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On earth, the skeletons of Osteicthyes and all their descendants are made of a mixture of collagen and calcium. We can do this because Earth contains food sources for all these animals containing vitamins such as Vitamin C and D, but there's no reason why extraterrestrial food materials would contain specifically those vitamins, especially since they would hail from a completely different tree of life.

So, my question is: Is there any material that could be used to form an endoskeleton other than calcium and collagen that can be readily sourced on Earth, or at least could be without having major side-effects to life, ecology etc.?

To explain the last part, if I was to give them copper skeletons, I would have to make sure that there were plants there that contained plenty of copper. And for that, I'd need to design an alternate biochemistry, which is really, really time-consuming.

So, basically, this is what I'd like to see from answerers:

  • The material you think would work
  • An example of where it can be sourced in real life
  • The properties of such a skeleton I'd need to know about

I don't mind a material that isn't abundant in Earth food, as long as it doesn't mean alternate biochemistry. If you'd like to downvote or vote to close, please tell me why as well, as that's much more helpful.

Note: I have technically accepted an answer, but I'm still open to more suggestions. If you'd like to answer, go ahead by all means.

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You could replace bone tissue entirely with a "bio-steel", Iron with a small percentage of elemental Carbon and possibly Silicon, Nickel, Chromium, and/or Manganese to improve it's mechanical properties. The problem is not raw materials or even current biology, most life on earth already uses Iron as a basic component of our bodily make up, the problem is one of precipitating the skeleton in a controlled fashion because this is what happens in humans when Iron precipitates in the blood. You'd need a new suite of Bone Cells that control the process but that could be done.

Steel bones won't break, although an excess of carbon in the bone would be a new and interesting disease effectively changing them into Cast Iron which would break under heavy loads or impacts, they'll buckle like tube bent at too sharp an angle crushing the marrow and squirting it out through the blood supply vessels directly into the blood stream. Such injuries would be rarer than breaks in normal humans but with the potential for far greater harm.

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    $\begingroup$ Eurgh. I would hate to work in this species equivalent of A&E. Angle grinders and hydraulic presses would be medical equipment... $\endgroup$ – Joe Bloggs Jun 29 '18 at 12:30
  • $\begingroup$ Aluminium would be much lighter. Also, I guess bones would be massively reused as construction material :D $\endgroup$ – Madlozoz Jun 29 '18 at 12:35
  • $\begingroup$ @JoeBloggs Yeah pretty much, although you'd probably want a diamond saw, the dust is less of an issue than with an angle grinder. $\endgroup$ – Ash Jul 1 '18 at 12:00
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    $\begingroup$ @Madlozoz Aluminium is pretty reactive, it would make surgery really dicey, lighter yes but I think steel is safer, either way I would anticipate that once they have the pyrotechology for forging them bones would be melted down and used for all sorts. "This sword is made from the skulls of my fallen foes, fear me, etc..." I don't think that would work with aluminium though it oxidises too quickly in most solid fuel set ups. $\endgroup$ – Ash Jul 1 '18 at 12:04
  • $\begingroup$ @Ash By the way, I don't plan to have any native sapients on this planet. There was one primitive extinct civilization, and a few extant dolphin-standard species, but none with the technology to have metallurgy. $\endgroup$ – SealBoi Jul 2 '18 at 11:19
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Is there any material that could be used to form an endoskeleton other than calcium and collagen that can be readily sourced on Earth?

Well, if you want to go for something abundant, go for Silicon and Aluminum oxides.

They make up a large part of the rocks around us, and rocks are know to be sturdy and handle well compressive loads.

However, you cannot take rid of the Calcium in the bones without changing our biochemistry: Ca+ ion is fundamental for our cells, and bones are a large buffer for them.

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    $\begingroup$ +1 for the calcium buffer bit. $\endgroup$ – Renan Jun 28 '18 at 14:01
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If you want a different material you're not going to get around a different biochemistry - the more different the material the more different the biochemistry.

That being said, you don't really need to completely invent a new biochemistry: First of all "bone" is nothing more than organic tissue that was mineralized in a controlled manner - any organism that has minerals other calcium available could feasibly be able to use them to make bones (no further biochemical explanation needed up to this point, if you want/need more details just think about how the organism takes up and processes these minerals - it must already have biochemsitry to handle them).

Secondly there are some cool/weird animals on earth that do use materials other than calcium and collagen: while replacement of calcium is a bit rare (mostly because calcium mineralises [and dissolves] relatively easy in the usual ph-7.2 enviroment; some organisms can just use any micro particles though) collagen can be replaced with lots of things (carbonate, chitin & cellulose among others).

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  • $\begingroup$ I specially like the bit about tests. I always found them fascinating. They can harden and soften their skeleton in a very incredible way in a fraction of a second. $\endgroup$ – Renan Jun 28 '18 at 14:04
  • $\begingroup$ @Renan Do you have a source for that? Their skeleton being composed of various hard substances, I find it hard to believe that they can easily soften it. $\endgroup$ – Orphevs Jun 28 '18 at 17:28
  • $\begingroup$ @Orphevs I've seen people holding them. I think it's not that ossicles go soft - they can't - but rather they let water out and then get saggy when you pick them up from the ground. $\endgroup$ – Renan Jun 28 '18 at 18:02
  • $\begingroup$ @Renan I can't find a direct translation of test to my language, but it seems to refer to the rigid shells of e.g. sea urchins. In my experience, those don't go soft, even when drying up. Instead, the soft tissue loses water while their skeleton remains. There might be a language barrier here, could you help me out by giving an example of what you mean? Thank you. $\endgroup$ – Orphevs Jun 28 '18 at 18:48
  • $\begingroup$ @Orphevs oh... I had thought it meant the living animals, not their shells. I was thinking of plain old starfish. $\endgroup$ – Renan Jun 28 '18 at 19:10
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Fluid or air filled tissue or bladders, similar to erectile tissue. Goodyear experimented with inflatable planes a few decades ago. Not blimps, but heavier than air vehicles made of flexible material stiffened by air pressure.

