Fossil footprints show 1.4-million-year-old human relative traveled in all-male groups

Fossil footprints discovered at a site in northern Kenya indicate that a 1.4-million-year-old human relative, likely Paranthropus boisei, had larger body sizes and different social grouping patterns than previously understood. The findings, published on July 27, 2026, stem from an analysis of trackways preserved at the Ileret site, east of Lake Turkana, according to researchers. The footprints reveal that some individuals stood up to 1.7 meters tall, challenging earlier estimates based on skeletal remains. The tracks also suggest that groups of this species may have traveled in all-male packs, a behavior not previously documented for early hominins.

The footprints were left in soft mud near an ancient lake and include tracks from multiple individuals of varying sizes. The researchers estimate that the largest individual weighed around 50 kilograms, significantly more than the typical 30–40 kilograms inferred from fragmentary fossils. The trackways show a clear size separation, with larger footprints clustered together and smaller ones in a separate group. This pattern, according to the study, points to a possible division by sex, where adult males moved together while females and juveniles formed distinct groups—a social structure resembling that of some modern primates.

This discovery matters because it provides direct behavioral evidence that is rarely preserved in the fossil record. Unlike bones, footprints capture a moment in time, revealing how these ancient relatives moved and interacted. The size estimates also force a reassessment of Paranthropus boisei, a species known for its robust skull and massive chewing teeth, but whose postcranial anatomy has remained poorly understood. The new data suggest that sexual dimorphism—differences in body size between males and females—was more pronounced than previously thought, which could influence interpretations of their social organization and ecological niche.

The study, led by a team from the Max Planck Institute for Evolutionary Anthropology and other institutions, analyzed a total of 97 footprints from five distinct trackways. The footprints date to 1.4 million years ago, based on the well-established stratigraphy of the Koobi Fora Formation. The largest footprint measures 27 centimeters in length, corresponding to an individual approximately 1.7 meters tall. The researchers used modern human and chimpanzee foot proportions to estimate stature and body mass, acknowledging some uncertainty in these extrapolations. The site has yielded hominin footprints before, but this is the first time such clear size segregation has been documented.

Earlier discoveries at Ileret include 1.5-million-year-old footprints attributed to Homo erectus, which showed more mixed-size groups. The contrast with the new Paranthropus boisei tracks highlights diversity in hominin social behavior during the early Pleistocene. The research team plans to continue excavations in the area, hoping to find additional trackways that could clarify whether this pattern was typical or an anomaly. They also aim to refine body size estimates using more sophisticated modeling techniques.

According to the report, the findings could reshape our understanding of how early human relatives adapted to their environments. If Paranthropus boisei did travel in all-male groups, it might reflect a strategy for foraging or predator avoidance distinct from that of contemporaneous Homo species. The study underscores the value of footprint evidence in filling gaps left by the skeletal record, offering a rare glimpse into the daily lives of our ancient kin.