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It is clear that an organism can only grow so large before the systems required to keep it alive need to become impossibly efficient. Circulatory systems, respiratory systems, nervous systems, etc. have to constantly fight against gravity, atmospheric conditions and resistance.

I'm interested in gravity more. I read an unsourced statement somewhere that on Earth, an animal cannot grow to more than the size of the Pentagon due to the gravity (weight). Are there any plausible models or rough scales representing the relationship between gravity and land animal size? Are they linear? Logarithmic? It don't require perfection, I just need something more concrete than the square-cube law.

(Assume that atmospheric pressure and composition remain fairly constant.)

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closed as primarily opinion-based by JBH, GerardFalla, Frostfyre, StephenG, Renan Dec 5 '18 at 21:52

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Relationship is complicated. Depends on a lot of other factors, like if it is a land or water animal, atmosphere, pressure (and these two depend on gravity) and so on. Do you have any restrains? Like, for example, if you want your animal be land or oceanic one, in what atmosphere it lives, and probably more? I'm afraid answer that takes every possibility into account could get too long for Q&A format. $\endgroup$ – Mołot Dec 5 '18 at 15:01
  • $\begingroup$ How concrete do you want this relationship to be? A fairly rough relationship on the effects of gravity on animal size could probably be made by comparing the largest land critters with the largest ocean critters (who are able to compensate for gravity through buoyancy and thus grow larger). $\endgroup$ – Giter Dec 5 '18 at 15:39
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    $\begingroup$ I apologize for doing this to you, but I need to VTC as primarily opinion-based. We have only one datapoint: Earth. We have no idea how any other gravity will actually affect animal evolution (and we barely understand how evolution, including physical development, works here). Answers to this question can never be anything other than a guess because there's only the one perspective to work with. If you're writing a story, create what you want. If you're asking out of curiosity, well.... $\endgroup$ – JBH Dec 5 '18 at 16:12
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    $\begingroup$ @NightKing Just a thought, but if you go to biology.stackexchange.com and figure out how to phrase the question so they like it, I'm sure they'd be pleased to help. $\endgroup$ – Measure of despare. Dec 5 '18 at 16:52
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    $\begingroup$ @JBH the fact that you don't have enough data, or even the fact that enough data does not exist, does not make it opinion based. If there is no relationship, it is an answer, not a proof of question being opinion based. $\endgroup$ – Mołot Dec 5 '18 at 20:43