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

Mike Habib's statement that "the arms were not under strong selection
for increased resistance to load" erroneously assumes that evolution
always creates the "perfect creature" - a very common misperception
among people. The fact that there is a high incidence of pathologies
shows that evolution had not yet kept pace to the factors causing those
injuries, i.e., that T rex has not yet achieved that mythical peak of
"evolutionary perfection." 

Gould was fond of evolutionary "imperfections" 

Kenneth Carpenter, Ph.D.
Curator of Lower Vertebrate Paleontology & Chief Preparator
Department of Earth Sciences
Denver Museum of Nature & Science
2001 Colorado Blvd.
Denver, CO 80205 USA

Office phone: 303-370-6392
Museum fax: 303-331-6492
For PDFs of some of my publications, as well as information of the Cedar
Mountain Project:
(if you have problems with the link, cut and paste it into the browser
address bar)
The scientific method is a myth:

-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf
Of Michael Habib
Sent: Tuesday, January 01, 2008 10:56 AM
To: dinosaur@usc.edu
Subject: Re: Do not misunderestimate the king was Re: Evolution of

> 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,
> 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.


--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