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Re: SPECULATION: pterosaur extinction versus bird survival
"Please excuse my naivety, but is it possible that Pterosaur lungs were
arranged radically differently from those of birds and other
dinosaurs? When I look at pterosaurs.net's skeletal reconstruction of
_Quetzalcoatlus_ (http://www.pterosaurs.net/Quetzalcoatlus.html) I
can't help thinking that all that neck space is wasted if they are
built at all like modern animals. But what if the lungs were partly
in the neck itself? Or less radically, perhaps the tubing from the
mouth to the lungs proper could absorb some of the oxygen en route?
Is this just stupid? Go on, tell me -- I can take it :-)"
Well, the two living outgroups that bracket dinosaurs are the crocodilians and the birds. The crocs have lungs that are somewhat like the dead-end types we find in other reptiles, but they also have a sort of "chambered" appearance. They use a hepatic pump system (literally using their liver with a diaphragm to push air into and out of their lungs) to breathe. Birds, of course, have small lungs surrounded by a complicated air-sac system. Birds move their belly in and out, and by doing so move air through the air-sac system. The air first moves into the most posterior air sacs as it comes down the trachea and then travels anteriorly back toward the neck. By doing so, the oxygen-rich air is pushed in a single direction (posterior to anterior) through the lungs of the bird. This one-way air flow, without the in- and out-type respiration we see in ourselves or reptiles, dramatically increases the amount of oxygen birds can extract fro!
m inhaled air. It would be like having a continuous flow of air over your lungs that constantly supplied you with oxygen. In certain experiments, birds and mammals of equal weight are exposed to air pressures and oxygen concentrations similar to those you find near the top of Mt. Everest. The birds do fine; the mammals pass out or asphixiate.
If pterosaurs share a common ancestor with dinosaurs (which they appear to), and if the hollowness of their bones is correlated with similar structures like those of birds, then we might suspect pterosaurs had an oxygen-extracting system similar to that of birds. Many birds have incredibly long trachea that actually loop around inside their chest after leaving the neck (the trumpeter swan, for instance), and they manage to breathe just fine. Therefore, there is nothing in living dinosaur relatives (crocs, birds) that supports extra air sacs in the neck or oxygen-absorbing qualities in the trachea. The apparent common ancestry of pterosaurs and dinosaurs would suggest that if pterosaurs were endothermic, active fliers like birds, we might suspect their respiratory systems were similar, although perhaps not idenitical.
Great question, I think.
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