A new study documents a set of fossil footprints preserving a snapshot of "fossil behavior" from an ancient hominin group along a lakeshore in northern Kenya around 1.4 million years ago.
An international team of researchers from the US and Kenya found tracks showing eight Paranthropus boisei individuals — an extinct "cousin" of modern humans — in one place at one time. All of the individuals are thought to be adults, and some appear to have been much larger in body size than previous estimates based on rare fossil bones.
Large footprints, large bodies
Analytical methods that this research team pioneered in 2024 helped distinguish these new tracks as belonging to Paranthropus boisei, based on their apparent foot anatomy and movement patterns. However, their sizes were surprising. "The sizes of the footprints indicate human-like body sizes – up to 1.8 meters tall and around 75 kilograms", says lead author Kevin Hatala, of Chatham University and an associated researcher of the Department of Human Origins at the Max Planck Institute for Evolutionary Anthropology in Leipzig.
Until recently, the overwhelming majority of Paranthropus boisei fossils were skulls with massive jaws and teeth, and little has been known about their anatomy from the neck down. But these latest findings challenge earlier studies that suggested Paranthropus boisei was considerably smaller than the contemporary Homo erectus, which is a possible direct ancestor of modern humans.
Fossil footprint surfaces are known to form very quickly and therefore can also be a useful window into hominin behavior and group dynamics. "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", says 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."
This discovery adds an important behavioral dimension to the fossil record of Paranthropus boisei, a species that lived alongside early members of the genus Homo, yet took a different evolutionary path.
Returning to the lake shore
A growing assemblage of ancient human footprints in lake margin environments also points toward this being an important habitat with critical resources for our extinct relatives. "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", says co-author Kay Behrensmeyer of the Smithsonian Institution.
At this point, the research team has documented hundreds of hominin footprints across more than a half-dozen sites in this region. Behrensmeyer predicts that, "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."
Building a photo album of the past
The team will be back in Kenya this year to continue research into these special fossil footprint sites. "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," says Hatala.
Co-author Purity Kiura of the National Museums of Kenya adds, "The discovery of these fossil footprints along the margins of Lake Turkana reinforces the region's global importance in understanding human evolution, preserving remarkable evidence of how our ancient relatives lived 1.4 million years ago. It further strengthens Kenya's position as one of the world's leading paleoanthropological landscapes and highlights our responsibility to protect this irreplaceable heritage."
Combining new analytical approaches with exceptional fossil footprint sites, the study demonstrates that ancient tracks can reveal the anatomy and movement of extinct human relatives, while also providing rare insights into their social lives and environments.
