Scientists claim to have discovered a new branch of the human family tree -- a species that was light, short, and fond of chewy plants.

An international team, led by the University of New South Wales in Australia, has identified and named the species Homo gautengensis, which is said to be the earliest recognised species of Homo.

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.

However, detailed scrutiny and comparison with the other fossils, the scientists have claimed 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 kilogrammes.

It existed until perhaps about 600 000 years ago but the scientists do 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,” lead scientist Darren Curnoe said.

Its remains were found in the same caves as those of two distant relatives in 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.

The findings are to be published in the ‘Journal of Comparative Human Biology’.