Ancient Fossil Footsteps Found in Kenya May Hint That an Early Human Relative Was Larger Than Previously Thought

The trackway sheds light on how some hominins moved around their environments and with one another

Riley Black | Science Correspondent

July 27, 2026 3:08 p.m.

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Fossil tracks found in the 1.4-million-year-old rock of Kenya have revealed a few fleeting moments of our early relatives’ history. The footprints record the steps of multiple individual hominins, preserved alongside those of ancient hippos and water birds. Depending on what species of early human left the tracks, the findings might significantly alter researchers’ understanding of one of the hominins.

A team led by paleontologist Kay Behrensmeyer, of the Smithsonian’s National Museum of Natural History, found the first tracks in 1978. Working at a field area in Kenya known as Koobi Fora, Behrensmeyer and other researchers were trying to learn more about the area’s geology. The rocks held critical clues about the geologic age and environment of the layers where paleoanthropologists were finding hominin fossils. “My crew was digging trenches in the area so we could see the layers of rock,” Behrensmeyer recalls in a statement, and “in the walls of one of these trenches were these big, weird indentations that clearly looked like hippo prints to me.”

Kimolo Mulwa, an excavator on the team, cleared off the rock layers the hippo tracks were situated in. Tracks are often found on broad surfaces that contain other impressions. When Behrensmeyer checked in on what Mulwa was uncovering, Behrensmeyer says, “he had a big grin on his face.” Mulwa had uncovered two footprints left by an ancient human.

Tantalizing as the footprints were, though, the team had other research to do. They covered the tracks back up until they could return and give the impressions their full attention. In 2016 and 2023, field teams did just that, going to the site and uncovering even more hominin footprints. Behrensmeyer and colleagues describe the tracks today in a new Proceedings of the National Academy of Sciences study.

While early expansions of the site didn’t turn up any additional hominin tracks, the team eventually found evidence for at least seven individuals. The aggregation makes social sense. “Hominins are not solitary creatures,” says Chatham University associate professor of biology and study lead Kevin Hatala, noting that “when we find footprints of one hominin, there is a high probability of finding more nearby.”

Another discovery made in the same area slightly complicates the identity of which hominins left the tracks behind. In 2024, Hatala, Behrensmeyer and other researchers described tracks made by two different hominins on the same surface dating to about 1.5 million years ago. One was a close relative of ours, Homo erectus, with body proportions more similar to us. The other was Paranthropus, belonging to a different branch of the human family tree. Paranthropus were generally thought of as being shorter, with bodies still better suited to moving through the trees than on the ground, and set apart by deep, strong jaws.

Because a hominin did not perish and become preserved in the rock, or leave any other telltale clue, it’s tricky to be certain which species walked over the lakeshore. The size of the tracks is more consistent with Homo erectus. The seven hominin individuals that left the different tracks on the surface were all believed to be over five feet tall, whereas adult Paranthropus have been reconstructed as being between four and five feet tall. But the shape and inferred anatomy of the feet that made the impressions look more consistent with the foot skeletons of Paranthropus.

If the footprints were left by Paranthropus, as Behrensmeyer and Hatala suspect, the size difference alters how experts understand these early humans. “We haven’t known all that much about Paranthropus body size,” Hatala says, because experts haven’t found that many bones other than the skull that can confidently be attributed to Paranthropus. Estimates based upon comparisons between skull and body size in other early humans has led to the reconstructions of Paranthropus, but there is no appropriate skeleton to check against. Larger bones and footprints have often been attributed to Homo erectus or other hominins closer to us because Paranthropus was thought to be smaller. “But maybe these species were much closer in size than previously thought,” Hatala says.

A larger body size for Paranthropus would alter how researchers understand this ancient human relative. Larger size affects how much food is required in a day, how far hominins could travel and even which predators might consider them prey. If future work bears the team’s hypothesis out, the tracks would help open an array of reconsiderations about a poorly understood member of our distant family.

The work at the site in Kenya will certainly continue as Hatala, Behrensmeyer and others continue to analyze the fossil footprints. “My role is to try to figure out the geology of why it was such a good time and place to preserve footprints,” Behrensmeyer says. Understanding the nature of the sediments that preserved the tracks reveals clues about the ancient environment and insights on the types of rocks that might hold additional hominin footprints.

“One of the most surprising aspects of this project has been the number of hominin footprint sites we are finding,” Hatala says. Conditions along ancient waterways between 1.4 and 1.6 million years ago seemed ideal for preserving impressions from hominins, hippos and many other creatures that lived in what’s now East Africa. A trackway is not a static piece of rock but rather a time capsule. Each site, Hatala says, “is giving us a unique snapshot into hominin life.”

Riley Black | | Read More

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.