Neornithes Gadow, 1893 - living birds
   Neognathae Pycraft 1900 see Cohort Neognathae Pycraft, 1900
     Neoaves Sibley et al. 1988 see Subcohort Neoaves Sibley et al., 1988
       [Order] Charadriiformes Huxley, 1867 - shorebirds, gulls, auks
         Family Alcidae Vigors, 1825 - auks
           Genus Ptychoramphus Brandt, 1837 [monotypic]
             Ptychoramphus aleuticus (Pallas, 1811) - Cassin's auklet
               Ptychoramphus aleuticus aleuticus (Pallas, 1811)