Even-toed Ungulate on:
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The even-toed ungulates (Artiodactyla , ) are
Two formerly widespread, but now extinct, families of even-toed ungulates were
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—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
, or pointing posteriorly. By contrast, odd-toed ungulate
Odd-toed ungulates, mammals which constitute the taxonomic order Perissodactyla (, ), are animals—ungulates—who have reduced the weight-bearing toes to three (rhinoceroses and tapirs, with tapirs still using four toes on the front legs) o ...
s bear weight on an odd number of the five toes. Another difference between the two is that many other even-toed ungulates (with the exception of Suina) digest plant cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
in one or more stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
chambers rather than in their intestine as the odd-toed ungulates do.
Cetaceans (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, dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s, and porpoises) evolved from even-toed ungulates, and are therefore often classified under the same taxonomic branch because a species cannot outgrow its evolutionary ancestry; some modern taxonomists combine the two under the name Cetartiodactyla , while others opt to include cetaceans in the already-existing Artiodactyla.
The roughly 270 land-based even-toed ungulate species include 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, peccaries
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North ...
, 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 ...
es, antelopes, deer
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the re ...
, giraffes, camels, llama
The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a meat and pack animal by Andean cultures since the Pre-Columbian era.
Llamas are social animals and live with others as a herd. Their wool is soft ...
s, alpaca
The alpaca (''Lama pacos'') is a species of South American camelid mammal. It is similar to, and often confused with, the llama. However, alpacas are often noticeably smaller than llamas. The two animals are closely related and can success ...
s, sheep
Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...
, goat
The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...
s, and cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
. Many are herbivores, but suids are omnivorous, while cetaceans are almost exclusively carnivorous. Many of these are of great dietary, economic, and cultural importance to humans.
Evolutionary history
The oldest fossils of even-toed ungulates date back to the earlyEocene
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'', " ...
(about 53 million years ago). Since these findings almost simultaneously appeared in Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
, Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
, and North America, it is very difficult to accurately determine the origin of artiodactyls. The fossils are classified as belonging to the family Dichobunidae
Dichobunidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia. The Dichobunidae include some of the earliest known artiodactyls, such as '' Diacodexis''.
Description ...
; their best-known and best-preserved member is ''Diacodexis
''Diacodexis'' is an extinct genus of small herbivore mammals belonging to the family Dichobunidae which lived in North America, Europe and Pakistan from 55.4 mya to 46.2 mya and existing for approximately .
Description
''Diacodexis'' is the ...
''. These were small animals, some as small as a hare, with a slim build, lanky legs, and a long tail. Their hind legs were much longer than their front legs. The early to middle Eocene saw the emergence of the ancestors of most of today's mammals.
Two formerly widespread, but now extinct, families of even-toed ungulates were Entelodont
Entelodontidae, the entelodonts, are 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 Middle Miocene epochs, about 38-19 millio ...
idae and Anthracotheriidae
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 Eura ...
. Entelodonts existed from the middle Eocene to the early Miocene
The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages.
The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...
in 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 ...
and North America. They had a stocky body with short legs and a massive head, which was characterized by two humps on the lower jaw bone. Anthracotheres had a large, porcine (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 ...
-like) build, with short legs and an elongated muzzle. This group appeared in the middle Eocene up until the Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58late Miocene and occupied Africa and Asia—they never got to the Americas.
The camels (
South America was settled by even-toed ungulates only in the Pliocene, after the
The classification of artiodactyls was hotly debated because the ocean-dwelling cetaceans evolved from the land-dwelling even-toed ungulates. Some
In the 1990s, biological systematics used not only morphology and fossils to classify organisms, but also 
The oldest cetaceans date back to the early Eocene (53 million years ago), whereas the oldest known hippopotamus dates back only to the Miocene (15 million years ago). 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. Research is therefore focused on anthracotheres (family Anthracotheriidae); one dating from the Eocene to Miocene was declared to be "hippo-like" upon discovery in the 19th century. A study from 2005 showed that the anthracotheres and hippopotamuses have very similar
Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other
The four summarized Artiodactyla taxa are divided into ten extant families:
* The camelids (
Artiodactyls are generally
Even-toed ungulates bear their name because they have an even number of
File:Hippopotamus-foot.jpg, Hippopotamuses have all four toes pointing out.
File:Sow-foot.jpg, For pigs and other biungulates the second and fifth toes are directed backwards.
File:Dromedar-Fuss.jpg, When camels have only two toes present, the claws are transformed into nails.
When camels have only two toes present, the 
In even-toed ungulates, the bones of the stylopodium (upper arm or thigh bone) and
Four families of even-toed ungulates have cranial appendages. These
palmate
as in the
There are two trends in terms of teeth within Artiodactyla. The Suina and hippopotamuses have a relatively large number of teeth (with some pigs having 44); their dentition is more adapted to a squeezing mastication, which is characteristic of omnivores. Camels and ruminants have fewer teeth; there is often a yawning
The 
The social behavior of even-toed ungulates varies from species to species. Generally, there is a tendency to merge into larger groups, but some live alone or in pairs. Species living in groups often have a hierarchy, both among males and females. Some species also live in harem groups, with one male, several females, and their common offspring. In other species, the females and juveniles stay together, while males are solitary or live in bachelor groups and seek out females only during
Generally, even-toed ungulates tend to have long gestation periods, smaller litter sizes, and more highly developed newborns. As with many other mammals, species in
Artiodactyls have been hunted by primitive humans for various reasons: for meat or
The endangerment level of each even-toed ungulate is different. Some species are
Ungulate Taxonomy: A new perspective from Groves and Grubb (2011)
{{DEFAULTSORT:Even-Toed Ungulate Extant Ypresian first appearances
Tylopoda
Tylopoda (meaning "calloused foot") is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels ...