An inverted chitin exoskeleton. Squids and octopuses are mollusks but they have a beak which evolved from a shell. An arthropod could evolve in a similar direction.

Keratin, like hair or nails, or rhinoceros horn.

Any solid material that can precipitate out of bodily fluid could conceivably be used after some evolution, so look into the composition of kidney stones, gall stones, gout, etc.

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    $\begingroup$ Are you calling OP a giant dick? $\endgroup$ – pipe Jun 29 '18 at 8:09
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look at what other biominerals are available. most hard parts are a biomineral in either a carbohydrate or protein matrix.

bones are made of calcium phosphate in a protein matrix, and the further you get from that the more you will have to change the biochemistry. I have tried to list these from the ones requiring the least change to the most change.

  1. Many shells are made of calcium carbonate, often mixed with chitin and/or proteins for strength. this is probably the most likely material and will require little to no change in biochemistry.

  2. A few rare creature use iron sulfide as the mineral component of their shells.

  3. limpet teeth the strongest biomineral known is made of iron oxyhydroxide again with a chitin matrix.

  4. Silicates are common in micro-organisms and plants, they are very slow to form so they would impede growth in animals however.

  5. Some bacteria deposit copper sulfide.

  6. metallic gold can be deposited by some some bacteria but the difficulty of getting gold in to solution will require drastically change your creatures biochemistry.

  7. if you want to go hypothetical, Chalcopyrite, or copper-iron-sulfide could be biologically produced.

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Found materials.

Lots of organisms use found materials to produce exoskeletons. Foraminiferans make their tests out of sand. Hermit crabs scavenge shells from other creatures. Caddisfly larvae usually make do with sand, but these caddisflies were provided gold and jewels, and obligingly made do.

https://featuredcreature.com/oh-you-facy-huh-caddisfly-larvae-construct-elaborate-cases-out-of-gold-rubies-and-other-precious-stones/ caddisly gold and jewels

So too the alternate endoskeleton. Your creatures use found materials deemed appropriate in composition, shape and size, taking them into their bodies and using them as bones. Like our bones, they are connected by collagen and ligments, and moved by muscles. These materials will of course vary in shape and size. Many will be rocks or crystals of appropriate shape and size. Some might be materials produced by other organisms, like coral or shells. Some of these found bones might be actual bones grown by a different creature.

Like a hermit crab, such a creature will keep an eye out for a better bone as it goes about its business. A bone which breaks or degenerated or is outgrown will be replaced when the opportunity arises, or other bones within the body rearranged to make do.

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  • $\begingroup$ I like the answer, but it doesnt explain where the previous skeletons come from. I also assume this heavily restricts size. $\endgroup$ – Demigan Jun 28 '18 at 19:50
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    $\begingroup$ @Demigan - this is what you refer to: " Many will be rocks or crystals of appropriate shape and size. Some might be materials produced by other organisms, like coral or shells. Some of these found bones might be actual bones grown by a different creature.". Previous skeletons will depend on if there are any animals in this environment which make regular bones. Re size - if you find an elephant skeleton you can be elephant sized. $\endgroup$ – Willk Jun 28 '18 at 20:51
  • $\begingroup$ Didn't read it that way, derp, sorry. $\endgroup$ – Demigan Jun 28 '18 at 21:29
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Graphene alloys. Graphene is made from Carbon, one of the most abundand materials in the universe and what we ourselves are made off for a large part. It'll take a (possibly impossible) leap in evolution that will keep large bone-supported creatures from appearing for billions years longer and likely require extremely long growth times to become adults, but once you are there... Very strong bones, possibly exoskeletons depending on how much Graphene is in the alloy and how heavy the rest of the alloy is and the gravitational pull of the planet.

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    $\begingroup$ Maybe not as much of a jump as you think. Graphene has been found in nature, albeit in small quantities, and carbon nanotubes are an intrinsic part of original Damascus steel, which until recently was forged centuries ago. It's likely the result of the wootz steel used in their production, which was formed in India in furnaces using types of local clay and wood and driven by monsoon winds; so it's safe to say they weren't trying to make carbon nanotubes; they just kind of did. You would just need a planet in which copious amounts of graphene had formed through similar processes. $\endgroup$ – Michael Eric Oberlin Jun 29 '18 at 2:36
  • $\begingroup$ @Michael Eric Oberlin could you link a source? I'm very interestwd in that $\endgroup$ – Demigan Jun 29 '18 at 6:49
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    $\begingroup$ Well, the wiki on wootz steel contains a good deal of the information. You might also check out link.springer.com/chapter/10.1007/978-3-540-88201-5_35, which I believe is one of the early scientific papers on the study. $\endgroup$ – Michael Eric Oberlin Jun 29 '18 at 8:19

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