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RE: Archosaur Origins (& the Clade Cemetery)



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Larry Febo
>
> The characteristics of
> preorbital
> fenestra and advanced mesotarsal ankle are just convergences. I always
> assumed these characters were strong definitions of the group "Archosaur".
> Do we now eliminate these characters as synapomorphies of this
> major group?
>
Just a few word of caution:

On-going, EXTREMELY comprehensive work is strongly suggesting that the taxa
in "Prolacertiformes sensu Peters (or most everyone else)" represent a
polyphyletic assemblage within Diapsida.  There does seem to be a core group
of true prolacertiforms (containing the famous batch: Prolacerta,
Protosaurus, the tanystropheids), but many of the other guys included in
Peter's website & recent papers are showing up at various other points in
the diapsid reptiles.

Also, just because the pterosaurian preorbital fenestra may be
non-homologous with the archosauriform antorbital fenestra doesn't mean that
these aren't valid synapomorphies for their respective groups.  For example,
loss of hindlimbs is a valid synapomorphy for caecillians, for derived
cetaceans, and for derived snakes even though this state (loss of hindlimbs)
evolved more than once in the history of tetrapods.

The pterosaurian ankle is apparently much less mesotarsal than typical
considered, as related by Dave Unwin:
http://www.cmnh.org/fun/dinosaur-archive/2000May/msg00518.html

> Also,...is Ornithodira dead without a fight? I assumed there would be some
> kind of rebuttal to Dave`s phylogeny. Aren`t there still some
> (Padian?) that
> still think lagosuchids and pterosaurs are closely related?....

That remains to be seen.  Don't know who else is specifically working on
pterosaur origins these days.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796