Class Mammalia Linnaeus, 1758 - mammals Subclass Boreosphenida Luo, Cifelli & Kielan-Jaworowska, 2001 - tribotherians see Clade Boreosphenida Luo, Cifelli & Kielan-Jaworowska 2001 Infraclass Metatheria Huxley, 1880 Order †Deltatheroida Kielan-Jaworowska, 1982