ASU scientists uncover new fossils – and a new species of ancient human ancestor

The fossils found in northeastern Ethiopia date between 2.6 to 2.8 million years ago and shed new light on human evolution

Arizona State University

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image: 

 Ledi-Geraru paleontological team searching for
fossils in the Lee Adoyta Basin where the genera
Homo and Australopithecus have been recovered.

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Credit: Kaye Reed, Arizona State University

A team of international scientists has discovered new fossils at a field site in Africa that indicate Australopithecus, and the oldest specimens of Homo, coexisted at the same place in Africa at the same time — between 2.6 and 2.8 million years ago. The paleoanthropologists discovered a new species of Australopithecus that has never been found anywhere.  

 

The Ledi-Geraru Research Project is led by scientists at Arizona State University and the site has revealed the oldest member of the genus Homo and the earliest Oldowan stone tools on the planet. 

The research team concluded that the Ledi-Geraru Australopithecus teeth are a new species, rather than belonging to Australopithecus afarensis (the famous ‘Lucy’), confirming that there is still no evidence of Lucy’s kind younger 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 been co-director of the Ledi-Geraru Research Project since 2002. 

 

Ledi-Geraru

 

What fossils did they find to help them tell this story? Teeth, 13 of them to be exact. 

 

This field site has been famous before. In 2013 a team led by Reed discovered the jaw of the earliest Homo specimen ever found at 2.8 million years old. This new paper details new teeth found at the site that belong to both the genus Homo and a new species of the genus 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.” 

The team cannot name the species yet based on the teeth alone; more fossils are needed before that can happen. 

How old are the fossils?

 

How do scientists know these fossil teeth are millions of years old? 

 

Volcanoes. 

 

The Afar region is still an active rifting environment. There were a lot of volcanoes and tectonic activity and when these volcanoes erupted ash, the ash contained crystals called feldspars that allow the scientists to date them, explained Christopher Campisano, a geologist at ASU.  

 

“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.”

 

Finding fossils and dating the landscape not only helps scientists understand the species –  it helps them recreate the environment millions of years ago. The modern faulted badlands of Ledi-Geraru, where the fossils were found are a stark contrast to the landscape these hominins traversed 2.6 – 2.8 million years ago. Back then, rivers migrated across a vegetated landscape into shallow lakes that expanded and contracted over time. 

 

Ramon Arrowsmith, a geologist at ASU, has been working with the Ledi-Geraru Research Project since 2002. He explained the area has an interpretable geologic record with good age control for the geologic time range of 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.”

 

What’s next?

 

Reed said the team is examining tooth enamel now to find out what they can about what these species were eating. There are still remaining questions the team will continue to work on. 

 

Were the early Homo and this unidentified species of Australopithecus eating the same things? Were they fighting for or sharing resources? Did they pass each other daily? Who were the ancestors of these species? 

 

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.”

The paper “New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,” was published in the journal Nature. The team of scientists and field team working on this project is widespread and many work at Arizona State University, or are alumni of ASU. 

 

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. 

 

Reed and Campisano talk more about this project in an in-depth interview you can view here. 

  

“These are teeth from Turtle Flat as we were

discovering them — you can see what the
ground behind looked like, and how amazing
it was that Omar Abdulla first saw them on
the surface,” said Amy Rector, Virginia Commonwealth University scientist.

Credit

Amy Rector, Virginia Commonwealth University

The 13 fossil teeth collected in the Ledi-Geraru Research Area from 2015-2018.

The collections at LD 750 and LD 760 localities represent a newly-discovered
species of Australopithecus. LD 302 and AS 100 represent early Homo already
known from the LD 350 mandible discovered in 2013.

Credit

Brian Villmoare: University of Nevada Las Vegas

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Journal

Nature

DOI

10.1038/s41586-025-09390-4 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia

Article Publication Date

13-Aug-2025

Discovery of new fossils — and a new species of ancient human ancestor — reveals insights on evolution

UNLV anthropologist and international research team unearth Ethiopian fossils; findings published in Aug. 13 issue of Nature journal

University of Nevada, Las Vegas

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UNLV anthropology professor Brian Villmoare (right, in blue shirt) and colleagues screening at the Ledi-Geraru research site in 2018. 

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Credit: Image courtesy of Brian Villmoare/UNLV

The discovery of new fossils and a new species of ancient ancestor may help shift the perception of human evolution from linear evolution to that of a tree with many branches, new UNLV research published today in the journal Nature shows.

