AL 129-1 is the 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 3-3.2 million years old. Its characteristics include an elliptical Lateral condyle and an oblique femoral shaft like in humans, indicating bipedalism.
Read more about AL 129-1: Discovery