The fossil discoveries double the number of known monotreme species during the Cretaceous Period.

Australian researchers have found evidence of the oldest known platypus and a new species, dubbed 'echidnapus', which has a platypus-like anatomy alongside features that more closely resemble an ...

Six monotremes living in the same place at the same time, 100 million years ago at Lightning Ridge, NSW. Clockwise from lower left: Opalios splendens, a newly described species dubbed an ...

A new study suggests the platypus and echidna — the only egg-laying mammals — had a water-dwelling ancestor. The finding could upend what’s known of their evolution.

Biologists have confirmed the existence of a 200-million-year-old species of egg-laying mammal that has been assumed to be extinct.