What's your stance on bringing back extinct species?

[Anomalocaris]

The beauty of a fantasy creature impossible to exist is it conveniently didn’t exist, so there is conveniently no evidence to provide any definitive set of characteristics for it, like there would be with a real creature that did exist, so whose defining traits leaves evidence and be identified and itemized.

So whether dragon’s characteristics are all feasible in a real organism, as demonstrated by their all being found in some other creatures, depends entirely on what your personal opinions of entire body of necessary characteristics required to qualify something to be a dragon.     If some of the necessary characteristics are it would be big and weigh hundred of pounds at least and it can fly under the power of muscles similar to those found in living organisms, then that would be a physics violation right there.    being able to generate in its gut or mouth fire hotter than the fire used to smelt ordinary metal and having its digestive tract survive the ordeal ?   both would be quite unparalleled in living or dead organisms.

As to the flying/weight issue:

https://en.m.wikipedia.org/wiki/Quetzalc...0%2520lb).

Generalized weight, based on some studies that have historically found extremely low weight estimates for Quetzalcoatlus, was as low as 70 kg (150 lb) for a 10 m (32 ft 10 in) individual. A majority of estimates published since the 2000s have been substantially higher, around 200–250 kg (440–550 lb).

And the fire thing isn’t as much of an issue as you seem to think. I assume you’re aware that Bombardier beetles manage to defend themselves without cooking their innards. I can easily imagine a mechanism where methane produced in the gut is ignited by the animal as it leaves the mouth, perhaps by a spark from tooth gnashing or some such. Methane burns at about 3500F, more than hot enough to melt iron, gold, and silver.

Boru

like with aerodynamic flying,  difficulty is scale.  the  rate of heat dissipation is usually a function of surface area, where as the amount of heat generated is usually a function of the volume involved in the reaction.   volume goes up by the cube of dimension and area by the square,  so maintaint a lower temperature than the heat source through rapid heat dissipation gets increasingly difficult the larger the creature or the heat generating device.    So the ability of a firing spitting creature or flame thrower to surviving by dissipating waste heat faster than it is being generated, and thus keep its temperature lower than the temperature of the flame, decreased rapidly as the scale of the creature or flame thrower gets bigger.       so if a beatle can survive a transient exoteric reaction in its innards doesn’t mean a larger creature, say a cat or dog, much less a dragon, can survive the same thermodynamic feat,  especially if it involves not just a transient exoteric reaction,  but a sustained jet of flame able to break down castle doors.