Ardi provides new look to the last common ancestor of chimpanzees and humans
“Ardi” is the nickname given to a partial skeleton of a female Ardipithecus fossil, which lived 4.4 million years ago in what is now Aramis, Ethiopia. A special issue with 11 articles thoroughly describing the Homid species ,Ardipithecus ramidus, will be published on 2 October 2009 issue of “Science“. These articles describe detailed analyses of Ardi’s partial skeleton and the remains of at least 35 of her colleagues.
The last common ancestor shared by humans and chimpanzees is thought to have lived six or more million years ago. Though Ardipithecus is not itself this last common ancestor, it likely shared many of this ancestor’s characteristics. For comparison, Ardipithecus is more than a million years older than the “Lucy” female partial skeleton of Australopithecus afarensis. Until the discovery of the new Ardipithecus remains, the fossil record contained scant evidence of other hominids older than Australopithecus.
The partial skeleton of Ardi bears almost complete skull, hands, feet, limbs and pelvis,might have weighed 50 kilograms and stood about 120 centimeters tall. This makes her as big as a chimpanzee and brain size also matches to that of chimps. But unlike modern day chimpanzees she did not knuckle-walk or swing through the trees, Instead, she walked upright, planting her feet flat on the ground.
To the surprise of many Ardi doesnot resemble a chimpanzee, gorilla, or any of our closest living primate relatives. Ardipithecus ramidus evolved a few million years after humans evolutionary family diverged from a lineage that led to chimpanzees ,but it was not transitional between African apes and humans. Until now, researchers have generally assumed that last common ancestor of chimps and humans was thought to be much more chimpanzee-like than human-like , adapted for swinging and hanging from tree branches, and perhaps walked on its knuckles while on the ground.
Ardipithecus challenges these assumptions as they do not appear to have been knuckle-walkers, or to have spent much time swinging and hanging from tree-branches, especially as chimps do. Overall, the findings suggest that hominids and African apes have each followed different evolutionary pathways from last common ancestor, which thus makes living chimpanzees and gorillas poor models for the last common ancestor.
Link to the october 2 issue of science journal
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