My Little Pony: Friendship Is Magic/WMG/Setting/Dragons

Scaly fire-breathing reptiles, ponies don't have much concrete information on them, so guesses appear. If you have guesses on other things then:

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Dragon birth and development.
As of Owls..., we see that dragons are an infanticidal and cannibalistic species. Also, Spike is consistently referred to as a baby dragon, yet is at the same level of comprehension and cognitive development as the rest of the residents of Equestria. I suppose that, like other reptiles, dragons are able to take care of themselves nearly from birth, and they are in a constant danger of being eaten by their bigger relatives. Princess Celestia realized this and how intelligent dragons are, and so created a mutually symbiotic relationship between her students (to give them an assistant and teach them leadership skills) and baby dragons (who learn from their pony and get protection from their larger kin) to make everyone happy. Not sure what happens when Spike grows up, though. Maybe Celestia is pulling a Baron Wulfenbach, making it so the next generation of dragons is fully of friendly allies to the ponies?

There are millions of different things that could affect a dragon's maturation, not just greed.
In Season 1, we saw 2 dragons that were not only highly typical, but almost exactly alike, save for color (one red, one green) and the presence of retractable claws (in the green one). However, Spike has had no less than 3 different visions of his adult self: the fat, lizard-like beast he's turned into in "The Cutie Mark Chronicles", the very manly Imagine Spot in "A Dog and Pony Show", and most recently, in "Secret of my Excess", a wingless and more puffy version of the typical beastie. All of these could be valid adult forms dragons can take, and there are simply a huge variety of factors that can trigger dragon-puberty.
 * Spike actually assumes the form from "The Cutie Mark Chronicles" for a moment during "Secret of My Excess." It happens when he destroys Sugarcube Corner.

Spike's fantasy in A Dog And A Pony Show was not purely his imagination.
A dragon whelp who is not allowed to practice greed and consequently is kept from having his abnormal growth spike can eventually slowly grow into a Dragon Knight, a creature with less physical power and longevity than a true dragon, but more intelligent and adapted to life in society. Those cases are very rare, though. A Dragon Knight is always fantastically brave, generous and devoted to the protection of the ones he loves and cares for - qualities that are absolutely necessary to transcend the feral dragon instincts and to become a Dragon Knight in the first place.

Dragon life cycle theories.
It's likely that dragon mothers lay only one egg at a time, since dragons don't appear to be common in Equestria - if they were, they would have overrun the land. Alternatively, most of the dragons spawned are killed in battles over hoards, with only the strongest surviving. While a dragon whelp displays at least the same potential for intelligence as any pony, when raised by a dragon, they will only be as intelligent as the dragon raising them for obvious reasons.

When a dragon whelp becomes of age, he experiences a greed and growth surge (as depicted in Secret To My Excess) which leads him to fight his mother (and siblings if available) for the hoard and the lair. The losers are either killed or flee the battle to try and find a new lair. Possibly the dragon shown in Dragonshy was uprooted like this. The hoard in the cave may not have been originally its own - perhaps it was left there from the death of the previous owner.

Only in absence of gold and jewelry nearby will a whelp start collecting anything else it can put its claws on. A dragon's greed surge eventually resides to manageable levels. Only after this does the dragon truly mature, gaining wings and regaining a certain level of sentience. For the rest of their life, their main activity will be protecting their hoard. It is possible that from that point on a dragon's intelligence increases all throughout its life, therefore extremely ancient dragons may become as intelligent as ponies, if not more.

Adult dragons chase off infant dragons as soon as they can begin hoarding.
This prevents the adult from having to fight the child, and helps with species distribution and propagation. It also means that the green dragon wasn't being a jerk; that's just as civil as any interaction between a mature and a semi-mature dragon gets.

