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Re: Platypus (therapsid?)
On Mon, 12 Jun 1995, Phillip Bigelow wrote:
> Begin [Lillegraven] quotes:
> "All living therian mammals are viviparous, but marsupial developement
> shows a series of features such as thin eggshell and vestigial egg-tooth
> that strongly indicates a previously oviparous habit....."
Marsupials sometimes retain fertilised eggs, suppressing their development,
perhaps the eggshell is needed for physical or immunological protection at
such times. I'm not saying it's apomorphic, though.
> "All [living] marsupials are also born with a reptile-like articular-
The same applies to eutherian embryos at the equivalent stage - the
difference is that marsupials are born earlier.
> So it seems that, reproductively, at least, marsupials are only a "shade"
> different from monotremes. It is only a matter of degree, not of style.
> I don't have access to MacIntyre's paper, so I don't know what evidence he
> gives to support his position. His paper is a little dated by now, and he
> seems to be the only one with that point of view.
To me it seems like the greatest similarity is between the therian groups.