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Oftentimes, western dragons are depicted not just as BIG but also as THICK. I've given up on making dragons any larger than a draft horse, but wish to avoid making further compromises. However, the issue is that an overwhelming majority of an animal's weight is almost always their muscles and thick limbs mean lots of extra weight.

So, the dragon. I made them stand at around 180 cm tall at the shoulders and weigh at most 500 kg. A justification for why dragons could become so heavy was supposed to be their ability to use synthesize and use graphene and high-strength carbon nanotubes to reinforce their tissues.

Now, it wouldn't normally make sense for a creature's anatomy to go out of its way to appear as aesthetically pleasing to humans as possible, but dragons in this scenario are genetically engineered from the ground up.

Of course, such buzzwords won't fix the issue of making a dragon appear swole without being swole. I have two strategies to decrease their weight. The first one is the simplest:

Dragon legs have extremely large bones with somewhat thin walls and a honeycomb structure inside for additional reinforcement. These bones are much larger than what the dragon would theoretically need to support their own weight, even when landing.

Its weight isn't negligible, but still much less dense than pure muscle.

However, I'm unsure if this decision would have unforeseen consequences, considering the largest bones are in the dragon's landing gear (their four legs) that doubles as terrestrial locomotion.

Would there be any drawbacks to giving dragons unnecessarily large leg and arm (foreleg) bones?

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    $\begingroup$ This Q might get more attention if the title and body questions better aligned with what you're trying to achieve. The title is asking for our permission to use hollow bones (apparently everywhere in a dragon), like bird bones. You don't need our permission to do anything. The actual question is asking about the size of the bones, but the title and body text are discussing the hollow nature of the bones. In short, your questions are pretty unfocused. Could you edit you Q to clean this up? What are you really asking? (*continued*) $\endgroup$ Jul 16 at 3:06
  • $\begingroup$ NOTE: The science-based tag might be a hair strong since we're talking about dragons or, at it's simplest, impossibly large birds (see the Square-Cube Law). An important part of your edit should be to explain why it's important that you have a scientifically plausible justification for your rule, because by definition, it's implausible if not impossible - but that doesn't mean it's not a great rationalization for your dragons. $\endgroup$ Jul 16 at 3:08
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    $\begingroup$ note dinosaurs and birds made everything else hollow before making limbs hollow. hollow ribs, vertebra, and even pelvis. Even then most of a birds limb bones are not hollow. you need a few solid bones for bone marrow, and you might as well leave it to the bones under the most stress. the bigger they are the less sense making them hollow has, limb bones tend to need as much strength as possible. Also what size are your dragons. $\endgroup$
    – John
    Jul 16 at 4:34
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These bones are much larger than what the dragon would theoretically need to support their own weight, even when landing.

Life is a fine balance between different needs, and as such it hates whatever is "much larger than needed", because it's a waste of resources which could be better used for something else. That's why unused muscles shrinks and used ones grows.

If your dragons are putting their resources in growing bones larger than needed, they will be underdeveloping other organs or functions, with the result of becoming unfit for their environment.

One possibility would be that their daily calcium need is lo large that, in order to keep their bones healthy, they spend most of the day gulping stones instead of hoarding gold or trapping princesses. If that is not possible, they would probably succumb to bone fracture, the same way a big herbivore will starve if there is not enough grass to graze.

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    $\begingroup$ Unless dragon bones use gold where ours use calcium, then they would have a use for hoarding gold and maybe time to do it. $\endgroup$
    – Lupus590
    Jul 16 at 13:38
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Bone mass isn't the only limiting factor to flight. Flight is a balance between mass, gravity, buoyancy, and lifting force. Bird bones being so frail is a compromise evolution made in birds to reduce the lifting force necessary for flight.

If your dragons have heavier bone structures (for whatever reason, @LDutch raises good reasons why this will require justification if they are naturally evolved), then whatever flight performance you wish for them to have will simply require more lift force. Lift force that comes from wings requires muscle power applied as a function of wingbeats per period of time and wing area (bigger wings beat more slowly).