UNLV anthropologist Brian Villmoare and a team of international scientists discovered new fossils at a field site in Ethiopia that indicate Australopithecus, and the oldest specimens of Homo, coexisted between 2.6 and 2.8 million years ago at the same place in Africa.

The scientists found 13 teeth at the Ledi-Geraru site and determined that, although some belong to the genus Homo, a set of upper and lower teeth belong to a new species of the genus Australopithecus. This new species is distinct from the well-known Australopithecus afarensis (the famous ‘Lucy’), which last appears at roughly 2.95 million years ago and was discovered in nearby Hadar.  

The presence of both species in the same location shows that human evolution is less linear and more tree-like, said Villmoare, associate professor of anthropology and lead author of the paper.

“We used to think of human evolution as fairly linear, with a steady march from an ape-like ancestor to modern Homo sapiens. Instead, humans have branched out multiple times into different niches. Our pattern of evolution is not particularly unusual, and what has happened to humans has happened to every other tree of life,” he said.

“This is what we should be finding in the human fossil record," Villmoare said. "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 Ledi-Geraru site is the same field site where a team of researchers discovered the jaw of the earliest Homo specimen ever found at 2.8 million years old. Villmoare has worked with the Ledi-Geraru Research Project and scientists at the Institute of Human Origins at Arizona State University since 2002.

“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," he said.

“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 researchers haven’t named the species yet. More fossils and further study are needed.

About the Study

“New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,” by Villmoare et al., was published Aug. 13 in the journal Nature. The scientists and field team working on this project span multiple universities.

---

Journal

Nature

DOI

10.1038/s41586-025-09390-4 

Article Title

New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,

Article Publication Date

13-Aug-2025

Discovery confirms early species of hominins co-existed in Ethiopia

New findings document the geological age, context and anatomy of hominin fossils discovered at the Ledi-Geraru Research Project, Ethiopia

University of Arkansas

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Lucas Delezene, associate professor of anthropology.

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Credit: University Relations

While we know much of the story of how humans evolved, the puzzle is still missing critical pieces. For example, fossil evidence for human evolution between 2 and 3 million years ago is patchy. It’s frustrating because we know that the branch of the hominin family tree that includes humans, or Homo sapiens, appears in the fossil record for the first time in this period.  

Today, Homo sapiens (which anthropologists shorten to Homo), is the only hominin species alive. But in the past, Homo wasn’t alone. We coexisted and competed with other branches of the human family tree. Research supported by the National Science Foundation and the Leakey Foundation and published in Nature now fills in a piece of the ongoing evolutionary puzzle, placing two early species of hominin side-by-side. 

A team working in the Afar Region of Ethiopia, at the site of Ledi-Geraru, reports hominin fossils that date between 2.6 and 3.0 million years old. Lucas Delezene, an associate professor of anthropology at the University of Arkansas, was second author on a paper that incorporated the work of more than 20 researchers from North America, Africa and Europe. 

The team found fossils of Homo that confirm the earliest evidence for the human lineage at 2.8 million years ago as well as evidence of Homo at 2.6 million years ago, solidifying the antiquity of Homo. Unexpectedly, the team also found evidence that Homo overlapped at the site with a different type of hominin, Australopithecus, at 2.6 million years ago.  

This was a surprise because Australopithecus was thought to be extinct in the area by about 3 million years ago. The famous Australopithecus fossil known as Lucy was found at a nearby site, but her species disappeared from the fossil record at 3 million years ago.  

“People often think evolution is a linear progression,” explains Delezene, “like the March of Progress, but in reality humans are only one species that make up a twig of a bigger family tree — it’s quite bushy and what we found is another twig that was previously unknown. The idea that Homo appears and immediately spreads around the planet and replaces all other hominin species is not accurate. Homo lived side-by-side with many other hominin species throughout Africa. What’s neat is that Homo overlaps with different hominin species in different places.” 

For example, from southern Ethiopia to southern Africa, the earliest species of Homo overlapped with a hominin known as Paranthropus, which is well known for its massive teeth and chewing muscles and a diet reliant on grass in some parts of its range. However, in the Afar Region of Ethiopia, no Paranthropus fossils have ever been found.  

Instead, the team working at Ledi-Geraru found that Homo overlap with a different type of hominin, Australopithecus. How all of these hominin species divided up resources is the question of ongoing research. Did Homo nod to the other hominin species on their way to hunting and gathering in the morning, or did the various species consume similar resources? Did Homo eat the same things in Ethiopia where it coexisted with Australopithecus as it did in the south where it coexisted with Paranthropus, or was its diet flexible?  

