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Re: Re: Birds and dinosaurs



>One additional reason I have for rejecting the strict cladistic
>position is that when using the "Linnaean" approach changes in
>the best available phylogeny do not necessarily require a change
>in the classification. This leads to more stable taxonomy, and thus
>to a more usable taxonomy.

Is stability something that must be achieved, even at the cost of obscuring
our knowledge of relationships?  If so, why put whales in Mammalia, when
they are equally "stable" in Pisces?  Obviously, no serious systemicist has
done so for over one hundred years (and, in fact, Pisces was long ago
abandoned because of its paraphyletic status).

Recognizing that the former example is ridiculous, why should we settle for
the same process, albeit with more closely related taxa, as in:
>
>For instance, there was a suggestion made in one journal that
>the troodontids are the closest sister group to birds, while most
>other analyses conclude that the dromaeosaurids are the closest
>sister group to the birds. In a "Linnaean" taxonomy in which
>birds are a seperate class these two cldograms lead to the exact
>same classification.  This allows for a more stable delimitation
>of all three groups.

No, it doesn't.  All three are as stabley deliminated as they were before:
Troodontidae remains Troodontidae, Dromaeosauridae remains Dromaeosauridae,
and Aves [or Avialae, take your pick] remains Aves [Avialae]. This remains
true if you use a strictly Linnean system or the most rabidly pattern
cladistic system.  What you lose through the process described above is a
statement of relationship.

Ultimately, either troodontids or dromaeosaurids are closer to the birds, or
they are closer to each other than either is to birds.  When you actually
work in the nitty gritty of theropod relationships, nothing is gained by
obscuring the pattern of phylogeny with a nonconcordant taxonomy.

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