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Re: Final post!!!




>       Darwin not only said that natural groups should have a common
> ancestor, but in his own words (in eloquent 19th Century prose) said that
if
> modification in sister lineages occurred at greatly different rates that
the
> more modified lineage should be given a higher taxonomic rank.

    In that case, sauropods and thyreophorans need thier own taxonomic rank
too.  They are as derived relative to the first dinosaurs as birds are.
Although I support using paraphyletic groups in the cases where the grade
represents a distinctive morphology and lifestyle from a descendant clade
(e.g. "fish"), I don't see what the value of this would be in the case of
splitting birds off from a group which keeps animals every bit as derived.
If you are going to designate a grade as well as a clade, there ought to be
something that unifies it from both its outgroups and descendants other than
"they didn't fly and they were gone by the end of the Cretaceous".

>   Even Michael Benton in his recent Vertebrate Paleontology book
classifies
> them in separate taxa, although he did put a cross-referencing marker
> (functionally similar to those I use) to show that birds are descendants
of
> dinosaurs.

    Benton discussed birds in a separate chapter as a matter of convenience.
He explicitly states "birds are derived theropod dinosaurs".

LNJ
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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
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