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The largest flying bird in the article had a wingspan of 24 feet and an estimated weight of 90 pounds. By contrast the largest pterosaur was Quetzalcoatlus nor
by btilly 4y ago
The largest flying bird in the article had a wingspan of 24 feet and an estimated weight of 90 pounds.
By contrast the largest pterosaur was Quetzalcoatlus northropi with a wingspan estimated around 36 feet and a weight around 500 pounds. (Fun trivia, its outstretched middle finger, half that wing, is the longest vertebrate digit in the fossil record.)
Why did pterosaurs get so much bigger? Because of a simple quirk of vertebrate genetics!
It turns out that there are things which are evolutionarily easy to change (like your overall size, or when you hit puberty) and things that are essentially impossible. One of the things that is essentially impossible is the sequencing of when different parts of your body hit growth spurts. Hands+feet grow relatively early, but arms and legs only catch up near adulthood. It's cute when puppies and human babies have big hands and feet but stubby arms and legs. However it has consequences for flying vertebrates.
Birds have a wind that is all made out of their arms. Bats have a wing that is half arm, then half hand. Therefore both birds and bats are unable to fly until near adulthood because their arms have not yet grown yet, so their wings can't support their weight. This imposes a huge parenting burden as the young have to be taken care of. And the bigger the adult size, the bigger the parenting burden!
But pterosaurs had a wing constructed entirely out of their hands! Because hands grow early, models say that pterosaurs should have been able to fly from birth. Fossils of juvenile pterosaurs that died at sea confirm that they actually could. And because of that a large pterosaur would not impose a parenting burden, which means that pterosaurs were free to grow much larger than birds or bats.
This did not become important until birds evolved. Animals tend to compete through specialization. Each species focuses on what it is best at, and then they coexist. But feathers are more aerodynamic than a pterodactyl's fur. Therefore birds flew faster and farther while using less energy. The only thing that a pterosaur was better than a bird at was being big. So after birds appeared, the small pterosaurs all disappeared, and the big ones got REALLY big!
- herodoturtle 4y agoThis was an awesome comment just wanted to say thanks!
- leavethegun 4y ago
- rex_lupi 4y agoAbsolutely fascinating! Hope you didn't just make it all up /s
- gennarro 4y agoHad the same exact thought. Thank you!
- btilly 4y agoI did not make it up. The size of pterodactyls; https://en.wikipedia.org/wiki/Quetzalcoatlus https://en.wikipedia.org/wiki/Quetzalcoatlus Pterodactyls could fly from birth: https://www.newscientist.com/article/2284950-baby-pterosaurs-could-fly-within-minutes-of-hatching-from-their-eggs/ https://www.newscientist.com/article/2284950-baby-pterosaurs... And the bit on Resource Partitioning in https://www.khanacademy.org/science/ap-biology/ecology-ap/community-ecology/a/niches-competition https://www.khanacademy.org/science/ap-biology/ecology-ap/co... has the principle that in the presence of competition, animals focus on whatever niche lets them outcompete. But while I'm throwing out trivia on flight, have you ever wondered why bats only fly at night? It is because their wings have very thin skin. This is an even better aerodynamic surface than feathers, but offers them NO protection from sunburn!
- andrewflnr 4y agoOk, but the key point is the causative link between wing structure and size, for which you have not cited anything. The only theory I've heard on that front is that being able to both launch and flap with their arms basically allowed them to use the same, larger muscles for both, rather than having to split them, which increased their size ceiling while still being able to launch. http://markwitton-com.blogspot.com/2018/05/why-we-think-giant-pterosaurs-could-fly.html?m=1 http://markwitton-com.blogspot.com/2018/05/why-we-think-gian... (This is more precisely answering the question "how could they get so big?", but still pretty germane.)
- btilly 4y agoI didn't cite a causative link between wing structure and size. There were plenty of small pterosaurs. I cited a causative link between wing structure and parenting demands. And that is tied to the fact that babies can't fly if their wings don't support it. I have no idea from which article I ran across the connection between wing structure and juvenile flight. But the idea stuck because I was familiar with heterochrony from having read too much Stephen J. Gould when I was younger. However it is an observable fact that baby bats and birds do not fly, while fossil evidence says that pterosaurs did. The amount of parenting effort that birds require is also well-documented.