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.[1] 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.[1]