Speculative biology -- the affairs of dragons

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stoppedcaring
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Speculative biology -- the affairs of dragons

Postby stoppedcaring » Wed Jul 30, 2014 3:48 pm UTC

This is more hard science discussion than fictional science per se, so I wanted to put it here.

I've seen some speculations about how dragons could have evolved, like this, but none of them ever seem particularly convincing. Swim bladders that collect hydrogen and help the dragon float while letting it breathe fire, blah blah blah...no. And the explanation of wings is even worse -- "A mutation gave lizards an extra pair of limbs, which evolved into wings" -- do they know how evolution works? A massive mutation to add an additional pair of limbs would almost invariably screw up a bunch of other stuff. Even if it didn't, the new limbs would have inadequate blood supply, useless musculature, and no spinal attachments. And even if this did somehow present a survival advantage, a massive mutation like that isn't going to be consistently passed on.

Coming up with a good speculative biology for the evolution of dragons requires more than "Oh, look, a mutation." There needs to be specific selection pressures to help each of the steps along. I was thinking something along these lines...

Morphology

The Draco volans lizard from Asia is basically a dragon. Extra ribs, unattached in the front, that are pulled out by muscles to form gliding wings:

Spoiler:
Image


They can glide from tree to tree pretty well, flying-squirrel-style. Of course, they're quite small, and the placement of their ribs is not ideal for further developments. But some of its extinct cousins, like Kuehneosuchus, were larger and had higher-mounted rib-wings:

Spoiler:
Image


They fit their gliding-from-tree-to-tree niche well. But what environmental selection pressures could have turned something like this into a full-on dragon?

I was thinking that an aquatic component might spur things along. Gliding between trees is good and all, but imagine a population of kuehneosaurids branching out into a seaside or lagoon environment with lots of fish in the water and lots of high cliffs. Being able to launch from a high point and glide down to hit a fish would be a pretty neat hunting trick, and help support larger morphologies and a larger population. Cliffs offer longer glide times as well, meaning that improvements in glide control would be more rapidly selected for.

Anything that would help with glide path control would be a huge advantage -- it's not like fish can't change direction, after all. So it wouldn't be difficult to progressively evolve more musculature to control wing attitude and shape. The more muscle connections formed, the more finely-tuned gliding flight would become, and at some point the protodragons would be able to use the wings along with their whole bodies to add speed, perhaps just skimming over the surface of the water. Lepidosauromorphs like kuenhneosaurids (related to modern iguanas) have a primitive sprawling gait which allows for sinusoidal trunk and tail movements similar to fish and crocodiles, so full-body movements to add speed (and thus add range and lift) wouldn't be hard to develop.

Of course, when one of these protodragons did hit the water, its wings would only be in the way. So the ability to fold them up against the body would be a huge help, leading to advantages for ever-higher-seated rib sockets. More space between the wings and the back means more room for movement, which adds control and strength. True elbow joints probably couldn't evolve, but perhaps vertebral elongation would allow for a similar effect.

Over time, flapping action could evolve. It would still probably require a launch (at least at first), and the skeletal structure wouldn't be anything like bat or bird or pterosaur wings (which evolved from tetrapodal limbs), but that wouldn't keep it from becoming highly efficient. A steady diet of fish, small mammals, and smaller reptiles would support significant growth in size. Ease of takeoff is a huge advantage, of course, and so adaptation would move in that direction until you ended up with large, four-legged, fully-winged flying reptiles. Takes care of morphology.

Fire-breathing

Anything that actually proposes breathing fire is, of course, ridiculous. Methane or hydrogen bladders? Please.

But transitioning from arboreal life to an aquatic/terrestrial environment would surely open the population up to predation, particularly at small sizes. Depending on the time and environment, there could be any number of natural predators for these lizards. Wings are great for gliding, but they make you rather vulnerable to attack; a torn or broken wing will screw you up pretty bad, and gliding tends to prefer slender, skinnier anatomy, so the early protodragons wouldn't be flush with physical strength. It wouldn't take long for a predator to do serious close-in damage.

Thus, a defense mechanism which can keep predators at bay will be hugely useful. Certain cobras and even some vipers have the ability to spit venom, which would definitely come in handy. It's unlikely the protodragons would evolve the same type of venom that snakes have, though, since it would have to evolve independently. My chemistry-fu is not my strongest asset, but I'm fairly certain there are some biologically-constructible compounds which would serve as an excellent deterrent to attack. Perhaps something with a caustic peroxide component?

Peroxides, of course, can act as excellent oxidizers. The more caustic the venom becomes, though, the more dangerous it is to the protodragon itself. The lizards would likely evolve some sort of inhibiting compound in their saliva to prevent self-harm; once this was established, though, the causticity of the venom would skyrocket...and with it, the potential to act as a rapid oxidizer. I think the transition from caustic venom to oxidizing venom could happen pretty naturally. The faster the damage is done, the more of a deterrent it is to the predator. And an oxidizing venom replacing a caustic venom means the dragons can use it for hunting as well, because they wouldn't be swallowing anything very harmful.

