The jury will have to stay out on this one at the moment

Dr Chris Stringer, Natural History Museum, London

The discovery, reported in Nature magazine, was made in the Middle Awash area of Ethiopia. The fragmentary fossils include a jawbone with teeth, several hand and foot bones, parts of arm bones and a piece of collarbone.

It is thought they represent at least five individuals of a new subspecies of Ardipithicus, called Ardipithecus ramidus kaddaba, that date to between 5.8 and 5.2 million years ago.

Yohannes Haile-Selassie of the University of California at Berkeley, US, the scientist who discovered them, believes further fossil discoveries may prove the species to be a new one, which would be called Ardipithecus kadabba.

More evidence

Haile-Selassie says that distinctive features of the teeth are shared only with later hominids and have never been found in living or fossil apes, indicating that the creatures are early hominids rather than early chimpanzees or a common ancestor.

"These fossils lack the primitive canines and specialised incisors and molars of all chimpanzees and they look like other later hominids in their skeletons," he says.

But this latest claim comes not long after fossil-hunters working in Kenya said they had found the oldest ever hominid - a six million year old creature called Orrorin tugenensis and dubbed "Millennium Man". That claim was also based on fragmentary fossils: a piece of jaw with some teeth, a fingertip, an arm and a leg bone.

The scientists put Orrorin on the human line and relegated Ardipithecus to a chimpanzee ancestor. Haile-Selassie and his colleagues believe it to be the other way round. Clearly both teams cannot be right and Dr Chris Stringer of the Natural History Museum, London, UK, says more fossil evidence will be needed to resolve the issue.

"The jury will have to stay out on this one at the moment," he said. "This latest discovery is very interesting, but it's very fragmentary. It's difficult to say yet whether Ardipithecus really is on the human line."

Pelvic bone

He said that a much more complete skeleton of Ardipithecus, including a pelvic bone, had been discovered, and when the details of that were made public it could settle the debate over whether the creature walked upright or not.

Yohannes Haile-Selassie examines an Ardipithecus ramidus kadabba canine tooth

"I will remain cautious until the more complete material comes out," he said. More fossils will also be needed to convince some palaeontologists of the role of Millennium Man in human evolution.

If the latest Ethiopian discovery is proved correct, the scientists believe it will require a fundamental reassessment of the origins of hominids, because the creatures lived in a forested habitat rather than the savannah.

Dr Stanley Ambrose of the University of Illinois, US, who worked on the chemistry of the ancient soils accompanying the fossils, said: "The expectation was that we would find hominids in savannah grassland sites that date back to about eight million years ago. That hasn't happened. All older hominids have been found in forested environments."

Looking northwest across the Middle Awash discovery site