Ancodonta is an infraorder of semiaquatic artiodactyl

ungulate Ungulates ( ) are members of the diverse clade Ungulata which primarily consists of large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses, and tapirs; and even-toed ungulates such as cattle, pigs, giraffes, cam ...

s including modern

hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...

and all

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s closer to hippos than to

cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

ns (

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

s). Ancodonts first appeared in the Middle Eocene, with some of the earliest representatives found in fossil deposits in

Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical United Nations geoscheme for Asia#South-eastern Asia, south-eastern region of Asia, consistin ...

. Throughout their evolutionary history they have occupied different browsing and grazing niches in

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago a ...

and

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. 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 The pygmy hippopotamus or pygmy hippo (''Choeropsis liberiensis'') is a small Hippopotamidae, hippopotamid which is native to the forests and swamps of West Africa, primarily in Liberia, with small populations in Sierra Leone, Guinea, and Ivory C ...

'' and ''

Hippopotamus The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...

''. The interrelationships within the ancodonts has been contended. The traditional notion is that there at minimum two families Anthracotheriidae and

Hippopotamidae Hippopotamidae is a family of stout, naked-skinned, and semiaquatic artiodactyl mammals, possessing three-chambered stomachs and walking on four toes on each foot. While they resemble pigs physiologically, their closest living relatives are t ...

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 The bothriodontines are a paraphyletic assemblage of anthracotheres that originated from Eurasia in the late middle Eocene (Bartonian). The group can be distinguished from other anthracothere lineages by their upper molars with the mesostyle tha ...

are among the closest to the ancestry of hippos, with the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

aged '' Epirigenys'' from Lokon, Turkana,

Kenya ) , national_anthem = "Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

being the sister taxon to hippos. In response of this many similar clade names have been used for this clade (Hippopotamoidea, Anthracotherioidea, and Hippopotamidamorpha). The placement of Ancodonta among the artiodactyls originally based on basic morphological work that they were the sister group to

pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...

s and peccaries, placed in the suborder Suiformes. However molecular work has found this not to be the case, as the closest relatives are the

cetacean Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

s. Cetaceans and ancodonts are now classified in the suborder Whippomorpha. This led to some theories that the last common ancestors of hippos and whales was a semiaquatic mammal, but in a 2015 genomic study that compared the genes responsible in aquatic adaptations within Whippomorpha found it to be the result of convergent evolution, as opposed to shared ancestry. This resolves the issue of how hippos and whales developed their aquatic adaptation despite modern hippos appearing much later in the fossil record than whales.

References

Eocene first appearances Whippomorphs Mammal infraorders {{eventoedungulate-stub