A "remarkably complete" 3.8-million-year-old skull of an early human was excavated by Palaeontologists in Ethiopia and the discovery has the potential to change the understanding of human evolution, Aljazeera reports.

The find, known as "MRD", revealed the face of a presumed ancestor of the species famously represented by Lucy, the celebrated Ethiopian partial skeleton found in 1974.

Scientists have long known this species - A anamensis - existed but the discovered facial remains were limited to jaws and teeth.

The newly found fossil includes much of the skull and face.

"This skull is one of the most complete fossils of hominids more than three 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 on Wednesday in the journal Nature.

Fred Spoor of the Natural History Museum of London wrote in a commentary accompanying the studies the discovery "looks set to become another celebrated icon of human evolution". 

The fossil was found in 2016 in what was once sand deposited in a river delta on the shore of a lake. 

At a news 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 his attention.

"I did not believe my eyes when I saw the rest of the skull," Haile-Selassie recalled, describing the discovery as "a eureka moment and a dream come true". 

The 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.

However, MRD reveals the two species co-existed for about 100,000 years, a finding that Haile-Selassie called a "game-changer in our understanding of human evolution during the Pliocene".