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Re: Cladistics and extinction



Jonathan Wagner wrote:

>         In the case you were discussing, your tendancy to think
> non-phylogenetically has you emphasizing the wrong point.  You want to know
> why the non-avain dinosaurs went extinct.  You seem to think it is
> unreasonable that these animals, which obviously had some flaw that led to
> their extinction, should not be their own seperate group.

      Regardless of if I'm thinking "flaw" or "bad luck", there there 
must have been reasons.  My point is that paraphyletic concepts are 
useful in discussions of evolution, even if you don't want to include 
them in the formal taxonomy.  If you are trying to figure out why one 
group went extinct and another closely related group survived, or why 
one group had a big adaptive radiation toward particular kinds of 
niches while a closely related group did not, morphological differences 
(indicators of lifestyle) are probably at least as important as common 
descent.  
     Homologies mat be useful in determining common descent, but 
morphology dictates lifestyle (or rather vice-versa), and THESE are the 
clues to an organisms sucess or failure (at a certain time under certain 
circumstances).
     For another example, how could you discuss the evolution of 
endothermy in birds and mammals without the concept of "reptile?"  What 
if the LOSS of a certain trait ultimately results in a groups demise?  
Lets pretend for a moment that birds and mammals evolved endothermy to 
exploit a small niche which then dried up, causing them to go extinct.  
What if the loss of more primitve reptilian characteristics ultimately 
caused the EXTINCTION of birds and mammals?  Wouldn't the concept of 
"reptile" be useful then?  Not amniote- REPTILE.

> If one looks for "fatal flaws" in each extinct group, one will never
> get as far as fast as if one looks at derived characters in the
> clades that survived.

     You are assuming that it is always the DERIVED characters that will 
always be the key to survival.  If the underived condition ultimately 
turns out to be more advantageous, then the surviving group would be 
paraphyletic.

LN Jeff
O-