Which early human ancestor species is represented by the fossil skeleton 'Lucy'?

Lucy represents Australopithecus afarensis, an early hominin species that lived in East Africa about 3.9–2.9 million years ago.

Her fossil, catalogued as AL 288-1, was discovered in 1974 at Hadar in Ethiopia by Donald Johanson and Tom Gray. The remains include several hundred bone fragments and preserve roughly 40% of a single skeleton. Lucy was a female who stood about 1.1 metres tall and lived approximately 3.2 million years ago.

Lucy is especially important because her skeleton combines a small, ape-like braincase with anatomical features adapted for upright walking. Her pelvis, knee, and foot suggest habitual bipedalism, supporting the idea that walking on two legs evolved before the dramatic enlargement of the human brain. Her nickname came from the Beatles song “Lucy in the Sky with Diamonds,” which was playing during the discovery team's celebration.

A common mix-up is calling Lucy “the first human.” She was not a member of our genus, Homo, but an earlier australopithecine relative. Other A. afarensis evidence includes the famous Laetoli footprints in Tanzania, dated to about 3.66 million years ago.