A lower jaw bone and five teeth discovered on a hillside in Ethiopia are the oldest remains ever found that belong to the genus Homo, the lineage that ultimately led to modern humans.
Fossil hunters spotted the jaw poking out of a rocky slope in the dry and dusty Afar region of the country about 250 miles from Addis Ababa.
The US-led research team believes the individual lived about 2.8m years ago, when the now parched landscape was open grassland and shrubs nourished by tree-lined rivers and wetlands.
The remains are about 400,000 years older than fossils which had previously held the record as the earliest known specimens on the Homo lineage.
The discovery sheds light on a profoundly important but poorly understood period in human evolution that played out between two and three million years ago, when humans began the crucial transformation from ape-like animals into forms that used tools and eventually began to resemble modern humans.
“This is the the first inkling we have of that transition to modern behaviour. We were no longer solving problems with our bodies but with our brains,” said Brian Villmoare at the University of Nevada in Las Vegas.