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RE: Archosaur Origins...was:MESENOSAURUS ERRATA.



> 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