After Emry & Storer, 1981, Joeckel & Stavas, 1996, McKenna & Bell, 1997 and Norris, 2000

<==o †Protoceratidae Marsh, 1891
   |--o †Leptotragulus [Leptotragulinae]
   |  |-- †L. ?clarki
   |  `-- †L. medius
   `--+--o †“Leptoreodontinae” [Leptotragulinae, in part]
      |  |--o †Leptoreodon [Camelomeryx, Hesperomeryx, Merycodesmus]
      |  |  |-- †L. major
      |  |  |-- †L. pusillus
      |  |  |-- †L. edwardsi
      |  |  `-- †L. leptolophus
      |  |-- †Toromeryx
      |  |-- †Heteromeryx dispar
      |  `?- †Poabromylus kayi
      `--+--o †Protoceratinae Marsh, 1891
         |  |--o †Pseudoprotoceras Cook, 1934
         |  |  |-- †P. longinaris Cook, 1934
         |  |  |-- †P. semicinctus (Cope, 1889)
         |  |  `-- †P. taylori Emry & Storer, 1981
         |  |-- †Protoceras celer
         |  `-- †Paratoceras
         `--o †Synthetoceratinae
            |--o †Synthetoceratini
            |  |-- †Lambdoceras
            |  |-- †Prosynthetoceras texanus
            |  `-- †Synthetoceras tricornatus
            `--o †Kyptoceratini
               |-- †Syndyoceras cooki
               `-- †Kyptoceras amatorum

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