[1] Other South American native ungulate groups also possibly belong to the clade, but their placement is uncertain.

[5] The enigmatic aquatic Desmostylia have also been suggested to be related to perissodactyls in some studies, though others recover them as members of afrotherian clade Tethytheria.

[6] The Northern Hemisphere "condylarth" group Phenacodontidae has been placed as closely related to perissodactyls in some studies, though others recover it as unrelated.

[1] Panperissodactyla is preferred over the older Mesaxonia which was originally coined by Othniel Charles Marsh in 1884, as equivalent to the modern Perissodactyla.

Richard Owen's original definition of Perissodactyla included the modern members in addition to the now known to be unrelated Hyracoidea.