) were, during large parts of the Cenozoic, limited to North America; early forms like Cainotheriidae
Cainotheriidae is an extinct family of artiodactyls known from the Late Eocene to Middle Miocene of Europe. They are mostly found preserved in karstic deposits.
These animals were small in size, and generally did not exceed in height at the ...
occupied Europe. Among the North American camels were groups like the stocky, short-legged Merycoidodontidae
Merycoidodontoidea, sometimes called "oreodonts" or "ruminating hogs", is an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were gen ...
. They first appeared in the late Eocene and developed a great diversity of species in North America. Only in the late Miocene or early Pliocene did they migrate from North America into Eurasia. The North American varieties became extinct around 10,000 years ago.
Suina (including 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) have been around since the Eocene. In the late Eocene or the Oligocene, two families stayed in Eurasia and Africa; the peccaries
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North ...
, which became extinct in the Old World, exist today only in the Americas
The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World.
Along with th ...
.
South America was settled by even-toed ungulates only in the Pliocene, after the land bridge
In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea leve ...
at the Isthmus of Panama formed some three million years ago. With only the peccaries, lamoids (or llama
The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a meat and pack animal by Andean cultures since the Pre-Columbian era.
Llamas are social animals and live with others as a herd. Their wool is soft ...
s), and various species of capreoline deer, South America has comparatively fewer artiodactyl families than other continents, except Australia, which has no native species.
Taxonomy and phylogeny
The classification of artiodactyls was hotly debated because the ocean-dwelling cetaceans evolved from the land-dwelling even-toed ungulates. Some semiaquatic
In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below.
Semiaquatic animals
Semi aquatic animals include:
* Ve ...
even-toed ungulates (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 ...
es) are more closely related to the ocean-dwelling cetaceans than to the other even-toed ungulates.
This makes the Artiodactyla as traditionally defined a paraphyletic taxon, since it includes animals descended from a common ancestor
Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
, but does not include all of its descendants. Phylogenetic classification only recognizes monophyletic taxa; that is, groups that descend from a common ancestor and include all of its descendants. To address this problem, the traditional order Artiodactyla and infraorder Cetacea are sometimes subsumed into the more inclusive Cetartiodactyla taxon. An alternative approach is to include both land-dwelling even-toed ungulates and ocean-dwelling cetaceans in a revised Artiodactyla taxon.
Classification
* Order Artiodactyla/Clade Cetartiodactyla **SuborderTylopoda
Tylopoda (meaning "calloused foot") is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels ...
*** Family Anoplotheriidae
Anoplotheriidae is an extinct family of even-toed ungulates ( order Artiodactyla). They were endemic to Western Europe during the Eocene and Oligocene epochs about 48—23 million years ago (Mya), existing for about 25 million years. They disa ...
?
*** Family Cainotheriidae
Cainotheriidae is an extinct family of artiodactyls known from the Late Eocene to Middle Miocene of Europe. They are mostly found preserved in karstic deposits.
These animals were small in size, and generally did not exceed in height at the ...
*** Family Merycoidodontidae
Merycoidodontoidea, sometimes called "oreodonts" or "ruminating hogs", is an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were gen ...
*** Family Agriochoeridae
*** Family Camelidae
Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, ...
: camels and lamoids or llama
The llama (; ) (''Lama glama'') is a domesticated South American camelid, widely used as a meat and pack animal by Andean cultures since the Pre-Columbian era.
Llamas are social animals and live with others as a herd. Their wool is soft ...
s (7 extant and 13 extinct species)
*** Family Oromerycidae
Oromerycidae is a small (both in size and diversity), extinct family (biology), family of artiodactyls (even-toed hoofed mammals) closely related to living camels, known from the early to late Eocene of western North America.
Oromerycids are pl ...
*** Family Xiphodontidae
Xiphodontidae is an extinct family of even-toed ungulates (order Artiodactyla), endemic to Europe during the Eocene 40.4—33.9 million years ago, existing for about 7.5 million years. They were, most likely, all terrestrial herbivore ...
** Clade Artiofabula
Artiofabula is a clade made up of the Suina and the Cetruminantia. The clade was found in molecular phylogenetic analyses and contradicted traditional relationships based on morphological analyses.
Etymology
The name Artiofabula was derived ...
***Suborder Suina
**** Family Suidae: pigs (19 species)
**** Family Tayassuidae: peccaries (4 species)
**** Family Sanitheriidae
Sanitheriidae were extinct family of suoid artiodactyl ungulates that were once widely distributed in Africa, Europe, and South Asia, existing from the Early Miocene to the Middle Miocene. Unlike pigs and peccaries, the dentition and limb mor ...
****Family Doliochoeridae
Doliochoeridae is an extinct family of suoid artiodactyl ungulates that were once widely distributed in Eurasia and Africa from the Early Oligocene to the Late Miocene. Often referred in the past as Old World peccaries, the doliochoerids are now ...
