In November 1974, an Australopithecus afarensis skeleton, approximately 40 percent complete, was found in what Glynn Isaac called the East African Klondike. The skeleton was by far the most intact that had been unearthed, so it was a major discovery. Donald Johanson and Tomm Gray, who discovered it, were celebrating late into the night.
Johanson later said, "There was a tape recorder in the camp, and a tape of the Beatles song "Lucy in the Sky with Diamonds" went bellowing out into the night sky, and was played at full volume over and over again out of sheer exuberance."
That skeleton has been known as Lucy ever since.
Because Lucy's skeleton is so complete, scientists were able to discern much more about the appearance and habits of A. afarensis than had yet been determined. Although clearly bipedal, Lucy would have resembled an ape in many respects: her arms hung past her knees, and her face was more ape-shaped as well, with a correspondingly smaller cranial capacity.
Information taken from "The Chosen Primate" by Adam Kuper.