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The oldest know man - similar species likely walked on two branch as far back as 7 million age ago , a new study finds , and the uncovering spill light on what first set humans aside from our ape relative .
Researchers analyzed a thigh off-white ( thighbone ) and a pair of forearm bones ( ulnae ) fromSahelanthropus tchadensis , which may be the oldest have it off hominin — a relative of human being date from after our antecedent split from those of modern anthropoid — grant to the Smithsonian National Museum of Natural History . First unearth in Chad in north key Africa in 2001 , the remains are about 7 million age old .
An artistic interpretation of how Sahelanthropus may have moved. Bipedalism was common among the earliest known species of humankind, not only on the ground but also in trees. It coexisted with other types of movement in a tree environment, including quadrupedal (four-legged) movement using firm hand grips, clearly differing from that of gorillas and chimpanzees who use the back of their phalanges for support (“knuckle walking”).
The examination of the femur and ulna indicated thatS. tchadensisnot only walked on two feet but also go up trees , adding grounds that this enigmatic coinage was biped , as an earlier analysis of its skull figure paint a picture .
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Many traits set humans apart fromchimpanzeesand bonobo , our closest bread and butter relatives , such as our bigbrains , upright postures , opposable quarter round and largely hairless bodies . However , it persist uncertain which of these feature article begin splitting the Pan troglodytes and bonobo lineage asunder from that of hominins , a separation thatprevious researchsuggested begin bechance between 6 million and 10 million years ago .
These 3D models of the arm and leg bones. From left to right: the femur; the right and left ulnae. These remains were found in 2001 by the Franco-Chadian Paleoanthropological Mission (MPFT).
The fond skull ofS. tchadensisthat the scientists found revealed that the species was probably close to a Pan troglodytes in size and structure . Although its Einstein also appeared chimp - size , its face and tooth more closely resemble those of hominins , hint it may have been a confining congeneric of the last common ancestor of humans and chimps , the researcher said .
gauge by the slurred , big forehead ridgeline of the skull , the specimen , which the researchers nicknamed " Toumaï , " was in all likelihood virile . ( In the local Goran speech , " Toumaï " means " hope of life-time . " It is a name often given to babies born closely to the dry time of year in the vast , flat , tedious Djurab Desert of northern Chad where the fogy was unearth . )
Perhaps the most interesting feature film that Toumaï shares with other hominins is the anatomy of the scuttle at the fundament of the skull where the spinal electric cord emerges . In four - legged animals , this possibility is usually located toward the back of the skull and is orient back . However , inS. tchadensis , this opening is positioned near the middle of the skull and is orient downwardly . This suggests thatS. tchadensiswas two-footed , meaning it walk on two branch , Daniel Lieberman , a human evolutionary biologist at Harvard University who was not involved in the newfangled study , wrote in a comment published inNature .
The Djurab Desert in Chad, where researchers excavated the fossil remains ofSahelanthropus tchadensis.
Toumaï lent reinforcement to the idea that bipedalism may have help set the earliest hominins aside from their relation . However , until now , away from this skull , researchers knew ofS. tchadensisonly from a few jaw fragments and some tooth . Without more bones from the rest of the consistence , some researcher reserved judgment as to whetherS. tchadensiswas a biped , Lieberman notice .
Ancient leg and arm bones
In the unexampled field , the researchers analyzed three more fossils they tie in withS. tchadensis — the femur and two ulnae . The scientist in the first place recuperate these subdivision and branch off-white at the same fourth dimension and site as the otherS. tchadensisfossils . The team consort these stay withS. tchadensisbecause no other bombastic primate was regain in the sphere , although they said it was impossible to screw whether the fogy belonged to Toumaï .
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The researchers canvass both the outside shapes of the bones and their internal microscopical structures . Next , they liken these data with comparable particular from living and fossil species , including chimp , gorillas , orangutang , nonextant apes from the same epoch , modern humans , ancient humans , and hominins such asOrrorin , Ardipithecusand australopithecines ( Australopithecusand kin ) .
Franck Guy (left) and Guillaume Daver (right) at the Palevoprim laboratory at Poitiers in France (CNRS/University of Poitiers).
The base of the femoris ’s cervix come out to be oriented slightly toward the front of the body and flattened , and the upper part of the thigh bone was also slightly flattened — all traits antecedently see in experience two-footed hominins . Moreover , the site at which the muscles of the cheek attach are rich and homo - like . And the fussy - sectional shape of the second joint bone suggests it could resist the kind of sidewise - bending forces see during walk on two legs .
All of these determination in the thighbone suggested thatS. tchadensiswas usually bipedal , perhaps on the ground , or perchance also in the timberland canopy .
" Our study shows that the Chadian species has a curing of selected anatomical features that intelligibly indicate that our oldest known representative were do bipedalism , on the ground and on the trees , " study co - author Franck Guy , a paleoanthropologist at the University of Poitiers in France , distinguish Live Science .
An example of analysis performed to interpret the locomotion ofSahelanthropus tchadensis. Here we see a 3D cortical thickness variation map for the femurs of (from left to right)Sahelanthropus, a human, a chimpanzee and a gorilla. This analysis enables scientists to understand the variations of mechanical constraints on the femur and to interpret these constraints in terms of movement type.
In contrast , the left over and right forearm finger cymbals are chimpanzee - like and well adapt to climbing trees ; they possess extremely curved shafts that advise the bearing of powerful forearm muscles , and the shape of the cubitus articulatio suggest that they could cope with high force when flexed .
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The thighbone did not keep the joints at either end , so the key features " postulate to prove bipedalism are miss , " Lieberman tell Live Science in an e-mail . " But they did a good job with what they had uncommitted to them . "
All in all , " the primal finding is that the earliest hominins were bipeds of some sort , reinforcing the grounds that theevolutionof bipedalism is what set the human stock on a disjoined track from the apes , " Lieberman said in the electronic mail . " But , like our closest surviving chimpanzee congeneric , other hominins still retained abilities to climb trees . "
The scientists detailed their finding online Wednesday ( Aug. 24 ) in the journalNature .
to begin with published on Live Science .