Dragons propagate in the same way cuckoos do.
Dragons appear to be, by and large, solitary creatures. Despite being intelligent enough to speak and understand various concepts, their violent and greedy natures mostly leave them unable to form relationships, or a real civilization, between their own kind. Even the acts of courting and mating might be difficult, and they don't raise their own offspring. Once a female has mated with a male, she goes somewhere far away from other dragons and leaves her eggs in various places, never to be seen by the mother again. If the dragon egg is lucky enough, it might be discovered by another creature and is adopted. Unfortunately, their tendency for violence and greed is genetic and the young dragon eventually takes over the area and causes much havoc for the other inhabitants without the proper intervention.

Dragons hide eggs that are close to hatching near places with lots of stuff to hoard.
After hatching in a safe place, the baby dragon starts collecting things, which spurs growth, with helps with collecting, and without anyone to stop the process, this allows the dragon to reach physical maturity in a matter of days. The baby dragon is small enough to get started without anyone noticing it, and by the time people realize it's there, it is large enough that they can't stop it.

Dragons usually reach physical maturity before mental/emotional maturity.
Given the events of Secret of My Excess, this is almost certainly true, but putting it in words anyway. Dragons can reach physical maturity almost instantly once they start hoarding, and that fast growth is a very useful survival trait, which implies that most dragons make use of it.

Continuing that line of thought, Spike's pony upbringing has actually stunted his growth. On the upside, he's unusually well-educated and socialized by dragon standards.
 * It could make sense. Humans stay in baby/child phase for much longer than other species. While it does leave young humans more vulnerable, babies and children can learn new things a lot faster. By staying as children longer, they have more time to learn new things. With most animal species, the young learn new things a lot better, so it's completely plausible that Spike will learn more than most dragons can because he stays in a younger state longer.

The influence of greed doesn't always result in an adult dragon being a mindless brute.
Because we've seen several adult dragons, with hoards, that spoke coherently (an ability Giant!Spike loses) and could be reasoned with (it took the reminder of a big gesture to Rarity to bring 'Spike-wikey' back). The one in Dragonshy was protective of his hoard (understandably, Rarity was trying to nick stuff), but backed down once he was scared/talked into leaving, and the one in "Owl's Well That Ends Well" just showed that dragons don't like baby dragons in their lairs eating their hoard/food. Which again is reasonable, even if trying to kill Spike wasn't.

Zecora's explanation seems to suggest that Giant!Spike results in the way he does because he is able to hoard as much as he pleases without being held back. Were Spike able to gather a hoard with some limitations (Rarity knows what's worth keeping, and they kind-of share a love of gems) we may see a different result. If this episode did show dragon puberty - on a warped, quick scale - then Twilight can't keep Spike a baby forever. They're going to have to find some way of managing it while he's living among ponies in a place with a lot to get his attention.

The ponies didn't know how Spike would react to being given so much, so quickly, or that he would come to the conclusion he could just take. If they'd known -- and Twilight should have been made aware her adopted son was such a risk -- they would have reacted differently and Spike may not have had this destructive growth-spurt. On the other hoof, if Ponyville had known they needed to treat their little dragon differently for fear of him turning into an uncontrollable monster…the poor little guy may not have been able to stay in the first place. (Also, Celestia, you had to have known about this? Why didn't you tell Twilight?).
 * Spike wasn't really mindless, he just wasn't interested in talking. He was clearly capable of understanding everypony that talked to them, and actually used a fairly clever trick to disable the Wonderbolts instead of just trying his fire breath. Spike was actually talked down without being stared into submission first, even if it took Rarity to do it. And while we haven't seen how other dragons act when they're not guarding their hordes, the reactions of Fluttershy and Rarity imply that Spike was acting as expected.

All Dragons are Male
Well, technically they have no gender, but appear masculine. They reproduce asexually by spitting out eggs like Nameks in Dragon Ball.
 * That, or female look and sound VERY much like guys and come mating season they have to check if they have the correct biological partner.

