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Martin Human writes (quoting Darren Naish):
>> Just about everyone is familiar with the arguments presented here:
>> that dinosaur nasal passages are simply not big enough in
>> cross-sectional area to allow the high lung-ventilation rates employed
>> by tachymetabolic tetrapods, nor do RT 'fit' into these
>So why can't they breathe thru their mouths as do lots of fast moving
>mammals (horses, cattle, humans)?
Just about everyone is familiar with the arguments???
Nevertheless, in response to the question of mouth breathing...
Horses are obligate nose breathers (whether at rest or during exercise). In
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.
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!!!
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.
Terry D. Jones
Oregon State University
Dept. of Zoology
3029 Cordley Hall
Corvallis, OR 97331-2914