[Phylum] Chordata Bateson, 1885 - chordates
   Subphylum Craniata auct.
     Infraphylum Vertebrata Lamarck, 1801 - vertebrates
       Superclass Gnathostomata Gegenbaur, 1874 - jawed vertebrates
         Class Chondrichthyes Huxley, 1880 - cartilaginous fishes
           Subclass Euselachii Hay, 1902 - sharks, rays, and related fossils
             Infraclass †Hybodonta [monotypic] - hybodonts
               Order †Hybodontiformes Patterson, 1966
                 Family †Sphenacanthidae Maisey, 1982, "nom. praeval."
                   1 ?Genus †Xenosynechodus Glickman, 1980
                   2 Genus †Sphenacanthus Agassiz, 1837