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February 11, 2012
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Speculative Anatomy - Dragon PAS system by LeccathuFurvicael Speculative Anatomy - Dragon PAS system by LeccathuFurvicael
I love my science classes, giving me inspiration to work on speculative dragon anatomy some more. XD

This time, I've explored a little into the pulmonary air sac system and how it might be helpful for draconic wing anatomy and respiration. Here is some more detail in terms of 'explaining' the decision to use the PAS system in this way for a dragon wing plan (this can be read in the comments, but this is to save viewers' time):

I have mostly been using pterosaur aerodynamics and flight physiology to help find what might work best for a dragon. In the case of the dragons I think of, they are usually about 10-15 feet in length with 30-foot wingspans (15ft for each wing). In a particular scientific article - "Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism" by Leon P. A. M. Claessens, Patrick M. O'Connor, David M. Unwin (seen here [link] ), numerous specimens have been studied, and as the animals became bigger, there has been observation of the presence of pneumatic structures in the body. The article states,

"There is a strong correlation between pneumaticity and size. Pneumaticity is generally absent in small pterosaurs, or confined to the vertebral column, but is almost always present in individuals with wingspans in excess of 2.5 metres and seemingly universal in all taxa with wingspans of 5 metres or more (Fig. 4). This suggests that density reduction via the replacement of bone and bone marrow by air-filled pneumatic diverticula likely played a critical role in circumventing limits imposed by allometric increases in body mass, enabling the evolution of large and even giant size in several clades." (Claessens, et. al.)

Subcutaneous air sacs are also seen in larger birds. To further quote the article:

"In birds, pneumaticity of forelimb elements distal to the elbow is restricted to large-bodied forms such as pelicans, vultures and bustards (Table S3). In these birds an extensive subcutaneous diverticular network, originating from the clavicular air sac, is responsible for pneumatization of skeletal elements distant from the main pulmonary system [20]. The occurrence of pneumatic foramina in distal limb elements of ornithocheiroids and azhdarchoids, and of a layer of spongy subdermal tissue in an exceptionally well-preserved fragment of wing membrane of an azhdarchoid pterosaur [16], [42], together suggest that a subcutaneous air sac system was present in at least some pterodactyloids. The primary role of such a system is likely to have been density reduction, as in birds [43], but it may have had other advantages. Differential inflation of subcutaneous air sacs along the wing membrane could have altered the mechanical properties (e.g., relative stiffness) of flight control surfaces in large-bodied pterodactyloids (Fig. 3d). In addition, this system may have assisted with thermoregulation [16], and could have also served as an intra- or interspecific signalling device during display behavior, similar to some living birds [44]. Thus, the presence of a subcutaneous air sac system likely played an important role in the functional and ecomorphological diversification of pterodactyloid pterosaurs." (Claessens, et. al.)

I hope this may have had helped me explain my perspective and my decision to include this theory into my speculative dragon anatomy.

Originally pencil sketches redrawn and colored in Photoshop CS5.

Art Stephanie Dziezyk/LeccathuFurvicael 2012. Do not redistribute, copy, alter, etc., any portion of this image without permission from me, the artist.
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PineRain Featured By Owner Jun 26, 2014  Hobbyist General Artist
Cool idea!
Inked14 Featured By Owner Jun 19, 2014
I have always loved dragons ever since I was a little girl and I love t learn about what they  were like or how they worked! When I saw this I was blown away, I had  never heard about this before such a interesting branch of anatomy, this is so cool! I also have a friend who is obsessed with (or unconditionally loves as she calls it) Dragons and Dinosaurs and I showed this to her and she was absolutely ecstatic and is going to incorporate this structural design into her drawings. She and I did have two most likely very stupid questions, one, how exactly did the air sac inflate and deflate? Did the bone itself expand or is this something else? And two, why couldn't this also work with the bat-like multi-fingered design, wouldn't it provide even more lift?
LeccathuFurvicael Featured By Owner Jun 26, 2014
Stupid questions are only stupid to those who think too confidently of their own opinions and knowledge. : ) So no worries! You pose good points, and I'll do my best to answer them as I can.

My best guess is that the air sac would inflate and deflate via a sphincter-like valve that would connect to air sacs in the bones (these bones are known as pneumatized bones - meaning that they are invaded by air sacs) and on to the lungs, or perhaps, more reasonably, have a vascular connection to the blood vessels in around the forelimb, much in the same structure as seen in swim bladders in most fish. Gases would be released from and absorbed into the blood through a delicate network of vessels known as the 'rete mirabile' in fish (translates to 'wonderful net'), and may work for the pneumatic air sacs in the wings of dragons.

If you take a look at how fish move up and down in the water, and notice that they aren't really using their fins to move vertically, that is that swim bladder at work, and the rete mirabile taking in and out gases from that bladder. Some fish have swim bladders that connect to their mouths, and they are fish that can swallow air from above the surface of the water, and may not have as much of a developed gas exchange system as those whose swim bladders aren't connected to their mouths. Betta fish are examples of fish who breathe air outside of the water, and actually depend on having access to air, otherwise they will literally drown. There are tons of other fish, mostly in fresh water with shallow depths or low oxygen content, that have similar systems to get oxygen from the air. But, for the air sacs in dragon wings, they may use similar physiology for any of these fish.

