A major discovery in Ethiopia sheds new light on our family tree. Fossilized teeth reveal surprising cohabitation between two hominin lineages more than 2.5 million years ago.
These fossils, unearthed at the Ledi-Geraru site, suggest a much more bushy evolutionary history than the linear narrative often imagined. The meticulous analysis of these remains helps document a pivotal period, still poorly understood, when several cousin species shared the same landscape.
Detail of the distal cone (orange lines) and bilobed contour (blue lines) observed on the A. afarensis M 1 specimen AL 400-1 (right) contrasting with the generally more equilateral occlusal profile of the LD 760 M 1 specimen (left). An unexpected cohabitation
Researchers have identified thirteen teeth, precisely dated thanks to the surrounding volcanic ash layers. Ten of them, 2.63 million years old, belong to a representative of the genus Australopithecus. Their distinctive morphology does not match any known species of this group, potentially indicating a new lineage.
Three other teeth, slightly younger and older, are attributed to the genus Homo. This direct association in the same sediments is rare evidence of coexistence. It invalidates the idea of a simple and immediate replacement of Australopithecus by the genus Homo.
The Ledi-Geraru site is already famous for yielding the oldest known Homo jaw. The presence of some of the most archaic Oldowan stone tools completes this picture for understanding the origins of our lineage. This area was then a grassy plain with seasonal waterways.
A flourishing evolutionary bush
This discovery fits into an increasingly complex paleoanthropological landscape for the Pliocene. Up to four different hominin lineages may have coexisted in eastern Africa around 2.5 million years ago. Australopithecus garhi and Paranthropus probably completed this picture alongside the genera documented at Ledi-Geraru.
The morphological distinction of the Australopithecus teeth from those of A. afarensis and A. garhi is notable. The peculiarities of the cusps and canines indicate a different adaptation or specialization. The scientific team remains cautious and awaits the discovery of more fossils before officially proposing a new species name.
Future study of the isotopic composition of the tooth enamel will provide key information about the diets of these species. These analyses will help understand whether they exploited distinct ecological niches or if direct competition for food existed. The question of their actual interaction remains open.
Article author: Cédric DEPOND