# 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:** 1
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [September 4, 2014, 9:23pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/1 "2014-09-04T21:23:54Z")
[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? ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [September 4, 2014, 10:28pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/2 "2014-09-04T22:28:07Z")
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. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 4, 2014, 11:36pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/3 "2014-09-04T23:36:43Z")
Depends on your environment. Are you allowed to increase atmospheric oxygen? Because in the Jurassic oxygen and CO2 levels were higher than today. That means more oxygen for large creatures to breathe, and higher plant productivity to support larger animals. Bring a Brachiosaur to today’s ecosystems and it would be gasping for air, and would starve to death because its digestive system wouldn’t be adapted to present-day plants. ---
**Author:** ![The\_Joker\_and\_the\_Thief](https://avatars.discourse-cdn.com/v4/letter/t/e79b87/32.png) [@The\_Joker\_and\_the\_Thief](https://boards.straightdope.com/u/The_Joker_and_the_Thief)\ **Post date:** [September 5, 2014, 1:12am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/4 "2014-09-05T01:12:57Z")
> [@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? I have no idea how they can claim that that’s the heaviest dinosaur to ever live.\* [Wikipedia](http://en.wikipedia.org/wiki/Dinosaur_size#Heaviest_dinosaurs) lists [at](http://en.wikipedia.org/wiki/Argentinosaurus_huinculensis) [least](http://en.wikipedia.org/wiki/Puertasaurus_reuili) [five](http://en.wikipedia.org/wiki/Futalognkosaurus_dukei) [dinosaurs](http://en.wikipedia.org/wiki/Antarctosaurus) with greater masses; including [one](http://en.wikipedia.org/wiki/Amphicoelias_fragillimus) that is twice the weight. It’s an exceptional find in terms of completeness, and it’s a huge dinosaur, but it’s not breaking any records. Huge dinosaurs keep on being discovered because paleontologists know that big dinosaurs get more press and publicity, and thus have an incentive to inflate estimates and focus on bigger dinosaurs. It’s the same reason that we hear about the cure for cancer every other day; it’s how to keep the money flowing in. Also, Dreadnoughtus is a bastardization of Latin, even by the lax standards of academic Latin. actually, I do know how. They claim that all of the other, larger dinosaurs are irrelevant because there aren’t enough bones, which seems like a nice way to shit on other researchers’ work. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [September 5, 2014, 1:21am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/5 "2014-09-05T01:21:55Z")
Very good physics based analysis here : [The Size of the Largest Land Animal](http://www.miketaylor.org.uk/dino/hokkanen/Size-Hokkanen.html) ---
**Author:** ![The\_Joker\_and\_the\_Thief](https://avatars.discourse-cdn.com/v4/letter/t/e79b87/32.png) [@The\_Joker\_and\_the\_Thief](https://boards.straightdope.com/u/The_Joker_and_the_Thief)\ **Post date:** [September 5, 2014, 1:33am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/6 "2014-09-05T01:33:38Z")
> [@am77494](#): > > Very good physics based analysis here : [The Size of the Largest Land Animal](http://www.miketaylor.org.uk/dino/hokkanen/Size-Hokkanen.html) Interesting. For anyone who doesn’t want to read it, the upper bounds are bones: 100-1000 metric tons muscles: 170 metric tons locomotion: 100-600 metric tons The article notes that these bounds are likely underestimates as larger animals likely have adaptations that allow for larger size and cannot be accounted for by scaling up smaller models. For reference, the largest known dinosaur has a mass of 122 metric tons, though this somewhat speculative as the bones were lost in the late 1800s. ---
**Author:** ![Sailboat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sailboat/32/461_2.png) [@Sailboat](https://boards.straightdope.com/u/Sailboat)\ **Post date:** [September 5, 2014, 1:55am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/7 "2014-09-05T01:55:32Z")
The Wikipedia article on dinosaur size lists Dreadnoughtus at sixth place in mass, at 59.3 tons. ---
**Author:** ![j\_sum1](https://avatars.discourse-cdn.com/v4/letter/j/8baadc/32.png) [@j\_sum1](https://boards.straightdope.com/u/j_sum1)\ **Post date:** [September 5, 2014, 2:39am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/8 "2014-09-05T02:39:45Z")
At what point do issues such as circulation and transportation of oxygen to tissues become relevant? I know that the latter renders infeasible the mega insects that we visualised in 50s sci-fi movies. ---
**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, 4:07am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/9 "2014-09-05T04:07:59Z")
[This paper](http://onlinelibrary.wiley.com/doi/10.1111/j.1469-185X.2010.00137.x/full) (which focuses on sauropods and how/why some of them were able to have gotten so large, but can also be extrapolated to any large terrestrial animal) discusses some of the constraints which must be addressed for extreme gigantism. It doesn’t necessarily address the question of maximum size, but it does discuss the many issues with which a very large animal must contend. ---
**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:** [September 5, 2014, 11:50am UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/10 "2014-09-05T11:50:30Z")
> [@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. 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. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [September 5, 2014, 12:15pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/11 "2014-09-05T12:15:45Z")
