A mysterious fossilized foot found years ago in Ethiopia belongs to a controversial and enigmatic human relative that lived at the same time as our ancestor "Lucy," a new study finds.

This discovery was years in the making. In 2009, scientists found the 3.4 million-year-old fossil foot that has toes designed for life in the trees. Now, newly discovered fossilized teeth and jaw bones found in the vicinity of the so-called "Burtele foot" suggest that members of Lucy's species, Australopithecus afarensis, lived side by side with another now-extinct human relative, Australopithecus deyiremeda, who lived from around 3.5 million to 3.3 million years ago.

The research, published Wednesday (Nov. 26) in the journal Nature, suggests Au. deyiremeda had an odd blend of features shared with members of Lucy's species, such as smaller canine teeth, as well as primitive characteristics seen in more ancient and ape-like hominins, such as opposable big toes that supported tree climbing.

But, like Lucy, Au. deyiremeda walked on two legs when on the ground, showing that different hominins living at the same time moved very differently from one another.

"What we are learning now is that, yes, bipedality was the key component of our evolutionary history, but there were so many ways to walk on two legs while on the ground," study first author Yohannes Haile-Selassie, a paleoanthropologist and director of Arizona State University's Institute of Human Origins, told Live Science.

He said that there were "a lot of experiments in bipedality," with different elements of the foot, pelvis and leg bones evolving at different rates and at different times.

The researchers found 13 new tooth and jaw fossil fragments of the same age close to where the Burtele foot was discovered. When compared with dental remains from other hominin species, these were "confidently" assigned to Au. deyiremeda, the researchers wrote in the new study. Based on their similar age and location, the team believe the teeth and foot belonged to members of the same species.

A chemical analysis of the tooth enamel revealed that, while both Lucy's species and Au. deyiremeda called Woranso-Mille home, they didn't need to fight for resources. Au. deyiremeda lived in a wooded environment and mainly ate from trees and shrubs, whereas Au. afarensis had a broad diet and lived in more open habitats.

"I think dietary differences and locomotion adaptation differences would be the best way to coexist," Haile-Selassie said. "Is that a surprise? Maybe not, because we know that modern primates today — closely related primates — they live together in the same area."

New finds shed light on diet and locomotion in Australopithecus deyiremeda
Yohannes Haile-Selassie, Gary T. Schwartz, Thomas C. Prang, Beverly Z. Saylor, Alan Deino, Luis Gibert, Anna Ragni & Naomi E. Levin
Nature (2025)Cite this article

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Abstract
The naming of Australopithecus deyiremeda1 from Woranso-Mille (less than 3.59 to more than 3.33 million years) indicated the presence of a species contemporaneous with Australopithecus afarensis in the Ethiopian Afar Rift. A partial foot (BRT-VP-2/73)2 and several isolated teeth from two Burtele (BRT) localities, however, were not identified to the species level. Recently recovered dentognathic specimens clarify not only the taxonomic affinity of the BRT hominin specimens but also shed light on the diet and locomotion of A. deyiremeda. Here we present a comparative description of these specimens and show that they are attributable to A. deyiremeda. We also find it parsimonious to attribute the BRT foot to this species based on the absence of other hominin species at BRT. The new material demonstrates that overall, A. deyiremeda was dentally and postcranially more primitive than A. afarensis, particularly in aspects of canine and premolar morphology, and in its retention of pedal grasping traits. Furthermore, the low and less variable distributions of its dental enamel δ13C values are similar to those from Ardipithecus ramidus and Australopithecus anamensis, indicating a reliance on C3 foods. This suggests that A. deyiremeda had a dietary strategy similar to the earlier A. ramidus and A. anamensis. The BRT foot and its assignment to A. deyiremeda provides conclusive evidence that arboreality was a significant component of the positional behaviour of this australopith, further corroborating that some degree of arboreality persisted among Pliocene hominins