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Believability of a fantasy creature can go so far. Case in point--the title feature. I have first seen it on a Ringwraith's winged mount...

enter image description here

...then on Smaug...

enter image description here

...and finally on the dragons of Tui T. Sutherland's Wings of Fire series.

enter image description here

I never understood the appeal. Bats don't have it. Pterosaurs certainly didn't have it. It doesn't add to the wings' appeal--it just makes them look scrawnier.

enter image description here

Without the need for a spike growing from its elbows, a bat's wings look better and cover more surface area needed for flight. So in regards to adaptation, what point would elbow spikes on a creature's wings serve?

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    $\begingroup$ Stabbing things? $\endgroup$ – bendl Aug 30 '17 at 1:33
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    $\begingroup$ Flung off-center in a ground battle, elbow-spiked creatures dig them into the ground to either slow or stop undesired direction travel, or possibly as an anchor to leverage a quick pivot move to escape a blow. Also good way to inject a poison. $\endgroup$ – N2ition Aug 30 '17 at 1:35
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    $\begingroup$ The points at the back of bat wings are actually fingertips rather than elbows. A creature may (fictionally) need spikes there in order to manipulate things while not flying. They may use them to hold their infants. They may use them to move about while hanging upside down. They may use them to fight while not flying. they may use them for grooming or holding food. $\endgroup$ – smatterer Aug 30 '17 at 1:56
  • $\begingroup$ Those are static wicks... to discharge electricity cause by the air molecules during flight! $\endgroup$ – user6760 Aug 30 '17 at 4:10
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    $\begingroup$ @smatterer I don't think he's talking about the fingertips. The middle of the wings of all these creatures have an additional finger-like structure protruding from the actual elbow. $\endgroup$ – KSmarts Aug 30 '17 at 17:09
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This is what's known as drawing a picture without understanding anatomy

First the bat:
Bat
As you can see, it has a clear elbow, wrist (unlabelled), thumb and 4 fingers. Spikes on the ends of the fingers would not be unreasonable.

Next, one of the "dragons". This has a couple of problems
Wyvern
It seems to have a finger coming out of its elbow with a spike on the end and a couple of extra fingers with the thumb but is missing the first short finger on the leading edge of the wing so only one extra in practice. A quick glance at a bat would have shown that this was incorrect but when does that stop anyone.

Note that this error has not been made on GoT. There's no general rule, it's a mixed bag as to whether people get this wrong or not.

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    $\begingroup$ That does not answer the question. $\endgroup$ – JohnWDailey Aug 30 '17 at 12:10
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    $\begingroup$ @JohnWDailey, you seem to be asking us to turn a bug into a feature, I'm explaining that it's a bug. $\endgroup$ – Separatrix Aug 30 '17 at 12:36
  • $\begingroup$ Assuming you restructured the "hand" I could see spikes being a part of growth. Many canonical dragons tend to grow forever, so perhaps the finger spikes are just the beginning of the wings expanding. The growth of the dragon being sub-optimal due to its size. $\endgroup$ – user2259716 Aug 30 '17 at 16:27
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    $\begingroup$ I think the question is about the apparent "finger coming out of its elbow with a spike on the end", as all the creatures mentioned have them. $\endgroup$ – KSmarts Aug 30 '17 at 17:02
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    $\begingroup$ Extra fingers are hardly a problem. That part seems pretty OK. $\endgroup$ – Mołot Feb 8 '18 at 8:46
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The elbow spike is quite simply an extension or enlargement of the olecranon. This is the distal attachment for the triceps muscles, and will be important in dragon flight. Evolutionarily speaking, this enlargement allowed archaic proto-dragons to broaden the muscles and tendons that attach to the mid-arm, allowing for stronger wing strokes, easier take offs and increased gliding & in flight arm stability. Eventually, this will also lead to larger dragons, able to take advantage of the increased wing power. The actual visible spike itself is just dragon eye candy.

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    $\begingroup$ +1 This is the best "real explanation" so far. It certainly sounds plausible. Also, the claw spikes on the trailing edge could be a carry over of defensive spikes when dragons were smaller (like the spikes that some fish have in their dorsal fin). The spikes would be largely useless now (except for, maybe, hatchlings) but there may be no evolutionary pressure to remove them. $\endgroup$ – ShadoCat Aug 30 '17 at 17:34
  • $\begingroup$ Right. Those trailing edge spikes are just left over claws. Much like what you see on the wings of archaic birds or the already mentioned hoatzin. $\endgroup$ – elemtilas Aug 30 '17 at 22:13
  • $\begingroup$ @elemtilas How do the wings fold when rested? $\endgroup$ – JohnWDailey Aug 30 '17 at 23:24
  • $\begingroup$ The olecranon spike would rest alongside the body when the wings are folded. I know the images up above show the spike at kind of funky angles (as if it really were an finger bone!); but I think the spike would probably most naturally grow from the proximal end of the olecranon, parallel to the ulna. If the dragon "crosses" his wing-arms, those spikes will stick out to either side. If he rest his wing-arms folded while lying down, the spikes will rest alongside his chest. Now, you might ask, well what happens when his wings are extended, for example in flight --- if he bring his wing-arms... $\endgroup$ – elemtilas Aug 31 '17 at 2:16
  • $\begingroup$ ...back the wrong way, won't he stab himself in the sides? Well, I'm sure when he was an ungainly little pip, he probably did give himself a few jabs. Like any adolescent learning fine motor skills, a dragon will learn where to aim those spikes so as not to injure himself. And anyway, dragonhide is tough. I doubt he'd do much damage. Probably give himself little more than an aching rib. I'd also suggest that, as he plies the air with his wings, a dragon might rotate his wing-arms slightly. This would not only catch the air, but also turn that spike away from his body and any inadvertent jabs. $\endgroup$ – elemtilas Aug 31 '17 at 2:22
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Dailey I am here again to help you with your delightful biological schemings! Jumping off from Separatrix' fine bat diagram I have figured it out.

