Researchers have determined that 3.4-million-year-old foot bones discovered in Ethiopia belong to Australopithecus deyiremeda, a species that coexisted with Australopithecus afarensis. The find highlights dietary differences that likely allowed peaceful overlap between the two groups. This challenges linear views of human evolution.
In 2009, Yohannes Haile-Selassie of Arizona State University and his team unearthed eight hominin bones forming a right foot at Burtele in Ethiopia's Afar region. Dated to 3.4 million years ago, the bones featured a gorilla-like opposable big toe, indicating tree-climbing capabilities. These traits distinguished them from nearby Australopithecus afarensis fossils, including the famous Lucy specimen from the same area.
Haile-Selassie noted early on, “We knew from the very beginning that it didn’t belong to Lucy’s species.” Initial theories pointed to either another Australopithecus species or the older Ardipithecus genus, which also had an opposable toe and lived in Ethiopia over a million years prior.
The puzzle deepened in 2015 when jaw and teeth remains from the site led to the naming of Australopithecus deyiremeda as a new species. Though suspected, the foot's differing age prevented a firm link. That changed in 2016 with the discovery of an A. deyiremeda lower jawbone just 300 meters away, matching the foot's geological age and confirming its attribution.
Analysis of carbon isotopes in the teeth revealed key differences: A. deyiremeda mainly ate from trees and shrubs, while A. afarensis favored grasses. This dietary separation suggests minimal food competition, enabling coexistence. “They must have seen each other, spent time in the same area doing their own things,” Haile-Selassie said. He added, “One may have seen members of Australopithecus deyiremeda in the trees while members of A. afarensis were roaming in the grasslands nearby.”
The evidence underscores a non-linear human evolution, with multiple related species sharing spaces. Haile-Selassie explained, “Some had argued that there was only one hominin species at any given time giving rise to a newer form. Now, we know that our evolution was not linear. There were multiple closely related hominin species living at the same time even in close geographic proximity and living in harmony, suggesting that coexistence is deep in our ancestry.”
Carrie Mongle of Stony Brook University called it “exciting we are starting to get a better understanding of hominin diversity in the Pliocene [around 3 million years ago].” The research appears in Nature (DOI: 10.1038/s41586-025-09714-4).