We know that Homo eventually becomes a culturally reliant tool user and occasionally consumed meat. But the oldest Homo fossils at Ledi-Geraru predate any evidence of tool manufacture or meat consumption. Did Homo evolve those traits to avoid competing with other hominin species? Competition among these various hominin species likely set the stage for the evolution of the traits that ultimately made humans a globally widespread and successful species. 

The fossils published in the Nature paper are all teeth. Teeth are often the best-preserved fossils because their enamel coating provides better protection from the ravages of time and the elements.  

Delezene, a hominin dental expert, says, “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.” 

While the new fossils fill in a piece of the puzzle, there is still a long way to go before we have a complete picture of human evolution. While there is evidence for the teeth of early Homo and the new Australopithecus, the team doesn’t know what their heads or the rest of their bodies looked like. The multi-national collaboration, done in partnership with the local community of Afar people, will continue its work looking for more fossils, ideally with continued funding.  

---

Journal

Nature

DOI

10.1038/s41586-025-09390-4 

Method of Research

Observational study

Subject of Research

People

Article Title

New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia

Article Publication Date

13-Aug-2025

 

Years after an earthquake, rivers still carry the mountains downstream

Sediment surge after the Wenchuan Quake offers clues to mountain-building mechanics and reveals long-term hazards

University of California - Santa Barbara

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Powerful floodwaters carried landslide debris down the Min River, leaving boulders perched atop what remains of this bridge.

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Credit: Gen Li et al.

(Santa Barbara, Calif.) — On May 12, 2008, the magnitude 7.9 Wenchuan Earthquake shook central China, its destructive tremors spreading from the flank of the Longmen Shan, or Dragon's Gate Mountains, along the eastern margin of the Tibetan Plateau.

Over 69,000 people died in the disaster, nearly a third are thought to be from geohazards like the more than 60,000 landslides that rushed down the slopes of the Longmen Shan.

After more than a decade and a half of work, scientists finally have an account of the fate of the landslide debris. Surveys of a reservoir downstream of the epicenter revealed how and how quickly the region’s major river moved this sediment, as well as the effect it had on the river channel itself. The results, published in Nature, suggest that the hazards caused by megaquakes may last long after the ground has settled. What’s more, they offer insights into a fundamental question of Earth science: How do earthquakes build mountains?

Shaking the mountains loose

The Wenchuan Earthquake delivered rock and soil into the region’s streams and rivers. Researchers are interested in how much of this material gets swept away by the river, known as the sediment flux. Previous case studies revealed that this comes in two varieties: suspended sediment in the water column; and bedload in the form of coarse material — from gravels to boulders — rolling and bouncing along the river bottom.

“Before our work, people mostly focused on the sediment of very fine size,” said first author Gen Li, an assistant professor in UC Santa Barbara’s Department of Earth Science. Measuring the flux of suspended sediment is relatively straightforward; simply collecting samples of the river water will do. It’s a routine activity conducted by government agencies.

Scientists find that suspended sediment flux increases after earthquakes. But this is only part of the picture.

It's long been known that bedload carried by rivers after earthquakes can fill up river channels with sediment. Flooding often follows earthquakes, and scientists believe that this pulse of sediment freed by a quake is to blame. The increased bedload raises the riverbed, so the river overflows from the shallower channel. Unfortunately, it has been very difficult to make direct measurements of this bedload flux.

A small stroke of luck amid a disaster

In 2001, the Sichuan Provincial Electric Power Company began constructing the Zipingpu Dam. By 2006, the structure began to impound the Min River, which drains part of the Longmen Mountains. The reservoir is located 20 kilometers downstream of the Wenchuan Earthquake’s epicenter. By mere happenstance, it became the perfect sediment trap for a team of curious geologists.

In collaboration with the Chinese Bureau of Hydrology, Li and his co-authors began surveying the sediment flowing into the reservoir. The agency monitors the suspended sediment flux each day, but the scientists would need more data to characterize the river’s bedload.

This seemingly straightforward task required an enormous effort spanning over a decade of field campaigns. The team spent days on a boat mapping the bottom of the reservoir with sonar. The changes from one field expedition to the next built up an account of how much total sediment had accumulated in the reservoir over time.

It was then a simple matter to calculate the bedload flux: just subtract the suspended load flux from the total sediment flux.

Large results

The research team found that total sediment flux in the Min River grew sixfold after the Wenchuan Earthquake. However, the bedload component increased by 20 times. This meant bedload accounted for roughly 65% of the overall sediment flowing through the river after the earthquake. Values of around 20% are more typical of mountain rivers of this size.

