|Family:|| Hippopotamidae |
† Trilobophorous Geze, 1985
Hippopotamids are 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 the cetaceans. Hippopotamids constitute the family Hippopotamidae.
There are two living species of hippopotamid in two genera; the pygmy hippo, Choeropsis liberiensis of the forests of west Africa, and the common hippo, Hippopotamus amphibius .
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 their snouts. 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 on each foot. Their stomachs have three chambers, but they are not true ruminants.
The living species are smooth-skinned and lack both sebaceous glands and sweat glands. The outer epidermis is relatively thin, so hippos dehydrate rapidly in dry environments.
Both the incisors and canines are large and tusk-like, although the canine tusks are by far the larger. The tusks grow throughout life. The postcanine teeth are large and complex, suited for chewing the plant matter that comprises their diets. The number of incisors varies even within the same species, but the general dental formula is given in the table below:
The hippopotamids are descended from the anthracotheres, a family of semiaquatic and terrestrial artiodactyls that appeared in the late Eocene, and are thought to have resembled small- or narrow-headed hippos. The hippos split off from the anthracotheres some time during the Miocene. After the appearance of the hippopotamids, the remaining anthracotheres went into a decline brought about by a combination of climatic change and competition with their descendants, until the last genus, Merycopotamus , died out in the early Pliocene of India.
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 evolutionary lineages, the hippos proper and the pygmy hippos, respectively; these lineages could arguably be considered subfamilies, but their relationship to each other – apart from being fairly distant relatives – is not well resolved.
The enigmatic Miocene Kenyapotamus is insufficiently known to be assigned a place in the hippo phylogeny with any degree of certainty. In addition, the genus Hexaprotodon , in a sense now restricted to an extinct group of animals once living around the northern and northeastern Indian Ocean, which formerly included most ancient hippos, has turned out to be paraphyletic.
Hippopotamidae's placement within Artiodactyla can be represented in the following cladogram:
The lower canine teeth of hippopotamids are similar in function and structure to the tusks of elephants. While hippopotamids and elephants are only very distantly related within the Mammalia, the lower canine teeth of both groups are long and have a slight curve, and species of both families use this structure when fighting.
The systematics and taxonomy used here mostly follows the review of Boisserie (2005) and the American Society of Mammalogists.
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, camels, sheep, deer, and hippopotamuses. Cetaceans such as whales, dolphins, and porpoises are also classified as even-toed ungulates, 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.
The hippopotamus, also called the hippo, common hippopotamus or river hippopotamus, is a large, mostly herbivorous, semiaquatic mammal and ungulate native to sub-Saharan Africa. It is one of only two extant species in the family Hippopotamidae, the other being the pygmy hippopotamus. The name comes from the ancient Greek for "river horse" (ἱπποπόταμος).
The even-toed ungulates are ungulates—hoofed animals—which bear weight equally on two of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, odd-toed ungulates bear weight on an odd number of the five toes. Another difference between the two with the exception of Suina many other even-toed ungulates digest plant cellulose in one or more stomach chambers rather than in their intestine as the odd-toed ungulates do.
The pygmy hippopotamus 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.
Suidae is a family of artiodactyl mammals which are commonly called pigs, hogs, or boars. In addition to numerous fossil species, 18 extant species are currently recognized, classified into between four and eight genera. Within this family, the genus Sus includes the domestic pig, Sus scrofa domesticus or Sus domesticus, and many species of wild pig from Europe to the Pacific. Other genera include babirusas and warthogs. All suids, or swine, are native to the Old World, ranging from Asia to Europe and Africa.
Hippopotamus is a genus of artiodactyl mammals consisting of one extant species, Hippopotamus amphibius, also known as the 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.
Aquatic and semiaquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the European otter. They are not a taxon and are not unified by any distinct biological grouping, but rather their dependence on and integral relation to aquatic ecosystems. The level of dependence on aquatic life varies greatly among species. Among freshwater taxa, the Amazonian manatee and river dolphins are completely aquatic and fully dependent on aquatic ecosystems. Semiaquatic freshwater taxa include the Baikal seal, which feeds underwater but rests, molts, and breeds on land; and the capybara and hippopotamus which are able to venture in and out of water in search of food.
Hippopotamus gorgops is an extinct species of hippopotamus. It first appeared in Africa during the late Pliocene, and eventually migrated into Europe during the early Pleistocene. It became extinct during the Middle Pleistocene. Fossil records found at Ubeidiya, Israel suggested that they migrated out of Africa around 1.6 million years ago. Some have speculated that H. gorgops and H. behemoth are actually the same species given their similar sizes and where they have been found scientist believe it behaved almost identical to modern day hippopotamuses.
Hexaprotodon is a genus of Hippopotamidae that was often applied to the pygmy hippopotamus before its reclassification into the genus Choeropsis. The name Hexaprotodon means "six front teeth" as some of the fossil forms have three pairs of incisors. The genus sensu lato, including African taxa, has been suggested to be paraphyletic with respect to both species of living hippopotamus. The uncontroversial, core Asian members of the genus most closely related to the type H. sivalensis were widespread throughout the Late Neogene and Quaternary of South and Southeast Asia, with the oldest records coming from the Late Miocene Siwaliks. They were extinct by the Late Middle Pleistocene in Southeast Asia, but survived in India until the terminal Pleistocene, with the latest dates being around 16,467–15,660 cal years Before Present.
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. 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 animals that contains all living cetaceans and hippopotamuses, as well as their extinct relatives, I.E Entelodonts, Andrewsarchus. 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 Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.
The Cyprus dwarf hippopotamus or Cypriot pygmy hippopotamus is an extinct species of hippopotamus that inhabited the island of Cyprus until the early Holocene.
Lemerle's dwarf hippopotamus is an extinct species of Malagasy hippopotamus.
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. The various species are believed to have survived into the Holocene epoch.
Hippopotamus laloumena is an extinct species of hippopotamus from Holocene Madagascar. H. laloumena was much larger than other Malagasy hippos, 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 dwarf hippopotamus or Madagascan dwarf hippopotamus, is a recently extinct species of Malagasy hippopotamus.
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.