Two papers published in Science this week by a US lead team describe the discovery of the oldest known fossil of the Homo genus – the lineage leading to humans.
The fossil, found in a site called Ledi-Geraru in Ethiopia, is composed of the left side of the lower jaw with five teeth. The back molar teeth are smaller than those of other hominins, a feature that distinguishes humans from more primitive ancestors.
The remains are thought to be 2.8 million years old, predating researchers estimates as to our ancestors emergence by 400,000 years.
The fossil record for that time is sparse; before this the earliest discovery of the Homo genus was from 2.35 million years ago.
Professor Brian Villamoare from the University of Nevada in Las Vagas said the fossil marks a “major adaptive transition”. Crucially this discovery helps fill the gap in the fossil record since the iconic hominin Lucy – Australopithecus afarensis dated as 3 million years old and unearthed 40 miles away from this discovery.
The ape-like Australopithecus afarensis died out and was superseded by two different human forms one called Paranthropus, with a small brain, large teeth and strong jaw muscles and the other more successful Homo lineage, with larger brains.
The discovery may be a new species of Homo that lived before Homo habalis.
Dating of the fossil could help resolve a key question in human evolution – what caused our primitive ancestors to climb down from trees and make their homes on the ground?
The research team have since returned to the site of discovery however Villamoare said he cannot yet talk about what they did or did not find. Until more evidence is found, the mystery will remain as to whether this discovery does represent a link between Australopithecus afarensis and Homo habilis.