Cryptozoological Evolution

[AzurePhoenix]

Just to get off the ground, something that big would have to be warm blooded. And I've seen musculature digrams with a good amount of muscle at the wing-shoulders. Never did a great job though. They have a keel and all that, but they seem to forget to modify the arrangement to allow for the forelegs. Not that I know how to do so. Maybe I'll try. I am working on draconic anatomy at the moment anyway and will need to tackle the problem eventually....

[Mokele]

One theory on wings for insects deals with wings initially being used to absorb heat. Larger surface area for the sun to warm up.

 

IIRC, there have actually been experiments done that give some pretty firm support to that theory. But it's not my area, so I'm not really "in the know".

 

If they are cold, wings could have provided an extra heating surface when they lounge around in the sun.

 

Except that many reptiles have already evolved ways of doing that, usually simply involving expanding the ribcage in order to flatten the body or by changing color to a dark skin tone when basking. It's possible that the ability to flatten the ribcage can lead to collapsible rib-wings like the flying lizard of genus Draco, but you won't see it in truly large animals, since their thermal inertia means they don't face quite as bad of a problem as small reptiles in the same habitat, since they retain heat through sheer bulk to a degree. Also, in large animals such heat collectors would need to be a lot larger (proportionally) than in small animals before they begin offering aerodynamic advantages.

 

Mokele

[AzurePhoenix]

How difficult is is for a ectotherm to make the transition to an endotherm anyway?

[Mokele]

How difficult is is for a ectotherm to make the transition to an endotherm anyway?

 

Well, we know it's happened twice (birds and mammals evolved endothermy independently), so it's not a one-time0only thing. But beyond that, it's hard to say. Maybe it's easy if the situation is right, but then what's the right situation? The difficulty of extrapolating metabolism from fossils makes it even more difficult.

 

I wouldn't put it past reptiles to produce endothermic descendants again, though. Cuban crocs are my bet, or varanid lizards.

 

Mokele

[AzurePhoenix]

Even some sharks come close

[Hellbender]

Varanids are already pretty close to being endothermic, right? I know a lot of bony fish such as mackerel are endotherms, as well as lamnid sharks, as azure pointed out above. Also I read that some type of sea turtle is endothermic, but I will have to google that and see which one it was.

 

Question for Mokele: Is there any evidence that pterosaurs were endothermic as well? Some fossils have been found with hairlike filaments, but I am not quite sure if this is a definite indicator of warm-bloodedness.

 

edit: its the leatherback sea turtle, and it is partially warm-blooded, apparently allowing it to migrate into colder waters.

[Hellbender]

Cuban crocs are my bet

 

interesting, but why cuban crocs? Are they already pretty close like varanids?

[Auburngirl05]

Aren't there some large species of fish that are functionally endothermic? Or maybe homeothermic would be the more correct term because I'm not sure if their heat is internally generated, but I'm pretty sure there have been some noteworthy studies on the topic.

[AzurePhoenix]

I'm fairly certain the pterosaurs would be. They were several steps of modern archosaurs (crocs are these, right?) which were far more derived, with four chambered hearts and such, and I think that dinos (also archosaurs, or at least derived from them) probably obtained warm blooded traits fairly early on. The fact that pterosaurs evolved towards a highly energetic lifestyle would seem to indicate that they would also move towrds endothermy, or may have even started out with it by gift of some predisposed ancestor.

 

Sorry, Mokele would know better than I. If only highschool offered courses in paleontology and herpetology.

[Mokele]

Varanids are already pretty close to being endothermic, right?

 

Well, they're active and have a high metabolism for a reptile, but they're still a long way from actual endothermy.

 

its the leatherback sea turtle, and it is partially warm-blooded, apparently allowing it to migrate into colder waters.

 

Actually, that data has since been withdrawn; it was a measurement error. It has mass homeothermy, but it's basal metabolism is as expected for a reptile of its size.

 

Is there any evidence that pterosaurs were endothermic as well? Some fossils have been found with hairlike filaments, but I am not quite sure if this is a definite indicator of warm-bloodedness.

 

Well, AFIAK, the consensus on the fillaments is that they're tough fibers that served to strengthen and support the wing membrane.

 

As for metabolism, maybe. Given that they could actively fly, which requires a very high aerobic metabolism, it's very likely that they were endotherms. But, we only have two groups of large true-flyers now, so can we really assume that for the past? Maybe pterosaurs were ecotherms with some sort of biological "trick" that no longer exists to manage flight? As always with the metabolism of extinct animals, we can't be certain.

 

interesting, but why cuban crocs? Are they already pretty close like varanids?

