Australia has a reputation of being filled with wildlife that wants to kill you.
Blue-ringed octopuses, bull sharks, and box jellyfish swim along the coasts.
Saltwater crocodiles haunt the estuaries.
Funnel web spiders contain a deadly neurotoxin, while huntsman spiders are less likely to
cause serious illness but far more likely to terrify humans with their speed and size.
And we’ve done an entire episode on the incredibly lethal inland taipan and its close
relatives that live in other parts of the continent.
But occasionally the most unexpected species can turn violent.
If you wander through the grassy fields of Australia,
you might come across a scene like this - a kangaroo wading chest deep in water, with
a look on his face that says “come on in, the water’s great.”
If the kangaroo succeeds in luring its opponent into the water, it will ferociously drown
it by holding its head underwater until its no longer putting up a fight.
Many dogs and dingos have met their end in this way.
And in 2022, a man was even killed when he suffered extensive head injuries including
a broken jaw as he attempted to rescue his two dogs from a large kangaroo.
These fluffy, grass-eating, hopping animals, who fill the same ecological niche as deer
do in other parts of the world, can also be quite dangerous.
Only about five people per year seek medical attention after a kangaroo encounter, and
it’s rare for kangaroos to kill someone, but they’re clearly capable of it.
Because fighting for dominance in the world of kangaroos is common - and it's like the
animal form of MMA.
Boxing, kicking, grappling are all tools used to take down their opponent.
A fight usually starts with one male smacking another in the face.
Both then stand up tall, lean their heads back and start to grapple each other with
their hands.
The next move is the kick - which can be a devastating blow due to their giant claws
huge muscles in their legs.
A kick like this would be enough to disembowel a human.
During the hitting and kicking the kangaroos try to wrestle each other to the ground.
Eventually one will give up, and a winner emerges.
Watching a kangaroo fight like this makes you glad to not be a kangaroo.
Because their strength, aggressive behavior, and weird physiology make these animals a
force to be reckoned with.
Kangaroos, wallabies, bettongs, quokkas, and rat kangaroos all belong to the Macropod family,
a name that means “big foot.”
They’re descended from arboreal marsupials, who enjoyed a lush, rainforest environment
in Australia about 50 million years ago.
As the environment changed to a more patchwork forest, and then became even drier and more
like a desert, the Macropodidae family exploded into a variety of different forms.
Small, mouse-like marsupials like potoroos and bettongs descended from one line, while
the larger kangaroos and wallabies descended from another.
In fact, there was even a brief period around 15 million years ago when a carnivorous species
of kangaroo hunted other animals.
Marsupials and placental mammals diverged from a common ancestor more than 125 million
years ago.
And the reproductive strategy of marsupials evolved to be extremely different from ours
in that time.
Today, there are six species of kangaroos across Australia and New Guinea, and they
all belong to the marsupial family, who are known for carrying their young in pouches.
Kangaroos give birth after just a month of pregnancy, and their young are among the largest
and most developed of any marsupial—despite the fact that they’re still blind, furless,
barely able to move, and weigh less than 2 pounds.
Once they are born, they crawl into their mothers pouch, where they spend another six
months feeding off her milk and finishing their growth.
Once they’re out of the pouch, they become whats called “young at foot,” and that’s
when the joeys really start developing the skills that make them such formidable fighters,
and incredibly efficient hoppers.
Based on the fossil record, it seems that hopping as a form of locomotion appeared about
20 million years ago.
But it wasn’t until much more recently that the fastest of the modern species, red kangaroos,
appeared.
And it’s this largest of the kangaroos that scientists have been studying for decades,
because hopping is rare among vertebrates.
It’s used mainly by frogs and small mammals.
Nothing else anywhere near the size of a red kangaroo hops—yet these marsupials reach
great speeds doing so.
In 1973, a group of researchers taught red kangaroos to hop on a treadmill and wear a
mask while doing so, in order to measure their oxygen consumption.
[6] In most mammals, the faster they run, the higher the energy costs for the body,
but the opposite is true for kangaroos.
Their energy and oxygen requirements are high when they start hopping, but as they go faster,
those aerobic demands don’t change.
Hopping at speeds of 15 km/h is much less energetically costly for kangaroos than for
other mammals of similar sizes, and they can comfortably hop at speeds of 20-25 km/h for
quite some time.
If they’re being chased by predators and really need to sprint, they can attain speeds
of 65-70 km/h, which puts them among the fastest land animals in the world.
Their speed and energy efficiency are the result of a number of adaptations.
First, there’s the size of their hindlimbs, which are twice as long as their fore limbs.
These give them a base from which to spring off of, essentially using a bipedal form of
movement.
Then there are the tough tendons of their ankles and knees.
These elastic bands store energy in a way that doesn’t rely exclusively on mechanical
muscle movement.
But their muscles are impressive, too.
The skeletal muscle mass of red kangaroos is about 50% of their total body mass, making
them among the buffest of mammals.
Most large mammals, like humans and cows, only have 35-40% of their mass made up of
skeletal muscle.
And for kangaroos, the majority of that muscle is centered around their pelvis and hindlimbs,
where they need to generate the spring for their hopping.
Kangaroos also have a high density of mitochondria in their muscle, as well as a high level of
capillary density and blood volumes.
Basically, this means their muscles are super-charged, like those of a racing horse.
