is usually estimated from isolated skeletal elements — a femur, a pelvis fragment, a tooth — and scaled against comparative anatomy. Footprints offer a different, complementary line of evidence: the size, depth, and pressure distribution of a track, combined with stride length and foot proportions, can be used to model the body mass and stature of the individual who made it, and, with enough tracks, to compare individuals against each other directly.
Applying that approach to the GaJi10 trackway, the research team — led by Kevin G. Hatala of Chatham University and the Max Planck Institute for Evolutionary Anthropology, with Neil T. Roach of Harvard University and Purity Kiura of the National Museums of Kenya — found that some of the individuals who left these tracks stood as tall as 1.8 meters (5.9 feet) and weighed roughly 75 kilograms. That is substantially larger than the compact, robust build typically associated with Paranthropus boisei in skeletal reconstructions, and it suggests the species had a wider range of body sizes than the existing fossil record of bones alone had captured.
Traveling together, not alone
The trackway’s real novelty, though, is what it implies about behavior. According to the research team, the pattern of tracks is consistent with eight individuals — interpreted as mostly adult males — moving across the same stretch of lakeshore mud at roughly the same time, oriented the same direction, with a single track heading the opposite way. That is difficult to explain as a coincidence of unrelated individuals crossing the same spot at different moments; it reads instead as a group moving together, a pattern that, if it holds up, pushes evidence for social or group-coordinated movement in hominins back well over a million years and into a species that has more often been imagined as smaller-bodied and less socially organized than genus Homo.
That inference matters because behavior almost never fossilizes. Bones and teeth can tell you a great deal about diet, growth, and anatomy, but they are silent on whether an individual walked with others. A single trackway, frozen in place by rapid burial and never re-exposed to erosion or trampling before excavation, is one of the only kinds of direct evidence in the entire hominin fossil record that can speak to that question at all.
A US–Kenya collaboration, and a site that stays in Kenya
The GaJi10 findings are the product of a collaborative research program spanning Chatham University and the Max Planck Institute for Evolutionary Anthropology in the United States and Germany, Harvard University, and the National Museums of Kenya — the Kenyan institution responsible for the country’s paleontological heritage and a co-author institution on the paper itself, not merely a permitting body. That structure reflects the norm for major East African hominin fieldwork: the fossils and the trackway surface itself remain in Kenya, under Kenyan institutional custody, with international collaborators contributing analytical expertise rather than removing material for study abroad. For a discovery this significant, that in-situ stewardship arrangement is worth stating plainly — it is the model that keeps a country’s fossil heritage, and the ongoing scientific narrative built on it, anchored in the nation where it was found.
Why this trackway, and not just another hominin fossil
Multi-individual hominin trackways are rare. Most footprint sites preserve one or two tracks, or a short, ambiguous sequence. A surface with 21 clearly attributable tracks, from a single, tightly dated depositional event, is unusual enough that it allows researchers to ask questions — about relative body size across individuals, about direction of travel, about whether tracks cluster in time — that isolated bones simply cannot answer. Combined with the age of the site (1.43 million years, placing it within the broader window in which Paranthropus boisei and early Homo erectus both occupied the Turkana Basin), the GaJi10 trackway adds a rare behavioral data point to a fossil record that is otherwise built almost entirely from isolated skeletal remains.
Source
Primary reporting on this research, including the height and track-count figures cited above, comes from Smithsonian Institution press materials on the study, cross-checked against independent science-press coverage of the same PNAS paper (Hatala et al., Proceedings of the National Academy of Sciences 123(31): e2530996123, 2026). Readers seeking the full methodology and dataset should consult the PNAS article directly.
