View on Selam's skeleton. Visible are the skull, the spine with some ribs as well as the completely preserved right and the partially preserved left scapula. (c) Zeray Alemseged / Dikika Research Project
The pre-human species Australopithecus afarensis was already more than three million years upright on two legs, but still spent a lot of time climbing in the trees. This is shown by the first fully preserved shoulder blade of the species that anthropologists David Green and Zeresenay Alemseged have now studied. The joint is more like that of monkeys than of humans, the two report. The question of whether the genus Australopithecus moved mainly on two legs or whether it was also at home in the treetops at the same time, was hotly debated among anthropologists for decades. "These remarkable fossils now provide strong evidence that the pre-human still climbed at this stage of human evolution, " David Green concludes.

Lucy has no shoulder blades

One of the best known representatives of the species Australopithecus afarensis is Lucy, a skeleton found in Ethiopia in 1974, of a woman about 25 years old. Of Lucy's shoulder blade, however, are only a few splinters, so the question of the function of the front extremities remained controversial. Green and Alemseged were now able to examine the shoulder joint of a three-year-old Australopithecus girl known as Selam.

The Ethiopian anthropologist Alemseged discovered the skeleton in 2000 in his homeland. The bones were, however, surrounded by sandstone, which had to be removed in laborious detail work. "Since shoulder blades are as thin as paper, they rarely petrify, " says Alemseged. "If you find them, then almost always just as fragments." All the more pleased the two researchers, this time to be able to recover an intact shoulder blade. display

Grabbing over head instead of hanging with hanging arms

The shape of the joint clearly shows, according to the researchers, that Australopithecus was still an active climber. In humans, the anatomy of the scapula changes throughout life, but in the premenaries the shape remained the same in children and adults, as evidenced by the splinters obtained from Lucy and other adult Australopithecus skeletons. This suggests that the resemblance to the shoulder bones of monkeys was not a relic. The shoulder joint still had the function to allow over-head movements, as they are needed when climbing.

1.5 million years after Lucy and Selam, the scapula had undergone a fundamental transformation. The species Homo erectus, which lived in East Africa 1.8 million years ago, already had a typical human shoulder joint. "This transformation was probably part of the birth of our own genus Homo, " writes anthropologist Susan Larson of Stony Brook University in New York State in a commentary to the study. "This suggests that the early humans became increasingly dependent on tools and culture to survive."

David Green (Midwestern University, Illinois) and Zeresenay Alemseged (California Academy of Sciences): Science, Vol. 338, p. 514, doi: 10.1126 / science.1227123 © - Ute Kehse


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