August 13, 2025
Panel a shows the Ledi-Geraru LD 760-115979 right canine compared with mirrored left canines from Hadar A. afarensis. Panels b–d compare the LD 760 tooth with a right canine from A. afarensis and a mirrored left canine from A. garhi. The LD 760 canine has a simple, chisel-like wear pattern, unlike the multi-faceted wear of A. afarensis or the broad curved basin seen in A. garhi. Images are oriented to emphasize these differences and are not to scale. Fossil photos of the A. garhi holotype courtesy of the Middle Awash research project.
At a sunbaked outcrop in Ethiopia’s Afar Region, a handful of teeth are challenging the old story of a single, linear march from ape-like ancestors to us. Instead, they hint at a crowded evolutionary landscape where early Homo and a newly recognized Australopithecus species lived side by side between about 2.78 and 2.59 million years ago, well after Lucy’s kind disappeared from the fossil record around 2.95 million years ago.
In a study published Aug. 13 in Nature, an international team led by UNLV anthropologist Brian Villmoare describes 13 teeth that include early Homo and a distinct set from a previously unknown Australopithecus. The find underscores that human evolution resembled a branching tree more than a straight ladder.
Two Lineages, One Landscape
The fossils come from layers bracketed by precisely dated volcanic ash. Among them are:
- Homo teeth at 2.78 million and 2.59 million years old, including a premolar matching earlier finds like the 2.8 Ma LD 350-1 mandible reported with the Institute of Human Origins.
- Australopithecus teeth at 2.63 million years old, a tight cluster from one individual that differs from both A. afarensis and A. garhi.
“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,” said lead author Brian Villmoare of the University of Nevada, Las Vegas. He added, “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.”
A Fossil Gap Finally Fills
For decades, sites spanning 2.95 to 2.0 million years ago have been rare, leaving a gap in the record as Australopithecus declined and Homo and Paranthropus emerged. Ledi-Geraru offers a rare, well-dated sequence, with 40Ar/39Ar ages of 2.593 ± 0.006 Ma for the Giddi Sands Tuff and 2.631 ± 0.011 Ma for the Lee Adoyta Tuffs, firmly anchoring the fossils in time.
What The Teeth Reveal
Tooth anatomy holds evolutionary clues. The Homo teeth show derived features like mesiodistal compression in the third premolar compared with pre-3.0 Ma australopiths. The Australopithecus individual has squarer lower molars, lacks the distinctive bilobate buccal contour of A. afarensis, and does not show the reduced hypocone or upper canine “talon” basin seen in A. garhi. These traits point to a non-robust australopith unlike any previously known.
Why It Matters Now
The overlap of early Homo and Australopithecus before 2.5 million years ago suggests a mosaic of parallel lineages, not simple ancestor-replacement. Between 3.0 and 2.5 million years ago, eastern Africa may have hosted as many as four hominin lineages: early Homo, A. garhi, the new Ledi-Geraru Australopithecus, and Paranthropus.
Key Findings At A Glance
- Early Homo teeth at 2.78 Ma and 2.59 Ma extend our lineage’s antiquity.
- Australopithecus teeth at 2.63 Ma represent a distinct species, adding to late Pliocene diversity.
- Multiple hominin lineages coexisted in eastern Africa between 3.0 and 2.5 Ma.
- High-precision 40Ar/39Ar dating brackets the fossils within key ash layers.
- Morphology supports non-robust australopith diversity late in the Pliocene.
From Lucy To A Forest Of Branches
Lucy’s species, A. afarensis, once seemed a tidy ancestor to later hominins. Its disappearance around 2.95 million years ago opened a dynamic interval now shown to be filled with early Homo and multiple australopiths. The Ledi-Geraru finds strengthen earlier hints of hominin diversity by 2.5 million years ago, in step with Paranthropus records from Kenya and Tanzania.
Climate, Niche, And Survival
The late Pliocene in East Africa was becoming drier and more open. Yet both Homo and Australopithecus occupied the same habitats at Ledi-Geraru, raising questions about diet, mobility, and resource use. Why Australopithecus persisted in Afar until at least 2.5 Ma, while Paranthropus appeared elsewhere, remains a puzzle explored in paleoecology studies.
What Comes Next
The new Australopithecus species remains unnamed, with only dental evidence so far. The authors urge caution, but the pattern is clear: evolution tried multiple hominin solutions in the late Pliocene. More fossils—jaws, skulls, limb bones—will help test whether diet, tool use, or subtle ecological differences explain the overlap.
“This is what we should be finding in the human fossil record. 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.”
Context In The Wider Record
The teeth build on a 2.8-million-year-old Homo mandible from the same area, pushing our lineage closer to the end of A. afarensis. Elsewhere, sites in the Omo-Turkana Basin and northern Tanzania preserve early Homo and Paranthropus after about 2.0 Ma. Afar now stands out for keeping Australopithecus in the mix well after Lucy’s time.
A Closing Question
If early Homo was not uniquely tied to open, arid habitats, what factors truly drove its rise and persistence during this crowded evolutionary moment? Each new fossil from these layers could reshape our understanding of how climate, chance, and competition intertwined.
Study Details
“New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia,” by Brian Villmoare and colleagues, appears in the Aug. 13 issue of Nature. The work combines high-resolution dating with detailed dental comparisons, placing the fossils between the Gurumaha, Lee Adoyta, and Giddi Sands layers. The team concludes that eastern Africa’s hominin diversity was already in place by 2.5 Ma, with at least three lineages in Afar alone.
The Asboli Homo molars, predating other Homo specimens in the region by over 150,000 years, likely belong to the same species seen later at Hadar and Mille-Logya. The Lee Adoyta australopith teeth differ from A. afarensis and A. garhi, pointing to a new species awaiting further discovery.
In the end, the Ledi-Geraru teeth deliver a humbling message: our origins were not a straight path. They were a tangle of branches, many lost to time, with only a few leading to us.
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