Anthracotheriidae is a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of extinct,

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 exta ...

-like 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, ...

s related to

es and

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. The oldest genus, ''

Elomeryx ''Elomeryx'' is an extinct genus of artiodactyl ungulate, and is among the earliest known anthracotheres. The genus was extremely widespread, first being found in Asia in the middle Eocene, in Europe during the latest Eocene, and having spread to ...

'', first appeared during the middle

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

in Asia. They thrived in Africa and Eurasia, with a few species ultimately entering North America during 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 t ...

. They died out in Europe and Africa during the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

, 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 The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

discovered, ''

Anthracotherium ''Anthracotherium'' (from el, ἄνθραξ , 'coal' and el, θηρίον 'beast') was a genus of extinct artiodactyl ungulate mammals, characterized by having 44 teeth, with five semi-crescentic cusps on the crowns of the upper molars. The g ...

'', which means "coal beast", as the first fossils of it were found in

Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya) to the beginning o ...

-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. In life, the average anthracothere would have resembled a skinny hippopotamus with a comparatively small, narrow head and most likely pig-like in general appearance. They had four or five toes on each foot, and broad feet suited to walking on soft mud. They had full sets of about 44 teeth with five semicrescentric cusps on the upper molars, which, in some species, were adapted for digging up the roots of aquatic plants.

Evolutionary relationships

Some skeletal characters of anthracotheres suggest they are related to hippos. The nature of the sediments in which they are fossilized implies they were amphibious, which supports the view, based on anatomical evidence, that they were ancestors of the hippopotamuses. In many respects, especially the anatomy of the lower jaw, ''Anthracotherium'', as with other members of the family, is allied to the hippopotamus, of which it is probably an ancestral form. However, one study suggests, instead of anthracotheres, another pig-like group of artiodactyls, called palaeochoerids, are the true

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

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 ar ...

. Recent evidence, gained from comparative gene sequencing, further suggests that hippos are the closest living relatives of whales, so, if anthracotheres are stem hippos, they would also be related to whales in a clade provisionally called Whippomorpha. However, the earliest known anthracotheres appear in the fossil record in the middle

, well after the archaeocetes had taken up totally aquatic lifestyles. Although phylogenetic analyses of molecular data on extant animals strongly support the notion that hippopotamids are the closest relatives of cetaceans (whales, dolphins and porpoises), the two groups are unlikely to be closely related when extant and extinct artiodactyls are analyzed. Cetaceans originated about 50 million years ago in south Asia, whereas the family Hippopotamidae is only 15 million years old, and the first hippopotamids are only 6 million years old. Yet, analyses of fossil clades have not resolved the issue of cetacean relations. Another study has offered a suggestion that anthracotheres are part of a clade that also consists of entelodonts (and even ''

Andrewsarchus ''Andrewsarchus'' () is an extinct genus of mammal that lived during the middle Eocene epoch in what is now Inner Mongolia, China. Only one species is usually recognized, ''A. mongoliensis'', known from a single skull of great size discovered ...

'') and that is a sister clade to other cetancodonts, with '' Siamotherium'' as the most basal member of the clade Cetacodontamorpha.

References

{{Taxonbar, from=Q574319 Piacenzian extinctions Eocene first appearances Prehistoric mammal families Taxa named by Joseph Leidy Paraphyletic groups