Ungulates (meaning roughly "being hoofed" or "hoofed animal") are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive. There is some dispute as to whether Ungulata is a cladistic (evolution-based) group, or merely a phenetic group or folk taxon (similar, but not necessarily related), because not all ungulates appear as closely related as once believed. Ungulata was formerly considered an order which has since been split into:
As a descriptive term, "ungulate" normally excludes cetaceans, which are now known to share a common ancestor with Artiodactyla and form the clade Cetartiodactyla with them. Members of the orders Perissodactyla and Artiodactyla are called the 'true ungulates' to distinguish them from 'subungulates' (Paenungulata) which include members from the afrotherian orders Proboscidea, Sirenia and Hyracoidea.
Commonly known examples of ungulates living today are the horse, zebra, donkey, cattle/bison, rhinoceros, camel, hippopotamus, tapir, goat, pig, sheep, giraffe, okapi, moose, elk, deer, antelope, and gazelle.
Perissodactyla and Artiodactyla comprise the largest portion of ungulates, and also include the majority of large land mammals. These two groups first appeared during the late Paleocene and early Eocene (about 54 million years ago), rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time.
Although whales and dolphins (Cetacea) do not possess most of the typical morphological characteristics of ungulates, recent discoveries indicate that they are descended from early artiodactyls, and thus are directly related to other even-toed ungulates such as cattle, with hippopotamuses being their closest living relatives. As a result of these discoveries, the new order Cetartiodactyla has been proposed to include the members of Artiodactyla and Cetacea, to reflect their common ancestry; however, strictly speaking, this is merely a matter of nomenclature, since it is possible simply to recognize Cetacea as a subgroup of Artiodactyla.
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