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I've been spending a lot of time developing aliens for a comic I'm working on, in the skeletal structure department I've run into a bit of a roadblock, how to design a spine for a species that is kind of humanoid, but weighs several hundred pounds more. The spine also needs to be transferable to members of the same species that are over 30 feet tall, living in a somewhat reduced gravity.

My current ideas are; making the spine segments wider, thus providing more support, and adding muscles to reduce stress; adding a secondary spine, so instead of having a single spine in the middle of their back, they have two spines running in sideways arcs up their back (this wouldn't be much of a problem as far as making the torso wide, they already have very broad shoulders and such); lastly, I am thinking of removing the spine and replacing it with something that would resemble an oobleck spine, so it is soft and malleable (which would negate the problem of destroying the back over time as it would be a flexible tube-like organ), but then during times of combat there is a system of muscles that squeezes the spine and causes it to harden.

Are any of these feasible or useful in any way?

edit: Giraffe spines have the same number of vertebrae as a human neck, but they are far larger, and seem to lock together like puzzle pieces. could using less, larger vertebrae be helpful in this situation? I imagine it would make the spine stronger, but less flexible.

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  • $\begingroup$ I would suggest you look at the skeleton of the eastern gorilla, maybe giraffe skeletons, or even dinosaur skeletons for inspiration. Oobleck would be useless for a spine, you have to support the upper body weight (everything above the hips) at all times. You need something that is stiff at all times. Spnies are common to the design of many animals for a good reason. $\endgroup$ – Gary Walker Aug 16 '17 at 4:17
  • $\begingroup$ I'm not sure what you mean by "transferable to members of the same species" These aliens can remove their spines and swap them? $\endgroup$ – Nate White Aug 16 '17 at 5:27
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    $\begingroup$ Really just look at the problems heavy people have with their spines. At 6'5" and three hundred pounds, no matter how strong I am, I occasionally have issues with a bulging disc in my lower spine. This isn't hypothetical, I am slightly gigantic. What you need is vascular, renewable padding between the spinal segments. Or even just finding a better way to route nerve channels away from the spine, so when something does slip it doesn't hurt so dang much. $\endgroup$ – Sean Boddy Aug 16 '17 at 13:22
  • $\begingroup$ I highly recommend looking at the tensegrity viewpoint for how the spine works, such as shown in this video. The spine actually operates very differently than most of us think it does. The spine, when properly aligned to leverage the principle of tensegrity is 3x stronger than it is when it has to collapse that tensegrity. $\endgroup$ – Cort Ammon Aug 16 '17 at 19:17
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Vacuoles and turgor pressure! (what's turgor pressure?)

A firm, fresh cucumber is firm because it is full of water. As it dries out (wilts), it loses water content and becomes weak and rubbery.

A functional spine could be made from a tube composed of a network of vacuole-rich cells which, when properly hydrated, could remain firm and erect indefinitely. However, to do that these cells would need to possess a structure analogous to a plant's cell walls, because the amount of turgor pressure a plant cell's full vacuoles exert on the plant cell (to provide firmness and structure) would cause an animal cell's membrane to lysis (burst) and the cell would die.

One problem with this suggestion is that we observe changes in turgor pressure in plants and fungi that just go much slower than we'd want our new spines to be able to adjust themselves for motility purposes: a solid tube of these cells won't do the trick. So, you could build a network of vertebrae out of these vacuole-rich cells instead of from bone that basically functions the same way, but is much more "plastic" and faster to heal/self-adjust than we are accustomed to. (Imagine a slipped disc working itself out in 30 minutes!)

I assume by "transferable" you mean scalable, i.e. the same design will work for 30 foot tall humanoids in reduced gravity. I guess a 30 foot humanoid would have a ~10 foot spine, and while that would certainly be pushing it for a continuous structure (plants that grow to 30 feet tall do so with woody cellulose, i.e. a very thick cell wall offering no medium-term motility, in the way a vine might curl around a branch in an afternoon), I see no reason the vacuole-vertebrae would not work in this case.

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Why do you need a spine as we have it? The spine provides a flexible torso, and an earth life, this developed because locomotion in earlier forms required the undulation of the entire organism. Look how a snake moves, or a fish swims. In terrestrial mammals, the spine and back are an important part of locomotion as well, as they add power to the stride.

