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Re: Fossil suggests platypus lived in dinosaur times



On Jan 29, 2008 5:22 PM, Tim Williams <twilliams_alpha@hotmail.com> wrote:
>
> Yes, I have reservations about the cladogram too.  (What is _Hadrocodium_ 
> doing in the Monotremata, for example?)

Nitpick: it's in stem-_Monotremata_, not _Monotremata_ (a crown group).

>  But I have reservations about every cladogram because, as a cladogram, it's 
> just one phylogenetic hypothesis that will stand or fall depending upon 
> future data.  (This isn't a criticism of cladistics; it's just recognizing 
> the limits of a cladogram.)  I doubt if the topology presented by Rowe &c is 
> the last word.  Other fossil monotremes will turn up, and they'll spawn other 
> hypotheses about the evolution of monotremes, which may or may not accord 
> with that proposed by Rowe &c.

That's the sense I got. It seems that more data is needed.

Someone mentioned that one stem-monotreme lineage crossing the K/Pg is
more likely than two monotreme lineages (i.e., stem-platypuses and
stem-tachyglossids). But if both lineages were ecologically
undifferentiated, maybe not. (We can be pretty sure, it seems to me,
that they were geographically undifferentiated, at the very least.)

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T. Michael Keesey
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