Again, my chemistry is not the best, but I recalled reading about chlorine trifluoride:
In a comment to my post on putting out fires last week, one commenter mentioned the utility of the good old sand bucket, and wondered if there was anything that would go on to set the sand on fire. Thanks to a note from reader Robert L., I can report that there is indeed such a reagent: chlorine triflouride.

I have not encountered this fine substance myself, but reading up on its properties immediately gives it a spot on my “no way, no how” list. Let's put it this way: during World War II, the Germans were very interested in using it in self-igniting flamethrowers, but found it too nasty to work with. It is apparently about the most vigorous fluorinating agent known, and is much more difficult to handle than fluorine gas. That’s one of those statements you don’t get to hear very often, and it should be enough to make any sensible chemist turn around smartly and head down the hall in the other direction.

The compound also a stronger oxidizing agent than oxygen itself, which also puts it into rare territory. That means that it can potentially go on to “burn” things that you would normally consider already burnt to hell and gone, and a practical consequence of that is that it’ll start roaring reactions with things like bricks and asbestos tile. It’s been used in the semiconductor industry to clean oxides off of surfaces, at which activity it no doubt excels.

There’s a report from the early 1950s of a one-ton spill of the stuff. It burned its way through a foot of concrete floor and chewed up another meter of sand and gravel beneath, completing a day that I'm sure no one involved ever forgot. That process, I should add, would necessarily have been accompanied by copious amounts of horribly toxic and corrosive by-products: it’s bad enough when your reagent ignites wet sand, but the clouds of hot hydrofluoric acid are your special door prize if you’re foolhardy enough to hang around and watch the fireworks.

I’ll let the late John Clark describe the stuff, since he had first-hand experience in attempts to use it as rocket fuel. From his classic Ignition! we have:

"It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water-with which it reacts explosively. It can be kept in some of the ordinary structural metals-steel, copper, aluminium, etc.-because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminium keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes."

Obviously, I doubt there is any peroxide compound nearly as powerful as chlorine trifluoride, and actually making chlorine trifluoride is out of the question, but I can imagine something more along those lines. Being able to spray a thin stream of venom that causes instant oxidization burns and can sometimes ignite what it hits...that's a HUGE weapon. And getting to an "always-ignites" status is the next logical step.

So there you have it. A six-limbed, fire-spitting, flying dragon.

Any objections? Any chemistry experts want to take this to task?

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Re: Speculative biology -- the affairs of dragons

Postby Hypnosifl » Wed Jul 30, 2014 4:07 pm UTC

stoppedcaring wrote:And the explanation of wings is even worse -- "A mutation gave lizards an extra pair of limbs, which evolved into wings" -- do they know how evolution works? A massive mutation to add an additional pair of limbs would almost invariably screw up a bunch of other stuff.

You could always just design the dragon to look more like Smaug from the Hobbit movie, with the front limbs as wings rather than four normal limbs and then an extra pair of wings sprouting out of the sides. Something like a pterosaur, but with a more snake-like body. Plenty of older depictions of dragons do show them with just two legs and a pair of wings, like this one from 1551:

Image

Or this one from a manuscript dated 1236-1250:

Image
stoppedcaring wrote:Obviously, I doubt there is any peroxide compound nearly as powerful as chlorine trifluoride, and actually making chlorine trifluoride is out of the question, but I can imagine something more along those lines. Being able to spray a thin stream of venom that causes instant oxidization burns and can sometimes ignite what it hits...that's a HUGE weapon. And getting to an "always-ignites" status is the next logical step.

Similar to what you're suggesting, we do have the real-world example of the Bombardier Beetle which squirts boiling-hot chemicals from its butt (they aren't stored boiling hot in its body, but the chemical reaction that causes them to squirt out also heats them up). There's a good discussion of how it may have evolved here. As you suggest, a peroxide compound is involved:
Secretory cells produce hydroquinones and hydrogen peroxide (and perhaps other chemicals, depending on the species), which collect in a reservoir. The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. This chamber is lined with cells that secrete catalases and peroxidases. When the contents of the reservior are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones. These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it. Under pressure of the released gasses, the valve is forced closed, and the chemicals are expelled explosively through openings at the tip of the abdomen.

Just choose a somewhat different set of chemicals that are more likely to actually ignite when mixed, and you could have an apparent "fire-breather"--not sure what specific chemicals would fit the bill though.
Last edited by Hypnosifl on Wed Jul 30, 2014 4:35 pm UTC, edited 3 times in total.

