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Re: Archaeopteryx



----- Original Message ----- 
From: "T. Michael Keesey" <mightyodinn@yahoo.com>
To: "Mailing List - Dinosaur" <dinosaur@usc.edu>
Sent: Monday, June 16, 2003 1:32 PM
Subject: Re: Archaeopteryx


> --- Dinogeorge@aol.com wrote:
> >
> > Incidentally, considering that Neornithes includes all birds that are
> > supposed to have only wing digits 2, 3, 4 whereas Archaeopteryx
evidently has
> > only wing digits 1, 2, 3, this particular definition of Aves might
include
> > all theropods down to Ceratosauria, the latest theropods known to have
digits
> > 2, 3, and 4 (along with 1) in their manus.
>
> First of all, it would have to go further than _Ceratosauria_, since
> ceratosaurs have a reduced fourth digit.
>
> Secondly, the only reason the digits of _Archaeopteryx_ are thought to be
> I-II-III is by homology with basal saurischians (e.g. herrerasaurids,
> _Eoraptor_), which have reduced digits IV and V. This, incidentally, is
the
> only reason *any* tetanuran theropod is thought to have I-II-III, or that
*any*
> non-tetanuran avepodan theropod (ceratosaurs, coleophysoids, etc.) is
thought
> to have I-II-III-IV. So what goes for Archie goes equally easily for the
rest.
>
> Thirdly, I defy you to find a convenient point in this sequence to insert
a
> ceratosaurian ancestor: _Avialae_ -> _Pygostylia_ -> _Ornithothoraces_ ->
> _Ornithurae_ (sensu stricto) -> _Carinatae_ (sensu stricto) ->
_Neornithes_
>
> Finally, the frame shift hypothesis (that digits shifted identity at some
point
> in tetanuran, or possibly avepodan, history) easily explains this apparent
discrepancy.

I suppose I ought to know, but didn't Tony Thulborn publish something on
this?  Can anyone remember the reference?  Was it in the Eistadt (sp?!)
volume?

Incidentally, I think I got my terminology confused earlier when I wrote
"Saurischia > Aves"  . What I meant was "Saurischia includes Aves".

Cheers
Colin