A mysterious fossilized foot discovered in Ethiopia suggests the existence of a little-known human ancestor who lived at the same time as the famous Lucy.
Until now, Lucy’s species, Australopithecus afarensis, was considered the only human ancestor living in this region more than three million years ago.
However, this 2009 discovery in Burtele, in northeastern Ethiopia, could even call into question Lucy’s status as a direct ancestor of Homo sapiens, according to a scientific study published Wednesday in the journal Nature.
The foot does not belong to Lucy’s species, as it features an opposable big toe—similar to a thumb—allowing grasping of tree branches, like monkeys.
The scientists who discovered the bones concluded in 2015 that they belonged to a previously unknown hominid species, Australopithecus deyiremeda, based on jaws roughly 3.4 million years old also found in Burtele.
Until now, the team could not say for certain whether the “Burtele foot” belonged to this new species. But in this new Nature study, the researchers report that newly found fossils—including a jawbone with 12 teeth—confirm that the foot belonged to Australopithecus deyiremeda.
“We have no doubt that the Burtele foot belongs to the same species as these teeth and this jaw,” said lead author Yohannes Haile-Selassie of the University of Arizona.
A possible ancestor of Homo sapiens?
The researchers also found new clues linking this species to Homo sapiens.
A scan of the teeth suggests Australopithecus deyiremeda was more primitive than its relative Lucy. Its diet consisted mainly of leaves, fruits, and nuts from trees.
Its grasping big toe also indicates that this relative of Homo sapiens spent much more time in trees. These toes played an important role in human evolution, signaling the shift from tree-dwelling to upright walking.
Whether Australopithecus deyiremeda and Lucy’s species lived side by side remains debated among scientists.
New findings suggest Australopithecus deyiremeda spent more time in wooded areas and in trees, while Australopithecus afarensis—Lucy’s species—lived more on the ground. These differences may have allowed both species to coexist.
This shows that “coexistence is deeply rooted in our ancestry,” Haile-Selassie notes.
Searching for our origins
John McNabb, a Paleolithic archaeologist at the University of Southampton, welcomed the new research.
“There will always be skeptics, but I think these new discoveries, along with validation of previous ones, will help more researchers accept Australopithecus deyiremeda,” he said. Though not part of the study, he noted that the findings “add a new element to the equation” in the search for humanity’s true ancestor.
Lucy’s species remains the most important ancestor because her foot is more similar to that of modern humans compared to the more primitive Australopithecus deyiremeda, the researchers acknowledge.
But this discovery “opens the possibility that we may still find other species from this period, since it seems australopithecines were experimenting with the idea of being bipedal,” Haile-Selassie adds.
For a long time, Lucy—found in 1974—was considered the earliest known human ancestor, but she was surpassed in 1994 by Ardi, a female Ardipithecus ramidus who lived 4.5 million years ago, also in present-day Ethiopia.