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Re: Speculative biology -- the affairs of dragons

Postby Xenomortis » Wed Jul 30, 2014 4:19 pm UTC

Would six limbs leave enough room for the required flight muscles? Ok, we're not looking at limbs in the traditional sense - you're talking about extensions of the rib cage - so maybe it could work out.
One problem is that these would make for relatively poor wings (compared to other vertebrate wings) - the lack of joints in the extended ribs means they'd have much limited control.

A dragon with four limbs is much easier; flight has evolved at least three times in vertebrates.
Image

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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Wed Jul 30, 2014 4:39 pm UTC

Yeah, the four-limbed-dragon design of Smaug is basically a Wyvern (though Smaug himself is of course massively, massively larger than could realistically be possible). Similar to pteranodons, really; it's now known that pteranodons were quadrupedal, just as we saw from Smaug in the last film.

I don't know much about the phylogeny of pteranodons -- was there a more serpentine/reptilian protopteranodon which could have branched out into something more Wyvernlike/batlike?

"Hypnosifl wrote:...we do have the real-world example of the Bombardier Beetle which squirts boiling-hot chemicals from its butt (they aren't stored boiling hot in its body, but the chemical reaction that causes them to squirt out also heats them up). There's a good discussion of how it may have evolved here. As you suggest, a peroxide compound is involved. Just choose a somewhat different set of chemicals that are more likely to actually ignite when mixed, and you could have an apparent "fire-breather"--not sure what specific chemicals would fit the bill though.

Yes, the Bombardier Beetle was a partial inspiration. I was thinking more along the lines of a hypergolic reagent than a dual-ignition system, though, because a dual-ignition system is going to be more complicated, more difficult to evolve, and more metabolically taxing. Not only are many reagents chemically similar to something like a caustic/toxic venom, but using a reagent removes the need for the dragon to actually carry "fuel". Breathe fire at a man's face and he'll be warm for a little while; set a man on fire and he'll be warm for the rest of his life.

Ranged attacks are better with a reagent, too; if the stream ignites immediately after leaving the dragon's mouth, it'll spread out and have a poor range, but if it only ignites when it makes contact with something burnable, it can go much farther.

Xenomortis wrote:Would six limbs leave enough room for the required flight muscles? Ok, we're not looking at limbs in the traditional sense - you're talking about extensions of the rib cage - so maybe it could work out.
One problem is that these would make for relatively poor wings (compared to other vertebrate wings) - the lack of joints in the extended ribs means they'd have much limited control.

That's where I'd be counting on the need for a safe fold-away mechanism to increase the vertical size of the vertebrae, perhaps even moving the rib socket up on vertebral spurs:
Image
This would allow for greater torque on the rib bones and a larger range of motion. In theory.

A dragon with four limbs is much easier; flight has evolved at least three times in vertebrates.

Indeed, and we could simply branch off from protopteranodons. But coming up with an added viable six-limbed dragon is part of the fun.

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Re: Speculative biology -- the affairs of dragons

Postby Xenomortis » Wed Jul 30, 2014 4:53 pm UTC

stoppedcaring wrote:Yeah, the four-limbed-dragon design of Smaug is basically a Wyvern (though Smaug himself is of course massively, massively larger than could realistically be possible). Similar to pteranodons, really; it's now known that pteranodons were quadrupedal, just as we saw from Smaug in the last film.

I don't know much about the phylogeny of pteranodons -- was there a more serpentine/reptilian protopteranodon which could have branched out into something more Wyvernlike/batlike?


Well you don't have them be closely related to the pterosaurs - as has been said, vertebrates have evolved flight at least three times already, why not a fourth time?
Besides, branching off pterosauria wouldn't give the classical dragon wing look (i.e. bat-like), the pterosaur wing is formed by the arm and an extended digit, rather than being formed from a hand and extended digits.
Image

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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Wed Jul 30, 2014 5:07 pm UTC

Xenomortis wrote:
stoppedcaring wrote:Yeah, the four-limbed-dragon design of Smaug is basically a Wyvern (though Smaug himself is of course massively, massively larger than could realistically be possible). Similar to pteranodons, really; it's now known that pteranodons were quadrupedal, just as we saw from Smaug in the last film.

I don't know much about the phylogeny of pteranodons -- was there a more serpentine/reptilian protopteranodon which could have branched out into something more Wyvernlike/batlike?


Well you don't have them be closely related to the pterosaurs - as has been said, vertebrates have evolved flight at least three times already, why not a fourth time?

Then what would the closest relative of the Wyvern-dragon be? And what environment and selection pressures could give rise to something like that? We don't know much about the evolution of bats, sadly, but it would probably have to be a similar sequence.

