Fossil find sheds light
2006-09-20 14:33
Paris - Palaeontologists say they have uncovered a nearly complete skeleton of a hominid child who lived at a key stage in primate evolution more than three million years ago.
The fossilised remains of the child, estimated to have died at the age of three and who was probably a female, shed light on a hotly disputed branch of the human tree known as Australopithecus afarensis.
The best-known A afarensis is the famous fossil Lucy, recovered in Ethiopia in 1974 and who, for more than 20 years, was the earliest known member of the hominid family.
Hominids are primates who split from apes between five and seven million years ago.
They are considered the forerunners of anatomically modern humans, who appeared on the scene about 200&nbso;0000 years ago.
Still unclear, though, is the exact line of genealogy from these small, rather ape-like creatures to the rise of the powerfully-brained H sapiens.
Failed branch of the human tree
Once thought by some to be our ancestor, A afarensis is now widely considered to be a failed branch of the human tree, for many experts suspect the hominid was anatomically far closer to apes than humans.
Its brain, adjusted to its body size, was not much larger than that of a chimpanzee and although it no longer had the large canines that distinguished apes from hominids, it had relatively large chewing teeth that were still primitive.
The new fossil was found in Dikika, in Ethiopia's Awash Valley, on the opposite bank to where Lucy and other A afarensis remains were found, the experts report on Thursday in Nature, the weekly British science journal.
In pain-staking work spanning three years to scrape away the rock in which the bones are imbedded, researchers led by Zeresenay Alemseged, an Ethiopian based with the Max Planck Institute in Leipzig, eastern Germany, found the skull, lower jaw, all but two of the teeth, collar bones, vertebrae and knee caps of the long-dead child.
Mine of information
"The remarkably complete... skeleton is a veritable mine of information about a crucial stage in human evolutionary history," exulted Bernard Wood, an anthropologist at George Washington University, Washington, said in a review.
The structure and placing of the bones confirms that A afarensis probably only walked on two feet "rarely, if at all", said Wood.
In addition, the infant's shoulder bone, the scapula, more closely resembles that of a gorilla than of a modern human, and its strongly curved finger bones suggest a hand structure designed for climbing trees.
A final pointer to ape-like characteristics is the presence of a tiny throat bone, the hyoid.
Dating of the sediment in which the bones were found suggests the child lived between 3.31 and 3.35 million years ago, and was probably buried shortly after a flood in what was then a delta region, riven by streams that flowed into a lake.
Remains of an extinct species of a three-toed horse called Hipparion, as well as of giraffes, antelopes, crocodiles, rhinoceroses, white rhinos and rodents were found in the sediment, testifying to abundant wildlife at the time.