RE: Embryological evidence that bird fingers are I, II, III

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of David Marjanovic
> Sent: Thursday, August 11, 2011 6:35 AM
> To: DML
> Subject: Re: Embryological evidence that bird fingers are I, II, III
> 
> >  It appeared that the enemies of the Frame Shift had lost their  
> > battle.
> 
> That's debatable, but in any case the paper, which I'm 
> reading right now, _destroys_ the the frameshift hypothesis.
> 
> -- Frameshift: digits I and V disappear, digits II to IV 
> assume the anatomies of digits I to III.

That isn't quite what the Frameshift proposes. You are still applying Owenian 
models of homology to the situation, but the
Frameshift model interprets the assignment of homology of condensation and of 
chondrification and ossification to be separate
phenomena, under separate genetic control.

While in most organisms the two sets of homologies match up, the Frameshift 
model proposes that chondrification/ossification phase
of identity assignment has moved over. Thus the ossified homologs for the avian 
digits ARE digits I-III of non-birds, and the genes
and gene products that specify them are the same. However, the "starter 
material" used are the condensations that in other organisms
become digits II-IV.

So the frameshift specifies that it isn't simply that "digits II to IV assumes 
the anatomies of digits I to III"; it is
"condensation positions II to IV develop into anatomical digits I to III". They 
ARE digits I-III from all gene-product standpoints.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA