Australopithecus anamensis Skull Discovery: A ‘Game Changer’ in Human Evolution
Before the famed Australopithecus afarensis Lucy roamed the land of Ethiopia some 3.18 million years ago, one of her progenitors, an Australopithecus anamensis, met its demise in what is now the paleontological site of Woranso-Mille, in the Afar Region of Ethiopia. The discovery of the first known A. anamensis cranium at the site is being touted now as a “game changer in our understanding of human evolution during the Pliocene."
The Importance of the A. anamensis Cranium
Yohannes Haile-Selassie of the Cleveland Museum of Natural History, Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology and their colleagues have been named as the first to find a cranium of A. anamensis (which they refer to as ‘MRD’).
Composite image of human hands holding “MRD” by Jennifer Taylor, courtesy of the Cleveland Museum of Natural History. Photography by Dale Omori and Liz Russell.
Before now, the hominid species was primarily known by teeth, or when researchers were lucky, jaws. That’s part of why the discovery of a cranium is such a big deal. Haile-Selassie expressed his excitement upon the discovery, saying, “I couldn’t believe my eyes when I spotted the rest of the cranium. It was a eureka moment and a dream come true.”
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Yohannes Haile-Selassie, PhD with “MRD” cranium. Photograph courtesy of the Cleveland Museum of Natural History.
The cranium was discovered in 2016 and extensively studied since then. The results of the team’s findings are published online in two papers in the journal Nature. It has been dated to 3.8 million years old, and Melillo said it was identified as A. anamensis due to the morphological features of its upper jaw and canine tooth. After years of analyzing the cranium, Melillo said it is “good to finally be able to put a face to the name.”
Information garnered from the A. anamensis cranium has been combined with data taken from more than 12,600 fossil specimens representing about 85 mammalian species at the Woranso-Mille site to discover what life was like there 3.8 and about 3.0 million years ago. One of the most important finds to be made so far is that A. anamensis and A. afarensis co-existed for approximately 100,000 years.
As the Max Planck Institute explains, “This temporal overlap challenges the widely-accepted idea of a linear transition between these two early human ancestors.” Haile-Selassie has declared, “This is a game changer in our understanding of human evolution during the Pliocene.”
The 3.8 million-year-old cranium of Australopithecus anamensis is remarkably complete. © Dale Omori, Cleveland Museum of Natural History
And Melillo explains:
“We used to think that A. anamensis gradually turned into A. afarensis over time. We still think that these two species had an ancestor-descendent relationship, but this new discovery suggests that the two species were actually living together in the Afar for quite some time. It changes our understanding of the evolutionary process and brings up new questions - were these animals competing for food or space?”
Where Did A. anamensis Live?
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. They present their findings on the cranium and the environment where the A. anamensis once lived in a Nature paper as well.
Saylor and her colleagues found that the A. anamensis cranium was located in the sands of a delta where a river once flowed from the highlands of the Ethiopian plateau into a lake. The Max Planck Institute reports that the geology team analyzed the fossil pollen grains and chemical remains of fossil plant and algae to identify what the environment would have been like when the A. anamensis lived there. Naomi Levin, a co-author on the study from University of Michigan, says that the A. anamensis “lived near a large lake in a region that was dry.”
The cranium was discovered in 2016 at Miro Dora, Mille district of the Afar Regional State in Ethiopia. © Yohannes Haile-Selassie, Cleveland Museum of Natural History
A New Face in the Hominid Crowd
A. anamensis is the oldest known member of the Australopithecus genus. With an almost complete cranium, researchers are able to examine a unique set of facial features . Haile-Selassie said that the fossil “has a mix of primitive and derived facial and cranial features that I didn’t expect to see on a single individual.”
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Human ancestor photomontage by Jennifer Taylor, courtesy of the Cleveland Museum of Natural History. Facial reconstruction by John Gurche made possible through generous contribution by Susan and George Klein.
There is an interesting mix of some more primitive characteristics, such as features from Ardipithecus and Sahelanthropus and characteristics of later species, such as A. afarensis, which means that this cranium is also providing a bridge between hominids. As Melillo says:
“Until now, we had a big gap between the earliest-known human ancestors, which are about 6 million years old, and species like 'Lucy', which are two to three million years old. One of the most exciting aspects of this discovery is how it bridges the morphological space between these two groups.”
Left: Facial reconstruction of Australopithecus anamensis by John Gurche made possible through generous contribution by Susan and George Klein. Photograph by Matt Crow, courtesy of the Cleveland Museum of Natural History. Right: The Hidden Treasures of Ethiopia’ exhibit at Houston Museum of Natural Science featuring a model of “Lucy”. ( Jason Kuffer/CC BY NC ND 2.0 )
Top Image: Facial reconstruction of Australopithecus anamensis by John Gurche made possible through generous contribution by Susan and George Klein. Photograph by Matt Crow, courtesy of the Cleveland Museum of Natural History.