Ungulates are members of the diverse clade Euungulata, which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to be a polyphyletic and thereby invalid clade based on molecular data. As a result, true ungulates had since been reclassified to the newer clade Euungulata in 2001 within the clade Laurasiatheria while Paenungulata has been reclassified to a distant clade Afrotheria. Living ungulates are divided into two orders: Perissodactyla including equines, rhinoceroses, and tapirs; and Artiodactyla including cattle, antelope, pigs, giraffes, camels, sheep, deer, and hippopotamuses, among others. Cetaceans such as whales, dolphins, and porpoises are also classified as artiodactyls, although they do not have hooves. Most terrestrial ungulates use the hoofed tips of their toes to support their body weight while standing or moving. Two other orders of ungulates, Notoungulata and Litopterna, both native to South America, became extinct at the end of the Pleistocene, around 12,000 years ago.
Artiodactyls are placental mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine. Molecular biology, along with new fossil discoveries, has found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
Moschidae is a family of pecoran even-toed ungulates, containing the musk deer (Moschus) and its extinct relatives. They are characterized by long 'saber teeth' instead of horns, antlers or ossicones, modest size and a lack of facial glands. While various Oligocene and Miocene pecorans were previously assigned to this family, recent studies find that most should be assigned to their own clades, although further research would need to confirm these traits. As a result, Micromeryx, Hispanomeryx, and Moschus are the only undisputed moschid members, making them known from at least 18 Ma. The group was abundant across Eurasia and North America during the Miocene, but afterwards declined to only the extant genus Moschus by the early Pleistocene.
Tylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels are introduced. The group has a long fossil history in North America and Eurasia. Tylopoda appeared during the Eocene around 50 million years ago.
Cainotherium is an extinct genus of rabbit-sized prehistoric even-toed ungulates. These herbivores lived in Europe from the Eocene until the early Miocene. The skeletal anatomy of these hare-like animals suggest they, along with other members of Cainotheriidae, belong to the artiodactyl suborder Tylopoda, together with oreodonts and modern camelids. Species had cloven hooves, similar to those of bovids or deer, although the shape and length of the limbs suggests that the living animals moved by leaping, like a rabbit. The shape of the teeth also suggests a rabbit-like diet of nibbled vegetation, while the size of the auditory bulla and shape of the brain suggest that it would have had good senses of hearing and smell.
The Antilocapridae are a family of ruminant artiodactyls endemic to North America. Their closest extant relatives are the giraffids. Only one species, the pronghorn, is living today; all other members of the family are extinct. The living pronghorn is a small ruminant mammal resembling an antelope.
Merycoidodontoidea, previously known as "oreodonts" or "ruminating hogs," are an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were generally hog-like, and the group has traditionally been placed within the Suina, though some recent work suggests they may have been more closely related to camels. "Oreodont" means "mountain teeth," referring to the appearance of the molars. Most oreodonts were sheep-sized, though some genera grew to the size of cattle. They were heavy-bodied, with short four-toed hooves and comparatively long tails.
Syndyoceras is a small extinct genus of Artiodactyla, of the family Protoceratidae, endemic to central North America from the Miocene epoch, existing for approximately 4.2 million years.
Synthetoceras tricornatus is a large, extinct protoceratid, endemic to North America during the Late Miocene, 10.3—5.3 Ma, existing for approximately 5 million years. Fossils have been recovered from Nebraska and Texas.
The Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.
Kyptoceras is a small extinct artiodactyl ungulate mammal of the family Protoceratidae, endemic to southeastern North America from the Miocene to Early Pliocene epoch 23.03—3.6 Ma, existing for approximately 19.43 million years. The species name, amatorum, comes in honor of all amateur fossil collectors, including Frank Garcia the amateur who found it and donated it to the Florida Museum of Natural History.
Pseudoprotoceras is an extinct genus of Artiodactyla, of the family Protoceratidae, endemic to central North America. It lived during the Late Eocene 37.2—33.9 Ma, existing for approximately 3 million years. Pseudoprotoceras resembled hornless deer, but were more closely related to camelids.
Toromeryx is a medium-sized extinct genus of Artiodactyla, of the family Protoceratidae, endemic to southwestern North America from the Eocene epoch 46.2—42 Ma, existing for approximately 4.2 million years.
Synthetoceratinae is an extinct subfamily of Protoceratidae, deer-like herbivorous mammals belonging to the order Artiodactyla. They were endemic to North America during the Miocene epoch, living 23.03—3.9 Ma, existing for approximately 19.13 million years.
Kyptoceratini is an extinct tribe of the subfamily Synthetoceratinae, deer-like mammals within the family Protoceratidae belonging to the order Artiodactyla, endemic to North America during the Miocene through Pliocene, living 23.03—3.6 Ma, existing for approximately 19.43 million years.
Synthetoceratini is an extinct tribe of the subfamily Synthetoceratinae within the family Protoceratidae belonging to the order Artiodactyla endemic to North America during the Miocene, living epoch 20.6—4.9 Ma, existing for approximately 15.7 million years.
Lambdoceras is an extinct genus of Protoceratidae belonging to the order Artiodactyla endemic to North America during the Miocene, living epoch 20.6—13.6 Ma, existing for approximately 7 million years.
Cainotheriidae is an extinct family of artiodactyls known from the Late Eocene to Middle Miocene of Europe. They are mostly found preserved in karstic deposits.
Microbunodon was a genus of extinct artiodactyl mammals in the family Anthracotheriidae. It lived between the upper Eocene and the lower Pliocene. Its fossil remains have been found in Europe and Asia.
Ancodonta is an infraorder of artiodactyl ungulates including modern hippopotamus and all mammals closer to hippos than to cetaceans (whales). Ancodonts first appeared in the Middle Eocene, with some of the earliest representatives found in fossil deposits in Southeast Asia. Throughout their evolutionary history they have occupied different browsing and grazing niches in North America, Eurasia and Africa. The last continent is notable as they were among the first laurasiatherian mammals to have migrated to Africa from Europe, where they competed with the native afrothere herbivores for the same niches. Of the nearly 50 genera that have existed, only two of them are extant – Choeropsis and Hippopotamus. The interrelationships within the ancodonts has been contended. The traditional notion is that there at minimum two families Anthracotheriidae and Hippopotamidae and were merely sister taxa. However many detailed research of the dentition among ancodonts, as well as how some anthracotheres were similar to hippos in appearance, lead the current consensus where Anthracotheriidae is paraphyletic to Hippopotamidae. Among the anthracotheres, members of Bothriodontinae are among the closest to the ancestry of hippos, with the Oligocene aged Epirigenys from Lokon, Turkana, Kenya being the sister taxon to hippos. In response of this many similar clade names have been used for this clade.
