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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.)

T. Michael Keesey
Director of Technology
Exopolis, Inc.
2894 Rowena Avenue Ste. B
Los Angeles, California 90039