# What's the upper limit on the size of land-animals? **URL:** \ **Category:** Factual Questions\ **Created:** [September 4, 2014, 9:23pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525 "2014-09-04T21:23:54Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [September 5, 2014, 11:46pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/21 "2014-09-05T23:46:23Z")
> [@Hector\_St\_Clare](#): > > I don’t know exactly what the levels were in the Jurassic (I’m vaguely recalling someone telling me 35%), but more of a good thing isn’t _always_ better. Depends on when in the Jurassic. Oxygen levels crashed during the Triassic (e.g., down to ~15%), so at the beginning of the Jurassic, O[sub]2[/sub] levels were low. They began climbing, and by the end of the period where slightly higher than current levels (i.e., around 22-23%). During the Cretaceous, they climbed further still, and peaked at around 27% in the late Cretaceous. Throughout the Tertiary, they fell steadily to the current levels. It was during the late Carboniferous/early Permian that oxygen levels reached their maximum, at around 35%. It should be noted that, in the mid-Jurassic, when sauropods had their “Golden Age” and birds first appear, oxygen levels were still lower than they are today. ---
**Author:** ![Hector\_St\_Clare](https://avatars.discourse-cdn.com/v4/letter/h/b5ac83/32.png) [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)\ **Post date:** [September 6, 2014, 1:33am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/22 "2014-09-06T01:33:06Z")
> [@Darwins\_Finch](#): > > Depends on when in the Jurassic. Oxygen levels crashed during the Triassic (e.g., down to ~15%), so at the beginning of the Jurassic, O[sub]2[/sub] levels were low. They began climbing, and by the end of the period where slightly higher than current levels (i.e., around 22-23%). During the Cretaceous, they climbed further still, and peaked at around 27% in the late Cretaceous. Throughout the Tertiary, they fell steadily to the current levels. > > It was during the late Carboniferous/early Permian that oxygen levels reached their maximum, at around 35%. > > It should be noted that, in the mid-Jurassic, when sauropods had their “Golden Age” and birds first appear, oxygen levels were still lower than they are today. Cool, thanks. I remember hearing about the ‘35% oxygen’ thing from a biogeochemist at my research station a couple years ago, for some reason it stuck in my head. Do they think that plants and animals around the late Carboniferous had more of a problem with oxidative stress than they do today? And did they have particular mechanisms to deal with it? ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [September 6, 2014, 3:16am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/23 "2014-09-06T03:16:59Z")
> [@Hector\_St\_Clare](#): > > Do they think that plants and animals around the late Carboniferous had more of a problem with oxidative stress than they do today? And did they have particular mechanisms to deal with it? That, I’m not entirely certain of. [This paper](http://rspb.royalsocietypublishing.org/content/early/2010/03/04/rspb.2010.0001.full) discusses some of the effects of increased oxygen on insects during the Carboniferous. And chapter 5 of [this book](http://books.google.com/books?id=9f7rafLJbWUC&printsec=frontcover&dq=Amniote+Origins:+Completing+the+Transition+to+Land&hl=en&sa=X&ei=OnsKVO-eFcK3ogSat4LYBQ&ved=0CB8Q6AEwAA#v=onepage&q=chapter%205&f=false) discusses the effects of increased oxygen on early tetrapods. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [September 6, 2014, 8:43am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/24 "2014-09-06T08:43:46Z")
[QUOTE=jtur88] You’d need to specify the number of legs. The size limit for a huge millipede would be much higher than the size limit for a huge biped. [/quote] > [@iiandyiiii](#): > > I don’t think so. The upper limit for arthropods, if I understand their physiology correctly, is based on their respiration, and limits them to much smaller sizes than vertebrates, in general. How about a millipedal dinosaur analog? A hexapodal dinosaur-like creature is quite easy to imagine; how about an octopodal dino? A centipod? a millipod? I bet there are much stranger things out there in the universe, even if they are rare. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [September 7, 2014, 2:19am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/25 "2014-09-07T02:19:06Z")
