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Any person who was once a stupid teen knows how it feels to break a bone and be stupid enough to pretend like nothing happened to hide the injury for weeks on end until their parents notice.... It is to say the least incredibly painful, and moving the broken limb normally acting like nothing happened is even more painful, but even just lying down not doing anything is painful enough.

I was wondering about the possibility of bones that when hit don't just shatter or split but actually deforms and bends like a metal.

Imagine you fall from your skate and bend the forearm boned in an L shape, just use some friends and bend it back straight.

Can metal-like bones exist in earthlike conditions or are most metals or similar material toxic or too "bendy" and not strong enough?

The reason for my question is because I'm imagining a turtle kind of humanoid but it's actually just people with shells and have nothing to do with turtles, no scales and no green skin and normal limbs and jaw with human like face but I wanted to make them as "invulnerable" as possible, not to defend themselves from predators but from their own stupidity or as most call it "courage" as they spend a lot of time climbing giant mountains/trees. It's quite normal to see those turtle guys falling from trees, or mountains or trees on top of mountains.

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  • $\begingroup$ "just use some friends and bend it back straight" - how strong are your friends (or how soft are your bones)? $\endgroup$
    – Alexander
    Apr 13, 2020 at 17:44
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    $\begingroup$ I guess I must have been a smart teen, then :-) But metal bones are certainly possible, at least as a surgical replacement. Titanium is most common. $\endgroup$
    – jamesqf
    Apr 13, 2020 at 18:10
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    $\begingroup$ Actually it is very hard to unbend a bent metal bar into a straight shape; it most commonly involves repeated hammer blows, and the final shape is seldom true. $\endgroup$
    – AlexP
    Apr 13, 2020 at 20:21
  • $\begingroup$ Do you have in mind any specific metal? Remember our human standard bones are made out of Calcium, and Calcium actually is a metal. $\endgroup$ Apr 14, 2020 at 3:07
  • $\begingroup$ @CarlosZamora: Our bones are most definitely not made of calcium. Have you never seen a bone? Among others, calcium is just a little harder than lead; it can be cut with a knife; calcium reacts spontaneously with water and humid air. $\endgroup$
    – AlexP
    Apr 14, 2020 at 5:56

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Most metals, once bent, are very difficult to get back into shape. Metal that is difficult to bend, shatters under force. Metal that is easy to bend, crumples under force and is permanently weakened. If you really want metal, you're going to have to make up some alien metal.

Instead, I would suggest cartilage. Hard, yet pliable. These aliens could have skeletons of various types of carilage, even some wrapped around the organs for more protection. When force is applied to cartilage, it will bend and then pop back into place. If it's a less pliable cartilage and is bent too far, it may break or not be able to fix itself, but it can be popped back out with little effort. Healing cartilage is rather difficult in humans, but make your aliens have a more dense cell population and a greater blood supply to the cartilage and it will repair more rapidly. There are three types of cartilage.

  • Hyaline Cartilage- Provides a smooth surface enabling tissue to slide, is firm yet flexible, and provides support. Found in the trachea, ribs, nose, and larynx in humans.

  • Elastic Cartilage- A lightweight shaping material with moderate elasticity. Used for non-load bearing support, such as forming the ear in humans.

  • Fibrocartilage- Tough, very strong, found between the vertebrae as shock absorbers and at the ends of ligaments and tendons as anchors in humans. Not flexible.

For your purposes I'd recommend having the load bearing bones of your creature be thick tubes of fibrocartilage with a gel substance inside. Make their shell an outer layer of Hyaline cartilage, with inner shock absorbers of gel filled fibrocartilage sacks. You want the impact to gently flow through the body and into the ground, rather than hitting the ground in a challenge. The ground always wins. Id say giving them the ability to suck up into their shell would work the best, since the human frame cant be reinforced enough to withstand a fall and still resemble a human. The cartilage skeleton would prevent them from breaking bones from impact despite being inside their shell. Their brains would have to be smaller and their heads bigger, I'd think, to prevent concussions. Have the brain surrounded by a very thick gel. Not completely wrapped tightly with cartilage like you'd think, which would prevent the brain from expanding slightly as it tends to do throughout the day. Hopefully this helps, I'm sorry I couldnt think of any way metal could work but I think this is a great alternative

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Are you postulating biology very similar to Earth, where megafauna are composed of proteins, with mineralized bones (not necessarily calcium)? I can't think of plausible biochemistries for that (I'm not a biochemist), but I wouldn't rule it out entirely.

If you're thinking of an un-Earth-like biology, then I don't see why the rigid bones couldn't be made literally out of metal. Iron at least, possibly aluminum. More exotic metals tend to have problems with the quantity available on a planet, but aren't absolutely impossible either.

Some functions of human bone would have to be moved elsewhere in the body (if those functions are even necessary). You'd not put something like marrow into these, as bending the bone might crimp off structures and flow necessary to survival. If the organs were in a ribcage or ribcage analog, those organs have to be designed in such a way that they are somewhat functional even if pinched or obstructed. This presents some serious challenge, as things like the lungs need the bronchial tubes to be open (there are solutions though, multiple redundant openings/nostrils placed such that all are unlikely to be blocked, and such that they're not long and narrow... on a human you might put these between the ribs directly into the lung). The heart itself (or any muscular pump) would be another. Organs like the liver and pancreas however, should be quite tolerable of being twisted into other shapes for a period of a few days or weeks.

So, on that note... the body would need a way of re-straightening these bones. If they aren't bent too badly, the organism might limp along for a long time without remedy. But in such cases, they weren't in too much danger from those injuries even with the brittle style of bone. Where this gives them a distinct advantage are those injuries where you or I would be crippled and require amputation (or serious, modern, medical attention).

Some biological mechanism would need to identify the region of this metal bone that was deformed, and the body would begin dissolving the metal. Likely until that portion of the bone was gone entirely. For a dent in a skull-like bone, it'd just eat it away until there was a large hole where the dent used to be, for a long bone until that bone was severed. Only then would it begin the process of reforming the metal.

The real question is how the mechanism compels the organism to reorient itself so that the new bone is straight and not malformed. We don't have such a mechanism (though we'd benefit from that too... humans eventually learned to set and splint simple breaks so that the bone would heal straight, but other animals can do no such thing). Perhaps these metal turtles go into a sort of hibernation or inactivty, and unconscious/reflexive movements reposition them for optimal results for the process.

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