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.
The hippopotamus (; pl.: hippopotamuses; also shortened to hippo, further qualified as the common hippopotamus, Nile hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus. Its name comes from the ancient Greek for "river horse".
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.
The pygmy hippopotamus or pygmy hippo is a small hippopotamid which is native to the forests and swamps of West Africa, primarily in Liberia, with small populations in Sierra Leone, Guinea, and Ivory Coast. It has been extirpated from Nigeria.
Hippopotamus is a genus of artiodactyl mammals consisting of one extant species, Hippopotamus amphibius, the river hippopotamus, and several extinct species from both recent and prehistoric times. It belongs to the family Hippopotamidae, which also includes the pygmy hippopotamus and a number of extinct genera.
Anthracotherium is an extinct genus of artiodactyls characterized by having 44 teeth, with five semi-crescentic cusps on the crowns of the upper molars. The genus ranged from the middle Eocene period until the early Miocene, having a distribution throughout Eurasia. Material subjectively assigned to Anthracotherium from Pakistan suggests the last species died out soon after the start of the Miocene.
Hippopotamus gorgops is an extinct species of Hippopotamus known from remains found in Northern Africa, Eastern Africa, and the Levant. One of the largest hippopotamus species, it first appeared during the late Pliocene-Early Pleistocene, and became extinct during the early Middle Pleistocene.
Hexaprotodon is an extinct genus of hippopotamid known from Asia and possibly Africa and Europe. The name Hexaprotodon means "six front teeth" as some of the fossil forms have three pairs of incisors. The pygmy hippopotamus was historically placed in the genus, but today is generally placed in its own genus. The core Asian members of the genus ranged from the Indian subcontinent to Southeast Asia, and are thought to have had an aquatic ecology similar to that of the living common hippopotamus. The last members of the genus became extinct during the Late Pleistocene, perhaps as recently as 15,000 years ago.
Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, Elomeryx, first appeared during the middle Eocene in Asia. They thrived in Africa and Eurasia, with a few species ultimately entering North America during the Oligocene. They died out in Europe and Africa during the Miocene, possibly due to a combination of climatic changes and competition with other artiodactyls, including pigs and true hippopotamuses. The youngest genus, Merycopotamus, died out in Asia during the late Pliocene, possibly for the same reasons. The family is named after the first genus discovered, Anthracotherium, which means "coal beast", as the first fossils of it were found in Paleogene-aged coal beds in France. Fossil remains of the anthracothere genus were discovered by the Harvard University and Geological Survey of Pakistan joint research project (Y-GSP) in the well-dated middle and late Miocene deposits of the Pothohar Plateau in northern Pakistan.
Kenyapotamus is a possible ancestor of living hippopotamuses that lived roughly 16 million to 8 million years ago during the Miocene epoch. Its name reflects that its fossils were first found in modern-day Kenya.
Whippomorpha or Cetancodonta is a group of artiodactyls that contains all living cetaceans and hippopotamuses. All whippomorphs are descendants of the last common ancestor of Hippopotamus amphibius and Tursiops truncatus. This makes it a crown group. Whippomorpha is a suborder within the order Artiodactyla. The placement of Whippomorpha within Artiodactyla is a matter of some contention, as hippopotamuses were previously considered to be more closely related to Suidae (pigs) and Tayassuidae (peccaries). Most contemporary scientific phylogenetic and morphological research studies link hippopotamuses with cetaceans, and genetic evidence has overwhelmingly supported an evolutionary relationship between Hippopotamidae and Cetacea. Modern whippomorphs all share a number of behavioural and physiological traits; such as a dense layer of subcutaneous fat and largely hairless bodies. They exhibit amphibious and aquatic behaviors and possess similar auditory structures.
The Cypriot pygmy hippopotamus is an extinct species of dwarf hippopotamus that inhabited the island of Cyprus from the Pleistocene until the early Holocene. One the smallest known hippopotamus species, it was comparable in size to the living pygmy hippopotamus though it was more closely related to the common hippopotamus, with its small body size a result of insular dwarfism. It represented one of only two large terrestrial mammals on Cyprus alongside the Cyprus dwarf elephant. The species became extinct around 12,000 years ago following the arrival of humans on Cyprus, and potential evidence of human hunting has been found at the Aetokremnos rockshelter on the southern coast of the island.
Merycopotamus is an extinct genus of Asian anthracothere that appeared during the Middle Miocene, and died out in the Late Pliocene. At the height of the genus' influence, species ranged throughout South Asia. With the extinction of the last species, M. dissimilis, the lineage of anthracotheres came to an end. Merycopotamus was closely related to the anthracothere genus Libycosaurus, which, unlike the former, never left Africa. In fact, some African fossils originally placed in Merycopotamus, but are now referred to Libycosaurus.
Archaeopotamus is an extinct genus of Hippopotamidae that lived between 7.5 and 2.58 million years ago in Africa and the Middle East. The genus was described in 2005 to encompass species of hippos that were previously grouped in Hexaprotodon.
Several species of Malagasy hippopotamus lived on the island of Madagascar but are now believed to be extinct. The animals were very similar to the extant hippopotamus and pygmy hippopotamus. The fossil record suggests that at least one species of hippopotamus lived until about 1,000 years ago and other evidence suggests that the species may have survived until much more recently. The taxonomy of these animals is not resolved and not widely studied.
Suinae is a subfamily of artiodactyl mammals that includes several of the extant members of Suidae and their closest relatives – the domestic pig and related species, such as babirusas. Several extinct species within the Suidae are classified in subfamilies other than Suinae. However, the classification of the extinct members of the Suoidea – the larger group that includes the Suidae, the peccary family (Tayassuidae), and related extinct species – is controversial, and different classifications vary in the number of subfamilies within Suidae and their contents. Some classifications, such as the one proposed by paleontologist Jan van der Made in 2010, even exclude from Suinae some extant taxa of Suidae, placing these excluded taxa in other subfamilies.
Hippopotamus laloumena is an extinct species of hippopotamus from Pleistocene and Holocene Madagascar, making it the oldest of Malagasy hippopotamus. H. laloumena was much larger than other Malagasy hippopotamus, but was still somewhat smaller than the common hippopotamus. However, little is known about the species because it was identified with only a lower jaw and limb bones. It was described in 1990 by French palaeontologists M. Faure and Guerin, the fossils recovered from a site near Mananjary on the east coast of Madagascar. The species name derives from Malagasy laloumena "hippopotamus".
Hippopotamus madagascariensis, the Madagascar or Madagascan dwarf hippopotamus, is an extinct species of hippopotamus, endemic to the island of Madagascar. Known only from bones, it is believed to have gone extinct sometime after 1500. It was one of three hippopotamus species, the Malagasy hippopotamuses, which were native to Madagascar and are all extinct.
Saotherium is an extinct genus of hippopotamid from the Early Pliocene of Africa, specifically Chad. It is represented by a single species, S. mingoz. The earliest fossils appear at the start of the Pliocene, while the latest are dated to about 4 mya.
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.
