In the latest twist in human evolution, scientists have discovered a mysterious foot found in Ethiopia belonged to a previously unknown ancient relative.
Dated to approximately 3.4 million years ago, this species was probably similar to Lucy, an ancient relative of man 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 site in northeastern Ethiopia where it was discovered in 2009 — was clearly different.
Burtele's fossilized foot, with an opposite big toe reminiscent of a human thumb, suggests its owner was an experienced climber and spent more time in the trees than Lucy, the study says.
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 examine new fossils, including a jawbone with 12 teeth, that were found at the same site.
Identifying them as Australopithecus deyiremeda, they discovered that Burtele's foot belonged to the same species.
John Rowan, associate professor of human evolution at Britain's Cambridge University, said their conclusion was “very reasonable.”
“We now have much stronger evidence that closely related but adaptively distinct species existed at the same time,” Rowan, who was not associated with the study, said in an email to NBC News on Thursday.
The study also looked at how these species live in the same habitat. A research team led by Johannes Haile-Selassie of Arizona State University concluded that the new species spends most of its time in the forest.
The study said Lucy, or Australopithecus afarensis, most likely roamed the land, and then suggested that the two species likely ate differently and used the landscape differently.
Numerous studies of newly discovered teeth have shown that A. deyiremeda was more primitive than Lucy and likely fed on leaves, fruits and nuts, the study said.
“These differences meant they were unlikely to compete directly for the same resources,” Ashley LA said. Wiseman is a research assistant professor at the Macdonald Institute for Archaeological Research, which is also based at Britain's University of Cambridge.
Underscoring the discovery's broader impact on our understanding of evolution, Wiseman said in an email Thursday that the findings remind us “that human evolution was not a straight ladder along which one species evolves into another.”
Instead, she says, it should be viewed as a family tree in which several so-called “cousins” live simultaneously, each with different ways of surviving. “Did they interact? We'll probably never know the answer to that question,” she added.
Rowan also argued that as the number of well-documented species related to humans grows, so do our questions about our origins. “Which species were our direct ancestors? Which species were close relatives? That's the hard part,” he said. “As species diversity increases, so does the number of plausible reconstructions of how human evolution occurred.”
And Wiseman cautioned against a single species definition, which must be based on well-preserved skull parts and fossils from many related individuals. She said while the new study confirms the existence of A. deyiremeda, it “does not rule out all other alternative interpretations.”
