'Early humans ate grass like a cow'

Researchers found that Australopithecus bahrelghazali chomped its way through rushes and grasses rather than soft fruits preferred by its chimpanzee cousins, thanks to its powerful jaws and big grinding teeth.

The study shows the ancestral human diet diverged from that of the apes much sooner than previously thought, the 'Daily Mail' reported.

It provides early evidence of humans adapting their diet to suit their environment.

Researchers analysed the amount of carbon in teeth from A bahrelghazali specimens dug up from a fossil site in Chad with the help of a laser that freed carbon from the enamel.

This showed the creature's diet would have been rich in C4 plants - so-called because they contain four carbon atoms - such as grasses and sedges.

Similar evidence has shown the diet of other early humans in Africa like Paranthropus boisei was dominated by C4 plants.

However, these fossils predate P boisei by more than one and a half million years - suggesting their diet shifted relatively early to help exploit the local ecology of newly emerging habitats.

Ape-like A bahrelghazali had projecting jaws and was much smaller in size than modern humans. It walked upright but was probably unable to make tools.

It grew up to almost five feet tall and weighed up to eight stone - very similar to modern chimpanzees. Its brain was about a third of modern humans' and its jaws projected more than ours.

A bahrelghazali survived in an environment more open than usual by changing its diet to include C4 plants - the exploitation of which is uncommon among today's great apes including chimpanzees, said researcher Julia Lee-Thorp.

"Our data show by about 3.5 million years ago A bahrelghazali was fully engaged in exploiting C4 biomass," Lee-Thorp, of Oxford University, said.

"The results imply australopithecines (early humans or hominids) had become broad generalists foraging opportunistically for locally abundant resources that included significant quantities of savannah resources, unlike chimps," said Lee-Thorp.