The footprints offer a rare look at ancient human relatives crossing paths

Two ancient hominid species with slightly different gaits interbred in East Africa.

Traces preserved on what was once a muddy lakeshore show that the two species, each built to walk in their own way, hung out there about 1.5 million years ago.

Newly discovered footprints in northern Kenya, and previously discovered tracks at a nearby site, provide glimpses of coexistence and possibly direct contact between ancient hominid species over a period of up to 200,000 years, says paleoanthropologist Kevin Hatala of Chatham University in Pittsburgh. colleagues.

Two walking patterns appear in footprints found along an ancient lake at Koobi Fora, a group of deposits at the eastern end of present-day Lake Turkana, scientists report Nov. 29. Science. A comparable distinction applies to footprints excavated in field work led by Hatala nearly 20 years ago at Ileret, another roughly 1.5-million-year-old Kenyan site, the team says. (SN: 26.2.09).

They included prints showing signs of human foot anatomy and gait Homo erectusa possible direct ancestor of H. sapienssays Hatala. H. erectuswhich lived from about 2 million to about 117,000 years ago, ate a variety of energy-dense foods to support its large brain (SN: 18.12.19).

Impressions that show less resemblance to the feet and step pattern of people today belonged to him Paranthropus boiseiinvestigators suspect. Small brained, big jawed P. boiseiwhich dates between 2.3 million and 1.2 million years ago, had a taste for grasses and flowering plants called watermelons (SN: 5/2/11).

Researchers have known for nearly 50 years that East African fossils of H. erectus AND P. boisei date to roughly the same time in nearby locations. But those fossils accumulated slowly, and researchers could not determine whether the two species simultaneously inhabited the same place.

The preserved footprints analyzed in the new study solve that problem, says paleoanthropologist Jeremy DeSilva of Dartmouth College, who was not part of Hatala’s team. “Now we know for sure that these two species [hominids] they share the same landscape and walk with slightly different gaits.”

Closely spaced footprints at the new Koobi Fora site, consisting of three H. erectus impressions and a trail of 12 impressions left by a P. boisei individual, were formed and then buried by lakeside sediments within a few days at most, the researchers say. So were the tracks of birds and large animals such as antelopes and wild horses.

“If Homo AND Paranthropy individuals passed through the area hours a day, or seconds to a minute apart, they would have been aware of each other’s existence in this shared landscape,” Hatala says.

If chimpanzees and gorillas can feed peacefully on the same tree, then it is possible H. erectus AND P. boisei “We came across a 1.5-million-year-old version of a 7-Eleven store” in a lake that contained a variety of desirable foods, says paleoanthropologist Bernard Wood of George Washington University in Washington, D.C. Wood was not involved in the new study. .

While the trace findings suggest that H. erectus AND P. boisei interacted, “if they competed or when, potentially due to climatic or environmental pressures, cannot be determined with the current evidence,” says paleoanthropologist Rita Sorrentino of the University of Bologna, Italy.

Whatever happened along the ancient shore of the lake, the Kenya tracks support an earlier report of divergent upright postures among even older hominid species. In Tanzania’s Laetoli country, 3.6-million-year-old footprints include human impressions of Lucy’s species. Australopithecus afarensis and more chimpanzee tracks of an unidentified hominid species (SN: 13.11.24 ; SN: 12/1/21).

In the new study, researchers compared 3-D digital models of tracks and tracks of ancient hominids with those made by humans today—including Kenyan herders who rarely or never wear shoes—traversing muddy ground like that along the lake. ancient. Mud tracks made by chimpanzees provided a further comparison.

The arches formed in human footprints when walking through the mud look very much like those left behind H. erectus in the ancient lake, says Hatala. This finding shows that H. erectus moved his legs as much as we do now, he says.

P. boisei The footprints featured a flatter arch than those of today’s humans, indicating that their foot movements and perhaps their anatomy differed from ours, Hatala says.

P. boisei – but no H. erectus — also possessed big toes that protruded more than those of humans today, but less than that seen in chimpanzees. P. boiseithe thumbs may have been more mobile than those of the H. erectus or modern people, suggests Hatala.

These foot disparities underlie two comparable effective forms of walking. “The road to which we attribute P. boisei reflects a fairly fast walking speed, and there is no evidence that they were out of balance or less able to walk on two legs than H. erectus“, says Hatala.