Tuesday, 15 December 2020

The evolutionary origin of dragon flight

Perhaps some of you know the ‘dragon’ series of books by Marie Brennan. They are very enjoyable fantasy novels, describing the consecutive adventures of a woman in a fictional world resembling late 19-century Earth quite a bit. There are of course disparities, such as the existence of dragons. 

The protagonist is a young woman, or she is at the start of the first book; in later volumes she is older. She wishes to study Natural History, not at all a proper endeavour for a young woman in her rather Victorian world. To find out more about her and her adventures, you should read the books for yourself, because this post mostly deals with the cover art of one the books: 'Within the sanctuary of wings'. 

You can have a look at all the covers on the site of the artist, Todd Lockwood, where you can also buy prints and have a better look at the covers. 

 

Click to enlarge; copyright Todd Lockwood

Here is the cover in question. I think you can guess why it caught my interest, well, other than this being creative and high-quality art. The four creatures form an obvious succession, starting with a six-legged dog-lizard wingless beastie in front. The distance between its hind and middle legs is larger than between the middle and front legs, which is interesting, but the really important detail is the little membrane connecting the hind part of the middle leg to the torso. 

In the next stage, that membrane is a lot larger, and that second 'protodraco' seems to be gliding as much as it is running. The middle legs stick out sideways a bit; do they even hit the ground? The third stage has undeniable wings, and the fourth stage is all about wings. That one is a proper dragon, with four walking legs and two wings. I think this cover is a diagram of the evolutionary history of flight in dragons. 

The covers of all these books betray an obvious biological interest, which is completely in keeping with the content of the books: the heroine builds her career on the scientific study of dragons, and the readers get to hear interesting snippets here and there. When I saw the cover, I was curious whether this apparent evolutionary history also featured on the books, but I did not find that there. 

Would this progression from a running hexapod with six walking legs to a clade with four walking legs and two wings work? Regular readers will know that Furahan hexapods gave rise to flying forms as well, so I had to devise an evolutionary background for them, just as had been done for these dragons. Actually, hexapods did not only gave rise to the four-winged tetrapterates, but also to two-winged bipterates. On paper there is even a third flying clade, but I haven't worked much on that one yet. 

A basic concept in evolution is that an organ or feature will not develop just because some future descendent, a few million times removed, may make good use of whatever the organ does. That structure must convey some advantage in its early stage, or why would it be there? That advantage is unlikely to be true flight. But the future wing could help in gliding down from a tree or a cliff, or it could help the animal to jump higher and longer, or to run better. If you read about the evolution of flight in pterosaurs, birds and bats, you will find such explanations. I think that the winglets in the 'protodracones' on the cover show that, in dragons, flight evolved 'from the ground up', starting with more efficient running. 

Click to enlarge; copyright Gert van Dijk

At present, that is not how Furahan tetrapterates or bipterates got into the air. They took the 'down towards the ground' route. The rough sketch above was my first try at finding a shape for such animals. This is an arboreal species with folding leg flaps on all six of its legs. They crawl up into trees and then jump out of them and glide away, somewhat clumsily. 

Once the evolution of such gliders is jump-started (sorry for that one), the next stage is likely to involve optimization. The animals will probably not be very good at flying in the beginning, so it may pay for them to have an aerodynamically stable body plan. A stable flight scheme would make them less maneuverable, but at least it should keep them airborne without sophisticated neural control. The easiest way to achieve a stable shape would be to have the centre of lift directly above the centre of gravity, and in turn the easiest way to get there is probably to use the middle limbs as the main or only wings. 

There are intriguing other possibilities though, because the hexapod Bauplan in principle allows  not just one, but two or even all three pairs of limbs to be used for flight. With less than three pairs the next question is which pairs of limbs should be used for that? Any such design must also look into how the remaining legs must be adapted, so the animal will make aerodynamic sense while also being able to move about on the ground. 

Such things might be good material for another post, but I would not be surprised if readers run away with these and better ideas long before I will ever get around to writing that post. 

48 comments:

AlliHater said...

I've seen that book, it's got some really interesting concepts based on how biology and fantasy can come together.

That said, two things about the book bother me: namely, the co-existence of dragons and mundane animals, and the sapient species encountered later.

