Summary: An international research team working at Ledi-Geraru in Ethiopia has uncovered fossil evidence showing that early members of the genus Homo and a previously unrecognized species of Australopithecus lived side-by-side in the same place between about 2.6 and 2.8 million years ago. The discovery includes 13 australopith teeth that differ from Australopithecus afarensis (famously represented by “Lucy”) and strengthens the case that Lucy’s species is not present in deposits younger than 2.95 million years. Precise volcanic ash dating using feldspar crystals brackets the fossils and supports a more complex, branching model of human evolution in which multiple hominin lineages overlapped in time and space.
Key Facts
- Two hominin lineages coexisted: The oldest known Homo remains and a new Australopithecus species were recovered from the same locality.
- Precise age control from volcanic ash: Feldspar-bearing ash layers above and below the finds constrain their age to roughly 2.6–2.8 million years.
- Complex evolutionary picture: The evidence supports a “bushy tree” model of human evolution with overlapping, non-linear lineages.
Researchers from the Ledi-Geraru Research Project, led by scientists at Arizona State University, report the new finds. Ledi-Geraru has already produced the earliest known Homo mandible and the oldest Oldowan stone tools, and the newly described dental material adds crucial detail to the picture of hominin diversity in the Afar region during a key interval in human evolution.
The team identified 13 teeth attributed to an Australopithecus that differ in dental morphology from A. afarensis. Because these teeth do not match the anatomy of Lucy’s species and because there is no evidence of A. afarensis younger than 2.95 million years, the researchers interpret the Ledi-Geraru specimens as representing a distinct australopith lineage. At the same time, additional teeth from the same deposits are attributable to early Homo, reinforcing the presence of at least two different hominin lineages occupying the Afar landscape contemporaneously.
“This research challenges the simplistic image of evolution as a linear progression from ape to Neanderthal to modern human,” said ASU paleoecologist Kaye Reed. “Instead, the fossil record points to overlapping lineages — a bushy evolutionary tree in which multiple forms coexisted and some ultimately went extinct.” Reed has co-directed the Ledi-Geraru Research Project since 2002 and serves as Research Scientist at the Institute of Human Origins and President’s Professor Emerita at ASU’s School of Human Evolution and Social Change.
Ledi-Geraru discoveries and dental evidence
The new report focuses on dental remains because teeth are durable, taxonomically informative, and frequent in the fossil record. Ledi-Geraru first drew global attention in 2013 when Reed and colleagues described the earliest known Homo jaw dated to about 2.8 million years. The current paper adds new Homo and Australopithecus teeth from sediments dated between 2.6 and 2.8 million years, confirming the antiquity of our lineage and highlighting the need for more fossils to clarify anatomical and ecological differences between these groups.
Lead author Brian Villmoare emphasized that while the dental and mandibular evidence shows what early Homo looked like, the sample remains small. More complete skeletal finds would improve understanding of the morphological distinctions and how these taxa could coexist at the same location.
How were the fossils dated?
Dating at Ledi-Geraru relies on volcanic ash layers that contain dateable feldspar crystals. The Afar region is geologically active, and eruptions deposited ash layers that are preserved between sedimentary units. By dating ash layers above and below fossil-bearing horizons, geologists can bracket the fossils’ ages. ASU geologist Christopher Campisano explained that dating the volcanic eruptions provides reliable age control for the deposits that hosted these hominins.
The sedimentary sequence at Ledi-Geraru preserves a landscape very different from the modern badlands: 2.6–2.8 million years ago the area featured vegetated floodplains, migrating rivers, and shallow lakes that expanded and contracted through time. This environmental context, combined with precise geochronology, helps researchers reconstruct the habitat and resources available to the hominins who lived there.
Geologist Ramon Arrowsmith noted that the site has an interpretable geologic record with good age control across the interval from about 2.3 to 2.95 million years, making it possible to place the new fossils accurately within a critical time window for early human evolution.
Next steps and open questions
Researchers are now analyzing tooth enamel for dietary signals to learn what these hominins ate and whether the early Homo and the newly described Australopithecus shared or competed for resources. Key questions remain: Did these species occupy the same niches? Did they encounter each other daily? Which lineages were ancestral to others? The team stresses that more fossils are necessary to answer these questions and to build a fuller picture of hominin diversity and behavior in eastern Africa.
“Every exciting fossil discovery raises new questions,” Reed said. “Paleontology depends on finding more material and training new field researchers to explore places that have not yet yielded fossils.”
The study, titled “New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,” appears in the journal Nature. The research team includes many scientists who work at, or are alumni of, Arizona State University, reflecting long-term collaboration on the Ledi-Geraru Research Project.
ASU-affiliated authors on the paper 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.
About this evolutionary neuroscience research news
Author: Joseph Caspermeyer
Source: Arizona State University
Contact: Joseph Caspermeyer – Arizona State University
Image: Image credited to Neuroscience News
Original Research: Open access. “New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia” by Kaye Reed et al., published in Nature. DOI: 10.1038/s41586-025-09390-4
Abstract
New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia
The interval between about three and two million years ago is a pivotal period in human evolution—when the genera Homo and Paranthropus first appear and when the putative ancestor Australopithecus afarensis disappears from the record. In eastern Africa, testing hypotheses about the ecological contexts that produced these changes has been limited by a sparse fossil record for this interval. We describe the age, geologic context, and dental morphology of new hominin fossils from the Ledi-Geraru area that fill this gap. We report the presence of Homo at 2.78 and 2.59 million years ago and Australopithecus at 2.63 million years ago. Although the australopith specimens cannot yet be assigned to a known species, their morphology differs from A. afarensis and A. garhi. These specimens indicate that Australopithecus and early Homo coexisted as two non-robust lineages in the Afar Region before 2.5 million years ago, revealing greater hominin diversity than previously recognized. Accordingly, as many as four hominin lineages—early Homo, Paranthropus, A. garhi, and the newly discovered Ledi-Geraru Australopithecus—may have been present in eastern Africa between 3.0 and 2.5 million years ago.