Dragon forelimb placement

Question

Most dragons (before Skyrim and GoT) had six limbs in total, four legs and a pair of wings.

The question is how would a dragon's forelimbs be placed? It's obvious they have good terrestrial capabilities, without having long noodle legs. But then there's the flight muscle, it needs lots of space and a large attachment site, same goes for the wings. But how should I put the front legs on the dragon so that it doesn't interfere with the wings' motion? Sure, those things only move during climb out, but it' still troubling. Whatever I choose should be compact.

How and where would the front limbs of the dragon connect to the rest of the skeleton?

Depends on the dragon's attitude in flight. The wings must attach to the spinal column so that when the dragon assumes the flight attitude the attachment is above the center of gravity (or maybe a little forward of it if the dragon has a suitable tail which can act as an airfoil). Conversely, if you fix the attachment of the wings to the spinal column you can assume that in flight the dragon will assume the attitude which brings the center of gravity below the wing attachment point. As for the muscles, they don't interfere; flight muscles attach most likely to the sternum, unlike limb muscles. — AlexP, Apr 06 '19 at 17:44
There is no way to answer this question where it would connect would depend entirely on how and where the limb evolved, what joints it has, and where the muscles are ect. flight musculature is not uniform in vertebrates. Birds and bats have a very different layout of flight muscles for instance. Since we don't know these things we can not give a definitive answer, there are many many correct answers. The only thing you can do is lay out the limbs so their range of movements do not meet each other. — John, Apr 06 '19 at 21:33
I can suggest you look at the art from, A Natural History of Dragons: A Memoir by Lady Trent, it has probably the most sound anatomy I have ever seen for dragons, with a minimum of interference between the limbs. This will show you at least one way it can be done. — John, Apr 06 '19 at 21:38
But do dragons really need large flight muscles? If they exist in a world with magic, then a reasonable explanation is that they evolved a natural flight magic that offsets their mass and lets their wings be much weaker than otherwise required. Same explanation for the firebreathing - human mages study to recreate the same fire spells that dragons know genetically. — Sir Adelaide, Apr 07 '19 at 12:12
The 2-legged/2-winged 4-limbed dragons (a.k.a. "wyverns") have been recorded since 752 AD, when mentioned as being on the banners of the Kingdom of Wessex (which itself existed from 519 AD until the 10th century - how early it was using a wyvern is unknown), and the Oriental-style 4-legged/0-wings 4-limbed Dragons are recorded from 323 BC in Mesopotamian art. So, I would argue that "most dragons before Skyrim and GoT" did not have 6 limbs, just the ones that you personally were most familiar with. Given how large China and India are, the wingless versions are probably the most prevalent — Chronocidal, Apr 23 '19 at 10:37

Liam Morris · Answer 1 · 2019-04-06T20:01:05.390

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Im not an avian biologists so i do not know if this configuration would be biomechanically sound, however it may prove to be some help to you.

Credit to Christopher Stoll

Shown here is a break down of the skin, muscle and bone layers of Toothless from the How to Train Your Dragon series. This image clearly depicts how and where the bones connect and where the muscle attatches to the skeleton. As i mentioned, i am not an avian biologist so i do not know if this setup would actually be functional in the real world, you may very well be able to draw inspiration from this though.

Edit: As you specified for an image containing the pectoralis, i found another one that depicts it.

