Hippopotamidae

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Hippopotamidae

Hippopotamuses are the members of the family

Family (biology)

In biological classification, family is a taxonomic rank. Exact details of formal nomenclature depend on the Nomenclature Codes which applies....
Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.

opotamids are large mammals, with short, stumpy legs, and barrel-shaped bodies. They have large heads, with broad mouths, and nostrils placed at the top of the snout. Like pigs, they have four toes, but unlike pigs, all of the toes are used in walking.

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Encyclopedia

Hippopotamuses are the members of the family

Family (biology)

Characteristics

Hippopotamids are large mammals, with short, stumpy legs, and barrel-shaped bodies. They have large heads, with broad mouths, and nostrils placed at the top of the snout. Like pigs, they have four toes, but unlike pigs, all of the toes are used in walking. Hippopotamids are unguligrade, although, unlike most other such animals, they have no hooves, instead using a pad of tough connective tissue. Their stomach has three chambers, but they are not true ruminant

Ruminant

Physiologically, a ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach, known as the rumen, then regurgitating the semi-digested mass, now known as cud, and chewing it again....
s.

The living species are both smooth-skinned, and lack both sebaceous gland

Sebaceous gland

Sebaceous glands are small glands in the skin which secrete an oily matter in the hair follicles to lubricate the skin and hair of animals. In humans, they are found in greatest abundance on the face and scalp, though they are distributed throughout all skin sites except the palms and soles....
s and sweat gland

Sweat gland

The skin contains two different groups of sweat glands: apocrine sweat glands and merocrine sweat glands. Both gland types contain myoepithelial cells , specialized epithelial cells located between the gland cells and the underlying basal lamina....
s. The outer epidermis

Epidermis (skin)

The epidermis is the outermost layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment....
is relatively thin, so that hippos dehydrate rapidly in dry environments.

Both the incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below....
s and canines are large and tusk-like, although the canine tusks are by far the largest. The tusks grow throughout life. The postcanine teeth are large and complex, suited for chewing the plant matter that composes their diet. The number of incisors varies even within the same species, but the general dental formula

Dentition

Dentition is the tooth development of teeth and their arrangement in the mouth.All mammals except the monotremes, the xenarthrans, the pangolins, and the cetaceans have up to four distinct types of teeth, with a maximum number for each....
is:

Evolution

The hippopotamids are descended from the anthracotheres, a family of semi-aquatic artiodactyls that appeared sometime during the late Eocene

Eocene

The Eocene Geologic time scale is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era....
, and are popularly thought to have resembled small- or narrow-headed hippos. More specifically, the hippos split off from the anthracotheres some time during the Miocene

Miocene

The Miocene is a Geologic time scale of the Neogene period and extends from about 23.03 to 5.33 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified but the exact dates of the start and end of the period are uncertain....
. After the appearance of the true hippopotamids, the anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, Merycopotamus

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 southern Asia....
, died out in the early Pliocene
Pliocene

The Pliocene epoch is the period in the geologic timescale that extends from 5.332 million to 1.806 million years before present.The Pliocene is the second epoch of the Neogene period in the Cenozoic era....
of Africa.

There were once many species of hippopotamid, but only two survive today: Hippopotamus amphibius, and Choeropsis liberiensis. They are the last survivors of two major evolution
Evolution

In biology, evolution is change in the heritability trait of a population of organisms from one generation to the next. These changes are caused by a combination of three main processes: variation, reproduction, and selection....
ary lineages, the hippos proper and the pygmy hippos, respectively; these lineages could arguably be considered subfamilies but their relationships to each other - apart from being fairly distant relatives - are not well resolved.

The enigmatic Miocene
Miocene

The Miocene is a Geologic time scale of the Neogene period and extends from about 23.03 to 5.33 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified but the exact dates of the start and end of the period are uncertain....
Kenyapotamus

Kenyapotamus

Kenyapotamus is an extinct ancestor of the modern Hippopotamus which lived in Africa roughly 16 million to 8 million years ago during the Miocene epoch....
is insufficiently known to be assigned a place in the hippo phylogeny with any degree of certainty. In addition, the genus
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
Hexaprotodon

Hexaprotodon

Hexaprotodon is a genus of Hippopotamidae that is sometimes applied to the pygmy hippopotamus. Pygmy hippos may be classified as either Choeropsis liberiensis or Hexaprotodon liberiensis....
, in a sense now restricted to an extinct group of animals once living around the northern and northeastern Indian Ocean
Indian Ocean

The Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface. It is bounded on the north by Asia ; on the west by Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean ....
, which formerly included most ancient hippos, turned out to be paraphyletic.

Species
The systematics and taxonomy
Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
used here mostly follows the review of Boisserie (2005).

