Re: T. rex was a 'slow-turning plodder'...

[Michael Habib <mhabib5@jhmi.edu>]

> The idea that it was lighter comes from accounting for honeycomb 
> structures in the bones and air sacs, present in T. rex but not in 
> elephants. Now, I think 3 tons is pushing it, but I can see a 5-ton 
> rex. If this case for a lighter rex can be vindicated, I'd like to see 
> how that would affect speed and turning velocity estimates.

The theropod-style skeletal elements, with their thinner walls and 
larger medullary cavities (compared to mammals) probably doesn't do 
much to reduce overall mass (the reason being that the overall volume 
of bones tends to be greater).  In modern avians, for example, the 
skeleton accounts for about the same relative proportion of body mass 
as it does in mammals.  Thus, despite having highly pneumatized 
skeletons and thin-walled bones, the lightened bony architecture does 
not so much reduce the whole mass of the animal, but rather allows for 
the skeleton to be expanded without total mass increasing appreciably.

Cheers,

--Mike H.