*** Clade Cetruminantia
The Cetruminantia are a clade made up of the Cetancodontamorpha (or Whippomorpha) and their closest living relatives, the Ruminantia.
Cetruminantia's placement within Artiodactyla can be represented in the following cladogram: (see fig S1 ...
****Clade Cetancodontamorpha
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". Attempts have been m ...
***** Genus '' Andrewsarchus''?
***** Family Entelodontidae
***** Suborder Whippomorpha
Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans (whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives, i.e. Entelodonts and Andrewsarchus. All Whippomorphs are descendants of the la ...
****** Family Raoellidae
The Raoellidae, previously grouped within Helohyidae, are an extinct family of semiaquatic digitigrade artiodactyls in the clade Whippomorpha. Fossils of raoellids are found in Eocene strata of South and Southeast Asia.
An exceptionally complet ...
****** Superfamily Dichobunoidea – paraphyletic to Cetacea and Raoellidae
******* Family Dichobunidae
Dichobunidae is an extinct family of basal artiodactyl mammals from the early Eocene to late Oligocene of North America, Europe, and Asia. The Dichobunidae include some of the earliest known artiodactyls, such as '' Diacodexis''.
Description ...
******* Family Helohyidae
Helohyidae were a group of artiodactyl mammals.
They were most prominent in the mid-to-upper Eocene (~50 to 39 million years ago).
Description
Helohyidae share vague similarities to present-day pigs, though were slimmer in build. They possess ...
******* Family Choeropotamidae
Choeropotamidae, also known as Haplobunodontidae, are a family of extinct mammals, extinct herbivores, belonging to artiodactyls. They lived between the lower/middle Eocene and lower Oligocene (about 48 - 30 million years ago) and their remai ...
******* Family Cebochoeridae
******* Family Mixtotheriidae
****** Infraorder Ancodonta
Ancodonta is an infraorder of semiaquatic artiodactyl ungulates including modern hippopotamus and all mammals closer to hippos than to cetaceans (whales). Ancodonts first appeared in the Middle Eocene, with some of the earliest representatives ...
******* Family Anthracotheriidae
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 Eura ...
– paraphyletic to Hippopotamidae
******* Family 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 ...
: hippos (two species)
****** Infraorder Cetacea: whales (about 90 species)
*******Parvorder Archaeoceti
Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include the initial ...
******** Family Pakicetidae
Pakicetidae ("Pakistani whales") is an extinct family of Archaeoceti (early whales) that lived during the Early Eocene in Pakistan.
Description
described the first pakicetid, ''Ichthyolestes'', but at the time they did not recognize it as a cet ...
******** Family Ambulocetidae
Ambulocetidae is a family of early cetaceans from Pakistan. The genus '' Ambulocetus'', after which the family is named, is by far the most complete and well-known ambulocetid genus due to the excavation of an 80% complete specimen of ''Ambulocet ...
******** Family Remingtonocetidae
Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg.
Description
Remingtonocetids have long and narrow skulls with the external nare openings located ...
******** Family Basilosauridae
Basilosauridae is a family of extinct cetaceans. They lived during the middle to the early late Eocene and are known from all continents, including Antarctica. They were probably the first fully aquatic cetaceans.Buono M, Fordyce R.E., Marx F.G. ...
******* Parvorder Mysticeti: baleen whales
******** Superfamily Balaenoidea: right whales
********* Family Balaenidae: greater right whales (four species)
********* Family Cetotheriidae
Cetotheriidae is a family of baleen whales (parvorder Mysticeti). The family is known to have existed from the Late Oligocene to the Early Pleistocene before going extinct. Although some phylogenetic studies conducted by recovered the livin ...
: pygmy right whale
The pygmy right whale (''Caperea marginata'') is a species of baleen whale. It may be a member of the cetotheres, a family of baleen whales which until 2012 were thought to be extinct; ''C. marginata'' has otherwise been considered the monotyp ...
(one species)
******** Superfamily Balaenopteroidea: large baleen whales
********* Family Balaenopteridae: slender-back rorquals and humpback whale
The humpback whale (''Megaptera novaeangliae'') is a species of baleen whale. It is a rorqual (a member of the family Balaenopteridae) and is the only species in the genus ''Megaptera''. Adults range in length from and weigh up to . The hu ...
(eight species)
********* Family Eschrichtiidae: gray whale (one species)
******* Parvorder Odontoceti: toothed whales
******** Superfamily Delphinoidea
Delphinoidea is the largest group of toothed whales with 66 genera in 6 families. The largest living member of the superfamily is the killer whale, which can reach 6 tons, while the smallest is the vaquita.
Taxonomy
Based on McGowen ''et al''., ...
: oceanic dolphin
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...
s, porpoises, and others
********* Family Delphinidae
Oceanic dolphins or Delphinidae are a widely distributed family of dolphins that live in the sea. Close to forty extant species are recognised. They include several big species whose common names contain "whale" rather than "dolphin", such as the ...
: oceanic true dolphins (38 species)
********* Family Monodontidae
The cetacean family Monodontidae comprises two living whale species, the narwhal and the beluga whale and at least four extinct species, known from the fossil record. Beluga and Narwhal are native to coastal regions and pack ice around the Arctic ...
