Class Mammalia Linnaeus, 1758 - mammals Subclass Theria Parker & Haswell, 1897 Order Didelphimorphia Gill, 1872 Family Didelphidae Gray, 1821 - American opossums Subfamily Didelphinae Gray, 1821 Genus Thylamys Gray, 1843 Thylamys pusillus (Desmarest, 1804) - common fat-tailed mouse opossum