A huge dinosaur discovered in South Africa is a previously unknown species that sheds light on the evolution of the largest creatures ever to walk the earth, a scientist said today.

Adam Yates, a palaeontologist at Johannesburg's Wits University, said the seven-metre-long Aardonyx Celestae occupied a "very significant position in the family tree of dinosaurs".

"This new dinosaur is helping us complete and revise our picture of how the truly giant dinosaurs first got going," he told reporters.

Yates said the almost complete fossil remains of the vegetarian giant that existed in the Jurassic period 195 million years ago were discovered in the town of Senekal in South Africa's Free State province by a student five years ago. However, they have just classified as a separate species.

"Aardonyx probably walked on its hind legs but could drop to all fours as well. It had flattened feet with large claws that supported its body weight on the inside of the foot and a robust thigh for supporting weight," he said.

Dubbed Aardonyx Celestae, a combination of Afrikaans and Greek that means "Earth Claw", fossils of the seven-metre long dinosaur were uncovered in the central Free State province by a team of post-graduate students from Johannesburg's Witswatersrand University.

"We knew that there were likely to be some fossils in these bone beds but we did not expect to find anything of this magnitude," said Adam Yates, who supervised the work.

The Aardonyx appears to be ancestors of the massive sauropod dinosaurs, the largest backboned animals ever to walk on land, he said.

The fossils from a partial skeleton unveiled came from a young dinosaur, Yates said.  "Growth rings in the rib and shoulder blade sections show that Aardonyx was not full grown - it was probably less than 10 years when it died near a river or stream," he said.

Yates said the Aardonyx was a vegetarian, with a wide gaping mouth and a powerful back. Its claws measured about five centimetres long, and it likely walked on two legs, but was strong enough to drop on all fours as well.

The fossils will be put on display at the Transvaal Museum in the South African capital Pretoria.

source: Reuters/AFP

photos: University of the Witswatersrand & flickr/sigmaration