What is a fossil?

Trilobite Sinespinaspis markhami from the Lower Silurian of the Forbes district, New South Wales. Source: Museum Victoria.

The word fossil comes from the Latin fossilis meaning 'dug up'. Fossils are the remains, moulds, or traces of organisms that died a long time ago and were preserved in (usually) sedimentary rocks such as sandstones, siltstones, shales or limestones.

Fossils provide evidence of past forms of life. These can include:

• plant remains such as leaves, wood, sap and pollens;
• shells or other parts of invertebrates such as corals, worms, snails and sea urchins;
• skeletons from vertebrates such as dinosaurs, fish, birds and mammals.

About 250000 different fossil species have been identified to date.