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Query on RT function
I posted a lengthy item a while ago regarding the Reuben paper on RT's (or
lack of) in dinos and was half expecting to get flamed for my trouble.
Instead it was virtually ignored! Nothing daunted, here we go again.
My question this time refers to figure 1 of Reuben's Science paper. For
those of you without copies, the figure shows a vertical cross-section of a
bird skull with air flow marked for both inspiration and expiration cycles.
Beneath each skull is a graph of water content in the air at various points.
Inhaled air comes in at 3 mg/L and by the time it has reached the end of the
nasal passage/RT section the content has risen to 54 mg/L. Exhaled air comes
from the lung at 54 mg/L (ie no increase in water content from the lungs)
and after passing through the nasal passage/RT section again is exhaled with
a water content of 17.5 mg/L. We are told in the paper that RT's serve as
counter-current heat exchangers (which seems reasonable) and thus reduce the
otherwise dramatically accelerated rates of respiratory evaporative heat and
water loss that would accompany high lung ventilation rates associated with
endothermy. The data shown in figure 1, however, suggest, at least
superficially, that most, if not all, the water that is lost in fact comes
from the nasal passage/RT in the first place, which seems at odds with the
suggested function? Can anyone shed any light on this apparent
contradiction? Just how good is the evidence that RT's do conserve water
loss? Does anyone have the corresponding figures for ectotherms, or for
endotherms without RT's? Is there experimental evidence that removal of RT's
increases respiratory water loss? Lots of questions - does anyone have the
answers? To my untrained eye the evidence in the Reuben paper looks more
like a temperature control mechanism rather than a water conservation one.
HyperWorks Reference Software (The Dinosaur Encyclopaedia)