> [@eburacum45](#): > > How about a millipedal dinosaur analog? A hexapodal dinosaur-like creature is quite easy to imagine; how about an octopodal dino? A centipod? a millipod? I bet there are much stranger things out there in the universe, even if they are rare. At some point having a body that long serviced by a single set of lungs and a single digestive track would be a problem. Some hypothesize that the largest sauropods had to be near-continual eating machines as it was. ---
**Author:** ![Hector\_St\_Clare](https://avatars.discourse-cdn.com/v4/letter/h/b5ac83/32.png) [@Hector\_St\_Clare](https://boards.straightdope.com/u/Hector_St_Clare)\ **Post date:** [September 7, 2014, 3:32am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/26 "2014-09-07T03:32:26Z")
> [@Lumpy](#): > > At some point having a body that long serviced by a single set of lungs and a single digestive track would be a problem. Some hypothesize that the largest sauropods had to be near-continual eating machines as it was. Metabolic rate decreases monotonically with size (roughly, with the 0.75 power of bodymass, though the exact number is disputed), so large animals have to eat less often than small ones. (or more precisely, have to eat a lower proportion of their bodymass per unit time). Hummingbirds are a lot closer to ‘continual eating machines’ than, say, sperm whales. ---
**Author:** ![EdwinAmi](https://avatars.discourse-cdn.com/v4/letter/e/5fc32e/32.png) [@EdwinAmi](https://boards.straightdope.com/u/EdwinAmi)\ **Post date:** [September 7, 2014, 5:18am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/27 "2014-09-07T05:18:50Z")
well… here’s the thing about all this stuff everyone’s saying it’s all based on bones and muscles and vascular systems _ **as they have evolved so far** _ if in the future huge animals evolve, new, better bones and other such systems may evolve ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 6:56am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/28 "2014-10-03T06:56:41Z")
> [@aldiboronti](#): > > [Newly discovered dinosaur Dreadnoughtus](http://www.washingtonpost.com/news/speaking-of-science/wp/2014/09/04/this-is-the-kind-of-dinosaur-you-find-in-hollywood/) takes crown for for largest terrestrial animal with a body mass that can be accurately determined. > > “Measurements of bones from its hind leg and foreleg revealed that the animal was 65 tons, and still growing when it died in the Patagonian hills of Argentina about 77 million years ago.” > > Scientists seem to keep finding larger and larger dinosaurs. There has to be a physical limitation to their size though. What’s the approximate upper limit for land-animal body mass? How much bigger could they get? Insects where very big back than too. I read the reason why insects today are smaller and cannot get bigger is there is less oxygen in the air. But back than insects where big.I wonder what humans would look like and size if they where around that timeline. But if modern humans today gone in time machine to that timeline I’m sure the atmospheric pressure would be too much. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [October 3, 2014, 7:52am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/29 "2014-10-03T07:52:02Z")
> [@sweat209](#): > > Insects where very big back than too. > > I read the reason why insects today are smaller and cannot get bigger is there is less oxygen in the air. > > But back than insects where big.I wonder what humans would look like and size if they where around that timeline. > > But if modern humans today gone in time machine to that timeline I’m sure the atmospheric pressure would be too much. The atmospheric pressure wasn’t significantly worse, and humans don’t have the same limitations related to oxygen as insects. Humans growing up in high altitude, and thus less oxygen, don’t end up shorter. Neither was the conditions back then such that all insects grew larger due to increased oxygen levels, the higher oxygen just raised the upper limit on size, allowing some species to evolve into “monsters” by today’s standards. Not being an expert I’m not even sure current science reports that much, but it definitely doesn’t support your musings. ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 7:58am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/30 "2014-10-03T07:58:19Z")
