The evolutionary quirks of Australian animals

800px-Reliefmap_of_AustraliaAustralia is home to many interesting phenomena, amongst them its weird and wonderful wildlife. 86% of plants, 84% of mammals and 45% of birds found in Australia are not seen anywhere else in the world.

Australia became separated from the rest of the world when it broke away from Antarctica between 85 and 30 million years ago. The isolation of Australia, combined with its harsh, arid climate has allowed for the evolution of unique species, each filling a particular ecological niche.

Australia’s unique flora and fauna make it one of most fascinating places in the world to biology. The following is a highly scientific* ranking of some of the extraordinary creatures found in Australia, and why they are fascinating to science**.

#5 : The Kangaroo

kangaroo
Credit: Louise Walker

Kangaroos are marsupials, meaning that the females have a pouch in which they will rear the baby kangaroo (joey). Marsupials are also found in North and South America, but are most abundant in Australia.

Famous for using their very strong hind legs to bounce across the Australian plains, the kangaroo and its smaller relative the wallaby use this bouncing to travel great distances, allowing them to survive in the harsh desert conditions of their home country.

There are many different species of kangaroo. The largest, the Red Kangaroo, can grow up to 6 ft 7 in tall.

There’s a persistent rumour that kangaroos are so named because the first Western explorers asked the native Aborigines what those bouncing things were, and the Aborigine replied with their word for “I don’t know”, this being “Can-ga-roo”. However, this is not true, the word “kangaroo” actually derives from “gangurru”, the native word for a Grey Kangaroo.

#4 : The Koala

koala
Credit: Louise Walker

Another famous Aussie native, the koala is found on the east coast. Despite appearances and the fact that it is sometimes called a “koala bear”, it is not a bear at all. It is a marsupial and, like the kangaroo, rears its young (also called a joey) in a pouch.

Koalas famously subsist on nothing but eucalyptus leaves which makes them very slow and lazy. Some people believe that the eucalyptus has a narcotic-like effect on the koalas, a bit like being stoned. But the koalas’ sedentary lifestyle is actually due to a lack of nutrition in its diet leaves; meaning that digestion takes up a lot of energy leaving very little left over for things like moving. With regard to its picky eating habits, the koala may seem a little like its non-cousin the panda, in that they both spend all day eating something which isn’t actually very nutritious. The major difference is that koalas are voracious breeders. When the male is ready to mate, he makes a noise which has been likened to “a pig on a motorcycle”.

As you can see from the picture, koalas have two opposable thumbs. This allows them to climb trees and grab small branches with ease. A recent paper has also detailed that koalas adopt their famous “tree hugging” pose to help them lose body heat.

#3 : The Little Penguin

penguin
Credit: Fir0002/Flagstaffotos, commons.wikimedia,org

The smallest breed of penguin in the world, the Little Penguin stands at 30-35 cm in height. Found only in Australia and New Zealand, these penguins famously participate in the “penguin parade” on Phillip Island, near Melbourne. The penguins spend up to a month at sea feeding, but some will return to their nests at dusk, often to feed their hungry chicks.

When the time comes to return from the sea, the little penguins have evolved a great survival technique – they form groups of 10-20 in the sea, then choose one unfortunate penguin who has to make sure the coast is clear. This scout penguin runs up and down the beach a few times to make sure there are no predators so that the other birds can return safely to their nests.

For more information on the little penguin colony on Phillip Island, Victoria, see this link.

#2 : The Inland Taipan

Photo credit: Bjoertvedt, commons.wikimedia.org
Credit: Bjoertvedt, commons.wikimedia.org

This snake gets the honour of being ranked number 2 because it is the most venomous snake in a country full of venomous snakes – which I think is quite a feat.

The title of “most venomous snake” was awarded to the Inland Taipan as its venom has the lowest LD50 score when tested in mice. This means that a very small amount of toxin is needed to cause death in 50% of subjects when compared to venom from other snakes. The Inland Taipan is also highly venomous when used on human heart cells in culture. One drop of venom is enough to kill 100 men.

Despite its highly venomous nature, the Inland Taipan is actually quite placid and rarely attacks humans. The world’s second most venomous snake, the eastern (or common) brown snake is generally more aggressive and has more fatalities to its name, according to this rather baffling Wikipedia list.

Although it is the most venomous snake in the world, the Inland Taipan is not the most venomous animal in the world. This honour is usually bestowed on the Box Jellyfish. Guess which country this comes from ….

Perhaps the need to be tough enough to survive Australia’s harsh environment may explain why the country contains an abnormally large amount of deadly creatures.

#1 : The Platypus

Credit: John Lewin, commons.wikimedia.org
Credit: John Lewin, commons.wikimedia.org

When the platypus was first discovered by early Western explorers, the scientists back home thought this duck-billed, beaver-like, egg laying creature was a hoax. The platypus and the hedgehog-like echidna (also Australian) are the only living examples of monotremes, or egg laying mammal. They are classed as mammals because they lactate and are warm-blooded (although actually their blood is cooler than most mammals).

Sequencing of the platypus genome in 2008 revealed that it shares genetic characteristics with birds and reptiles along with mammals. Because of this finding, monotremes are believed to have formed a separate branch on the evolutionary tree, very early into the evolution of mammals. This makes the monotremes especially fascinating to science because they give us clues about our evolution that no other animals can.

The reason that the platypus gets top ranking (as opposed to fellow monotreme the echidna) is the extra evolutionary level the platypus brings – the males have a venomous spur on their ankles which can cause severe pain and swelling in humans. This spur is believed to be used during fights between males for the attention of a female.

So there’s your number one weird Australian animal – frankly, what’s not to love about a furry mammalian bird-reptile which, when angered, will give you a nasty kick with its poisonous ankle?

*by “scientific” I mean “in my opinion”.

** this does not include the many varieties of spiders found in Australia for no other reason than I don’t want scary spider pictures on my blog.

Post by: Louise Walker

1 thought on “The evolutionary quirks of Australian animals

Leave a Comment

Share This