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Re: a challenge to the cladists



At 02:15 PM 12/3/96 -0500, Bonnie Blackwell wrote:

>I still for all the discussion of cladistics over the last year - and
>believe me that has been alot - fail to understand why cladists choose
>to ignore an important variable in their analysis.  And given that
>most paleontologists doing cladistics are trained as geologists, this
>is a failing i really find hard to understand.  WHY DO YOU CHOOSE TO
>IGNORE TIME? 

For the same reason that anyone else studying the evolutionary
relationships of living things ignores time: because lineages that preserve
ancestral characters do not conveniently die off simply because descendants
with derived characters happen to arise. If you had to build time in as a
variable, you would have an impossible task working out the relationships
of animals that are alive today. There are certainly living examples today
of animals that have a larger suite of ancestral characters than other
living members of the same lineage. Nonetheless, they both exist at the
same time.  
 
For example, I believe it is generally accepted that ammonites are a
derived lineage of nautiloids. Nonetheless, the ammonites became extinct at
the end of the Cretaceous but the nautiloids live on to the present. If we
did not have fossils of the earlier forms of knowledge, but had to base our
taxonomy on the living nautilus and the extinct ammonites, would we be
unable to conclude that ammonites were derived from nautiloids because the
chambered nautilus occurs later in time? 

If I am wrong about the relationships of ammonites and nautiloids, this
should not affect the example. You can substitute a group of your choice. 

--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net