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This is a colour photograph of a fossil bone set against a black background. This bone is an opalised fossil of a femur, or thigh bone, of a hypsilophodont dinosaur. The blue colouration of this opalised fossil bone is clearly visible.
This opalised bone is a dinosaur femur, or thigh bone, found on the opal fields of Lightning Ridge in New South Wales. It is estimated to be 106 million years old. Opalised dinosaur bones are found only in Australia and most come from Lightning Ridge, where they occur in marine and freshwater sediments of the Cretaceous Period (141-65 million years ago). All opalised dinosaur fossils, including this one, are single bones, not part of a skeleton.
An opalised fossil bone is a special type of replacement fossil that is formed when the original remains are completely dissolved or destroyed and are later replaced by new materials. Opalisation occurs when the bone dissolves away, a silica-rich gel fills the resulting hole, and an opalised cast fossil is created.
Fossils are the remains, moulds or traces of dead plants or animals preserved in rock, mostly sedimentary rock such as sandstones, siltstones, shales and limestones. Fossils provide invaluable information about the Earth's past, including the evolution of plants and animals, the age and formation of rocks, previous climatic and environmental conditions, and the former positions of the continents.
This fossil bone is the femur of a hypsilophodont dinosaur, a fast and agile herbivore that lived on every continent during the Cretaceous Period. Hypsilophodons were small, about 2 m long, 0.6 m tall and weighed about 68 kg. They stood on their long hind legs, which were about twice as long as their front legs, and had a long stiff tail for balance while running quickly. They had small heads with strong beak-like jaws, 28-30 cheek teeth and cheek pouches for storing food while chewing.
Australian dinosaur bones are rare because of Australia's largely open landscape where exposed fossils are often destroyed by weathering. Most of Australia's dinosaur bones come from north-central Queensland in rocks about 140 million years old. Bones of dinosaurs including theropods, protoceratopsians, ankylosaurs, 'Muttaburrasaurus' and hypsilophodons have been found. Fossil dinosaur trackways and footprints are much more common than bone fossils in Australia.