Twenty-one fossil footprints on an ancient lakeshore in northern Kenya record eight hominins moving across the same surface about 1.43 million years ago, giving researchers an unusually direct look at body size and possible group movement in Paranthropus boisei.
The GaJi10 trackway, described July 27 in Proceedings of the National Academy of Sciences, also carries deeper prints from hippopotamuses, antelope and other animals. Volcanic ash in the surrounding Koobi Fora Formation provided the age estimate.
Researchers attribute the hominin tracks to Paranthropus based on foot anatomy and movement patterns developed in earlier comparative work. The assignment is an interpretation, not a genetic identification: the footprints are unexpectedly large and overlap in size with tracks linked to Homo erectus, which lived in the same region.
A site found in 1978 kept yielding tracks
Smithsonian geologist Kay Behrensmeyer first noticed a deep hippopotamus print in 1978 while a field crew exposed the sediment layer. Brushing the surface revealed two hominin tracks. After initial study, the team reburied the site in sand to protect it.
Researchers returned in 2016 and 2023 and uncovered a much broader track surface. The final mapped assemblage contains 21 hominin prints associated with eight individuals, plus numerous animal tracks.
Footprints preserve behavior on a time scale that bones rarely can: a step is made in seconds, and several prints on one surface can show which individuals were present together. They do not reveal how long a group remained together or the relationships among its members.
Larger bodies than the bones suggested
Measurements of the prints produced maximum body-size estimates near 1.8 meters, or 6 feet, and 75 kilograms, or 165 pounds. Those values are larger than many estimates built from the limited Paranthropus skeletal record and bring the largest track makers into the range often associated with Homo erectus.
That size overlap is scientifically important because both hominins occupied the Lake Turkana landscape. The authors favor Paranthropus for GaJi10 because of the shape and apparent gait of the tracks, while the body-size result expands rather than erases the uncertainty around species assignment.
Evidence of movement together, not a full social census
Most of the prints are adult-sized and run in broadly similar directions. The team interprets the surface as evidence that multiple individuals, possibly mostly adult males, traveled together.
That pattern may point to a more complex social structure than isolated bones imply. But one preserved moment cannot establish whether the group was stable, how mating worked, or why the individuals crossed the mudflat.
The eastern Lake Turkana region now contains hundreds of hominin footprints deposited over more than 100,000 years. Combined with earlier sites preserving both Paranthropus-like and Homo erectus-like tracks, the record shows that multiple human relatives repeatedly used the same lakeshore environments.
The team plans more fieldwork in Kenya. Each new surface can test whether the GaJi10 pattern was exceptional or part of a recurring way these hominins moved through the landscape.