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Re: Speculative biology -- the affairs of dragons

Postby Copper Bezel » Thu Jul 31, 2014 9:08 am UTC

Honestly, though, we don't know much about the origins of pterosaurs or the flighted maniraptorans, either. As I understand it, it's actually still a point of debate whether winged-but-flightless maniraptorans like velociraptor were stuck in a pre-flight stage or secondarily flightless like many of today's birds. The further back you go, the more you're depending on only the most prominent species to tell the story.

A parallel group of archosaurs or a parallel group of theropods could have developed flight independently with slightly different results.

From the three groups, there are a few generalizations you can make. All started small. All or two of three started with high metabolisms and probably carnivorous / insectivorous diets. Only one started bipedal before adapatations that led to flight (and neither bats nor pterosaurs are proper bipeds in any case), so this isn't a requirement at all. At least two were arboreal, which seems to be the only environment where incomplete flying mechanisms are of selective benefit (and there are only like fifteen independently evolved such mechanisms in play today ans you noted earlier.)

So, you know, work from there. It's not difficult to propose some feisty little archosaur, maybe or maybe not within dinosauria, that climbed trees and jumped after insects and found itself more successful when it had big webbed scoop hands for catching them, and then somewhere a few hundred generations later found that they also made really good air brakes for the inevitable pratfall that comes of jumping out of trees at things, and then....
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Re: Speculative biology -- the affairs of dragons

Postby Xanthir » Thu Jul 31, 2014 1:20 pm UTC

stoppedcaring wrote:And the explanation of wings is even worse -- "A mutation gave lizards an extra pair of limbs, which evolved into wings" -- do they know how evolution works? A massive mutation to add an additional pair of limbs would almost invariably screw up a bunch of other stuff. Even if it didn't, the new limbs would have inadequate blood supply, useless musculature, and no spinal attachments. And even if this did somehow present a survival advantage, a massive mutation like that isn't going to be consistently passed on.


Do *you* know how evolution works? ^_^ Extra limbs happen *all the time*, and they're not just random sacks of unconnected flesh, they're full limbs with full connection into the rest of the body. Our homeobox genes are pretty good at duplication via segmentation. You'd get plenty of other weird effects, but it's definitely not an automatic dead weight.
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Re: Speculative biology -- the affairs of dragons

Postby Xenomortis » Thu Jul 31, 2014 1:27 pm UTC

On the other hand, I don't know of any vertebrate species that has/had more than four limbs.
So whilst random mutations do, on occasion, add a fully functional 5th limb to an organism, there doesn't appear to be a selection advantage to it.
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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Thu Jul 31, 2014 2:36 pm UTC

Xanthir wrote:Extra limbs happen *all the time*, and they're not just random sacks of unconnected flesh, they're full limbs with full connection into the rest of the body. Our homeobox genes are pretty good at duplication via segmentation. You'd get plenty of other weird effects, but it's definitely not an automatic dead weight.
Xenomortis wrote:On the other hand, I don't know of any vertebrate species that has/had more than four limbs.
So whilst random mutations do, on occasion, add a fully functional 5th limb to an organism, there doesn't appear to be a selection advantage to it.

That was my point -- yes, extra limbs can come from mutations, and yes they are connected, but suggesting that this provided an immediate selection advantage and spread throughout the population is highly implausible.

Copper Bezel wrote:The further back you go, the more you're depending on only the most prominent species to tell the story.

Highly, highly frustrating.

From the three groups, there are a few generalizations you can make. All started small. All or two of three started with high metabolisms and probably carnivorous / insectivorous diets. Only one started bipedal before adapatations that led to flight (and neither bats nor pterosaurs are proper bipeds in any case), so this isn't a requirement at all. At least two were arboreal, which seems to be the only environment where incomplete flying mechanisms are of selective benefit (and there are only like fifteen independently evolved such mechanisms in play today ans you noted earlier.)

So, you know, work from there. It's not difficult to propose some feisty little archosaur, maybe or maybe not within dinosauria, that climbed trees and jumped after insects and found itself more successful when it had big webbed scoop hands for catching them, and then somewhere a few hundred generations later found that they also made really good air brakes for the inevitable pratfall that comes of jumping out of trees at things, and then....

Something appropriately serpentine. Probably iguana-related, not unlike Draco volans and the kuehnesaurids themselves.

If the production of the hypergolic peroxide reagent was the result of symbiotic bacteria, it could end up jumping species so that you could have both wyverns and six-limbed dragons that both spat fire, albeit with slightly different mechanisms.

Archosaurs had the huge advantage of already having feathers before they began evolving into birds. Feathers are nice because they allow for a smooth airfoil without much added weight; creatures like bats and pterosaurs only have skin stretched over bone. So the wing structure would have to have significant curvature, like a Wright plane. There would probably also be wing-warping as a control mechanism.

As far as thrust is concerned, I'm thinking the tail could be used in an almost dolphin-like fashion, to push the dragon forward.

