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

[Michael Habib <mhabib5@jhmi.edu>]

On Saturday, June 9, 2007, at 09:37  AM, Brandon Pilcher wrote:

> > 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).
>
> Are adjustments for size taken in account here (i.e. we're not 
> comparing the bones of a T. rex with those of a bipedal savanna ape)?

More or less.  My understanding is that the bone walls of large mammals 
and large theropods* both become proportionately thicker at larger 
sizes, as would would be expected from allometric constraints.  I doubt 
that anyone has made a reliable estimate of proportional skeletal mass 
between tyrannosaurs and similar sized mammals (ie. elephants and kin), 
but I strongly suspect they are quite close.

Cheers,

--Mike H.


* The exception being large soaring birds, specifically marine forms 
like pseudodontorns, which actually become proportionately thinner 
walled at large sizes.  The same trend is seen in pterosaurs (at a very 
rough scale, that is).    In both cases, buckling and compressive loads 
are prevented and/or alleviated by use of very large internal bracing 
networks.  In the case of pterosaurs, at least, I doubt that the 
overall skeletal mass is actually very low, even though the ratio of 
bone radius to cortical breadth is low.