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Re: sauropod lung collapse

Evidently Yahoo beta has a few bugs... sorry about the blank. Comments below, 
between the pluses.

----- Original Message ----
From: Michael Habib <mhabib5@jhmi.edu>
To: dinosaur@usc.edu
Sent: Wednesday, January 11, 2006 12:25:07 AM
Subject: Re: sauropod lung collapse

> The main point is that the inability to use the neck as a snorkle in 
> no way excludes semi-aquatic lifestyle from the list of plausible 
> sauropod lifestyle choices. It is known that relative to metabolism, 
> dive-time scales positively to mass. If a 1 ton croc can hold it's 
> breath for 30-45 minutes, then a large sauropod might plausibly have 
> gone much longer than an hour on stored O2...

Well, all of the other problems with the idea of aquatic sauropods 
aside for the moment, that still means that the animal must exit the 
water entirely every time it wants to breathe, which is vastly 
different from a whale, seal, or other aquatic air-breather allowing 
its lungs to collapse at depth, then allowing re-expansion upon 
surfacing and taking a breath at the surface.  
I'm assuming that w/ the waterline at mid-flank breathing might be constrained 
but not impossible.
Not only is this not 
feasible in and of itself, but the animals would have to consistently 
find very deep pools with conveniently sloped sides.  Unless 
water-filled craters were common, it seems unlikely that a sauropod 
coming from say, a flood plain away from the coast, would find bodies 
of water 80 feet deep all over the place.
??? Why is deep water necessary?
> Also, their ability to store and conserve O2 may have allowed them to 
> deflate their lungs prior to submerging, reducing bouyancy to the 
> point that walking on the bottom was practical.

Collapsing the lungs first (I'm not sure how this would be 
accomplished) would leave a very small amount of available oxygen.  
Remember, when the lungs of an aquatic animal collapse, the gas hasn't 
just disappeared, it's mostly just taking up far less volume.  Yes, 
blood O2 storage is important and some of the gas under pressure does 
leave the lungs and get stored in the blood instead in derived aquatic 
species.  Just the same, the collapse of the lungs is a result of 
reduced gas volume (from increased exterior pressure), not muscular 
action, and the gas stored in the lungs is still important.
I must have used the wrong term. By "deflate" I meant "exhale most of your air".
When I exhale I have negative bouyancy, and can walk on the bottom of the pool.
> During deep diving, the lungs of seals and sea lions are totally
> collapsed.  Which is normal.  They evolved that way.

Yes, but the lungs are not collapsed when the animal is trying to 
breath.  Breathing is accomplished at the surface, without a long 
'snorkle' so the gas takes up standard volume.

> One last question:  Do penguin lungs collapse during dives?  What role
> does their air sacs play during diving?

The lungs will decrease in volume some, but they are very dense and 
spongy, unlike the lungs of a mammal or lepidosaurian.  The air sacs 
will collapse under pressure, which helps to reduce the density of the 
diving penguin, and thus helps it stay down.  The same goes for air 
trapped in the feathers.  I do not know how inflated the air sacs are 
before descent, but there's a paper by Sato et al. from the last year 
or two that looked at air intake modulation prior to dives in penguins.

>>     A decent test may be to study the morphology of the ribs for
>> continuous
>> submersers like aquatic species like sirenians and dolphins versus
>> those of
>> temporary submersers like hippos and crocs, and rare submersers like
>> horses,
>> etc., and determine the variabilities. The presence of dense bone to
>> counteract
>> bouyancy, rounded ribs to counter external pressure, a round
>> thoracic cavity
>> rather than "slab-sided" for equalization of pressure around the rib
>> case, etc.

Actually, the bones of sirenians and cetaceans are essentially polar 
opposites with regards to overall element density.  Sirenians have 
thick, high-density bones.  Cetaceans have bones that are extremely 
'spongy' and porous.  The overall density of the elements is very low 
in cetaceans.  I'm not sure that a round thoracic cavity would actually 
equalize pressure, though it might equalize stress due to high pressure 
around the perimeter of the thorax (at least until you get to an animal 
of sufficient size such that pressure differences are high at the top 
and bottom of the body).

Of course, the problems with respiration are not the only problems with 
aquatic sauropods.  In fact, there was never really any evidence for 
them being aquatic in the first place.  The original spark that started 
that idea was that they were too large to be terrestrial.  This wasn't 
stupid, but it was misinformed.  With better knowledge of biomechanics 
(and a better knowledge of animals past and present), it becomes quite 
apparent that a sauropod would be able to support its weight on land.  
At that point, there is no further reason to model them as aquatic.  
The habitats they inhabited were often dry (or at least not full of 100 
foot water pits), the limbs show terrestrial adaptations, the food 
availability underwater for herbivory would have been pretty minimal 
(compared to the amount required), 
Again, why 100' pits? Most aquatic plants/fish/crustaceans are in the first 3m 
of water column. (Yes I said fish... put a sauropod in my farm pond, and in 15 
minutes every fish in it would be bellyup from O2 dep.)
and trackways indicated prolonged 
overland travel.  Of course, I'm guessing these last bits are 
recognized by nearly everyone on the list, I suppose it's just the 
snorkle bit under debate.
Yeah, pretty much. I'm persuaded, however, that obtaining enough food must have 
been a huge problem for them, (and us when its time to explain how they did 
it). Perhaps they weren't too proud too get their feet wet?

--Mike Habib