Queensland's ancient past

There are many different ways that a fossil is preserved:

• Original material; original bone, shell or exoskeleton is preserved.
• Replacement; the original shell or skeleton is replaced by some other mineral whilst preserving the fine detail of the fossil. Petrified wood is an example of this where cell walls of wood are replaced by silicon dioxide.
• Compression; fossil remains are flattened by the force of compression of the overlying sediment which buried the organism. Fossil plants are often preserved in this way.
• Impression; Fossil material is compressed and then dissolved leaving only a trace of the organism.
• Natural moulds and casts; skeletal material within the sedimentary rock is dissolved leaving a space. If the space remains empty then both internal and external moulds of the fossil can be formed. If the space is filled by chemicals deposited in the rock a natural cast is formed. Opalised fossils are examples of natural casts.
• Permineralisation; a fossil consisting of porous material has its pores filled up with minerals. This makes the fossil more robust and heavier. Many fossil bones are preserved in this way.
• Special preservation: some fossils are preserved in exceptional circumstances. These include mummification, freezing, preservation in amber and desiccation.

When first learning about prehistoric animals, it is sometimes easy to get confused about what exactly is and isn't a dinosaur. Dinosaurs belonged to a group of reptiles that includes birds, crocodiles and other prehistoric animals such as pterosaurs. All of these animals are called the 'archosaurs', a group of reptiles that first appeared about 250 million years ago.

Like other reptiles, dinosaurs had a tough scaly skin, although smaller species sometimes had a soft feathery down similar to ducks. Most dinosaurs laid shelled eggs in nests and some may have cared for their young.

Dinosaurs were animals, closely related to crocodiles and birds, that lived in the Mesozoic era between 230 and 65 million years ago. All dinosaurs had four limbs, lived on land and breathed air. Dinosaurs walked on two or four legs. Some ate plants, others were fearsome carnivores. Many dinosaurs bore great armour plates and shields, which helped them fend off predatory dinosaurs.

Well after the mass extinction at the end of the Cretaceous Period, which saw the demise of giant land-dwelling dinosaurs and ocean-going marine reptiles, a new wave of giants evolved on the planet. The “Megafauna” were the giants of their time, giant versions of what we see today, from almost every animal group. Giant frogs, lizards, snakes, birds and mammals. Some megafauna live today, such as the Elephant, Rhinoceros, Whales and crocodiles.

Australia has a few remaining native megafauna, such as the Red Kangaroo, Emu and Estuarine Crocodile, whilst the oceans that surround our continent are home to the largest living marine megafauna, like the Blue Whale, Giant Squid, Whale Shark and Leather-back turtle. However, Australia didn’t always have so few native megafauna, instead our island continent was once home to the largest ever monotremes (egg-laying mammals), marsupials (pouched mammals), lizards and birds. Evidence of these extinct megafauna can be found across Australia as fossilised remains found in deep dark caves, eroding from river and creek banks, in ancient swampy peat bogs and dried-up salt lakes, and even eroding from old beach dunes.

There is abundant evidence of vulcanicity in eastern Australia and some of the most recent volcanoes occurred in northeastern Queensland.