The savannas of northern Australia contain a diverse range of
unique animals and plants that are not found anywhere else in the
world. What is the reason for this high level of endemism?
For example, why don’t Australian savannas have large
mammals like wildebeest, giraffes, lions and zebras that are found
in African savannas? Why is it that northern Australia shares
similar plants and animals to Papua New Guinea yet is quite
distinct from the rest of Asia? Why is Australian mammalian fauna
dominated by marsupials, and why have placental mammals such as
monkeys or tigers not found their way here during times of lower
sea level? The answers to these questions can be best explained
through an understanding of Australia’s evolutionary past and
long history of isolation from the other continents in the
Long before savannas had begun their evolution, Australia was
part of the great southern landmass known as Gondwana. Gondwana
consisted of what is now Africa, New Zealand, Australia, India,
Madagascar, South America and the Antarctic. This super-continent
straddled the south pole, but because of the disposition of the
other land masses among other reasons, Gondwana was not ice-bound
but was home to a great variety of plants and animals.
Around 165 million years ago this landmass began to break up,
first with India separating followed by Africa and New Zealand. It
was during this period that dinosaurs such as the
Muttaburrasaurus would have been roaming in forests of
conifers, cycads and ferns during long dark winters and
continuously light summers.
Muttaburrasaurus: a Gondwanan a long way from home
A Muttaburrasaurus skeleton in the Queensland Museum. Source:
Muttaburrasaurus was a plant-eating dinosaur that
lived between 112 and 104 million years ago in the early Cretaceous
period. It was a “bird-hipped” or ornithopod dinosaur
that had four legs but could raise itself up on its hind legs like
the better-known Iguanodon. Adults weighed around four
tonnes and were around 9 metres long.
Fossilised bones of Muttaburrasaurus have been found in
— where else — Muttaburra, a town just north-east of
Longreach in Queensland’s savanna country.
However this dinosaur is hardly a 'savanna' or even an
Australian dinosaur as it lived long before Australia was a
separate continent and in conditions quite unlike the savannas of
When Muttaburrasaurus was alive, Gondwana was breaking up
but what was to become Australia and Antarctica were still locked
together close to the southern pole, so the climate would have been
very cool, with long, dark winters and landscapes of temperate
forests. These forests would have lacked flowering plants like
eucalypts and wattles as (whole system of flowering plants,
pollinated by birds and insects had not yet flourished) but rather
would have been dominated by conifers, cycads and ferns.
The great Gondwana Break-up
Forty-five million years after the separation of Africa, South
America split off from Gondwana, leaving Australia and Antarctica
the last of the Gondwanan plates to be connected. Eventually,
around 45 million years ago, Australia made its break from
Antarctica and began its gradual drift north towards the
While Australia was in the long process of separating from the
Antarctic, the large dinosaurs disappeared, their demise thought to
be precipitated by global changes in the climate and environment
and then by an asteroid impact around 65 million years ago, which
marked the end of the Cretaceous era. The main survivors of that
great lineage are thought to be a group of smaller theropod
dinosaurs that evolved beaks, a skin covered in feathers and, for
many of them, the ability to fly — the group we know
today as birds.
Mammals flourished as the dinosaurs declined, rapidly evolving
into a variety of different types including a range of early
marsupials which are thought to have originated in north America,
reaching Australia via South America and the Antarctic before those
continents separated. As Australia finally separated from the
Antarctic and drifted northwards, further migration into Australia
was blocked and Antarctica became isolated by a circumpolar ocean
and cooled, eventually becoming covered in glaciers and ice.
During this northward journey at the leisurely pace of a few
centimetres a year, Australia experienced major climatic shifts
that resulted in cycles of expanding and contracting rainforests.
In fact, during the early Miocene (15–-20 million years ago)
the majority of the Australian continent was covered in rainforest.
It is thought that many of Australia’s land animal groups had
their origins in this rainforest age, with many of them filling
similar roles to placental mammals on other continents. During this
time northern Australia had wolf-like thylacines, cow-sized
herbivores known as Neohelos and marsupial lions. Other animals
included platypus, and carnivorous kangaroos.
Spread of savannas
Trees like Eucalyptus can be seen as not just being well adapted to
fire, but also as promoting fire. Photo: Kathryn Thorburn
By the mid-Miocene, around 15 million years ago, Australia had
drifted north to the mid latitudes, and this combined with other
global changes led to gradual drying and cooling of the climate.
Consequently, the rainforests began to contract as the continent
dried out and fire became more frequent in the environment. As
rainforests contracted they were replaced by savanna vegetation,
dominated by Eucalyptus and Casuarina species. For
many of the rainforest mammals of the time, this drier savanna
environment proved too hostile and led to their gradual extinction.
Nonetheless, many animals either managed to adapt to the savanna
conditions or persist in contracting rainforest refuges. Some of
these survivors can still be found today in the wet rainforests of
North Eastern Queensland and Papua New Guinea.
The age of ice and giants
A Diprotodon— rather like a wombat the size of a minibus.
From the fossil record we can ascertain that between 40,000 and
2 million years ago, Australian savannas would have been more
comparable to the African savannas of today, for they contained a
diverse collection of large animals known as megafauna.
Though the megafauna of this period were unlikely to have been
as large as an elephant, the savannas during this time would have
hosted 3 metre tall kangaroos, giant goannas reaching 7 metres
long, giant land crocodiles, 3 metres high flightless birds
weighing 500 kilograms, and giant marsupial herbivores known as
However, all of Australia’s megafauna weighing more than
100 kilograms perished in the late Quaternary which was about
40,000 years ago. The cause of this mass extinction has been
debated by scientists for more than a century, with the main
arguments being climate change, over-hunting by Aboriginal people,
or landscape change caused by Aboriginal fire-stick farming.
The over-hunting hypothesis is popular given the timing of
events, with Aboriginal people thought to have arrived in Australia
between 40,000 and 60,000 years ago. By contrast, it is thought
that the megafauna of Africa such as rhinos, giraffes and lions
managed to persist as they evolved in tandem with human beings.
Product of isolation
The 40 million-year period of Australia’s isolation
permitted the evolution of its plants and animals without the
impact of fauna arriving from other continents. However, this
isolation ended 15 million years ago when Australia collided with
South East Asia. This collision formed the highlands of New Guinea
and during periods of low sea level connected north Australia with
New Guinea permitting the dispersal of animals and plants. Also
resulting from the collision were the islands of Wallacea which
acted as stepping stones for plants and animals from South East
Asia to disperse into Australia. However, the presence of a deep
sea channel known as Wallace’s line has prevented most
mammals from ever reaching Australia, with the exception of bats
and rats. As a result, Australia’s mammalian fauna remains
dominated by marsupials and free from the placental mammals of Asia
such as monkeys and tigers.
Questions for savanna management
An understanding of our evolutionary past stimulates interesting
questions about how we should manage the savannas of northern
Australia. Should we introduce some of the existing megafauna from
other continents, such as the Komodo dragon from Indonesia, to make
up for the disappearance of our own prehistoric megafauna? Should
we maintain existing populations of feral animals such as buffaloes
as a replacement for a diprotodon? Should we manage our landscapes
to represent savannas 70,000 years before human occupation, or 200
years before European arrival? However, the fact is that a lot of
evolutionary time has passed since the extinction of megafauna and
arrival of human beings. How we decide to manage our landscapes is
not determined by what we may want, but limited by what we can
actually do, and such a dramatic return to our ancient landscapes
is likely to be unrealistic.
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