Reinforcing a fused ribcage to be more bullet resistant, how?

Question

So, dragons, wyverns, gryphons, bird people, pterosaurs, etc...

Every flier shares the problem of toughness (the lack of it) when compared to grounded creatures. The only path we can go down on is decreasing the size of the hit location and making less important structures capable of retaining some of their function with a bullet hole or two in them.

Thankfully, giant pterosaurs had torsos about 60 centimeters in length. Well, they were definitely deeper and wider than a human's though. Anyway, we can use that to our advantage, well, that and the fact that their ribcage was definitely fused.

If we were to turn that ribcage into armor, we'd need to cover less area, but the organs would be subjected to more blunt-force trauma, not to mention the chance of chunks of the armor breaking off and getting lodged in them.

Sigh.

How should I fix that, or should I just give it up altogether?

Some additional tools I use for creature design:

• Many large flying creatures in my setting have "air blubbers", which are layers of flexible aerogel, made out of strong, fibrous material; the aerogel's density is 0.2 grams per cubic centimeter.
• Abalone shells are very impressive, especially their shock resistance.
• Also, my creatures can synthesize and use carbon nanotubes in their bodies.

Answer 1

I don't think reinforcing is the way to go.

Shaping seems better, so shapes that funnel bullets away from the more vital organs either by the way they deform when hit or their initial shape.

A quick idea is like a liquid sac where the stress lines are all vertical. Whichever stress line is hit goes inwards slowing the bullet, but the important thing is all organs get pushed to either side of the line rather than staying in front of the bullet. Hell of a shock to get shot, but less lethal perhaps.

Answer 2

Stopping bullets is hard. Our body armor is a composite made out of hard layers designed to absorb the impact, but these are brittle as a result and crack easily (so easily that just dropping a plate to the ground several times can degrade the armor). The layers below that are more ductile materials designed to catch the bullet remains and shards of armor that are pushed farther. Its rather hard to make a biological alternative unless you have a lot of space to put it like on an Elephant.

You have to look for alternatives, and the best biological one I know would be high-grade spidersilks spun into the skin and as a network between the rest of the organs.

Many spidersilks are similar to Kevlar in bullet resistance, which is why people have thought about harvesting it. However some spidersilks make Kevlar blush, like that of the Bark Spider (1) which is supposedly 10 times stronger.

There are many advantages to spidersilk in its toughness and comparative lightness. Having thousands if not millions of glands near the skin weaving this type of silk (without the sticky components) and having the cells pull these strands between themselves you could create a thick layer of highly resistant skin and flesh. The only thing you need then is a layer of fat or similar to absorb and spread the shock before it reaches the fused ribcage.

I suggest you do find some way to strengthen that ribcage as well, as even with the bullet stopped the ribcage will likely still break from the shockwave of larger rifles.

(1): https://en.m.wikipedia.org/wiki/Darwin%27s_bark_spider

Answer 3

Woven fibrocartilage.

Bone is very strong and can withstand stresses without breaking. Ideally the animal perceives these stresses which come on gradually and changes behavior to lessen them. Sudden stresses such as blunt force trauma can often be withstood by bones. Bones are evolved to withstand typical environmental stresses. When a bone fails it breaks catastrophically and a broken bone can ultimately mean death for an animal which cannot feed or flee.

A bullet wound is a different situation and requires a different approach. A bullet delivers too much force for any single structure to withstand. A bone will break. For this situation, one needs redundant barriers to the bullet, any one of which can fail but in which aggregate slows the bullet and limits damage to internal organs. Failure of even multiple barriers should not mean catastrophic crippling of the animal. The barriers should be quick to regenerate.

I propose that the bones (or at least the ribcage) of this animal be made of woven fibrocartilage.

https://websites.delta.edu/biotutor/Tutorial.Tissues/fibrocart.frames.html

This material is similar to but stronger than tendon, and weaker but less brittle than bone. Like individual strands in a rope conferring strength to the rope as a whole, individual strands of fibrocartilage in the ribs will deform and stretch before failing, slowing the bullet.

This is how a Kevlar bulletproof vest works.

https://www.howitworksdaily.com/question-of-the-day-how-does-kevlar-stop-a-bullet/#:~:text=Kevlar%20is%20able%20to%20stop%20a%20bullet%20due%20to%20its%20molecular%20structure.&text=When%20a%20bullet%20hits%20the,stretching%20force%20on%20the%20fibres.

Inside a bulletproof vest are many strips and layers of Kevlar. When a bullet hits the vest, it tries to force it through the layers, but to do this it must push the fibres apart. The fibres are woven and resist this very effectively. The movement is translated into a stretching force on the fibres. Some will break, but most will absorb the energy of the bullet by stretching a small amount.

Shards of hard fibrocartilage will not shatter off, delivering damage to deep structures. Fibrocartilage is minimally vascular and heals fast which is one of the main roles of this molecule in our own bodies.

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I have mused on the advantages for a cartilage skeleton for a flier. Cartilage is less dense than bone and so lighter. In a creature which did not need to fight gravity on a daily basis but for whom limiting weight was important, a non-bone skeleton might help achieve that end.