I'm trying to write hack-ish (As in, I'm a hack) science fiction that is realistic except where it is inconvenient to me. That being said, animals are not an area I want to handwave. I want the animals on a planet humans colonize to fall under different categories than those of Earth. I've got some stuff "down pat", but I've hit a roadblock in trying to come up with some alternative skin coatings. On Earth, we have things like

  • Scales
  • Fur
  • Bare Skin
  • Feathers And
  • Exoskeletons

I ask you; What sort of skin/coating might an animal from a planet with 20% lower gravity and higher air pressure at sea level evolve?

Right now, I'm thinking that some animals might take indigestible components of their food and force them to go through a "Deconstruction system" where they are processed into a form that can be excreted as a paste over the body that hardens to provide protection and insulation based on what they've eaten. Is this viable?

  • $\begingroup$ It sounds like a cocoon that can fly. If you want a tender soft skin go for gel/jelly type such as slime and for protection opt for crystalline type the organism's DNA is silicon based so it is no surprise if it can grow quartz on its back and covers the entire body. If you want airborne capable just make up a organ that produce hydrogen or helium gas for buoyancy then it can also breathe flame through it nostril. Bonus: camouflage. $\endgroup$ – user6760 Apr 5 '15 at 8:34
  • $\begingroup$ @user6760 Thank you for your contribution! I would never have thought of that. $\endgroup$ – Jetscooters Apr 5 '15 at 13:46
  • $\begingroup$ Sounds like pooping. If it's indigestible, how does it get broken down, transported, and then used in some manner that relies on its detailed properties? $\endgroup$ – JDługosz Apr 5 '15 at 19:33
  • $\begingroup$ @JDługosz I should clarify, indigestible is probably not the best way to put it. What I SHOULD say is unusable or unnecessary for NUTRITION. Once it's passed through the digestive system of the creature, if it was defined as unneeded but usable, it would be sent through a "deconstruction system". Or, now that I think of it, give them hyper effective digestion and combine the two systems. They would still not be able to digest, process, or use things impervious to acid/enzymes in any way. $\endgroup$ – Jetscooters Apr 5 '15 at 20:12
  • $\begingroup$ Many things are used without being broken down further. If you envision something beyond (large) molecules, you need a way of transporting it and dealing with the size. Maybe whole organells or cell structures like tubuels are scavenged intact, unlike the situation here. Diatom shells come to mind: hard in-organic parts can be used as dead building blocks without the animal having the specialized (from another branch of life) ability to produce them or process that substance in raw form. $\endgroup$ – JDługosz Apr 5 '15 at 20:19

Always consider the purpose and desired behaviors of an organ when trying to determine how it will look.

Every skin material is "chosen" because it fits a role. Scales are great because they are rather impervious (which is a big deal if you are in an environment where dodging blows is difficult, or where forces like sandstorms reign supreme). Exoskeletons do this to an extreme, though they pay a price in terms of growing pains. Bare skin, on the other hand, focuses on maximum flexibility and pliability.

Generally speaking, if you look at skins of animals on Earth, gravity and air pressure have little to nothing to do with choices. The skin supports very little of the body, so the effects of gravity are minimal (other than the feet. The skin of the feet can be interesting). Air pressure has almost no effect at all until you get down into the single-digit torr range (vacuums) where the ability to create a pressure tight seal becomes useful.

As for your deconstruction system, it seems valid to me. Elephants do the same thing with mud. The only concern I might have is the health concerns of spreading processed waste (and the energy it takes to process it).

It actually strikes me as what I think of as a "falling off the bicycle" point for evolution. Realistically speaking, its much cheaper to maintain a skin compound that is emitted from the skin, rather than manually applied, especially when you think about the need for adults to spread matter on the children before they learn to do it themselves. In famine cycles, you'd have a double-whammy of no food and more damage from the outside environment. However, this sort of strange thing does seem to happen from time to time. Every now and then evolution picks something really wonky and runs with it. I recently ran across a species of bird where the males announce their stature to the females by blowing up a large inflatable red sack under their beak. The sac is nearly as large as the bird, when fully inflated, and takes 20 minutes for the male to inflate. This is totally absurd, and yet has proven to be the most effective way to pass his genes from generation to generation.

If I saw a species with such a waste-matter insulation, I would expect to see them on the bleeding edge of what their genome could do for the scenario. It clearly chose a strange solution to the problem, one which is not genetically very sound... but genetics is not proud, it simply goes for what works.

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I'd agree with @cort that the conditions you mention would not have a dramatic effect on the type of outer coating of an animal - so it wouldn't differ much from Earth where (as you point out) there are several choices.

Perhaps the excretions could be from specific points on the skin which add to the base of the previous excretions and lengthen them, resulting in... hair! But if you want to toughen up the creature, they could be strong and thick like quills. Or to shield their skin they could be fluffy and downy. And feathers (while not the same as hair) are just a special adaptation of the same idea.

What would be more important to your creatures would be adapting to their environment - sea creatures don't have fur or feathers. There are some evolutionary compromises (penguins, fur seals, polar bears) but these animals spend most of their time out of the water. So, perhaps you have to design your creature(s) to match the way they live, and invent some useful details if you want them to be "interesting". For example, if it may be predated upon in an aquatic environment, perhaps it has an outer layer of slime which allows it to slip out of the grasp of predators. Or to take that one step further, a whole outer layer of skin which it can shed. Or pouches of foul goo covering them which deter predators.

But animals here on earth have already developed almost every variation I can think of.

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