Early Monotremes were Semiaquatic Burrowers, Paleontologists Find

Up until now, the accepted understanding about these egg-laying was that they were both descended from a land-bound ancestor. And while the platypus ancestors became semiaquatic, the echidnas stayed on the land, or so the story went. But an analysis of a single humerus bone from Kryoryctes cadburyi — a prehistoric monotreme mammal that lived in what is now Victoria, Australia during the Early Cretaceous epoch — suggests that echidnas evolved from semiaquatic ancestors and that the amphibious lifestyle of the modern platypus had its origins at least 100 million years ago.