This result wasn’t particularly surprising to co-author Josh West. He had suspected that fluxes would be very high after a major earthquake, with a significant amount of bedload transport.

But the team wasn’t interested only in the bedload flux. They also wanted to know how long it would take the Min River to clear the pulse of material liberated by the earthquake. The elevated flux persisted for at least ten years, up to the last field expedition the authors took before publishing their results.

“In fact, from the data we’ve collected so far, there’s no evidence yet of the total sediment flux declining back to background levels,” said West, an Earth Sciences professor at the University of Southern California.

The findings have major implications for how we manage natural disasters. “Usually, we think the influence from earthquakes may last, at most, a few years after the main shock,” Li said. “But this data shows that this is not true.” The cascade of hazards induced by a large earthquake can persist far longer than people may expect, possibly decades.

The long tail of geohazards

Insights in this paper will help researchers and officials understand the cascade of hazards that can occur after a major earthquake. This happens when one event triggers a whole sequence that amplifies the initial danger. “Earthquake-triggered landslides are a great example,” West said.

“As we prepare for natural disasters, we often think of them as being discrete events,” he continued. Costs and actions are framed in terms of preparing for this event and dealing with its immediate aftermath. “But what’s left out of that is the longer tail that follows.”

For instance, it’s foolish to rebuild in the same way in the same place, the authors said. The risks aren’t merely as high as they were before; they’ve actually increased because the landscape has changed. A stopped-up river can’t accommodate the same 10-year flood it could have before. West’s group is continuing to investigate the cascading hazards from earthquakes and other similar events as part of a growing group of researchers working together to tackle this grand challenge.

Small clues to big questions

Understanding sediment transport after earthquakes is also crucial to answering certain fundamental questions in geology. For instance, how do earthquakes build mountains?

In theory, earthquakes uplift mountains, causing them to grow. But this paper highlights how earthquakes also erode mountains by causing landslides. So, which dominates? Like so many answers in science, that depends on the details.

In a previous study, Li had measured the number of landslides caused by the Wenchuan Earthquake by painstakingly comparing satellite images of the Longmen Mountains from before and after May 2008. In that paper, he calculated that this one event mobilized about 3 cubic kilometers of material. “That is around half of the sediment flux of all the rivers in the world over one year,” he said.

In the same paper, Li used satellite observations published by scientists at the French Bureau of Geological and Mining Research to calculate the total volume rock uplifted by the Wenchuan Earthquake. He found that roughly the same amount of material was added to the base of the mountains as eroded from its slopes. Again, scientists face the question of erosion versus uplift.

Li’s previous analysis only captured the first part of the story, though. Whether a mountain grows or shrinks after an earthquake depends on how quickly its rivers can carry away the resulting landslide debris, Li explained. And their new surveys revealed that the Min River had already carried away 10% of that mass over ten years.

“The fact that the pace was sustained for ten years ... was a surprise on its own,” West said. However, it’s hard to extrapolate from this into the future because the watershed will evolve over the next decades, he added. The matter remains an open question.

There are many earthquakes in tectonically active mountains, so earthquake-induced landslides are a major component of erosion in these ranges. However, many factors influence the balance of uplift and erosion in mountains across the globe. Water and ice, rivers and glaciers, even plants and animals can cause erosion. The effects of earthquakes are nuanced as well. The magnitude of the quake, composition of the rock and dynamics of the watershed all affect the outcomes.

Li has begun investigating these details. He’s curious why the proportion of bedload in the Min River was so high after the 2008 earthquake. The bedload isn’t this high in all mountain rivers in seismically active regions, he explained. For instance, rivers in the Himalayas didn’t seem to experience such a high bedload flux after the 2015 Gorkha Earthquake in Nepal.

Answering this question requires studying the composition of the landslide material itself. Details like the kind of rock a mountain is made of can make an enormous difference in the number of landslides and size of debris, how sediment is transported and how quickly it flows downstream. Li’s team is working to combine data on grain size with advanced models describing how particles will behave as they travel down the watershed.

In science, answers always lead to more questions. And while the authors have their sights on solving a new set of quandaries, they’re quite proud of their contributions so far. As West said, “It’s very satisfying to have been able to quantify something that we’ve struggled to quantify before and that has a wide range of relevance, from hazards to long-term consequences for understanding the evolution of topography over long periods of time.”

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Journal

Nature

 

Satellite imagery of the Longmen Mountains reveals the destruction wrought by the Wenchuan Earthquake. There’s no snow depicted in this false-color composite image; all of the white patches are landslides.

Credit

Gen Li et al.