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Re: Back to the dino-bird thang



At 02:42 PM 12/4/96 -0500, Robert Meyerson wrote:

>[ 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 ]

Let's hope so, but I couldn't resist this...

>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.

Subphylum? SUBPHYLUM?!?!   

Greater love hath no man for dinosaurs than me (equal, perhaps, but not
greater), but elevating Archosauria to a rank equal to Vertebrata does not
seem a solution to me.

(For those who aren't aware, Vertebrata is the major subphylum of the
traditional Phylum Chordata, which also includes the subphyla
Cephalochordata (lancets) and Urochordata (tunicates)).

> It is the major taxonomic divisions that help define the
> crutial and the coolest breakthroughs in the history of life.

Traditionally, yes.  Which is why the relatively minor differences between
lampreys and sharks and trout and lungfish and frogs and Stegosaurus and
aye-ayes have always been grouped closely together in the subphylum
Vertebrata: they possess very similar body plans, much different from the
other subphyla within Chordata, much less other animals.

>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. 

No, mammals are traditionally (and cladistically, for that matter) NOT left
out of Amniota.  In fact, they are one of the mainstays of the group.
Amniota has always been considered to include Mammalia, because (after all)
some mammals DO lay hard shelled eggs, and all presumably had ancestors
which did.

> 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.

And you would remove snakes from Tetrapoda because they lack limbs, and have
all sorts of cool digging adaptations, right?

And turtles, they REALLY have to be removed from Vertebrata, because their
limb girdles are inside their ribcages!

(Of course, there *is* a solution that gets around this: recognize distinct
subgroups of larger groups, in a hiearchical manner).

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

"Aiyeeeeeeeee....."
        -K.II

:-)

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877