Getting to a point of takeoff from a standstill would be most challenging. The quadruped dragons would probably always have to at least start a sprint before taking off.

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Re: Speculative biology -- the affairs of dragons

Postby Copper Bezel » Thu Jul 31, 2014 5:02 pm UTC

Minor-minor clarification - pterosaurs were archosaurs, too, but only had hair-like protofeathers, which is why they went the inflated membrane route, and they also remained quadrupeds the entire time - I'm not actually sure if there are any bats with a bipedal stance and gait, for that matter. Wyverns might actually end up the same way, with reduced rather than bolstered rear limbs and a sprawling quadrupedal gait.

Structurally, it's also worth noting that bats and pterosaurs have very different approaches to the "membrane." Since both managed powered flight with their wings and one branch of pterosaurs retained long, bony tails as control surfaces, I think you don't need to worry about tails as a propulsion mechanism.
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Re: Speculative biology -- the affairs of dragons

Postby Xenomortis » Thu Jul 31, 2014 6:02 pm UTC

stoppedcaring wrote:Getting to a point of takeoff from a standstill would be most challenging. The quadruped dragons would probably always have to at least start a sprint before taking off.

The pterosaurs managed it, as do vampire bats now (although they're much smaller).
Due to their quadruped stance, they're able to utilise their flight muscles to push themselves off the ground, vaulting into the air.
Birds have to make do with their leg muscles, which are nowhere near as strong.
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Re: Speculative biology -- the affairs of dragons

Postby Copper Bezel » Thu Jul 31, 2014 6:07 pm UTC

Is there any validity to that rocking "launch" posture that some people proposed the larger pterosaurs might have used at the end of the run? Where the arms / wings have that catapult action to them to make the jump and allow the wings to spread in time to catch some airflow?
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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Thu Jul 31, 2014 6:14 pm UTC

Copper Bezel wrote:Structurally, it's also worth noting that bats and pterosaurs have very different approaches to the "membrane." Since both managed powered flight with their wings and one branch of pterosaurs retained long, bony tails as control surfaces, I think you don't need to worry about tails as a propulsion mechanism.

Not with the Wyvern design, no. But the quadruped+wing design might be more challenging. The rib-based wings won't have as much of a range of motion for flapping, even if the rib socket moves up onto vertical vertebral spurs, and so you're going to need to get upward and forward thrust from somewhere else.

I was thinking of a skeletal design something like this:

Image

Definitely optimized for forward-flying at high speed. I was thinking the tail could be used to help thrust, or at least stabilize while the whole upper body was put into thrust.

Xenomortis wrote:
stoppedcaring wrote:Getting to a point of takeoff from a standstill would be most challenging. The quadruped dragons would probably always have to at least start a sprint before taking off.

The pterosaurs managed it, as do vampire bats now (although they're much smaller).
Due to their quadruped stance, they're able to utilise their flight muscles to push themselves off the ground, vaulting into the air.
Birds have to make do with their leg muscles, which are nowhere near as strong.

Ever seen a crocodile gallop? That would be a major advantage of having four limbs plus wings. Especially if the same motion translated into midair thrust.

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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Fri Aug 01, 2014 6:23 pm UTC

As far as possible reagents are concerned, disodium peroxide or one of its hydrates looks promising. It's an extremely caustic base even at low purity, meaning it would serve as an excellent deterrent to attack even without its oxidization properties. Mix in a little calcium carbide, and the hypergolic reaction once it hits fuel will be accelerated by an oxy-acetylene flame.

Not sure what would be needed in order to fire it in a stream, nor whether any salivary compound could inhibit its explosive properties.

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Re: Speculative biology -- the affairs of dragons

Postby PolakoVoador » Fri Aug 01, 2014 7:11 pm UTC

Let's remember that evolution already managed some fairly big flying vertebrates:

Spoilered imagem:

Spoiler:
Image

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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Fri Aug 01, 2014 7:22 pm UTC

Holy mother of

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Re: Speculative biology -- the affairs of dragons

Postby thoughtfully » Fri Aug 01, 2014 8:09 pm UTC

stoppedcaring wrote:Holy mother of

It's a common practice to depict dinosaurs and the like in improbably upright postures to elicit the maximum response. Could that critter really support itself upright as shown? Would it have impressed you as much if it was shown rather more horizontally?

A grizzly standing up is rather more fearsome than one on all fours, after all. Gotta watch that pesky limbic system, it can throw you off :)
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Re: Speculative biology -- the affairs of dragons

Postby speising » Fri Aug 01, 2014 8:43 pm UTC

PolakoVoador wrote:Let's remember that evolution already managed some fairly big flying vertebrates:

Spoilered imagem:

Spoiler:
Image

my first thought was it's wearing a fetching beret.

