Dinosaurs are classified as a group of reptiles, although some of their features are found in mammals and birds living today rather than in reptiles. It appears that at least some dinosaurs were warm-blooded, and that they walked with an upright, not sprawling gait.
Two types of dinosaurs are recognised based on the structure of their pelvis. There is the group known as the saurischia (lizard hipped) which includes the giant four-legged sauropods such as Apatosaurus and Brachiosaurus, plus the two-legged carnivores such as Tyrannosaurus. The second group is the ornithischia (bird hipped) with Stegosaurus and Muttaburrasaurus as examples.
Dinosaurs were a dominant form of life on Earth for over 100 million years during the Mesozoic era. (Humans and their ancestors have only been around for 2-3 million years and can only be considered to have dominated the world for the last 50-100,000 years).
Dinosaurs can be considered to be one of the most spectacular and successful groups of animals of all time. They inhabited most regions of the world of their time from above the Arctic and Antarctic circles to anywhere in between.
Dinosaurs are known to have grown to an immense size up to 43 m in the case of "Seismosaurus". Most of the time we think of dinosaurs as big and it is this perception of large size that helps to maintain their reputation as fascinating though sometimes frightening beasts. However, some dinosaurs were very small. Compsognathus was the size of a chicken. Mussaurus was even smaller and is named after a mouse because of its tiny size.
Dinosaurs lived in Australia although only a few have been found so far. More dinosaurs have been found in North America and Asia because people have spent more time looking for them and a great deal of money has been invested in the search.
Over the past ten years signifcant advances have been made in Australia in the search for dinosaurs. As time goes on and the search continues we can expect more dinosaurs to be found.
Most of the dinosaur fossils found in Australia come from three areas in eastern Australia. These are southern Victoria, Lightning Ridge in New South Wales, and central Queensland.
Australia is the only place in the world where opalised fossils have been found. This includes opalised dinosaur fossils. These come mainly from Lightning Ridge in New South Wales. No complete skeletons have yet been found, only isolated opalised bones.
Dinosaurs became extinct about 65 million years ago at what is known as the Cretaceous/Tertiary (K/T) boundary. It is thought that at this time a large meteorite or other extra-terrestrial object struck the earth. The impact would have caused huge dark clouds of fine dust to block out the sun. Without sunlight, the plants would have died, and, without plants to eat, herbivorous animals including dinosaurs would have starved to death. This in turn would have caused the death of the carnivorous dinosaurs that fed on the herbivores.
More recent work claims that the extinction of the dinosaurs may have been caused by a combination of factors - such as a meteorite colliding at a time when volcanoes were already adding huge amounts of dust to the atmosphere. Whatever the cause, something had such a profound effect on life on Earth at the end of the Cretaceous that it ended the presence of a most significant animal group.
Copyright © Australian Museum, 2003
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