1.3 Moving Australia

Evolution of Australian Biota
Topic 3: Moving Australia
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Points
 discuss current research into the evolutionary relationships between
extinct species, including megafauna and extant Australian species
 identify changes in the distribution of Australian species, as rainforests
contracted and sclerophyll communities and grasslands spread, as
indicated by fossil evidence
 Discuss current theories that provide a model to account for these
Moving Australia
We know about 300 million
years ago (mya) Australia was
part of a very large continent
called Pangaea. Australia was
attached to many other
landmasses at that this time.
About 150mya this large land
mass began to split up.
Moving Australia
If this history of the movement of
the continents is correct, it should
explain the current distribution of
various plants and animals. There
are very few plants and animals
found naturally (without the help
of people) all over the world.
Moving Australia
Some insects, bats and birds are widespread because they can fly.
Coconuts are found in many parts of the world because they can
drift over the ocean. All other living things tend to inhabit six
separate (biogeographic) regions, there are few species that live in
more than one of these. (See 1.3.1 Biogeographical Regions)
Moving Australia
Although the climate and other conditions may be similar, the
animals and plants present are different. Plate tectonics and the
theory of evolution provide us with an explanation for the current
distribution of plants and animals, especially mammals.
Moving Australia
For example, Australia and nearby islands contains the only
monotremes and most of the marsupials found in the world. It is
also home to a few native placentals, particularly bats, rats and
Moving Australia
When Australia and Antarctica separated from Africa and India
about 150mya, mammals had only evolved to the point where
most in the world were monotremes (lay eggs) or marsupials (have
a pouch), there were few placentals (bare live young which are
nourished before birth in the uterus).
Moving Australia
This separation of landmasses isolated these three groups of
mammals on our continent. While placentals continued to evolve
in the rest of the world, those in Australia became extinct as the
Australian continent drifted to its present position and its climate
Moving Australia
About 15 million years
ago the part of Earth’s
crust containing the
Australian continent
collided with the one
carrying Asia. When this
happened, it allowed such
placentals as mice and rats
to reach Australia by
island hopping.
Moving Australia
We can also explain the distribution of plants, such as the family
Proteaceae. Well known examples include Banksia and Grevillea.
The earliest fossils of these plants in Australia date from around
65mya and their current distribution is shown below in red.
Moving Australia
These plants are not readily dispersed and their colonisation of an
area depends on land connections. Their current distribution can
be explained by the fact that they evolved when the continents
were still joined as Gondwana.
Moving Australia
Once the continents
separated, parallel
evolution took place
in their isolated
environments. The
evolved forms are all
similar enough to
belong to the family
Protaeceae but have
developed into a
number of different
species on each
If we could somehow go back to Australia during the Pleistocene
around two million years ago, we would find the vegetation
reasonably familiar. However, although you would recognise much
of the fauna, it would be obvious there was something different.
They were big!
Megafauna is a group of animals which includes very large
kangaroos, wallabies, wombats, the huge Diprotodon, giant running
birds and a giant python.
One of the largest herbivores was the Diprotodon, a lumbering
marsupial that was the size of a hippopotamus. Another was the
cow sized Palochestes with its short tapirlike snout. They served
as prey for an equally large group of carnivores.
Another member of the megafauna is Procoptodon which is the
short faced kangaroo and was around 3 metres tall! It became
extinct in the Pleisotcene and is related to the modern day grey
and red kangaroos.
Fossil evidence indicates a giant kangaroo of this time had a diet of
meat. Related to the present day musky rat-kangaroos, the
powerful-toothed giant rat-kangaroo (Ekaltadeta ima) probably
walked on all fours. This giant is estimated to have weighed up to
60 kilograms.
If marsupial prey escaped from the killer kangaroos, they had to be
careful in the forests as well. A 130 kilogram or more marsupial
lion could drop from a branch. There were at least 8 known
species related to present day wombats and koalas.
Also present were the marsupial wolves, doglike animals of the
forest floor. The last surviving member of this group was the
thylacine, which became extinct in 1936. So what caused the
extinction of the megafauna?
In other parts of the world there is evidence of human involvement
in the extinction of animals including the woolly mammoth in the
arctic and the Moa in New Zealand. Could humans have caused
As Australia moved towards the
equator, the increasing aridity of the
climate saw changes in vegetation that
affected the populations of herbivores
and thus carnivores. This change is
apparent at Lake Callobonna, in South
Australia, where many fossils of
Diprotodon have been found. Now a
series of dried out saltpans, Lake
Callobonna once had enough
vegetation to support a large
population of these large marsupials.
Was it climate change?
-Watch Megafauna Video

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