Pelicans are also known to have pneumatic propatagia (the skin that connects the wrist of the wing to the shoulder), and used for sexual displays, but sadly I've found very little on how they work. If I do find anything, I will hopefully understand the process better and share the information. : )

Also, the air sac would be much like a swim bladder in composition - a sac of elastic tissue that would expand and contract depending on how full it is of gases. I imagine it to be somewhat like a transitional epithelium (seen in mammalian bladders), but perhaps less robust to maintain a light weight in the wing.

And, finally, on your question of why the PAS system wouldn't work for a multi-fingered wing - well, it's mostly due to my lack of imagination I think XD. I hadn't thought of the rete mirabile design when I initially created this, so perhaps it could work to allow permeation into the wing digits despite how thin that cross-section of the wing is.

Thank you so very very much on asking your questions, and I really would love to see what your friend does with these concepts!! : D
Ikleyvey Featured By Owner May 18, 2014  Hobbyist General Artist
Wow, I had no idea about this structure! So it's used to compensate for the weight? But does it reduce the mobility of the wing? It seems logical for large pterosaurs to have these sacs. It would be great if dragons could inflate the sacs wen needed, for example, when they are on long flights. This is very interesting!
LeccathuFurvicael Featured By Owner May 18, 2014
As far as I know, these pneumatic air sac systems were used to reduce weight, and perhaps may aid in maintaining an airfoil shape to the wing while flying at lower speeds. I do not think it would reduce mobility, as airflow into the sacs would be controlled with small fluctuations, allowing the sacs to deflate when the wings are folded (or perhaps the motion of closing the wings forces the air out, which could be an issue considering the breath pattern of the animal. Huh - maybe even the act of flight itself forces air in and out of the lungs, semi-similar to a kangaroo's breath pattern guided by the motion of its hind limbs as they exert force on the kangaroo's diaphragm... I need to do some research on this!)

Thank you very much for your comment! ^^ You've helped the process of exploration continue for me by asking the questions that you have. : ) Cheers!
Ikleyvey Featured By Owner May 19, 2014  Hobbyist General Artist
I'm glad i could help ^_^
If the sacks don't affect mobility negatively, I don't see a reason why they wouldn't have them, it could only benefit their ability! But maybe the wing motion deciding the pace of their breathing (meaning them being completely tied) would be very limiting... This information is great, I love discovering new mechanisms that could potentially help dragons fly. Thanks for the explanation!
LeccathuFurvicael Featured By Owner May 24, 2014
You are very welcome! ^^ I definitely encourage looking at :iconjconway:'s pterosaur information and artwork for sure - great stuff. ^^
QuazarShark Featured By Owner Aug 2, 2012
Hmm, I've not heard about this before. I'm somewhat surprised that *TarawynWorldwalker hasn't hooted at me about this, is it a particularly obscure theory?

I have to agree slightly with :iconalister-murkerry: in that draconic wings (the way you and most people draw them) are bat-based and have a lot of mobility thanks to all those digits. Pterosaur wings have just that one big one, and would really have a need for something that can change the shape a bit more, I think.
It would seem a shame to sacrifice that degree of mobility in the digits and arms just for wing volume. In terms of big dragons keeping the wings rigid for long soaring flight though, I think it might be worth the "expense" of such a complicated and vulnerable mechanism.
Also it's fucking cool so who cares really?
LeccathuFurvicael Featured By Owner Aug 2, 2012
Well, it's at least not very often talked about except in the world of pterosaur research and birds that have these pnuematized sacs in their wings such as pelicans.

I do completely agree about how bats don't have to worry about a loss of camber due to the fact that their wing membrane immediately takes on a camber when air begins to flow with some speed over the surface - they use a lot of the muscles in the wing membrane to mediate that natural camber effect.

For smaller dragons with similar multi-fingered wings, they may not need the pneumatized sacs at all; I imagine perhaps larger individuals may utilize those sacs to some degree to produce a camber while they are still gaining enough speed to create lift, especially if starting from a vertical takeoff as a pigeon might (pigeons utilize a mechanism known as 'clap and fling' to expedite the generation of lift by creating smaller vortices as they clap the backs of their wings together and peel them away from each other on the downstroke - for more insight on this, there is a blog known as AeroEvo that can be searched for easily, along with searching for 'clap and fling' takeoff). Larger birds seem to be unable to utilize this mechanism due to weight, sheer size, or something I haven't found out yet, but this is slightly off-course when talking about membranous wings.

I probably need to update my info on all of this in the main artist's description - I learn new things about this stuff all of the time! And you are right - it's pretty fucking cool, and it's fun to speculate. :D Thanks for your awesome comment!
Fluffysminion Featured By Owner Jul 30, 2012  Hobbyist General Artist
That's really interesting, I find it fascinating techniques adopted to facilitate flight, there always seems to be something else to learn about them.
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