Dragons have two separate "lifecycles" they can go down.
In the first one, which 99.9% of dragons go through, they accumulate a large hoard and magically grow faster and faster. In nature this is encouraged by adults, but limited by lack of loot to hoard of their own. The larger their hoard gets the more they mature, and after a certain amount of time that maturity becomes permanent. When Spike gets a whole bunch of loot in "Secret of My Excess," he artificially accelerates the process. Along this path dragons lose a part of their intelligence, but Spike took it even further. You can see this in action with many stupid adolescents and very stupid adults. Spike seems to be the most intelligent dragon we know.

Along the other path, we get Eastern dragons. They take even longer to grow up(thousand years, anyone?) and never gather a hoard. They instead learn wisdom and knowledge taking the long way around, and when they finally reach maturity are some of the smartest and wisest being in Equestria. Spike is on the first steps of this road, having been raised by ponies and now rejected dragon society. One possible "smart" dragon is Discord. He is not actually what everyone thinks he is, but an ancient dragon driven insane by the tide of years, until he broke under his chaotic duties and tried to take over. His appearance does resemble many Eastern dragon traditions, albeit all at once.

Dragons hoard treasure not because of greed, but to use as a food supply.
This is implied by Spike's desire to eat gemstones.
 * Perhaps dragons must ingest gemstones in order to fuel their fire.
 * Or to mimic the dragon from Beowulf.
 * The dragon in "Dragonshy" seems to use his mostly as a bed
 * However, the dragon on "Owl's Well That Ends Well" seems to confirm this
 * I think they do so as a mating display. Older dragons don't really consume gems but like to display them for potential mates because a large hoard can be used to feed many offspring (or given dragon longevity, feed an offspring for a long time). That's why older dragons hoard gems while Spike tries to eat them every chance he gets when not trying to impress Rarity. In fact, Spike helping Rarity with the gem accumulation might be a subconscious mating display.

Equestrian dragons function more like intelligent animals than sentient beings. However, due to being raised by the ponies of Canterlot, Spike has developed super-intelligence.
In the show, we've only seen three dragons, Spike, one in "Dragonshy", and one in "Owls Well That Ends Well". Spike, who is supposed to be a child, appears much more intelligent than the second one, who said at most four words and communicated with grunts and roars the rest of time. The third didn't even say that much. This would explain why Fluttershy reacted the way she did when she first met Spike, and why she didn't know that he could talk. Because, young dragons normally can't.
 * Or perhaps it's because Twilight temporarily aged him up into an adult when her power went out of control?
 * It's also possible that dragons simply have a language all their own. The dragon in "Dragonshy" certainly seemed intelligent enough and displays a myriad of different complex attitudes and expressions that suggest intelligence (including sarcastic skepticism) and even tries to rationalize his actions (albeit somewhat poorly). He started communicated in the pony's tongue because he was forced to. If anything, dragons seem to be slightly more intelligent than ponies (the number of learned skills Spike alone possesses is ridiculous, and he's just a baby) as none of the ponies seem to be able to communicate with any other creature in their own tongue.
 * "Secret of My Excess" gives us a nice bit of background into how dragons work in Equestria. The greedier (and more mature) Spike got, the more animalistic he became. As a baby, he spoke normally, as an adolescent, he resorted to Hulk Speak, and as an adult, he just roared. The implication seems to be that while dragons have the potential to function and speak on pony levels, it becomes harder and harder to do so as they mature, which might be why the dragon from "Dragonshy" spoke in a rather forced, childish manner.

Dragons are immortal.
As in they are incapable of dying of old age (a "nap" for them can last for a hundred years!) or disease but they can be killed by external forces (although this is very difficult). Celestia will eventually age and die herself as despite her power she is still mortal (albeit long-lived). Spike is being groomed to be Equestria's eternal guardian and defender as he will far outlive anyone else in the series.

