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Re: K/T impact (was Re: [for some reason] Tim's theory)

On Tue, 15 May 2001, David Marjamovic wrote:

> If eutherians (include placentals) are thought to originate from Asia
> (this is not completely sure, AFAIK) and were superior competitors to
> metatherians (include marsupials), then we'd expect that there were no 
> marsupials in LK Asia.

But there _was_ an invasion of placentals moving, apparently, from North
to South and timed just at the K/T.  If the new animals invaded and
were successful enough to leave a pretty good fossil record, niche
space had to be surrendered by the marsupials.  This has nothing at all to
do with Asia.  On the contrary, the success of different body plans is
utterly dependent on the context of specific niches.  For argument's sake,
the placentals evolving in Asia may have been involved arms races with
marsupials, such that marsupials were more competitive there.

> In short, marsupial extinctions at the K-T in NA aren't consistent at all
> with placental replacement. Makes the choice rather easy.

Then how exactly did marsupials get snuffed when placentals
didn't?  Marsupial bolide homing device?