Ungulate

Ungulates (pronounced /ˈʌŋɡjəleɪts/) are any members of a diverse group of primarily large mammals with hoofs. These include odd-toed ungulates such as horses and rhinoceroses, and even-toed ungulates such as cattle, pigs, giraffes, camels, deer, and hippopotamuses, as well as sub-ungulates such as elephants. Most terrestrial ungulates use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. The term means, roughly, 'being hoofed' or 'hoofed animal'. As a descriptive term, 'ungulate' normally excludes cetaceans (whales, dolphins, porpoises), as they do not possess most of the typical morphological characteristics of ungulates, but recent discoveries indicate that they are descended from early artiodactyls. Ungulates are typically herbivorous (though some modern species are omnivorous, such as pigs, and some prehistoric ones were carnivorous, like mesonychians), and many employ specialized gut-bacteria to allow them to digest cellulose. Ungulata, which used to be considered an order, has been split into the following: Perissodactyla (odd-toed ungulates), Artiodactyla (even-toed ungulates), Tubulidentata (aardvarks), Hyracoidea (hyraxes), Sirenia (dugongs and manatees), Proboscidea (elephants) and occasionally Cetacea (whales and dolphins). However, in 2009 morphological and molecular work has found that aardvarks, hyraxes, sea cows, and elephants are more closely related to sengis, tenrecs, and golden moles than to the perissodactyls and artiodactyls, and form Afrotheria. Elephants, sea cows, and hyraxes are grouped together in the clade Paenungulata, while the aardvark has been considered as either a close relative to them or a close relative to sengis in the clade Afroinsectiphilia. This is a striking example of convergent evolution. There is now some dispute as to whether this smaller Ungulata is a cladistic (evolution-based) group, or merely a phenetic group (form taxon) or folk taxon (similar, but not necessarily related). Some studies have indeed found the mesaxonian ungulates and paraxonian ungulates to form a monophyletic lineage, closely related to either the Ferae (the carnivorans and the pangolins) in the clade Fereuungulata or to the bats. Other studies found the two orders not that closely related, as some place the perissodactyls as close relatives to bats and Ferae in Pegasoferae and others place the artiodactyls as close relatives to bats. Below is a simplified taxonomy (assuming that ungulates do indeed form a natural grouping) with the extant families, in order of the relationships. Keep in mind that there are still some grey areas of conflict, such as the case with relationship of the pecoran families and the baleen whale families. See each family for the relationships of the species as well as the controversies in their respective article. Below is the general consensus of the phylogeny of the ungulate families. Perissodactyla and Artiodactyla include the majority of large land mammals. These two groups first appeared during the late Paleocene, rapidly spreading to a wide variety of species on numerous continents, and have developed in parallel since that time. Some scientists believed that modern ungulates are descended from an evolutionary grade of mammals known as the condylarths; the earliest known member of the group was the tiny Protungulatum, an ungulate that co-existed with the last of non-avian dinosaurs 66 million years ago; however, many authorities do not consider it a true placental, let alone an ungulate. The enigmatic dinoceratans were among the first large herbivorous mammals, although their exact relationship with other mammals is still debated with one of the theories being that they might just be distant relatives to living ungulates; the most recent study recovers them as within the true ungulate assemblage, closest to Carodnia.