Re: Do not misunderestimate the king was Re: Evolution of tyrannosauroid

[Michael Habib <mhabib5@jhmi.edu>]

> Thanks, David. There is much new data in Lipkin and Carpenter's paper 
> in  the
> T rex book due out soon. The evidence includes various pathologies 
> (stress
> fractures, fractures, muscle avulsions of the humerus) that it it 
> clear that
> the  forelimbs are placed under a great deal of stress. Remarkably, the
> incidence (as  %) of these pathologies of JUST the forelimb bones 
> (including scapula,
> coracoid,  and furcula) is highest of any theropod...

> ...Thus, the new evidences from the entire forelimb system of
> T rex show  the forelimb was used actively.

Very interesting stuff!  One thought to toss out, though: given the 
extremely high incidence of pathologies, is it conceivable that the 
arms were 1) used actively but 2) not actually terribly important.  
That is, Lipkin and Carpenter obviously show that the forelimbs were 
subjected to substantial loads and thus were not kept out of harms way. 
 At the same time, the safety factor was apparently quite low, as the 
forelimbs were regularly being pushed beyond their failure points.  
This suggests to me, at least, that the arms were not under strong 
selection for increased resistance to load.  Safety factors do vary, of 
course, but they appear to be pretty consistent within clades, based on 
the work published so far.  The fact that tyrannosaurs seemed to have a 
strangely low safety factor makes me wonder a bit.

Cheers,

--Mike H.


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu