Our family tree has grown once again with the identification of another new species of early human ancestor, based on a fresh analysis of a partial skull found decades ago in South Africa's famous Sterkfontein Caves, near Johannesburg.
Identified and named as Homo gautengensis by anthropologist Dr Darren Curnoe, of the UNSW School of Biological, Earth Environmental Sciences, the surprise finding is the earliest recognised species of Homo. While earlier fossils belong to the genus Homo, none have yet been classified in any species.
The identification is based on a partial skull - known only by its museum catalogue number Stw 53 - along with two other partial skulls, several jaws, teeth and other bones found at various times at Sterkfontein and other nearby caves.
Although Stw 53 had been first scientifically reported back in 1977, it had lain largely ignored for many years until Dr Curnoe undertook a restoration and fresh reconstruction of the fossil, working with the renowned South African paleoanthropologist Phillip Tobias. The finding will be reported soon in HOMO - Journal of Comparative Human Biology.
Initially the pair concluded that the skull was a member of another early human species, Homo habilis, thought to be a direct ancestor of humans. But after years of detailed scrutiny and comparison with the other fossils, Dr Curnoe is now sure that it was sufficiently different to warrant its classification as its own species and that it arose earlier than Homo habilis.
Dating of the fossils showed that Homo gautengensis walked upright in southern Africa as long as two million years ago and, fully grown, stood just over a metre tall and weighed only about 50 kilograms. It existed until perhaps about 600,000 years ago but Dr Curnoe does not believe it gave rise to our own species, Homo sapiens.
Its molar and pre-molar teeth were relatively large, suggesting that its diet included plant material that required plenty of chewing.
"The stone tools it used were fairly primitive, but those and its use of fire show us that it was using technology to obtain and perhaps prepare its food," says Dr Curnoe.
Its remains were found in the same caves as those of two distant relatives within the human family tree, Australopithecus robustus and Australopithecus africanus. Homo gautengensis seems to have been a more specialised omnivore adapted to life on solid ground, whereas the more ape-like A. africanus, had longer arms and other adaptations for climbing trees.
However, he says the broader significance of the find, like the recent discovery of another new African hominin species Australopithecus sediba - by a team involving UNSW dating expert Dr Andy Herries - lies in what it adds to the surprising number of new human and human-like species announced in recent years and the growing complexity of the human evolutionary story.
Darren Curnoe - 02 9385 8929 firstname.lastname@example.org
UNSW Faculty of Science - Bob Beale 0411 705 435 email@example.com