Vertebrata Cuvier, 1812 - vertebrates
   Gnathostomata
     Teleostomi
       Tetrapoda Goodrich, 1930
         Amniota Haeckel, 1866 - amniotes
           Class Mammalia Linnaeus, 1758 - mammals
             Subclass Theria Parker & Haswell, 1897
               Theria of Metatherian-Eutherian grade
                 Infraclass Eutheria Gill, 1872
                   Order Sirenia Gill, 1872 - sea cows
                     1 Family †Prorastomidae Cope, 1889
                     2 Family Dugongidae Gray, 1821 - dugong and sea cow
                     3 Family Manatidae Gray, 1821, nom. illeg. see Family Trichechidae Gill, 1872
                     4 Family †Protosirenidae Sickenberg, 1934 see Subfamily Protosireninae Sickenberg, 1934