: Arctic whales; narwhal and beluga The beluga whale (/bɪˈluːɡə/) (Delphinapterus leucas) is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the wh ...
(two species)
********* Family Phocoenidae
Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals ...
: porpoises (six species)
******** Superfamily Physeteroidea
Physeteroidea is a superfamily that includes three extant species of whales: the sperm whale, in the genus ''Physeter'', and the pygmy sperm whale and dwarf sperm whale, in the genus ''Kogia''. In the past, these genera have sometimes been unite ...
: sperm whales
The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus '' Physeter'' and one of three extant species in the sperm whale fam ...
********* Family Kogiidae: lesser sperm whales (two species)
********* Family Physeteridae: sperm whale (one species)
******** Superfamily Platanistoidea
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
: river dolphin
River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant riv ...
s
********* Family Iniidae
Iniidae is a family of river dolphins containing one living genus, ''Inia'', and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.
Iniidae a ...
: South American river dolphins (two species)
********* Family Lipotidae
Lipotidae is a family of river dolphins containing the possibly extinct baiji of China and the fossil genus ''Parapontoporia'' from the Late Miocene and Pliocene of the Pacific coast of North America. The genus '' Prolipotes'', which is based on ...
: Chinese river dolphin
The baiji (; IPA: ; ''Lipotes vexillifer'', ''Lipotes'' meaning "left behind" and ''vexillifer'' "flag bearer") is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolph ...
(one species, possibly extinct)
********* Family Platanistidae: South Asian river dolphin
South Asian river dolphins are toothed whales in the genus ''Platanista'', which inhabit fresh water habitats in the northern Indian subcontinent. They were historically considered to be one species (''P. gangetica'') with the Ganges river dol ...
(one species)
********* Family Pontoporiidae: La Plata dolphin (one species)
******** Superfamily Ziphioidea
********* Family Ziphidae: beaked whale
Beaked whales (systematic name Ziphiidae) are a family of cetaceans noted as being one of the least known groups of mammals because of their deep-sea habitat and apparent low abundance. Only three or four of the 24 species are reasonably well-k ...
s (22 species)
**** Clade Ruminantia
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
morpha
***** Suborder Ruminantia
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
****** Infraorder Tragulina
Tragulina (also known as Traguliformes) is an infraorder of even-toed ungulates. Only the chevrotains survive to the present, including the genera '' Tragulus'' (the mouse deer) and ''Hyemoschus'', all within the family Tragulidae.
Taxonomy and ...
******* Family Amphimerycidae
******* Family Prodremotheriidae
******* Family Protoceratidae
Protoceratidae is an extinct family of herbivorous North American artiodactyls (even-toed ungulates) that lived during the Eocene through Pliocene at around 46.2—4.9 Mya, existing for about 41 million years.
Classification
Protoceratidae was ...
******* Family Hypertragulidae
Hypertragulidae is an extinct family of artiodactyl ungulates that lived in North America, Europe, and Asia from the Eocene until the Miocene, living 46.2—13.6 million years ago, existing for about 33 million years.
The Hypertragulidae are ...
******* Family Praetragulidae
******* Family Tragulidae
The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star.
Computer scientists and mathematicians often v ...
: chevrotains (ten species)
******* Family Archaeomerycidae
******* Family Lophiomerycidae
****** Infraorder Pecora
Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, ''Hydropotes'' and '' Moschus''. The name “Pec ...
******* Family Gelocidae
The Gelocidae are an extinct group of hornless ruminants, ruminantia that are estimated to have lived during the Eocene and Oligocene epochs, from 36 MYA (unit), MYA to 6 MYA. The family generally includes extinct hornless ruminants which do not ...
******* Family Palaeomerycidae
******* Family Antilocapridae
The Antilocapridae are a family of artiodactyls endemic to North America. Their closest extant relatives are the giraffids with which they comprise the superfamily Giraffoidea. Only one species, the pronghorn (''Antilocapra americana''), is ...
: pronghorn
The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American a ...
(one species)
******* Family Climacoceratidae
Climacoceratidae is a family of superficially deer-like artiodactyl ungulates which lived in the Miocene epoch in Africa. They are close to the ancestry of giraffes, with some genera, such as '' Prolibytherium'', originally classified as giraffes ...
******* Family Giraffidae
The Giraffidae are a family of ruminant artiodactyl mammals that share a common ancestor with deer and bovids. This family, once a diverse group spread throughout Eurasia and Africa, presently comprises only two extant genera, the giraffe (one ...
: okapi
The okapi (; ''Okapia johnstoni''), also known as the forest giraffe, Congolese giraffe, or zebra giraffe, is an artiodactyl mammal that is endemic to the northeast Democratic Republic of the Congo in central Africa. It is the only species ...
and four species of giraffe (five species total)
******* Family Hoplitomerycidae
''Hoplitomeryx'' is a genus of extinct deer-like ruminants which lived on the former Gargano Island during the Miocene and the Early Pliocene, now a peninsula on the east coast of South Italy. ''Hoplitomeryx'', also known as "prongdeer", ha ...
******* Family Cervidae
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reind ...
: deer
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the re ...
(49 species)
******* Family Leptomerycidae
******* Family Moschidae
Moschidae is a family of pecoran even-toed ungulates, containing the musk deer (''Moschus'') and its extinct relatives. They are characterized by long 'saber teeth' instead of horns, antlers or ossicones, modest size (''Moschus'' only reaches ; ...
