A bit of a further expansion of my last question. I am looking for alternatives to regular bone of earth (hydroxyapatite) because my superearth would have about 50% more gravity than that of earth. While 50% probably isn't enough to force animals to use other bone compositions, I'd rather take an "odd" route with my creatures instead. Bones would have to be:

- Regeneratable

- Biologically possible

- Compatible with the organism's immune system

- Have weird traits, color, formation, impact on the body etc!

I was thinking something akin to dentin, being found in our teeth. Density doesn't matter for me, as long as it doesn't reach lead-levels. Along with that, I'd rather use something that has some interesting properties, like pyrite, which oxygizes in a matter of days, or silica, which is rather transparant. Heck, even some biological "plastics" would work! If you do however, have a more speculative material/composition, please note where/how organisms could utilise/find it! The atmosphere is rather earthlike in composition, although it is quite a bit denser if that makes a difference. If possible, it shouldn't be something too earthlike, but it should still be viable and common throughout other worlds. Thank you in advance, feel free to ask any questions!

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    $\begingroup$ have you looked at the other skeletal materials used in earth animals that have evolved like chitin, aragonite, calcium carbonate, silica, or goethite? $\endgroup$
    – John
    Jun 23, 2021 at 11:33

2 Answers 2



I am going to recycle an answer! But as regards weird skeletons this is a good one because instead of bones your creatures are full of juice.

from Would biological hydraulics be worth evolving in tetrapods?

Velvet worms are terrestrial animals that use hydraulic legs. Model your creature on them.

velvet worms http://www.abc.net.au/science/articles/2011/09/05/3306983.htm

on the hydraulic skeleton of velvet worms Periodic Tables Unifying Living Organisms at the Molecular Level:The Predictive Power of the Law of PeriodicityNov 8, 2017 by Antonio Lima-de-Faria

Velvet worms have legs but do not have a skeleton. All of the functions of the skeleton are done via hydraulics.

If you are dead set that your creature will have an endoskeleton, hydraulic appendages are still very much an option. You may be familiar with a method vertebrates (including humans) use to produce a temporarily rigid organ using only hydraulic pressure.

  • $\begingroup$ Great idea, I could imagine this helping a lot with higher gravity worlds! $\endgroup$
    – Explunky
    Jun 24, 2021 at 7:11

Do you know why toothpaste contains fluorine? Because it replaces the OH group in hydroxyapatite and form fluorapatite

Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula $Ca_5(PO_4)_3F$ (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, yellow, violet, or colorless), the pure mineral is colorless, as expected for a material lacking transition metals. Along with hydroxylapatite, it can be a component of tooth enamel, but for industrial use both minerals are mined in the form of phosphate rock, whose usual mineral composition is primarily fluorapatite but often with significant amounts of the other.

Fluorapatite is found in the teeth of sharks and other fishes in varying concentrations. It is also present in human teeth that have been exposed to fluoride ions, for example, through water fluoridation or by using fluoride-containing toothpaste.

It's practically behind the corner in terms of biochemistry.

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    $\begingroup$ Seems like a reasonable replacement, would this have any impact on the structure of the bone itself, and would it be more stiffer? $\endgroup$
    – Explunky
    Jun 22, 2021 at 15:42

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