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Why is Lightning Ridge important?
 110 million years ago the supercontinent Gondwana was a wilderness of forests of pines, ferns and palms separated by tracts of shallow sea. Dinosaurs and their relatives dominated this landscape, as well as our rare and tiny mammal ancestors. Near the edge of this ancient continent, fragments of the remains of these animals accumulated in the sands of the inland sea. Today deposits at Lightning Ridge in northern New South Wales yield some of the rarest, most beautiful and precious fossils in the world.
 
Precious gems, valuable fossils. The jaws of two ancient mammals Steropodon galmani (left) and Kollikodon ritchiei (right). Both are formed from opal. Kollikodon's species name honours palaeontologist Alex Ritchie of the Australian Museum whose persistent consultation with Lightning Ridge opal miners over many years resulted in the discovery of many important fossils such as Steropodon and Kollikodon. [Photos: Australian Museum]
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The sandstone at Lightning Ridge once formed the floor of an ancient shallow inland sea where plants, aquatic life and occasionally the bones and teeth of animals were preserved. As they tunnel through these sediments searching for precious opal, miners sometimes find these fossils.
The most famous and significant fossils from Lightning Ridge are those of some early mammals. Mammal fossils are not often found in Cretaceous fossil deposits, since the generally rare, tiny and delicate mammals of this period were far outnumbered by the more successful and diverse dinosaurs. In Australia Cretaceous mammal fossils are almost unknown, which is why the Lightning Ridge fossils are so important. Steropodon, for example, was one of the ancestors of the modern Platypus and echidnas of Australia and New Guinea.
Australian contemporaries of the Lightning Ridge mammals were dinosaurs such as the herbivore Muttaburrasaurus langdoni, here fending off a predatory allosaurid theropod. [Reconstruction: Anne Musser]
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What happened in Australia?
Early Cretaceous 110 million years ago
Time line and position of the continents during formation of the Lightning Ridge fossil deposits
The Australian continent (red) was much further south than its present day position. Australia was still connected to Antarctica and South America, and together formed part of the supercontinent Gondwana. At this time, much of Gondwana, including Australia, was well inside the Antarctic circle. The Cretaceous Period lasted from 141 million years to 65 million years ago, when mass extinctions wiped out many forms of life on earth, including non-avian dinosaurs.
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Finding Fossil in the Opal Mines
Fossils of other animals living at the time of these ancestral egg-layers have also been found at Lightning Ridge. Dinosaurs, including giant long-necked sauropods munched on vegetation along with the 1.5m long Lightning Beast Fulgurotherium australe. Perhaps these smaller dinosaurs moved in herds like modern antelope, always on the lookout for predators like the carnivorous theropod Rapator ornitholestoides, which reached a length of about 6m. Pterosaurs flew in the air and fish, lungfish, crocodiles and marine reptiles, such as long-necked plesiosaurs lived in the oceans.
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Palaeontologists search for fossils in underground opal mines (top) and in rubble processed by mining equipment to remove opal (bottom). [Photos: Jenni Brammall & Henk Godthelp]
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Palaeontologists searching for fossils of dinosaurs and primitive mammals at Lightning Ridge consult with opal miners to see what they have found, or obtain permission to sift through spoil heaps and excavate in opal mines. Without the help of miners, many fossils, including Steropodon and Kollikodon, would never have been recognised. As well as being beautiful gems, the rare and often valuable fossils from Lightning Ridge have the potential to solve many mysteries about our ancient mammalian ancestors.
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In addition to fossils of the platypus- like Steropodon galmani Lightning Ridge also yields dinosaur fossils such as the small hypsilophodontid Fulgurotherium australe (left). [Reconstruction: Anne Musser]