Namely, a creature that is immobile and stone(like) during the day and mobile at night. Something like the old cartoon, but they don't have to be sentient.

  • They don't have to be actual stone, just something like stone, and unable to move.
  • They don't have to fly either.
  • Other than humans, would they have any predators?

That kind of creature is possible. First to make them hard as stone their skin have to be evolved differently. When sun light hits their skin it should turn hard either due to evaporation of water content of skin or they get stored in other parts of body to avoid water loss. These kind of creature might evolve in areas where there extreme heat during day and suitable temperature during night. So these creatures might turn into stone like to survive in these conditions. Any birds or any other animals who can break their hard stone like skin during day or have digestive enzymes that dissolves hard rock like outer layer might be their predators (considering they can survive the extreme environment during day).

  • $\begingroup$ I like this idea. I was thinking it could involve heat, but wasn't sure how it would happen. $\endgroup$ – AndyD273 Apr 26 '15 at 18:06
  • $\begingroup$ I have also the same idea. However, if the creature remains in a dark place with few light, it won't change its skin. $\endgroup$ – pys Apr 26 '15 at 18:14

The first thought that comes to mind for me isn't what the current answers have dictated. Why does the creature need to have some sort of skin that "changes" form?

First, the satisfy the day/night criteria, we can say that this creature has evolved to sleep during the day and not the night. Nocturnal, like bats.

Because the creature now sleeps in the daytime, we're automatically satisfying the immobility factor.

All that's left is how it turns "rock hard", which is simple.

Think "extendable armor plating". First, the theory: When you have 2 thick pieces of material like so:

|=====||=====| (where each |=====| section represents a plate)

The plates can't move back and forth. They're very sturdy as well. So how do we give this the ability to move? First, we have to modify the plates. I think having diagonal connection slots would do the trick. If there were a muscle under each plate that pushes it up slightly, and the creature had slight hunch (or a lot of curvature), it could look something like this:

\=====/ \=====/ \=====/ (where the \ and / represent the the sides of the plates)
   |       |       |    (each | represents a muscle in the extended position)

As you can see, in this setup, the armor plates are no longer touching while the muscles are extended, which means that they're effectively "mobile" plates. Now our creature has full mobility when needed, and when it needs to hunch over and go to sleep, pull all the muscles tight, and the plates fall into place perfectly, creating a seamless "shell".

These plates can be made of really thick skin, if you want, or even bone. With the right bone density, these things could be ridiculously tough to kill.


I don't think such a creature would be able to evolve naturaly. I can't think of any material that reacts to light by turning hard as stone. I see two possiblilities:

1: The creature sleeps during the day and doesn't move. But it would be able to move if you wake it, even during the day. You could say it's armour is so hard and thick that it doesn't feel anything, so it would be very hard to wake the creature.

2: You'd have to use magic.

Furthermore, seeing as they have an almost impervious armour there is probably another creature hunting them. Why else would they need their armour. And because the armour works best at daytime it is probably a predator that hunts in daytime. But I don't know what creature that could be, probably not a creature that we know.


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