The Ledi-Geraru jawbone. Credit: William Kimbel/Arizona State University

An extraordinary fossil find in the desert of Ethiopia is pushing back the dawn of humankind by approximately half a million years, and rewriting what we know about the evolutionary branching that eventually led to modern humans.

A fossilized lower jaw, with five small teeth, is reportedly connecting the dots between primitive ancestors and modern humans. The specimen is the bone of one of the very first humans – it represents the oldest known human genus Homo - and comes from a time when humans split from the more ape-like ancestors, Australopithecus, identified by the best known fossil skeleton “Lucy”, according to CBC News.

The find is more than 400,000 years older than the oldest fossils belonging to the early humans who eventually gave rise to Homo sapiens, our modern species.

The jawbone was found close to where Lucy was discovered in 1974. The specimen of Australopithecus afarensis, dubbed Lucy, is from 3.2 million years ago. The species walked upright, but only stood a meter tall and had a small brain. This contrasts with the species Homo, “characterized by an upright, bipedal posture, sophisticated tool-making abilities and a relatively large braincase”, reports BBC News. The Ethiopian jawbone seems to share traits similar to both species, and may be a transitional fossil, filling in an evolutionary gap.

Graduate student of Arizona State University in the U.S., Chalachew Seyoum pulled the 2.8 million-year-old jawbone from the earth at the Ledi-Geraru research area in Ethiopia in 2013. “The moment I found it, I realized that it was important, as this is the time period represented by few (human) fossils in Eastern Africa,” he tells BBC News.

Paleoanthropologist Brian Villmoare of University of Nevada, and colleagues published a study in the journal Science on the research into the jawbone. Villmoare says, “In spite of a lot of searching, fossils on the Homo lineage older than two million years ago are very rare. To have a glimpse of the very earliest phase of our lineage’s evolution is particularly exciting.”

Source: ancient-origins.net