Why Does Australia Have Unique & Unusual Animals?
How the continents were formed
Up until about 250 millions of years ago the world had just one huge super-continent called Pangaea. Animals and plants were able to move and intermix with one another.
About 200 million years ago this super-continent broke up into two continents (Laurasia and Gondwana).
About 60 million years ago Gondwana broke up into what was to later become South America, Africa, Antarctica, India and Australia. Australia then slowly drifted far away from all the other continents.
Australia has been isolated from the rest of the world by vast oceans. The animals and plants which were originally here no longer had contact with creatures from other parts of the world and evolved in isolations from animals in other parts of the world. That is why animals in Australia are so different.
Marsupials mammals got their name from the Latin word “marsupium” which means pouch. All marsupials have an external pouch located on their mother’s abdomen (tummy) in which they carry their young.
Marsupials differ for other mammals in that they give birth to very small underdeveloped babies who must make a dangerous journey from the mother’s birth canal at the bottom to the pouch located on her abdomen. They do this by crawling up the mother's tummy to the pouch. This is the most dangerous time of a young marsupial's life as these babies could easily fall off and die.
Once safely in the mother’s pouch the baby, called a Joey, attaches itself to a milk teat where it feeds and grows into a baby animal. A baby kangaroo may live in its mothers pouch for as long as 6 months.
Marsupials of Australia, may have originated in modern day China (East Laurasia). They probably arrived in Australia around 50 million years ago via North America, South America and through the Antarctica.
Once Australia separated from the other continents and started to drift southward the marsupials stranded on it didn't have any competition from more advanced placental mammals. Without competition the marsupials diverged into the over 140 different species of marsupial found in Australia today. Some descendants of those original marsupials even almost hopped their way back towards China reaching as far as Indonesia and Papua New Guinea. (Unfortunately the original marsupials in other parts of the world couldn't compete with placental mammals and became extinct.)
What is a Monotreme?
A monotreme is a primitive mammal that lays eggs like a bird or reptile but feeds its babies milk like a mammal. Monotremes are warm blooded but have a slightly lower metabolic and heart rate than other mammals. This means they need less energy than equivalent sized mammals. Monotremes have fur but no teeth.
There are only two types of monotremes in the world, both of which are found in Australia. These are the Echidna and the duck-billed platypus. Monotremes lays tiny leathery eggs. The babies lick milk from the fur on their mother's abdomen.
DID YOU KNOW
Monotreme means "one hole". This is because these animals have only opening for their anus, urinary and reproductive tracts. This is similar to birds and reptiles.
Why are there Marsupials & Monotremes in Australia?
Marsupials and Monotremes are Better Suited for the Australian Environment
Originally, while all the continents were joined together, there were primitive mammals of all sorts in Australia.
When Australia broke off from Gondwana and started drifting off to the south, the environment started to get drier and sparser. Monotremes and marsupial mammals were well suited for the new harsher environment than the placental mammals. Then, about 34 million years ago, there was a huge world-wide extinction event, possibly caused by large scale bombardment of the earth by objects from outer space such as meteors. This seems to have affected the placental mammals more than it did the others. From then onwards monotremes and marsupial mammals seem to have thrived in Australia and placental mammals slowly became extinct.
It is believed that these animals were better suited for Australia's harsh arid environment because of their lower metabolic rate and less demanding reproductive system.
Marsupials became the dominant mammals in Australia.
Native Australian Animals
Australian Mammals There are three types of mammals in Australia
Monotremes are the oldest mamas to populate Australia, first appearing between 145–99 million years ago. Two out of the five known species of monotremes in the world today live here. These are the Echidna and Platypus.
Marsupials appeared about 64-65 million years ago and are the second oldest type of mammal found in Australia. They occupy every niche of the Australian habitat and range from the large Red Kangaroo to marsupials of the tiniest size.
Placental Mammals found in Australia today are relatively recent arrivals, bats were the first to arrive getting here about 23 million years ago. Rodents arrived about 5-10 million years ago. These animals reached Australia by flying and crossing the seas that separated Australian from Asia when Australia slowly stated drifting closer to Asia making crossings to the continent possible. These placental mammals make up a very small percentage of the total mammalian population. Humans introduced a number of animals. The Dingo was the first of these coming here about 5000 years ago.
Australian Birds Australia has 800 species of birds, 350 are found only in Australasia
Ratites such as the Emu and Cassowary, which are large flightless birds similar to the ostrich.
Megapods such as the Mallee fowl, trace their ancestry as far back as Gondwanan time. These birds are stocky birds which look somewhat like chickens. They have small heads and large feet (that’s why the name "megapod" meaning big-feet).
Parrots found unique to Australia comprise nearly 20% of the world's know species. These include the cockatoo.
Other birds such as the Kookaburra is the world's largest kingfisher.
Australian Amphibians and Reptiles There are three types of mammals in Australia
Four families of native frogs inhabit the continent.
Australia has two species of crocodile. The Saltwater Crocodile is the world's largest and can grow to 1,000 kilos and is known to attack humans. Fresh water crocodiles are much smaller and do not attack humans.
There are 35 species of freshwater turtles. Six species of sea turtle also visit the coastlines.