Ungulates (meaning roughly "being hoofe" or "hoofed animal") are several groups of mammals most of which use the tips of their toes, usually hoofed, to sustain their whole bodyweight while moving. They make up several orders of mammals, of which six to eight survive. There is some dispute as to whether Ungulata are a cladistic (evolution-based) group, or merely a phenetic group (similar, but not necessarily related), because not all ungulates appear as closely related as once believed. Ungulata was considered an order which has been split into Perissodactyla, Artiodactyla, Tubulidentata, Hyracoidea, Sirenia, and Proboscidea. Members of the orders Perissodactyla, Artiodactyla, and Cetacea are called the 'true ungulates' to distinguish them from 'subungulates' (paenungulata) which include members from the Proboscidea, Sirenia, Hyracoidea, and Tubulidentata orders.