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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-
                                                                  quadrate
> jaw-joint."

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.
(Subclasses?)
                                                                  Bill Adlam