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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.

=====
=====> T. Michael Keesey <keesey@bigfoot.com>
=====> The Dinosauricon <http://dinosauricon.com>
=====> BloodySteak <http://bloodysteak.com>
=====> Instant Messenger <Ric Blayze>
=====

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