birds don't breathe the way we do...........

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Yesterday I looked in on my Dino 101 class (which started Wednesday).  It's taught by people at the University of Alberta.  It's the first Coursera class I've taken for which you can earn college credit (if you are willing to pay [$240?  something like that] to take proctored exams).  I didn't look into the details, because I don't care about earning credit, but it's interesting that it's a possibility.

Anyway.  Back to something far more mind-bending and interesting.....

In one of the lectures, they were talking about size, and said that "largest" isn't straightforward.  "Tallest," "heaviest," and "longest" often aren't all in one package.

They said that dino sizes are usually estimates.  Skeletons are incomplete more often than they are complete....  Weight is the hardest to estimate.  Fossil bones weigh more than non-fossilized bones....

Then things started to get strange (to me) -- they just tossed out the fact that dinos have air sacs, like birds, which means that a rhino-size dino would not weigh as much as a rhino.

Now wait just a minute.  I knew that fish (some fish?) have air sacs.  But birds?  Birds have air sacs?

Google is my friend.  This article has nice helpful illustrations.  Note that Wikipedia agrees about the whole air sac plan, as does the Virginia Tech vet school, so I am ready to believe it is true (having seen it described in different words in three different places).

Birds breathe completely (but COMPLETELY) differently than we do!

I had no idea!

They have lungs, but their lungs are inflexible.  They have a whole bunch of air sacs which do expand and contract, and the air goes here and there in all those sacs (I confess, I have not carefully read either article), so that birds get oxygen whether inhaling or exhaling.

They have no diaphragm.  It's their skeletal muscles they breathe with.

They have no alveoli (they have other structures that replace the function of alveoli).

Did you know this???

It's clear that I learned about mammalian respiration, once upon a time, and then extrapolated in error to others who breathe the same air we breathe.

I am boggled that I have lived my whole life without a clue that there are multiple systems for breathing air, happening every minute of every day, right here on Earth, amongst different warm-blooded creatures!  What a huge thing, going on all around me, all day every day, and I never had clue one.

[shaking head]

I have been learning a lot of things lately, but that is the one that is the biggest and most striking.

Now I'm wondering how reptiles breathe (and amphibians), and if dinos breathed like birds, or what!  I don't think I'm going to stop right now to find out (I've got several more Dino lectures to listen to for this week, and poetry class starts today!), but what a huge thing to have never known!

Two little words -- "air sacs" -- in one lecture, and a part of my world view has completely rearranged itself. 

Wow.  Amazing.

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