“That’s a lot of fossil turtles for one location,” said Dr Smith, from the Australian Opal Centre, who is a PhD graduand of the University of New South Wales, Sydney.

Her thesis subject was Australian fossil turtles.

“One-hundred million years ago, Lightning Ridge was a turtle paradise,” she said.

Dr Smith returned recently from Canada, where she presented a talk on fossil turtles at an international symposium at the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta.

The symposium was held in honour of Gene Gaffney, a leading authority on fossil turtles.

Delegates included earth scientists from Europe, Russia, Asia, USA and South America.

“I’m very grateful to friends and supporters who helped finance my trip to Canada,”Dr Smith said.

“It’s incredibly exciting that turtle specimens donated to the Australian Opal Centre by opal miners are generating interest among palaeontologists all over the world.

“Turtles have been around for well over 200 million years.

“Opalised fossils that are 100 million years old are throwing light on turtle evolution in the Southern Hemisphere.

“Some of the Lightning Ridge fossils reveal the earliest evidence for two major groups of turtles – the horned turtles or meiolaniids, and the chelids, which are similar to turtles in rivers and dams around Lightning Ridge today.”

Meiolaniids were giant land turtles with horns and tail clubs that became extinct about 1000 years ago.

The best known meiolaniid fossils are from Lord Howe Island but they also occur on mainland Australia, other Pacific islands and South America.

“Although the Lightning Ridge meiolaniids were small, probably without horns, these fossils are important on a world scale,” Dr Smith said.

“This is because they contradict the current scientific theory that meiolaniids are a modern group related to turtles from Asia and the Northern Hemisphere.

“The Lightning Ridge fossils show that meiolaniids are an extremely old group that originated in the Southern Hemisphere.

“They also provide new data on the breakup of the ancient supercontinent Gondwana, and on turtle biology and relationships.

“Palaeontologist s have been arguing for two hundred years about the nearest relatives of turtles.

Opalised turtles also offer clues about turtle ancestry, which is one of the great unsolved problems of palaeontology.”