Opinions from M. R. Voorhies 1990
- 'Aelurodon platyrhinus is a subjective synonym of Aelurodon ferox'
- 'Aelurodon platyrhinus is a subjective synonym of Aelurodon ferox' according to Evander 1986
- 'Amblycastor is a subjective synonym of Anchitheriomys'
- 'Amblycastor is a subjective synonym of Anchitheriomys' according to Schreuder 1951
- 'Amblycastor fluminis is recombined as Anchitheriomys fluminis' according to Schreuder 1951
- 'Amblycastor fluminis is recombined as Anchitheriomys fluminis'
- 'Amebelodon sinclairi is a subjective synonym of Amebelodon fricki'
- 'Aphelops ceratorhinus is a subjective synonym of Peraceras crassus'
- 'Aphelops kimballensis is a subjective synonym of Aphelops mutilus'
- 'Barbouromeryx milleri is recombined as Bouromeryx milleri'
- 'Barbouromeryx nebrascensis is a subjective synonym of Bouromeryx americanus'
- 'Barbouromeryx pawniensis is recombined as Bouromeryx pawniensis'
- 'Barbouromeryx pseudonebrascensis is a subjective synonym of Bouromeryx americanus'
- 'Barbouromeryx submilleri is recombined as Bouromeryx submilleri'
- 'Barbouromeryx supernebrascensis is a subjective synonym of Bouromeryx americanus'
- 'Bassariscus antiquus is recombined as Probassariscus antiquus'
- 'Bassariscus nevadensis is a subjective synonym of Probassariscus antiquus'
- 'Bassariscus parvus is a subjective synonym of Probassariscus antiquus'
- 'Blastomeryx mefferdi is a subjective synonym of Blastomeryx gemmifer'
- 'Brachygale is a subjective synonym of Sthenictis'
- 'Canis (Epicyon) haydeni is recombined as Epicyon haydeni'
- 'Canis saevus is recombined as Epicyon saevus'
- 'Canis temerarius is recombined as Tomarctus temerarius'
- 'Canis temerarius is recombined as Tomarctus temerarius' according to Sutton 1977
- 'Canis vafer is recombined as Leptocyon vafer'
- 'Canis vafer is recombined as Leptocyon vafer' according to Storer 1975
- 'Castor (Eucastor) tortus is recombined as Eucastor tortus'
- 'Cervus warreni is recombined as Merycodus warreni'
- 'Cosoryx burgensis is a subjective synonym of Merycodus furcatus'
- 'Cosoryx furcatus is recombined as Merycodus furcatus'
- 'Cranioceras granti is a subjective synonym of Cranioceras unicornis'
- 'Cynodesmus cuspidatus is recombined as Carpocyon cuspidatus'
- 'Cynodesmus cuspidatus is recombined as Carpocyon cuspidatus' according to Evander 1986
- 'Cynodesmus euthos is recombined as Tomarctus euthos'
- 'Daphoenodon niobrarensis is a subjective synonym of Daphoenodon superbus'
- 'Domninoides storeri is a subjective synonym of Domninoides valentinensis'
- 'Domninoides storeri belongs to Domninoides' according to L. Russell 1976
- 'Dromomeryx parvus is a subjective synonym of Bouromeryx americanus'
- 'Eusmilus whitfordi is recombined as Barbourofelis whitfordi'
- 'Gnomomys is a subjective synonym of Tregomys'
- 'Gnomomys saltus is a subjective synonym of Tregomys shotwelli'
- 'Goniodontomys belongs to Cricetidae'
- 'Goniodontomys belongs to Cricetidae' according to Repenning 1987
- 'Goniodontomys disjunctus belongs to Goniodontomys'
- 'Goniodontomys disjunctus belongs to Goniodontomys' according to Repenning 1987
- 'Goniodontomys disjunctus is recombined as Microtoscoptes disjunctus' according to L. Martin 1975
- 'Hipparion gratum is recombined as Pseudhipparion gratum'
- 'Homocamelus is a subjective synonym of Aepycamelus'
- 'Homocamelus caninus is a subjective synonym of Aepycamelus robustus'
- 'Hypohippus matthewi is recombined as Megahippus matthewi'
- 'Hypsoparia is a subjective synonym of Leptarctus'
- 'Hypsoparia is a subjective synonym of Leptarctus' according to Sutton 1977
- 'Hypsoparia bozemanensis is a subjective synonym of Leptarctus primus' according to Sutton 1977
- 'Hypsoparia bozemanensis is recombined as Leptarctus bozemanensis'
- 'Hystrix (Hystricops) venustus is recombined as Hystricops venustus'
- 'Longirostromeryx merriami is a subjective synonym of Longirostromeryx wellsi'