Your question: "What point would elbow spikes serve?" is not relevant to dragons, because the spikes are not at the elbow. Allow me to explain.

First the bat. bat with parts labeled

Now Smaug enter image description here

Smaug has an additional finger in his wing proximal to the spike on his "elbow"!

This solves the problem: the "elbow" on dragons is not the juncture of the humerus and radius/ulna, but rather a wrist-equivalent. The humerus, radius and ulna are condensed into short, powerful, proximal structures as happened in the whale and icthyosaur. This fact leads to the conclusion that the dragon wing is in fact derived from a flipper, and dragons are evolved from aquatic ancestors.

The role played by the radius and ulna in bats and birds is played by elongated carpal bones in dragons - a long "wrist". The evolutionary equivalent of fingers spread from this site to form distal webs similar to those in the bat as well as proximal webs as seen in Smaug and related dragons. Additional digits not used in the webs persist as "spikes" or nearly formed hand-like structures (like Smaug has).

That gives Smaug more than 5 fingers, you may protest. But that is OK. Dragons are polydactylous. Polydactylous cats get by just fine.
enter image description here

ADDENDUM @KSmarts comment made me think that it worth adding an image showing how a dewclaw could be very medial, as is the case for a dog. In the dragon that dewclaw oriented phalange would not be reduced to just one bone and would extend out to be the medial wing finger. dewclaw diagram from https://www.joshuanava.biz/human-figure/paws-and-hind-legs.html with my text box added

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  • $\begingroup$ If the apparent elbow is actually the wrist, why do all the digits except one meet at a further point and have an extra joint? $\endgroup$ – KSmarts Aug 30 '17 at 17:11
  • $\begingroup$ @KSmarts - I am looking at my hand. Yours is probably similar. My fingers, except one, diverge from my palm at the same point which is the end of the metacarpals. That extra medial wing finger the dragons have is a thumb equivalent, similar to a dewclaw, and one or more of their more proximal carpal (wrist) bones are elongated. $\endgroup$ – Willk Aug 30 '17 at 18:26
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Given that many Dragons also have claws, the wing spikes could be vestigial appendages that once were claws. They could also possibly be used in self defense, though the movement of a wing isn't designed for stabbing forward with significant force.

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  • $\begingroup$ Claws are present on finger tips... not on elbow... $\endgroup$ – L.Dutch Aug 30 '17 at 5:24
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    $\begingroup$ @L.Dutch as mentioned above, the wing tip is not actually where the equivalent to the hand is located, but rather it is located in what appears to be the elbow. The rest of the wing is actually the result of finger bones growing longer to support the webbed area in between. Bat wings have their own wikipedia page, which has a useful diagram .<en.wikipedia.org/wiki/Bat_wing_development> $\endgroup$ – Braydon Aug 30 '17 at 5:38
  • $\begingroup$ you are probably confusing helbow and wrist. The wing tip, also in the link you provide, is located at the wrist. $\endgroup$ – L.Dutch Aug 30 '17 at 5:59
  • $\begingroup$ @L.Dutch No, the wrist is in the middle of the wing, and the wing tip is an extended finger. Maybe this image is more clear. link $\endgroup$ – Braydon Aug 30 '17 at 6:16
  • $\begingroup$ askabiologist.asu.edu/sites/default/files/resources/articles/… helbow is clean $\endgroup$ – L.Dutch Aug 30 '17 at 6:18
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The first joint in the arm is the elbow, the second is the wrist, where you have the hand and fingers. Claws are likely here and primitive birds have them, for example the Hoatzin (at least when young). They can be used for climbing and gaining additional purchase.

Actually, this is one of the more believable features of these mythical animals.

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  • $\begingroup$ The "dragons" have an undeniable extra finger on the elbow $\endgroup$ – Separatrix Aug 30 '17 at 7:19
  • $\begingroup$ Ah - my mistake - I was referring to fingers/claws on the front of the wing, where they are clearly adaptations of fingers (whatever the number). However, I see now that the original question was referring to apparent skeletal structures from the elbow - they could perhaps though be cartilagenous intended to strengthen the wing in flight.. $\endgroup$ – Lee Leon Aug 30 '17 at 9:12
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I don't think they serve any biological function - they are there because artists wanted them there, and then became a 'tradition' which other artists copied. For instance, in 1978 Michael Whelan drew his first cover for one of Anne McCaffrey's Dragonriders of Pern books - The White Dragon. Book cover link (I tried to add the pic inline, but it won't play ball and claims it is too large, even though it isn't!)

In his book Works of Wonder, Whelan says he based the dragon on bat and crocodile, and asked McCaffrey questions on how it should look. I guess the 'claws' on the wing-fingertips are there to make it look less like a bat's wing, and more 'alien'.

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  • $\begingroup$ I see no elbow spike on that image. $\endgroup$ – JohnWDailey Aug 30 '17 at 14:20
  • $\begingroup$ That illustrator placed the spike where it should go if dragons are anatomically like birds and bats. $\endgroup$ – Willk Aug 30 '17 at 18:29

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