Addis Ababa: In a remarkable discovery, a "complete" skull belonging to an early human ancestor of Lucy's species that lived 3.8 million years ago has been discovered in Ethiopia.
The 3.8-million-year-old fossil cranium called "MRD" represents a time interval between 4.1 and 3.6 million years ago when early human ancestor fossils are extremely rare, especially outside the Woranso-Mille area.
MRD generates new information on the overall craniofacial morphology of Australopithecus anamensis, a species that is widely accepted to have been the ancestor of Lucy's species -- Australopithecus afarensis.
MRD also shows that Lucy's species and its hypothesized ancestor, A. anamensis, coexisted for approximately 100,000 years, challenging previous assumptions of a linear transition between these two early human ancestors.
According to Dr Yohannes Haile-Selassie, Cleveland Museum of Natural History Curator and Case Western Reserve University Adjunct Professor, this is a game changer in our understanding of human evolution during the Pliocene (the Pliocene Epoch extends from 5.333 million to 2.58 million years BP).
The results were published online in two papers in the journal Nature.
The team discovered the cranium "MRD" from the Woranso-Mille paleontological site, located in the Afar region of Ethiopia. The Woranso-Mille project has been conducting field research in the central Afar region of Ethiopia since 2004.
The first piece of MRD, the upper jaw, was found by Ali Bereino (a local Afar worker) on February 10, 2016.
The specimen was exposed on the surface, and further investigation of the area resulted in the recovery of the rest of the cranium.
"I couldn't believe my eyes when I spotted the rest of the cranium. It was a eureka moment and a dream come true," said Haile-Selassie.
In the second paper, Beverly Saylor of Case Western Reserve University and her colleagues determined the age of the fossil as 3.8 million years by dating minerals in layers of volcanic rocks nearby.
"Incredible exposures and the volcanic layers that episodically blanketed the land surface and lake floor allowed us to map out this varied landscape and how it changed over time," said Saylor.
Among the most important findings was that Australopithecus anamensis and its descendant species, the well-known Australopithecus afarensis, coexisted for a period of at least 100,000 years.
Australopithecus anamensis is the oldest known member of the genus Australopithecus. The species was previously only known through teeth and jaw fragments, all dated to between 4.2 and 3.9 million years ago.
The similarities between the preserved dentition of the 3.8-million-year-old MRD and the previously known teeth and jaw fragments of A. anamensis led to a positive identification of MRD as a member of A. anamensis.
Dr Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology in Germany said: "A. anamensis was already a species that we knew quite a bit about, but this is the first cranium of the species ever discovered. It is good to finally be able to put a face to the name."