: musk deer (seven species)
******* Family Bovidae
The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, and caprines. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, t ...
: cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
, buffalo, goat-antelope
The subfamily Caprinae, also sometimes referred to as the tribe Caprini, is part of the ruminant family Bovidae, and consists of mostly medium-sized bovids. A member of this subfamily is called a caprine, or, more informally, a goat-antelope (a ...
, antelope, and others (135 species)
Research history
In the 1990s, biological systematics used not only morphology and fossils to classify organisms, but also molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...
. Molecular biology involves sequencing an organism's DNA and RNA and comparing the sequence with that of other living beings—the more similar they are, the more closely they are related. Comparison of even-toed ungulate and cetaceans genetic material has shown that the closest living relatives of 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 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 ...
es is the paraphyletic group Artiodactyla.
Dan Graur and Desmond Higgins were among the first to come to this conclusion, and included a paper published in 1994. However, they did not recognize hippopotamuses and classified the ruminant
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
s as the sister group of cetaceans. Subsequent studies established the close relationship between hippopotamuses and cetaceans; these studies were based on casein genes, SINEs
Sines () is a city and a municipality in Portugal. The municipality, divided into two parishes, has around 14,214 inhabitants (2021) in an area of . Sines holds an important oil refinery and several petrochemical industries. It is also a popular ...
, fibrinogen
Fibrinogen (factor I) is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood cl ...
sequences, cytochrome
Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of bi ...
and rRNA
Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosoma ...
sequences, IRBP (and vWF) gene sequences, adrenergic receptors, and apolipoprotein
Apolipoproteins are proteins that bind lipids (oil-soluble substances such as fats, cholesterol and fat soluble vitamins) to form lipoproteins. They transport lipids in blood, cerebrospinal fluid and lymph.
The lipid components of lipoproteins ...
s.
In 2001, the fossil limbs of a ''Pakicetus
''Pakicetus'' is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Pakistan during the Eocene, about 50 million years ago. It was a wolf-like animal, about to long, and lived in and around water where it a ...
'' (amphibioid cetacean the size of a wolf) and '' Ichthyolestes'' (an early whale the size of a fox) were found in Pakistan. They were both archaeocete
Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean Evolutionary radiation, radiation, t ...
s ("ancient whales") from about 48 million years ago (in the Eocene). These findings showed that archaeocetes were more terrestrial than previously thought, and that the special construction of the talus (ankle bone) with a double-rolled joint surface, previously thought to be unique to even-toed ungulates, were also in early cetaceans. The mesonychid
Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely ...
s, another type of ungulate, did not show this special construction of the talus, and thus was concluded to not have the same ancestors as cetaceans.
The oldest cetaceans date back to the early Eocene (53 million years ago), whereas the oldest known hippopotamus dates back only to the Miocene (15 million years ago). 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. Research is therefore focused on anthracotheres (family Anthracotheriidae); one dating from the Eocene to Miocene was declared to be "hippo-like" upon discovery in the 19th century. A study from 2005 showed that the anthracotheres and hippopotamuses have very similar skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
s, but differed in the adaptations of their teeth. It was nevertheless believed that cetaceans and anthracothereres descended from a common ancestor, and that hippopotamuses developed from anthracotheres. A study published in 2015 was able to confirm this, but also revealed that hippopotamuses were derived from older anthracotherians. The newly introduced genus '' Epirigenys'' from eastern Africa is thus the sister group of hippos.
Morphological classification of Artiodactyla
Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
postulated a close relationship between camels and ruminants as early as the mid-1700s. Henri de Blainville recognized the similar anatomy of the limbs of pigs and hippos, and British zoologist Richard Owen coined the term "even-toed ungulates" and the scientific name "Artiodactyla" in 1848.
Internal morphology (mainly the stomach and the molars) were used for classification. Suines (including 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) and hippopotamuses have molars with well-developed roots and a simple stomach that digests food. Thus, they were grouped together as non-ruminants (Porcine). All other even-toed ungulates have molars with a selenodont
Selenodont teeth are the type of molars and premolars commonly found in ruminant herbivores. They are characterized by low crowns, and crescent-shaped cusps when viewed from above (crown view).
The term comes from the Ancient Greek roots (, ' ...
construction (crescent-shaped cusps) and have the ability to ruminate, which requires regurgitating food and re-chewing it. Differences in stomach construction indicated that rumination evolved independently between tylopods and ruminant
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
s; therefore, tylopods were excluded from Ruminantia
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
.
The taxonomy that was widely accepted by the end of the 20th century was:
Morphological classification of Cetacea
Modern cetaceans are highly adapted sea creatures which, morphologically, have little in common with land mammals; they are similar to other marine mammal
Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
s, such as seals
Seals may refer to:
* Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly:
** Earless seal, or "true seal"
** Fur seal
* Seal (emblem), a device to impress an emblem, used as a means of a ...
and sea cow
The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct f ...
s, due to convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
. However, they evolved from originally terrestrial mammals. The most likely ancestors were long thought to be mesonychids—large, carnivorous animals from the early Cenozoic (Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...
and Eocene), which had hooves
The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rumi ...
instead of claw
A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...
s on their feet. Their molars were adapted to a carnivorous diet, resembling the teeth in modern toothed whale
The toothed whales (also called odontocetes, systematic name Odontoceti) are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and sperm whales. Seventy-three species of ...
s, and, unlike other mammals, have a uniform construction.
