Obdurodon dicksoni was a large, spoon-billed platypus from the Riversleigh area of northern Australia. Its skull is one of the most perfect fossils known from the area. Older Obdurodon species are known from central Australia. Obdurodon probably fed on insect larvae, yabbies and other crustaceans, and perhaps small vertebrates such as frogs and fish. Unlike the living Platypus, these fossil platypuses had functional molar teeth.
Obdurodon was a monotreme, or mammal that lays eggs. Monotremes have been around longer than any other group of living mammals; the oldest known, the mouse-sized Teinolophos trusleri, lived alongside the dinosaurs 115 million years ago. Steropodon galmani, the oldest platypus-like monotreme, is known from an opalised lower jaw from Lightning Ridge in New South Wales.
Monotremes are only found today in Australia and New Guinea. However, fossils from Argentina of the 61 million-year-old platypus Monotrematum sudamericanum show they once had a wider range across ancient Gondwana. And while Australia is now home to just one species of Platypus and one Short-beaked Echidna, the fossil record shows there were once at least three species of platypuses with adult teeth, and three mainland Australian long-beaked echidnas, including one the size of a sheep (long-beaked echidnas are now only found in New Guinea; the Western Beaked Echidna hasn’t been recorded in Australia since 1901). The toothless living Platypus, Ornithorhynchus anatinus, is probably descended from one of the earlier Obdurodon species with functional teeth.
Miocene, 20–15 million years ago, Riversleigh, Queensland, Australia