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Re: Unidirectional [...] Science



--- On Fri, 1/15/10, gsp1954@aol.com <gsp1954@aol.com> wrote:

> Being one who was around at the time, 

Yeah, me too...

> it used to be widely
> thought that the 
> aquatic sauropods could walk on the meters deep bottoms of
> rivers and lakes 
> while snorkeling with their necks vertical. 

I never understood what the exact advantage of that scenario would be. Waters 
that deep are generally weed-free, for starters... 

> Even whales and
> crocs cannot 
> inhale with their lungs well below the surface, and
> elasmosaurs probably had 
> to bring their lungs near the surface to inhale. 

These seem like solid assumptions, w/ the caveat that elasmosaurs might have 
had some variant of the avian-style system. I note in passing that penguins 
have air sacs, yet there is apparently little or no _skeletal_ evidence of 
that. 

> It has
> never been argued 
> that sauropods swimming with the tops of their backs on the
> surface could not 
> inhale as can all animals. 

Yes it has, on this list. 'Difficulty of inhalation' (DOI) under conditions 
even less stressful than the 'backs on the surface' scenario has been argued as 
rebuttal of my thesis regarding: 1) the advantage to sauropods of utilizing 
swampy terrain as refuge from theropods (as well as temperature extremes and 
also a source of high browse), and 2) the suitability of their body design for 
utilizing that type of terrain. 

I stress that the proposition that "sauropods used their necks as snorkels in 
deep water" is not relevant in any way to that thesis, is not mentioned as part 
of that thesis, does not appear in any cartooning that I have done around that 
thesis, and in fact, that proposition has NEVER been argued in the affirmative 
by me. While I am at it, I will stress that LACK of terrestrial locomotive 
competence has also never been a component of that thesis.

> There is no evidence that unidirectional air flow or air sacs can improve 
> underwater breathing, 

Upon comparison of the two systems (mammalian vs avian), I strongly disagree.  
This is based in part on personal observations, and in part on mechanical 
considerations. 

In addition to those observations previously mentioned: as any free-diver 
knows, skeletal movements are not constrained by the pressures encountered 
while diving (up to 19000 kg/m2, in personal experience). 

Were it anatomically possible for me to aerate my lungs to any degree by 
manipulating my skeleton, as opposed to being completely dependant on the 
diaphragm system, an increase in my current ability to overcome external 
pressure while "inhaling" would be a natural consequence. It is important to 
understand that in mammals, the lungs must be actively expanded by muscle power 
alone, and contraction occurs by relaxation (i.e., deflation is the relaxed 
state). 

In birds, inspiration and expiration are driven by movements of the skeleton, 
particularly the ribs and sternum, and the relaxed state is _between_ full 
deflation and full inflation.  In other words, the elasticity of the skeleton 
itself can play a role in inspiration under pressure. When the ribs are in a 
neutral position relative to ambient pressure, (further) expiration can be 
actively caused by 'contraction' of the sternum and ribs. When the driving 
muscles are relaxed, skeletal elasticity can return the ribs to neutral 
position, which in itself creates some inspiration, even in the extreme case 
where external pressure cannot be overcome by the muscles driving the skeleton. 

Further, it is not possible to aerate "dead-end" or "tidal" lungs by small 
steps. You either can fill your lungs adequately w/ one breath, or you can't. 
The same is apparently NOT true of the uni-directional system, the lungs of 
which do not deflate, and can be aerated by small, sequential additions of air. 

These additions can be accomplished in part by manipulation of the legs, and in 
the case of a quadruped, quite likely the back plays a role.

Long story short, the  unidirectional air sac system has significant mechanical 
advantages over the mammalian system when working against ambient pressure.

As previously stated, this makes the ancient falsification (ca. 1905?) of 
snorkeling appear itself to be falsified, and that is relevant in a minor way 
to science. That statement in no way makes the claim that "sauropods were 
aquatic", "amphibious", or "deep snorkelers". Nor is it "drivel".  

BTW -- "ventilation by walking" will also be an element in the debate centered 
around the energetics surrounding the "hoovering" or "mowing machine" foraging 
debate, and the implications of having a long, skinny neck in the 1st place. In 
hindsight, I now see that ridiculous neck in itself as prime evidence of 
avian-style respiration.

> there is no
> evidence that 
> sauropods were better adapted for the same than similar
> sized animals with dead 
> end lungs, 

I disagree, in that sauropods almost surely had both unidirectional air flow 
AND air sacs. See above.

> and there is no more reason to conclude
> sauropods were aquatic 

Who is concluding that? Or advancing that thesis?

> than there was before the publication of the croc
> respiration paper which 
> makes to claim that sauropods were amphibious. 

I have not read the paper, but doubt the authors make the claim that "sauropods 
were amphibious". Which begs the question; who is making that claim? And in 
what way are they basing that claim on that paper?

Long post, chop likely, will post repair for those that care...