The dragons are shown filling niches on land sea and air alike, which would be a huge problem with competition with other vertebrate clades (and in fact, the existence of an entire separate hexapod clade along with the tetrapods, which would have had one outcompete the other long ago. They could at least replace some mundane animals with dragon equivalents (see "Fantastic Fauna Counterpart" on TV Tropes for more info).

As for the sapient dragon species: again with the anthropocentric humanoid body plan... it's even worse when the text literally says that the upright stance makes them really poor flyers and mostly just glide, which makes one wonder why an intelligent species would necessarily have to look humanoid at all if it's actually detrimental to them.

anthony said...

Hmm, not sure about the limbs but wouldn't that dragon in the image be incredibly un-aerodynamic, especially if it was a large one? All those extraneous horns and sails, plus the long tail, seem horrendously ill-designed for a large flyer that should be trying to save as much weight load as possible.

Bumble Beast said...

That dragon evolution...makes literally zero sense.

First there is the issue of "Pandorization", aka "adding extra limbs onto an animal by just copy-pasting existing limbs". And look how the first proto-dragon is running: its legs don't even sync up properly and is expecting a sudden faceplant.

Second, there is the idea of the second pair of limbs being freed from locomotion, whereas there's this trend of "cephalization" where the limbs nearest the head are modified, like mantises or crabs. But then, having the frontmost pair of limbs become wings wouldn't be feasible since there would be so much weight behind the wings, which would tip it over backwards in flight.

Third, the extra pair of limbs would just hinder the placement of flight muscles as well as getting in the way of wing movement, at the very least have both pairs of forelimbs become wings, to make the best use of getting as much wing surface area as possible to get such a big animal off the ground?

And finally, there's simply tge entire issue of what appears to be a canid-like cursorial runner evolving flight out of nowhere. Flight that evolves from parachuting or arboreal gliding seems like a logical transition (and indeed is how birds, bats and pterosaurs all independently developed true flight) but a runner that just sprouts "sails" is a very unlikely transition.

Honestly, it's just too much trouble trying to make a "realistic" hexapodal dragon and the most obvious solution is to just make it a wyvern-styled tetrapod and look to pterosaurs for believable flight proportions.

Sigmund Nastrazzurro said...

AlliHater, anthony, Bumble Beast: I wasn't arguing that the end product of this production line, a large heavy dragon with two wings, would be taken seriously as a flying animal. Of course it makes no biomechanical sense. No argument there.

This is one of those few occasions in which I was prepared to overlook the impossibility of it all. I take offence at biomechanical nonsense in a book or film when the makers expressly wish me to believe that it all can actually work. However, when they say 'it's not meant to be taken seriously; we hope you just enjoy our fantasy', then I may do so. Most Creature Design makes no sense; the Star Wars zoology is silly (the Banta is a good example of that) but can be enjoyed; Avatar's hexapods shouldn't walk the way they do; there is no way Dune's sand worms would be able to move, let alone swim quickly though sand; the list goes on.

Personally I class the dragon novels as fantasy, and I hardly read fantasy. But when something is well-made and highly enjoyable in other aspects, I may be persuaded to turn off my scientific enquiry mode and suspend disbelief. For a short time.

But rest assured that that mode will be at a high setting when it comes to Furahan hexapod-derived flyers...

kevin the horse said...

Don't the main clade of flying Furahan hexapods have four wings? (the Flygs and Seasoars from the site if I recall right?) I wonder how such an arrangement came about.

Helios said...

how could mammals evolve powered flight? they'd have constraints like lack of air sacs and solid bones

Unknown said...

grr, I did not say that; please don't attribute things to me. (i get the feeling that the first three commenters should be screaming bloody murder at birds and pterosaurs for having such large legs and beaks and ornamentation all over)
:D

Having read the books, I recall them mostly focusing on the behavior, anatomy, and behavior for various smaller clades within the broad umbrella of "dragon" (ie, hummingbirds, ospreys, and vorpal-sized penguins, rather than "how did birds get in the air?")

...with a background theme of working to understand just how lightweight the bones must be for dragons to fly (and then how to replicate that in manmade structures before flying dragons are driven extinct by nations discovering that dragonbones make ideal support structures in balloons and gliders)

um, Kevin, the main post already answered that.

-anthony docimo.

Anonymous said...