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Re: Speculative biology -- the affairs of dragons

Postby Mokele » Fri Aug 01, 2014 9:11 pm UTC

thoughtfully wrote:
stoppedcaring wrote:Holy mother of

It's a common practice to depict dinosaurs and the like in improbably upright postures to elicit the maximum response. Could that critter really support itself upright as shown? Would it have impressed you as much if it was shown rather more horizontally?

A grizzly standing up is rather more fearsome than one on all fours, after all. Gotta watch that pesky limbic system, it can throw you off :)


It definitely could have, and more relevantly, it probably had to.

The pterosaur torso didn't really have much in the way of flexibility due to the notarium and sacrum, which locked almost all the body vertebrae into fused rigid structures, and Azhdarchids had fairly rigid necks, composed of a few highly elongate vertebrae (much like giraffes). Add in the large discrepancy between the hind and forelimb length, and there's not much left it can do, especially since large animals tend to keep their legs as close to pillar-like as possible to minimize costs. Obviously the head goes up and down, like a giraffe, and resting posture is unknown, but near-vertical minimizes torques associated with that gigantic head.

However, Azhdarchids are pretty extreme, and smaller, more "typical" pterosaurs likely did not adopt such dramatic poses. However, they are very, VERY weird animals, and get weirder with every discovery.
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Re: Speculative biology -- the affairs of dragons

Postby Sockmonkey » Thu Aug 07, 2014 3:55 pm UTC

Four limbs plus flapping wings means your critter will be carrying a good deal of dead weight in flight.
Pterosaurs saved a crapload of weight by having their wings do double duty as the main weight-bearing limbs on the ground.
That let them get away with having much smaller and less muscled hind limbs than a bird of the same size would need.
That's one of the reasons the largest flying birds didn't get to be the size of Quetzalcoatl.

Bats have the same walking on all fours advantage as pterosaurs, but they're stuck with crappy mammalian lungs rather than the air-sacs and unidirectional lung system of awesomeness birds and pterosaurs had.
They make up for it a bit by having the wing stroke assist in pumping the diaphragm, but don't expect to be seeing eagle-sized bats anytime soon, much less giant ones.

Now if you're dead-set on the four-legs-plus-wings layout there is a way to make it work.
Rib wings are no biggie to evolve. We see them in many modern and prehistoric lizard species.
Forget about flapping those things though. The layout of the bones and muscles just isn't made to deliver that kind of power.
If you want powered flight in your rib-winged lizard/archosaur give it webbed feet and have it flap those for propulsion while leaving the rib-wings as a passive lift surface.

That way you get the same double-duty advantage from your walking muscles that bats and pterosaurs have.
It's suspected that basal archosaurs had the same unidirectional flow and air sac setup that birds have so it's no stretch to provide your dragon with a similar system.

Fun fact: Modern crocs and monitors don't have air sacs but they do have unidirectional lungs which partially accounts for their stupidly high energy levels compared to other reptiles. Crocs also have an efficient four-chamber heat like mammals while monitors have a three-chamber heart that manages to mimic the flow of a four-chamber through some clever shaping.
Call it a three-point-five chamber. :wink:

Anyhow, while plenty of arboreal critters have become gliders, it's actually pretty rare for good gliders to switch to powered flight. Apparently the evolutionary rule is that unless you flap a bit from the very beginning, you never evolve the proper flight muscles and dead-end at gliding. (proper powered flight only ever evolved a total of three times in vertebrates)

Anyhow, back to our potential lizard-dragon thingy.
W start with a small monitor or croc since those have the best potential to evolve the systems for energy-demanding flight.
Next we evolve it to something akin to the basilisk lizard that runs on water.
Then we gradually introduce wing ribs which would be a great help to a water runner since the lift allows the legs to devote all their energy into propulsion without fighting to keep itself from sinking. Even the proto-wings are going to be helpful for this so we get our incremental improvements.
From there we gradually make the wing bigger and better shaped for lift giving our lizard the ability to go from just running on water to long striding leaps further boosted by flapping it's webbed feet for extra distance.
(note how we go straight from running to proto-flapping so it never loses the instinct to wave it's feet while airborne)
Skip ahead skip ahead, kapow!
We have our flying lizard-dragon-thingy and flight has evolved a fourth time in vertebrates.
The tail would be reduced to a nub and the rib-wings would remain stationary lift surfaces with propulsion and steering all being done with the feet. We get flying while keeping good climbing and running abilities.
Skip ahead skip ahead, gradually evolve it bigger etc etc.
Mission accomplished.

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Re: Speculative biology -- the affairs of dragons

Postby Flumble » Sun Aug 10, 2014 11:53 am UTC

Sockmonkey wrote:Now if you're dead-set on the four-legs-plus-wings layout there is a way to make it work.
Rib wings are no biggie to evolve. We see them in many modern and prehistoric lizard species.
Forget about flapping those things though. The layout of the bones and muscles just isn't made to deliver that kind of power.
If you want powered flight in your rib-winged lizard/archosaur give it webbed feet and have it flap those for propulsion while leaving the rib-wings as a passive lift surface.

