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Re: [GSP1954@aol.com: MORE DINOSAUR ENERGETICS]



Van Smith wrote:

> Terry D. Jones wrote:
> 
> > ... For the same reason ectotherms have narrower nasal
> > passages since they have lower metabolism and
> > correspondingly low lung ventilation rates....

> > This is not a result of our work, but it is a law of physics
> > (Poiseuille's law:  flow rate is proportional to radius^4  --
> > in other words,  decreasing the radius of a tube by 1/2
> > increases the resistance to flow 16x).
> 
> No one is debating physics (see below).
> 
> > Regardless of how many specimens you observe
> > (our data set may not have been large, but they were
> > significant... ...this law still governs the size of the
> > nasal passage--you can't have an endotherm with
> > a narrow nasal passage (relative to body mass).
> 
> This seems like a very hasty conclusion to jump from
> Poiseuille's Law to nostril sizes of endotherms vs.
> ectotherms........
> 
> > It may appear that some endotherms have relativeley
> > narrow air passages (or that some ectotherms have large air
> > passages), but when compared with body mass, the
> > relationship holds true--there is an approximately 4-fold
> > gap between the nasal x.s. area of modern endo- and
> > ectotherms when compared to body mass. 

All I know about this is what I've seen on this grapevine.  Ihe
application of Poiseuille's law in this case confuses me.

Does a human really have 16 times the aerobic capacity of a
similar-sized reptile?  A human jogger might maintain a speed of 4
meters per second.  Is a big lizard's sustained speed limited to 25 cm
per second, even on a warm day?  (I don't know.)

Flow is proportional to radius^4 in highly viscous situations, like
blood seeping through capillaries.  Rough calculations suggest that the
Reynolds number for air in a nostril is about 100,000.  In such cases,
inertia matters much more than viscosity.  Generally, flow varies as
radius^2.

If a dinosaur had 25% of the nostril area of a mammal, one might expect
the dinosaur to have 25% of the mammal's aerobic capacity.  However, it
sounds as if RTs cause turbulence, and turbulence is a big restriction
at high Reynolds numbers.  If the dinosaur's nostrils were
aerodynamically cleaner than a mammal's, the dinosaur may have been able
to breathe _faster_ through smaller nostrils than a mammal through
larger ones.

In respiration, losing moisture is losing heat.  As a massive herbivore,
a sauropod may have had heat to spare on cool nights and needed to dump
all the heat it could on hot days.  That may account for a lack of RTs. 
Without RTs, it seems that small nostrils could have a big capacity.

As I said, this confuses me.  Have I got it wrong?

- Stephen Throop