I`m pretty sure that cover shows the ontogeny of a single species. There`s nothing concrete in the books about dragon evolution (the pseudo-Victorians don`t have genetics yet, obviously, and no fossils because of dragonbone`s rapid decay), and the dragons are pretty obviously designed without any consideration for phylogeny, like most fantastic creatures - a random hodgepodge of traits.
There is, of course, that "developmental lability" thing, not that it makes much sense without magic - which isn`t there btw, this is a very low-fantasy setting. Which is exactly why the silly parts (such as the creation of the aforementioned dragon-eople from eggs dipped in human blood) stick out like a sore thumb.

The Lady Trent books are very good in most regards, but biology is really not one of them. The author herself isn`t even interested in it, she`s an anthropologist and clearly prefers to write about cultures and stuff - which she does in the sequel book, and I just wonder why she didn`t do that from the start cause she does it much better.

$wampm0nster said...

How would a Furahan wing that can also function as a leg work? That would neatly bypass the centaurism issues but then how exactly does the vampire bat on Earth fold its wing so neatly as to act as a proper leg, as opposed to other bats that just clumsily waddle on floppy wings? That could be something worth considering...

Unknown said...

I wish I knew how a Furahan wing-leg worked, $wampm0nster...hopefully, that will be one of the parts of The Book.

Vampire bats fold their wings up like any other bat;


>not that it makes much sense without magic

except that developmental plasticisity(sp) is a real thing in IRL animals and plants - no magic needed.

you *do* realize that there is more than two books in the Lady Trent series, right?

-anthony docimo

Electric Eggs said...

Would a creature with an odd number of wings make sense? Sorta like an airborne version of the "odd-walkers" discussion?

Sharkhondra said...

I wonder if a mountain goat-like creature living in high clifftops could make for a sensible predecessor for a clade of flying alien animals.

Unknown said...
This comment has been removed by the author.
Anonymous said...

>except that developmental plasticisity(sp) is a real thing in IRL animals and plants - no magic needed.
That`s just phenotype variation, and Lady Trent`s developmental lability seems to involve actual genetic modification by environmental factors that introduces new traits entirely. Sometimes it`s a more realistic random mutation and other times it`s just supernaturally deliberate.

>you *do* realize that there is more than two books in the Lady Trent series, right?
Yes? There is, in fact, five of them, not counting short stories, plus the standalone sequel Turning Darkness Into Light, which focuses on archaeology and linguistics instead of questionable spec-biology.

>Would a creature with an odd number of wings make sense? Sorta like an airborne version of the "odd-walkers" discussion?
That was discussed in one of the tetropters posts, I believe.

Unknown said...

Sharkhonda - yes, yes they could.

Electric Eggs: yes they make a lot of sense - the blog here discussed that numerous times, including with the Nereus posts you may enjoy searching and reading.


hey, Anon, I'm going to tell you something that used to be told to me: If you don't like it, STOP READING IT.

(not sure how you tell the difference between "new traits entirely" and traits that don't get used much)
-anthony docimo

Anonymous said...

> If you don't like it, STOP READING IT.
If you don`t understand the difference between honest criticism and unwarranted hate, stop answering to it. I literally said I consider the books very good in the first comment, and I only came here to correct the misinterpretation of the book cover in the post anyway, so get all the way off my back before we both get banned or something.

Sigmund Nastrazzurro said...

-Anthony: if I included you as an addressee in the wrong context, I apologise.

-I will not address all comments in turn this time, as the discussion seems to be taking a wrong turn. However, I do not understand where the idea comes from that Furahan flying forms walk on their wings. Mind you, pterosaurs did, so the idea is in fact attractive. As all hexapods will receive a makeover anyway, perhaps they will...

-As for the tone of some recent comments, I must say I do not approve. I do not even know whether I can in fact ban people, and do not intend to try. I have only ever deleted comments that were in fact advertisements. I hope to keep the discussion civil and would like to remind everyone that speculative biology is an intellectual pastime, a game if you like. I may prefer science fiction over fantasy, but others may feel different; fine! Please keep a sense of proportion, and do not forget your sense of humour.

Johnny said...

Could something like a rusp fly? A long serpentine body with plenty of small wings that flap and undulate in a waving pattern?

my name is Carl, hello said...

