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(CNN) - A "remarkably complete" skull belonging to a human ancestor who lived 3.8 million years ago was discovered in Ethiopia.
This is the first time that a skull belonging to Australopithecus anamensis is found and the discovery sheds light on the evolutionary history of the first human ancestors.
Researchers have been working on the study of the Woranso-Mille Paleoanthropological Research Project in the regional state of Afar, in Ethiopia, for 15 years. On February 16, 2016, the upper jaw was discovered. They searched the area for more pieces for 16 hours and recovered the rest of the skull.
A detailed analysis of the skull and where it was found was published Wednesday in the journal Nature.
"I couldn't believe my eyes when I saw the rest of the skull," said Yohannes Haile-Selassie, author of the study and curator of physical anthropology at the Cleveland Museum of Natural History. “It was an eureka moment and a dream come true. This is one of the most important specimens we have found so far on the site. ”
The skull was discovered in 2016.
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The skull, known as MRD, represents the early human ancestor known as Australopithecus anamensis that lived between 3.9 and 4.2 million years ago. They are the ancestor of Australopithecus afarensis, to which Lucy's famous skeleton belonged, and is believed to have given rise to our genus, Homo. Afarensis arrived later, living between 3 and 3.8 million years ago.
The MRD skull was found only 55 kilometers north of where Lucy's skeleton was recovered in 1974. An international team of geologists, paleobotanists and paleoanthropologists helped determine the age of the skull by studying the habitat where it was found.
The skull of anamensis, which probably belonged to a man, was transported a short distance downstream after death and buried by sediments in a delta, according to Beverly Saylor, author of the study and professor of stratigraphy and sedimentology at Case Western Reserve University .
He probably lived along the river, which was surrounded by trees. The largest area far from the river was land of open bushes.
“MRD lived near a large lake in a region that was dry. We are eager to do more work in these warehouses to understand the environment of the MRD sample, the relationship with climate change and how it affected human evolution, if it did, ”said Naomi Levin, co-author of the University of Michigan study .
Previously, researchers believed that anamensis, which was previously known only from isolated bone fragments, died and resulted in afarensis. But the discovery of the skull reveals that the two species probably overlapped and coexisted for at least 100,000 years.
This challenges the idea that human ancestors evolved in a linear manner.
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Knowing anamensis
The researchers found a face they had never seen before.
The characteristics of the skull were cataloged to compare them with all other known hominid species in eastern and southern Africa. Certain aspects of the skull also revealed how it could be related to other species.
The skull of anamensis.
Australopiths in general were known for their huge faces, according to Stephanie Melillo, co-author of the study and postdoctoral researcher at the Max Planck Institute for Evolutionary Anthropology. But the evolution towards a more human face began with the origin of our genre, Homo. It was then that the first humans used tools and ate foods that had been more processed.
As the oldest known member of the Australopithecus genus, anamensis possesses a mixture of intriguing characteristics. It has an outstanding face and the cheekbones project forward.
It is the beginning of the huge face, created to process really difficult diets and chew hard foods, Melillo said. The bones of the face were built to withstand the tension. The canine teeth found in the skull were very large, but they are still relatively small next to the afarensis canines.
The long, narrow brain box is small, like other primitive human ancestors, and researchers are still trying to understand what caused brain capacity to increase when the genus Homo arrived on the scene. Haile-Selassie's theory is that Homo used more tools, consumed more meat and moved into his open habitat, which led them to make more decisions.
"MRD has a mixture of primitive facial and cranial features and derivatives that I did not expect to see in a single individual," said Haile-Selassie.
Some of the characteristics are in species that appeared later, while others are more closely related to older primitive ancestors.
“Until now, we had a big gap between the oldest known human ancestors, who are about six 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 unites the morphological space between these two groups, ”said Melillo.
An evolutionary key
Identifying anamensis is allowing researchers to understand how the first human ancestors evolved.
They compared the characteristics of the MRD skull with a 3.9 million-year-old skull fragment that had not been assigned to a species, known as the Belohdelie frontal. Now that researchers know what anamensis was like, Belohdelie's front has been identified as afarensis, belonging to Lucy's species.
Confirming the identity of this fragment makes afarensis alive 3.9 million years ago, suggesting that the two species actually coexisted for at least 100,000 years.
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"Traditionally, we have thought about our evolution in a linear fashion," said Haile-Selassie. “But they must have overlapped for at least 100,000 years. This changes their relationship. How did a new species appear when the parental species were there?
An idea is isolation. Small populations can exist by themselves and undergo many changes over time, enough to distinguish themselves from a parent species, he said. This means that they can coexist.
Anamensis and afarensis lived in areas close to each other, so geologists are studying the idea of isolation in populations. The area was active and diverse, full of cliffs and the aftermath of volcanic eruptions. The continent was also weakening due to the rupture, which could lead to isolation. It is a link between evolution and the environment, Saylor said.
"We used to think that A. anamensis gradually became A. afarensis over time," Melillo said. “We still think that these two species had an ancestral-descendant relationship, but this new discovery suggests that the two species lived together in Afar for quite some time. It changes our understanding of the evolutionary process and raises new questions: Did these animals compete for food or space? ”
If the populations were mixed or not, it is under discussion. But for now researchers are eager to learn more about this early human ancestor.
"TO. anamensis was already a species we knew quite a lot, but this is the first skull of the species discovered, ”said Melillo. "It's good to finally put a face to the name."
Ethiopia
