'you are marvellous'), is a collection of several hundred pieces of fossilized bone comprising 40 percent of the skeleton of a female of the hominin species Australopithecus afarensis.

It was discovered in 1974 in Ethiopia, at Hadar, a site in the Awash Valley of the Afar Triangle, by Donald Johanson, a paleoanthropologist of the Cleveland Museum of Natural History.

"We have multiple [hominin] species in the same time period," said Yohannes Haile-Selassie, director of the Institute of Human Origins at Arizona State University.

Without further data to contextualize Dart's find, anthropologists could not prove whether bipedality, intelligence, or some other trait had first distinguished proto-humans from their great ape relatives.

[11] French geologist and paleoanthropologist Maurice Taieb discovered the Hadar Formation for paleoanthropology in 1970 in the Afar Triangle of Ethiopia, then in Hararghe province; he recognized its potential as a likely repository of the fossils and artifacts of human origins.

An expedition was soon mounted with seven French and four American participants; in the autumn of 1973 the team began surveying sites around Hadar for signs related to the origin of humans.

The lower end of a femur was found near it, and when he fitted them together, the angle of the knee joint clearly showed that this fossil, reference AL 129-1, was an upright walking hominin.

Then, on the morning of November 24, 1974, near the Awash River, Johanson abandoned a plan to update his field notes and joined graduate student Tom Gray to search Locality 162 for bone fossils.

[15][16][17][18][1][2] By Johanson's later (published) accounts, both he and Tom Gray spent two hours on the increasingly hot and arid plain, surveying the dusty terrain.

At first view nothing was immediately visible, but as they turned to leave a fossil caught Johanson's eye; an arm bone fragment was lying on the slope.

[3][19] In the afternoon, all members of the expedition returned to the gully to section off the site and prepare it for careful excavation and collection, which eventually took three weeks.

The creature had a small brain like a chimpanzee, but the pelvis and leg bones were almost identical in function to those of modern humans, showing with certainty that Lucy's species were hominins that had stood upright and had walked erect.

[22] With the permission of the government of Ethiopia, Johanson brought all the skeletal fragments to the Cleveland Museum of Natural History in Ohio, where they were stabilized and reconstructed by anthropologist Owen Lovejoy.

[23] Additional finds of A. afarensis were made during the 1970s and forward, gaining for anthropologists a better understanding of the ranges of morphic variability and sexual dimorphism within the species.

Excavation, preservation, and analysis of the specimen Ardi was very difficult and time-consuming; work was begun in 1992, with the results not fully published until October 2009.

These efforts were hindered by several factors: the rocks in the recovery area were chemically altered or reworked by volcanic activity; datable crystals were very scarce in the sample material; and there was a complete absence of pumice clasts at Hadar.

Published in the American Journal of Physical Anthropology,[29] researchers suggest that fossil damage did not shorten the transverse process and that Lucy's sacrum was in this state from the beginning.

This specific study points to Lucy's sacrum having four sacral segments which researchers[29] say conforms with the "long-back" model of hominoid vertebral evolution.

[30] Discussed in the Journal,[29] researchers conclude that Lucy having only four sacral segments is consistent with other findings related to early Miocene hominoids.

Australopithecus afarensis seems to have had the same conical rib-cage found in today's non-human great apes (like the chimpanzee and gorilla), which allows room for a large stomach and the longer intestine needed for digesting voluminous plant matter.

Fully 60% of the blood supply of non-human apes is used in the digestion process, greatly impeding the development of brain function (which is limited thereby to using about 10% of the circulation).

During evolution of the human lineage these muscles seem to have weakened with the loss of the myosin gene MYH16, a two base-pair deletion that occurred possibly about 2.4 million years ago.

[33] Rak et al. concluded that this morphology arose "independently in gorillas and hominins", and that A. afarensis is "too derived to occupy a position as a common ancestor of both the Homo and robust australopith clades".

[34] Work at the American Museum of Natural History uncovered a possible Theropithecus vertebral fragment that was found mixed in with Lucy's vertebrae, but confirmed the remainder belonged to her.

[40] At the American Museum of Natural History in New York City a diorama presents Australopithecus afarensis and other human predecessors, showing each species and its habitat and explaining the behaviors and capabilities assigned to each.

[9] In September 2008, between the exhibits in Houston and Seattle, the skeletal assembly was taken to the University of Texas at Austin for 10 days to perform high-resolution CT scans of the fossils.