Can't the muscles in the chest and back area evolve to support powered flight? I imagine flapping the (proto-)wings once can come in handy to avoid an attack by a predator or scare them away by unfolding the wings, which encourages muscle development. Is there a physical limitation to the muscles or bones that prevents this?

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Re: Speculative biology -- the affairs of dragons

Postby Mokele » Sun Aug 10, 2014 7:12 pm UTC

Flumble wrote:
Sockmonkey wrote:Now if you're dead-set on the four-legs-plus-wings layout there is a way to make it work.
Rib wings are no biggie to evolve. We see them in many modern and prehistoric lizard species.
Forget about flapping those things though. The layout of the bones and muscles just isn't made to deliver that kind of power.
If you want powered flight in your rib-winged lizard/archosaur give it webbed feet and have it flap those for propulsion while leaving the rib-wings as a passive lift surface.

Can't the muscles in the chest and back area evolve to support powered flight? I imagine flapping the (proto-)wings once can come in handy to avoid an attack by a predator or scare them away by unfolding the wings, which encourages muscle development. Is there a physical limitation to the muscles or bones that prevents this?


I think part of this is where to anchor the muscles. Flying vertebrates wrap their flight power muscles around a fairly large, quasi-rigid ribcage, meaning that you can have muscles with both large cross-section (therefore force) and long fibers (therefore length excursion and velocity), thus high work and power output. Something like Draco volans has a relatively small sternum, with most ribs being "free" and thus able to open to form wings. Opening/closing in preparation for gliding is one thing, and is easily handled by the relatively weak, short muscles attaching from the vertebrae to the ribs. You can make those muscles with greater cross-section, but if you're going to make them longer, you basically need to change the geometry of their attachments, and thus need somewhere to anchor them that's further away from the insertion on the ribs.

I'm not sure the rib bones could really withstand the forces of being used to flap, either - no vertebrate uses the ribs directly for locomotion, only as a support structure for the body, either as part of a quasi-rigid ribcage or free by embedded in muscular layers. They could hypertrophy I guess, but IIRC they never seem to get that thick layer of cortical bone like limb bones get, even in species where they do hypertrophy (many secondarily aquatic species like manatees), just a thin layer around mostly spongy bone.
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Re: Speculative biology -- the affairs of dragons

Postby Copper Bezel » Sun Aug 10, 2014 7:23 pm UTC

And you'd still need to develop something like an elbow to have any meaningful control of the airfoil during flapping, too. Trickier still when the wings are supported by a fan of bones that all run from base to wingtip.
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Re: Speculative biology -- the affairs of dragons

Postby Sockmonkey » Mon Aug 11, 2014 2:45 am UTC

Yep, plus you would still have the issue of the legs being dead weight during flight. Ideally you want as much of your muscle as possible doing double duty for both flight and walking like this bugger.
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Re: Speculative biology -- the affairs of dragons

Postby jewish_scientist » Mon Aug 18, 2014 4:30 am UTC

I have an idea on how a dragon could 'breath fire'.

Imagine a shepherd and his flock are confronted by a dragon. The dragon opens its mouth and a large, yellow substance is projected. The shepherd runs toward town, but not before the his forearm is touched by the yellow projectile. The substance causes unbearable pain to spread across his arm. Between the fact that he is in a lot of pain and there was a huge dragon right there, the shepherd does not get a particularly good look at the projectile. In town, he sees a doctor, who identifies the wound as a burn. Some zoologist interviews the shepherd. Over the years the zoologist talks to several survives of dragon attacks. They all relate similar stories. The zoologist concludes the dragon can breath fire. That all seems reasonable (assuming that dragons are real and like to eat sheep). However, there is another explanation for what the yellow substance is.

The yellow substance was not fire, but rather stomach acid.

Note:I have absolutely no reason to believe that stomach acid is yellow. It very when might not be. As long as the acid is yellow, red, white or light blue I'll be o.k.

In humans, stomach acid is mostly hydrochloric acid with a ph between 1 to 5. It is there for reasonable to believe that a dragon would have similar stomach acid. The MSDS for hydrochloric acid says several times that it can cause chemical burns. The doctors of the time would have never seen a chemical burn before. The closest injury they had was a thermal burn; usually caused by fire [citation needed]. Given the inaccurate description and injuries resulting from exposure, it is understandable that the zoologist thought that the liquid was a flame.


Now that I explained why people could have though that dragons can breath fire, I will now explain why dragons would projectile vomit.

This ability to spray acid at a target has many uses. It can be an effective offensive or defensive weapon. Vultures use there vomit in the same way [http://animals.howstuffworks.com/birds/vulture-vomit1.htm].

