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RE: Embryological evidence that bird fingers are I, II, III
> 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: firstname.lastname@example.org Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Science & Global Change Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA