I have this adaptable canine ish shaped animal. Its legs are longer though. Its body's flesh is like regular animals with fur; not sluggy.

It can alter the "hardness"(there's probably a better word for it than this, but I don't know what it is) of its body, creating supports when needed. This can be used to reposition the "joints"(not exactly joints, but bendy places) on its limbs when transitioning from biped to quadruped movement and back again. To fit through small holes by "softening" its entire body. To reach down a curvy pipe for something. In the case of spiky variants, only "hardening" their spikes when needed so the amount of furniture casualties is kept to a minimum. To prank people by "softening" an area on its arm and screaming that they broke its arm when they touch an arm. And many more!

Do you know of any ways for the creature to make its ability work? This would need to support super human like strength.

If not I guess it could just be shapeshifty magic. Magic use is fine and all but I like to try to find natural ways before I resort to that.

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    $\begingroup$ A good place to start would be the hydrostatic skeleton, an example of which is the penis which as we all know can be soft or hard. It can allow your creature to transition from a flaccid state (to get through narrow openings and be flexible) to a more solid one that can stand upright and move about. It should work for spikes too. But I am unsure if it fulfils the "repositioning joints" part; that requires something much closer to shape-shifting. $\endgroup$
    – KeizerHarm
    Jan 12, 2021 at 22:49
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    $\begingroup$ @KeizerHarm this puts images in my head which i do not like $\endgroup$
    – Topcode
    Jan 12, 2021 at 22:54
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    $\begingroup$ I would also suggest looking at How can an amorphous creature change viscocity at will? and How do slime supports their weight and reach higher places? $\endgroup$
    – KeizerHarm
    Jan 12, 2021 at 22:57
  • $\begingroup$ It would take time to rearrange the animal with this fiber and hook scheme. Not something to be done on the fly. $\endgroup$
    – Willk
    Jan 13, 2021 at 2:06
  • $\begingroup$ Like the cat in the webcomic "Something Positive." $\endgroup$
    – NomadMaker
    Jan 13, 2021 at 19:34

3 Answers 3


Going out on a (variable-length) limb...

So nothing I know of has a structure that can do exactly what you're discussing, except some kind of hydrostatic/hydraulic system, although I have an idea that might be interesting.

  • Hydrostatic systems could work. For strength, however, a regular hydrostatic system might not be enough. A hydrostatic system could have some way of converting a fluid into a solid chemically and vice versa, so it wasn't constantly needing to be under high pressure to maintain structure. Imagine something akin to a crystal, and the appropriate enzyme reaction causes it to either crystallize or break down into a fluid/gel. Super strength would need something a little rigid to apply force. If the creature "overdid" things, there might be some internal injury when the crystal broke, but it could then be rendered down into a soft form, reshaped, and reformed into a crystal.
  • A hydraulic system might be an organic version of the hydraulic cylinder you'd see on a piece of engineering equipment (or a telescoping rod). This would be a more rigid structure overall. The hydraulics wouldn't be for force, but almost exclusively for changing limb length/shape. The materials could be something with a little give (like various carbon tubules/structures) but still allowing great strength. The hydraulic "bone" could extend or shrink, changing the length of a rigid limb. Multiple joints in a series of such hydraulics (akin to what The Square Cube Law was proposing) would allow multiple points for bending. If the hydraulic fluid could liquify and solidify like in the hydrostatic example, the "outer" carbon matrix could give flexibility, while an inner hard crystal structure could supply hardness and prevent the hydraulics from failing and causing the limb to suddenly shrink/extend.

If you didn't like hydraulics, you could probably come up with a limb that used a rotational motion (like a threaded rod screwing in and out) to extend, or an interrupted screw/series of intercalating discs that could change length and then re-intercalate to a rigid structure.

  • Tents and tinker toys: But what if we switch up our understanding of bones all together? What if they were like tinker toys? Imagine if the bones of your creature functioned more like a series of carbon rods for a tent. A bundle would be strong, and the ends would slide back and forth into slots like the joins on tent rods (or connecting pieces for tinker toys). The rods could be all in parallel and joined, making a rigid limb. Some kind of muscle-like structure could cause the rods to move forward or back to adjust the length of a limb, then clip back into place to make the limb rigid again. If multiple rods all terminated at the same spot, you'd have a "joint" where all the joins could come undone and the limb could bend. The joins could either be designed to allow rotation or be very good at disconnecting/reconnecting on the fly. And by sliding a few rods back and forth, a joint can be made rigid, or a "frozen" joint made flexible.

Given loose/flexible tissue & skin, these moving/length-adjusting rods could let a limb change the position of a joint, extend or retract the length of a limb, or reinforce a limb's strength with multiple rods to use super strength. Extend an arm like a pole-arm to maximize leverage in a slash, then shrink it down to allow maximum strength and small size to apply great force.

All these schemes would probably mean while a limb was changing, the creature's limbs would temporarily be much less rigid/load-bearing. So transformation would be a time of vulnerability and weakness. The OP has asked for some illustrations; I'm not a great artist and only so-so on biomechanics, so don't judge too harshly!




  • $\begingroup$ Ah yes! The tinker toys thing is just what I was looking for, but I didn't know if it would work and I couldnt figure out how to explain it properly. My original idea had some type of hook thing to keep them together, but this is better. $\endgroup$ Jan 25, 2021 at 16:21
  • $\begingroup$ It sounds a bit complicated though. Could you draw me some pictures illustrating the tinker toy bone rods working? $\endgroup$ Jan 30, 2021 at 3:54
  • $\begingroup$ @Chickenpeep Chickenpeep I hope these make sense, they're fairly simplistic. The motion of the rods back and forth will resemble the contraction of muscle. Otherwise imagine how a stick figure made of bundles of reeds would move. You'd need various binding proteins to keep it all together, but they could respond to chemical signals to slide, loosen, and rebind as needed. Again, the changing would be a vulnerable time with everything out of place. Shape-changing "on the fly" would be very dangerous and risk injury. $\endgroup$
    – DWKraus
    Jan 30, 2021 at 14:57

I do not think any creature we know of could change where they have joints. What you can do though is having a creature that has many joints. Spiders have seven segments in each leg, so that's six joints.

Now imagine that your creature has that or more joints, and that each joint is a ball bearing which would allow movement like a human arm around the shoulder. The creature can decide in which direction they want a joint to move at any time. If they want to appear to have an "elbow" or "knee" at a given point, they move that joint while keeping all others fixed.

Finally, if the creature has a loose skin such as a shar pei's face all over its limbs, it may give the illusion of being able to morph its skeleton underneath its hide. By relaxing all of its joints it would be flexible like a land octopus. By going hard on all of them it could go stiff in an instant (no, not like that).


I thought about this a while back, and one solution I came up with would be for the "skeleton" to be filled with a large number of short, hard, thin rods. By using muscles to squeeze the rods together, they would act like a single solid object. If the muscles were relaxed the rods would pull apart and could slide around relative to one another, allowing that area to bend.

  • $\begingroup$ and/or direct electrical stimulation at specific points, there are plenty of substances that can have their mechanical properties altered with current(notably, even after the current is cut). the trouble with using muscles is the constant strain involved without constant skeletal support, the energy usage & mechanical strain just to walk would be intense if it were expected to be at any worthwhile rate. $\endgroup$
    – Giu Piete
    Jan 24, 2021 at 8:24
  • $\begingroup$ This seems closest to my original idea, but a constant strain required to do it doesn't sound good. Is there a way to lock it into place without that? $\endgroup$ Jan 25, 2021 at 16:14

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