 

Not in metabolism, but they display some interesting behaviors that could lead down an often-traveled path of croc evolution. Cubans are much more terrestrial than other crocs, with longer, stronger legs; they can actually gallop as adults, while most crocs can only do this as juveniles. That's helped by their smallish size (9 foot males and 7 foot females are average). Interestingly, they also appear to be pack hunters. (The curiously flattened teeth in the back of their mouths and some fossils lead some to suspect they evolved pack hunting to take down Pleistocene ground-sloths).

 

Anyhow, this is significant because running crocodiles are a repeated theme in their evolution. They actually started out as small, erect runners about the size of dogs, became aquatic and large, but have returned to terrestrially active predations at least 2 times since the dinosaurs, possibly more (sketchy fossil evidence so we can't be sure). We don't know if these running crocs ever were endothermic, for the same reason we don't know about the dinosaurs, namely that the only stuff that fossilizes is correlated to metabolism, not causally linked.

 

Given that close relatives of the crocs who retained the active, terrestrial lifestyle eventually became dinosaurs and then birds, it's possible they were warm, cold, or something in between.

 

They were several steps of modern archosaurs (crocs are these, right?) which were far more derived, with four chambered hearts and such, and I think that dinos (also archosaurs, or at least derived from them) probably obtained warm blooded traits fairly early on.

 

Yes, crocs and dinos are archosaurs. And yes, the 4 chambered heart seems likely for dinos and pterosaurs. But the problem is whether that (and the other derived traits you mention) truly indicates endothermy? Sure, it's correlated with it, but there's a painfully small sample size of modern endotherm taxa, so how can we be sure, especially since we know that the four-chambered heart can be possessed by cold-bloods (crocs).

 

To complicate things, many amphibian hearts have varying decress of ventricular separation, and all reptile hearts (aside from crocs) are effectively 5-chambered, via temporary muscular ridges and valves that only show up during contractions. Indeed, if we go by taxa, complex hearts are more strongly correlated to aquatic/amphibious lifestyle than to endothermy.

 

Never simple, is it?

 

Mokele

[Kygron]

It could happen as described, but would take a *LONG* time, and all intermediates would have to offer advantage over the prior situation (hardly a given).

 

I was considering how a dragon would evolve throught those intermediates. I'll say that perhaps the forelimbs would become wing-like structures FIRST, and then later the limb-gene would mutate to give them a new set of forelimbs. Once those become fully functional, the wings would further specialize into "true" wings.

[Hellbender]

Thank you, Mokele. Its always best to hear it directly from someone like a herpetologist then to read it somewhere online, where you aren't even sure if it is up to date.

[Hellbender]

Well, they're active and have a high metabolism for a reptile, but they're still a long way from actual endothermy.

 

Yes, that is what I have read. Once, when reading about Komodo Lizards somewhere, it said something about them being "almost warm-blooded". Some sources aren't always that reliable I guess.

 

Actually, that data has since been withdrawn; it was a measurement error. It has mass homeothermy, but it's basal metabolism is as expected for a reptile of its size.

 

Oops then I retract what I put earler about it then.

 

Well, AFIAK, the consensus on the fillaments is that they're tough fibers that served to strengthen and support the wing membrane.

 

Since it seems like the wing membrane was only stretched skin with only the "pinky" finger for support along the top, this makes sense.

 

Not in metabolism, but they display some interesting behaviors that could lead down an often-traveled path of croc evolution. Cubans are much more terrestrial than other crocs, with longer, stronger legs; they can actually gallop as adults, while most crocs can only do this as juveniles. That's helped by their smallish size (9 foot males and 7 foot females are average). Interestingly, they also appear to be pack hunters. (The curiously flattened teeth in the back of their mouths and some fossils lead some to suspect they evolved pack hunting to take down Pleistocene ground-sloths).

 

Now this is something interesting I have never heard about before. I will have to read more about this.

 

Anyhow, this is significant because running crocodiles are a repeated theme in their evolution. They actually started out as small, erect runners about the size of dogs, became aquatic and large, but have returned to terrestrially active predations at least 2 times since the dinosaurs, possibly more

 

Postosuchous comes to mind here as well as other, little crurotarsians one wouldn't recognize as croc relatives. Pretty interesting stuff considering what was said before about cuban crocs.

 

Indeed, if we go by taxa, complex hearts are more strongly correlated to aquatic/amphibious lifestyle than to endothermy.

 

interesting. why is this, you think?

[Hellbender]

I was considering how a dragon would evolve throught those intermediates.

 

If we are talking wings, for example, you would have to demonstrate how these intermediate forms of wings would be beneficial to the organism in each stage of their development.

 

I'll say that perhaps the forelimbs would become wing-like structures FIRST

 

Good, this is a feature that evolved seperately in bats, birds and pterosaurs, all the known flying verebrates. Explain why it would be advantageous for a large reptile to fly.

