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RE: Unified Cladistics



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Jeffrey Willson
>
> Betty Cunningham <bettyc@flyinggoat.com> posted to the DINOSAUR list:
>
> >>>
> Know what?  Someday everybody will agree on some unifying cladistic
> methodology, and then you can have a databank of these animals and run
> cladistic tests whenever you damn well feel like, AND get the same results
> no matter who does the stupid tree
> >>>
>
>
> But that would take all the fun out of it !!!
>
>
> Seriously though, how in the world are we ever going to arive at
> a *general
> agreement* on the unifying cladistic methodology?

On the contrary: there IS general agreement on the unifying cladisitic
methodology.

The differences are in the particulars, not the methold: which particular
characters to use, how to code them, etc.

As in Nick Pharris' excellent post, these depend in large part on the
particular experiment (and PLEASE!!!! remember, a cladistic analysis is a
type of experiment; it isn't a be-all and end-all of the life sciences) you
are running: which taxa are being compared.

_Archaeopteryx_ might be described in one fashion in a test comparing the
relationships of _Euparkeria_, _Ornithosuchus_, _Lagerpeton_,
_Lesothosaurus_, _Coelophysis_, _Archaeopteryx_, _Icthyornis_, and _Gallus_;
you would use a very different bunch of characters (in this case, more
finely detailed) to test the relationships of _Velociraptor_,
_Sinornithosaurus_, _Deinonychus_, _Archaeopteryx_, _Rahonavis_,
_Unenlagia_, _Confuciusornis_, and _Sinornis_.

In the first test mentioned, _Archaeopteryx_ stands in for Tetanurae, and
Avetheropoda, and Coelurosauria, and Maniraptoriformes, and Maniraptora,
Eumaniraptora, Avialae, and Aves: the characters used to describe it will
cover the anatomy in relatively general terms.

In the second test, the study would ignore all those tetanurine and
avetheropod and coelurosaur and maniraptoriform and maniraptoran and
eumaniraptoran features: these are shared by all the taxa being examined.
Instead, it would be more concerned with the nitty-gritty distribution of
the fine details of eumaniraptoran anatomy.

Remember that a cladogram does *NOT* describe an organism; it describes an
hypothesis of the phylogenetic position of the organism.  _Archaeopteryx_
remains the same animal in both tests; but the two tests are examining very
different questions.

Hope this helps.

                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