# Where are the small aquatic mammals? **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2005, 4:12am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742 "2005-04-11T04:12:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 4:12am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/1 "2005-04-11T04:12:18Z")
Why are there no chihuahua sized porpoise? Or rat sized seals? I’m not talking about small semi-aquatics like beaver, mink, or otter. What I’m wondering about are the full time aquatics like cetaceans or the mostly aquatic like sea lions and seals. All that I’ve ever seen are man sized or much larger. Why? On land, we have large animals like elephants and giraffes, all the way down to jerboas and tiny South American tree monkeys and even others well under a pound. Are there no small aquatic mammals? (Reasons if so, please) Or do they exist and just don’t get any press? A whale the size of a small mouth bass would be so cool, ya know? ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [April 11, 2005, 4:29am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/2 "2005-04-11T04:29:03Z")
Warm-bloodedness, small body size, and the relatively high heat conduction properties of water don’t make for a good mix. But I give you [the Russian Desman](http://animaldiversity.ummz.umich.edu/site/accounts/information/Desmana_moschata.html) (there’s a Spanish Desman as well, though nobody expects one! :)) and [the otter shrews](http://animaldiversity.ummz.umich.edu/site/accounts/classification/Potamogalinae.html#Potamogalinae), as examples of small aquatic insectivores. The otters, including the sea otter, are obvious qauatic fissiped carnivores. There are several groups of rodents with aquatic members, the most obvious being the beaver and muskrat. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 4:32am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/3 "2005-04-11T04:32:56Z")
But, I already discounted the semi aquatics, like beaver and otter in the OP. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 4:44am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/4 "2005-04-11T04:44:14Z")
_Marine_ mammals may a better term for what I’m looking for… (thanks for the reply, tho. ) Would seals and sea lions be Marine or Aquatic? Anyways, hopefully this narrows down my question a bit. Small Marine Mammals. ---
**Author:** ![yBeayf](https://avatars.discourse-cdn.com/v4/letter/y/e274bd/32.png) [@yBeayf](https://boards.straightdope.com/u/yBeayf)\ **Post date:** [April 11, 2005, 4:49am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/5 "2005-04-11T04:49:13Z")
Part of it is that fish have thousands of offspring over the course of their life. Mammals (and for that matter, birds and reptiles) just don’t breed fast enough to make up for numbers lost to predation, so the only examples of higher vertebrates we see in the oceans are those that are big enough to not be immediately eaten as soon as they get in the water. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 11, 2005, 5:19am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/6 "2005-04-11T05:19:26Z")
Of course there is no factual answer to your question, but **Poylcarp** ’s first sentence probably explains it. Heat loss is much, much great in water than in air. Smaller animals have more surface area per unit volume explosed to the elements. Bigger animals have to eat more, of course, but they can eat less per pound than smaller animals, without losing more heat. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [April 11, 2005, 5:39am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/7 "2005-04-11T05:39:05Z")
The fact that whales evolved from land-dwelling mammals that were about horse-sized argues for the theory that sea life tends to select for larger size in warm-blooded creatures. ---
**Author:** ![Pullet](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Pullet](https://boards.straightdope.com/u/Pullet)\ **Post date:** [April 11, 2005, 6:33am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/8 "2005-04-11T06:33:19Z")
The crappy part with many “why” questions in evolution is that the answer is usually “that’s just the way it happened.” There are so many variables. It is difficult to point to one or the other as the defining reason unless the question is demonstrated in so many different places that some overarching controling principle is likely. For example, the reason why there are not fist-sized one-celled organisms is because physics won’t allow diffusion across the cell’s membranes and volume efficiently enough to continue its life. So, the cell divides to keep its surface area to volume ratio optimal. Hence, why every living thing is comprised of cells (or cell) that are more or less the same size. Why aren’t there tiny aquatic mammals? Heat conservation is likely. So is reproductive rate (although I would argue that the typical mouse replicates fast enough to beat out predation). Evolutionary happenstance. Irritating as all hell. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 11, 2005, 7:00am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/9 "2005-04-11T07:00:35Z")
> [@yBeayf](#): > > Part of it is that fish have thousands of offspring over the course of their life. Mammals (and for that matter, birds and reptiles) just don’t breed fast enough to make up for numbers lost to predation, so the only examples of higher vertebrates we see in the oceans are those that are big enough to not be immediately eaten as soon as they get in the water. I don’t follow this. Are you claiming that the rate of predation is higher in the water then on land? If so, what is the basis of this claim? And surely a great white shark can gobble up a dolphin calf with ease, if the mother fails to protect it. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 11, 2005, 7:21am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/10 "2005-04-11T07:21:50Z")
There are otters that live primarily in marine environments; sea otters. I know you discounted these in the OP, but I honestly can’t understand why; they are more agile on land than seals, but not particularly more or less amphibious. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [April 11, 2005, 7:36am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/11 "2005-04-11T07:36:39Z")
> [@Mangetout](#): > > There are otters that live primarily in marine environments; sea otters. I know you discounted these in the OP, but I honestly can’t understand why; they are more agile on land than seals, but not particularly more or less amphibious. One significant difference in physiology, besides feet vs flippers, is that otters don’t have a layer of blubber as do pinnipeads (seals, sea lions, and walruses). They rely on their dense fur to trap air for insulation. Also, when they are in the water, they are rarely submerged, like pinnipeds. Most of the time they float on their backs with at least half of their body above the surface. This might be enough to explain their ability to maintain a smallerl body size. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 11, 2005, 8:45am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/12 "2005-04-11T08:45:16Z")
