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.