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

But researchers found that the Burtele foot — named after the place in northeastern Ethiopia where it was discovered in 2009 — was unmistakably different.

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

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 the foot belonged to a new species until they were able to study new fossils, including a jawbone with 12 teeth, that were found at the same site.

After identifying them as Australopithecus deyiremeda, they found the Burtele foot belonged to the same species.

John Rowan, an assistant professor in 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, there lived a closely related but adaptively distinct species,” 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 from Arizona State University, concluded that the new species spent much of its time in the forest.

Lucy, or Australopithecus afarensis, likely roamed the ground, the study said, before going on to suggest that the two species likely had different diets and used the landscape in different ways.

Multiple examinations of the newly found teeth indicated that A. deyiremeda was more primitive than Lucy and likely relied on a diet of leaves, fruit and nuts, the study said.

“These differences meant that they were unlikely to be directly competing for the same resources,” said Ashleigh L.A. Wiseman, an assistant research professor at the McDonald Institute for Archaeological Research, which is also based at the U.K.’s University of Cambridge.

Highlighting the broader impact of this discovery on our understanding of evolution, Wiseman said in an email Thursday that the findings reminded us “that human evolution wasn’t a straight ladder with one species turning into the next.”

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

Rowan also contended that as the number of well-documented human-related species grows, so do our questions about our ancestry. “Which species were our direct ancestors? Which were close relatives? That’s the tricky part,” he said. “As species diversity grows, so do the number of plausible reconstructions for how human evolution played out.”

And Wiseman cautioned against making definitive species assignments, as those should rest on well-preserved parts of skull and fossils that belong to multiple associated individuals. While the new research strengthens the case for A. deyiremeda’s existence, she said, it “doesn’t remove all other alternative interpretations.”

This article was originally published on NBCNews.com