Wool is known for its difficulty to digest [https://archive.org/stream/jresv27n5p459/jresv27n5p459_A1b#page/n0/mode/2up]. A dragon could use its acid to begin breaking down the wool before the sheep enter the body. This would let the dragon leave and do other things while the sheep are being pre-digested.

I can think of no better way for an animal to mark its territory than to leave half-dissolved tree trunks around. Cellulose dissolved by hydrochloric acid produces sugar [http://www.green-trust.org/2000/biofuel/wood_sac.pdf]. I suppose that a dragon could lick up its vomit after making its territory to get a nice energy boost.


P.S. Two interesting things I learned while researching for this post.

1: Your stomach decreases in ph when you eat.
2: Honey is a very effective treatment for burns and other wounds http://www.ncbi.nlm.nih.gov/pubmed/11702616. I mean, it can compete with modern medicine. It is just unbelievable. Literally, you need to read this article to believe it. [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2686636/]
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Re: Speculative biology -- the affairs of dragons

Postby LaserGuy » Mon Aug 18, 2014 6:52 pm UTC

Related to fire breathing, one place to start is the bombardier beetle, which apparently stores hydroquinones and hydrogen peroxide in separate chambers in its abdomen, and can force them into a mixing chamber when threatened. The two react (with some enzymes) to produce a superheated jet of nasty chemicals that it sprays at threats. Here's a video of one in action.

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Re: Speculative biology -- the affairs of dragons

Postby Izawwlgood » Mon Aug 18, 2014 7:10 pm UTC

Something that confuses me about the beetle is the stance it selects. It's basically placing it's underside and head in the direct line of fire.

jewish_scientist wrote:The yellow substance was not fire, but rather stomach acid.
Have you ever vomited? Stomach acid is certainly acidic, but it is not nearly at a concentration that will cause caustic burns in mere moments of exposure. Human stomach acid is roughly roughly 1M during stomach churning, IIRC. Basically at a vertebrates worst, you'd have to leave the gastric juice in place for an hour or so before you started getting any real chemical burning going on. But,

jewish_scientist wrote:The zoologist concludes the dragon can breath fire.
Why wouldn't they just conclude that the dragon spits caustic acid?

jewish_scientist wrote: A dragon could use its acid to begin breaking down the wool before the sheep enter the body.
This is a feeding strategy only observed in organisms that consume something much much much larger than them. Like, flies landing on a piece of food. For all other organisms, this strategy would waste an enormous amount of nutrients, and additionally, would potentially place the kill at risk of being stolen. There's a reason snakes swallow their prey whole and then retreat to digest, instead of barfing up acid on them, letting them dissolve, and swallowing bits of goop.
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Re: Speculative biology -- the affairs of dragons

Postby speising » Mon Aug 18, 2014 8:05 pm UTC

otoh, some animals, like herons, vomit for other reasons (to reduce take off weight) , so it's imaginable this might evolve into an offensive weapon, with increasing acid concentration.

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Re: Speculative biology -- the affairs of dragons

Postby Izawwlgood » Mon Aug 18, 2014 8:11 pm UTC

I'm not disputing that vomiting has utility in life, I'm disputing vomiting as a 'pre-digestion' ploy. There are snakes that spit venom to blind their prey, but AFAIK, there are no vertebrates that eat via spitting up digestive juices, and sucking up the digested prey.
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Re: Speculative biology -- the affairs of dragons

Postby Mokele » Mon Aug 18, 2014 9:20 pm UTC

Izawwlgood wrote:I'm not disputing that vomiting has utility in life, I'm disputing vomiting as a 'pre-digestion' ploy. There are snakes that spit venom to blind their prey, but AFAIK, there are no vertebrates that eat via spitting up digestive juices, and sucking up the digested prey.


The closest would be venomous snakes, whose venom can begin to break down the prey's tissues prior to ingestion. It's been suggested that this "pre-digestion" allows vipers to effectively prey on large prey at high latitudes and altitudes.
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Re: Speculative biology -- the affairs of dragons

Postby stoppedcaring » Tue Aug 26, 2014 5:18 pm UTC

Izawwlgood wrote:I'm not disputing that vomiting has utility in life, I'm disputing vomiting as a 'pre-digestion' ploy. There are snakes that spit venom to blind their prey, but AFAIK, there are no vertebrates that eat via spitting up digestive juices, and sucking up the digested prey.

Yeah, it was the venom-spitting that I was originally thinking could provide a pathway to fire-breathing. If they evolved a caustic venom with oxidizing properties, it could progress to a hypergolic oxidizer over time as the dragon evolved the necessary subsystems to protect itself from the oxidizer.

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Re: Speculative biology -- the affairs of dragons

Postby ikrase » Thu Oct 09, 2014 2:01 am UTC

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