Fossils from Ethiopia are reshaping one of the biggest stories in human history. Instead of a neat march from ape-like ancestors to modern humans, evidence from the Ledi-Geraru field site points to a much messier and more fascinating reality: several human relatives may have shared the same African landscape at the same time. An international research team studying fossils from the site found evidence that Australopithecus and the earliest known members of Homo lived in the same region between about 2.6 and 2.8 million years ago — and the fossils also point to an Australopithecus species that has not been found anywhere else on Earth.
The Ledi-Geraru Research Project, led by scientists at Arizona State University, has already earned a major place in human origins research. The site has produced the oldest known member of the genus Homo and the earliest known Oldowan stone tools on Earth. The new findings, published in Nature in August 2025, add a further remarkable chapter to that legacy.
The Power of 13 Ancient Teeth
The key evidence came from teeth — just 13 fossil teeth, found in ancient sediments, yet enough to help researchers identify a remarkable moment in human evolution. Ledi-Geraru was already famous before these finds. In 2013, a team led by Kaye Reed discovered a 2.8-million-year-old jaw from the earliest known Homo specimen. The 2025 study adds another layer to that story by describing teeth from both Homo and an unidentified species of Australopithecus.
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"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," said Brian Villmoare, lead author and ASU alumnus. "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."
For now, the mysterious Australopithecus species remains unnamed. Teeth can reveal a great deal, but scientists need more fossil material before they can formally name the species and understand where it fits on the human family tree. The team determined that the Ledi-Geraru Australopithecus teeth did not belong to Australopithecus afarensis — the famous 'Lucy'. That finding supports the view that there is still no evidence of Lucy's species surviving later than 2.95 million years ago.
Model of a male Australopithecus afarensis at the Natural History Museum Vienna. (Wolfgang Sauber/CC BY-SA 4.0) Wikimedia Commons
How Volcanoes Help Date Human Ancestors
How can researchers know that tiny fossil teeth are millions of years old? The answer comes from volcanoes. Ethiopia's Afar region remains an active rifting zone, shaped by tectonic forces and volcanic eruptions. Millions of years ago, eruptions spread ash across the landscape. That ash contained feldspar crystals, which scientists can date to determine when the eruptions happened, explained ASU geologist Christopher Campisano.
"We can date the eruptions that were happening on the landscape when they're deposited," said Campisano. "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."
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That volcanic timeline gives scientists more than an age estimate. It also helps them rebuild the world these ancient hominins inhabited. Today, the Ledi-Geraru area is a rugged landscape of faulted badlands. But between 2.6 and 2.8 million years ago, it looked very different. Ancient rivers crossed a greener environment, feeding shallow lakes that grew and shrank over time. Lucas Delezene, a specialist in hominin teeth at the University of Arkansas, noted that the differences between Homo and Australopithecus teeth are subtle but unmistakable: "When we get down to the picky details, the teeth of Homo and Australopithecus look different. The differences are subtle, but once you see them, you can't unsee them. They're very consistent."
The 13 fossil teeth collected at the Ledi-Geraru Research Area from 2015 to 2018. Collections at LD 750 and LD 760 represent a newly discovered species of Australopithecus*, while LD 302 and AS 100 represent early* Homo. (Brian Villmoare/Arizona State University) ASU News
Human Evolution Was Not a Straight Line
The Ledi-Geraru findings add to a growing picture of early human evolution as a crowded, branching story. The 2025 Nature study reported Homo fossils at 2.78 and 2.59 million years ago, along with Australopithecus at 2.63 million years ago. It also noted that as many as four hominin lineages may have lived in eastern Africa between 3.0 and 2.5 million years ago: early Homo, Paranthropus, A. garhi, and the Ledi-Geraru Australopithecus. This picture of multiple coexisting lineages is increasingly supported by other recent discoveries, including the 2025 identification of a Paranthropus jaw from the same Afar region.
"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," said ASU paleoecologist Kaye Reed. "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." Brian Villmoare put it in equally vivid terms: "Nature experimented with different ways to be a human as the climate became drier in East Africa, and earlier more ape-like species went extinct."
The hominin fossil record as known in 2024, showing the overlapping timelines of multiple lineages including the newly identified Homo sp. (Ledi-Geraru). (John Rowan and Bernard Wood/CC BY 4.0) Wikimedia Commons
Together, these discoveries point away from a simple ladder of progress. Instead, early human evolution looks more like a landscape filled with overlapping experiments — some of which led nowhere, while one eventually led to us. The Ledi-Geraru team is now examining tooth enamel to determine what these ancient species were eating, and whether Homo and the new Australopithecus were competing for the same resources or occupying different ecological niches. The questions that remain are as compelling as the answers already found.
Top image: Researcher examining Ledi-Geraru fossils under a headlamp. Source: Arizona State University
By Gary Manners
References
Delezene, L. (quoted in) 2025. Discovery Confirms Early Species of Hominins Co-existed in Ethiopia. University of Arkansas Research. Available at: https://arkansasresearch.uark.edu/discovery-confirms-early-species-of-hominins-co-existed-in-ethiopia/
Gonzaga, S. 2025. Human evolution complexity revealed in new African fossils. EarthSky. Available at: https://earthsky.org/earth/human-evolution-complexity-new-african-fossils/
Hawks, J. 2025. New hominin teeth from Ledi-Geraru, Ethiopia. John Hawks Paleoanthropology. Available at: https://www.johnhawks.net/p/new-hominin-teeth-from-ledi-geraru
Reed, K. (quoted in) 2025. ASU scientists uncover new fossils — and a new species of ancient human ancestor. Arizona State University News. Available at: https://news.asu.edu/20250813-science-and-technology-asu-scientists-uncover-new-fossils-and-new-species-ancient-human
ScienceDaily. 2026. Stunning fossil discovery in Ethiopia rewrites human origins. ScienceDaily. Available at: https://www.sciencedaily.com/releases/2026/05/260515234644.htm
UNLV. 2025. Discovery of New Fossils — and New Species of Ancient Human Ancestor — Reveals Insights on Evolution. University of Nevada, Las Vegas. Available at: https://www.unlv.edu/news/release/discovery-new-fossils-and-new-species-ancient-human-ancestor-reveals-insights
Villmoare, B., et al. 2025. New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia. Nature. Available at: https://www.nature.com/articles/s41586-025-09390-4
