Anthracotheriidae is a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of extinct,

hippopotamus The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Sahar ...

-like

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...

s related to

es and

whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...

s. The oldest genus, '' Elomeryx'', first appeared during the middle

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

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 (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

. They died out in Europe and Africa during the

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

, possibly due to a combination of climatic changes and competition with other artiodactyls, including pigs and hippopotamuses. The youngest genus, ''

Merycopotamus ''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 and South East Asia (Indonesia ...

'', died out in Asia during the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

-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 The Pothohar Plateau (, : ''Pо̄ṭhoā̀r Paṭhār''; , ''Satāh Murtafā Pо̄ṭhohār''), also spelled Pothwar, is a plateau in the Sindh Sagar Doab, Sind Sagar Doab of northern Punjab, Pakistan, Punjab, Pakistan, located between the Indus ...

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 that instead of anthracotheres, another pig-like group of artiodactyls, the 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 are th ...

. 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 Whippomorpha or Cetancodonta is a suborder of artiodactyls that contains all living cetaceans (whales, dolphins, and porpoises) and the hippopotamids. This makes it a crown group. Whippomorpha is a suborder within the order Artiodactyla (even-t ...

. However, the earliest known anthracotheres appear in the fossil record in the middle

, well after the

archaeocetes Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is an obsolete paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include th ...

had already 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 the

Tethys Sea The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasia ...

between India and China, whereas the family Hippopotamidae is only 15 million years old, and the first Asian 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

entelodont Entelodontidae is an extinct family of pig-like artiodactyls (even-toed ungulates) which inhabited the Northern Hemisphere (Asia, Europe, and North America) from the late Eocene to the early Miocene epochs, about 38-19 million years ago. Their ...

s (and even ''

Andrewsarchus ''Andrewsarchus'' (), meaning "Roy Chapman Andrews, Andrews' ruler", is an extinct genus of artiodactyl that lived during the Eocene, Middle Eocene in what is now China. The genus was species description, first described by Henry Fairfield Osb ...

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

Cetacodontamorpha Cetancodontamorpha is a total clade of artiodactyls defined, according to Spaulding ''et al''., as Whippomorpha "plus all extinct taxa more closely related to extant members of Whippomorpha than to any other living species". Whippomorpha is th ...

References

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