Where do kangaroos come from, why do they hop, and should we kill them?

Where do kangaroos come from, why do they hop, and should we kill them?

/ By Anna Salleh

Some 30 million years ago in an Australian rainforest, a small possum-like animal climbed down from the trees and evolved into an amazing array of creatures.

One of these was a giant, leaf-munching kangaroo called Procoptodon goliah that weighed hundreds of kilograms, possibly walked like a dinosaur, and went extinct about 15,000 years ago.

Then there’s the famous red kangaroo that still bounds across our endless plains — weighing up to 92 kilograms, it’s the biggest marsupial alive today.

Meanwhile, in the rainforests of Queensland lives the tiny clambering musky rat-kangaroo, weighing not much more than half a kilogram. This species is a living fossil, having been around for tens of millions of years.

This surprisingly diverse group of animals is made up of over 60 species, but as the scientific name “macropod” — or more specifically, “macropodiform” — implies, they are all united by one thing: big feet.

The term ‘kangaroo’ comes from the Aboriginal word “gangarru”, from the Guugu Yimithirr language, which is spoken in far north Queensland.

It’s not a scientific name and is used to describe a range of animals, some of which may be only distantly related to the big kangaroos we are most familiar with.

The fast-hopping red, eastern grey and western grey kangaroos can be regarded as the only true kangaroos, by the narrowest definition, says wildlife ecologist, Graeme Coulson of Melbourne University.

What makes a kangaroo as compared to a wallaby, he says, are differences in genes, teeth, body size, habitat and diet.

Kangaroos tend to be larger, and graze on grasslands, while wallabies are smaller and have a more mixed diet that includes browsing on leaves.

A wallaroo, by the way, also eats grass and is somewhere between a kangaroo and a wallaby (no surprise there, given its name!).

Kangaroos and wallaroos are among the most common species in the kangaroo family, and it’s thought they owe their success, in part, to the size of their teeth.

The rise of the kangaroo

The earliest terrestrial ancestor of the kangaroo family, which evolved when the Australian continent was covered in rainforest, probably looked a bit like the tiny musky rat-kangaroo.

It belongs to an ancient group of animals that includes bettongs and potoroos, which don’t get much bigger than 3kg, tend to live in dense forest, and eat fruit, insects and fungi instead of grass.

They also curl their tails, which is a likely a hangover from having come from the trees, Dr Coulson says.

As the climate changed over tens of millions of years, drier sclerophyll forests started replacing rainforests.

Some animals, like the giant Procoptodon, developed the ability to browse on the tough leaves and stems of these new types of forests.

But while species like this stayed in the forest, the red and grey kangaroos ventured out into the open and expanding grasslands, where they managed to outlive their giant cousins.

“Some people regard the kangaroos as the last of the megafauna,” Dr Coulson says.

The success of the red and grey kangaroos appears to have been made possible by the evolution of special teeth with higher crowns, which gave them the ability to chew for hours on tough and abrasive grass.

These animals also have an amazing “conveyor belt” of molars that ensure fresh chewing teeth come on line as the animal matures, says Dr Coulson.

There’s debate over what exactly killed off Australia’s megafauna, including Procoptodon, but the finger has been pointed at both climate change and hunting, says evolutionary biologist Matthew Phillips of the Queensland University of Technology.

“There’s competing hypotheses and massive arguments around them,” Dr Phillips says, adding that both ideas have merit.

He speculates that Procoptodon would have moved slower than the true kangaroos, which meant it would be more likely to get caught — and provide the hunter with a jackpot in terms of meat quantity.

But, says Dr Phillips, the continual drying out of the Australian continent suggests there might have been a shortage of food needed to feed the massive beasts.

And the fact that bigger animals breed slower means Procoptodon would have found it harder to build up numbers after a fall in their population.

Some experts suggest Procoptodon didn’t hop like today’s kangaroos, but instead walked on two feet like a dinosaur.

Whatever the case, there seems little doubt that the true kangaroos have always been the most efficient hoppers in town.

The art of hopping and walking on five legs

Hopping basically means getting around by jumping on your hind legs, but kangaroos are unusual because most animals that do this are small.

But it turns out hopping can be such an efficient way for kangaroos to get around — some have been clocked going as fast as 64 kilometres an hour — experts are now wondering why more animals don’t do it!

The secret to the kangaroo’s hop is the leverage it gets from its long feet and long shin bones, says Dr Natalie Warburton of Murdoch University, who studies how animals move.

Experts aren’t sure when, or how many times, hopping evolved, but Dr Phillips wonders whether it might have emerged as a way for the ancestral kangaroo to manage a growing range of activities.

Beyond climbing trees, it also had to be able to run about and dig for food on the forest floor.

“Hopping means the hind limbs can become specialised for locomotion and the forelimbs can become specialised for digging and climbing,” he says.

The big red and grey kangaroos are the “pinnacle” of hopping evolution, Dr Warburton says, adding this could have something to do with them venturing out into vast open spaces.

“Hopping is going to be potentially useful for when the forests open up and when grasslands spread,” agrees Dr Phillips.

But while hopping is great for getting around fast, it’s not so good when you want to slow down.

“It’s very hard to hop slowly, like it’s hard to run slowly,” Dr Warburton says.