Hmm, that comment on "wing walkers" is interesting and the comparison to pterosaurs is very significant: I remember reading about a study that mentioned that the wing-vaulting launch of pterosaurs allowed them a more forceful takeoff: birds are constrained in weight limits by their relatively weak bipedal launch, bats launch with their wings but lack hollow bones and air sacs that make them lighter, but pterosaurs got the sweet double benefit of pbeumatized bones and forelimb launching, which is explained how some grew to the size of giraffes but could still fly. Probably something worth considering for Furahan flyers, and if Furaha's atmosphere is denser or its gravity lower maybe the flyers could get EVEN bigger...

Magma dog said...

These concepts of transitional flyers look interesting, but how about: them being juveniles of flying creatures that are arboreal gliders as babies while they are still too weak to flap their wings, and as they grow stronger they eventually leave the canopy as they mature and fully take to the sky (also making the adult and infant fill different niches and reducing competition).

Unknown said...

Mr. Nastrazzurro,
I offer my humble apologies for several things - for snapping at the other Anthony (to whom you replied initially) in earlier discussions in this thread, as well as at Anon.

Johnny - a flying rusp would certainly be an intriging sight...though I wonder how much the body would have to be modified - like a barnacle or tunicate, perhaps?

Unknown said...

that was my apology, to which I once again failed to attribute myself.

-anthony docimo

Abbydon said...

@Johnny: I'm not a specialist in aerodynamics but I suspect it would be difficult to fly with lots of wings and a flexible body. However, there are some airplanes with six wings called three-surface aircraft since they have canards, a main wing and a tailplane. A six winged animal therefore isn't entirely implausible and there are actually some extinct insects that appear to have six wings. Remember that there is a difference between fixed wings and flapping wings though.

Unlike typical airplanes tandem wing airplanes have a pair of approximately identical wings (and no tailplane). I suppose it might be possible to have more than two wings in this configuration but I am not quite sure of the benefits and again it may not work with flapping wings.

Jojira said...

How likely would a fully aquatic, air breathing animal develop powered flight and go from aquatic to airborne without a terrestrial intermediate?

Sigmund Nastrazzurro said...

Johnny: Interesting. Something like that could certainly swim, so there is little doubt that the ppropulsion would work. The problem would probably be 'suspension': in water, the body might ore or less be equal in specific mass to water, so there would be little tendency for it to sink as a whole, or to have it front or hind end sink while the other is kept up ('pitching'). In a flying animal, pitching might be a big problem. But if the winglets beat in such a way that the pitching forces are equally distributed, it need not pitch. Whether it could yaw at will might be more difficult. somehow it seems very unlikely, but not impossible. perhaps there are people with a better understanding of aerodynamics who may help...

Carl: good insights! I was not looking for maximally large flyers, but I definitely like the possibility of having them aboard.

Magma dog: also interesting; ontogeny recapitulates ontogeny, but now not in embryos but in active animals. That is fascinating; mind you, at every stage the animal would have to be completely functional, and then I wonder whether it would be easier to have it develop quickly in a sheltered environment while it is vulnerable and very dysfunctional, or to have it active and about, less vulnerable but also less dysfunctional, but for a longer time? Is this why bird young stay in nests?

Anthony: don't worry, it's fine.

Abbydon; see above; I don't know either...

Jojira: That sounds like a very difficult step to me. But we are straying very far from the subject at hand. Why not try the speculative evolution forum? There is thread there entitled 'questions that do not need their own page', or something similar.

Margette said...

I like the ontogeny idea. There's certainly an appeal to metamorphosis and I can see that in the case of flying hexapods who lay lots of eggs and leave them to chance without further care, it would make sense for the babies to be independent right away even if they can't fly yet. Sort of like how carnivorous, terrestrial frogs start life as aquatic, herbivorous tadpoles, and gradually transition between the two as they mature.

Sigmund Nastrazzurro said...

Margette: ... and with three groups of hexapodal 'avians', one group could follow this pattern, while the others follow other evo-devo paths. I like it.

Patsy said...

Three groups of hexapodal avians? interesting. how would the three clades differ from each other, and how do they all coexist? the pterosaurs were all outcompeted by the birds except the giant azdarchids who made it all the way to the end of the cretaceous, and today bats avoid avian rivalry by being nocturnal. Do furahan flyers have similar issues?

flying penguin said...

could any flightless birds today re evolve flight

Unknown said...

