Fossils are remnants of ancient life preserved in sedimentary rocks and provide a record of life and its evolution on the Earth spanning billions of years. They are common for the Phanerozoic, commencing at the Precambrian to Cambrian boundary, and are characterised by complex animals and terrestrial plants (see Figure 10.1). Fossils are named from the Latin fossilis, which means ‘dug up’ or ‘dug out’.

A fossil is most commonly the hard parts of an animal or plant, such as shell, bone or wood, which can be subject to mineral replacement during diagenesis of the host sediment, as in opalised bone and silicified wood (see Box 10.1). A fossil may also be the impression made when an organism came to rest in soft sediment which then hardened into rock. In rare cases a fossil can consist of the preserved tissues of an organism, such as when it has been encased in amber, ice or pitch or replicated by very early mineral replacement before rotting away. Finally, a fossil can be the preservation of tracks or trails left by an organism moving across or burrowing into soft sediment that then turned into rock (see Figure 10.11). Preservation of this type is called a trace fossil.

The first fossils identified in Australia were recovered by the expeditions of Nicolas Baudin, in 1800–1803, and Matthew Flinders, in 1801–1803. Among other early finds were fossil ferns in shale near Parramatta, in Sydney, and fossils of bird and mammal bones in the Wellington Caves, south of Dubbo, found by the explorer Thomas Mitchell, in 1830. Research and publication on Australian fossils date from the mid 19th century, most notably undertaken by Frederick McCoy, appointed as professor of natural science at Melbourne University in 1854. Since then the pace of investigations has moved rapidly, with new discoveries still common.