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.
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.
The Leatherback is an interesting case. 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.
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.
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.
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?
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:
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.
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?
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.
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.
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.
This is true for warm-blooded animals in general