Unfortunately, the true kangaroos can’t walk like humans because they don’t seem to be very good at moving their legs independently of each other on land.

So they’ve invented a unique form of locomotion called “pentapedal walking”, which involves making a tripod between their hands and their tail, so they can move their back legs at the same time.

“They put their hands down, bring their tail underneath their back legs and then take their bodyweight on their tail and arms so that they can lift up both their legs together and bring them forward.”

While we’re on the subject of getting around, the ability of the kangaroo to move — or not — is said to explain why it features on Australia’s Commonwealth Coat of Arms.

Supposedly the kangaroo helps symbolise a nation moving forward because it can’t move backwards easily, although Dr Warburton doubts anyone has actually tested this.

But we do know kangaroos are good swimmers — miraculously being able to move their back limbs independently when they are water.

“When they swim they use their legs in an alternating fashion, like a dog paddle.”

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And kangaroos are also good fighters.

In fact, says Dr Warburton, male kangaroos have “disproportionately large” muscles in their arms to help them do this.

“Those are the muscles they use to grab hold of an opponent and hold them near them so they can try and kick them with their big back feet.”

But being a heavyweight has its downside.

“If there’s a drought, it’s the males that tend to die off because they have much bigger energy requirements to support those huge bodies and those big muscles.”

National plague or national icon?

Rainfall does indeed affect kangaroo numbers through its impact on the amount of grass around.

A recently published 40-year study found kangaroo numbers on the western plains of NSW varied from 18 million during good seasons to about 5 million during drought years.

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And all this brings us to the elephant — or should we say, kangaroo — in the room: the touchy subject of whether there are too many kangaroos on the continent.

Some argue kangaroos are vermin that should be shot to keep their numbers in check, and to support a valuable industry selling their meat and skins.

Others say kangaroos are being inhumanely slaughtered, because it is impossible to enforce “humane shooting” codes, and, especially as a native species, should be protected.

Estimates from aerial surveys suggest there are around 40 million red and grey kangaroos and wallaroos in Australia — although the numbers, along with the question of whether they are under threat from humans, is the subject of debate.

Dr Coulson, who advises governments on kangaroo culling quotas, says there is little chance that commercially harvested species will go the way of the Procoptodon.

But, he says there are endangered macropods, especially among the smaller species which are preyed on by foxes and cats, and even the true kangaroos have been wiped out in some areas of the country.

“It’s very hard to generalise.”

Dr Coulson says land clearing by early European settlers in Australia suited kangaroos because it created more open areas.

But in some areas there is now too much open space for true kangaroos, which feed at night but need shelter in the day.

Dr Coulson cites the Wimmera wheat growing area in Victoria as an example of a place cleared to the point where there are now no kangaroos at all.

“They’ve basically just disappeared from the landscape.”

Growing urban development also means kangaroo numbers are declining because they’re being squeezed out, run over or attacked by dogs, he adds.

“There are whole areas that currently have kangaroos that in 20 or 30 years simply won’t,” Dr Coulson says.

So, what does the future hold for the kangaroo?

Some argue we should farm and eat kangaroos as more ecologically appropriate alternatives to hard-hoofed cattle and sheep.

But there are challenges here.

If everyone in Australia switched to eating kangaroo sausages and steaks, we’d need to have many more kangaroos than we do now.

But kangaroos need to free range over vast areas and can’t be farmed in the usual way because their muscles waste away when they’re cooped up, Dr Coulson says.

And roo-proof fences can be controversial.

Dr Coulson says alternatives to culling such as relocation, birth control and attempts to scare the animals off using bright lights and ultrasound have limited or dubious ability to manage roo populations.

And he suggests the problem with kangaroo numbers in some areas is a symptom of something deeper.

“We are clearly dealing with an imbalance, and it’s mostly because we’ve changed the proportion of forest and grassland in a way that’s favoured the kangaroo.”

He says one way forward is to plant more trees on farms, especially in areas where clearing has encouraged kangaroos — something that might bring other benefits to farms.

“That to me is a more natural way to control numbers.”

Dr Coulson also supports the idea of replacing annual pasture grasses with perennial ones — like kangaroo grass — that are more drought proof and grow all year round, providing more food for stock and kangaroos to share.

These ideas, along with enlisting the help of predators like dingoes, are in line with suggestions being made by advocates of ethical wildlife control, such as conservation biologist Dr Daniel Ramp at the University of Technology, Sydney.

Dr Ramp, who is also on the board of animals welfare group Voiceless, argues that current estimates of kangaroo numbers are unreliable and we don’t know if the animals are at risk from humans.

He says, as a nation, we “like the idea” of kangaroos — for example, as a national icon — but we are ultimately not very accepting of them.

“We relate to them symbolically but at the end of the day we persecute them,” Dr Ramp says, adding we need to learn how to better share the land with this native animal.

Dr Coulson supports the widely held view that kangaroos can be pests in some situations.

He says commercially harvested species are very abundant and it’s “inevitable” they will compete with livestock, and in large enough numbers can also endanger other animal species and plants in places like national parks.

“Whether this impact justifies killing kangaroos is a moral judgment,” Dr Coulson says.

But he is favourable towards the idea of humans sharing space with kangaroos.

“Kangaroos are not the enemy, it shouldn’t be a black-or-white debate.”