Mammaliaformes Rowe 1988
   [crown] Mammalia Linnaeus 1758 [Rowe 1988], nom. cl. inval. see Class Mammalia Linnaeus, 1758
     Prototheria Gill 1872 [O'Leary, Allard, Novacek, Meng & Gatesy 2004] see Subclass Prototheria Gill, 1872
       [crown] Monotremata Bonaparte 1837 [Rowe 1988] see Order Monotremata Bonaparte, 1837
         1.1[2] †Megalibgwilia robusta (Dun, 1895)
         1.2 Tachyglossus aculeatus (Shaw, 1792) - short-beaked echidna
         2.1[3] †Obdurodon insignis Woodburne & Tedford, 1975
         2.2 Ornithorhynchus anatinus (Shaw, 1799) - platypus