Species in the australopith group - which also includes Au. africanus from South Africa - but its discovery confirmed our ancient relatives habitually walked upright, and that this feature of the human lineage occurred long before the evolution of bigger brains.
Australopithecus afarensis discoveries in the 1970s, including Lucy and the Laetoli fooprints, confirmed our ancient relatives were bipedal - walking upright on two legs - before big brains evolved.
However, this conclusion is controversial and many scientists, including Johanson, say there are other plausible explanations for the breakages, such as being trampled by stampeding animals after death. afarensis possessed both ape-like and human-like characteristics.
The top of its skull (the cranial vault) was slightly domed and its brain was comparable in size to a chimpanzee's.
As the team found more and more fragments, they began to appreciate that they were uncovering an extraordinary skeleton. Lucy's skeleton consists of 47 out of 207 bones, including parts of the arms, legs, spine, ribs and pelvis, as well as the lower jaw and several other skull fragments.
However, most of the hand and foot bones are missing.
Its story began to take shape in late November 1974 in Ethiopia, with the discovery of the skeleton of a small female, nicknamed Lucy.
More than 40 years later, Australopithecus afarensis is one of the best-represented species in the hominin fossil record. afarensis belongs to the genus Australopithecus, a group of small-bodied and small-brained early hominin species (human relatives) that were capable of upright walking but not well adapted for travelling long distances on the ground. anamensis and Kenyanthropus platyops - probably gave rise to two more recent hominin groups, Homo and Paranthropus, before 2.5 million years ago. afarensis wasn't the first member of the group discovered - that was the Au.
Johanson later recounted that his pulse quickened as he realised it belonged not to a monkey but a hominin.The researchers believe the injuries observed were severe enough that internal organs could also have been damaged.Based on their evidence, the team suggest that Lucy died falling out of a tree.Lucy measured just 1.05 metres tall and would have weighed around 28kg.Yet an erupted wisdom tooth and the fact that certain bones were fused suggested Lucy was a young adult.