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On a tangential note, I'm still trying to wrap my head around the notion that a flying reptile the size of Quetzalcoatlus (believed to have wingspan on the orde

by curtis 8y ago

On a tangential note, I'm still trying to wrap my head around the notion that a flying reptile the size of Quetzalcoatlus (believed to have wingspan on the order of 10 meters) could ever get airborne. This has made me wonder if it's possible that juvenile Quetzalcoatlus could fly but adult Quetzalcoatlus could not. Natural selection would presumably select towards smaller and smaller wings on adults, but maybe this could be offset by a serious evolutionary advantage bestowed on juveniles from being able to fly. I don't know of any bird existing or extinct with this kind of lifecycle, but maybe you can find something similar in insects?

andrewflnr 8y ago
The idea of older individuals being flightless is specifically addressed in the Plos article linked at the top. Basically, the large individuals still have lots of flight-optimized characteristics that you would expect to have atrophied if they weren't flying.
- curtis 8y ago
  From the referenced article [https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0013982 https://journals.plos.org/plosone/article?id=10.1371/journal...]: > It is possible, however, that giant pterosaurs represent old, flightless individuals of a species that were capable of flight when younger, their flight anatomy simply being retained from a previous stage in their life history. However, if the maximum flight sizes suggested by Sato et al. [17] and Chatterjee and Templin [19] are correct at 41kg (5.1 m span) or 70 kg (6.65 m with ‘heavy’ estimates), then the largest azhdarchids would have grown up to six times the mass and twice the wingspan of their terminal flight size. It seems unlikely that enormous azhdarchids would continue to develop their physiologically expensive flight apparatus, and coincidentally with a mechanically appropriate scaling regime, throughout such extensive growth under flightless conditions. The same point is true, though to a lesser extent, for large Pteranodon that also bear obvious flight characteristics despite having exceeded the suggested wingspan limits of flight. If anything, the scaling regimes of pterosaur wings dictate that the flight characteristics of giant pterosaurs (the size of their deltopectoral crests, robustness of their joints) - become more exaggerated with size and age (e.g. [76]), precisely the opposite of what would be expected in animals that lost their flight ability as they grew older. This doesn't help me understand the physics of large flying reptiles, but it does make a plausible argument that they were in fact real.
btilly 8y ago
No, pterosaurs had wings built out of hand bones, and hands develop their size early in vertebrates. Therefore if you've got the right proportions to fly as a grownup, you should be able to as a kid. Whether that was right to birth is still debated, but certainly they could fly from being young. By contrast birds and bats use arm bones in their wings, and so cannot fly until nearly an adult. That imposes child care needs on the parents that are pretty severe if you are large. Now when species compete, they usually don't do it head on. Instead each specializes on what it does better. Pterosaurs couldn't do much about the fact that feathers are more efficient flight surfaces than their hair. But they had one advantage - it was easier for them to grow big. And that is why at the end of their time, the last niche that they held was a freakishly big carrion eater. (And dinosaurs could make for some freakishly big carrion for them to eat!)
- DuskStar 8y ago
  > No, pterosaurs had wings built out of hand bones, and hands develop their size early in vertebrates. Therefore if you've got the right proportions to fly as a grownup, you should be able to as a kid. Whether that was right to birth is still debated, but certainly they could fly from being young. You've got the GP's question exactly backwards - they aren't questioning whether the juveniles could fly, only the adults. If you develop the full hand size early in life, and that supports flying with 20kg of mass, a 15kg juvenile is going to have a much better time of things than a 50kg adult. (Numbers pulled out of my ass, I'm not sure what the actual ones would be)
- grawprog 8y ago
  Bat's have hand wings. Their order Chiroptera means hand wing. Their wings are elongated hands and fingers. https://www.researchgate.net/figure/Anatomic-structure-of-bat-wing_fig1_259399127 https://www.researchgate.net/figure/Anatomic-structure-of-ba...
Rhinobird 8y ago
They may have been able to fly because, perhaps, the air pressure was different back then. 2 bar or more http://levenspiel.com/wp-content/uploads/2016/02/DinosaurW.pdf http://levenspiel.com/wp-content/uploads/2016/02/DinosaurW.p... Going back even further, there's giant insects. Bugs today are limited in size to the efficiency of their respiratory system. They don't have lungs like vertebrates. Air just sorta diffuses through their bodies. I you raise insects in a high oxygen environment, after a few generations they get bigger. The size of bugs before the dinosaurs indicate a higher oxygen content. https://www.livescience.com/1083-oxygen-giant-bugs.html https://www.livescience.com/1083-oxygen-giant-bugs.html
- curtis 8y ago
  I'm under the impression that a higher prehistorical concentration of oxygen in the atmosphere is widely accepted at this point. Higher atmospheric pressure is not something I've heard anything about though. Wikipedia has a nice graph showing high and low estimates for the historical oxygen level: https://en.wikipedia.org/wiki/Geological_history_of_oxygen#/media/File:Oxygenation-atm-2.svg https://en.wikipedia.org/wiki/Geological_history_of_oxygen#/....
  - marcosdumay 8y ago
    I don't think anybody is claiming that Earth gained extra nitrogen (how would it?). So, while it lost oxygen, it also had to lose some air pressure. I imagine there was some huge pressure loss at the oxygen catastrophe.
    - int_19h 8y ago
      You also need to account for CO2.
      - marcosdumay 8y ago
        There is almost no CO2 on the atmosphere.
    - 8y ago

by curtis 8y ago

andrewflnr 8y ago

The idea of older individuals being flightless is specifically addressed in the Plos article linked at the top. Basically, the large individuals still have lots of flight-optimized characteristics that you would expect to have atrophied if they weren't flying.

