Ancient footprints in Kenya reveal the story of a smaller-brained, big-jawed human.

About 1.5 million years ago, members of the genus Homo walked along a lakeshore in Africa, only hours apart from another hominin, likely the smaller-brained, big-jawed Paranthropus.

The discovery challenges long-held views, such as those proposed by evolutionary biologist Ernst Mayr in the 1950s, that different hominin species never coexisted in time and space.

A new study published in Science reveals that their intermingled footprints, preserved in ancient mud, provide the clearest evidence yet that these two species inhabited the same place on the same day.

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Footprint of Homo Erectus, as suspected. Credit: Science.org

While fossils of Homo Erectus and Paranthropus Boisei have been found together in sediment layers, such remains often accumulate over thousands of years, leaving room for doubt.

The footprints, however, capture a moment in time when these early ancestors shared a landscape – perhaps they may have even encountered each other.

The footprints, discovered in 2021 at Koobi Fora near Lake Turkana in Kenya, were first identified by Richard Loki of the Turkana Basin Institute. The site, known for its rich fossil history, has yielded remains from five hominin species dating back as far as 4.2 million years. The well-preserved prints show intricate details, such as toes skidding in the mud.

Footprint of Paranthropus Boisei, as suspected. Credit: Science.org

A closer analysis by paleoanthropologists Kevin Hatala of Chatham University and Neil Roach of Harvard University revealed that the prints were left by at least two individuals. A trackway of 13 steps heading east suggests one person was moving quickly, while three isolated prints, less than a meter away, lead north. Based on their shapes, the isolated prints likely belonged to members of Homo, while the trackway’s flatter impressions suggest Paranthropus.

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Earlier studies show that Homo feet created distinct arches while walking, a feature absent in Australopithecus prints at Laetoli, Tanzania, 3.66 million years ago. At Koobi Fora, the flatter prints suggest a slightly more flexible big toe, hinting at evolutionary adaptations for climbing trees, though less pronounced than in chimpanzees.

Nearby fossil beds dated to the same period contain remains of two upright-walking hominins, Homo Erectus and Paranthropus Boisei, supporting the idea that these species were likely responsible for the footprints. To make sure it’s them, researchers yet need fossilized feet from these species.

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