Mystery foot suggests a second early human relative lived alongside Lucy

In the latest twist in human evolution, scientists have discovered that a mysterious foot found in Ethiopia belonged to a previously unknown ancient relative.

Dated to about 3.4 million years ago, the species was likely similar to Lucy, an ancient human relative who lived in the area around the same time, according to a study published Wednesday in the scientific journal Nature.

But researchers found that Burtele’s foot – named after the place in northeastern Ethiopia where it was discovered in 2009 – was undeniably different.

With an opposable big toe resembling a human thumb, Burtele’s fossilized foot suggests its owner was a skilled climber, spending more time in trees than Lucy, the study found.

For decades, Lucy’s species was considered the ancestor of all later hominids – an ancient relative more closely related to humans, including Homo sapiens, than to chimpanzees.

Scientists were unable to confirm that the foot belonged to a new species until they were able to study new fossils, including a 12-toothed jawbone, discovered at the same site.

After identifying them as Australopithecus deyiremeda, they discovered that Burtele’s foot belonged to the same species.

John Rowan, assistant professor of human evolution at Britain’s University of Cambridge, said their conclusion was “very reasonable.”

“Now we have much stronger evidence that, at the same time, a closely related but adaptively distinct species lived,” Rowan, who was not associated with the study, told NBC News in an email Thursday.

The study also looked at how these species shared the same environment. The research team, led by Yohannes Haile-Selassie of Arizona State University, concluded that the new species spent most of its time in the forest.

Lucy, or Australopithecus afarensis, likely roamed the ground, the study found, before suggesting the two species likely had different diets and used the landscape in different ways.

Multiple examinations of the newly discovered teeth indicated that A. deyiremeda was more primitive than Lucy and likely relied on a diet of leaves, fruits and nuts, according to the study.

“These differences meant they were unlikely to be in direct competition for the same resources,” said Ashleigh LA Wiseman, research assistant professor at the McDonald Institute of Archaeological Research, also based at the University of Cambridge in the UK.

Underscoring the discovery’s broader impact on our understanding of evolution, Wiseman said in an email Thursday that the results remind us “that human evolution was not a straight ladder with one species transforming into another.”

Instead, she said, it should be thought of as a family tree with several so-called “cousins” living at the same time, and each having a different way of surviving. “Did they interact? We will probably never know the answer to that question,” she added.

Rowan also argued that as the number of well-documented human species increases, so do our questions about our ancestry. “What species were our direct ancestors? What were our close relatives? That’s the tricky part,” he said. “As species diversity increases, so does the number of plausible reconstructions of how human evolution happened.”

And Wiseman cautioned against making definitive species assignments, as these would have to rely on well-preserved skull parts and fossils belonging to multiple associated individuals. Although the new research strengthens the case for the existence of A. deyiremeda, she said, “does not eliminate all other alternative interpretations.”