Opinions from G. G. Simpson 1930
- 'Amphicyon amnicola is a subjective synonym of Amphicyon sinapius'
- 'Amphicyon pontoni belongs to Amphicyon'
- 'Auchenia major is recombined as Megatylopus major'
- 'Auchenia major is recombined as Procamelus major' according to Leidy and F. Lucas 1896
- 'Auchenia major is recombined as Pliauchenia major' according to Cope 1892
- 'Auchenia minimus is a subjective synonym of Pliauchenia minor' according to Cope 1892
- 'Auchenia minimus is recombined as Procamelus minimus'
- 'Auchenia minimus is recombined as Procamelus minimus' according to Leidy and F. Lucas 1896
- 'Procamelus minor is a nomen dubium'
- 'Dicotyles antiquus is recombined as Perchoerus antiquus'
- 'Dicotyles antiquus belongs to Dicotyles' according to Marsh 1870
- 'Hipparion phosphorum belongs to Hipparion'
- 'Hippotherium ingenuum is recombined as Hipparion ingenuum'
- 'Hippotherium ingenuum is recombined as Hipparion ingenuum' according to Hay 1930
- 'Hippotherium plicatile is recombined as Hipparion plicatile'
- 'Hippotherium princeps is a nomen dubium'
- 'Hydrochoerus pinckneyi is recombined as Neochoerus pinckneyi'
- 'Hydrochoerus pinckneyi is recombined as Neochoerus pinckneyi' according to Simpson 1929
- 'Hydrochoerus pinckneyi is recombined as Neochoerus pinckneyi' according to Hay 1928
- 'Hydrochoerus pinckneyi is recombined as Neochoerus pinckneyi' according to Hay 1927
- 'Hydrochoerus pinckneyi belongs to Hydrochoerus' according to Hay 1923
- 'Leptarctus progressus belongs to Leptarctus'
- 'Mastodon rugosidens is recombined as Serridentinus rugosidens'
- 'Mastodon rugosidens belongs to Mastodon' according to Leidy 1890
- 'Merychippus gunteri belongs to Merychippus'
- 'Merychippus isonesus secundus is recombined as Merychippus secundus'
- 'Merychippus westoni belongs to Merychippus'
- 'Pliomastodon sellardsi belongs to Pliomastodon'
- 'Protocamelus virginiensis is recombined as Tanupolama virginiensis'
- 'Protocamelus virginiensis is recombined as Camelops virginiensis' according to Hay 1929
- 'Protocamelus virginiensis is recombined as Auchenia virginiensis' according to Leidy 1892
- 'Rhinoceros longipes is recombined as Aphelops longipes'
- 'Rhinoceros matutinus is recombined as Diceratherium matutinum'
- 'Rhinoceros proterus is recombined as Teleoceras proterus'