- 'Machaerodus niobrarensis is a nomen dubium'
- 'Megalomeryx is a nomen dubium'
- 'Megalomeryx niobrarensis is a nomen dubium'
- 'Meryceros is a subjective synonym of Merycodus'
- 'Meryceros is a subjective synonym of Merycodus' according to Forsten 1970
- 'Meryceros (Submeryceros) was reranked as Submeryceros and belongs to Antilocapridae'
- 'Meryceros (Submeryceros) crucianus is recombined as Submeryceros crucianus'
- 'Meryceros joraki is recombined as Merycodus joraki'
- 'Meryceros major is recombined as Merycodus major'
- 'Meryceros minimus is recombined as Submeryceros minimus'
- 'Meryceros minor is recombined as Submeryceros minor'
- 'Meryceros nenzelensis is a subjective synonym of Merycodus warreni'
- 'Merychippus mirabilis is recombined as Pliohippus mirabilis'
- 'Merychyus major is recombined as Ustatochoerus major'
- 'Merychyus medius is recombined as Ustatochoerus medius'
- 'Miochomys is a subjective synonym of Copemys'
- 'Miochomys niobrariensis is recombined as Copemys niobrariensis'
- 'Mustela parviloba is recombined as Martes parviloba'
- 'Mustela parviloba belongs to Mustela' according to Cope 1873
- 'Neohipparion niobrarense is a subjective synonym of Parahippus cognatus'
- 'Palaeomeryx americanus is recombined as Bouromeryx americanus'
- 'Palaeomeryx madisonius is a subjective synonym of Bouromeryx americanus'
- 'Peraceras troxelli is a subjective synonym of Peraceras superciliosum'
- 'Peromyscus kelloggae is a subjective synonym of Copemys niobrariensis'
- 'Plioceros belongs to Antilocapridae'
- 'Plioceros floblairi is recombined as Sphenophalos floblairi'
- 'Pliohippus pernix belongs to Pliohippus'
- 'Pliohippus robustus is a subjective synonym of Pliohippus supremus'
- 'Probassariscus belongs to Procyonidae'
- 'Procamelus madisonius is a subjective synonym of Aepycamelus robustus'
- 'Procamelus robustus is recombined as Aepycamelus robustus'
- 'Propliophenacomys parkeri is recombined as Cseria parkeri'
- 'Prosomys belongs to Cricetidae'
- 'Prosomys mimus belongs to Prosomys'
- 'Prosomys mimus is recombined as Promimomys mimus' according to L. Martin 1975
- 'Prosthennops xiphodonticus is recombined as Dyseohyus xiphodonticus'
- 'Protohippus placidus is recombined as Calippus placidus'
- 'Protohippus supremus is recombined as Pliohippus supremus'
- 'Pseudoceras potteri is a subjective synonym of Pseudoceras skinneri'
- 'Ramoceros belongs to Antilocapridae'
- 'Ramoceros (Paramoceros) howardae is a subjective synonym of Ramoceros osborni'
- 'Ramoceros (Paramoceros) kansanus is a subjective synonym of Ramoceros osborni'
- 'Ramoceros hitchcockensis is a subjective synonym of Ramoceros osborni'
- 'Rhinoceros crassus is recombined as Peraceras crassus'
- 'Serbelodon barbourensis is recombined as Amebelodon barbourensis'
- 'Stegomastodon primitivus is a subjective synonym of Stegomastodon mirificus'
- 'Steneofiber pansus is recombined as Eucastor pansus'
- 'Steneofiber pansus belongs to Steneofiber' according to Cope 1874
- 'Stenogale robusta is recombined as Sthenictis robustus'
- 'Teleoceras major belongs to Teleoceras'
- 'Teleoceras minor is a subjective synonym of Teleoceras medicornutum'
- 'Teleoceras minor belongs to Teleoceras' according to Olcott 1909
- 'Teleoceras schultzi is a subjective synonym of Teleoceras fossiger'
- 'Tetrabelodon lulli is recombined as Gomphotherium lulli'
- 'Tetrabelodon osborni is recombined as Gomphotherium osborni'
- 'Tetrabelodon willistoni is a subjective synonym of Gomphotherium osborni'
- 'Torynobelodon barnumbrowni belongs to Torynobelodon'
- 'Torynobelodon barnumbrowni belongs to Torynobelodon' according to Osborn 1936
- 'Tregomys belongs to Cricetidae'
- 'Tregomys shotwelli belongs to Tregomys'
- 'Trilophodon abeli is a subjective synonym of Gomphotherium osborni'
- 'Trilophodon gregorii is a subjective synonym of Gomphotherium osborni'
- 'Trilophodon phippsi is a subjective synonym of Gomphotherium lulli'