Assuming they are naturally evolved organisms, this means that for any given increase in bone density (and thus creature mass), they need a more-than-proportionate increase in muscle mass of the wing (and legs). Muscle mass is heavy, so an additional increase is needed to lift the requisite muscle mass, etc.

The creature now also needs a higher caloric intake. This is where I differ from @LDutch: The organism doesn't have to make compromises elsewhere in the body, as long as there are available energy resources to bring in from outside the system.

Heavy dragons are hungry dragons, but denser bone structure - especially in the legs - facilitates predatory behavior by adding momentum to claw strikes. This is part of why it makes sense that fantasy dragons are viewed as a menace: in order to sustain that kind of mass, at that kind of energy output, the creature is likely wreaking havoc with the local ecology - or at the very least considers livestock to be an obscenely convenient source of easy protein and fats.

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Bones already work much in the way you describe.

Look at this femur for example: https://www.google.com/search?q=femur+cross+section&oq=femur+cross+section&aqs=chrome..69i57j0l2j0i22i30l2.10425j0j7&client=ms-android-samsung&sourceid=chrome-mobile&ie=UTF-8#imgrc=dIRLPBbsIdAJhM

You have an outer "shell" that has some thickness. Near the center it becomes hollow*. At the outer ends more forces are located in different directions and these are supported by the criss-crossing of small bone supports. The more forces are located there the more dense these bone supports get.

Your honeycomb structure would actually give weaker bones in that respect. You would have honeycomb in the center where its not necessary and would add unnecesary weight, at the top it would need to be smaller and denser honeycombs to support the extra forces or risk breaking the bone.

You are probably better off using different materials. Special Spidersilks to reduce the weight of skin, tendons, bones and other facia in the body without sacrificing strength. The drawback being making it harder to heal when it gets damaged and requiring a lot of clever bodily designs to migrate spidersilk strands through the body.

Other options are Graphene reinforcements. While complete Graphene structures is likely too hard the addition of Carbon Nanotubes helps strengthen materials, allowing you to keep them lighter. Many processes of the creation of Graphene can already be done through biological processes such as certain bacteria. It would not be too much of a stretch to say your bio-engineered creature can do this and add it to its bodily structures.

*although partially filled up with bone marrow it always amazes me how people make hollow bones on birds and raptors significant, while most living beings essentially do the same.

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  • $\begingroup$ The size of the honeycomb part of bones can be amazing. In Vancouver, I saw a sculpture made from just the honeycomb area of a whale bone. It was several feet by several feet in size and I had to ask what the heck the substance was because I couldn't understand how to make something like that. $\endgroup$
    – David R
    Jul 16 at 14:00
  • $\begingroup$ the honeycomb does not make the bone weaker, honeycomb is actually very common in bone, when you see bones without it it is usually due to poor cleaning methods, or because they are pneumaticized which adds strength due to active pressurization. $\endgroup$
    – John
    Jul 16 at 14:33
  • $\begingroup$ @John you must misunderstand me. With "honeycomb" I assume a hexagonal structure within the bone, not the criss-crossing of bone supports that I quite literally already describe. Also the OP wants to fill the entire bone with honeycomb structure, which like I said is inefficient since you don't want to fill the entire bone with it but only the parts that take stresses. $\endgroup$
    – Demigan
    Jul 16 at 15:02
  • $\begingroup$ "the OP wants to fill the entire bone with honeycomb structure" that's a pretty strong leap form what the OP describes. And there is no reason to suspect actual hexagons, honeycomb structure is well known and accepted description of trabecular bone. $\endgroup$
    – John
    Jul 16 at 16:54
  • $\begingroup$ @John why is it a strong leap? If it is not about honeycomb structures, then the OP is asking about how normal bones with a thinner walls would work. But he specifically mentions Honeycomb structures as ADDITIONAL reinforcements, rather than reinforcements that already exist. Even if he's not talking about hexagons but about trading thinner walls with more trabecular bone structure my answer still applies: it would weigh more as less bone is supportive in ways it should be supportive. Also downvoting is for questions that are truly bad, rather than you disagree with for some reason. $\endgroup$
    – Demigan
    Jul 16 at 17:20

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