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This is just a piece of jaw armed with some teeth but it says a lot about the history of mankind. Several research teams describe this Thursday in the magazines Science and Nature a hominid fossil unearthed in the Afar region in northeastern Ethiopia . Dating from there 2.8 million years he would be the oldest evidence ever found of a kind of representative Homo , which includes modern man. Until then, the specialists ranged appeared some 400 000 years later, there are 2.4 million years. The conditions of this emergence, in a natural environment in metamorphosis are also informed by another study, also published in Science .
This is the Ethiopian paleontologist Chalachew Seyoum of the University of Arizona State, who put their hands on the precious fossil, during an excavation campaign in January 2013 on the site of Ledi-Geraru in the Ethiopian state of Afar . An area famous among paleontologists because of the many hominid remains that have been discovered. Among them, the famous Australopithecus “Lucy”, uncovered in 1974 and dating there are about 3.2 million years. Designated in the excavations catalog under the name “LD 350-1,” the fossil-Ledi Geraru corresponds to the left mandible of an adult individual. Two premolars and three molars are still attached to it.
To estimate the age, geologists from the State University of Pennsylvania studied the volcanic rocks that surrounded the site. Their analysis of radioactive isotopes have established an age of about 2.8 million years. “The Afar region, located in the valley of the Great African Rift, is experiencing tectonic expansion phenomenon, which enabled these old rocks from 2.8 million years to be registered, and then exposed outdoors through a process of erosion and upon the occurrence of geological faults “ says Erin DiMaggio, a geologist at the State University of Pennsylvania. The oldest fossil assigned to the genus Homo known before, called “AL 666-1″ is also derived also Afar; it dates from there about 2.3 to 2.4 million years.
Reflecting on the characteristics of the mandible LD 350-1, anthropologists from the State University Arizona noted some similarities with that of Australopithecus afarensis , the species which includes Lucy: the receding chin shape particular. An observation not necessarily surprising insofar as the latest specimens of Australopithecus are elderly “only” 200,000 years older than the mandible LD 350-1. However, it also has attributes rather “modern”, ending up much later among representatives of the genus Homo : the overall proportion of the jaw, fine molars and premolars symmetric 
“Until then, the period -3–2000000 years was documented by a small number of fossils. Yet this is a crucial time for human evolution, since it was the birthplace of our own line “, enthusiasm Brian Villmoare, University of Nevada, who took part in study. “This new fossil, which has its own character to Australopithecus and others specific to early Homo, illustrates the transition between these two groups , believes his side William Kimbel, University of Arizona State, co-author of the study. But the fact that LD 350-1 shows typical specialties like Homo class with certainty in this category. “ To the question “a piece of mandible is it enough to assign an individual a place in our family tree?” , paleontologist boot key: “A complete skeleton guarantees anyway not the absence of debate “.
The question is what, around -2.8 million years ago triggered the transition from Australopithecus to the genus Homo better command of bipedalism and capable of using stone tools. A common hypothesis is that of climate change, which led to an aridity of the environment. This would have favored the least arboreal species more adapted to the open landscape of the savannah. A theory that seems partly supported by another study published in Science this week.
A wooded landscape less than that experienced by Lucy
To make the matter clear, paleontologists from the Universities of Arizona State and Pennsylvania have studied the fossils of mammals on the site of Ledi-Geraru at the same time as mandible LD 350-1. They found that the fauna of this period – antelope, elephants, crocodiles and other hippos – precisely matched that of an open and covered rivers, like it can be found currently in the Serengeti National Park Tanzania. A wooded landscape significantly less than reconstituted in connection with the remains of Australopithecus Lucy. Is it enough to support the thesis that the middle of the transformation is the direct cause of the emergence of the genus Homo? “It is too early to say , moderates Kaye Reed of the University of Arizona State. We need more fossils, and that’s why we continue our research in the field. “
In addition to the time and cause of their emergence, the precise sequence of onset of Homo and the different actors involved also continue to debate. “We know there are 2 million years ago, three species of Homo were in Africa: Homo habilis Homo rudolfensis and probably early representatives Homo erectus “, says Fred Spoor of University College London. To clarify the relationship between these species, the anthropologist had the idea to virtually reconstruct the fossil of the first Homo habilis described in 1964, and compare it with the remains of other officials type Homo .
The results, published in the journal Nature concomitantly with Science , confirms the great diversity of the genus Homo . Surprise: they also suggest the existence of a common ancestor to the genus Homo who lived there more than 2.3 million years. Is it possible that the latter is the hominid discovered Ledi-Geraru? “With our digital reconstruction of Homo habilis, we could get an idea of the nature of his ancestor, but no existing fossil corresponded him hitherto , says Fred Spoor. This is when the mandible LD 350-1 arrived as “on demand”, effectively providing a possible link between Autralopithecus afarensis and Homo habilis . It’s really a nice discovery “
Read also: Discovery of a mandible in Ethiopia:” It is possible that we find the oldest remains yet ”
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