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Re: DINOSAUR digest 66



Terry D. Jones wrote:

> Horses are obligate nose breathers (whether at rest or during exercise).

I'm not sure what this means. When I gallop a horse he breathes thru his 
_mouth_.

> other endotherms, breathing through the mouth is generally a response to
> extended periods of heavy of exercise.  This is a means of facilitating
> increased lung ventilation.  A secondary result of mouth breathing is that
> heat generated by high activity levels is dumped (at the expense of water
> reclamation via RT's).  At rest and at moderate activity levels, endotherms
> are nose breathers.

Ok so far

> All extant ectotherms (and, as we have shown, at least four groups of
> dinosaurs) lack RT's in the nasal passage.  No known animal has a similar
> strucuture in the mouth!!!

Ok, but who says dinos hmust have RTs to be endothermic?

> Therefore, if, as suggested by the question, dinosaurs were obligate mouth
> breathers and thereby maintained high ventilation rates, they would have
> increased both water and heat loss.

I'm not sure my question obliges them to breather thru their mouths, only at 
times of extreme effort. Do ostriches have Rts btw? They (and other birds) 
certainly breather thru their mouths after effort and to lose heat. Who cares 
about water loss if you are escaping from a predator? You can live to make up 
the deficit later. 

Nathan Myhrvold wrote:

> This is interesting, however it does beg the question of why 100% oxygen
> is used for humans in medical situations (and in some veternary cases) .
> I have naively assumed that this is done because the (approximately)
> five fold increase in oxygen partial pressure allows better oxygenation
> in individuals with impared ventilation.  

and interestingly, it is used in diving decompression accidents and
decompression stops, where the increased 02 gradient helps eliminate
N2 which has been absorbed by the tissues (it also helps to irrigate
those tissues which may be suffering from and 02 lack due to gas
embolisms, ruptured alveoli etc).

martin