Johannesburg - An ancient dinosaur nesting site, the oldest ever found, has been excavated in the Free State, the University of the Witwatersrand said on Wednesday.
Paleontologists found clutches of eggs, many with embryos, as well as tiny dinosaur footprints.
Researchers said this was the oldest known evidence showing that dinosaur hatchlings remained at the nesting site long enough to at least double in size.
The nests were from the prosauropod dinosaur known as the Massospondylus and were 190-million-year-old.
Bruce Rubidge, director of the Bernard Price Institute at Wits, said the research project, at the Golden Gate Highlands National Park, had been underway since 2005.
"First it was the oldest dinosaur eggs and embryos, [that were discovered]; now it is the oldest evidence of dinosaur nesting behaviour."
At least ten nests were found at several levels. Each one had up to 34 round eggs in tightly-clustered clutches. The researchers said the distribution of the nests in the sediments showed the dinosaurs returned repeatedly to the site, and apparently nested together.
The research was led by Canadian palaeontologist, Robert Reisz, a professor of biology at the University of Toronto.
Hans-Dieter Sues from the Smithsonian Institute in the United States, Eric Roberts from James Cook University in Australia, and Adam Yates from Wits, were part of the team. Reisz said he suspected there were many more nests in the cliff still covered by tons of rock.
"We predict that many more nests will be eroded out in time as natural weathering processes continue."
The team's findings have been published in the current issue of the journal, Proceedings of the National Academy of Sciences.
David Evans, a curator of Vertebrate Palaeontology at the Royal Ontario Museum in Canada, said that although the fossil record of dinosaurs was extensive, very little was known of their reproductive biology.
"This amazing series of nests gives us the first detailed look at dinosaur reproduction early in their evolutionary history," he said.
The fossils were found in sedimentary rocks that date from the early Jurassic period.
The Massospondylus was a relative of the giant, long-necked sauropods of the Jurassic and Cretaceous periods.