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).
These dinosaurs had pelvis structures similar to
modern day birds. They only ate plants (they were
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'
This group includes all of the dinosaurs that were
However some were herbivores. Two main types of
Saurischians include the Theropods
and the Sauropods.
Theropods walked on their hind
legs. Their footprints show longer toes than the
with the toes less spread. Some scientists believe
that they were clever hunters.
with saw-like teeth.
- 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
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).
with peg-like teeth.
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).
most dinosaurs become preserved as fossils?
No, not at all. Dinosaur fossils are very rare,
especially in Australia. This is because dinosaurs
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
entire dinosaurs preserved as fossils?
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
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
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.