> [@naita](#): > > The atmospheric pressure wasn’t significantly worse, and humans don’t have the same limitations related to oxygen as insects. Humans growing up in high altitude, and thus less oxygen, don’t end up shorter. > > Neither was the conditions back then such that all insects grew larger due to increased oxygen levels, the higher oxygen just raised the upper limit on size, allowing some species to evolve into “monsters” by today’s standards. > > Not being an expert I’m not even sure current science reports that much, but it definitely doesn’t support your musings. But humans are evolved for today’s oxygen so if modern humans today gone in time machine to that timeline the oxygen would be much higher than what modern humans today are use to. ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 8:19am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/31 "2014-10-03T08:19:26Z")
> [@CookingWithGas](#): > > It’s not that an animal can’t be as big as the ants in “Them,” it’s that ants can’t scale up to that size with the same proportions. I don’t know about circulation and oxygen, but their legs simply wouldn’t hold up their body weight. You mean why animal can’t be size have ants? I don’t know , I don’t have have answer to that. But for some reason arthropods have a lot of legs. > [@](#): > > ants can’t scale up to that size with the same proportions. I don’t know about circulation and oxygen, but their legs simply wouldn’t hold up their body weight. But the more legs it has more it can support it body. Just trying standing up on one leg and you see how much heavy you are and more work is involved. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [October 3, 2014, 2:49pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/32 "2014-10-03T14:49:29Z")
If vertebrates had evolved with three pairs of limbs instead of two, that would probably be workable or even better in some cases. But beyond that you would get diminishing returns. Too many legs would simply be in each others way. P.S. In one RPG campaign the game master asked for suggestions for a tunnel monster (to be created magically against some evil dwarfs). I came up with the Dwarf Eater: a six-limbed weasel-like creature about the thickness of a black bear and fifteen feet long. The dice gods must have liked the concept because it ended up clearing out most of a dwarf mine. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [October 3, 2014, 3:08pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/33 "2014-10-03T15:08:52Z")
> [@sweat209](#): > > But humans are evolved for today’s oxygen so if modern humans today gone in time machine to that timeline the oxygen would be much higher than what modern humans today are use to. Yes, and it would do nothing to their size. Oxygen level is not a determining factor for the size of an animal. You do realize there were lots of small animals around at that time as well? ---
**Author:** ![iiandyiiii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iiandyiiii/32/7924_2.png) [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)\ **Post date:** [October 3, 2014, 3:12pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/34 "2014-10-03T15:12:47Z")
> [@sweat209](#): > > You mean why animal can’t be size have ants? I’ve read this sentence about 10 times and I still have no idea what it’s supposed to say. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [October 3, 2014, 3:41pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/35 "2014-10-03T15:41:31Z")
I think he’s asking if the reverse of the ant problem is true - if you could scale down (say) a mammal to ant-size. ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 10:23pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/36 "2014-10-03T22:23:41Z")
> [@Really\_Not\_All\_That\_Bright](#): > > I think he’s asking if the reverse of the ant problem is true - if you could scale down (say) a mammal to ant-size. Yes that is what I was saying.But I don’t think you can scale down humans or animals because organs and circulation system would also have to be scale down.And there may be limit to how small it can be before it does not work. Even in the movie honey I shrunk the kids from what I understand you would not even see much being that small. ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 10:40pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/37 "2014-10-03T22:40:03Z")
