# Why are most marine mammals “largish”? **URL:** \ **Category:** Factual Questions\ **Created:** [July 16, 2019, 2:30am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157 "2019-07-16T02:30:03Z")\ **Posts on this page:** 13\ **Page:** 2
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 16, 2019, 1:24pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/21 "2019-07-16T13:24:54Z")
Loanwords in English can be properly pluralized either according to English rules or according to the rules of their language of origin: Both are correct (though some might not be used much, like “bacteriums”). So “platypuses” and “octopuses” are both fine. The difficulty is that “platypus” and “octopus” both look like they originated as Latin 2nd-declension masculine nouns, in which case they _would_ pluralize by replacing the -us with -i. But they’re not; they actually originate with Greek, so pluralizing them according to their language of origin would mean using Greek rules, not Latin. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [July 16, 2019, 1:30pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/22 "2019-07-16T13:30:22Z")
Size is a variable when considered as an evolutionary characteristic. It has both advantages and disadvantages. Underwater the energy costs of larger size are about thermal issues, mostly keeping in heat. On land the energy cost has to include keeping the body off the ground, and a much greater budget for locomotion. (hence the very long necks on the largest of dinosaurs) A significant advantage of size is survival against predation, as well as the thermal issues. Land animals can deal with thermal issues with sweat, and basking, which are not as effective underwater, and generally only deal with issue where retention of heat is not an objective. Puffins inhabit a large range of latitudes. Puffin size in these populations varies directly with latitude, each population having the size that balances the benefits of largeness and smallness. Tris * * * I believe in secrets you were not meant to know. Of course, I never talk about them. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 16, 2019, 3:18pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/23 "2019-07-16T15:18:13Z")
> [@Filbert](#): > > Actually Leatherback turtles appear to be able to keep a significantly [higher](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.559.2704&rep=rep1&type=pdf)[Pdf] body temperature than the surrounding water, at least the adults. > > They sometimes show up surprisingly far North, where other turtles would be too cold to keep active, including round the UK on occasion. It’s probably not co-incidence that they are the largest turtle species. The [Leatherback is an interesting case.](http://bytesizebio.net/2010/11/20/warm-blooded-turtles/) Using the popular terms “warm-blooded” and “cold-blooded” oversimplifies things. Animal physiologists use the contrasting terms _endothermic_ (generating body heat mostly by internal metabolic processes, like mammals and birds) and _ectothermic_ (getting heat mostly from the environment like most reptiles and amphibians), and _homeothermic_ (maintaining a stable body temperature) and _poikilothermic_ (having a variable body temperature). Leatherbacks generate a significant amount of metabolic heat because they are always swimming. But they can get away without having much insulation because they are so big they lose body heat slowly. (Maintaining body heat through huge size has been referred to as gigantothermy.) They also have a countercurrent exchange system at the base of their flippers that prevent them from losing so much heat through them. The Leatherback is endothermic and homeothermic to a degree, but not as good at it as a mammal. But the reason it can do this is because of its size. Smaller sea turtles are confined to the tropics and subtropics or areas of warm currents further north. If they enter water that is too cold they become too sluggish to feed. ---
**Author:** ![Wallaby](https://avatars.discourse-cdn.com/v4/letter/w/dc4da7/32.png) [@Wallaby](https://boards.straightdope.com/u/Wallaby)\ **Post date:** [July 16, 2019, 11:30pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/24 "2019-07-16T23:30:07Z")
> [@puzzlegal](#): > > And, hmm, platypus (what’s the plural?) are tiny, but they live where it’s very warm. Actually, platypus live in pretty much all parts of Australia where there are suitable rivers - from the tropics to snowy mountains. However, they don’t like it _ **too** _ hot, and are one of the many species whose habitats are threatened by global warming. There’s a thought they may become restricted to the south-eastern forests and Tasmania. Interestingly, their core body temperature is far lower than most mammals, and it can vary much more than other mammals, depending on activity, weather etc. However, when incubating eggs, they do keep their temerature more constant. Very interesting creatures. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [July 17, 2019, 2:13am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/25 "2019-07-17T02:13:32Z")
> [@purplehorseshoe](#): > > Whale lungs collapse during a deep dive? How do they deal with that? Gracefully. As **brossa** has noted, the oxygen they need is in their blood & muscles, from the breathing they did prior to the dive. The fact that their lungs hold a relatively small amount (which has compressed with depth) is unimportant. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [July 17, 2019, 3:20am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/26 "2019-07-17T03:20:52Z")
> [@Xema](#): > > Gracefully. > > As **brossa** has noted, the oxygen they need is in their blood & muscles, from the breathing they did prior to the dive. The fact that their lungs hold a relatively small amount (which has compressed with depth) is unimportant. It’s not a collapsed lung in the same sense as a person having a collapsed lung - in people, a collapsed lung means that there is a hole in the lung somewhere that allows air into the potential space between the lung and chest wall. In that scenario, contraction of the diaphragm and expansion of the chest wall just pull air into that space, and the lung itself shrivels up and no longer exchanges gas well. In the whale, the collapse is just from the external pressure being so high that the air is all squeezed into a smaller volume; so small that the alveoli go completely flat, and the residual compressed air sits in the larger airways like the bronchi. Incidentally, this limits the absorption of high-pressure gases into the bloodstream, since they are somewhat sequestered from the air-exchange surfaces. Alveoli are coated with a thin layer of lubricating surfactant, which modulates their elastic behavior. Without surfactant, an alveolus that collapses completely is very difficult to reopen; it requires high pressures to ‘pop’ it open, after which it expands more easily (remember how a latex balloon is hardest to blow up right at the beginning, but gets easier the larger the balloon gets). Research on some diving mammals has shown that their surfactant is better at allowing collapsed alveoli to re-expand than that of land mammals. Their lungs also tolerate larger forces than ours do; their standard breath moves more air than our most violent cough or sneeze. ---
