Australian dinosaurs

What are the main dinosaur groups?

Scientists divide dinosaurs into two main groups, based upon their pelvis structure.

• The Ornithischians or 'bird-hipped' dinosaurs (e.g. the Muttaburrasaurus).
  

  A Ornithischian dinosaur foot.

  These dinosaurs had pelvis structures similar to modern day birds. They only ate plants (they were all herbivores) and had sharp saw-like teeth for slashing plant leaves and stems. Some walked about on their two hind legs only, others walked on all four. Footprints made by these dinosaurs are bird-like in appearance, with spread out toes.
   
• The Saurischians, or 'lizard-hipped' dinosaurs.
  This group includes all of the dinosaurs that were carnivores. However some were herbivores. Two main types of Saurischians include the Theropods and the Sauropods.

• A Theropod with saw-like teeth.

  Theropods walked on their hind legs. Their footprints show longer toes than the Ornithopods, with the toes less spread. Some scientists believe that they were clever hunters.
   
• Sauropods were large plant-eating dinosaurs. A small one would have been the size of a present day elephant, and the large ones were amongst the

  A Sauropod with peg-like teeth.

  biggest animals the Earth has known. They moved around slowly on all four legs, and seem to have travelled in herds, with the adults on the outside of the group to protect the young. Their long necks were adapted to reaching the high vegetation of the Cretaceous forest. Sauropod teeth were peg-like and weak, showing that they swallowed the leaves and stems whole and without much chewing and grinding. Footprints made by Sauropods are large, rounded (rear feet) and U-shaped (front feet). (e.g. the Rhoetosaurus).

How did dinosaurs become fossils?

To make a dinosaur fossil, parts of or a whole skeleton had to be buried in mud or other sediment before it was able to decay or break down. This may have happened when bodies were washed into a lake by a flood, or when a dinosaur died in the mud of a water hole, and the skeleton was buried. After what may be millions of years of continued burial by sediment, the sediment hardens into rock and the bones turn into fossils. (See the Australian dinosaur fossil locations interactive).

Did most dinosaurs become preserved as fossils?

No, not at all. Dinosaur fossils are very rare, especially in Australia. This is because dinosaurs were 'terrestrial' animals (they lived on land), and when they died, they would not often be buried in sediment. Marine animals are much more likely to be buried and become fossils.

Were entire dinosaurs preserved as fossils?

Minmi dinosaur skeleton fossil.

While it is uncommon, several excellent examples have been discovered overseas and are displayed in some of the world's top museums. In Australia, however, these finds are rare due largely to unsuitable environmental conditions.

Many of the dinosaur discoveries are of single bones, or parts of skeletons with many pieces missing. Occasionally imprints of dinosaur skin and other soft tissues are found along with harder body parts such as bone. There are two main types of fossils that scientists call 'body fossils' and 'trace fossils'.

Body fossils are what most people think of as fossils; any part of the actual plant or animal such as leaves, teeth or bones.

Trace fossils are fossils that don't actually include parts of the body but give us clues as to how the animal lived. Examples include footprints, where dinosaurs walked over soft mud, and the tracks were covered over and preserved. Some dinosaurs are known only from their footprints. Other trace fossils include stomach stones ('gastroliths'). Dinosaurs that were herbivores swallowed pebbles to help them digest coarse plant matter, and these are sometimes found. Occasionally nests, eggs, and droppings are found.

Although scientists now have very advanced techniques they use to help predict where fossils may be found, many fossils are destroyed by surface weathering before they are discovered. Other fossils are extremely fragmented by the time scientists discover them. Two of Australia's best dinosaur fossil areas in Victoria and Queensland often produce fossils that are made up of bone fragments scattered throughout a large area of sedimentary rock.

How do scientists identify dinosaurs from pieces of bone or part skeletons?

Fossil pieces are painstakingly protected and removed from the rock and then taken back to the laboratory for preservation and study. Scientists compare new fossil finds in detail with other dinosaur fossils that have been found around the world. This helps them to classify dinosaurs into particular groups.