Sure, and in fact different survival strategies aren’t all that surprising, given that otters are not (I think) as closely related to pinnipeds as they are to each other. I suppose the bottom line answer is that, aside from pure bad luck (i.e. the potential ancestor population of a small-sized cetacean/pinniped being wiped out by some catastrophe), the reason we don’t have small cetaceans and pinnipeds is going to be one of: - It just wouldn’t work that way - perhaps conditions are simply so harsh that only certain solutions work at all. or - Some other animal with a different solution to small-body-size survival (in that particular environment) has already staked out the niche - for example, if you think about it, penguins and seals do pretty much the same thing; they even have _broadly_ similar adaptations of body to survive in similar environments - it may just be that there are no smaller seals (in those environments where both exist together) because _the penguins are better at being small seals than genuine small seals could ever be_ - likewise, it may be that there are no huge penguins _because the seals are better at being huge penguins than genuine huge penguins could ever be_. If that makes any sense. ---
**Author:** ![Grendel\_s\_Father](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grendel\_s\_Father](https://boards.straightdope.com/u/Grendel_s_Father)\ **Post date:** [April 11, 2005, 11:13am UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/13 "2005-04-11T11:13:40Z")
> [@Mangetout](#): > > - Some other animal with a different solution to small-body-size survival (in that particular environment) has already staked out the niche - for example, if you think about it, penguins and seals do pretty much the same thing; they even have _broadly_ similar adaptations of body to survive in similar environments - it may just be that there are no smaller seals (in those environments where both exist together) because _the penguins are better at being small seals than genuine small seals could ever be_ - likewise, it may be that there are no huge penguins _because the seals are better at being huge penguins than genuine huge penguins could ever be_. If that makes any sense. I would guess that this kind of competition is a larger factor than most of the posts here have suggested. A whale the size of a small mouth bass would be cool, but it would probably be in direct competition with fish, which evolved long before mammals and are well suited to their niche. Mammals would have a hard time pushing the already well adapted fish aside if they started getting smaller, and the added body heat issue would make it nearly impossible (or at least very unlikely to happen). ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 1:39pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/14 "2005-04-11T13:39:36Z")
Okay, the niche argument is making sense. Thanks all. As for the dismissing of otters, whelks, and what have you, in my mind as I pondered this, I was principally thinking of the truly marine adapted. Flippers instead of feet, fluked tails and/or rear limbs, no discernable neck, sleek bodies… That type of marine mammal. In one reference work I found, polar bears were listed as a marine mammal! Sure they are, if we consider behavior… ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 11, 2005, 1:53pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/15 "2005-04-11T13:53:39Z")
> [@NoClueBoy](#): > > As for the dismissing of otters, whelks, and what have you, in my mind as I pondered this, I was principally thinking of the truly marine adapted. Flippers instead of feet, fluked tails and/or rear limbs, no discernable neck, sleek bodies… That type of marine mammal. Sorry to keep banging on about otters, but in terms of marine adaptation, water vole is to otter as otter is to sea lion as sea lion is to seal as seal is to dolphin as dolphin is to whale (I know they aren’t necessarily closely related, but they occupy the same sorts of niches and body-forms that their related ancestors might have) - there’s no particularly sharp dividing line, only arbitrary ones. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 2:05pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/16 "2005-04-11T14:05:20Z")
And I took the arbitrary one. Besides, an ottter shot my Pa. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 11, 2005, 2:27pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/17 "2005-04-11T14:27:54Z")
What about the whelk? ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [April 11, 2005, 2:54pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/18 "2005-04-11T14:54:19Z")
You are as obsessed with whelks as Ford Prefect, I swear. They never caught the whelk. I’m still searching for him on major golf courses to this day. ---
**Author:** ![wonderwench](https://avatars.discourse-cdn.com/v4/letter/w/35a633/32.png) [@wonderwench](https://boards.straightdope.com/u/wonderwench)\ **Post date:** [April 11, 2005, 3:02pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/19 "2005-04-11T15:02:45Z")
> [@yBeayf](#): > > Part of it is that fish have thousands of offspring over the course of their life. Mammals (and for that matter, birds and reptiles) just don’t breed fast enough to make up for numbers lost to predation, so the only examples of higher vertebrates we see in the oceans are those that are big enough to not be immediately eaten as soon as they get in the water. Bingo. That was my initial thought as well. The ocean is a big bowl of food. Little mammals just can’t breed fast enough and there isn’t a way for them to burrow away for protection as they do on land. The beach environments don’t provide adequate shelter either. 90% of baby rabbits never grow up. The average lifespan for those that do reach maturity is less than two years. And they have underground burrows in which to hide from predators. ---
**Author:** ![Twoflower](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/twoflower/32/22_2.png) [@Twoflower](https://boards.straightdope.com/u/Twoflower)\ **Post date:** [April 11, 2005, 4:12pm UTC](https://boards.straightdope.com/t/where-are-the-small-aquatic-mammals/298742/20 "2005-04-11T16:12:22Z")
> [@John Mace](#): > > I don’t follow this. Are you claiming that the rate of predation is higher in the water then on land? If so, what is the basis of this claim? And surely a great white shark can gobble up a dolphin calf with ease, if the mother fails to protect it. Absolutely – there’s nowhere to hide in the open ocean. No undergound dens, no forest or brushlands, you’re just out there. If you’re air-dependent & therefore surface- bound, it’s best not to be snack-sized. The smaller marine mammals such as seals and sea otters all live in rocky shore areas or kelp forests where there are mammal-apporpriate hiding places. The larger pelagic (open-ocean going)species keep their young very close to them until they’re big enough to fend off the average predator.