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About 1.5 million years ago, two different species in the human evolutionary line strolled along the shore of a muddy lake in northern Kenya, crossing paths with the footprints of deer, horses, warthogs, giant storks and other animals. Hoy left the trackways behind.
These tracks turned into fossils that scientists have now discovered at a site called Koobi Fora, providing the first evidence that these two species – Paranthropus boisei and Homo erectus – roamed the same landscape, literally crossing paths. crossed the The discovery raises interesting questions about the relationship between the two species and any competition for resources.
Paranthropus boisei, the more distantly related of the two to modern humans, lived from about 2.3 to 1.2 million years ago, and was about 4 feet 6 inches (137 cm) tall. They had a skull designed for large chewing muscles, including a cranial crest like male gorillas, as well as large molars. Their feet had monkey-like features including a big toe.
Homo erectus, an early member of our evolutionary line with body proportions similar to Homo sapiens, lived from about 1.89 million to 110,000 years ago, with a height of about 4 ft 9 in to 6 ft 1 in (145–185 cm ) was They had eyebrow ridges and a larger brain than Pronthropus boisii, though smaller than ours.
Researchers found footprints in the vicinity of Lake Turkana in 2021. They identified a long trackway of 12 footprints, each about 10.25 inches (26 cm) long, attributed to an adult Paranthropus boisii individual based on their shape and movement patterns.
Three isolated footprints, 8–9.25 in (20.5–23.5 cm) long and similar to modern ones, were roughly perpendicular to the main trackway. Two were complete enough to be attributed to Homo erectus, possibly a juvenile. The third was difficult to assign with confidence.
The trackways appear to have been left within hours or perhaps days — the mud never dried and cracked — and the individuals may have even seen each other, the researchers said. There was no evidence of communication.
“Fossil footprints give us a clear picture of this moment 1.5 million years ago. Different human ancestors may have passed each other, wandering in deep water, possibly hunting and congregating. ” said biologist Louise Leckie, director. Koobi Fora Research Project and co-author of the study published Thursday in the journal Science Opens a New Tab.
The researchers reanalyzed the trackways that had previously been discovered nearby, determining that the two species coexisted on fossiliferous mud surfaces over a period spanning about 200,000 years.
“It’s possible that they’re in direct competition, but it’s also possible that they’re not in direct competition and that both have access to the resources they need in this shared landscape,” said the expert at Chatham University in Pittsburgh. said Kevin Hatala, biologist and lead author of the study.
Nutritional differences have reduced competition.
“Paranthropus boisii ate low-quality forage that likely required repeated chewing. Homo erectus was likely a carnivore, using tools to butcher carcasses, and in its diet There was also meat,” Leckie said.
The human and chimpanzee lineage split in Africa about 7 million years ago. Species in the human lineage are called hominins.
Footprints provide information about anatomy, locomotion, behavior and environment that skeletal fossils or stone tools cannot. The feet of these two species were physically distinct, and their gaits were different.
“The tracks we attribute to Homo erectus look very much like modern humans, with a long arch of sediment in the middle of the track that suggests a stiff foot and walking gait,” said the Harvard University evolutionist. indicates including pushing the fingers”. Biologist and study co-author Neil Roach.
“Paranthropus tracks lack this long arch and indicate a more flat-footed gait. Additionally, Paranthropus tracks show a larger toe that is slightly more mobile than the other feet. These two aspects are more similar to a chimpanzee’s walk, although there is clearly a difference between chimpanzee and human footprints,” Roach said.
Paranthropus boisei disappeared a few hundred thousand years after these footprints, while Homo erectus flourished. Possibly the direct ancestor of Homo sapiens, Homo erectus was the first human species to spread out of Africa.
The fossil site was a resource-rich lake shore near a river mouth.
“The fact that we consistently see two hominin species in these landscapes, despite the presence of dangerous animals like hippos and crocodiles, suggests that these environments were so important to our ancestors,” Roach said. were worth the risk of going there,” Roach said. .
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