> [@j\_sum1](#): > > At what point do issues such as circulation and transportation of oxygen to tissues become relevant? I know that the latter renders infeasible the mega insects that we visualised in 50s sci-fi movies. 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. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 5, 2014, 12:43pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/12 "2014-09-05T12:43:09Z")
There’s a lot of focus on the structural integrity/strength of a large animal’s body, but for a long time I’ve wondered about fluid mechanics. Pressure at the bottom of a static column of liquid is proportional to the column’s height. In addition to the problem of moving blood through a humungous network of vessels, you’d also have the problem of blood pressure in the lower extremities being _much_ higher than in the upper extremities. For an animal 33 feet tall, the blood pressure at the bottom of its feet will be about 15 psi _greater_ than whatever the pressure is in its head. Compare this with human blood pressure, typically ~2 psi at the upper arm. You’d also experience massive fluctuations in pressure as you move a limb up or down, which is extremely important in the animal’s brain. Example, if you (a human being) do a handstand, the blood pressure inside your head rises by about 2.5 psi. Taller animals have it even worse. ISTR that giraffes have specially adapted blood vessels in their necks to keep the pressure in their head from skyrocketing when the bend down to drink water. (note that whales don’t have this problem because regardless of their orientation, the external water pressure against each part of their body is very closely matched to the internal blood pressure at that same depth below the surface of the ocean; whales can be gigantic and not give a damn whether they’re head-up, level, or head-down). So for a land animal to be extremely large, blood vessel walls need to be much thicker than ours are in order to accomodate potentially very large pressures (even if those pressures are transient, as when stooping to drink ground water). Even capillaries would need to be thick-walled, lest they rupture on a regular basis. In addition to limiting O2 transfer, I expect the biological cost for constructing/maintaining such a vessel network might get pretty large. I’m at a loss to estimate an upper size limit, but surely the circulatory system is a determining factor. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [September 5, 2014, 12:46pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/13 "2014-09-05T12:46:48Z")
Here’s the info on giraffes: [Giraffe circulatory adaptations](http://en.wikipedia.org/wiki/Giraffe#Internal_systems) > [@Wikipedia](#): > > The circulatory system of the giraffe has several adaptations for its great height. Its heart, which can weigh more than 11 kg (25 lb) and measures about 60 cm (2 ft) long, must generate approximately double the blood pressure required for a human to maintain blood flow to the brain. As such, the wall of the heart can be as thick as 7.5 cm (3.0 in). Giraffes have unusually high heart rates for their size, at 150 beats per minute.:76 In the upper neck, a rete mirabile prevents excess blood flow to the brain when the giraffe lowers its head. The jugular veins also contain several (most commonly seven) valves to prevent blood flowing back into the head from the inferior vena cava and right atrium while the head is lowered. Conversely, the blood vessels in the lower legs are under great pressure (because of the weight of fluid pressing down on them). To solve this problem, the skin of the lower legs is thick and tight; preventing too much blood from pouring into them. ---
**Author:** ![filmstar-en](https://avatars.discourse-cdn.com/v4/letter/f/50afbb/32.png) [@filmstar-en](https://boards.straightdope.com/u/filmstar-en)\ **Post date:** [September 5, 2014, 12:57pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/14 "2014-09-05T12:57:58Z")
Insects have a simple breathing mechanism that relies on passive diffusion of gases through holes in each segment and internal tubes to deliver the air to cells. Some larger ones pump the abdomens to move air in and out, but the there is a limit to its efficiency. They have to keep the distance from the outside amosphere short to their cells short, which limits their size. Here is the giant Weta, the worlds biggest insect weighing in at 71g. [![]( " - YouTube") ](https://www.youtube.com/watch?v=7filPzTK4R4) Animals and Fish have a more advanced active respiration system that is energy intensive. Insects are limited by design. [http://breatheornot.com/2012/04/23/no-lungs-no-gills-how-do-insects-breathe/mo](http://breatheornot.com/2012/04/23/no-lungs-no-gills-how-do-insects-breathe/mo) It would be interesting to speculate how big they could get if atmospheric oxygen were higher, as it has been at various points in prehistory. ---
**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:** [September 5, 2014, 2:45pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/15 "2014-09-05T14:45:52Z")
> [@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.” Side question: how do they know it was still growing when they only have fossils? It says “bone growing cells will morph” in the article but there aren’t any left to look at. ---
