What kind of planet could a dragon evolve on?

By “dragon”, I am referring to winged monster creatures, at least superficially lizard-like, but more likely warm-blooded like dinosaurs are now believed to have been. Breathing fire is optional. I am trying to figure out what kind of planetary conditions could allow for the following creature to evolve:

– The size of a small airplane; for instance, about the size of a single-engine Cessna
– Capable of sustained flight, so not simply a glider
– Bat-like wings
– Somewhat elongated neck, with tail, and at least four limbs
– Breathes oxygen

Assume that all conditions are favorable. There are ample prey, nesting spots, and they will be apex predators and scavengers. What sort of planet is necessary for such dragons? Does it need lower gravity? Higher oxygen content?

This one?

Given a broad enough wingspan, why not?

It already happened on this planet. Quetzalcoatlus

Earth.

http://renne.ro/wp-content/uploads/quetzalcoatlus-plane-625x4501.jpg
http://en.wikipedia.org/wiki/Quetzalcoatlus

Not sure if it had a tail but surely that can’t be that big a stumbling block.

Breathing fire is going to be difficult. Both ignition (with what body parts?) and having internal body parts which can withstand such temperatures.

The biggest dinosaurs seem to have mainly lived during the Cretaceous so you might want to check out the conditions during that phase. http://en.wikipedia.org/wiki/Cretaceous

ETA: Damn you, TriPolar! (impotently shakes fist)

As far as breathing fire goes; it’s just barely possible that there are “hypergolic”* compounds that organic life can produce and handle; in that case the creature could spit twin converging sprays that ignite at a safe distance. Or it spits some organic equivalent of napalm - although igniting it would be a problem.

Or you could settle for it spitting something corrosive.

*Compounds that ignite upon contact with each other, used as rocket fuels typically

I’m imagining something heavier and more powerful than Quetzalcoatlus.

I’ll assume you’re thinking of something like the classic European dragon. Heavy, scaled body, four large limbs with heavy clawed feet. And a tough challenge for an armored knight. Except for the difference in appearance, you might be selling Quetzl short. Something that large wouldn’t be frail. It’s believed that it had to spring up into the air to take off. It would had to be able to do that with a full stomach in it’s 400-500lb. body or else fight off any competitors on the ground. But it probably couldn’t take off with the added weight of the average princess or young wizard riding on it’s back.

Another flying creature that developed on Earth wasArgentavis. It was the size of a snall plane. It may have been a glider, unable to fly solely under it’s own power, but different conditions might have allowed it to evolve into a better flyer. It’s possible that a bird resembling an eagle with a 20ft. plus wingspan could have evolved, but it would have been much lighter than a dragon, and unlikely to have great excess lifting power.

Changes in atmospheric conditions or gravity are tricky. They’ll tend to change a lot of things about animal life. And the factors making flight more efficient might tend to evolve lighter animals even if they are larger. But in the right conditions a large flying predator might evolve. It’s a matter of balancing all the factors. Less gravitional pull would result in a less dense atmosphere. But if the atmosphere had a higher proportion of oxygen it would make muscles more efficient. Perhaps it’s possible to get a denser atmosphere with greater proportions of heavy gases, but they can’t be so heavy that they displace all the oxygen.

When it comes to flight air density is actually much more of a factor than gravity. It’s the air that holds you up, and the denser the air the more weight a given area of wing can hold up. Greater air density also allows for more oxygen molecules per volume of air, so the percentage of oxygen could the same as on Earth but would still be a “greater” amount in the sense of more oxygen per unit of volume.

I wonder about reversing the breathe oxygen, spit fire trope. Plants emit oxygen as part of their respiration…would it be possible for an animal to do that? If so, an animal in a methane atmosphere (like on Titan) could breathe out a gout of oxygen into the methane atmosphere with potentially flamethrower-like effects.

A few years ago, on either Discovery or the Syfy channel, IIRC, there was a special about how fire-breathing dragons could have evolved on Earth. They postulated that there was some element that was far more common in that version of Earth than in real life, and dragons chewed it to breathe fire. The producers consulted scientists about it.

I’ve thought for awhile that a good weapon in a methane atmosphere would be a fuel-air mixture, except the “fuel” would be oxygen.

I remember a few years ago here there was a thread about how a dragon could evolve. From what I recall, there were good and interesting answers.

But when I searched, I couldn’t find it.

And time-travel, too; don’t forget the time-travel.

(Anne McCaffrey always swore that the Pern books were “science fiction,” not fantasy. Her son, Todd McCaffrey, who inherited the literary concession, maintains the same opinion. He’s a very nice chap…and absolutely full of beans.)

I’d say that the hypothetical home planet would have to have low gravity, yet a very dense atmosphere. As for the fire-breathing, I’ve talked to enough biologists who insist this is flatly impossible to have become convinced by them. If fire-breathing could have happened on earth…it probably already would have.

Two objections: one, accidental discharge of the fuel supply…like when an enemy sniper hits the flamethrower-carrying soldier right in the fuel tank. Two, all that energy in one place would be very attractive to parasites; they’d burrow right in and devour the fuel.

Despite my generally agreeing with you and what I said earlier, it seems the problem might be ignition. As countless Youtube videos produced by male teenagers will attest, a body is fully capable of projecting a flammable gas which can be ignited into a flame.

Can teeth or other biological parts create sparks?

If we can get the dragon to make some kind of flammable gas or liquid (not impossible…plenty of life already makes methane,) and simply have it release it via it’s mouth rather than anus, then ignition could be accomplished via an electrical arc.

So basically, combine the Quetzalcoatlus with an an electrical eel, and a cow’s ass for a mouth. :stuck_out_tongue:

Though obviously the problem here is the dragon being able to withstand the heat of it’s own fire.

The flames could simply be a venom spit by the creature. It could ‘burn’ the eyes of those exposed to it. Possibly it is sprayed with an expulsion of methane from the gut which ignited upon contact with villagers torches.

The ignition mechanism could be something as simple as generating a cavitation bubble like the Alpheidae shrimp creates with it’s specialized claw for stunning/killing prey. The collapsing bubble can exceed 4700c. Combine that with a compound with a low ignition point and you’ve got the start of an organic flamethrower.