I'm afraid not, Flying Penguin; maybe one could become a glider, perhaps a parachuter...but no powered flight.

anyway, as Mr. Nasatrazzurro says, this sort of discussion is best suited for the https://specevo.jcink.net/index.php?showforum=4


Bats don't have too much trouble with birds, Patsy - for the most part, they nest and eat differently; (and given that birds evolved in the Jurassic, they and the pterosaurs handled each other very well)..........though we don't know that the three Furahan flying groups *do* all coexist - there are some *very* isolated continents on Furaha, after all.

-Anthony Docimo

Sigmund Nastrazzurro said...

Patsy: I admit that I never read much about competition on the level of higher clades, although I probably should know more about that before spawning various avians. My guess is that various clades can coexist in time either if their overall fitness is more or less the same, or when they are apart, geographically, in biotope, time of day,or whatever.

flying penguin: sorry, but such questions are best asked on the forum

Anthony: I had already used your arguments to answer Patsy. As for geographical separation, I decided that The Book will not discuss at least one continent, the one farthest from all others. Who knows what happens there...

Shreeeep said...

Are all three clades of Furahan flyers of separate origins? Would be interesting if one clade was actually descended from another, having become flightless and then independently, secondarily re-evolved flight but in a different way...

a trump supporter with the intellectual capacity of a jellyfish said...

Have there been any depiction of the internal anatomy of the hexapods of Furaha? How does their anatomy become conducive to flight (hollow bones, air sacs, enhanced respiratory system, etc)?

Abbydon said...

Amphibians, reptiles and mammals exist side by side in biomes on Earth, so the idea that multiple clades of similar flying animals could coexist doesn't seem unreasonable. Making them distinct in some way so that a different one is dominant in each biome would perhaps make sense. Factors could include: day/night, moist/dry, hot/cold, etc. Of course, birds on Earth are widespread so it's not obvious if they have left niches unfilled. One potential possibility is a sea-based flying animal (i.e. flying fish or squid) as that would clearly be different to a land-based flying animal.

knuckle-walking sloth-horse said...

Aside from the hexapods, are there also non-hexapod, "invertbrate" flyers on Furaha? Like, bee-like pollinators or something

Czechoslovakian manatee said...

What do the "bipterates" look like? I wonder if they at least superficially somewhat resemble the dragons of this pic, would make an interesting reference

Sigmund Nastrazzurro said...

knuckle etc.: there are tetrapters (also search for 'tetropter')

Chechoslovak etc: The bipterates are at present caught up in The Great Hexapod Redesign Upheaval.

tribbetherium said...

I guess one issue with a dragon-like flyer would be the long tail, both birds and pterosaurs had a trend of progressively shorter tails over the course of their evolution and bats seem to have had short tails ever since they first flew, so perhaps long tails make flight inefficient?

Also, for bipterates: one solution for avoiding tripping of hexapods is for their middle pair of legs to be more widely spaced so the front and hind pairs swing in-between them without the limbs colliding. Could it be possible that with this arrangement it leads to the middle limbs being selected for "centaurism" which eventually give rise to wings?

return to donke said...

How about a six winged hexapod? think microraptor where all the limbs are wings

Sigmund Nastrazzurro said...

tribbetherium: I was always surprised by the long tails of some early pterosaurs. They look fascinating but must have disappeared for good reasons. I have never looked into that, but my guess is the following: aircraft have tails so the horizontal and vertcal control surfaces have a lever to work with. Birds have relatively shorter and lighter tails, and no separate vertical control surfaces. I think that their control mechanisms is simply vastly superior. It is only now with computer control that some aircraft start to lose al the big surfaces.
I once came up with the wider leg base for the middle legs of hexapods in this blog as one way to avoid leg clashing, and am therefore familiar with the concept. But I doubt that the wide stance would be a major argument to select these legs for flight. Their position near the middle might be a better argument.

Abbydon said...

Aerodynamic investigations into how birds fly are both interesting and complicated. Furthermore, the function of the tail seems to depend on the bird's lifestyle. However, theory suggests that the lift generated by a tail is proportional to the square of the maximum width. Everything beyond the point of maximum width adds drag but no lift. Therefore, to reduce drag tails should be short and increase in width to a maximum at the end. A long tail that starts out wide and tapers to a small point is aerodynamically inefficient.