**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, 4:16pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/16 "2014-09-05T16:16:23Z")
> [@Really\_Not\_All\_That\_Bright](#): > > Side question: how do they know it was still growing when they only have fossils? It says “bone growing cells will morph” in the article but there aren’t any left to look at. Per [the paper](http://www.nature.com/srep/2014/140904/srep06196/pdf/srep06196.pdf) (.pdf): > [@](#): > > Remarkably, multiple lines of evidence indicate that, despite its > enormous size, MPM-PV 1156 was not osteologically mature at > death. The scapula remains unfused to the coracoid (Fig. 2B, > Supplementary Fig. 15), and the posteromedial margin of the coracoid > foramen abuts the scapula; both of these morphologies have > been cited as indicators of osteological immaturity in sauropods50,51. > Moreover, although histological analysis of the humerus > indicates that its cortical bone has undergone extensive secondary > remodelling, the element retains a thick layer of vascularized > fibrolamellar bone between the remodelled inner cortex and the > periphery of the periosteal surface (see Supplementary Information). > It also lacks lines of arrested growth or an external fundamental > system52 (Fig. 2G), which may indicate osteological > immaturity53 (although Company54 proposed this as a synapomorphy > of Titanosauria rather than an indicator of ontogenetic stage). > A similar pattern is observed in the dorsal ribs, which are extensively > remodelled but retain primary fibrolamellar bone tissue > towards the periosteal surface. Recent analyses55,56 have suggested > that titanosaurs may have developed extensively remodelled tissues > after reaching sexual maturity but prior to attaining their > maximum size. Thus, the presence of unremodelled fibrolamellar > bone in the outer cortex of the MPM-PV 1156 humerus suggests > that this massive Dreadnoughtus individual was still growing at > the time of its death. ---
**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:** [September 5, 2014, 4:30pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/17 "2014-09-05T16:30:01Z")
Thanks. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [September 5, 2014, 5:30pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/18 "2014-09-05T17:30:15Z")
There’s some speculation that the teeny brains of sauropods mitigated the blood pressure problems mentioned above. ---
**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 5, 2014, 10:14pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/19 "2014-09-05T22:14:16Z")
> [@Lemur866](#): > > Depends on your environment. Are you allowed to increase atmospheric oxygen? Because in the Jurassic oxygen and CO2 levels were higher than today. That means more oxygen for large creatures to breathe, and higher plant productivity to support larger animals. > > Bring a Brachiosaur to today’s ecosystems and it would be gasping for air, and would starve to death because its digestive system wouldn’t be adapted to present-day plants. Photosynthesis (which I assume is what you’re using to infer higher plant productivity) uses carbon dioxide but is competitively inhibited by oxygen, so having higher levels of both (O2 and CO2) wouldn’t _necessarily_ give you higher productivity. It would depend on the balance between them, and also on temperature (high temperature promotes oxygenation relative to carboxylation, so oxygen becomes more of a ‘problem’.) Oxygen also has other negative effects on plants (and at high enough levels, for animals as well), due to its tendency to form extremely reactive species (superoxides, etc.). 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. > **[Oxygen toxicity](https://en.wikipedia.org/wiki/Oxygen_toxicity)** > > Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen (O2) at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes. Historically, the central nervous system condition was called the Paul Bert effect, and the pulmonary condition the Lorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen... ---
**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 5, 2014, 10:41pm UTC](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525/20 "2014-09-05T22:41:49Z")
> [@The\_Joker\_and\_the\_Thief](#): > > I have no idea how they can claim that that’s the heaviest dinosaur to ever live.\* > [Wikipedia](http://en.wikipedia.org/wiki/Dinosaur_size#Heaviest_dinosaurs) lists [at](http://en.wikipedia.org/wiki/Argentinosaurus_huinculensis) [least](http://en.wikipedia.org/wiki/Puertasaurus_reuili) [five](http://en.wikipedia.org/wiki/Futalognkosaurus_dukei) [dinosaurs](http://en.wikipedia.org/wiki/Antarctosaurus) with greater masses; including [one](http://en.wikipedia.org/wiki/Amphicoelias_fragillimus) that is twice the weight. It’s an exceptional find in terms of completeness, and it’s a huge dinosaur, but it’s not breaking any records. > Huge dinosaurs keep on being discovered because paleontologists know that big dinosaurs get more press and publicity, and thus have an incentive to inflate estimates and focus on bigger dinosaurs. It’s the same reason that we hear about the cure for cancer every other day; it’s how to keep the money flowing in. > > Also, Dreadnoughtus is a bastardization of Latin, even by the lax standards of academic Latin. > > actually, I do know how. They claim that all of the other, larger dinosaurs are irrelevant because there aren’t enough bones, which seems like a nice way to shit on other researchers’ work. They know there were titanosaurs bigger than Dreadnoughtus; what they don’t know is how much bigger. What’s unique about the Dreadnoughtus holotype is that they can be sure it’s mass falls into a fairly narrow range. With the larger sauropods, estimates can vary by a factor of two, which isn’t much more than an informed guess. [Next page](https://boards.straightdope.com/t/whats-the-upper-limit-on-the-size-of-land-animals/697525.md?page=2)