A groundbreaking discovery in Ethiopia's Afar region has revolutionized our understanding of human evolution, revealing that two distinct human ancestor species lived side by side between 2.6 and 2.8 million years ago. International researchers led by Arizona State University have uncovered 13 fossilized teeth belonging to a previously unknown species of Australopithecus that coexisted with the earliest members of our own genus Homo, fundamentally challenging the linear progression model of human evolution.
The remarkable findings, published in the journal Nature, come from the famous Ledi-Geraru Research Project site where scientists previously discovered the oldest known Homo specimen and the earliest stone tools on Earth. This latest research demonstrates that human evolution was far more complex than traditionally imagined, resembling what researchers describe as a "bushy tree" rather than a straight evolutionary line.
"This new research shows that the image many of us have in our minds of an ape to a Neanderthal to a modern human is not correct — evolution doesn't work like that," explains Kaye Reed, a research scientist at Arizona State University's Institute of Human Origins and co-director of the Ledi-Geraru Research Project since 2002.
"Here we have two hominin species that are together. And human evolution is not linear — it's a bushy tree; there are life forms that go extinct."
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Maps showing (left) the location of the Ledi-Geraru site withing Africa, and the location of the Australopithecus and Homo teeth on the right. (Erin DiMaggio of Penn State University/ASU)
The Teeth That Rewrote History
The discovery centers on 13 fossil teeth that tell an extraordinary story of ancient coexistence. These dental remains, found at different locations within the Ledi-Geraru site, belonged to both the genus Homo and a completely new species of Australopithecus that has never been identified anywhere else on Earth.
The research team concluded that the Ledi-Geraru Australopithecus teeth represent a new species, distinct from Australopithecus afarensis — the famous species represented by "Lucy," perhaps the most celebrated early human ancestor ever discovered. This finding confirms that there is still no evidence of Lucy's kind younger than 2.95 million years ago, suggesting this lineage went extinct while other hominin species continued to evolve.
Brian Villmoare, lead author and ASU alumnus now at the University of Nevada, Las Vegas, emphasizes the significance:
"The new finds of Homo teeth from 2.6- to 2.8-million-year-old sediments — reported in this paper — confirms the antiquity of our lineage. We know what the teeth and mandible of the earliest Homo look like, but that's it. This emphasizes the critical importance of finding additional fossils to understand the differences between Australopithecus and Homo, and potentially how they were able to overlap in the fossil record at the same location."
The 13 fossil teeth collected in the Ledi-Geraru Research Area from 2015-2018. (Brian Villmoare/ASU)
Volcanic Time Capsules
The precise dating of these ancient fossils relies on Ethiopia's geological gift — active volcanism. The Afar region remains one of Earth's most tectonically active areas, where volcanic eruptions have created natural time markers stretching back millions of years.
Christopher Campisano, a geologist at ASU and research scientist at the Institute of Human Origins, explains the dating process:
"We can date the eruptions that were happening on the landscape when they're deposited. And we know that these fossils are interbed between those eruptions, so we can date units above and below the fossils. We are dating the volcanic ash of the eruptions that were happening while they were on the landscape."
These volcanic ash layers contain crystals called feldspars that allow scientists to determine precise ages for the geological formations. The teeth were found sandwiched between volcanic ash layers, providing definitive proof of their antiquity between 2.6 and 2.8 million years ago.
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A model of “Lucy” the famous Australopithecus example. (Jason Kuffer/CC BY NC ND 2.0)
Reconstructing Ancient Landscapes
The fossil discoveries have enabled scientists to reconstruct the environment that existed millions of years ago, painting a vivid picture of the world these early hominins inhabited. The modern faulted badlands of Ledi-Geraru present a stark contrast to the landscape traversed by our ancestors 2.6 to 2.8 million years ago.
Ramon Arrowsmith, professor at ASU's School of Earth and Space Exploration and long-time collaborator with the Ledi-Geraru Research Project, describes the ancient environment: "The geology gives us the age and characteristics of the sedimentary deposits containing the fossils. It is essential for age control." His research reveals that rivers once migrated across a vegetated landscape into shallow lakes that expanded and contracted over time — a far cry from today's arid badlands.
This environmental context is crucial for understanding how multiple hominin species could coexist in the same region. The varied landscape likely provided different ecological niches that allowed separate species to thrive without direct competition for identical resources.
The team cannot yet name the new Australopithecus species based solely on teeth; more fossil discoveries are needed before formal taxonomic designation can occur. However, the implications of this discovery extend far beyond naming conventions, fundamentally altering our understanding of early human evolutionary pathways.
Questions for Future Research
The discovery raises fascinating questions about the relationship between these coexisting species. Reed and her team are now examining tooth enamel to determine dietary patterns and resource utilization. Critical questions remain unanswered: Were the early Homo and this unidentified Australopithecus species eating the same foods? Did they compete for resources or find ways to share the landscape? Did they encounter each other regularly, and what were their ancestral relationships?
Current research focuses on isotopic analysis of tooth enamel, which can reveal dietary preferences and environmental conditions. This technique examines chemical signatures preserved in ancient teeth to reconstruct what these hominins consumed and how they adapted to their surroundings.
The Ledi-Geraru site continues to yield remarkable insights into human evolution. In 2013, the same research team discovered the jaw of the earliest Homo specimen ever found at 2.8 million years old, establishing the site as one of the world's most important paleoanthropological locations. The combination of excellent preservation conditions, precise geological dating, and continued systematic excavation makes Ledi-Geraru uniquely valuable for understanding human origins.
Top image: The 2.6 million year old Australopithecus teeth found in Ledi-Geraru, Ethiopia. Source: Amy Rector Virginia Commonwealth University/Arizona State University
By Gary Manners
References
Villmoare, B. et al. 2025. New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia. Available at: https://www.nature.com/articles/s41586-025-09390-4
Arizona State University. 2025. ASU scientists uncover new fossils — and a new species of ancient human ancestor. Available at: https://news.asu.edu/20250813-science-and-technology-asu-scientists-uncover-new-fossils-and-new-species-ancient-human
