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Re: Tyrannosaurus was not a fat boy or girl



In a message dated 10/24/11 12:16:28 PM, augustoharo@gmail.com writes:

<< How is the degree at which pneumaticism reduces the density of the

body assessed in mass estimates? Although you can infer the proportion

of the skeleton which is pneumatic, it looks impossible to tell what

part of the non-skeletal volume is filled with air sacs. However, I

think I once read (probably from Gregory Paul) the claim that body

density is not much lower in birds than in other tetrapods because the

pneumatism is countered by a more solid lung in birds, contrasting

with the larger air cavity of the lung of other vertebrates. >>

Body density tends to be lower (I have seen values as low as 0.7 as I 
recall but that may reflect the air sacs complelely inflated rather than 
the 
average value for the bird) in most birds than is normal for tetrapods 
(around 
0.95 is probably a typical value). I have not however seen measurements for 
ratites at least some of which seem to have smaller trunk air-sacs than 
typical for birds. And theropods did not have pneumatic limb elements. I 
have 
been using 0.85 for most theropods but who knows. All the more since since 
their are disagreements with the extent of the air-sacs in theropods and in 
different kinds of theropods. Maybe they were limited to the ribcage as it 
seems 
they are in some ratites. Maybe they extended all the way on the flanks of 
the abdomen to the pelvis as is more typical of birds. 

GSPaul</HTML>