Phenacodontidae

Phenacodus (Greek: "deception" (phenax), "tooth' (odus)) is an extinct genus of mammals from the late Paleocene through middle Eocene, about 55 million years ago. It is one of the earliest and most primitive of the ungulates, typifying the family Phenacodontidae and the order Perissodactyla.

Phenacodontidae is an extinct family of large herbivorous mammals traditionally placed in the "wastebasket taxon" Condylarthra, which may instead represent early-stage perissodactyls. They lived from the late early Paleocene to early middle Eocene (about 60–50 million years ago) and their fossil remains have been found in North America and Europe. The only unequivocal Asian phenacodontid is Lophocion asiaticus.

Meniscotherium is an extinct genus of dog-sized mammal which lived 54–38 million years ago.

Tetraclaenodon was a genus of small and early ungulate mammals that was part of the Phenacodontidae family. It is the oldest and most primitive phenacodontid. Its fossils known from the Nacimiento Formation, New Mexico. In 2012, Tetraclaenodon was defined as the basalmost member of the clade containing "Phenacodontidae" and Altungulata. alt=fossil skull of early ungulate Tetraclaenodon puercensis|left|thumb|Life Restoration

Ectocion (sometimes Ectocyon) is an extinct genus of placental mammals of the family Phenacodontidae. The genus was earlier classified as Gidleyina (Simpson 1935) and Prosthecion (Patterson and West 1973) It reached 6 to 12 kg and was similar in size and morphology to Copecion. Both these herbivorous ungulates likely occupied similar ecological niches.