The Insane Biology of: Kangaroos

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 venomous inland taipan and its close relatives that live on 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 waiting chest deep in the 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 it's no longer putting up a fight many dogs and dingoes 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 fight usually starts with one male smacking another in the face both of them

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 and huge muscles in their legs a cake 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 betongs kawacas and rat kangaroos all belong to the macropod family a name that means Bigfoot 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 macropod family exploded into a variety of forms small mouse-like marsupials like potteroos and B tongs 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 two pounds or less than one kilogram once they're born they crawl into their mother's pouch where they spend another six months feeding off her milk and finishing their growth once they're out of the pouch they become what's 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 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 kilometers per hour is much less energy costly for kangaroos than for other mammals of similar sizes and they can comfortably hop at speeds of 20 to 25 kilometers per hour for quite some time if they're being chased by predators and really need to Sprint they can attain speeds of 65 to 70 kilometers per hour 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 hind limbs which are twice as long as their forelimbs 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 to 40 percent of their muscle mass made up of skeletal muscle and for kangaroos the majority of that muscle is centered around their pelvis and hind limbs 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 supercharged 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 their downright clumsy looking and surprisingly this slow movement requires a lot more energy their walking is called pentropedal 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 their 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 saxophone at the front and the two perform at the back food moves along this system almost like a conveyor belt rather than being stirred over and over again because food takes a long 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 but 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 gases 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 90 kilograms 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 Joey's will play fight usually 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 dingoes 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 it's 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 of its strange creatures the enormous the intelligent the scary the weird the buff you've probably marveled at the complexity of evolution and been in awe that the laws of physics could allow for such a variety of organisms on this planet at

least I know I have and for me my appreciation of the natural world skyrockets when I take the time to understand it the endless struggle between predators and prey is fascinating but by understanding differential equations you can create mathematical models for different scenarios to see how an increase of dingoes for example will affect a local kangaroo population the shell of a nautilus looks pretty cool but by understanding geometry you see that it's an incredible example of a logarithmic spiral towering trees flowing Rivers flowers or heads of broccoli these are all examples of fractals in nature

math allows us to perceive the patterns and realities of the universe and brilliant.org is how I learn all this math interactively brilliant has thousands of lessons like foundational geometry and algebra to Advanced differential equations and calculus you can also dive into neural networks data science or even Advanced physics all of which help me understand the world we live in and help me to write these videos the courses are sometimes challenging but brilliant doesn't penalize you or impede your progress instead they give you an in-depth explanation to guide you to the right answer so you can

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