Australosphenida (includes Monotremes: Echidnas and Platypuses)
This infraclass includes a number of extinct orders, as well as the sole recent order Monotremata (i.e. echidnas and platypuses). Baby echidnas and platypuses are known as 'puggles'.
Order: Monotremata
Family: Ornithorhynchidae (platypuses)
—No subordinate taxa
Family: Tachyglossidae (echidnas)
| Scientific Name | Author/s | Common Name | Last Record | Distribution | Status | Taxon Profile |
| Megalibgwilia owenii | Krefft, 1868 | Owen's echidna | Late Pleistocene | Australia | Extinct | Access |
| Megalibgwilia ramsayi | Owen, 1884 | Ramsay's echidna | c.48,000 BC | New South Wales & Tasmania, Australia | Invalid (synonym) | Access |
| Murrayglossus hacketti | (Glauert, 1914) | Hackett's giant echidna | c. 38,000 BC? | Western Australia, Australia | Extinct | Access |
| Zaglossus attenboroughi | Flannery & Groves, 1998 | Attenborough's echidna, Cyclops long-beaked echidna, Sir David's long-beaked echidna | (rediscovered) | Cyclops Mountains, New Guinea | Rediscovered | Access |
| Zaglossus hacketti | Glauert, 1914 | Hackett's giant echidna | c. 38,000 BC? | Western Australia, Australia | Extinct | Access |