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Re: Phyl tax misunderstandings



At 01:02 PM 14/11/1997 -0500, you wrote:
>Tom Holtz said (11/14/97; 1:43p):
>
>(out of context)
>
>>Or, there will always be a clade (Maniraptora) comprised of birds 
>>and all taxa sharing a more recent ancestor with birds than with
>>Ornithomimidae.
>
>As I have ranted before, you cannot DEFINE this evolutionary path into 
>existence.  I believe that is an hypothesis that has not yet been 
>"proved."  Just ask George Olshevsky or Alan Feduccia whether that clade 
>will always exist.

As I understand it from what Tom was saying, they would have to (assuming
they used this system) say that it does always exist, but would disagree
about what it contains.  IOW the clade is not a hypothesis at all but a
label - it includes all the taxa sharing the most recent common, etc etc
WHATEVER THEY HAPPEN TO BE.  The hypothesis is what organisms actually
belong in that clade.  By Feduccia's hypothesis I assume that his
"Maniraptoria" would contain no dinosaurs at all, since all of the
dinosaurs would by his view share a more recent common ancestor with birds
than with Ornithomimidae, but he could still use that term and it would
still be a real clade.  The only "hypothesis" attached to this is the
assumption that there are, indeed, organisms that share a more recent
common ancestor with birds than with Ornithomimidae, whatever they happen
to be - and if there aren't, then Maniraptoria =birds.

Now, how useful this all is is another matter!  If I have interpreted Tom's
explanation correctly Maniraptoria could, as viewed by different workers,
consist, birds aside, of completely different organisms - which does not
seem to reduce confusion very much, does it?
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@inforamp.net