Spike's fire transfer ability is a racial skill/ability of dragons.
Let's look at what we know about the dragons in My Little Pony Friendship Is Magic.
 * They tend to have hoards, many times what they could logically carry.
 * The dragon from "Dragonshy" per example, had a hoard large enough to comfortably use as a bed.
 * Similarly, the dragon in "Owl's Well That Ends Well" has an entire cave full of gemstones.
 * They occasionally move to new places.
 * The dragon from "Dragonshy" was mentioned as having recently moved to the mountain near ponyville. Additionally, the end of the episode clearly states he went to find a new place to hold his nap.
 * Dragons are at the very least capable of some inherent magic
 * More specifically, their relatively small wingspan implies they use some other means of propulsion for flight.
 * Also, the fire itself.
 * For one thing, they would have to eat tons and tons of high-calorie food, just for a single blast of fire.
 * Second, Spike's green fire suggests that maybe, the fire is not the result of a chemical reaction.
 * Dragons are EXTREMELY protective of their hoards.
 * "Dragonshy's" dragon per example, responded to Rarity's suggestion to let her take it from him by practically kicking her out of his cave.
 * "Owl's" dragon responded to Spike eating a few gems (and, admittedly, his challenge) by making what appeared to be a very serious attempt at killing Spike.

Add to this that Spike has also shown the capability of sending (small) objects by fire (ending of "Griffon the Brush-Off"), and a logical conclusion would be that dragons use their fire in nature for two things (other than combat/self defence/fun):
 * Quickly sending new additions to their existing hoard.
 * Moving their hoard without having to carry it.

In turn, this could possibly mean that Spike somehow sees Princess Celestia as his hoard (awkward), but also that somehow the Princess reverse-engineered his natural abilities to use him as a sentinent, living fax-device.

Dragons also have a monarchy or hierocracy like Ponies
Garble called Princess Celestia a namby pamby pony princess because Dragons have a strong ruler that is rarely seen unless you are causing serious crap to happen or are just very honored. His wrath is immense and most species fear him and or her. Possibly if one is introduced on the show he would be voiced by John Hurt for extra coolness.

Dragons are a dying species.
Fluttershy mentions that she's never seen a baby dragon before and didn't even know that Dragons could talk. Clearly they are a rare and mysterious breed that are extremely uncommon. Also as evidenced by Spike young dragons are very small and vulnerable creatures that can often fall prey to larger predators including other dragons. It also seems that dragon's eggs are rare themselves, since they live so long dragons rarely breed. This is why many dragons choose to donate their eggs to Celestia and her students in order to ensure that their young reach adulthood and ensure that dragons survive and to train them to possible weed out some of the behaviors and instincts that led to them almost dying out in the first place.
 * Probably Jossed in Dragon Quest. The dragon migration had numbers probably ranging in the millions. However, this may only apply to flying dragons.....
 * Millions is a bit of an exaggeration, there were at least hundreds of them, but there is no way to tell if that was the world population, or a fraction of it.

Dragons used to be a society before Discord or Celestia's reign.
It's generally taken for granted that rule of Equestria began with Discord's reign of terror or an Alicorn monarch that was dethroned, but eons ago, before Discord first appeared, the land was instead ruled by dragons, with Ponies and other races living under Dragon protection in relative peace. This came to an end when Discord finally appeared to establish his rule of Equestria, destroying Dragon society by inflaming the young dragons' greed and turning them feral. The species tore itself apart for Discord's amusement, leaving only solitary, wild dragons in the place of the land's protectors. Once he had destroyed one culture forever, Discord declared himself king and tormented the ponies until Luna and Celestia overthrew him. The dragon-hatching ritual unicorn students undertake is a part of a hope by Celestia that maybe one day the ponies can discover a way to undo Discord's curse and allow the dragons to escape extinction.

Spike's dragon species is native to Zecora's homeland.
It would explain why we haven't seen another dragon like him, and why Zecora is the ONLY one who knew a thing about what was happening to him in "The Secret of My Excess". Granted, Zecora knows a lot of things that other ponies don't know, but she did know a lot about Spike's species and we haven't even seen a dragon like Spike in the Everfree Forest.

Spike's species is native to the desert from "Over a Barrel".
It was mentioned that the buffalo herd had respect for dragons, and even did a lot to make Spike comfortable. It's possible his species is native to that area, and perhaps even have spiritual significance to the buffalo tribe.

