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Re: Back to the dino-bird thang



[ Can we please move along?  I *still* don't see any new ground being
  broken here.  If you guys (and I don't just mean Rob and Jeff) can't
  restrain yourselves I may just have to kill this thread.  -- MR ]

Jeff Poling writes;

>   Yes, another group of THEROPOD.  _Triceratops_ and _Velociraptor_ have
>approx. 155 My separating them, about the same amount of time between
>_Archaeopteryx_ and _Corvus_.  To use a recent phrase, no child would
>mistake a _Triceratops_ for a _Velociraptor_.  Does this mean the trike (or
>the 'raptor) is not a dinosaur?

As a firm believer in the Subphylum Archosauria (and placing Dinosauria just
 below Archosauria, I don't know the term), this is not a difficulty.  In my
 little world, the Class Aves is at the same level as the Class Saurischian
 or Ornithischian.  It is the major taxonomic divisions that help define the
 crutial and the coolest breakthroughs in the history of life.  Likewise,
 bird evolution is so cool that I place them at a different level than their
 theropod cousins.  This doesn't invalidate their phylogeny, but it does
 help to illustrate that their evolution makes them as different from
 _Velociraptor_, as _Velociraptor_ is from _Triceratops_.

>   It confuses the heck out of me where one makes the dileneation between
>where an animal is one thing then becomes something else.  Even after
>millions of years of evolution, humans are still primates, they're still
>mammals, they're still amniotes, they're still tetrapods, they're still
>vertebrates, they're still chordates.  Birds, too, are still amniotes, still
>tetrapods, still vertebrates and still chordates.  It doesn't make any sense
>to me to cut something out in the middle, especially when the modern form is
>not 100% completely different in every way, shape or form from the ancient
>one.

This is true if you want to see the big picture.  Yet by breaking up the
 lineages, we make them more manageable, and more effective for study.  We
 separate mammals from the amniotes because we consider the advent of live
 birth (as opposed to dead birth) to be cool enough to separate them out.
 We separate tetrapods out of the crossopterygians because we consider the
 advent of land limbs to be cool enough to separate them out.  Likewise, I
 consider the evolution of birds to be so cool, that they can be separated
 out from the "dinosaur branch."  Breaking off a limb here and there is no
 crime, and it doesn't invalidate the phylogeny, but it does make things
 easier to manuver.

The proliferation of transitional forms does make things interesting in
 terms of "who belongs with who," but when we get beyond the transitional
 forms (as we have with modern birds) we can be safe in dissecting out a new
 taxinomic delineation.

<Insert the Dennis Miller moniker here>

Rob Meyerson
Orphan Vertebrate Paleontologist

***
"If you go to Za'Ha'Dum, you will die."
        -K.