 

and then later the limb-gene would mutate to give them a new set of forelimbs. Once those become fully functional, the wings would further specialize into "true" wings.

 

Of course, you would have to demonstrate how the development of rudimentary front limbs (I am thinking of the Alien queen's little chest arms here, at least in the proposed early stages of this trait) would be advantageous and what selective pressures would select the gene for rudimentary little arms. In other words, why would the said dragon need another set of limbs so much? In all the flying animals, the front limbs are useful only for flying, while many have evolved prehensile feet to hold objects (food, nesting materials) while flying. Prehensile front limbs simply aren't required, they would be nice, and dragons certainly look goofy without them, but evolution already does a fine job modifying existing traits so that producing whole new ones isn't necessary.

[Ophiolite]

Forget amphibians and reptiles. Evolve them from fish and you can just convert another set of fins.

[Hellbender]

Forget amphibians and reptiles. Evolve them from fish and you can just convert another set of fins.

 

hey, there ya go.

[Kygron]

If we are talking wings' date=' for example, you would have to demonstrate how these intermediate forms of wings would be beneficial to the organism in each stage of their development.

...

Of course, you would have to demonstrate how the development of rudimentary front limbs ... would be advantageous and what selective pressures would select the gene for rudimentary little arms. In other words, why would the said dragon need another set of limbs so much? [/quote']

 

Lol, you take me too seriously. You're right, but I was just suggesting to the earier posters that it might be more reasonable to give a pterosaur a set of legs than to give a quadroped a set of legs that must then evolve to wings.

 

But to answer your question, I would say that a pterosaur with extra set of limbs would likely evolve BACK into some large quadroped. It would maintain the wings for the same reasons that they evolved originally. That would be better jumping/gliding or whatever, thought they would be of diminishing value. THEN when you have a dinosaur with a near vestigal set of wings, there may be some disruption in habitat that would allow that more adaptable creature to survive. The wings would become more usefull once again and there would be dragons!

[Kygron]

Forget amphibians and reptiles. Evolve them from fish and you can just convert another set of fins.

 

My hunch is that in eastern myths you will see dragons comming from the sea.

[Mokele]

Oops then I retract what I put earler about it then.

 

Don't worry, though: I only just found out that wasn't right a few days ago.

 

Now this is something interesting I have never heard about before. I will have to read more about this.

 

I doubt you'll find much: I don't think this info has been published yet. I learned it straight from the poor sods keeping them and the curator of the establishment. There were rumors before then, but everyone dismissed it until one of the keepers nearly became lunch.

 

interesting. why is this, you think?

 

Well, the complex hearts of most reptiles and amphibians are specially suited to deliberately allowing "leakage" in one direction or the other, in order to shunt blood flow around the body to either regulate body temperature (in conjunction with behavioral thermoregulation, of course) or extend the duration of dives.

 

Forget amphibians and reptiles. Evolve them from fish and you can just convert another set of fins.

 

Except that all fish have only 2 sets of paired appendages. All the other fins are single, and positioned along the dorsal or ventral midline. The only exception is that group of extinct fish I mentioned.

 

Mokele

[Hellbender]

Well, the complex hearts of most reptiles and amphibians are specially suited to deliberately allowing "leakage" in one direction or the other, in order to shunt blood flow around the body to either regulate body temperature (in conjunction with behavioral thermoregulation, of course) or extend the duration of dives.

 

I figured it had to do with their cold-blooded status. Thanks.

[Hellbender]

My hunch is that in eastern myths you will see dragons comming from the sea.

 

the european myth of the "lindormen" kind of reflects this. Lindorms, or lindwurms, are said to be terrestrial giant serpents that matured on land, then when they got too big, adapted to a marine habitat and were said to be responsible for sea serpent sightings. Just a little aside i wanted to relate.

[Hellbender]

Lol, you take me too seriously. You're right, but I was just suggesting to the earier posters that it might be more reasonable to give a pterosaur a set of legs than to give a quadroped a set of legs that must then evolve to wings.

 

I wasn't nitpicking (not that you think I was, just suggesting what you might want to consider for this.

 

But to answer your question, I would say that a pterosaur with extra set of limbs would likely evolve BACK into some large quadroped.

 

If this were the case, the wings would have to be converted again into forelimbs, unless for some reason it would be advantageous for it to be terrestrial, but still retain those wings. And again, with flight, we are talking more than just the large wings needed to fly. Stuff like lightweight skeletons, aerodynamic shape, etc. would have to be readapted for a purely terrestrial lifestyle.

