Mary Leakey discovered the famous Laetoli hominin footprints in Tanzania in 1978.
The footprints were preserved in a layer of volcanic ash at Laetoli. They show that early hominins walked upright about 3.6 million years ago, providing unusually direct evidence of ancient bipedal movement.
The trackway is generally associated with Australopithecus afarensis, the species also represented by the fossil skeleton nicknamed Lucy. The footprints are valuable because bones can show anatomy, while tracks record behavior at a particular moment.
Mary Leakey led the excavation and scientific investigation, working with an international team that included her son Richard Leakey and other researchers. The discovery is sometimes misdated because later excavations and analyses continued after 1978.