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. The fossils also point to an Australopithecus species that has not been found anywhere else.
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 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.
“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.”
Reed is a Research Scientist at the Institute of Human Origins and President’s Professor Emerita at the School of Human Evolution and Social Change at ASU. She has helped direct the Ledi Geraru Research Project since 2002.
The Power of 13 Ancient Teeth
The key evidence came from teeth. Thirteen fossil teeth, found in ancient sediments, helped researchers identify a remarkable moment in human evolution.
Ledi Geraru was already famous before these finds. In 2013, a team led by 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.
“The new finds of Homo teeth from 2.6 — 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.
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, a Research Scientist at the Institute of Human Origins and Associate Professor at the School of Human Evolution and Social Change.
“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.”
That volcanic timeline gives scientists more than an age estimate. It also helps them rebuild the world these ancient hominins inhabited.
A Very Different Ethiopia
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.
By studying the sediments around the fossils, researchers can reconstruct the habitats where early Homo and Australopithecus lived. That matters because the environment may help explain how several hominin lineages survived at the same time.
Ramon Arrowsmith, a geologist at ASU, has worked with the Ledi Geraru Research Project since 2002. He said the region preserves a readable geologic record with strong age control for deposits ranging from about 2.3 to 2.95 million years ago.
“It is a critical time period for human evolution as this new paper shows,” said Arrowsmith, professor at the School of Earth and Space Exploration. “The geology gives us the age and characteristics of the sedimentary deposits containing the fossils. It is essential for age control.”
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.
That picture has become even more intriguing since the Ledi Geraru paper appeared in 2025. In 2026, a University of Chicago led team reported a 2.6 million year old Paranthropus jaw from Ethiopia’s Afar region. That discovery placed another hominin lineage in the broader region during the same critical window and suggested that early human relatives were more widespread and ecologically flexible than once assumed.
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.
What Did These Ancient Relatives Eat?
Reed said the team is now studying tooth enamel to learn more about what these species ate. Diet could help answer one of the biggest mysteries raised by the fossils: how did early Homo and this unidentified Australopithecus share the same place?
Were they eating the same foods? Did they compete for the same resources? Did they avoid one another, or did they cross paths often? Were they part of a larger web of hominin species living across eastern Africa?
No one knows yet.
“Whenever you have an exciting discovery, if you’re a paleontologist, you always know that you need more information,” said Reed. “You need more fossils. That’s why it’s an important field to train people in and for people to go out and find their own sites and find places that we haven’t found fossils yet.”
“More fossils will help us tell the story of what happened to our ancestors a long time ago — but because we’re the survivors we know that it happened to us.”
A Major Clue From a Missing Chapter
The paper “New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,” was published in Nature in 2025. The research team included scientists and field researchers from multiple institutions, with many connected to Arizona State University as faculty members or alumni.
ASU alumni and current faculty authors include Associate Professor Brian Villmoare, Associate Professor Lucas Delezene, Professor Amy Rector, Associate Research Professor Erin DiMaggio, Research Professor David Feary, PhD Candidate Daniel Chupik, Instructor Dominique Garello, Assistant Professor Ellis M. Locke, Lecturer Joshua Robinson, Assistant Professor Irene Smail and the late Professor William Kimbel.
The fossils do not provide every answer. They do something just as important: they show that the story of human origins was more crowded, more competitive, and more unpredictable than the familiar textbook version suggests. Somewhere in that ancient mix of species, landscapes, diets, and chance events, the path to modern humans began to take shape.