In 2009, paleoanthropologists found eight bones from the foot of an ancient human ancestor in 3.4-million-year-old sediments at the paleontological site of Woranso-Mille in the Afar Rift in Ethiopia. According to new research, the fossil — named the Burtele foot — belongs to a hominin species called Australopithecus deyiremeda. The discovery provides further proof that two hominin species — Australopithecus deyiremeda and Australopithecus afarensis — co-existed at the same time and in the same region.
Australopithecus deyiremeda and Australopithecus afarensis. Image credit: Gemini AI.
“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,” said Arizona State University’s Professor Yohannes Haile-Selassie.
“However, it is not common practice in our field to name a species based on postcranial elements, so we were hoping that we would find something above the neck in clear association with the foot.
“Crania, jaws and teeth are usually the elements used in species recognition.”
“When the Burtele foot was announced, some teeth were already found from the same area, but we were not convinced the teeth were from the same level of sediments.”
“Then, in 2015, scientists announced a new species, Australopithecus deyiremeda, from the same area but did not include the foot into this species even though some of the specimens were found very close to the foot.”
“Over the past 10 years of returning to the field and finding more fossils, we now have specimens that we can confidently associate with the Burtele foot and with the species Australopithecus deyiremeda.”
Australopithecus deyiremeda’s foot is more primitive than the feet of Lucy’s species, Australopithecus afarensis.
It retained an opposable big toe which is important for climbing. But when on the ground, Australopithecus deyiremeda walked on two legs and it most likely pushed off on its second digit rather than its big toe like we, modern humans, do today.
“The presence of an abducted big toe in Ardipithecus ramidus was a big surprise because at 4.4 million-years-ago there was still an early hominin ancestor which retained an opposable big toe, which was totally unexpected,” Professor Haile-Selassie said.
“Then 1-million-years later, at 3.4-million-years ago, we find the Burtele foot, which is even more surprising.”
“This is a time when we see species like Australopithecus afarensis whose members were fully bipedal with an adducted big toe.”
“What that means is that bipedality — walking on two legs — in these early human ancestors came in various forms.”
“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.”
To get insight into the diet of Australopithecus deyiremeda, the authors sampled eight of the 25 teeth found at the Burtele localities for isotope analysis.
The process involves cleaning the teeth, making sure to only sample the enamel.
“I sample the tooth with a dental drill and a very tiny (< 1 mm) bit — this equipment is the same kind that dentists use to work on your teeth,” said University of Michigan’s Professor Naomi Levin said.
“With this drill I carefully remove small amounts of powder. I store that powder in a plastic vial and transport it back to our lab for isotopic analysis.”
“The results were surprising: while Lucy’s species was a mixed feeder, eating C3 (resources from trees and shrubs) and C4 plants (tropical grasses and sedges), Australopithecus deyiremeda was utilizing resources that are more on the C3 side.”
“I was surprised that the carbon isotope signal was so clear and so similar to the carbon isotope data from the older hominins Australopithecus ramidus and Australopithecus anamensis.”
“I thought the distinctions between the diet of Australopithecus deyiremeda and Australopithecus afarensis would be harder to identify but the isotope data show clearly that Australopithecus deyiremeda wasn’t accessing the same range of resources as Australopithecus afarensis, which is the earliest hominin shown to make use of C4 grass-based food resources.”
Another key data analysis was carefully establishing the age of the fossils and understanding the surrounding ancient environment in which the ancient hominins lived in.
“We have done a tremendous amount of careful field work at Woranso-Mille to establish how different fossil layers relate, which is crucial to understanding when and in what settings the different species lived,” said Case Western Reserve University’s Professor Beverly Saylor.
Along with the 25 teeth found at Burtele, the researchers also found the jaw of a 4.5-year-old juvenile that based on the anatomy of the teeth clearly belonged to Australopithecus deyiremeda.
“For a juvenile hominin of this age, we were able to see clear traces of a disconnect in growth between the front teeth (incisors) and the back chewing teeth (molars), much like is seen in living apes and in other early australopiths, like Lucy’s species,” said Arizona State University’s Professor Gary Schwartz.
“I think the biggest surprise was despite our growing awareness of how diverse these early australopith (i.e., early hominin) species were — in their size, in their diet, in their locomotor repertoires and in their anatomy — these early australopiths seem to be remarkably similar in the manner in which they grew up.”
A paper on the findings was published this week in the journal Nature.
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Y. Haile-Selassie et al. New finds shed light on diet and locomotion in Australopithecus deyiremeda. Nature, published online November 26, 2025; doi: 10.1038/s41586-025-09714-4