 

It would maintain the wings for the same reasons that they evolved originally. That would be better jumping/gliding or whatever, thought they would be of diminishing value.

 

Okay, but show how diminished wings would be an absolute necessity for the creature to maintain while being adapted to a terrestrial lifestyle.

[Kygron]

And again, with flight, we are talking more than just the large wings needed to fly. Stuff like lightweight skeletons, aerodynamic shape, etc. would have to be readapted for a purely terrestrial lifestyle.

 

Yes, I never said it would be quick. (also, it need not be "purely" terrestrial, perhaps the thing will live in trees like flying squirels or something)

 

Okay, but show how diminished wings would be an absolute necessity for the creature to maintain while being adapted to a terrestrial lifestyle.

 

On the contrary, show me how losing the wings would be an absolute necessity for the creature to be adapted to a terrestrial lifestyle.

 

In fact I believe my final few sentences that you didn't quote answer this question. The wings would atrophy slowly in the course of evolution. They would not vanish however, and would be available later to redevelop.

 

 

You seem to be of the opinion that an new organism must be perfectly suited to its environment in order to survive to develop into an new organism. If we re-examine the quote used:

... and all intermediates would have to offer advantage over the prior situation (hardly a given).

"advantage" and "situation" are used here, not "perfect" and "envoronment". I like to think of evolution as an ongoing process. No organism is EVER perfectly suited to its environment. Mutations, racial differences, and genes millions of years repressed are always around and available to resurface.

 

I realize that I'm in the completely hypothetical here, but I'm trying to envision a way to a dragon to evolve. "Six legged dinosaur evolves one set of legs into wings" works, hypothetically. I believe "four footed pterosaur readapts to land" works also, but with a higher probability. You are free to suggest why it would be a lower probability, but unless you believe I've entered the "unreasonable" I don't think it does much good to describe the subtleties of the process.

 

Unless of course, you're doing full research about alternate histories of earth and need some creative encouragement.

[Hellbender]

Yes, I never said it would be quick. (also, it need not be "purely" terrestrial, perhaps the thing will live in trees like flying squirels or something)

 

Okay. but I can't imagine tree-dwelling dragons

 

On the contrary, show me how losing the wings would be an absolute necessity for the creature to be adapted to a terrestrial lifestyle.

 

in the early stages of terrestrial development, it would not be an absolute necessity, you are right, but they would be pointless wastes of energy if they were retained in their original form in later stages of terrestrial development. It would be better if they were vestigial and useless like an ostrich's wings (I think this is what you meant).

 

In fact I believe my final few sentences that you didn't quote answer this question. The wings would atrophy slowly in the course of evolution. They would not vanish however, and would be available later to redevelop.

 

sorry I didn't quote them, but believe me when I say I meant to

 

If I said or implyed they needed to vanish, then I apologize. Ostrichs and other flightless birds retain useless (well, useless for flight anyways) wings. But you are right, vestigial wings for later redevelopment is feasible.

 

You seem to be of the opinion that an new organism must be perfectly suited to its environment in order to survive to develop into an new organism. If we re-examine the quote used

 

Not perfectly adapted, as many species show evidence of jury-rigged systems and vestigial parts. I thought you meant that the wings would not atrophy, but be simply retained in the same, or similar form for some reason, but it seems that I either don't remember, or read it wrong, and I apologize.

 

"advantage" and "situation" are used here, not "perfect" and "environment". I like to think of evolution as an ongoing process. No organism is EVER perfectly suited to its environment. Mutations, racial differences, and genes millions of years repressed are always around and available to resurface.

 

No argument here.

 

realize that I'm in the completely hypothetical here, but I'm trying to envision a way to a dragon to evolve. "Six legged dinosaur evolves one set of legs into wings" works, hypothetically. I believe "four footed pterosaur readapts to land" works also, but with a higher probability. You are free to suggest why it would be a lower probability, but unless you believe I've entered the "unreasonable" I don't think it does much good to describe the subtleties of the process.

 

And I am trying to help you envision this, for fun. But evolution is complicated as you know, and lots of things such as environmental conditions need to be taken into consideration. I wanted to discuss why the dragon would have to evolve to front limbs, and become a flyer again. I didn't say it was impossible, and I don't want to argue here, but I thought it would be fun to brainstorm this. The subtleties are important in actually envisioning such a thing.

 

Unless of course, you're doing full research about alternate histories of earth and need some creative encouragement.

 

I am not, but have read books on this. it is very interesting to me.

[Hellbender]

Okay, but show how diminished wings would be an absolute necessity for the creature to maintain while being adapted to a terrestrial lifestyle.

 

This is where I was wrong. You were saying that the diminished wings could serve a purpose, and we were both wrong in even assuming vestigial features have to do anything.