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

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

> > Then maybe the echidnas are ornithorhynchids and closely allied with
> > *Obdurodon*, too.
>
> That seems like a counsel of despair.  Given how specialized the two lines 
> were by the Miocene, the tachyglossans and platypodans must have diverged 
> a long time before.

How long? Oligocene? Eocene? And the Miocene itself took a long time, too.

Compare any late Eocene artiodactyls, including *Basilosaurus* and 
*Dorudon*, and then remember they had a common ancestor around the 
Palaeocene-Eocene boundary.

> > 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*.
>
> Yes, but the teeth of _Monotrematum_ show a striking resemblance to the 
> teeth of the ornithorhynchid _Obdurodon_.

This would tell us something if echidnas had different teeth. But we don't 
know that.

> It could be that _Monotrematum_ was a non-platypodan with 
> ornithorhynchid-like teeth.  But the most parsimonious explanation is that 
> _Monotrematum_ is an ornithorhynchid.

As I'm saying: maybe, if *M.* is an ornithorhynchid, then Tachyglossa and 
Platypoda are subsets of Ornithorhynchidae.