After Carroll, 1988, with species from “The Paleobiology Database”

<==o †Ophiacodontidae Nopska, 1923
   |-- †Archaeothyris florensis Reisz, 1972
   |--o †Baldwinonus Romer & Price, 1940
   |  |-- †B. trux Romer & Price, 1940 [AMNH-4780]
   |  `-- †B. dunkardensis Romer, 1952
   |--o †Clepsydrops Cope, 1875 [Archaeobelus]
   |  |?- †C. sp. [AMNH-4600]
   |  |-- †C. collettii Cope, 1875
   |  |-- †C. limbatus Cope, 1877
   |  |-- †C. natalis Cope, 1878
   |  `-- †C. vinslovii Cope, 1877
   |--o †Ophiacodon Marsh, 1878 [Arribasaurus, Theropleura, Poliosaurus, Winfieldia, Therosaurus, Diopeus] [6 valid species??]
   |  |?- †O. triangulata [AMNH-4167]
   |  |?- †O. watsoni [Therosaurus watsoni [AMNH-4604]]
   |  |?- †O. sp. [AMNH-24800]
   |  |-- †O. major Romer & Price, 1940 [AMNH-21047]
   |  |-- †O. uniformis (Cope, 1878) Romer & Price, 1940 [Poliosaurus]
   |  |-- †O. mirus Marsh, 1878 [AMNH-2900]
   |  |-- †O. navajovicus Romer & Price, 1940 [AMNH-4776]
   |  |-- †O. retroversus Romer & Price, 1940 [AMNH-21063]
   |  `-- †O. hilli Romer & Price 1940
   |?- †Protoclepsydrops haplous Carroll, 1964 [P. haplodus?]
   |-- †Stereophallodon ciscoensis Romer, 1937 [AMNH-4768]
   `-- †Stereorhachis dominans Gaudry, 1880

Reference(s):

Special thanks to:

Jos H. M. Dols, for gathering additional information and species of these animals.