h, dragons. Nearly every culture on Earth has legends about them: flying reptiles of terrible strength, voracious appetite and sometimes the ability to cook their own food with superheated breath. What would the world be like if dragons were real? Well, look around, because there are over a dozen species of dragon on Earth already, mostly in southeast Asia.
Indonesia's giant monitor lizard, Varanus komodoensis to the zoologists but more popularly known as the Komodo dragon, doesn't really count. It's certainly a powerful and carnivorous reptile, and while it doesn't breathe fire, it does have a mouth so toxic with bacterial decay that only one person has ever survived being bitten by one, while many hundreds have died. But it doesn't fly, so really it's just a glorified iguana.
True dragons—members of the genus Draco of the lizard family Agamidae— are also known as the "flying lizards" thanks to the scaly membrane which stretches between their fore and hind legs. The membrane is supported by ribs which grow away from the body, and at rest the whole structure folds securely against the lizard's sides. Like the gliding membranes of a flying squirrel, the "wings" of a dragon lizard permit the animal to glide from tree to tree without touching the ground. How cool is that?
Still, the dragons of myth have more in common with the unrelated flying reptiles of ages past. Today's dragons are actually the third and smallest group of reptiles to discover the art of flight. First in line were the pterosaurs, beginning with sparrow-sized pterodactyls during the Jurassic period (roughly 200 million years ago), which became larger over time and eventually gave way, during the Cretaceous period, to the larger pteranodons, and eventually the largest flying animal that ever lived: Quetzalcoatlus. The largest specimen ever found had an incredible wingspan of 15.5 m (51 feet)—bigger than most modern fighter planes! Sadly, the pterosaurs disappeared in the K-T asteroid impact 65 million years ago, which wiped out the dinosaurs.
Could their fossilized remains have spawned the dragon myth? We'll never know for sure; the idea seems plausible, but there's no evidence to support it. Still, the skeletons of the monster pterosaurs do not show the strong muscle attachments necessary for flapping. Like the modern albatross (or the even more modern hang glider), they were soaring creatures, unable to take off without a strong
headwind or a high cliff to jump from. And while their smaller kin, the pterodactyls, were flappers and could probably take off on their own, from the design of their mouths it's doubtful that either animal was any fiercer than a pelican or oversized seagull.
But the other type of flying reptile—archaeopteryx, the ancestor of modern birds—was probably a real handful. It was apparently a descendent of carnivorous theropod dinosaurs, similar to the savage velociraptors of Jurassic Park—not exactly the critters you want to see taking to the air! Still, archaeopteryx was only the size of a chicken, so for all its ferocity it would not have posed a major threat to human beings, if human beings had existed at that time.
The weighty issue of dragon flight
One thing we all know about dragons is that they're fully capable of killing and eating a grown man, even one with metal armor and weapons to protect himself. There are a handful of modern species whose larger members can accomplish this feat, including the tiger, the crocodile, the polar bear and grizzly, the great white shark and the anaconda. From a comparison with these creatures, we can speculate that a dragon of truly mythical appetite would need to mass somewhere between 250 and 1000 kilograms (550 to 2200 pounds).
But could an animal that heavy really take to the air? To find out, we can plug the numbers into some simple aerodynamic calculations. First of all, for any object or creature to fly, it has to generate lift which equals or exceeds its weight. This lift depends on a variety of factors, of which the most important are airspeed and wing area. And as it turns out, a creature in the range of 0.5 to 1.0 tons can be supported by about 45 square meters of wing, provided it's moving through the air at 6 to 10 meters per second (12 to 21 mph). This could be accomplished easily enough, either by waiting for a headwind the way an albatross does, or by dropping from a height the way dragon lizards and flying squirrels do. (In this case, a drop of 5 meters, or 15 feet, is sufficient.)
How long the creature could stay in the air depends on another variable: drag. And drag is sensitive to wing chord—it favors long, skinny wings over short, fat ones. The ideal dragon might look something like a sailplane, but unfortunately, gliders of this type are made of aluminum, and would be very difficult to reproduce using fragile skin and bones as the building materials. In practice, the wing would need to be fairly broad, with a reasonable compromise being a span of 15 meters and a chord or width of 3 meters.
