Meta- vs. eutherian K/T extinctions

["Ken Kinman" <kinman@hotmail.com>]

John,
     Well, the bolide scenario seems pretty parsimonious to me, and so 
catastrophic (especially for land vertebrates) that it is indeed often 
easier to explain what survived rather than what didn't (the exact opposite 
of how one would approach bacterial extinction).
      One big factor in why eutherians as a group did better than the 
metatherians is probably that they had more clades that lived underground.  
Who is going to do better during the catastrophe (especially in North 
America):
    (1) a ground squirrel (which may have stored food or been able to 
sustain itself on roots and tubers);
 or (2) a dumb-struck koala-like metatherian sitting in or under a tree and 
breathing in smoke.  A little simplistic, but you get the idea.  And not 
surprisingly, the only monotreme survivors are excellent diggers and readily 
retreat underground for protection.  Generalist scavengers like crocs (who 
could retreat into the water) also survived.  A bolide catastrophe (and its 
aftermath) makes perfect sense to me.
                ------Ken Kinman
P.S.  I understand about marsupials being a subclade (specifically a crown 
clade) of metatherians.  But aren't eutherians and placentals the same 
group?  Even McKenna made Placentalia as synonym of Eutheria.  Isn't 
Eutheria (unlike Metatheria) a crown group?
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