Muddy footprints found at a lakeside in Kenya provide intriguing evidence that two early human ancestors coexisted roughly 1.5 million years ago. These tracks indicate that two distinct species left their marks in the mud “within hours, or possibly days” of one another, according to paleontologist Louise Leakey, one of the researchers behind the findings presented in the journal Science.
The two species, Homo erectus and Paranthropus boisei, are known to have lived contemporaneously in the Turkana Basin, as suggested by earlier fossil discoveries. However, determining precise dates for fossils can often come with uncertainties; paleontologist William Harcourt-Smith noted that the dating can vary by several thousand years. “Fossil footprints provide a fixed moment in time,” he explained, highlighting the significance of this latest find.
Discovered in 2021 at Koobi Fora in Kenya, the fossilized footprints signify that these two ancestors may have been aware of each other’s presence. Kevin Hatala, a co-author of the study and paleoanthropologist at Chatham University in Pittsburgh, remarked, “They probably saw each other and influenced one another in some manner.”
Researchers were able to differentiate between the two species by analyzing the characteristics of the footprints, which reveal insights into foot anatomy and movement patterns. H. erectus exhibited a walking style resembling that of modern humans—typically landing heel-first, then rolling the weight onto the ball and toes before pushing off again. Conversely, the other species displayed a unique walking pattern, “different from anything else observed in the past,” according to co-author Erin Marie Williams-Hatala, a human evolutionary anatomist from Chatham University.
The footprints implied that the big toe of Paranthropus boisei had greater mobility compared to both H. erectus and contemporary humans. Researchers suggest that our primordial ancestors initially had hands and feet evolved for tree climbing. However, over time, adaptations occurred to facilitate upright walking.
This study contributes to a broader understanding of the transition to bipedalism—where species began walking on two feet—indicating that this evolution wasn’t linear but rather a diverse process. Harcourt-Smith explained that there are multiple gait mechanics, suggesting early humans could have developed various ways of moving across ancient muddy terrains.
