By Pooja Toshniwal PahariaReviewed by Lauren HardakerAug 28 2025A recent study published in Nature reports new fossil discoveries from Ledi-Geraru, Ethiopia. The study reveals that Australopithecus and Homo species coexisted 2.78 to 2.59 million years ago (Ma). The findings elucidate early hominin diversity and evolutionary dynamics during a poorly documented period in the human lineage.
Study: New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia. Image credit: sruilk/Shutterstock.com
Australopithecus afarensis disappeared during a critical evolutionary transition in East Africa between two and three Ma, a time when Homo and Paranthropus first emerged. Because the fossil record from this period is sparse, many details about this pivotal chapter in human evolution remain uncertain.
Recent discoveries from Ledi-Geraru, Ethiopia, offer rare insights into this period, revealing the co-occurrence of early Homo and Australopithecus before 2.5 Ma. These findings challenge linear models of hominin evolution and suggest a more complex scenario involving multiple contemporaneous taxa. Notably, the Afar state now provides the only definitive evidence of Australopithecus after 2.95 million years, including A. garhi and a newly identified but currently unassigned species of Australopithecus.
About The Study
In the present study, researchers investigated newly discovered hominin fossils from the Ledi-Geraru region (Afar, Ethiopia), focusing on the 3.0–2.0-million-year interval in human evolution.
The team conducted systematic surface surveys, stratigraphic mapping, and sedimentological analyses to recover and contextualize fossils, targeting sediments dated 2.78 to 2.59 Ma. They recovered 13 dental specimens dated between 2.78 and 2.59 Ma, analyzed through detailed morphological comparisons with known African hominin fossils (e.g., A. afarensis, A. garhi, and early Homo). Bootstrap resampling supported the analysis by extant primate metric variation. Using tephra layers and magnetostratigraphy, anchoring the fossils firmly within the 3.0–2.0 Ma window, enabled precise dating.
The researchers performed radiometric dating to establish chronological control. They used the ^40Ar/^39Ar technique for dating volcanic ash layers bracketing the fossils at the Berkeley Geochronology Center. They irradiated individual feldspar phenocrysts from the Giddi Sands Tuff, analysis of which yielded consistent plateau ages. The team obtained precise temporal constraints, considering 2.593 Ma as the weighted mean age of accepted grains. Furthermore, they correlated fossil horizons with dated tuffs (e.g., Gurumaha Tuff at 2.782 Ma, Lee Adoyta Tuff at 2.63 Ma), refining the stratigraphic framework.
The researchers recovered specimens from three main sedimentary packages: Gurumaha, Lee Adoyta, and Giddi Sands. They documented each fossil with GPS coordinates, in situ photographs, and database records. Examples include LD 302-23, a mandibular premolar from Gurumaha (2.78 Ma horizon), and LD 750-115670, a premolar from Lee Adoyta, situated between the 2.63 and 2.59 Ma tuffs. They also recovered multiple molars and partial dentitions from these packages, often in close stratigraphic association. They established a paleoenvironmental context using associated faunal remains and sediment characteristics, which shed light on ecological conditions and biogeographic patterns.
Results
Among the 13 recovered dental fossils, 10 specimens belonged to Australopithecus and three to early Homo lineages. The findings demonstrate that multiple hominin species coexisted in eastern Africa 2.5 Ma. Differences in morphology, Australopithecus with larger, more molarized teeth and Homo with reduced, gracile dentition, allowed taxonomic separation of the two lineages.
Specimens of Australopithecus that were around 2.6 Ma exhibited unique characteristics, distinct from A. afarensis and A. garhi. Their size, cusp patterns, and enamel thickness indicate an Australopithecus species that cannot yet be assigned at the species level in Ethiopia’s Afar Region. Early Homo teeth, such as those previously discovered near the 2.8 Ma mandible at the paleoanthropological site of Ledi-Geraru, provide evidence of cohabitation with Australopithecus.
From the Giddis Sands, AS 100-1a (M1) and AS 100-1b (M2) revealed crown morphologies more consistent with Homo than Australopithecus. The M2, in particular, exhibited derived traits, including a rhomboidal outline and close cusp placement, similar to (early) Homo specimens.
The results suggest that as many as four hominin lineages (early Homo, A. garhi, Paranthropus in other regions of eastern Africa but not yet in Afar, and the newly identified Australopithecus) were present in eastern Africa between 3.0 and 2.5 Ma. This diversity supports branching evolution with overlapping lineages and geographic variation.
Implications
The Ledi-Geraru fossil discoveries strengthen the case for Homo’s emergence before 2.5 Ma, extending the genus’s timeline beyond the LD 350-1 mandible (which established the existence of Homo at Ledi-Geraru by around 2.78 Ma). In addition, the discoveries demonstrate that early Homo overlapped with Australopithecus and other contemporaneous species.
The findings fill a critical gap in the fossil record and improve the understanding of the taxonomic diversity and evolutionary experimentation during this interval. Several human lineages coexisted in eastern and southern Africa 2.5 Ma, creating a dynamic environment. The selection mechanisms that controlled the evolutionary history of humans were highlighted by the decline and apparent disappearance of Australopithecus from eastern Africa about 2 Ma (though it persisted in South Africa as A. africanus slightly later), leaving Homo and Paranthropus as the dominating taxa.
The study also emphasizes that a drier, more open habitat was not uniquely associated with the appearance of Homo, raising questions about how these contemporaneous species partitioned their ecological niches.
Journal Reference
Villmoare, B., Delezene, L.K., Rector, A.L., et al. (2025). New discoveries of Australopithecus and Homo from Ledi-Geraru, Ethiopia. Nature, DOI: 10.1038/s41586-025-09390-4
https://www.nature.com/articles/s41586-025-09390-4
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