**Author:** ![Freddy\_the\_Pig](https://avatars.discourse-cdn.com/v4/letter/f/a587f6/32.png) [@Freddy\_the\_Pig](https://boards.straightdope.com/u/Freddy_the_Pig)\ **Post date:** [July 17, 2019, 6:17am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/27 "2019-07-17T06:17:19Z")
> [@Colibri](#): > > Because water conducts heat much better than air. A warm-blooded animal immersed in water loses heat much more rapidly than it does in air. Larger animals have a lower surface to volume area and lose heat slower. Even so, they need a thick layer of blubber to insulate themselves. A small mammal simply can’t have thick enough fat to keep itself warm. But what about penguins? Penguins are warm-blooded. The smaller Antarctic species, such as the Gentoo or Adelie, are not exactly tiny, but smaller than any marine mammal that I know of. And they live in sea water. They’re not full-time underwater like a dolphin or whale, but maybe comparable to a seal. Why are there no small penguin-sized marine mammals? Or are there? ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [July 17, 2019, 8:24am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/28 "2019-07-17T08:24:03Z")
> [@Freddy\_the\_Pig](#): > > Why are there no small penguin-sized marine mammals? Or are there? **Colibri** mentioned the Sea Otter, which I think is just about the length of an Emperor penguin. The sea otter has the very dense pelt, the penguins have the very impenetrable feathers, and both have [other temperature-management body features](https://www.coolantarctica.com/Antarctica%20fact%20file/science/cold_penguins.php): > [@](#): > > Penguins must remain active while in water to generate body heat. Unlike other warm blooded Antarctic marine animals such as seals and whales, penguins are still relatively small, so the “be big” strategy is not taken as far as needed to remain warm even at rest in the sea as in seals and whales. Partly land-dwelling marine mammals such as seals can AFAIK spend much longer in the water at a time than penguins, up to months or even years. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [July 17, 2019, 8:39am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/29 "2019-07-17T08:39:48Z")
There is a correlation between the size of an adult penguin and the coldness of the environment they inhabit. As a general rule, the colder the environment the larger the penguin. In addition, penguin feathers are highly efficient at insulating, even in water. They have a heat-exchange adaption to avoid heat-loss from their limbs. Birds in general tend to have higher body temperatures than mammals, maybe they burn more of their food as heat? ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [July 17, 2019, 9:35pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/30 "2019-07-17T21:35:00Z")
> [@Machine\_Elf](#): > > …Decompression sickness happens when nitrogen that was dissolved in your blood from the air in your lungs while you were in a high-pressure comes out of solution when you return to a low-pressure environment. It doesn’t matter whether you put the air in your lungs under low pressure and then move to a high-pressure environment (as whales do), or move to a high-pressure environment and then put the air in your lungs (as SCUBA divers do). > > [Repetitive free-diving (with minimal surface intervals) has been shown to cause decompression sickness.](https://skin-diver.com/2018/08/23/can-freediving-cause-dcs/) Thanks for posting this. I was scuba diving in the Caribbean back in May, and jumped in the water with a mask & snorkel during my surface interval between dives. I saw something on the bottom (about 20 feet down), and thought about swimming down to check it out, but was unsure if freediving affected my surface interval, so I stayed on the surface. Apparently I was correct to do so. [Can Freediving Cause DCS?](https://skin-diver.com/2018/08/23/can-freediving-cause-dcs/) > [@Fred Bove](#): > > Another situation that has not been studied involves freediving after scuba diving. There are several stories of divers getting DCS this way. A surface interval spent freediving is not really a surface interval and the calculation of decompression will not be correct. The best advice is to avoid freediving during surface intervals. If you want to snorkel, stay on the surface. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [July 17, 2019, 9:42pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/31 "2019-07-17T21:42:57Z")
> [@puzzlegal](#): > > And, hmm, platypus (what’s the plural?) are tiny, but they live where it’s very warm. Wikipedia describes them as being 0.7kg to 2.4kg (1.5 to 5.3 lb). That’s not exactly _tiny_. That’s almost 400 times heavier than the [smallest land mammal](https://en.wikipedia.org/wiki/Etruscan_shrew). ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [July 18, 2019, 3:50am UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/32 "2019-07-18T03:50:25Z")
I love how the wikipedia article mentions the shrew’s exact dentition. Some poor biologist counted the teeth of animals smaller than a finger _joint_ that musta been some magnifying glass. ---
**Author:** ![zimaane](https://avatars.discourse-cdn.com/v4/letter/z/a3d4f5/32.png) [@zimaane](https://boards.straightdope.com/u/zimaane)\ **Post date:** [July 18, 2019, 2:43pm UTC](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157/33 "2019-07-18T14:43:09Z")
> [@Broomstick](#): > > There is a correlation between the size of an adult penguin and the coldness of the environment they inhabit. As a general rule, the colder the environment the larger the penguin. In addition, penguin feathers are highly efficient at insulating, even in water. They have a heat-exchange adaption to avoid heat-loss from their limbs. Birds in general tend to have higher body temperatures than mammals, maybe they burn more of their food as heat? This is true for warm-blooded animals in general > **[Bergmann's rule](https://en.wikipedia.org/wiki/Bergmann%27s_rule)** > > Bergmann's rule is an ecogeographical rule that states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer regions. The rule derives from the relationship between size in linear dimensions meaning that both height and volume will increase in colder environments. Bergmann's rule only describes the overall size of the animals, but does not include body proportion... [Previous page](https://boards.straightdope.com/t/why-are-most-marine-mammals-largish/837157.md?page=1)