A team of researchers led by Cleveland Museum of Natural History Curator and Case Western Reserve University Adjunct Professor Yohannes Haile-Selassie found a previously unknown early human ancestor in the Afar region of Ethiopia that could change the way scientists view human evolution.
Described as a 3.8 million-year-old "remarkably complete" cranium, the fossil known as MRD was found in February 2016 after 15 years of digging at the Woranso Mille paleontological research site. Project geologists spent the last three years determining the age and context of the specimen.
"We found the specimen in two major pieces," sad Haile-Selassie. "The upper jaw, separated from the rest of the head, which perfectly joined.
"I couldn’t believe my eyes when I spotted the rest of the cranium," Haile-Selassie said. "It was a eureka moment and a dream come true.”
Researchers said in a Aug. 28 press release that the MRD cranium represents a time interval between 4.1 and 3.6 million years ago and generates new information on the overall craniofacial morphology of Australopithecus anamensis, a species 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.
“This is a game changer in our understanding of human evolution during the Pliocene,” Haile-Selassie said.
Human ancestor photomontage by Jennifer Taylor with MRD facial reconstruction by John Gurche, made with contributions by Susan and George Klein. [Courtesy Cleveland Museum of Natural History]
"The fossil was buried in the sandstone that was sand that was by a delta on the shore of a lake," said Beverly Saylor, professor of stratigraphy and sedimentology at Case. "We have been able to show by looking at the remains of the tentacle data in the delta deposits however, that even though there was a lake at that time, the environment around the area was arid, so there were forests on the shores of the lake and along the river that flowed into it, but the surrounding was dry with few trees.
"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,” Saylor said.
The Woranso-Mille project has been conducting field research in the central Afar region of Ethiopia since 2004. The project has collected more than 12,600 fossil specimens representing about 85 mammalian species. The fossil collection includes about 230 fossil hominin specimens dating to between
3.8 and 3 million years ago. But even in such a far-reaching project, this most recent find is unique.
"This specimen is actually the first specimen that gave us a glimpse of what the face of Australopithecus anamensis looked like," Haile-Selassie said. "What we've known about Australopithecus anamensis so far was limited to isolated jaw fragments and piece. We didn't have any remains of the face or the cranium except for one small fragment from the ear region."