Comment by xenadu02 | Hacker News Reader

Comment by xenadu02 | Hacker News Reader

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Bird lungs work very differently from mammals. They have air sacs in front of and behind the lungs that take up a significant portion of their body cavity. The lungs themselves don't expand or compress. Air moves unidirectionally through the lungs both during inhalation and exhalation so there is no time at which the lungs themselves are not operating optimally. It is a two-phase system... during inhalation the posterior air sac fills with fresh air as spent air accumulates in the anterior air sac. The effective blood gas exchange surface area is about double that of mammals as well.

Basically: bird lungs are "pipelined" and highly optimized to extract oxygen even at altitude.

A reminder of just how far back in genetic history birds and mammals went separate ways. Another being that birds have no X or Y chromosomes -- their genetic machinery for sex is very different from ours.

some birds have X and Z

and 2 of the same shape in the males, while females have different

W and Z.

And no neocortex. Smart birds like ravens rely on a traditional system of ganglia to be smart, not on that hyped six-layered neocortex covering most of the brain.

Do we know whether this is also a feature of dinosaur lungs ? It might make an interesting sidebar in a Jurassic Park sequel.

I believe the ancestor of bird lungs first evolved in a branch of theropoda. I'm not sure what drove that adaptation but it proved useful fodder when much later the avia branch of theropoda evolved flight. This also mirrors feathers which seem to have evolved long before flight. It is likely small lightweight avia already possessed feathers, light bones, and efficient lungs which allowed them to do a tiny bit of gliding in their jumps and that is what led to flight. Once flight exists there's really strong pressure to optimize to the limit given the metabolic cost of flying.

Mammals descend from synapsids which branched off before sauropsids branched off into theropoda, reptiles, etc.

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