The suspected relations can be shown as follows:
Inner systematics
Molecular findings and morphological indications suggest that artiodactyls as traditionally defined are paraphyletic with respect to cetaceans. Cetaceans are deeply nested within the former; the two groups together form a monophyletic taxon, for which the name Cetartiodactyla is sometimes used. Modern nomenclature divides Artiodactyla (or Cetartiodactyla) in four subordinate taxa: camelids (Tylopoda), pigs and peccaries (Suina), ruminants (Ruminantia), and hippos plus whales (Whippomorpha). The presumed lineages within Artiodactyla can be represented in the followingcladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
:(see e.g. Fig S10)
The four summarized Artiodactyla taxa are divided into ten extant families:
* The camelids (Tylopoda
Tylopoda (meaning "calloused foot") is a suborder of terrestrial herbivorous even-toed ungulates belonging to the order Artiodactyla. They are found in the wild in their native ranges of South America and Asia, while Australian feral camels ...
) comprise only one family, Camelidae
Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, ...
. It is a species-poor artiodactyl suborder of North American origin that is well adapted to extreme habitats—the dromedary
The dromedary (''Camelus dromedarius'' or ;), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large even-toed ungulate, of the genus ''Camelus'', with one hump on its back.
It is the tallest of the three species of ...
and Bactrian camels in the Old World deserts and the guanaco
The guanaco (; ''Lama guanicoe'') is a camelid native to South America, closely related to the llama. Guanacos are one of two wild South American camelids, the other being the vicuña, which lives at higher elevations.
Etymology
The guanaco ...
s, llamas, vicuña
The vicuña (''Lama vicugna'') or vicuna (both , very rarely spelled ''vicugna'', its former genus name) is one of the two wild South American camelids, which live in the high alpine areas of the Andes, the other being the guanaco, which live ...
s, and alpaca
The alpaca (''Lama pacos'') is a species of South American camelid mammal. It is similar to, and often confused with, the llama. However, alpacas are often noticeably smaller than llamas. The two animals are closely related and can success ...
s in South American high mountain regions.
* The pig-like creatures ( Suina) are made up of two families:
** The pigs ( Suidae) are limited to the Old World. These include the wild boar
The wild boar (''Sus scrofa''), also known as the wild swine, common wild pig, Eurasian wild pig, or simply wild pig, is a suid native to much of Eurasia and North Africa, and has been introduced to the Americas and Oceania. The species is ...
and the domesticated form, the domestic 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 ...
.
** The peccaries ( Tayassuidae) are named after glands on their belly and are indigenous to Central and South America.
* The ruminants (Ruminantia
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
) consist of six families:
** The mouse deer (Tragulidae
The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star.
Computer scientists and mathematicians often v ...
) are the smallest and most primitive even-toed-ruminants; they inhabit forests of Africa and Asia.
** The giraffe-like creatures (Giraffidae
The Giraffidae are a family of ruminant artiodactyl mammals that share a common ancestor with deer and bovids. This family, once a diverse group spread throughout Eurasia and Africa, presently comprises only two extant genera, the giraffe (one ...
) are composed of two species: the giraffe and the okapi
The okapi (; ''Okapia johnstoni''), also known as the forest giraffe, Congolese giraffe, or zebra giraffe, is an artiodactyl mammal that is endemic to the northeast Democratic Republic of the Congo in central Africa. It is the only species ...
.
** The musk deer (Moschidae
Moschidae is a family of pecoran even-toed ungulates, containing the musk deer (''Moschus'') and its extinct relatives. They are characterized by long 'saber teeth' instead of horns, antlers or ossicones, modest size (''Moschus'' only reaches ; ...
) is indigenous to East Asia.
** The antilocaprids (Antilocapridae
The Antilocapridae are a family of artiodactyls endemic to North America. Their closest extant relatives are the giraffids with which they comprise the superfamily Giraffoidea. Only one species, the pronghorn (''Antilocapra americana''), is ...
) of North America comprise only one extant species: the pronghorn
The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American a ...
.
** The deer (Cervidae
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reind ...
) are made up of about 45 species, which are characterized by a pair of antlers (generally only in males). They are spread across Europe, Asia, and the Americas. This group includes, among other species, the red deer
The red deer (''Cervus elaphus'') is one of the largest deer species. A male red deer is called a stag or hart, and a female is called a hind. The red deer inhabits most of Europe, the Caucasus Mountains region, Anatolia, Iran, and parts of we ...
, moose
The moose (in North America) or elk (in Eurasia) (''Alces alces'') is a member of the New World deer subfamily and is the only species in the genus ''Alces''. It is the largest and heaviest extant species in the deer family. Most adult ma ...
, elk
The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. The common ...
(wapiti), and reindeer
Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 sub ...
(caribou).
** The bovids (Bovidae
The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, and caprines. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, t ...
) are the most species-rich. Among them are cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
, sheep
Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...
, caprines, and antelopes.