If you are willing to forgo having a flexible torso, and have a rigid torso, you can have a single support column, that runs from the pelvis to the neck. Alternately, the bone column could be wide and hollow, with all the venerable bits inside, like an exo skeleton, but not necessarily a shell, it could still be covered with skin and hair/fur/feathers...

Look how robot torso's are envisioned, they seldom have a flexible spine. Think "Bender" from futurama.

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    $\begingroup$ You could also have a spine that works more like our arms or legs, with several rigid bones connected by joints. It would reduce flexibility but still allow for a reasonable amount, especially if the joints are ball-and-socket joints. $\endgroup$ – Mike Scott Aug 16 '17 at 7:18
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Human spine isn't what you want to take your inspiration from.

In addition to have evolved to allow and ease locomotion for fish-like creatures, all our land dwelling ancestors were quadruped. To sum it up, our spine is optimized for horizontal support and lateral movement of any part of our body, which is definitely not how you would define humanoid standing.

In short, our spine is a suspended bridge and what you are looking for is an architectural column. The first allows lateral freedom and is strong and supportive as long as it's horizontal while the later offers support as long as it's vertical.

If you want to be rigorous, concentrate on the environment and lifeforms of your planet :

  • What are the environment characteristics ?
  • Where did the first complex lifeforms appeared ? Therefore, what did they look like ?
  • What these lifeforms eveolved into ? Which subsequent steps and forks did their evolution took ?
  • And finally, what does your creature look like, given the evolutive path its ancestors endured ?

That way, you'll get something that is supported by their environment and they will look like the other creatures on the planet. Our spines grew in fishes that were the first vertebrates and every vertebrates have similar spines now. It's so old and basic in our evolution that it mostly didn't change, whether it was reptiles, dinosaurs, birds, mammals or whatever. That's why our way of standing and moving is so shitty compared to how our spine works - and why so many humans have back issues.

I hope it gave you some food for thought and a begining of solution.

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  • $\begingroup$ This is a valid point, and a fresh take on the issue. I particular like the guidance to concentrate on the other lifeforms of the OP's planet. $\endgroup$ – Tmartin Aug 16 '17 at 16:17
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Our current spinal architecture is pretty scaleable, easily capable of handling larger humanoid body masses. After all, toddlers of 30 pounds are skeletally very similar to adults of 250 pounds with no significant issues. Many modern back issues are not due to an inherent structural flaw in the spine but rather the poor ergonomic situations (a dozen hours a day sitting slouched over in an office chair/car seat) combined with poor physical fitness. It is the consequence of maximal adpative flexibility when it is subjected to prolonged repetitive stress. There are also other biological reasons why humans at the upper end of the size spectrum have issues, not really due to spinal problems other than folks with global bone growth issues. So when scaling humans to 30 feet, even in reduced gravity, you have other problems to consider, not the spinal structure.

The spine provides not only structural stability to the upper body, but also shock absorption, flexibility to the torso/head, and protection for the spinal cord. Simply making a solid or rigid spine would transfer a LOT of impact stress to our hips or skull. The spine is also the attachment site for many major muscle groups, so you can't just do away with it or duplicate it without also redesigning the entire musculature system.

Nerves really don't like to be pinched so you also can't have a fluid spine that goes rigid because you could easily compress nerves (the nerve outlets wouldn't be as static and protected as they are with a segmented spine). In a surprise stress situation you might even lose control of limbs if you were in an awkward position when your spine suddenly tightens up under muscle contraction and pinches off the motor nerves to your arms or legs.

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  • $\begingroup$ Sorry, I disagree. There are parts of spine design (most notably L3-L4 joint) that never fully adapted to vertical posture. Cavemen didn't suffer from this only because they died young (usually before 30). Design is adapted for horizontal station where it gives its best (think Diplodocus). $\endgroup$ – ZioByte Aug 17 '17 at 15:46
  • $\begingroup$ @ZioByte Our spines have been adapting to a vertical posture for millions of years. There is substantial anthropological evidence that the pronounced "S" curve to our spine is a response to poor posture and doesn't occur in indigenous cultures (they have a more vertically aligned "J" shape). So simply saying the human spine is poorly equipped to a vertical gait is incorrect. The OP asks about the need for a more sturdy spine without elaborating on how his heavier race differs anatomically from humans other than average size and height. There is no need to redesign the spine. $\endgroup$ – Jason K Aug 17 '17 at 17:54

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