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RE: The validity of cladograms (was Re: giant birds)



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Tracy Ford
>
> If yes, then why is it in paleontology, 90 % of the time,
> different authors
> come up with different cladograms? Why isn't there more of a consensus? T
> thought Cladograms were suppose to 'clean' things up, but there are now
> hundred's of node names? I personally don't care if diplodocus
> was first on
> a clade than Apatosaurus, they lived at the same time. Its like
> everyone is
> looking up a family list, and it's always different.

But, Tracy, that was the point of my poster at SVP this year:
How REALLY different are the different cladograms we are coming up with?

In fact, there is substantial congruence between the alternatives proposed
by various authors in (my poster example) coelurosaurs or in (a new example)
sauropods.  Most of the major groupings are consitently found by different
workers.  The differences tend to concern a smaller fraction of "problem
children" taxa (the various euhelopodids/mamenchisaurids among sauropods,
troodontids among theropods, etc.) which make the trees look different from
each other.

Even some problem children, like Tyrannosauridae, aren't THAT much of a
problem: all three alternative positions found in recent trees (just outside
Maniraptoriformes, as basal arctometatarsalians, or basal maniraptorans) are
only one or two nodes away from each other.  Noboby is finding them as (for
two examples) outside an _Allosaurus_-coelurosaur clade, or closer to modern
birds than are oviraptorosaurs.

More about this later,

                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): 301-314-7843