On Wednesday, scientists announced that a "remarkably complete" 3.8-million-year-old skull of an early human had been unearthed in Ethiopia, giving the modern world a rare first glimpse of how humans looked like some 3.8-million years ago.
"This skull is one of the most complete fossils of hominids more than 3 million years old," said Yohannes Haile-Selassie, the renowned Ethiopian paleoanthropologist of the Cleveland Museum of Natural History who is a co-author of two studies published Wednesday in the journal Nature.
The skull, known as "MRD", was discovered not far from the younger Lucy -- the ancient ancestor of modern humans -- and shows that the two species may have co-existed for about 100,000 years.
"MRD" is a game changer and redraws the history of human evolution
Australopithecus afarensis is one of the longest-lived and most studied early human species.The new skull, MRD, belongs to the species Australopithecus anamensis.
Lucy, the famous Australopithecus afarensis, was discovered in Ethiopia in 1974 and is 3.2 million years old.
"MRD" now "looks set to become another celebrated icon of human evolution," joining the ranks of other high-profile hominid findings, Fred Spoor of the Natural History Museum of London wrote in a commentary accompanying the studies.
"This is a game changer in our understanding of human evolution during the Pliocene," Haile-Selassie said.
Other lesser-known Australopithecus fossils that date back at least 3.9 million years, have been found but not complete, featuring only jaws and teeth and without the skull, scientists' understanding of the evolution of these extinct hominids have remained limited.
The latest finding challenges a previously held belief about how humans evolved.
"We thought A. anamensis (MRD) was gradually turning into A. afarensis (Lucy) over time," said Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology in Germany, a co-author of the Nature studies.
How a local guy stumbled upon the greatest discovery yet
At a press conference in Addis Ababa on Wednesday, Haile-Selassie described how Ali Bereino, a "local guy" from Afar, found the jaw of MRD and immediately brought it to Haile-Selassie's attention.
Discovered in February 2016 at the site of Woranso-Mille, just 55km from where Lucy was found in the Afar region of northeastern Ethiopia, MRD offers “the first glimpse of the face of Lucy’s ancestor”, according to a statement announcing the finding.
The cranium was soon found nearby, and workers spent days sifting through earth that was "1 percent dirt and 99 percent goat poop", Haile-Selassie said.
"People were not disgusted by it... but some of them of course had to cover their faces because the smell was so bad," he said.
It was a small price to pay for the discovery of such a complete specimen, he said.
"I did not believe my eyes when I saw the rest of the skull," recalled Haile-Selassie, who described the discovery as "a eureka moment and a dream come true".