"Is the dragon realistic or magic/k?"
To be clear, by realistic I mean Dragons which might have followed some sort of recognisable evolutionary path and might have evolved on Earth alongside the dinosaurs (as an example).
However, realistic Dragons are a headache from start to finish, especially if an author wishes to include historical/mythical hints to one. So I have quite a lot of sympathy for anyone who tries to create such a beast and a lot of admiration for anyone who can do so successfully.
The problems are numerous and what follows is a list of the biggest obstacles to the convincing existence of a "realistic" Dragon.
For a Dragon to fly it needs to have a sufficient and huge wingspan in order to generate lift. In order to stay in the air the wings needs to be able to create enough lift to counteract gravity's pull on the mass of the body. Birds get around this by being relatively small and very light, with honeycombed bones that reduce their weight and large, light feathers which increase the surface area of their wings. So at one end you have something the size of a Shitzu, sorry Shih-tzu, that is like a flying, fire-belching brick with the wingspan of a couple of albatrosses, while at the other extreme is something whose light, brittle bones that would shatter when it tried to land because it has the wingspan of a mid sized plane.
The muscle mass needed to generate that much lift would also have to be densely packed to manoeuver the wings, and still have to be light enough to not get in the way of the mathematics of flight. Which brings us back to the fact that a realistic Dragon must have limited size. Increasing size and therefore flaming/maiden snatching capability increase fragility and therefore the risk that the thing would snap its own wings just trying to take off.
Right, fine, scrap the wings! They can still breathe fire!
Dragons have to be big and capable of causing serious damage or (unless you are Terry Pratchett) they aren't worth the effort of putting into a story. So you could go down the giant lizard route, but then you're just writing about Komodo Dragons, which while cool and a little terrifying for existing at all, are not actually Dragons.
A realistic fire breathing Dragon would require a fairly interesting biological process capable of changing ordinary food, people, animals, cabbages etc, into FIRE. A certain movie posed two chemical glands which produce a combustible chemical when combined. Alternately simple fermentation by bacteria in the gut could produce methane or other combustible gas, to be stored in a Hindenberg-organ (too far?) for release and ignition at an appropriate time.
A single dragon a species does not make.
Funny how so many fantasy Dragons exist as singular anachronisms. Where did they come from? What happened to their Mum and Dad? Don't they want babies?
Wait, wasn't there a film about this?
Yes, yes there was (ten Dietrich Points to anyone who guesses what the film is) and it illustrates the problem with Dragon breeding rates. If Dragons do not breed quickly then they are going to be very wary of people (who do breed quickly, certainly compared to the lifespan of the average fantasy Dragon) who will be competing for territory and resources. If they do breed quickly then, assuming they are the average flying-killing-bad news type and not one of Pratchett's Swamp Dragons, then the world they inhabit is very quickly going to become a burnt-up cinder.
We tend not to think about it today but for your average medieval-type village sized society, the loss of a field of crops is a disaster. Such people cannot simply go to the shops and get a new supply of food. A Dragon who is marking their territory (?) or just being a general pain in the arse by burning things could very quickly reduce an entire nation to starvation by denying them the ability to reap a harvest.
In fact the entire world could be rendered infertile (read black 'n' crispy) by a relatively tiny number of cranky scaled airborne flame-throwers. Taking Earth as an example, give each Dragon an average territory of 2000 sq miles (wolf packs have been known to have a territory this large and they can't even fly) and taking into account the fact that only one-eight of Earth's surface is capable of supporting crops, 12,356 Dragons having a bad hair day would be enough to turn the world into a giant BBQ. Compare this to the 7,100,000,000 humans who have just about managed to avoid that scale of destruction (for now anyway).
Unless the Dragons agreed upon some sort of Dragon-crop-rotation which would allow people to replant and reproduce between each cull....
Allowing humans to recover between raids would probably give rise to a new occupational category: Dragon Slayer!! Or in the modern world, Agricultural Protection Associate. Given the brutal necessity of defending their land against Dragons, they might not be complete feckwits and therefore able to do the job.... Since evolution happens much more slowly than technological advancement, humans would therefore cause Dragon Extinction within a couple of generations at most.
All living things require nutrition, especially a fire-breathing Dragon. Given the calorific value of a food is actually based on setting it on fire (no really, but don't try this at home):
How many people does a Dragon need to eat?!
The average male human in the West is advised (apparently) to eat between 2000 and 2500 calories each day, unless he is a professional athlete, in which case it is about 6000.
How many calories would a two ton fire-breathing lizard need? A person contains around 77,000 calories (disregarding bones), and while a basic amount of human noms would sustain the Dragon's body, flaming would require additional, substantial calories. A typical elephant requires 40,000 calories per day. And elephants don't breathe no fire, yo.
That requirement could be reduced by having meals tied to stakes by helpful villagers. No need to chase those tasty virgins! Alternately the Dragon could be a seasonal pest, spending large periods of time dormant. Speaking of hibernation.
Gold gold gold gold gold.
Assuming the realistic Dragon carries a pilot light, one explanation I have for the whole gold hoard thing is that gold is a very good thermal conductor and would help to translate some of the Dragon's intense (I assume) body heat into the rock/earth of their lair thus warming the ambient subsurface temperature a few degrees (after a long time I'd guess), allowing the Dragon to survive the sub-zero temperatures that might occur during an ice age or that might be prevalent in their isolated mountain lair.
Alternately the GOLD acts as the colourful petals of a flower, or in the case of the Carrion flower, the scent of rotting meat, to attract gold-hungry human snackage.
That or Dragons evolved from magpies and never left the "Oooh! Shiny!" reaction behind.
This is too complicated, can I just say my Dragon is magickal?
All of the above can however be brushed aside with impunity by implying, hinting at or flat out telling me/us/the reader, that Dragons in any given world are magic/k and are fueled and sustained by it. Or that they are like nuclear reactors for magic/k, giving out a certain quantity of magic/k per horse/virgin wench devoured. But I'll go into that in more detail in Part Three.
If we start comparing Dragons to Nuclear reactors then all of a sudden we start to think that Nuclear is a power source that can also be used to destroy, and any Dark Lord who wants to crush the world to their rule would probably be wanting a Dragon to back up their legions.
That is a possible reading of The Hobbit, and let's be honest, who doesn't like Smaug?
To be continued in Part Three.
Question: Why does a regular dose of virgin placate a Dragon and prevent it from marauding, while everything/one else is simply food?
Answers below, the best ones will get a further 10 Dietrich points and a pithy response...