http://mythicalanimalscience.blogspot.com/2015/04/dragons.html

edited Apr 06 '19 at 20:01

answered Apr 06 '19 at 18:32

Liam Morris

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As always, where's the pectoralis major? – Mephistopheles Apr 06 '19 at 19:10
@Mephistopheles I have found a further image that shows the pectoralis, does this help you in any way? – Liam Morris Apr 06 '19 at 19:55
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@Mephistopheles Due to how it's positioned you cannot see it on the leg portion. It is hidden beneath what have to be the triceps as the attachment of the pectoralis is too high up. The weird "necktie" muscle is supposed to be the pectoralis major of the wings, but it's very small andhow it's positioned means it would move the front paws backwards and forwards with each wingbeat while losing some power. The second picture has the wingmuscles behind the front paws, which means the wings are farther behind and would have the dragon fly face downwards but it might work. – Demigan Apr 06 '19 at 19:59
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Regarding picture #2 Thank's you just solved (almost) all of my problems! – Mephistopheles Apr 06 '19 at 20:00
@Mephistopheles I have replaced that with one that shows the skeleton as well, does that solve the rest of your problems? – Liam Morris Apr 06 '19 at 20:01
@Demigan Flying face-downwards might not necessarily be an issue for a dragon as commonly they are shown to live on mountains and swooping down to catch their prey. Also, it flys facedown, it may not be as aerodynamic but it will naturally be looking where its prey (likely horses or deer) would be. – Liam Morris Apr 06 '19 at 20:13
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@LiamMorris not an unsurmountable problem, but the artist of the drawing was so focused on the wings that he forgot to give the front paws proper joints. It can only move the paws straight forwards, and is very limited in it's motion. Again this isn't insurmountable. The artist also forgot to make the lower ribs stronger, as right now the sternum would be pulled into the abdomen and wreak havoc with the organs there with each wingbeat. an elongated ribcage would make the dragon walk very stiffly but allow it to fly without commiting seppuku. – Demigan Apr 06 '19 at 20:13
I just realized why it would be bad to have the wing attachments in the western picture behind the front paws. The dragon wouldn't just fly with it's face down, it's wingbeat would be downwards and towards the hind legs. This means that the dragon would make it's face and chest rotate into the ground. The only way for it to fly would be to fly in a partially upright position. I'm not certain but a really long tail could counterbalance this and help stabilize the dragon and fit within the dragon mythos. Drawback is less power generation for maintaining altitude but more power generation forward – Demigan Apr 06 '19 at 20:25
@Demigan Perhaps as well, if the bones in the tail were fairly dense (increasing their weight) that could also help to bring the centre of mass back? – Liam Morris Apr 06 '19 at 20:29
I don't think it would help get the center of mass back. Elongating it would help if it retains the same mass, but any extra mass would mean larger muscles and wings required. This would become a rocket equation where each extra weight in the tail to counterbalance would require more (heavy!) muscles to keep in the air which are placed at the front of the dragon's center, so you need more weight at the tail... A very light tail with a heavy object at the end, also not uncommon, would help more. – Demigan Apr 06 '19 at 20:34
@Demigan Ah of course, i had not considered that. Although, a possible option might be to add a ‘wing’ at the end of the tail, like in the first image. This may help to push the tail further back wihout adding too much extra mass. The membrane may also increase the wing surface area of the dragon, potentially making back some of the cost of the added weight. – Liam Morris Apr 06 '19 at 20:44
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Let us continue this discussion in chat. – Demigan Apr 06 '19 at 20:46
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considering the first image basically has no flight muscles, no it cannot be sound. – John Apr 06 '19 at 21:34
@Demigan I'm not sure, why'd they fly upside-down? – Mephistopheles Apr 07 '19 at 13:35
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@Mephistopheles Not upside-down, face down. Demigan was saying because of where the dragon’s center of mass would be, it would be flying at a slightly funny angle. If you read our discussion in the chat above, we mentioned how to fix it and why it might be like that. In short, dragons may be gliding creatures which jump from high perches to get up to speed. They have 4 legs because, when they land, they can not take off from the ground, meaning they would need to walk somewhere high up to jump off to be able to fly. – Liam Morris Apr 07 '19 at 13:42
Demigan also suggested lengthening the tail but keeping the same mass to move the balance back, allowing it to fly at a less awkward angle and more aerodynamic position. – Liam Morris Apr 07 '19 at 13:44
Well, I never intended dragons to be busy songbirds. They'd only have anaerobic flight muscles that are used only during takeoff and climbout. – Mephistopheles Apr 07 '19 at 14:01
@Mephistopheles Seems reasonable enough. One thing though is, because of their size, they would need to be going relatively fast to prevent them ‘stalling’ in the air. Similar to planes, they would need a way of getting up to speed before take off (jumping off high perches) and staying at a relatively fast speed to make sure their wings can push enough air away to keep them airborne. Maintaining speed could be as easy as just diving down if need be, their wings should allow them to fly if going fast enough. – Liam Morris Apr 07 '19 at 14:12

score 7 · Answer 2 · answered Apr 06 '19 at 19:37

Split the forelimb.

Making a 6 limbed creature from a tetrapod body plan is tricky. WB stack is littered with efforts on this front. Here is a new idea.

First, comparative skeletal anatomy.

https://www.slideshare.net/OmerRasool1/comparative-anatomy-skeletal-system-71723331

Look at the whale. Now imagine splitting the distal forelimb into two limbs: one with the radius as core and the other with the ulna. The radius and associated digits (5 at baseline but you can add more digits; polydactyly is fine) becomes the robust wing, availing itself of the scapula and other support structures.

The ulna also has digits and is much less robust. It would not be a stocky limb to match the hindlimb but something more like a Tyrannosaurus. These small forelimbs would touch the ground and allow ambulation but for fast motion they are not the equal to the hind limbs.

Having powerful back legs, powerful wings and spindly forelimbs means these dragons would not look like Toothless or Smaug.

