Re: Platypuses may be older than we think...

[David Marjanovic <david.marjanovic@gmx.at>]

> Good point.  Nevertheless, monotremes (both living and extinct) can be 
> broadly divided into two categories: 'diggers' and 'swimmers'.  Modern 
> echidnas are diggers, and so was _Kryoryctes_ (based on humeral 
> morphology).

Fine, but the platypus digs burrows, too, so it's not that far away.

> _Obdurodon_ (for which a beautiful skull is known) is certainly a bona 
> fide platypus.

Agreed, but it's only Miocene.

> This same paper also supports the referral of _Monotrematum_ to the 
> Ornithorhynchidae, saying "...the lower molar morphology of _Monotrematum 
> sudamericanum_ agrees with previous statements that it is a monotreme 
> closely allied with _Obdurodon_."

Then maybe the echidnas are ornithorhynchids and closely allied with 
*Obdurodon*, too. With the presently known fossils, we won't find out. We 
still don't know any tachyglossan teeth, and we still don't know anything 
but teeth from *Monotrematum*.