Flinders University researchers reported three fossils from South Australia's outback: a lower molar, upper premolar and partial pectoral girdle from the 25-million-year-old species.
The finds suggest the animal kept adult teeth, could crush shelled prey such as yabbies, and had a forelimb structure similar to the modern platypus, indicating strong swimming ability.
Published in Australian Zoologist, the study expands a species previously known from scant remains and adds to evidence that inland South Australia once held river-and-lake ecosystems rich in fish, birds, reptiles and mammals.
Why did the platypus abandon its powerful teeth for the simple pads it has today?
As Australia turned to desert, how did the platypus survive when its entire ecosystem collapsed?