Coincidentally enough, these are just about the same dimensions as Quetzalcoatlus, whose weight estimates range from a kitelike 50 kg to a fairly formidable 220 kg (110 to 485 lbs). So if we're willing to accept a somewhat clumsier flier, the man-eating dragon of our dreams and nightmares is well within the realm of possibility.
And what about flapping? Would our dragon have to soar and glide like a sea bird, or could it possibly take off under its own power? This question gets a bit trickier to answer, but the bottom line is no, not really. Even a 10 kg (22-pound) tom turkey, with its enormous breast muscles, has trouble flying more than a football field or so. With better gliding wings it could go farther, but of course larger wings are harder to flap.
Using very rough calculations based on the 77 pounds-per-square-inch failure strength of a typical muscle, I estimate that a flapping dragon would need to have virtually its entire mass tied up in breast muscle, with not very much left over for the teeth and talons, the strong limbs and stronger stomach it would need to devour a human being. But a compromise design, with moderately large flapping muscles, could keep itself airborne more effectively than a pure glider could. And look cool doing it, yeah.
As for the ideal body shape, we can look once more to the sailplane for inspiration: long and skinny to minimize drag, and also to fit with the serpentine descriptions of dragon mythology. However, I'm going to assert that the body, or at least the head, needs to be at least half a meter wide, and preferably wider, so that our dragon can reasonably expect, if not so swallow people whole, then at least to bite them in half, or sever limbs and heads in a single gulp. For reference, here is a crude drawing of just such a creature, with a human alongside it for comparison. Scary, no?
Legendary lizard kings are a gas
A final thing we know about dragons is that they breathe fire. Interestingly, although this trait has never been documented in nature, it isn't anatomically difficult to achieve. The anaerobic gut bacteria found in many animals are producers of methane (CH4), a gas which burns readily in oxygen. Air mixtures of 5 to 14 percent methane are explosive, easily ignited and very hot, burning at 1875° to 2100° C. Termites, sheep and cattle are particularly good methane producers, but humans are in the running as well. Anecdotally, human farts are highly flammable, and there are also credible medical reports of flammable human burps, sometimes igniting spontaneously on contact with the air. (If you're thinking of trying any of this at home, look at those temperatures again and reconsider carefully. Lab Notes readers are not stupid.)
For a more reliable igniter, we can consider the gizzard. Many birds (like many dinosaurs before them) swallow stones, and store them in a pouch in their throat, to help grind up food. If dragons had a taste for flint (or better yet, flint and iron), their methane-laden belches could trigger a spasm in the gizzard which could easily spark a nasty flame.
Because methane is 45 percent lighter than air, it's tempting to consider its buoyancy as a method for offsetting the dragon's weight and improving its flight characteristics. Unfortunately, even a thousand-liter bladder of the stuff would provide only about half a kilogram of additional lift—enough to affect stability, but not carrying capacity. The figures improve somewhat if the interior of the dragon is very warm, but unless our creature has the size and shape of a hot-air balloon, it's still not going to do much good.
But it doesn't need to, because we've already proven that a giant, flying, fire-breathing, man-eating serpent or lizard is physically and anatomically possible. I'm not saying such a creature is likely to evolve naturally, or to compete effectively in the animal kingdom. Maybe it would, and maybe it wouldn't. But with the coming revolutions in genetic engineering, and the sad dearth of mythic monsters in the real world, I would say that the creature factories of tomorrow have their work cut out for them.
A word of warning: When we do finally succeed in bringing our inner demons to life, it might be a good idea to find a lover and settle down. Dragons are known, alas, to have a taste for virgins.
Wil McCarthy is a rocket guidance engineer, robot designer, science fiction author and occasional aquanaut. He has contributed to three interplanetary spacecraft, five communication and weather satellites, a line of landmine-clearing robots, and some other "really cool stuff" he can't tell us about. His short fiction has graced the pages of Analog, Asimov's, Science Fiction Age and other major publications, and his novel-length works include Aggressor Six, the New York Times notable Bloom, and The Collapsium.
