Sunday, October 21, 2007
Lucy (also given a second (Amharic) name: ድንቅነሽ dinqineš, "you are wonderful") is the common name of AL 288-1, the 40% complete Australopithecus afarensis skeleton discovered on November 30, 1974 by the International Afar Research Expedition (IARE; director: Maurice Taieb, co-directors: Donald Johanson and Yves Coppens) in the Awash Valley of Ethiopia's Afar Depression. Lucy is estimated to have lived 3.2 million years ago.
One of the most striking characteristics possessed by Lucy was a valgus knee, which indicated that she normally moved by walking upright. Her femoral head was small and her femoral neck was short, both primitive characteristics. Her greater trochanter, however, was clearly derived, being short and human like rather than taller than the femoral head. The length ratio of her humerus to femur was 84.6% compared to 71.8% for modern humans and 97.8% for common chimpanzees, indicating that either the arms of A. afarensis were beginning to shorten, the legs were beginning to lengthen, or that both were occurring simultaneously. Lucy also possessed a lumbar curve, another indicator of habitual bipedalism.
Johanson was able to recover Lucy's left innominate bone and sacrum. Though the sacrum was remarkably well preserved, the innominate was distorted, leading to two different reconstructions. The first reconstruction had little iliac flare and virtually no anterior wrap, creating an ilium that greatly resembled that of an ape. However, this reconstruction proved to be faulty, as the superior pubic rami would not have been able to connect if the right ilium was identical to the left. A later reconstruction by Tim White showed a broad iliac flare and a definite anterior wrap, indicating that Lucy had an unusually broad inner acetabular distance and unusually long superior pubic rami. Her pubic arch was over 90 degrees, similar to modern human females. Her acetabulum, however, was small and primitive, like that of a chimpanzee.
The cranial evidence recovered from Lucy are far less derived than her postcranium. Her neurocranium is small and primitive, while she possesses more spatulate canines than apes.
This was due to the earlier belief (1950-1970's) that increasing brain size of apes was the trigger for evolving towards humans. Before Lucy, a fossil called '1470' (Homo rudolfensis) with a brain capacity of about 800 cubic centimetres had been discovered, an ape with a bigger brain. If the older theory was correct, humans most likely evolved from the latter. However, it turned out Lucy was the older fossil, yet Lucy was bipedal (walked upright) and had a brain of only around 375 to 500 cc. These facts provided a basis to challenge the older views.
Posted by allenwoow at 10:31 AM