"The fact that eight, mostly adult male, Paranthropus boisei individuals seemingly traveled together as a group, without females or children, hints at a complex social structure in this species," said co-author Neil Roach of Harvard University. "They may have lived in large groups, where males competed for mates, but also tolerated each other at times for safety in a dangerous environment."

The pattern echoes the social lives of some living primates, where males travel together for safety. The team cautioned that a single trail captures only a brief moment and cannot describe a whole species' behavior.

Why did hominins keep returning to the lakeshore?

The new site joins a growing cluster of hominin footprints along the margins of ancient Lake Turkana. Researchers have now documented hundreds of prints at more than half a dozen sites across the region, including two areas roughly 40 kilometers apart that appear to date to the same period.

"To me, it is amazing that we have the same kind of lake margin deposits in two areas of East Turkana that are 40 kilometers apart, at about the same age," said co-author Kay Behrensmeyer of the Smithsonian Institution.

Behrensmeyer believes visits to the lakeshore may have stretched across more than 100,000 years. "If we can understand what geological conditions allowed these tracks to be preserved, we should know more about why hominins continued to return to the lake shore environment over more than 100,000 years," she said.

How did the team identify the trackmakers?

The team used analytical methods they first developed in 2024 to match foot anatomy and walking style to known hominin species. The classification matters because the Turkana region hosted several hominin lineages around 1.4 million years ago, including early members of the genus Homo.

Pinpointing Paranthropus boisei required ruling out those other hominins, including Homo erectus, by comparing the shape of each print and the biomechanics of the steps.

What's next?

The team plans to return to Kenya later this year to keep documenting surfaces. Each new site adds a frame to what Hatala calls a "photo album" of the Early Pleistocene, a geological epoch that began about 2.6 million years ago.

"Each site represents a snapshot of our past, and we are quickly building a photo album with several different windows to hominin anatomy, locomotion, behavior, and environments during the Early Pleistocene," Hatala said.

Co-author Purity Kiura of the National Museums of Kenya emphasized what the discovery means for science in her country. "The discovery of these fossil footprints along the margins of Lake Turkana reinforces the region's global importance in understanding human evolution," she said. "It further strengthens Kenya's position as one of the world's leading paleoanthropological landscapes and highlights our responsibility to protect this irreplaceable heritage."

The study is part of a broader effort to use footprint evidence alongside traditional bone fossils. Bones typically capture one individual at a time; prints can capture several at once, along with their pace, direction, and grouping. Together, the two lines of evidence are building a more detailed picture of how ancient human relatives lived, moved, and organized their groups.