Opinions from O. A. Peterson 1919
- 'Achaenodontidae belongs to Artiodactyla'
- 'Amynodon belongs to Amynodontinae'
- 'Amynodontidae was reranked as the subfamily Amynodontinae and belongs to Hyracodontidae'
- 'Anchitherium gracilis is recombined as Epihippus gracilis'
- 'Archaenodon is corrected as Achaenodon and belongs to Achaenodontidae'
- 'Archaenodon insolens is recombined as Achaenodon insolens'
- 'Bunomeryx belongs to Homacodontinae'
- 'Bunomeryx elegans belongs to Bunomeryx'
- 'Camelomeryx is a subjective synonym of Leptoreodon'
- 'Desmatotherium belongs to Hyrachyinae'
- 'Desmatotherium guyotii belongs to Desmatotherium'
- 'Dilophodon belongs to Ceratomorpha'
- 'Dilophodon minusculus belongs to Dilophodon'
- 'Diplobunops belongs to Anoplotheriidae'
- 'Diplobunops matthewi belongs to Diplobunops'
- 'Eomoropus belongs to Schizotheriinae'
- 'Eomoropus annectens belongs to Eomoropus'
- 'Epihippus belongs to Hyracotheriinae'
- 'Epihippus parvus belongs to Epihippus'
- 'Harpagolestes belongs to Mesonychidae'
- 'Helaletes belongs to Helaletinae'
- 'Helaletes boops belongs to Helaletes'
- 'Helaletes latidens is recombined as Parisectolophus latidens'
- 'Helaletidae belongs to Tapiroidea'
- 'Helaletinae belongs to Helaletidae'
- 'Homacodontidae was reranked as the subfamily Homacodontinae and belongs to Artiodactyla'
- 'Homogalax belongs to Homogalaxinae'
- 'Homogalaxinae belongs to Isectolophidae'
- 'Hylomeryx belongs to Homacodontinae'
- 'Hylomeryx annectens belongs to Hylomeryx'
- 'Hyrachyidae was reranked as the subfamily Hyrachyinae and belongs to Hyracodontidae'
- 'Hyrachyus belongs to Hyrachyinae'
- 'Hyrachyus grande belongs to Hyrachyus'
- 'Hyrachyus obliquidens is recombined as Prothyracodon obliquidens'
- 'Hyracodontidae belongs to Perissodactyla'
- 'Hyracodontinae belongs to Hyracodontidae'
- 'Hyracotheriinae belongs to Equidae'
- 'Ischyrotomus gidleyi belongs to Ischyrotomus'
- 'Isectolophidae belongs to Tapiroidea'
- 'Isectolophinae belongs to Isectolophidae'
- 'Isectolophus belongs to Isectolophinae'
- 'Isectolophus annectens belongs to Isectolophus'
- 'Isectolophus scotti belongs to Isectolophus'
- 'Leptoreodon belongs to Hypertragulidae'
- 'Leptoreodon marshi belongs to Leptoreodon'
- 'Leptotragulus belongs to Hypertragulidae'
- 'Leptotragulus medius belongs to Leptotragulus'
- 'Leptotragulus proavus belongs to Leptotragulus'
- 'Limnocyon belongs to Oxyaenidae'
- 'Limnocyon douglassi belongs to Limnocyon'
- 'Lophiodon nanus is recombined as Helaletes nanus'
- 'Mesomeryx belongs to Homacodontinae'
- 'Mesomeryx grangeri belongs to Mesomeryx'
- 'Mesonychidae belongs to Carnivora'
- 'Mesonyx uintensis is recombined as Harpagolestes uintensis'
- 'Mesonyx uintensis belongs to Mesonyx' according to Scott and Osborn 1887
- 'Miacidae belongs to Carnivora'
- 'Mimocyon belongs to Miacidae'
- 'Mimocyon longipes belongs to Mimocyon'
- 'Orohippus tapirinus is recombined as Eohippus tapirinus'
- 'Oromeryx belongs to Hypertragulidae'
- 'Oxyaenidae belongs to Carnivora'
- 'Oxyaenodon belongs to Oxyaenidae'
- 'Oxyaenodon dysclerus belongs to Oxyaenodon'
- 'Oxyaenodon dysodus belongs to Oxyaenodon'
- 'Parahyus belongs to Achaenodontidae'
- 'Parahyus vagus belongs to Parahyus'
- 'Parameryx is a subjective synonym of Leptotragulus'
- 'Parameryx laevis is a nomen dubium'
- 'Parameryx sulcatus is a nomen dubium'
- 'Paramys belongs to Ischyromyidae'
- 'Paramys (Ischyrotomus) was reranked as Ischyrotomus and belongs to Paramyidae'
- 'Paramys compressidens belongs to Paramys'
- 'Paramys medius belongs to Paramys'
- 'Paramys robustus is recombined as Ischyrotomus robustus'
- 'Paramys robustus belongs to Paramys' according to Matthew 1910
- 'Pareumys belongs to Muridae'
- 'Pareumys milleri belongs to Pareumys'
- 'Parisectolophus belongs to Isectolophinae'
- 'Pleurocyon belongs to Miacidae'
- 'Pleurocyon magnus belongs to Pleurocyon'
- 'Pleurocyon medius belongs to Pleurocyon'
- 'Prodaphaenus belongs to Miacidae'
- 'Prodaphaenus robustus belongs to Prodaphaenus'
- 'Prosciurus robustus belongs to Prosciurus'
- 'Protagriochoerus belongs to Agriochoeridae'
- 'Protagriochoerus annectens belongs to Protagriochoerus'
- 'Protelotherium is a subjective synonym of Achaenodon'
- 'Protelotherium uintense is recombined as Achaenodon uintense'
- 'Protelotherium uintense belongs to Protelotherium' according to Osborn 1895
- 'Prothyracodon belongs to Hyracodontinae'
- 'Prothyracodon uintense belongs to Prothyracodon'
- 'Prothyracodon uintensis belongs to Prothyracodon'
- 'Protoreodon belongs to Agriochoeridae'
- 'Protoreodon medius belongs to Protoreodon'
- 'Protylopus belongs to Camelidae'
- 'Protylopus annectens belongs to Protylopus'
- 'Protylopus petersoni belongs to Protylopus'
- 'Schizolophodon belongs to Isectolophinae'
- 'Schizolophodon cuspidens belongs to Schizolophodon'
- 'Sciuravus belongs to Paramyidae'
- 'Sciuravus altidens belongs to Sciuravus'
- 'Sciurus (Prosciurus) was reranked as Prosciurus and belongs to Paramyidae'
- 'Sphenomeryx belongs to Homacodontinae'
- 'Sphenomeryx quadricuspis belongs to Sphenomeryx'
- 'Systemodon is a subjective synonym of Eohippus'
- 'Systemodontinae is an invalid subgroup of Isectolophidae'
- 'Triplopodidae was reranked as the subfamily Triplopodinae and belongs to Hyracodontidae'
- 'Triplopus belongs to Triplopodinae'
- 'Triplopus cubitalis belongs to Triplopus'