Scientists have identified that foot bones found in Ethiopia belong to Australopithecus deyiremeda, a hominin species that lived alongside the well-known Lucy’s species, Australopithecus afarensis. The research, published in Nature and supported by the National Science Foundation and W.M. Keck Foundation, sheds light on how these two ancient human ancestors coexisted in the same region about 3.4 million years ago.
The fossils were discovered in 2009 at the Woranso-Mille site in the Afar Rift by Yohannes Haile-Selassie of Arizona State University. Subsequent analysis has now confirmed their association with A. deyiremeda. University of Michigan geochemist Naomi Levin participated in the study, analyzing dental isotopes to compare diets between the two species.
Levin stated: “Studying the environments of human ancestors gives us a peek into what life was like during a time of elevated carbon dioxide concentrations and insights into how some of them might have gained a competitive edge over others.” She added: “The last time carbon dioxide levels in the atmosphere were as high as today, the genus Homo hadn’t even appeared yet. Humans evolved during a time when carbon dioxide levels were decreasing, and they were adapting to changing environments. These fossils help us understand what life was like millions of years ago. If we don’t understand how humans have interacted with the environment going back in time, we have no perspective on today.”
Isotope data showed that A. deyiremeda primarily consumed foods from trees and shrubs, whereas A. afarensis had a broader diet that included tropical grasses and sedges as well as foods from trees and shrubs.
“Lucy’s species was figuring out how to take advantage of additional foods and they were walking in a different way. My data shows that A. deyiremeda had a more restricted diet than A. afarensis,” Levin said. “They were in the same environment, but doing different things. This is the way that organisms survive, and the way we are going to survive, is that we have to adapt.”
The Burtele Foot—belonging to A. deyiremeda—displayed features suitable for climbing, such as an opposable big toe and flexible toes, suggesting differences in locomotion compared to Lucy’s species.
Yohannes Haile-Selassie commented: “When we found the foot in 2009 and announced it in 2012, we knew that it was different from Lucy’s species, Australopithecus afarensis, which is widely known from that time… However, it is not common practice in our field to name a species based on postcranial elements—meaning elements below the neck—so we were hoping that we would find something above the neck in clear association with the foot.”
“So what that means is that bipedality—walking on two legs—in these early human ancestors came in various forms,” Haile-Selassie said. “The whole idea of finding specimens like the Burtele Foot tells you that there were many ways of walking on two legs when on the ground—there was not just one way until later.”
In addition to teeth found at Burtele, researchers also uncovered a juvenile jaw attributed to A. deyiremeda; this specimen revealed similarities between both species’ development but highlighted differences through geochemical analysis and anatomy.
Levin concluded: “We actually have a unique situation, which is that we can control what the future looks like, and that means how much carbon we put in the atmosphere… But we’re also going to have to adapt—we’re going to have to adapt to systems that rely less on fossil fuels and how to figure out how to live in a warmer world. This is how our species is going to survive.”
