Why Lizards Don’t Run Marathons

Why Lizards Don’t Run Marathons


[INTRO ♪] If you’ve ever seen a lizard move, you may have noticed that it runs, then stops for a bit, then runs again. Well, it turns out that lizards—some of them, anyway—can’t run and breathe at the same time. And this seems to be an evolutionary leftover from the time before the ancestors of four-legged creatures adapted to life on land— one that different groups of animals have found different ways to get around. For a lizard, running and breathing require
the same muscles. To run, a lizard has to contract its chest
muscles one after the other to help it scamper forward. And to breathe, it has to contract those same muscles in different ways. And it can’t do both at once. In a 1997 study published in The Journal of Experimental Biology, scientists put iguanas on treadmills. And they found that the faster the iguanas ran, the harder it was for them to breathe, which doesn’t make a lot of sense. If you’re fleeing or chasing down prey, wouldn’t you need to keep breathing so you can keep running? Well, a 1987 paper in Paleobiology suggested that this flaw in lizards’ body plan is an evolutionary holdover from when some vertebrates transitioned from living in the sea to living on land. The paper said that early tetrapods—a group that today includes four-limbed reptiles, amphibians, birds, and mammals—may have evolved from fish that lived in oxygen-poor waters and were only able to swim in short, rapid bursts. Sort of like how modern lizards move. And while those fish could breathe pretty well in water, that wasn’t quite the case for their descendants adapting to life on land— despite having a similar way of moving. It turns out that walking on land takes up
a whole lot more energy than swimming does. Also, that limitation of not being able to run while breathing may have forced these early ancestors to rely more on intense but tiring bursts of movement. But lizards have adapted to handle this as
best they can. Even if they have to stop and catch their breath, when they do move they can scurry around really fast— which may help them maximize what they can get out of a muscle configuration that limits their oxygen. Other lizards have also evolved better ways of breathing while running. For example, monitor lizards doesn’t seem to have a problem breathing while running, even when they’re running at a decent clip. A 1999 study published in Science found that this ability may be due to gular pumping. That is, monitor lizards—and some other lizard species as well—can expand and contract their throat to pump more fresh air into their lungs. The scientists in the study showed that when monitor lizards were experimentally prevented from doing this throat pumping, they breathed similarly to lizards that don’t have that evolutionary advantage. And these sorts of adaptations aren’t just limited to lizards. Most tetrapods have developed ways of breathing more effectively on land. The diaphragm muscle in mammals, for example, pushes air in and out of our lungs. Crocodiles have these as well. And over time, birds changed their locomotor posture, or the way they position their body while moving around, so that they didn’t need to use the same muscles for breathing and moving. Finally, horses and some other animals that can trot or run, like guinea fowl, breathe in a rhythm that coincides with their movements. This motion helps them move air in and out of their system more effectively. So while lizards’ start-and-stop running pattern may seem like an evolutionary problem, it’s actually a side effect of evolutionary innovation. Since then, animals have adapted through changes in their anatomy, behavior, and overall just making the best, most efficient use of the bodies that they have. Thanks for watching this episode of SciShow, and thanks to our patrons for supporting us. Patrons can submit their weird science questions to our QQ inbox and some of them get made into episodes like this one, so head over to patreon.com/scishow and ask away. [OUTRO ♪]

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    Afrika Smith

    So when the Lizards looked at the S.P.E.C.I.A.L chart, they just focused on agility and neglected Endurance. It's fun and challenging, but one mistake means instant death.

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    Joshua Sims

    Does that mean that dinosaurs would also have a start-stop running style? If avians only recently developed a good running/breathing posture, then I presume dinos would also have had trouble running and breathing.

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    Nick Rios

    So if you were to model a robot off of nature, what would the best general anatomy look like? Reptilian? Sapien? Cephalopoda?

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    Combat King 0

    2:59 – "It's actually a side effect of evolutionary innovation." The same words J J Abrams / Kathleen Kennedy will use to explain why cinema ticket sales have been so poor for Episode IX.

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    spindash64

    2:50 I think that’s a thing for a lot Of quadrupedal animals that run for any long duration of time. Like, supposedly one extra niche of bipedalism is not being limited to certain paces for efficient breathing

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    Fernando Alemán

    I was expecting a comment about the blood temperature as another reason why they can't run a lot.
    If you can't control your body temperature and running increases it …

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    greg the groove :: drum covers

    Aside from this spectacular information of lizard anatomy, if the lizards could breathe and run at the same time, I highly doubt they’d be able to register for the race. Having said that, if they’d provide a lizard to English translator, it could work. I’ll wait here to find out. 🙏🏻

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    Sarah Vittrup

    this infomation makes the clip from planet earth 2 even more amazing, imagion he the little lizzard was doing all that without air! :O

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    Jessica P

    Extending this even more to mammals: many have evolved what horses did, running in sync with their breathing. But this doesn't cool them off- only panting will do that. So to cool off, they must stop running and pant, or risk hyperthermia. Humans, as bipeds that can sweat, do not need to stop and pant. Thus, humans can- and do- run animals to death. It's called persistence hunting.

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    Max Mustermann

    Or God nerfed them because they were too overpowered and eating away too many birds and stuff. You should always mention alternative truths as well, so people can make up their own minds…

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    Alexa Robinson

    I was expecting comments about heat management and slow- and fast-twitch muscles. Interesting that it was about breathing.

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    Jonas Kircher

    You could have done a better job of explaining the biomechanics, this is part of every class on evolutionary biology, so there is hundreds of animations out there that give more information in 10 seconds than this video does in 3 minutes.

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    Luckyeti

    Physics: we have a picture of a black hole

    Chemistry: we’re able to recognize the structure of any molecule in a matter of minutes

    Biology: we’ll put these lizards on a treadmill

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    OLBICHL

    if only their breathing was synchrone to their running, so that they inhale and exhale due to them stretching their limbs or pulling it in… they would've been marathon legends then!

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    Bonewulfe

    The Diaphragm pulls air into the lungs, it doesn't push. The natural elasticity and musculature of the body push the air out

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    Flambo One

    You are ignoring the fact their defence mechanism of some to shed their tail to avoid predators. Why did they develop that trait?

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    John Drachenberg

    I like the part where the lizard is in front of the text, while the text is still in front of the background. Simple yet elegant editing, and I bet it took a moderate amount of work. Worth it.

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    Mostlyharmless1985

    As a boy, and yes even a childish adult, I’ve found that the anoles in my front yard were plenty quick enough to avoid me no matter how long I chased them.

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    Issou Amine

    Doesn't make sens huh !!! I hope you do understand that Lizards are as evolved as any other creature !! So saying it has trait while the other groups dont is a left over is a kinda dumb ! Why didnt the group evolved a way around it just as anyother group, again since they are evolved just as much as any other group !!

    Try again..a historical explanation isnt very good here.

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    That Dude There

    Seen a little maybe 3 foot iguana at my brothers shop in Titusville FL run! A dog wouldnt catch it in 30 feet! Fast lil creepy bastards

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    David Peters

    Cosesaurus, Sharovipteryx and other pterosaur ancestors got up on their hind limbs to overcome 'Carrier's Constraint" — which oddly was not mentioned as the name of the lateral undulation while trying to breathe issue.

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    Rosie Hawtrey

    OK mate, stand still next to a Varanid or a Tegu. One uses buccal pumping and the other uses a visceral diaphragm – both can run fast for a long distance – ask me how I know. I am a fast runner and my tegu, Priscus, left me standing for 300 yards – only caught him because he stopped under a car so I could grab him. He's also selectively warm blooded.

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