Australopithecus afarensis cumio

Australopithecus afarensis is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not take place until the 1970s. From 1972 to 1977, the International Afar Research Expedition—led by anthropologists Maurice Taieb, Donald Johanson and Yves Coppens—unearthed several hundreds of hominin specimens in Hadar, Afar Region, Ethiopia, the most significant being the exceedingly well-preserved skeleton AL 288-1 ("Lucy") and the site AL 333 ("the First Family"). Beginning in 1974, Mary Leakey led an expedition into Laetoli, Tanzania, and notably recovered fossil trackways. In 1978, the species was first described, but this was followed by arguments for splitting the wealth of specimens into different species given the wide range of variation which had been attributed to sexual dimorphism (normal differences between males and females). A. afarensis probably descended from A. anamensis and is hypothesised to have given rise to Homo, though the latter is debated.

A. afarensis had a tall face, a delicate brow ridge, and prognathism (the jaw jutted outwards). The jawbone was quite robust, similar to that of gorillas. The living size of A. afarensis is debated, with arguments for and against marked size differences between males and females. Lucy measured perhaps 105 cm (3 ft 5 in) in height and 25–37 kg (55–82 lb), but she was rather small for her species. In contrast, a presumed male was estimated at 165 cm (5 ft 5 in) and 45 kg (99 lb). A perceived difference in male and female size may simply be sampling bias. The leg bones as well as the Laetoli fossil trackways suggest A. afarensis was a competent biped, though somewhat less efficient at walking and slower at running than humans. The arm and shoulder bones have some similar aspects to those of orangutans and gorillas, which has variously been interpreted as either evidence of partial tree-dwelling (arboreality), or basal traits inherited from the chimpanzee–human last common ancestor with no adaptive functionality.