Ancient footprints preserved along the shores of Kenya's Lake Turkana are reshaping scientists' understanding of one of humanity's extinct relatives. A paper published today in Proceedings of the National Academy of Sciences describes a set of fossil trackways made by a group of ancient human relatives that were moving along a lakeshore more than 1.4 million years ago.
An international team of researchers from the U.S. and Kenya analyzed a trove of fossilized footprints that were left behind by a troop of eight Paranthropus boisei hominins, first discovered nearly 50 years ago in northern Kenya by Kay Behrensmeyer , senior research geologist and curator of vertebrate paleontology at the Smithsonian's National Museum of Natural History . Behrensmeyer's team initially discovered the trackway in 1978 and is studying how the local geology preserved so many ancient footprints at the site.
The study was led by Kevin Hatala , an associate professor of biology at Chatham University in Pittsburgh and an associate researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
"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.
The newly described track site provides one of the most detailed snapshots yet and emphasizes the global importance of paleoanthropology sites around Kenya's Lake Turkana according to Purity Kiura, a researcher at the National Museums of Kenya in Nairobi and co-author on the new paper.
"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," Kiura 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."
Behrensmeyer has conducted field work in this region since 1969. During the 1978 field season, some of her Kenyan colleagues were excavating a trench to examine different geologic layers when Behrensmeyer noticed a deep, rounded indentation in the rock—a hippo footprint. The crew excavated that layer and carefully brushed off the surface, revealing a pair of hominin tracks pressed into the ancient sediment.
The find was particularly exciting to Behrensmeyer because footprints provide insights into ancient human behavior that are often difficult to glean from fossilized bones and fragments.
"The special thing about footprints scientifically is that they preserve an instant in time," Behrensmeyer said. "They also allow people to relate to these fossils much more easily than an isolated piece of bone or jaw."
It would take several decades for scientists to understand the true extent of this fossil trackway, which was named GaJi10. After Behrensmeyer and her team studied the initial footprints, the site was buried in sand to protect it for future study. In 2016 and 2023, the team returned and revealed many more footprints preserved on the same layer. In total, the GaJi10 site preserves 21 footprints that were left by eight individuals, as well as tracks of numerous hippo, antelope and other animals.
The team used volcanic ash in the surrounding rock to date the trackway to the Early Pleistocene around 1.43 million years ago. At the time, the shores of Lake Turkana were inhabited by a range of animals, including crocodiles, elephants and two different species of ancient human relatives, or hominins: P. boisei , a stocky species with heavy-duty teeth, and Homo erectus , a potential direct ancestor of humans today.
In 2024, members of the research team, including Hatala and Behrensmeyer, described a slightly older trackway in the area that preserved prints from both species of ancient hominins , revealing that the two inhabited the same habitats for hundreds of thousands of years.
"We can't say how the two different hominins interacted on the mudflats, but we know they were both here at this time," Behrensmeyer said.
The team analyzed the anatomy and movement patterns of the GaJi10 fossil footprints and determined they were made by Paranthropus. The conclusion was surprising because the tracks were similar sizes to those left by H. erectus, which was long thought to be significantly larger than Paranthropus.
"The sizes of the footprints indicate human-like body sizes—up to 6 feet tall and around 165 pounds," Hatala said. Resizing Paranthropus provides evidence that two similarly sized hominins inhabited the same environment at the same time.
The new track site also reveals that adult male Paranthropus sometimes traveled in groups.
"The fact that eight, mostly adult male, P. boisei individuals seemingly traveled together as a group, without females or children, hints at a complex social structure in this species," said Neil Roach , a researcher at Harvard University who is also a coauthor of the new paper. "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 newly described track site is among hundreds of footprints that have been discovered along the eastern shore of Lake Turkana. These footprints were deposited over more than 100,000 years, and Behrensmeyer thinks that better understanding the geology that preserved the footprints could shed light on why local hominins frequented this lake margin environment.
The team is returning to Kenya later this year to continue investigating these fossil footprint sites. The prospect of new discoveries continues to excite Behrensmeyer.
"I never dreamed when we found these in 1978 that it would develop into such a large assemblage and provide such widespread insights into the ecology of these hominins," Behrensmeyer said.
In addition to Hatala, Behrensmeyer, Kiura and Roach, the study included authors affiliated with Rutgers University, George Washington University and Stony Brook University. The research was supported by the U.S. National Science Foundation and the Turkana Basin Institute (Kenya and Stony Brook University).
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