JOHANNESBURG — A newly discovered dinosaur species that roamed the Earth about 200 million years ago may help explain how the creatures evolved into the largest animals on land, scientists in South Africa said Wednesday.

The Aardonyx celestae was a 23-foot- (7-meter-) long small-headed herbivore with a huge barrel of a chest, and the scientists told reporters it could prove to be a missing evolutionary link.

This is a species "that no one has seen before and one that has a very significant position in the family tree of dinosaurs," said Australian paleontologist Adam Yates.

Yates, who is based at the University of the Witwatersrand's Bernard Price Institute for Paleontological Research, led the research with a number of other local and international scientists.

Their findings were published Wednesday in the Proceedings of The Royal Society B, a London-based peer-reviewed journal.

The Aardonyx celestae species walked on its hind legs but could drop to all fours. Yates said the creature found in South Africa stood nearly 6 feet (about 1.7 meters) high at the hip and weighed about 1,100 pounds (500 kilograms). It was about 10 years old when it died, and its death may have been caused by drought.

Yates says the Aardonyx celestae species shares many characteristics with the plant-eating herbivores that walked on two legs. But the new species also has similar attributes to later dinosaurs known as sauropods, or brontosaurs, that grew to massive sizes and went about on all fours with long necks and whip-like tails.

"The discovery of Aardonyx helps to fill a marked gap in our knowledge of sauropod evolution, showing how a primarily two-legged animal could start to acquire the specific features necessary for a life spent on all-fours," said Paul Barrett, a paleontologist at the British Natural History Museum who assisted on the dig that led to the finding but was not directly involved in the research.

The discovery of the new species was made by postgraduate student Marc Blackbeard, who was excavating two sites about five years ago.

Yates believes that the scientists may have stumbled onto a "paleontological oasis" in central South Africa that may yield further previously unknown dinosaur species.

Already they are working on the bones of two other specimens found at the site and said they also have unearthed some giant teeth believed to belong to a mysterious carnivorous dinosaur.

On the Net:http://web.wits.ac.za/Academic/Science/GeoSciences/BPI/