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How biologically plausible is my snake species? The young are about 25 meters long, and the adults average 90 meters. Their proportions are like an ordinary snake’s. What kinds of advantages and disadvantages would they have?

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    $\begingroup$ Advantages and disadvantages in what environment? Against what predators/prey? What is the gravity like on your planet? Bear in mind we need more details, and it's best to ask a specific question, narrowing it down to a single issue you need addressing, a single problem to solve - then additional questions can be asked in their own threads. "Advantages and disadvantages" is too broad as it asks for an unconstrained list, which is off-topic. See the meta post: catalogue of question types for clarification. $\endgroup$ Feb 5 at 23:54
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    $\begingroup$ @JBH "whether or not a fictional creature can factually exist in the real world. That's not what we do" we actually do that quite a lot, all the time in fact, "is this creature plausible in a relatively hard science world" is a very common style of question, something like 'how small can an intelligent humanoid be' is essentially the same thing for example, you've almost certainly answered or commented on many of them yourself, would you like me to go look and wave some specific examples at you? there will be many I'm sure, your other critiques may be good, that one isn't. $\endgroup$
    – Pelinore
    Feb 6 at 2:35
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    $\begingroup$ Advantage: no mongoose that big. Disadvantage: still got to check the weather forecast. $\endgroup$
    – user6760
    Feb 6 at 4:22
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    $\begingroup$ @JBH So you would like me to go get you examples then ;P how is a question about how close without any magic we could plausibly get to a fictional tinkerbell faery in a hard science alternate real world if evolution had produced one not effectively a "can this creature exist in the real world" question? we have (and frequently entertain) that sort of question all the time, you are trying to pretend we don't because you said something overly emphatic and got called ;) just accept you were wrong (or at least that you worded it a little to broadly) and bow out gracefully is my advice ;p $\endgroup$
    – Pelinore
    Feb 6 at 5:07
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    $\begingroup$ @JBH any of the anatomically correct series that doesn't involve fantastical features in the animal or magic is basically that type of question, any what's the largest a flying animal (of this or that sort) can be with real world physics on an earth like planet is that sort of question and those questions are allowed without question all the time, are you telling me we should have closed all those, because that's at a guess probably 20% or more of our content if rigorously applied. $\endgroup$
    – Pelinore
    Feb 6 at 5:14

2 Answers 2

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The largest snake to ever exist in real life was Titanoboa — at the very absolute maximum 15 meters long, 1$\frac{1}{4}$ metric tons, and a meter wide. From this several conclusions can be drawn. The primary one is that this snake is going to be about 270 metric tons (likely less assuming one of these points true) and six meters wide. It will be more useful to compare it to sauropod dinosaurs than to modern snakes.

Other takeaways:

They're going to need a lot of food

Kleiber's law implies that metabolism scales times the mass difference to the power of $\frac{3}{4}$. These snakes weigh ten thousand times (perhaps less) a real-life boa and therefore need about 1,000 times more caloric intake. Real-life boas eat something like a squirrel every week or so. This thing needs something a thousand times more massive than a squirrel at the same rate. That's about half a metric ton. There really just aren't that many half-metric-ton things walking around. Perhaps it eats bison.

They're going to need hollow bones

In modern constrictors like boids and pythonids, increased body size is achieved through larger vertebrae rather than an increase in the number of bones making up the skeleton, allowing for length estimates based on individual bones.

Individual Titanoboa vertebrae were already great in size, at or over ten centimeters across. Scale that up by a factor of 6 and the volume of the resultant 60+ centimeter-wide vertebrae increases by 216 times. Ergo, the bones are going to need air sacs within them so they can stand up under their own weight. This could presumably reduce the net weight of the snake enough to let it live; as forementioned, sauropods existed, so it's not unreasonable to believe that this could stand up under its own weight.

They're going to move differently

This thing may be able to move but likely won't be able to lift itself off the ground. 27 (or, for that matter, 1,000) kilos of snake have an easier time lifting themselves off the ground than 270 tons of snake. There will be no cobra-like rearing behavior. It can't climb trees because it's heavier than the tree. It won't like moving over less-than-completely-solid terrain, because it'll sink in, and the side-to-side movements snakes use to move will just push things like dirt and mud around rather than getting enough friction to push the snake.

They're going to eat differently

Per the above, it's going to have essentially no ability to wrap itself around prey. It is therefore probably going to have to be venomous to catch anything at all. How exactly 270 tons of snake is going to sneak up on food is your guess as good as mine, but it's certainly not going to act like anything we know of.

Overall:

Biologically plausible in any environment that exists or has ever existed on Earth? Hell to the no; there's hardly anything for it to eat and it's going to have a hard time catching it even if it was.

Biologically plausible in an indescribably thick, extremely noisy jungle where the smallest animal is the size of a whitetail deer and with a forest floor carpeted in dead trees so a really big snake has traction? Probably moreso. Throw in it being on an entirely different planet with lower gravity and that'll help.

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    $\begingroup$ The Community is starting the process of updating our Tour and primary Help Center page. This will include policy decisions and it's a great opportunity to help us define the next stage of Worldbuilding. Please join us at this Meta page and share your thoughts. Thanks! $\endgroup$
    – JBH
    Feb 6 at 16:32
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    $\begingroup$ They're going to eat differently? Well, sans any details to suggest any other mega fauna for them to predate on anything that size may have to essentially be a filter feeder, probably can't move fast enough to catch deer or bunnies, ambush hunting is possible of course but that may not be sufficient to guarantee adequate calories often enough for something this size .. haven't any hard stats to support that thought, just throwing it out there as something to think about. $\endgroup$
    – Pelinore
    Feb 7 at 5:32
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@KEY_ABRADE has already given a great answer, but I wanted add one point. Overcoming the mechanical problems of such a large snake might be helped by making it aquatic or semi-aquatic. The largest animals live in the ocean (the blue whale is likely the largest animal ever to live), because buoyancy dramatically reduces the force that their structure has to support. Indeed, whales experience crush injuries when out of water for only a few minutes.

The sea snake Palaeophis colossaeus that lived during the Cretaceous Period was a least 10 m long. I think that an aquatic lifestyle coupled with high temperatures could make your snake feasible. Reducing the surface gravity of the planet would of course help too.

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  • $\begingroup$ Making them live in the deep sea would go even further to help; deep-sea gigantism is a well-documented phenomenon and at that point the square-cube law actually can be an advantage, as there's less surface area to lose heat to, and larger creatures are more efficient overall with metabolism, so they can last longer between larger meals. One whalefall or catching a giant squid and the snake is set for a few weeks. The size wouldn't even be a disadvantage when hunting as the dark and water would obscure it from a distance. That might not fit with what the OP wants for narrative reasons, though. $\endgroup$
    – Aos Sidhe
    Feb 8 at 16:45

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