curtis 8y ago
From the referenced article [https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0013982 https://journals.plos.org/plosone/article?id=10.1371/journal...]: > It is possible, however, that giant pterosaurs represent old, flightless individuals of a species that were capable of flight when younger, their flight anatomy simply being retained from a previous stage in their life history. However, if the maximum flight sizes suggested by Sato et al. [17] and Chatterjee and Templin [19] are correct at 41kg (5.1 m span) or 70 kg (6.65 m with ‘heavy’ estimates), then the largest azhdarchids would have grown up to six times the mass and twice the wingspan of their terminal flight size. It seems unlikely that enormous azhdarchids would continue to develop their physiologically expensive flight apparatus, and coincidentally with a mechanically appropriate scaling regime, throughout such extensive growth under flightless conditions. The same point is true, though to a lesser extent, for large Pteranodon that also bear obvious flight characteristics despite having exceeded the suggested wingspan limits of flight. If anything, the scaling regimes of pterosaur wings dictate that the flight characteristics of giant pterosaurs (the size of their deltopectoral crests, robustness of their joints) - become more exaggerated with size and age (e.g. [76]), precisely the opposite of what would be expected in animals that lost their flight ability as they grew older. This doesn't help me understand the physics of large flying reptiles, but it does make a plausible argument that they were in fact real.

btilly 8y ago

No, pterosaurs had wings built out of hand bones, and hands develop their size early in vertebrates. Therefore if you've got the right proportions to fly as a grownup, you should be able to as a kid. Whether that was right to birth is still debated, but certainly they could fly from being young. By contrast birds and bats use arm bones in their wings, and so cannot fly until nearly an adult. That imposes child care needs on the parents that are pretty severe if you are large. Now when species compete, they usually don't do it head on. Instead each specializes on what it does better. Pterosaurs couldn't do much about the fact that feathers are more efficient flight surfaces than their hair. But they had one advantage - it was easier for them to grow big. And that is why at the end of their time, the last niche that they held was a freakishly big carrion eater. (And dinosaurs could make for some freakishly big carrion for them to eat!)

DuskStar 8y ago
> No, pterosaurs had wings built out of hand bones, and hands develop their size early in vertebrates. Therefore if you've got the right proportions to fly as a grownup, you should be able to as a kid. Whether that was right to birth is still debated, but certainly they could fly from being young. You've got the GP's question exactly backwards - they aren't questioning whether the juveniles could fly, only the adults. If you develop the full hand size early in life, and that supports flying with 20kg of mass, a 15kg juvenile is going to have a much better time of things than a 50kg adult. (Numbers pulled out of my ass, I'm not sure what the actual ones would be)
grawprog 8y ago
Bat's have hand wings. Their order Chiroptera means hand wing. Their wings are elongated hands and fingers. https://www.researchgate.net/figure/Anatomic-structure-of-bat-wing_fig1_259399127 https://www.researchgate.net/figure/Anatomic-structure-of-ba...

Rhinobird 8y ago

They may have been able to fly because, perhaps, the air pressure was different back then. 2 bar or more http://levenspiel.com/wp-content/uploads/2016/02/DinosaurW.pdf http://levenspiel.com/wp-content/uploads/2016/02/DinosaurW.p... Going back even further, there's giant insects. Bugs today are limited in size to the efficiency of their respiratory system. They don't have lungs like vertebrates. Air just sorta diffuses through their bodies. I you raise insects in a high oxygen environment, after a few generations they get bigger. The size of bugs before the dinosaurs indicate a higher oxygen content. https://www.livescience.com/1083-oxygen-giant-bugs.html https://www.livescience.com/1083-oxygen-giant-bugs.html

curtis 8y ago
I'm under the impression that a higher prehistorical concentration of oxygen in the atmosphere is widely accepted at this point. Higher atmospheric pressure is not something I've heard anything about though. Wikipedia has a nice graph showing high and low estimates for the historical oxygen level: https://en.wikipedia.org/wiki/Geological_history_of_oxygen#/media/File:Oxygenation-atm-2.svg https://en.wikipedia.org/wiki/Geological_history_of_oxygen#/....
- marcosdumay 8y ago
  I don't think anybody is claiming that Earth gained extra nitrogen (how would it?). So, while it lost oxygen, it also had to lose some air pressure. I imagine there was some huge pressure loss at the oxygen catastrophe.
  - int_19h 8y ago
    You also need to account for CO2.
    - marcosdumay 8y ago
      There is almost no CO2 on the atmosphere.
  - 8y ago