Australopithecines walked upright with brains barely bigger than a chimp's
Long before our own genus appeared, African hominins were striding on two legs with teeth much like ours and brains of roughly 350 to 600 cubic centimetres. The australopithecines are extinct as named groups, yet they may not be truly gone: Homo itself probably sprang from one of their late species.
The label covers mainly two genera: the lightly built Australopithecus, often called the gracile australopithecines, and the heavy-jawed Paranthropus, the robust ones. Some researchers also fold in Kenyanthropus, Ardipithecus and Praeanthropus. Together with Homo they form the human clade, the branch that split from the chimpanzee line. The name survives from an older scheme that treated them as a separate subfamily, the Australopithecinae.
Their skeletons show adaptation to bipedal walking, though their gait was not identical to ours. The ratio of forearm to upper arm was unusually high, close to the golden ratio. Adults are thought to have stood 1.2 to 1.5 metres tall and weighed 30 to 55 kilograms. Males and females differed in size more than in humans or chimpanzees, but less than in gorillas or orangutans. Their cheek teeth were big and thickly enamelled, while incisors and canines stayed small, and male canines were little larger than female ones, unlike in modern apes.
Most scientists hold that Homo emerged from within this group in Africa roughly two million years ago, but nobody agrees on which species was the parent. Almost every candidate has been proposed; A. garhi has looked promising, yet fossils are scarce, and pinning down the first true member of Homo remains difficult in itself. Marc Verhaegen has even suggested an australopithecine could have been ancestral to chimpanzees.
A minority, including Jens Lorenz Franzen, formerly head of palaeoanthropology at the Senckenberg institute, argues that robust forms reached Indonesia and China. A Chinese tooth described in 1957 resembled Paranthropus robustus, and three molars from Longgudong Cave at Jianshi were once assigned to Australopithecus. Later studies, including Zhang in 1984 and Liu and colleagues in 2010, placed those teeth within Homo erectus, though claims of Asian australopithecines persist.
Source: Australopithecine
