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Re: Mammal Reproduction
Rob Meyerson wrote:
>Multis did survive. We find them up into the early Tertiary.
Actually, I knew that they did survive, but what I meant with my
'probably' was in reference to their birth strategy, which we once
again cannot be certain of. For this group, however, I believe that
egg-laying most certainly is more likely.
As for the rest of your post, I am largely in agreement. It _would_ be
more elegant to assume that the common ancestor of marsupials and
placentals _was_ live-bearing. However, the monotremes throw a spanner
in the works. The authors of _Steropodon galmanni_ (the Cretaceous
monotreme) were of the opinion that at its molars were
tribosphenic. If this is correct, that would mean that the monotremes
share that common ancestor, making that common ancestor almost
certainly egg-laying. It is possible that the marsupials and
placentals shared a slightly more recent common ancestor that was
live-bearing, however (though there would not have been much time
available for this development).
It must be pointed out, however, that the views of _Steropodon_'s
authors are far from established, so the monotremes may not have been
tribosphenic anyway. So, are there any mammal experts out there who
can clarrify the current consensus of opinion here?