After Anderson, 1998, 2001, 2002, 2003a, b, & Anderson, Carroll & Rowe, 2003

<==o †Aistopoda Miall, 1875 [Aïstopoda Miall, 1875] (aistopods; aistopodit)
   |?- †“Ophiderpeton” swisshelmensis Thayer, 1985
   |-- †Lethiscus stocki Wellstead, 1982 [Lethiscidae Wellstead, 1982]
   `--+--o †Ophiderpeton Wright & Huxley, 1866 [Ophiderpetontidae Schwartz, 1908]
      |  |-- †O. kirktonense Milner, 1994
      |  `-- †O. brownriggi Wright & Huxley, 1866
      `--+--o †Oestocephalidae Anderson, 2003b
         |  |-- †Coloraderpeton brilli Vaughn, 1969
         |  `--o †Oestocephalus Cope, 1868 [taxonomic history]
         |     |?- †O. sp. [MCP323] [Carroll, 1998a]
         |     |-- †O. nanum (Hancock & Atthey, 1868)
         |     `-- †O. amphiuminum (Cope, 1868) [taxonomic history]
         `--o †Phlegethontioidea Cope, 1875 sensu Anderson, Carroll & Rowe, 2003
            |-- †Pseudophlegethontia turnbullorum Anderson, 2003 [Pseudophlegethontiidae Anderson, 2003] [taxonomic history]
            `--o †Phlegethontiidae Cope, 1875
               |?- †Dolichosoma
               |?- †"Phlegethontia" phanerhalpha Thayer, 1985 (nomen dubium)
               `--+-- †Sillerpeton permianum Lund, 1978
                  `--o †Phlegethontia Cope, 1871b [taxonomic history]
                     |-- †P. linearis Cope, 1871b [taxonomic history]
                     `-- †P. longissima (Fritsch, 1875) [taxonomic history]

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