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Re: Battat's hair; Prototheria



> Monotremata:  someone referred to the monotremes recently as possibly
> reptiles rather than mammals.  Monotreme mommas make milk--how can they
> not be mammals?  Do monotremes date back to the first Prototheria,
> or were there other orders of Prototheria that came and went between
> the first prototherian Elsie and the rise of the Monotremata?  And are
> Eutheria thought to have developed from Prototheria directly or from
> Metatheria (marsupials)?
> 
> George Pesely          peselyg@lynx.apsu.edu
> 
Some recent literature I've seen (but not read, yet) suggest that
Monotremata might actually be much closer to Theria (marsupials and
placentals) than has been previously recognized. I don't remember
off-hand where I've seen this, and I can't comment or criticize since
I haven't read the thing. 
As far as Theria is concerned, it seems pretty clear that eutherians
and metatherians had a common ancestor sometime in the Early-Middle
Cretaceous. It also appears that there is a true dichotomy in the
case of E and M; that is, one group did not evolve from the other,
and vice-versa. The anatomy and functions of the reproductive system,
in particular, seem to suggest that both groups are derived relative
to their common ancestor. It does not seem possible to derive the
metatherian reproductive system from that of the Eutheria, and
vice-versa. A good piece of literature on the subject is Mammal
Phylogeny (1993) edited by (if I remember correctly) Szalay, McKenna
and Novacek. Especially Volume 1.

Michel Chartier ;