Face of Ancient Human Ancestor That Lived 3.8 Million Years Ago Revealed: 'A Game Changer in Our Understanding of Human Evolution'

The face of an ancient human ancestor that lived 3.8 million years ago has been revealed by scientists following the discovery of a near-complete skull in Ethiopia's Woranso-Mille complex—an archaeological region that contains a trove of fossils relating to early human evolution.

The skull was found in 2016 by researchers working at the site. The international team dated it to 3.8 million years ago and, based on the morphological features, say it belongs to a male Australopithecus anamensis. This is a poorly understood early hominin species, the oldest in the Australopithecus genus. It was thought to have lived between 4.2 and 3.9 million years ago.

Until now, the craniofacial features of the species were almost completely unknown. Having a complete skull has now changed that. Researchers have named the specimen MRD, after its collection number MRD-VP-1/1.

Two studies have been published in the journal Nature. In the first, scientists described the fossil, provided a reconstruction of its face and discussed where it sits in the hominin family tree. In the second, researchers looked at how A. anamensis would have lived.

Early human evolution is not well understood—and as more fossils are discovered, the picture becomes even more complex. Different species of hominin—which includes the genus Homo, to which humans belong—lived at different times, overlapping in time and space, with new species emerging at different, unknown points.

Previously, it was thought A. anamensis was a forerunner to Australopithecus afarensis—the species that 'Lucy' the missing link belonged to. This species is thought to have lived between 3.9 and 2.9 million years ago.

The discovery of the A. anamensis skull, which dates to a period when A. afarensis also lived, shows the two species overlapped for at least 100,000 years—meaning a direct evolutionary line is highly unlikely. The team say the skull "fills a major gap in the fossil record" and "shows that at least two related hominin species co-existed in eastern Africa around 3.8 [million years] ago, further lending support to mid-Pliocene hominin diversity."

This overlap also raises the possibility that some fossils previously assigned to A. anamensis may belong to A. afarensis, with the latter emerging earlier than previously thought.

"This is a game changer in our understanding of human evolution during the Pliocene," lead author Yohannes Haile-Selassie said in a statement.

In the second study, researchers looked at the environment of the region at the time the fossil dates to. They say there would have been a "predominantly dry shrubland with varying proportions of grassland, wetland and riparian forest."

"MRD lived near a large lake in a region that was dry," Naomi Levin, study co-author, said in a statement. "We're eager to conduct more work in these deposits to understand the environment of the MRD specimen, the relationship to climate change and how it affected human evolution, if at all."

Fred Spoor from London's Natural History Museum, who was not involved in the research, said the skull "looks set to become another celebrated icon of human evolution." In a Nature article relating to the research, he wrote: "MRD is a great addition to the fossil record of human evolution. Its discovery will substantially affect our thinking on the origin of the genus Australopithecus specifically, and on the evolutionary family tree of early hominins more broadly."