Er, wait...

So there's this newly-discovered paleo-monotreme thingy.  Seems it was, back in the day, a platypus with nasty sharp pointy teeth.

Part of its name (Obdurodon tharalkooschild) is explained thus:

The second part of the name comes from an Indigenous Australian creation myth about the origin of the platypus. According to the story, in the Dreamtime, Tharalkoo was a headstrong female duck who disobeyed her parents' warnings not to swim downriver where Bigoon the water-rat could catch her...

Wait.  This is an ancient myth?

I are confoozed.  How long have there been rodents in Australia, anyway?

Update: Duh.  Seems Australia does have indigenous Muridae, including this critter.