* The whippomorpha
Whippomorpha or Cetancodonta is a group of animals that contains all living cetaceans (whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives, i.e. Entelodonts and Andrewsarchus. All Whippomorphs are descendants of the la ...
ns include hippos and cetaceans:
** The hippos (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 ...
) comprise two groups, the hippo
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 extant ...
and the pygmy hippo
The pygmy hippopotamus or pygmy hippo (''Choeropsis liberiensis'') 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 ...
.
** The whales ( Cetacea) comprise 72 species and two parvorders: toothed whales ( Odontoceti) and baleen whales ( Mysticeti)
Although deer, musk deer, and pronghorns have traditionally been summarized as cervids (Cervioidea), molecular studies provide different—and inconsistent—results, so the question of phylogenetic systematics of infraorder Pecora
Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, ''Hydropotes'' and '' Moschus''. The name “Pec ...
(the horned ruminants) for the time being, cannot be answered.
Anatomy
Artiodactyls are generally quadruped
Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...
s. Two major body types are known: Suinids and hippopotamuses are characterized by a stocky body, short legs, and a large head; camels and ruminants, though, have a more slender build and lanky legs. Size varies considerably; the smallest member, the mouse deer, often reaches a body length of only and a weight of . The largest member, the hippopotamus, can grow up to in length and weigh , and the giraffe can grow to be tall and in body length. All even-toed ungulates display some form of sexual dimorphism
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
: the males are consistently larger and heavier than the females. In deer, only the males boast antlers, and the horns of bovines are usually small or not present in females. Male Indian antelopes have a much darker coat than females.
Almost all even-toed ungulates have fur, with an exception being the nearly hairless hippopotamus. Fur varies in length and coloration depending on the habitat. Species in cooler regions can shed their coat. Camouflaged coats come in colors of yellow, gray, brown, or black tones.
Limbs
Even-toed ungulates bear their name because they have an even number of toe
Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plan ...
s (two or four)—in some peccaries, the hind legs
A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hind ...
have a reduction in the number of toes to three. The central axis of the leg is between the third and fourth toe. The first toe is missing in modern artiodactyls, and can only be found in now-extinct genera. The second and fifth toes are adapted differently between species:
claw
A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...
s are transformed into nails (while both are made of keratin
Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, ho ...
, claws are curved and pointed while nails are flat and dull). These claws consist of three parts: the plate (top and sides), the sole (bottom), and the bale (rear). In general, the claws of the forelegs are wider and blunter than those of the hind legs, and they are farther apart. Aside from camels, all even-toed ungulates put just the tip of the foremost phalanx on the ground.
In even-toed ungulates, the bones of the stylopodium (upper arm or thigh bone) and zygopodium
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in an ...
s (tibia and fibula) are usually elongated. The muscles of the limbs are predominantly localized, which ensures that artiodactyls often have very slender legs. A clavicle
The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the r ...
is never present, and the scapula
The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...
is very agile and swings back and forth for added mobility when running. The special construction of the legs causes the legs to be unable to rotate, which allows for greater stability when running at high speeds. In addition, many smaller artiodactyls have a very flexible body, contributing to their speed by increasing their stride length.
Head
Many even-toed ungulates have a relatively large head. The skull is elongated and rather narrow; thefrontal bone
The frontal bone is a bone in the human skull. The bone consists of two portions.'' Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, pa ...
is enlarged near the back and displaces the parietal bone
The parietal bones () are two bones in the skull which, when joined at a fibrous joint, form the sides and roof of the cranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is nam ...
, which forms only part of the side of the cranium (especially in ruminants).
Horns and antlers
Four families of even-toed ungulates have cranial appendages. These Pecora
Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, ''Hydropotes'' and '' Moschus''. The name “Pec ...
(with the exception of the musk deer), have one of four types of cranial appendages: true horns, antlers, ossicone
Ossicones are columnar or conical skin-covered bone structures on the heads of giraffes, male okapi, and some of their extinct relatives. Ossicones are distinguished from the superficially similar structures of horns and antlers by their uniqu ...
s, or pronghorn
The pronghorn (, ) (''Antilocapra americana'') is a species of artiodactyl (even-toed, hoofed) mammal indigenous to interior western and central North America. Though not an antelope, it is known colloquially in North America as the American a ...
s.
''True horns'' have a bone core that is covered in a permanent sheath of keratin, and are found only in the bovids
The Bovidae comprise the biological family of cloven-hoofed, ruminant mammals that includes cattle, bison, buffalo, antelopes, and caprines. A member of this family is called a bovid. With 143 extant species and 300 known extinct species, the ...
. ''Antlers'' are bony structures that are shed and replaced each year; they are found in deer (members of the family Cervidae
Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reind ...
). They grow from a permanent outgrowth of the frontal bone called the pedicle and can be branched, as in the white-tailed deer
The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
(''Odocoileus virginianus''), opalmate
as in the
moose
The moose (in North America) or elk (in Eurasia) (''Alces alces'') is a member of the New World deer subfamily and is the only species in the genus ''Alces''. It is the largest and heaviest extant species in the deer family. Most adult ma ...
(''Alces alces''). ''Ossicones'' are permanent bone structures that fuse to the frontal or parietal bones during an animal's life and are found only in the Giraffidae
The Giraffidae are a family of ruminant artiodactyl mammals that share a common ancestor with deer and bovids. This family, once a diverse group spread throughout Eurasia and Africa, presently comprises only two extant genera, the giraffe (one ...