It wouldn't be surprising if the general bird shape of a flying wing with a controllable tail shape is the optimum for all large flying animals. Variations in gravity and atmospheric pressure presumably change the threshold for "large" though.

Davide Gioia said...

The idea that pterosaurs were ultimately outcompeted by birds has now been largely abandoned, both because the two groups coexisted for millions of years and because we now know that up to the end of the Cretaceous pterosaurs were a lot more diversified than just azhdarchids http://www.eartharchives.org/articles/pterosaurs-maintained-high-diversity-until-the-end/.

Dennis said...

"a wide based tail that tapers to a point is inefficient for flight" but what about the Mexican free-tailed bat?

Abbydon said...

Free-tailed bats are certainly a valid counter example but, honestly, I don't know the answer.

It could be that the tails are relatively small and so a little extra drag is insignificant but that's a weak argument. That's especially true since the Brazilian Free-Tailed Bat is apparently the fastest flying animal.

It is the case that such "fast hawking" bats tend to have short tail membranes as larger membranes probably add drag at high speeds. I haven't seen this explicitly mentioned in any technical articles but perhaps the membrane has shrank but the tail hasn't yet. Again, this is a slightly weak argument though.

However, an interesting point made in papers on bat flight is that bat wings have more degrees of freedom than bird wings. This is due to muscles in the skin and the use of two limbs per wing. The tail membrane further adds capability. Perhaps this suggests that if a large hexapod evolved flight it would be more likely to incorporate multiple limbs in a single wing rather than have multiple independent wings like dragonflies.

I am now doomed to spend time looking into this as it is quite interesting.

Unknown said...

Abbydon,

for me at least, the use of multiple pairs of limbs in wings is something that only makes sense for gliding and parachuting. To carry the analogy, it would be like if dragonflies had the same number of wing muscles & attachment points as we're familiar with from them, but only one pair of wings, because the wing surfaces fused together.

>The tail membrane further adds capability.
in the sense of steering, yes; in the sense of being the equal of a wing, no.

-anthony docimo

and then there's Chunky, he's dead said...

if i recall correctly dragonflies are a bit of an outlier among four winged insects since other bugs have structures that connect their front and hind wings that make them flap in unison?

Sigmund Nastrazzurro said...

Sorry about the delay; real life...

Abbydon: you may well be correct that a wing with a tail may be optimal, but much of that probably depends on the subtlety of neural control over the wing configuration. Human-designed airplanes generally have vertical tail surfaces, whereas bats and birds do without them. This suggests superior control to me. Could an even better control do without a tail altogether?

Davide Gioia: I agree : there is room for simultaneous designs, side by side. On land, many different designs exist side-by-side, and no-one seems to argue that only one major design must exist at a given time.

Dennis and Abbydon: I do not know either why free-tailed bats work the way they do; could it be that that bat has superior control?

Abbydon and Anthony: hmmm; I must think about that. For the time being I willstick with multiple independent wings. But the multilimbed wing has an offwordly attraction...

... chunky...: and yet both insects with four independent wings and those with 'tied wings' all fly superbly. It is therefore not obviouos wht one should be prefeered over the other.

Abbydon said...

I think the main purpose of the vertical tail on aircraft is to add stability by producing forces that counteract other forces. This stabilises the aircraft when there is no control input from the pilot. Tailless aircraft are less stable and require more computer control along with additional control surfaces on the wings. For an animal the "pilot" can't take their hands from the controls so a vertical tail isn't really necessary. Interestingly, fish do have dorsal fins though which serve a similar purpose.

For insects, an advantage of independent wings over tied wings is that it becomes easier to hover. Wings produce more force on the downstroke than the upstroke (obviously). With tied wings this means the insect will move downwards while the wings are moving upwards. To drop less requires the wings beat faster which becomes more difficult as the animal becomes larger. In contrast, with independent wings this isn't a problem so larger insects can hover. This manoeuvrability is an advantage for large aerial predators (i.e. dragonflies) but less useful for most other insects I guess. The split between the two wing types was quite early in the evolution of insects though.

There is also the example of beetles which sort of have independent wings. The forewings are rigid protective structures but when flying they act like the fixed wings on aircraft to add lift. This might explain why some large beetles are still capable of flight. Beetles do however have to stick their legs out when they fly as they seem to use them as control surfaces.