Evolution of Australian Biota
Topic 1: Australia’s Past: Part of a Supercontinent
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT POINT
 Identify and describe evidence that supports the assertion
that Australia was once part of a landmass called Gondwana,
including:
 Matching continental margins
 Position of mid-ocean ridges
 Spreading zones between continental plates
 Fossils in common on Gondwanan continents, includgin
Glossopteris and Gangamopteris flora and marsupials
 Similarities between present-day organism on Gondwanan
continents.
Introduction
In the last topic you studied the
origin of living things on Earth,
from 4500 million years ago
until about 250 million years
ago. In this Unit you will look
at events that occurred in the
late Paleozioc (300myo) but
mainly the Mesozoic (23012myo) and Cenozoic (122myo).
This was the time in which
Australia broke away from a
large land mass and became an
island continent.
conservapedia.com
Introduction
Alfred Wallace was a natural
scientist in the mid 1800’s.
He if famous for his work on
evolution, but during his
travels he also studied how
geography affected the
distribution of species of
plants and animals.
Today we call this
biogeography
people.wku.edu
Introduction
Wallace studied thousands of plants and animals and kept thorough
records of where each was found. He recognised patterns in their
distribution and this led to his proposal of two separate
zoogeographical areas.
The line separating these areas is called Wallace’s line.
radford.edu
Introduction
Wallace’s line is a clear
boundary that snakes
between the Indonesian
islands in the northwest
and those in the southeast.
He noticed that, despite
having similar climate and
terrain, the north-western
islands (Sumatra, Java and
Bali) had fauna, in
particular bird species,
more similar to those of
the Asian mainland.
convictcreations.com
Introduction
Whereas in the southeast, the birds in Lombok and New Guinea
were more like those in Australia. At that point in time (1850ish),
there was no explanation for this phenomenon but Wallace
suggested that groups of organisms that were isolated evolved to
become different.
mail.colonial.net
His line divides the Asian and Australian Regions that coincides
with a deep mid-ocean ridge!
Introduction
In 1915, Alfred Wegener, a
German scientist, noticed that
identical fossils plants and
animals had been discovered on
opposite sides of the Atlantic
Ocean.
davidselvam.blogspot.com
Introduction
Knowing these organisms
could not have crossed the
ocean, he proposed the
theory of continental drift,
suggesting that all the
continents had once been
together forming a large
single mass of land. He
called this Pangaea.
en.wikipedia.org
Introduction
He proposed that the
continents then split up
into smaller units of land
which drifted to their
current positions around
the Earth. A large
amount of evidence to
support this theory has
been found over the
years.
davidselvam.blogspot.com
Introduction
In this section, we
will look at how the
theory of continental
drift could account
for Australia
becoming an island
continent and the
current evidence to
support this theory.
geekculture.com
How Australia Arose from Gondwana
Scientific studies over the past 100 years have led us to believe that
continents have indeed moved. It is believed that 250 million
years ago (mya), all the continents were joined together to form
one huge land mass called Pangaea.
indiana.edu
How Australia Arose from Gondwana
Forces beneath the surface of the Earth caused it to begin to break
apart about 225mya. Pangaea is thought to have eventually given
rise to the continents as we know them today.
images.yourdictionary.com
Lets have a look at the sequence of events
How Australia Arose from Gondwana
225 mya:
 Pangaea splits into two land masses – Laurasia to the north and
Gondwana to the south
paralleldivergence.com
How Australia Arose from Gondwana
180 mya:
 Gondwana begins to break
up, as does Laurasia in the
north. Australia is thought
to have been part of the
southern land mass and so
we will follow the breaking
up of Gondwana.
davidselvam.blogspot.com
How Australia Arose from Gondwana
135-100mya:
 Gondwana breaks into three
parts
 Africa and most of South
America
 Antarctica, Australia, New
Zealand and New Guinea
 India (India began drifting
northwards, towards the part
of Laurasia that would
become Asia.
davidselvam.blogspot.com
How Australia Arose from Gondwana
80 mya:
 New Zealand breaks away
davidselvam.blogspot.com
How Australia Arose from Gondwana
65 mya:
 Australia begins to
separate from
Antarctica (its still
attached by
Tasmania)
davidselvam.blogspot.com
How Australia Arose from Gondwana
60 mya:
 Final separation of the
tip of South America
from Gondwana
davidselvam.blogspot.com
How Australia Arose from Gondwana
45 mya:
 Australia becomes a
separate continent
and begins drifting
northwards, and
therefore becomes
hotter and dryer.
davidselvam.blogspot.com
How Australia Arose from Gondwana
There is both geological and biological evidence which supports
this theory.
Geological:
-matching continental margins
-position of mid-ocean ridges and spreading zones between
them
Biological:
-common fossils
-similar present-day organisms
davidselvam.blogspot.com
How Australia Arose from Gondwana
Although the theory of
continental drift was
proposed over 100 years
ago, finding sufficient
evidence to support it has
only come about fairly
recently. It was only in the
1960’s that a theory was
proposed that could
account for how continents
could drift.
en.wikipedia.org
How Australia Arose from Gondwana
Harry Hess, a geologist, proposed the theory of plate tectonics.
This theory provided an explanation as to how and why the
continents could be moving.
mnh.si.edu
How Australia Arose from Gondwana
He explained that continents were carried on large plates beneath
the ocean. These plates were positioned on top of the semi-molten
interior of the Earth. To understand this idea, picture a cracked
eggshell surrounding the contents of the raw egg.
thehawksnest.pbworks.com
How Australia Arose from Gondwana
The pieces of the eggshell represent the plates. As the plates move
their boundaries may collide, slide past one another or move apart.
If two pieces moved towards each other, they would converge on
one side but a gap would form on the opposite sides of each.
suu.edu
Activity
-Handout 1.1.1 Breaking up of Pangaea Diagram, students to
glue into their books.
-Visit the following website which shows an animation of the
process of the breaking up of Gondwana and subsequent
continental drift.
http://kartoweb.itc.nl/gondwana/gondwana.html