AL 129-1 is a fossilized knee joint of the species Australopithecus afarensis. It was discovered in Hadar, Ethiopia by Donald Johanson in November 1973. It is estimated to be 3.4 million years old. Its characteristics include an elliptical Lateral condyle and an oblique femoral shaft like that found in humans, indicating bipedalism.
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Johanson, D. C. and T. Taieb, 1976. A preliminary anatomical diagnosis of the first plio/pleistocene hominid discoveries in the central Afar, Ethiopia. Am. J. Phys. Anthropol. 45: 217-234.
"Australopithecus afarensis: AL 129-1". University of Texas. Retrieved. Can be read here.
Foley, Jim (2004). "Prominent Hominid Fossils". TalkOrigins Archive. Can be read here.