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Can an amphibian, such as an axolotl, grow otter-like fur?

This fur would need to be hydrophobic and hydrodynamic to enable streamlined movement through the water. Additionally, it would trap heat -- although amphibians are cold-blooded. It could be covered in a waxy substance like the feathers of many ducks and other sea birds.
Is this a possible adaptation? Even if it weren't full body coverage. Would it inhibit their abilities, such as passive gas exchange?

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  • $\begingroup$ If the fur trapped water, that would give an advantage to travelling over land between water. Thus, the amphibian could move when the water dries up or when the food supply goes low. $\endgroup$
    – David R
    Commented May 19 at 14:06

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Of course it could... but why would it want to?

Growing fur takes energy and resources. For mammals, that's energy and resources well-spent. Homeothermic animals use fur as insulation, so that they don't have to spend even more energy keeping their body temperature constant.

Poikilothermic animals have little need for insulation. They maintain their body heat by absorption from the environment, which would be slowed by fur. As poikilotherms have less available energy than homeotherms, spending some of it on growing fur is counterproductive. The fur would make it take longer to warm up, so their activity cycle would just be delayed... and they would have wasted resources on growing hair. Better to not grow the hair.

However, there might be an edge case where a furry amphibian could warm itself above water, and use its hydrophobic hairs to insulate itself in cool water. However, for the most part, the water temperature is going to be similar to that of the air temperature, and this wouldn't help.

That's not to say that some poikilotherms don't have hair. Some animals have urticating hairs, that they use as a weapon against creatures that might try to eat them. However, while this may look insulating, it's defensive.

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Not a biologist, so take my word with a grain of salt, but...

Highly unlikely but not impossible

Theoretically, with the correct impetus, anything can evolve to have anything. It just takes a mutation that produces that thing, and then that mutated thing having successful offspring. Amphibians don't naturally have fur or the like, so it would take a considerable mutation to produce something fur-adjacent. From there, evolution would take the fur towards the lowest-cost highest-reward result, which might be otter-similar fur if the situation allows. If the species can figure out how to manage passive gas exchange even with fur (or just forgo it entirely), and it is very favorable to the offspring to have fur, then maybe it'll happen at some point.

Of course this necessitates a mutation that produces something fur-adjacent. Whether this could happen or not with one simple mutation depends on the specific biology of your creature in question, as well as the DNA complexity, the rate at which mutations occur, etc.

Take designing species evolution as a worldbuilding task more handwavey though. At a certain point, if you overengineer absolutely everything about a species' evolution, you will find that everything that has evolved to be what it is today would not have evolved to be anything different, and your world will be mundane. If you want furry amphibians, go for it. The kind of science people question is "wait, why doesn't the toxic gas work on that member of the party who's an alien", not "wait, how did the amphibious alien species of which the party member is a part evolve to have fur in their environment". I for one would be totally fine reading or playing or watching something with furred amphibians, and so would much of your target audience, I suspect.

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Theoretically, near anything could evolve. However, one thing making this difficult is that, if memory serves, fur is thought to have evolved from scales. However, less likely doesn't mean impossible. Hope this helped!

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Are you asking about an actual amphibian on Earth, or an amphibian-like alien creature?

Amphibians do not grow fur, so no. Yes, the trait could evolve, after all it's happened already: the ancestors of mammals did not have fur and their ancestors did not have the scales that evolved into fur. However, amphibians that evolved fur would almost certainly be considered a new class descended from amphibians.

If you're not talking about Earth life, however, then you're trying to fit things into categories that weren't created for them, and they're probably not going to fit perfectly. Alien creatures might very well have fur and still be more similar to Earth amphibians than to anything else.

If you are talking about Earth life, a possible alternative would be a symbiotic relationship with algae. Look at some pictures of algae-covered turtles for an example.

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hair is just your cells defecating useless stuff, all cells defecate useless stuff....get some cells specialized in extruding out keratin-like escrements...and you get hair.

pretty much every animal evolved something like this hair,scales,feathers,spikes.... because it's just so cheap to use the stuff your body needs to throw away anyway as a defensive layer.

and I'm pretty sure every animal does build up protective layers after getting bruised...on some of our body parts we build calluses made of skin, on other body parts we build layers of keratin.

so I'm sure frogs like all animals already have a similar mechanism that could eventually be adapted to create fur.

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A 'furry' amphibian could evolve, depending on what you define as fur. Consider, for example the Hairy Frog (Trichobatrachus robustus), which can be found in central Africa. But the fur would obviously not have the same purpose (insulation) as it does in mammels.

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