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Re: SPECULATION: pterosaur extinction versus bird survival
Several things happened 65 million years ago that contributed to the K-T
extinction. One is the superplumes that spewed tons of toxins into the
environment and the other catastrophic geological activities that occurred.
Accompanying this is the ET impact that created the iridium layer, which
sent tons of debris into the atmosphere, and affected wolrdwide
But I take these two things one step further. I believe that after these
two types of events, not only was the atmospheric content changed, but also
the density was lowered, even slightly. After a giant asteroid, comet,
whatever, hits, lots of gas will be sent into space. I think that the
amount of gas sent into space lowered the density of Earth's atmosphere
slightly, but enough to take into account.
Now, this factors into other preexisting studies as well. Amber sample data
indicate 33% less oxygen after the K-T extinction (Amber is formed by way of
a lack of oxygen, so I am slightly skeptical about the amber studies'
accuracy). So not only was the overall composition changed, but the density
decreased as well.
Birds have a very efficient respiratory system, and accompanied by the wing
beats acting as bellows, they can have enough oxygen supplied to them. But
dinosaurs had a less efficient system, even if they had the unidirectional
air flow system, which I believe many did (but that's a different
discussion). Pterosaurs also had a less efficient breathing system than
birds. So this inability to cope with the new atmospheric conditions played
a major role in the deaths of many types of organisms.
Not only that, though, but as far a pterosaurs go, a less dense atmosphere
would be hazardousm, because at the K-T boundary, most were ocean gliders.
Thus, they needed strong air currents in their flying because of their
lifestyle. So when the atmospheric was density was decreased, and currents
changed, they found new flying conditions and were less efficient flyers in
the new atmosphere than birds.
The two different types of wings alone seem to indicate birds being better
fliers at a lower density. And because they are lgihter, they didn't need
the density as much.
So that's part of my theorizing...
Peace out, Demetrios Vital