Researchers analyzed footprints left by a troop of eight Paranthropus boisei individuals, originally encountered nearly 50 years ago by Smithsonian geologist Kay Behrensmeyer. During fieldwork in 1978, Behrensmeyer noticed an unexpected, hippo-sized depression in exposed rock. Careful excavation and brushing revealed two hominin tracks beneath a surface that had been silently recording movement since the Early Pleistocene.

Dating relied on volcanic ash layers embedded in the surrounding geology. By tying the trackway to an Early Pleistocene ash signature, the team estimated the prints at roughly 1.43 million years old. This places the hominins in a complex ecosystem including crocodiles and elephants, as well as multiple hominin species occupying the same landscape during that period.

The GaJi10 site is exceptionally detailed: it preserves 21 footprints attributed to eight individuals, alongside contemporaneous animal tracks. Importantly, the differing depths of impressions help distinguish deeper hippo and antelope marks from shallower hominin prints, revealing how varying trackmaker weights and substrate consistency shaped the record.

When the team compared footprint morphology and locomotion patterns, they concluded the tracks were made by Paranthropus—a surprising result because the impressions are similar in size to those expected for the larger-bodied Homo erectus. The findings suggest P. boisei individuals could have reached human-like body dimensions, up to about 6 feet tall and around 165 pounds, reshaping assumptions about relative size and niche differentiation.

Beyond body size, the trackways hint at social behavior. The simultaneous presence of mostly adult male P. boisei implies group travel without females or children, consistent with hypotheses about competition, intermittent tolerance, and movement through risky mudflat terrain.

Footprints also proved to be a “time-slice” of behavior that skeletal remains often cannot provide. As the authors note, tracks capture a fleeting moment: stance, gait, and interaction with substrate—evidence that can be directly compared across individuals and trackmakers.

The research team has since returned to Kenya, motivated by hundreds of related footprints in the broader Lake Turkana area. With better geological context, they expect to refine why these hominins repeatedly used the lakeshore and how changing conditions influenced track preservation.

Subject of Research: Not applicable
Article Title: New insights into hominin body size, locomotion, and behavior from Early Pleistocene trackways in northern Kenya
News Publication Date: Not provided in the text
Web References: https://naturalhistory.si.edu/staff/kay-behrensmeyer ; https://humanorigins.si.edu/evidence/human-fossils/species/paranthropus-boisei ; https://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus
References: Proceedings of the National Academy of Sciences
Image Credits: Kay Behrensmeyer, Smithsonian.

Keywords: Early humans; Hominins; Human origins; Paleoanthropology; Fossils; Taphonomy; Paleoecology; Paleoenvironments; Paleontology; Trace fossils