Lastly, their large tails swing in the opposite direction of their torso, helping them balance
out their weight so they don’t tip forward.
All these characteristics allow kangaroos to outrun most predators, and move across
wide distances in search of food.
Yet when kangaroos move more slowly, they’re downright clumsy looking, and surprisingly,
this slow movement requires a lot more energy.
Their “walking” is called pentapedal locomotion, referring to “five feet,” since their
tail is used like a fifth leg.
Because it’s more energetically costly to move this slowly, they don’t do it as often.
It means they have to be a little more choosy about where they’re getting food from—especially
since they eat almost exclusively grass.
As we mentioned earlier, kangaroos are basically the Australian version of deer: herbivores
who graze on grasses and live in large groups, called ‘mobs.’
But there’s one major difference between kangaroos and other grass-eaters—kangaroos
aren’t ruminants.
For animals who feed on grass and leaves, it’s difficult for the body to break down
so much fiber.
Ruminants like cows, sheep, and deer have four stomach compartments and will regurgitate
food in order to chew it a second time, a process known as “rumination.”
Kangaroos eat an equally fibrous diet, but their stomach has only two chambers, and they
don’t chew their cud.
In kangaroos, the two parts of the stomach are the sacciform at the front and the tubiform
in the back.
Food moves along this system almost like a conveyor belt, rather than being stirred over
and over again.
Because food takes a longer time to move through the digestive system of ruminants, they have
to eat in smaller bursts, whereas kangaroos can eat more at one time.
Kangaroos spend up to 10 hours a day feeding and their food is such an important source
of moisture that they can go days and even weeks without water, as long as they’re
still eating.
Another significant difference between the digestion of kangaroos and ruminants is how
the fermentation process works.
In order to extract nutrients from all those high-fiber greens, bacteria in these animals’
digestive systems help break down the food.
For ruminants, the hydrogen gas produced in this process is converted to methane by bacteria,
which the animals then burp or fart out.
Methane is a greenhouse gas that’s 30 times more potent than carbon dioxide, and 50 to
60 percent of it comes from the agricultural sector and the digestion of ruminating animals.
Since people like eating meat so much, this is a major problem, and scientists have been
experimenting with ways to get the animals burping less dangerous gasses.
Which is what led them to study kangaroos, whose digestive fermentation process doesn’t
release nearly as much methane - about 27% the amount of ruminants.
There are a couple reasons for this.
One is that the food moves more rapidly through the digestive tract of kangaroos, which washes
out some of the bacteria that might otherwise produce methane.
But other research has found that kangaroos have a different kind of bacteria in their
guts.
Fermentation always produces hydrogen gas, but instead of bacteria that turn it to methane,
kangaroos have bacteria that turn the gas into acetic acid, which aids in muscle growth.
Which leads us right back to where we started—the incredible strength of kangaroos.
Although different species of kangaroo grow to be different sizes, all of them are pretty
big.
And male red kangaroos, which are the largest, can grow to be absolutely massive.
An adult male can weigh 90kg and stand over 2 meters tall, which makes them significantly
larger than the average human.
And starting from the time they’re young, all types of kangaroos put their muscles to
use by learning how to fight.
Early in life, joeys will play-fight most frequently with their mothers, learning how
to move their limbs around.
Play-fighting continues throughout the lifespan of a kangaroo, with adult males often engaging
in ritualized fights where the goal isn’t really to hurt one another, so much as to
hone their skills.
Even females will play-fight, though it’s less frequent.
When things get more violent, though, is when kangaroos are trying to get access to something
like water or mating rights with females.
And scientists have found that different species have different styles of fighting.
Those who are slightly smaller break contact frequently and are more likely to kick each
other.
These kicks can be so damaging that males have evolved hardened dermal shields on their
bellies to avoid being disemboweled.
For larger species, like red kangaroos, the main form of fighting is grappling with the
head, neck, and shoulders.
The goal is to throw down the opponent, and the kangaroos do so by whatever means necessary.
The kangaroos will also occasionally fight off predators, like dingos, though they’re
just as likely to hop away to avoid being caught.
And in some cases as I mentioned before, they’ll even head for the closest watering hole and
drown any animal that gets too close to them.
In reality, this is a defensive maneuver as its only trying to protect itself from attack.
And it’s a strategy that can backfire if the water is very shallow or very deep—in
those cases, the kangaroos don’t have as much of an advantage and can easily be bitten
or drowned themselves.
Although the kangaroos are jacked mainly because of their need to fight and flee, the muscles
also seem to give them an advantage with the ladies.
Male kangaroos will sometimes stand in ways that show off their muscles, to entice females
and prove that they’re tough enough to handle newcomers.
But those big muscles come at a cost.
Adult males are more likely to die during droughts and other periods of environmental
stress, possibly because their bodies require more energy to maintain.
Clearly there are pros and cons to being super buff.
But it’s a strategy that’s worked well for the kangaroos so far, especially considering
the larger ones are currently less endangered than smaller species of marsupial.
Just remember, if you do run into them in the wild, it’s best to keep your distance.
If you’re really determined to get up close and personal with a marsupial, it’s probably
better to go for a wallaby.
If you’re watching this video, you’re probably drawn to the natural world and all
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an increase of dingoes will affect a local kangaroo population.
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