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RE: Archosaur Origins (& the Clade Cemetery)




Sereno in his 1991 paper on Basal Archosaurs states:
"Definition---Ornithodira includes Pterosauria, Scleromochlus, Dinosauromorpha (including birds), and all descendants of their common ancestor."


Therefore, I don't use the term ornithodirans any more. Archosauromorphs suits me just fine, and the thought of changing to a much more inclusive Ornithodira or cutting pterosaurs out of it----well, it would be a confusing mess. If Dave is right about pterosaurs being prolacertiforms, then Ornithodira should be abandoned.
The characters that were offer as synapomorphies of Ornithodira were apparently not synapomorphies at all. Ornithodira appears to be dead or dying, and hopefully PhyloCoders will not try to redefine it. Time to move on. I think there is a nice plot in the Clade Cemetery for "Ornithotarsi" as well.
-------Ken
*******************************************
From: "Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>
Reply-To: tholtz@geol.umd.edu
To: <david.marjanovic@gmx.at>, "The Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: RE: Archosaur Origins...was:MESENOSAURUS ERRATA.
Date: Thu, 23 Aug 2001 14:04:46 -0400


> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> > I get the impression that his claim is that Pterosaurs are not
> archosaurs,
> and
> > don`t belong to the group Ornithodira.
>
> Ornithodira is defined as (*Pterodactylus* + *Passer) -- unless this
> definition is changed (which is probable) when the PhyloCode is
> implemented,
> pterosaurs are always in Ornithodira.

Actually, Ornithodira has not to my knowledge ever had a formal formulaic
phylogenetic definition.  When Gauthier formed the term, the difference
between definition, diagnosis, and taxonomic composition wasn't dealt with
as clearly, so he did not give formulaic definitions for all his new taxa.
I don't recall if Sereno & Arcucci had such a definition, either.

While the above formula does exist on many websites, it has not (to my
knowledge) formally entered the literature.

One could make a better case for Ornithotarsi Gauthier 1986 being the
appropriate name for the node-based taxon joining Pterodactylus and Passer,
as this clade was specifically coined for a "dinosaur-pterosaur" group (to
the exclusion of other ornithodirans; at the time, Gauthier considered
Lagosuchus to be possibly outside a dinosaur-pterosaur clade).

One could also make the (to me very appealing case) for use of Haeckel's
taxon name Dracones, in which he included Dinosauria, Pterosauria, and Aves.
Haeckel (who coined the term phylogeny, among many other things) proposed
all sorts of classification schemes (mono-, para-, and polyphyletic in
modern terms), and each edition of his major work had various different
revisions of his taxonomies. Someday I'll have to hunt up again the edition
of Systematischen Phylogenie in which he uses Dracones.


              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



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