Genus Hippopotamus
Hippopotamus (genus)

Hippopotamus is the name of a genus consisting of one extant species, Hippopotamus amphibius, also known as the Hippopotamus, and several extinct species....
- true hippopotami
Hippopotamus amphibius - Hippopotamus
Hippopotamus

The hippopotamus or hippo is a large, mostly herbivore African mammal, one of only two Extant taxon species in the scientific classification Hippopotamidae ....
Hippopotamus antiquus - European Hippopotamus
European Hippopotamus

The European Hippopotamus was a species of hippopotamus that ranged across Europe, becoming extinct some time before the last Wisconsin glaciation at the end of the Pleistocene epoch....
(prehistoric)
Hippopotamus creutzburgi - Cretan Dwarf Hippopotamus
Cretan Dwarf Hippopotamus

The Cretan Dwarf Hippopotamus or Hippopotamus creutzburgi is an extinct Hippopotamidae. It lived during the Pleistocene on Crete.Two subspecies have been named: Hippopotamus creutzburgi creutzburgi and Hippopotamus creutzburgi parvus....
(prehistoric)
Hippopotamus minor - Cyprus Dwarf Hippopotamus
Cyprus Dwarf Hippopotamus

The Cyprus Dwarf Hippopotamus or Cypriot Pygmy Hippopotamus is an extinct species of hippo that inhabited the island of Cyprus until the early Holocene....
(prehistoric)
Hippopotamus melitensis - Maltese Hippopotamus
Maltese Hippopotamus

Hippopotamus melitensis is an extinct Hippopotamidae. It lived during the Pleistocene on Malta. The absence of predators led to the Insular_dwarfism of the hippos....
(prehistoric)
Hippopotamus pentlandi - Sicilian Hippopotamus
Sicilian Hippopotamus

Hippopotamus pentlandi is an extinct Hippopotamidae. It lived during the Pleistocene on Sicily. It was the smallest of the dwarf hippos known from the Mediterranean of the Pleistocene weighing in at 320 kg....
(prehistoric)
Hippopotamus lemerlei - Lemerle's Hippopotamus or Madagascan Dwarf Hippopotamus (prehistoric)
Hippopotamus laloumena - Lesser Madagascar Hippopotamus (prehistoric)
Hippopotamus gorgops - Gorgon-eyed Hippopotamus
Hippopotamus gorgops

Hippopotamus gorgops is an extinct species of hippopotamus. It first appeared in Africa during the late Miocene, and eventually migrated into Europe during the early Pliocene ....
(fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Tentatively placed into Hippopotamus:
Hippopotamus karumensis (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hippopotamus aethiopicus (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hippopotamus protamphibius (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hippopotamus coryndoni (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hippopotamus afarensis (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
) - formerly genus Trilobophorus
Genus Hexaprotodon
Hexaprotodon

Hexaprotodon is a genus of Hippopotamidae that is sometimes applied to the pygmy hippopotamus. Pygmy hippos may be classified as either Choeropsis liberiensis or Hexaprotodon liberiensis....
- hexaprotodons or Asian hippopotami

Hexaprotodon palaeindicus - Indian Hippopotamus (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hexaprotodon namadicus - Lesser Indian Hippopotamus (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
) - possibly same as H. palaeindicus
Hexaprotodon bruneti - Afar Hexaprotodon (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hexaprotodon sivalensis - Sivalik Hippopotamus (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Hexaprotodon sp. - Myanmar Hippopotamus (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
and some Indonesia
Indonesia

The Republic of Indonesia , is a transcontinental country in Southeast Asia and Oceania. Comprising Islands of Indonesia, it is the world's largest Archipelago state....
n species from the Pleistocene
Pleistocene

The Pleistocene is the epoch from 1.8 million to 10,000 years Before Present covering the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

Genus Archaeopotamus
Archaeopotamus

Archaeopotamus is an extinct genus of Hippopotamidae that lived between 7.5 and 1.8 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....
- formerly included in Hexaprotodon
Archaeopotamus harvardi (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
Archaeopotamus lothagamensis (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)
and 1-2 undescribed species

Genus Choeropsis
Choeropsis

Choeropsis is a genus of pygmy hippopotamuses.There are two known species, one of which is extinct:* Pygmy Hippopotamus ? Choeropsis liberiensis...
- pygmy hippopotami

Choeropsis liberiensis - Pygmy Hippopotamus
Pygmy Hippopotamus

The pygmy hippopotamus is a large mammal native to the forests and swamps of western Africa . The pygmy hippo is reclusive and nocturnal. It is one of only two extant species in the Hippopotamidae family , the other being its much larger cousin the common hippopotamus....
Choeropsis madagascariensis - Madagascan Pygmy Hippopotamus (prehistoric)

Genus Saotherium - formerly included in Hexaprotodon

Saotherium mingoz (fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
)