There is uncertainty regarding the placement of Perissodactyla; a grouping with Ferae has been proposed as the clade Zooamata while a grouping with Cetartiodactyla has been proposed as the clade Euungulata ("true ungulates").
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Within Fereuungulata, Carnivora and Pholidota form the clade Ferae while Cetacea and Artiodactyla form Cetartiodactyla.