Mammaliaformes Rowe 1988, nom. cl. inval. see Clade Mammaliaformes Rowe 1988 [Rowe 2020]
   [crown] Mammalia Linnaeus 1758 [Rowe 1988], nom. cl. inval. see Clade Mammalia Linnaeus 1758 [Rowe 2020]
     Prototheria Gill 1872 [O'Leary, Allard, Novacek, Meng & Gatesy 2004] see Subclass Prototheria Gill, 1872
       1 †Kollikodon ritchiei Flannery, Archer, Rich & Jones, 1995
       2[1] †Steropodon galmani Archer, Flannery, Ritchie & Molnar, 1985
       3[A] [crown] Monotremata Bonaparte 1837 [Rowe 1988], nom. cl. inval. see Clade Monotremata Fischer 1823 [Rowe, Bhullar & Wallace 2020]