Dragons have 3 subspiecies/races mirroring ponies.
They maybe have similar abilities what ponies have (plus dragons powers). Also not counting other dragonlike creatures. So we have: Also as a bonus (if we asume that Sea Ponies are part of My Little Pony Friendship Is Magic setting)
 * Wingless Dragons - Spike's race, maybe have some connection with ground, animals and plants.
 * "Animals" like ponies, perhaps?
 * Make sense, this propably reason why Unicorns hatch wingless dragon eggs and (maybe) keeping them as Familiars (if Spike is not only one)
 * Or possibly the Wingless Dragons have some sort of pact or agreement the ponies, supplying them with some of their eggs so the ponies can raise the dragons to defend them from some of the larger, nastier creatures out there. I can't imagine just what the dragons get out of this arrangement though.
 * Spike is great example, he like being with ponies, he feels natural with them, he even have crush on one pony, also he is good with animals (he takes care of Flutershy pets in Dragonshy), and he treat Bloomberk as character just like AJ.
 * "Good" with animals? When he see him at the end of the episode, he's at his wit's end, particularly with Angel.
 * Winged Dragons - like Red and Green ones, probably can walk on clouds and control weather.
 * Horned Dragons - unseen, with some magical powers (maybe like Dragons from D&D).
 * Water Dragons - Steven Magnet kind, they don't need to have hair.
 * Alternatively, Water Dragons ARE the Dragon equivalent to Unicorn Ponies. Steven at least certainty is magical...

"Dragon" is a broad term for several different species with very different form and temperament.
It doesn't take much effort to notice Spike is not very similar to the other two dragons the cast has encountered so far; his fire is green, and appears to be more on the harmless/magical side compared to the mundane but much more dangerous fire the other two possess. Additionally, he's flightless, and his grown shape is very different. However, the red dragon and green dragon, while appearing to be simple pallet swaps of the same species were also different kinds of dragon. The red one was a mountain dragon, intelligent but also a fairly lazy form of True Neutral; he just wanted a place to sleep for a long time, and preferred to deal with polite attempts to get him to leave by ignoring the ponies or displaying a token threat to get them out of his cave. When Dash kicked him in the face, he got angry, but even then he just roared and blew smoke in hopes the ponies would leave, and backed down when Fluttershy scolded him; it's possible it was a fairly young dragon. The green dragon, however, was a forest dragon, a more territorial and violent breed due to the general scarcity of gemstones in heavily wooded areas like the Everfree Forest. The extremely Disproportionate Retribution the green dragon presented to Spike's ineffectual challenge was simply the green dragon treating him as it would a challenger from its own species, while Spike attempting the same thing with the red dragon would have likely just resulted in the red dragon ignoring him or simply attempting to scare him off.

The giant lamprey eels in the gorge are actually a species of dragon.
Eels are see creatures, yet the gorge where Rainbow Dash's pet race takes place is nowhere near any body of water. They are gigantic, and look enough like dragons to guess. I suppose the ponies call them eels because that's what they also resemble- it is common knowledge in Equestria that they are only eels in name, much like a panda is sometimes called a "bear".
 * ...Pandas have been genetically proven to be bears. Anyway, those "Eels" are known as "Quarry Eels", but the theory that they could really be dragons is still valid.
 * The Quarray Eels could really be anything, not just dragons. They could be sea serpents adapted to life on land, mere land-dwelling eels, the heads of a single monster…

Spike is an Eastern dragon.

 * He is shown to be different from the other dragons in the series not just in appearance, but in other attributes as well. He seems to be more "magical", and in "Party of One" we can see him floating. He's short and stocky because he's a baby, but as he gets older he'll get longer and thinner, more strongly resembling the Eastern dragons we commonly see.
 * I don't know if this would make the guess Jossed, but in "Secret of my Excess", Spike's huge adult form is more or less a puffy, wingless variety of the usual dragon.
 * Spike could be a crossbreed.