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Re: Re: Archie the Dinosaur?



>>In phylogenetic taxonomy, once you are a member of the taxon, your
>>descendants will ALWAYS be a member of the taxon, no matter how derived they
>>become.  Trochilids (humingbirds) are birds, and maniraptorans, and
>>coelurosaurs, and avetheropods, and tetanurines, and theropods, and
>>saurischians, and dinosaurs.
>
>This presumes that the only admissible taxa are clades. It is certainly true
>that once you are a member of a clade, your descendants will always be
>members of that clade; but it is dogmatic to insist that all taxa be clades.
>Hummingbirds are (probably) dinosaurs only cladistically, not necessarily
>taxonomically.

One man's "dogma" is another's "operating system of taxonomy".  Fair enough,
but I specifically said above "In phylogenetic taxonomy".  Under other
systems of taxonomy, para- or polyphyletic taxa are acceptable.

>Also, your cladistic hierarchy is open to question, by me at any rate. People
>have been objecting from time to time about the lack of qualifiers in my
>discourse and about the positiveness with which I make some of my statements.
>Well, this objection applies equally to your statement that hummingbirds are
>birds, and maniraptorans, and so forth. We know that hummingbirds are birds,
>but the statement that birds are maniraptorans (for example) is not as secure

Actually, the taxon "Maniraptora" only exists within a cladistic context,
being one of the first cladistic taxa in dinosaur studies.  The definition
of Maniraptora is birds and all taxa closer to birds than to
Ornithimimidae.  If that taxon is later shown to contain Longisquama,
wombats, or fruit flies, it does not change the fact that, BY DEFINTION,
birds are maniraptorans.

>and depends on cladistic analysis whose correctness cannot be completely
>established no matter how many computers are used and how many professional
>paleontologists think it can. (Although even I happen to think it's probably
>correct.)

Obivously, no hypothesis or theory (be it the dinosaurian origin of birds, or
the disease theory of disease, or the hypothesis that Mickey Rowe is the
only sentient being in existence, and we are all products of his dream) can
hav its "correctness ... completely established".  However, hypotheses can
be supported or rejected based on additional data.  In fact, they can ONLY
be supported or rejected with additional data.

> By the time we work up to Saurischia in the hierarchy, my own
>analysis (as well as that of a couple other paleontologists) indicates it is
>a paraphyletic group diagnosed by a combination of plesiomorphies and
>homoplasies.
>
>It's time for the Happy Hunting Ground for Saurischia, as a clade, anyway.

This is certainly a good possibility, and in my dissertation I hedged my
bets and showed both alternative phylogenies (Saurischia v. Ornithischia and
Theropoda v. Phytodinosauria).  However, no one has yet been able to
demonstrate a monophyletic Phytodinosauria in a peer reviewed, published
analysis, including some (Paul Sereno, for instance) who once supported the
idea.

On the other hand, Gauthier listed several derived character states present
in basal sauropodomorphs and in theropods which are not found in
Ornithischia.  Thus, Saurischia is provisionally supported (as much as any
clade can be) until such time that a new analysis disputes it.

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