Running at speed would be bipedal. The dragon would rear up and run like a bird. Wings might be used while running for propulsion or to jump. Some people think this use is how birds evolved wings in the first place.
The small front limbs would lend themselves to more delicate manipulation. Dragons could sit up and have a smoke, or play cards.
Front limbs might move during flight because they retain a connection to the humerus. Probably it would be some sort of rhythmic movement mirroring the wings.
In general I think dragons are depicted as too robust. I picture this dragon as along the lines of a crane.

What if I made the bone larger, but hollow, and used my graphene-magic on it? — Mephistopheles, Apr 06 '19 at 19:45
All the bones should be hollow to reduce weight, bird style. Hollow long bones should not be too troublesome - mammals have hollow bones too, but use the space for bone marrow. Your dragon can make blood in its spleen and have air inside its hollow bones. — Willk, Apr 06 '19 at 20:08
Your forelimb description made me think, Wasn't there a question awhile back asking how a dragon would go about knitting/sewing? Ha, there was! — EveryBitHelps, Apr 06 '19 at 23:27
One problem with this proposal is the lack of necessary musculature. In terrestrial vertebrates, both bones are operated by the same set of muscles. In your dragon, you'd have to add new muscles, as well as rework the elbow entirely because you want the radius and ulna to face opposite each other rather than parallel. I do like the idea though. — John Dvorak, Apr 07 '19 at 12:08
@Willk nice idea but you don't have to assume that the ulna isn't robust enough; sizing anything up or down is pretty easy for evolution, it's merely a question of how long the growth phase is allowed. Just look at the images you provided yourself for examples :-) — toolforger, Apr 07 '19 at 16:39

score 7 · Answer 3 · answered Apr 06 '19 at 20:08

The problem with wings is the necessary amount of power to lift the creature.

This is a bird skeleton:

Note the size of the sternum (the bone that all your ribs connect to). It's massive in comparison to ours and stands far out of the chest while a human sternum is basically flat in comparison. This sternum is what your pectoralis major muscles are attached to (the chest muscles).

The sheer size is because the muscles attached to it, shown here:

These absolutely humongous muscles are required to lift the weight of the entire creature up in the air, and the larger the bird the more % of the bird must be pectoralis major muscles just to keep it in the air due to the square cube law, but you can ignore this for the sake of cool. Despite this suspension of belief on the part of the square cube law you still want a bodyplan that can handle 4 paws and 2 wings simultaneously.

Note how these skeletons lack a large scapula. In the first picture you can see it mentioned but it's tiny and largely immobilized because everything is focused on that up/down movement of the arms, not about reaching forwards, backwards, upwards or downwards.

Having to have muscles attached to the chest for these extra appandages would diminish the amount of muscles for your wings. You could slightly circumvent this through kinematic chains.

An example of a kinematic chain is your quadriceps of your leg, or any other muscle that moves over more than 1 joint in the body. If you have muscles pull on one end of the bone they are attached to, you can use that to pull on the quadriceps, the quadriceps us that to pull on the muscle one joint removed, allowing you to transfer the muscle power from one bodypart to another. You attach a portion of the pectoralis major muscles to the dragon's leg, and have muscles above it attached to the wing (likely an adapted version of the triceps, romboideus, one part of the deloideus and trapezius). When flying the leg will be pulled down in the same motion as the wings and the muscles above that will simultaneously pull on the wings, allowing you to transfer the muscle power that went into the leg into the wing as well. This isn't wildly efficient and would likely make the leg flop up and down with the wingbeats, but it's an option. Ofcourse if you time it right and pull just as hard on the leg as on the wings, the leg would effectively keep still during flight. Although you'd be better off pulling it in as it would stretch the muscles above it and with that pull the wings.

Although note in birds that swelling is the muscles to flap and the muscles to lift the limbs, birds layer thos muscles on top of each other. — John, Apr 06 '19 at 21:30

score 0 · Answer 4 · answered Apr 06 '19 at 23:09

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Any depiction by Larry Elmore should suffice. More like angles; their forelegs are actually arms, and the wings protrude from their back, beginning just below the shoulder blades.

_{Dragonlance's blue dragon, Skie, as pictured by Larry Elmore in the original cover art for, Dragons of Winter Night.}

answered Apr 06 '19 at 23:09

Mazura

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It's a nice picture, and typical Fantasy depiction... but from an anatomy point of view it is plainly insufficient. Wings typically require a massive muscle to beat them (it has to lift the whole body, after all), and it's very unclear in your picture where said muscle would be. Actually, it looks like there's no such muscle and the wings are just aesthetic but non-functional. – Matthieu M. Apr 07 '19 at 09:24

Dragon forelimb placement

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