What kind of footprint did Mary Leakey discovered?

Mary Leakey was a British archaeologist and anthropologist, who discovered the first skull of a fossil ape on Rusinga Island and also a noted robust Australopithecine called Zinjanthropus at Olduvai. From 1976 to 1981 Mary and her staff worked to uncover the Laetoli hominid footprint trail which was left in volcanic ashes.