How big can a land animal get?

I'm attempting to make an animal that could live on my fantasy planet, it has 97% the gravity of earth

So on an earth-like planet with 97% of earths gravity, how big could a land organism get?

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    $\begingroup$ This looks like a hypothetical question about the real world, instead of a question related to building a fictional world. Can you edit your post to more clearly highlight your worldbuilding purpose. $\endgroup$
    – sphennings
    Sep 22, 2021 at 2:58
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    $\begingroup$ 97% of earth gravity as the only difference doesn't seem to make that much of a deal. I guess you could look for the biggest animal that roamed on Earth and just add a tiny 20-30cm here or there? Could be more, but it'd become more and more in the territory of unlikely/unbelievable. $\endgroup$ Sep 22, 2021 at 13:26
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    $\begingroup$ @sphennings All questions about fictional worlds are hypothetical questions about real worlds, and vice verse. He would have to couch it in terms of "exoplanet 1418 was just discovered, how large could animals become there" for it to be inappropriate to the site. And he didn't. $\endgroup$
    – John O
    Sep 22, 2021 at 13:32
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    $\begingroup$ @JelliPapi And I'm the evil spider knight //(;_;)\\. Yes, it's cyrillic (not necessarily Russian) and is pronounced "Pilum" (more o' less). I agree with Sphennings here, it's not really worldbuilding as we lack clear worldbuilding intents : The Earth is too similar so nothing can emerge from that, and we lack some defining motion towards a precise goal.[...] $\endgroup$ Sep 22, 2021 at 14:15
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    $\begingroup$ [...] Something "big" can be many things (height and length, but also species type, capacities, etc.), and so doesn't represent any clear intent either. Hence I wish to ask at least this : What is your creature's purpose from an extradiegetic/creator point of view? If you don't know, another way to look at it is to detail your creature more and their environment, it will give indirectly your goals. $\endgroup$ Sep 22, 2021 at 14:15

2 Answers 2


As big as the source of food allows until gravity comes along.

Modern whales are huge, but that's mostly thanks to their food source. An average-sized humpback whale will eat 4,400-5,500 pounds of plankton, krill and small, schooling fish each day. Water physics also helps them stay buoyant so they can easily get away with gigantism. For sauropods their size was mostly dependent on the huge trees of their era.

With your gravity in mind I would say a 3% increase in size that is if the Patagotitan mayorum is the upper limit.

Other than that, a limiting factor may be body shape. Bigger animals need legs like pillars to support their body. Every part of their body is subject to the weight of what is above it. So I propose abandoning the vertical body plan entirely. A flat animal could easily exceed 120 feet in length or width. It depends on the legs. Does it walk on does it move like a slug? You could also have a pancake with hundreds of legs supporting its body. Technically it could get as big as the food source and its heart allows. If gravity doesn't kill the animal, lack of oxygen will.


In addition to the answer of LiveInAmbeR.

Other than food sources, a great determining factor is the supply of oxygen or whatever alternative oxydizer your planet has. High quantities of oxygen or high quality lungs can compensate for the lack of food.

Sauropods, the vegetarian ones had complex lung systems to cope their lackluster diet.

Energy is mostly oxygen, and biomass is mostly water, so you don't necesserily need a lot of food...just a lot of liquid and stuff to breathe, protein necessities are usually very low to maintain minimal survival.

As for gravity, if size is necessary for survival, nature will always find a way, always find a new structure which is stronger than it is heavier.

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    $\begingroup$ Energy is mostly oxygen? Not quite sure what you mean by that one... $\endgroup$ Sep 22, 2021 at 11:27
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    $\begingroup$ Welcome to the Worldbuilding Stack Exchange! May I suggest that you clarify your answer according to @MattBowyer's question? I think what you might mean is that oxygen is very important for releasing the chemical energy in food. Oxygen is not, per say, part of the energy (it isn't used up, only shifted around into different molecules). $\endgroup$ Sep 22, 2021 at 11:34

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