After Sequeira & Coates, 2000

<==o †Symmorida Zangerl, 1981 sensu Zangerl, 1990 [Symmoriiformes; Cladodontida Obruchev, 1967]
   |?- †Gutturensis neilsoni (Traquair, 1898b) Sequeira & Coates, 2000 [“Cladodus” neilsoni Traquair, 1898b; Symmorium neilsoni (Traquair, 1898b)]
   |--o †Symmoriidae Dean, 1909 non Zangerl, 1990
   |  |--o †Cobelodus [Styptobasis]
   |  |  `-- †C. aculeata (Cope, 1894) [C. acuteatus]
   |  |--o †Denaea Pruvost, 1922, U. Carb. NA.
   |  |  |-- †D. fournieri Pruvost, 1923a
   |  |  |-- †D. wangi Wang, Jin & Wang, 2004
   |  |  |-- †D. sp. 1 [L. Carb. EAs.] [Wang, Jin & Wang, 2004]
   |  |  `-- †D. sp. 2 [L. Carb. EAs.] [Wang, Jin & Wang, 2004]
   |  `--o †Symmorium Cope, 1893 [Cladodus in partim] Miss. Eu. Penn. NA.
   |     |-- †S. meccaensis Williams, 1985
   |     |-- †S. reniforme Cope, 1893
   |     `-- †S. sp.
   `--+--o †Falcatidae Zangerl, 1990 
      |  |-- †Falcatus falcatus (St. John & Worthren, 1875) [i>Stethacanthus] Miss. NA.
      |  `--o †Damocles [Stethacanthus] Miss. NA.
      |     |-- †D. serratus Lund, 1986
      |     `-- †D. attenuatus (Davis, 1883)
      `--o †Stethacanthidae Lund, 1974 sensu Zangerl, 1990
         |-- †Akmonistion zangerli Coates & Sequeira, 2001
         |-- †Bethacanthulus
         |-- †Orestiacanthus Penn. NA. 
         |-- †Stethacanthulus
         `--o †Stethacanthus Newberry, 1889 [Cladodus, Lambdodus, Physonemus] U. Dev. Penn. NA. Miss. Eu.
            |-- †S. altonensis “tumidus” (St. John & Worthen, 1875)
            |-- †S. sp. cf. S. altonensis [L. Carb. NA.] [Zidek, 1993]
            |-- †S. sp. cf. S. altonensis [L. Carb. EAs.] [Wang, Jin & Wang, 2004]
            |-- †S. mirabilis
            |-- †S. praecursor Hossakof & Bryant, 1918
            |-- †S. productus Lund & Zangerl, 1974
            |-- †S. thomasi Turner, 1982
            `-- †S. gansuensis Wang, Jin & Wang, 2004

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