What evidence shows that ancient platypuses once lived in South America?

Evidence that ancient platypuses once lived in South America comes from the discovery of fossilized remains in Patagonian sediments.1

In 1991, paleontologist Rosendo Pascual announced the discovery of a 62- to 63-million-year-old monotreme fossil, identified as the genus Monotrematum (M. sudamericanum). This finding confirmed that platypuses were once distributed across the southern continents of Gondwana, which were linked geographically via Antarctica during the Paleogene Period. These ancient, extinct relatives were more robust than the modern platypus and retained functional teeth.123