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November 2001

COOL BABIES: OPAL FOSSILS REVEAL ICY BIRTHING WATERS IN AUSTRALIAN OUTBACK

Exciting opal discoveries near Coober Pedy in South Australia suggest that Australia's ancient inland sea was a birthing ground for swimming reptiles.

120-million-year-old opalised bones of marine (saltwater) reptiles called plesiosaurs and ichthyosaurs have been discovered in a dry, dusty place called Moon Plain, 35 kilometres from the opal mining town of Coober Pedy.

Exciting opal discoveries near Coober Pedy in South Australia suggest that Australia's ancient inland sea was a birthing ground for swimming reptiles.

An artist's impression of a plesiosaur, swimming in an ancient sea.

Gem opal in fossil bones of the Addyman plesiosaur, an ancient marine reptile found at Andamooka in South Australia. The Addyman plesiosaur is the most complete plesiosaur skeleton found so far in Australia.	120-million-year-old opalised bones of marine (saltwater) reptiles called plesiosaurs and ichthyosaurs have been discovered in a dry, dusty place called Moon Plain, 35 kilometres from the opal mining town of Coober Pedy. Ichthyosaurs and plesiosaurs swam the world's oceans during the time of the dinosaurs. Plesiosaurs had long necks and four flippers; ichthyosaurs (the name means 'fish-lizard') were fast-swimming, dolphin-shaped reptiles - "the fast-swimming pursuit predators of the time," according to Ben Kear, a palaeontologist at the South Australian Museum. Ben is studying the opalised fossils of ancient marine reptiles from Australia. He says the most remarkable thing about the opal fossils from Moon Plain is that 95 per cent of them belong to babies or juveniles. "Baby plesiosaur fossils are very, very rare," says Ben, "and to get them in the numbers we have here to my mind can only mean we are looking at some sort of breeding ground." Around 120 million years ago, much of the Australian inland was covered by a vast sea, and Australia was much closer to the South Pole than it is today. Ben Kear says the Australian opal fields give "the first evidence from anywhere in the world where you have these kind of marine reptiles living in environments with icebergs." Ben thinks the reptiles were migrating into the Coober Pedy area to breed during the relative warmth of the polar summer. "They are seasonally coming down, migrating as the southern summer comes on and the ice retreats. The water get a bit warmer and like polar waters today, they are full of food - so what better place to have your offspring?" Mother and baby ichthyosaur fossils have also been found in large numbers at Holzmaden in Germany. Scientists think Holzmaden might also have been a birthing ground for ancient marine reptiles. (It was once thought that these ichthyosaurs were cannibals, because small ichthyosaur skeletons were found inside those of larger ichthyosaurs. Most reptiles lay eggs, so it was hard for scientists to accept that such early marine reptiles had developed live birth. However, the small skeletons were perfectly shaped - not jumbled up as if half-digested. The truth is, ichthyosaurs did indeed give birth to live young. There are even amazing fossils in which ichthyosaur embryos have been turned to stone half out of their mother's birth canal.) The opal fields of South Australia and New South Wales are fossil sites of international significance. The South Australian opal fields reveal amazing information about life in the ancient seas, while Lightning Ridge continues to produce incredible evidence about Australia's early mammals, dinosaurs and creatures of the rivers, land and skies. Australian opal is a spectacular relic from this remarkable lost world.
The ultimate jigsaw: palaeontologist Ben Kear putting together opalised fragments of the Addyman plesiosaur.
The opalised fossil shoulder blade (scapula) of a plesiosaur. Not all opal fossils are brightly coloured, because they contain non-precious opal called potch.
Opalised plesiosaur teeth. Photographs courtesy Ben Kear, South Australian Museum.

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