Newly Found Fossils Show Lucy Shared Her World With a Very Different Ancestor

The search for early human ancestors often reveals a picture that is more complex than expected. Each discovery adds another layer and shows that the evolutionary path was not a single, straight line. Instead, the mid Pliocene landscape was home to multiple hominin species, each experimenting with different ways of moving, feeding, and occupying their environment. The new fossils from the Burtele area of Woranso Mille in Ethiopia offer a revealing example of this diversity.

Researchers have now identified dentognathic material that connects the long discussed Burtele partial foot to Australopithecus deyiremeda. This connection is significant because the foot possessed an unusual blend of features that did not match what scientists previously knew from other hominins of the same age. The newly analyzed jaws, teeth, and isotopic data help resolve this puzzle and create a clearer picture of how this ancient species lived.

The study demonstrates that this early australopith retained a strong capacity for climbing while also practicing bipedal locomotion. It also shows that its diet relied heavily on foods associated with wooded habitats. These patterns highlight that early hominins did not progress in a uniform march toward modern human traits. Instead, they balanced new adaptations with older ones as they navigated different ecological conditions.

The Scientific Problem These Fossils Address

For years, the Burtele partial foot raised questions because it did not match the well known foot structure of Australopithecus afarensis, the species that includes the famous Lucy skeleton. The Burtele foot showed curved toes, a mobile big toe, and other characteristics that hinted at a climbing lifestyle. Yet it came from a time and place where A. afarensis was already well established.

Without reliably associated teeth or jaws, the Burtele foot could not be assigned to a species. This limited what scientists could conclude about its significance. Did it represent variation within A. afarensis, or did it belong to a different hominin with a distinct way of life? The lack of supporting evidence prevented a firm answer.

The discovery of new dentognathic material from the same stratigraphic horizon allows researchers to solve this long standing issue. The newly described teeth show specific features that match the previously established definition of A. deyiremeda. With this match confirmed, the Burtele foot can now be confidently linked to this species. This resolves a major gap in the fossil record of the mid Pliocene.

When and Where These Fossils Originated

The fossils come from the Burtele area within the broader Woranso Mille research region in the Ethiopian Afar. The geological context surrounding the finds is well constrained. The fossil bearing layers lie above a volcanic tuff dated to roughly 3.47 million years and fall within a paleomagnetic range that anchors them between approximately 3.59 and 3.33 million years old.

This places A. deyiremeda as a contemporary of A. afarensis. Importantly, no other hominin species has been identified in the same precise layers at Burtele. This strengthens the argument that the Burtele foot belongs to A. deyiremeda. The shared stratigraphic setting creates a coherent and scientifically sound association.

How the Researchers Investigated These Fossils

To interpret the importance of the new remains, the scientists employed several approaches. High resolution micro CT scanning allowed for detailed visualization of internal tooth anatomy and unerupted teeth that could not be examined by traditional means. This helped clarify dental features that are essential for species level identification.

Morphological comparison formed the core of the taxonomic assessment. The researchers compared the Burtele jaws and teeth with the holotype and paratypes of A. deyiremeda and with samples of A. afarensis. Key differences included the size and shape of canines, the structure of premolars, and the proportions of the first molars. These distinctions align clearly with A. deyiremeda.

For the pedal anatomy, the team measured metatarsals and phalanges from the Burtele foot and compared them statistically with modern humans, modern apes, and other fossil hominins. This analysis highlighted the unique combination of grasping related traits and bipedal adaptations.

Stable carbon isotope analysis of tooth enamel provided an independent line of evidence on diet. The δ13C values revealed a dietary signature dominated by C3 plant resources, which are typical of forested habitats.

Together, these methods create a multi layered understanding of how A. deyiremeda lived and what ecological strategies it used.

What the Discoveries Reveal

A Distinct Species with Distinct Dental Traits

The new mandible and isolated teeth show a dental pattern that fits the definition of A. deyiremeda. These traits include small upper canines without strong lingual ridges, premolars with relatively simple and primitive shapes, and first molars that are narrower from cheek to tongue compared with those of A. afarensis.

The match between these features and those of previously identified A. deyiremeda specimens creates a consistent taxonomic picture. This alignment supports the assignment of the Burtele foot to this species.

A Foot Built for Climbing and Walking

The Burtele foot displays a mosaic of ancient and advanced traits. Curved toes, long and slightly twisted phalanges, a relatively mobile big toe, and reduced midfoot rigidity indicate that this species retained a significant climbing ability. These features suggest that trees played a meaningful role in daily activities, whether for foraging, resting, escape from predators, or a combination of all three.

At the same time, the foot also shows adaptations for upright walking. Certain aspects of the metatarsals reflect a shift toward a more human like pattern of weight transfer, even though the arch was not yet fully developed. The anatomy indicates a dual strategy rather than a single specialized mode of locomotion.

A Diet Centered on Forest Foods

The stable isotope evidence shows that A. deyiremeda relied heavily on C3 plants. These include tree fruits, leaves, and other vegetation found in wooded or forest environments. The values are similar to those of older species such as A. ramidus and A. anamensis, suggesting continuity in dietary patterns among earlier hominins.

This contrasts with A. afarensis, which often shows more mixed diets that include both C3 and C4 resources. The narrower dietary range of A. deyiremeda implies that it occupied a different ecological niche, perhaps helping explain how multiple hominin species could live in the same region at the same time.

Why These Findings Matter

The research challenges the idea that early human evolution followed a single path toward the modern human body plan and diet. Instead, several insights emerge.

Multiple Forms of Bipedalism Existed Together

A. deyiremeda demonstrates that strong climbing ability persisted in some hominins long after bipedal locomotion appeared. This species walked on two legs but still relied on trees. This indicates that more than one locomotor strategy existed at the same time.

Diet and Locomotion Evolved Independently

Changes in foot anatomy did not necessarily track changes in diet. A. deyiremeda had chewing features associated with tough or fibrous foods, yet its locomotion remained partly arboreal. Evolutionary pressures guiding diet did not always match those guiding movement.

Ecological Diversity Supported Species Coexistence

Different hominins used the landscape in different ways. A forest focused feeder with climbing skills could avoid competition with a more open habitat feeder like A. afarensis. Divergent strategies allowed multiple species to persist.

What Still Needs to Be Learned

There are natural limitations. Postcranial fossils are limited, and interpretations of locomotion rely on partial remains. More complete skeletons would clarify how the hip, knee, and ankle functioned. Isotope data provide broad dietary categories but cannot identify specific foods. Additional evidence such as microwear patterns would strengthen understanding of diet. Further fieldwork may also reveal whether other hominins were present in Burtele.

A More Braided View of Human Evolution

The new evidence from the Woranso Mille region paints an image of early hominin evolution that is far more dynamic and varied than previously assumed. Australopithecus deyiremeda combined ancient traits with emerging ones, showing that evolution operated through experimentation rather than a linear process. This species walked upright but kept climbing. It chewed like earlier hominins but lived alongside more ground adapted relatives. Its diet favored forest foods even when nearby species had broadened their diets.

The discovery enriches our understanding of how early human relatives adapted to changing landscapes and how multiple evolutionary paths existed simultaneously. As new fossils continue to surface, our picture of human origins becomes more detailed, more complex, and more fascinating.

The research was published in Nature on November 26, 2025.