Washington: About 1.5 million years ago, individuals of two different species in the human evolutionary lineage trudged on a muddy lakeshore in northern Kenya, leaving behind intersecting trackways alongside the footprints of antelopes, horses, warthogs, giant storks and other animals.
These tracks turned into fossils that scientists have now discovered at a location called Koobi Fora, providing the first evidence that these two species – Paranthropus boisei and Homo erectus – shared the same landscape, literally crossing paths. The discovery raises intriguing questions about the relationship between the two species and any competition for resources.
Some of the footprints of two human species found side-by-side in Kenya.
Paranthropus boisei, the more distantly related to modern humans of the two, lived from about 2.3 million to 1.2 million years ago, standing up to about 137 centimetres tall. They had a skull adapted for large chewing muscles, including a cranial crest like those in male gorillas, as well as massive molars. Their feet bore ape-like traits including in the big toe.
Homo erectus, an early member of our evolutionary line with body proportions like those of Homo sapiens, lived from about 1.89 million to 110,000 years ago, ranging from about 145 centimetres to 185 centimetres tall. They had large brow ridges and bigger brains than Paranthropus boisei, though smaller than our species.
Scientists study fossil footprints for clues about co-existing species of early human ancestors at the excavation site on the eastern side of Lake Turkana in northern Kenya, in 2022.Credit: AP
The researchers found the footprints in 2021 near Lake Turkana. They identified one long track of 12 footprints, each about 26 centimetres long, attributed to an adult Paranthropus boisei individual based on their shape and the manner of locomotion.
Three isolated footprints, ranging from 20.5 centimetres to 23.5 centimetres long and resembling those of modern people, were almost perpendicular to the main track. Two were complete enough to attribute to Homo erectus, possibly a juvenile. The third was harder to assign confidently.
The researchers said the tracks appeared to have been left within hours or perhaps a couple of days and the individuals even may have seen each other. There was no evidence of interaction.
“The fossil footprints provide us a clear picture of that instant in time, 1.5 million years ago. The different human ancestors may well have passed by each other, wading in the shallow water, possibly hunting and gathering,” said paleoanthropologist Louise Leakey, director of the Koobi Fora Research Project and co-author of the study published on Thursday in the journal Science.
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