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Re: Platypuses may be older than we think...
Then maybe the echidnas are ornithorhynchids and closely allied with
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
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
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.