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re:cladistics (not a rant:)



Nick Longrich <longrich@stardot.com> wrote:

>Well, I have in a momentary lapse of strength succumbed to the dark side
>of the Force and am not making a tentative entry into the dark netherworld
>that is cladistics.

        Yesssss, feel the synapomorphies flow...  Release your paraphyly,
only monophyletic assembleges of organisms can defeat me...

>       As I understand it, Maniraptora is the sister group of
>Arcotmetatarsalia [sic] in a stem-based cladistics (or maybe it's not stem
>based but it isn't character-based)

        Ok, _cladistics_ aren't "stem-based", this is mildly nonsensical.
Taxa in Phylogenetic Taxonomy may be defined as node-based, stem-based, or
apomorphy-based.  As such, Maniraptora and the Arctometatarsali are
stem-based taxa.

>although Holtz 1994 uses Maniraptora to include both- am I right in
>assuming both these were character-based and are now stem-based? So
>what do we call Arctometatarsalia + Maniraptora exclusive of all
>other theropods?

        All right... Holtz accidentally(?) redefined Maniraptora in 1994 to
be the Apomorphy based taxon consisting of {+Theropoda, +maniraptoran hand}
(the first theropod with the maniraptoran hand, and all of it's
descendants).  This was based on the determination that the maniraptoran
hand, origionally used by Gauthier to support a basal coelurosaurian
dichotomy between Ornithomimidae (sorry Nino) and the Maniraptora, was
actually plesiomorphic for both groups.
        Now, Gauthier had actually intended Maniraptora to be defined as
{+Aves, -Ornithomimidae} (all animals more closely related to birds than to
ornithomimids) or somesuch, and thus Holtz was in error.  Holtz addressed
this in Holtz 1996 by restoring Maniraptora to {+Aves, -Ornithomimus}, and
redefined Arctometatarsali, previously {Theropoda, +arctometatarsal pes} to
{+Ornithomimus (or was it Bullatosauria, Dr. Holtz?), -Aves}.  At the time,
this restricted Maniraptora (in his 1994 phylogeny) to (Dromaeosauridae,
Aves/Avialae), now (Holtz, SVP poster) it is more like (Compsoganthus,
(Oviraptorsauria, (Dromaeosauridae, Aves/Avialae))) (sorry if I screwed that
up).
        Unless I mistunderstood completely, Holtz (1996) resurrected
{+Theropoda, +maniraptoran hand} as the definition of a new taxon,
Maniraptorforms [sic?].  Curiously, this fell after the author pointedly
referenced criticism of apomorphy-based taxa. I suppose only time will tell
if this definition will be changed to {+Maniraptora, +Arctometatarsali}, or
if the particular nature of this clade inspired Dr. Holtz to throw cauthion
to the wind.

>       Also, it seems to me that these things represent one of or the
>most important radiations of dinosaurs in their history,

        I'm sure Dr. Orenstein would agree.

>       Also, how is "Aves" defined, anyways? Stem based, character based,
>node based?

        It depends, Gauthier has used a crown-group definition (node-based)
of {+modern birds} (the most recent common ancestor of all living birds), I
am not sure about others.

        Wagner


+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
+--------------------------------------------------------------------------+