> [@Lumpy](#): > > If vertebrates had evolved with three pairs of limbs instead of two, that would probably be workable or even better in some cases. But beyond that you would get diminishing returns. Too many legs would simply be in each others way. > > P.S. In one RPG campaign the game master asked for suggestions for a tunnel monster (to be created magically against some evil dwarfs). I came up with the Dwarf Eater: a six-limbed weasel-like creature about the thickness of a black bear and fifteen feet long. The dice gods must have liked the concept because it ended up clearing out most of a dwarf mine. I wonder if dinosaurs never died out if some would look like this today. Remember some had hard exoskeleton systems. [http://www.rpgcreatures.com/bilder/CreatureA\_CronLychma\_.jpg](http://www.rpgcreatures.com/bilder/CreatureA_CronLychma_.jpg) [http://fc09.deviantart.net/fs71/f/2013/022/1/8/nymdrich\_\_\_creature\_concept\_by\_cloister-d5sbgz6.jpg](http://fc09.deviantart.net/fs71/f/2013/022/1/8/nymdrich___creature_concept_by_cloister-d5sbgz6.jpg) [![](http://4.bp.blogspot.com/-YaA4bq4r3Uc/UL8tt_lcZBI/AAAAAAAAAPI/gmLu0d1YTMI/s1600/Ghardachin.jpg) ](http://4.bp.blogspot.com/-YaA4bq4r3Uc/UL8tt_lcZBI/AAAAAAAAAPI/gmLu0d1YTMI/s1600/Ghardachin.jpg) [![](http://www.void-troopers.com/vt/wp-content/uploads/2011/06/alien_A006.jpg) ](http://www.void-troopers.com/vt/wp-content/uploads/2011/06/alien_A006.jpg) [![](http://1.bp.blogspot.com/-mzdRfZgq0t0/Uf-dDHM62oI/AAAAAAAABEg/m7YLoB6600s/s400/Wollaghin_post.jpg) ](http://1.bp.blogspot.com/-mzdRfZgq0t0/Uf-dDHM62oI/AAAAAAAABEg/m7YLoB6600s/s400/Wollaghin_post.jpg) When you take look at some of these sub types some may have evolve to look like above. [http://ayay.co.uk/backgrounds/dinosaurs/herbivore/duckbilled-dinosaurs-2.jpg](http://ayay.co.uk/backgrounds/dinosaurs/herbivore/duckbilled-dinosaurs-2.jpg) [http://ayay.co.uk/backgrounds/dinosaurs/strange/armoured-dinosaurs-2.jpg](http://ayay.co.uk/backgrounds/dinosaurs/strange/armoured-dinosaurs-2.jpg) [http://ayay.co.uk/backgrounds/dinosaurs/armoured/armoured-dinosaurs.jpg](http://ayay.co.uk/backgrounds/dinosaurs/armoured/armoured-dinosaurs.jpg) ---
**Author:** ![sweat209](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sweat209](https://boards.straightdope.com/u/sweat209)\ **Post date:** [October 3, 2014, 10:42pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/38 "2014-10-03T22:42:12Z")
> [@naita](#): > > Yes, and it would do nothing to their size. Oxygen level is not a determining factor for the size of an animal. You do realize there were lots of small animals around at that time as well? But it would be too much oxygen for the human body. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [October 4, 2014, 7:53am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/39 "2014-10-04T07:53:12Z")
> [@sweat209](#): > > But it would be too much oxygen for the human body. No, it wouldn’t. Oxygen toxicity happens around 50% oxygen. ([Oxygen - Wikipedia](http://en.wikipedia.org/wiki/Oxygen#Toxicity) ) And the highest levels in the atmosphere was 35%. The [Wikipedia article on the geological history of oxygen](http://en.wikipedia.org/wiki/Geological_history_of_oxygen) also confirms my suspicion earlier that science isn’t settled on oxygen levels leading to giant sizes. > [@](#): > > The large size of insects and amphibians in the Carboniferous period, where oxygen reached 35% of the atmosphere, has been attributed, to the limiting role of diffusion in these organisms’ metabolism.[citation needed] But Haldane’s essay[12] points out that it would only apply to insects. However, the biological basis for this correlation is not firm, and many lines of evidence show that oxygen concentration is not size-limiting in modern insects.[9] Interestingly, there is no significant correlation between atmospheric oxygen and maximum body size elsewhere in the geological record.[9] Ecological constraints can better explain the diminutive size of post-Carboniferous dragonflies - for instance, the appearance of flying competitors such as pterosaurs and birds and bats.[9] ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [October 4, 2014, 7:56am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/40 "2014-10-04T07:56:21Z")
> [@sweat209](#): > > I wonder if dinosaurs never died out if some would look like this today. > > Remember some had hard exoskeleton systems. No. Just no. Some of them had armor. They did not have exoskeletons. There’s no way they’d develop exoskeletal limbs, or extra limbs, or extra eyes, or … well most of what makes those fantasy creatures fantastical. [Previous page](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525.md?page=1) [Next page](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525.md?page=3)