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Even if they were semi aquatic, they would still have laid amniotic eggs, so
the embryos would have had to have been uricotelic, they could of course
have lost this ability on hatching. But all other amniote groups seem able
to use uricotelism when needed, even desert mammals can't do it, which seems
     It would be interesting to know how embryonic platypuses cope with
their waste nitrogen, are they uricotelic? and how long is the platypus
incubation period?
    Thanks for replying

----- Original Message -----
From: Dann Pigdon <
To: <
Sent: Saturday, March 03, 2001 9:52 PM
Subject: Re: Uricotelism

> > Patrick Mellor wrote:
> >
> > How could Postosuchus have sprayed mammal like urine, when all living
> > archosaurs (and most diapsids) are uricotelic? Also, I have a question
> > that I think is interesting: If living synapsids (mammals) are not
> > uricotelic but evolved from basal ammniotes along with diapsids, why
> > would they have ever lost something as advantageous in terms of water
> > retention as uricotelism?
> Perhaps the earliest small mammal-like animals were semi-aquatic? Maybe
> the Platypus is the mother of us all! :)
> --
> ____________________________________________________________
> Dann Pigdon                   Australian Dinosaurs:
> GIS Archaeologist          
> Melbourne, Australia        http://www.alphalink.com.au/~dannj/
> ____________________________________________________________