Mammalia Linnaeus 1758 [Rowe 1988], nom. cl. inval. see Class Mammalia Linnaeus, 1758
   Metatheria Huxley 1880 [O'Leary, Allard, Novacek, Meng & Gatesy 2004] see Infraclass Metatheria Huxley, 1880
     Marsupialiformes Vullo, Gheerbrant, de Muizon & Néraudeau, 2009
       [Order] †Polydolopimorphia Archer, 1984
         [Suborder] †Polydolopiformes Goin & Candela, 1996
           1 Family †Sillustaniidae Crochet & Sigé, 1996 [monotypic]
           2.1.1 Genus †Cocatherium Goin, Pascual, Tejedor, Gelfo, Woodburne, Case, Reguero, Bond, Lopez, Cione, Udrizar Sauthier, Balarino, Scasso, Medina & Ubaldon, 2006
           2.1.2 Genus †Roberthoffstetteria Marshall, de Muizon & Sigé, 1983
           2.2 Family †Polydolopidae Ameghino, 1897