. ''Pronghorns'', while similar to horns in that they have keratinous sheaths covering permanent bone cores, are deciduous.
All these cranial appendages can serve for posturing, battling for mating privilege, and for defense. In almost all cases, they are sexually dimorphic, and often found only on the males. One exception is the species ''Rangifer tarandus'', known as reindeer
Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 sub ...
in Europe or caribou in North America, where both sexes can grow antlers yearly, though the females' antlers are typically smaller and not always present.
Teeth
There are two trends in terms of teeth within Artiodactyla. The Suina and hippopotamuses have a relatively large number of teeth (with some pigs having 44); their dentition is more adapted to a squeezing mastication, which is characteristic of omnivores. Camels and ruminants have fewer teeth; there is often a yawning diastema
A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...
, a designated gap in the teeth where the molars are aligned for crushing plant matter.
The incisor
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s are often reduced in ruminants, and are completely absent in the upper jaw
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
. The canines are enlarged and tusk-like in the Suina, and are used for digging in the ground and for defense. In ruminants, the males' upper canines are enlarged and used as a weapon in certain species (mouse deer, musk deer, water deer
The water deer (''Hydropotes inermis'') is a small deer superficially more similar to a musk deer than a true deer. Native to China and Korea, there are two subspecies: the Chinese water deer (''Hydropotes inermis inermis'') and the Korean water ...
); species with frontal weapons are usually missing the upper canines. The lower canines of ruminants resemble the incisors, so that these animals have eight uniform teeth in the frontal part of the lower jaw
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
.
The molars of porcine have only a few bumps. In contrast, the camels and ruminants have bumps that are crescent-shaped cusps (selenodont
Selenodont teeth are the type of molars and premolars commonly found in ruminant herbivores. They are characterized by low crowns, and crescent-shaped cusps when viewed from above (crown view).
The term comes from the Ancient Greek roots (, ' ...
).
Senses
Artiodactyls have a well-developed sense of smell and sense of hearing. Unlike many other mammals, they have a poor sense of sight—moving objects are much easier to see than stationary ones. Similar to many other prey animals, their eyes are on the sides of the head, giving them an almost panoramic view.Digestive system
The ruminant
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
s (Ruminantia and Tylopoda) ruminate their food—they regurgitate and re-chew it. Ruminants' mouths often have additional salivary gland
The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands ( parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary ...
s, and the oral mucosa
The oral mucosa is the mucous membrane lining the inside of the mouth. It comprises stratified squamous epithelium, termed "oral epithelium", and an underlying connective tissue termed '' lamina propria''. The oral cavity has sometimes been des ...
is often heavily calloused to avoid injury from hard plant parts and to allow easier transport of roughly chewed food. Their stomachs are divided into three to four sections: the rumen
The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment al ...
, the reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions. The constellation is best viewed b ...
, the omasum
The omasum, also known as the bible, the fardel, the manyplies and the psalterium, is the third compartment of the stomach in ruminants. The omasum comes after the rumen and reticulum and before the abomasum. Different ruminants have different oma ...
, and the abomasum
The abomasum, also known as the maw,The Cham ...
. After the food is ingested, it is mixed with saliva in the rumen
The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment al ...
and reticulum
Reticulum is a small, faint constellation in the southern sky. Its name is Latin for a small net, or reticle—a net of crosshairs at the focus of a telescope eyepiece that is used to measure star positions. The constellation is best viewed b ...
and separates into layers of solid versus liquid material. The solids lump together to form a bolus (also known as the cud
Cud is a portion of food that returns from a ruminant's stomach to the mouth to be chewed for the second time. More precisely, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the phy ...
); this is regurgitated by reticular contractions while the glottis is closed. When the bolus enters the mouth, the fluid is squeezed out with the tongue and re-swallowed. The bolus is chewed slowly to completely mix it with saliva and to break it down. Ingested food passes to the "fermentation chamber" (rumen and reticulum), where it is kept in continual motion by rhythmic contractions. Cellulytic microbes (bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
, protozoa, and fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
) produce cellulase
Cellulase (EC 3.2.1.4; systematic name 4-β-D-glucan 4-glucanohydrolase) is any of several enzymes produced chiefly by fungi, bacteria, and protozoans that catalyze cellulolysis, the decomposition of cellulose and of some related polysacchar ...
, which is needed to break down the cellulose found in plant material. This form of digestion has two advantages: plants that are indigestible to other species can be digested and used, and the duration of the actual food consumption shortened; the animal spends only a short time out in the open with his head to the ground—rumination can take place later, in a sheltered area.
Tylopoda (camels, llamas, and alpacas) and chevrotains have three-chambered stomachs, while the rest of Ruminantia have four-chambered stomachs. The handicap of a heavy digestive system has increased selective pressure towards limbs that allow the animal to quickly escape predators. Most species within Suina have a simple two-chambered stomach that allows an omnivorous diet. The babirusa
The babirusas, also called deer-pigs ( id, babi rusa), are a genus, ''Babyrousa'', in the swine family found in the Indonesian islands of Sulawesi, Togian, Sula and Buru. All members of this genus were considered part of a single species unti ...
, however, is an herbivore, and has extra maxillary teeth
A tooth (plural, : teeth) is a hard, calcification, calcified structure found in the jaws (or mouths) of many vertebrates and used to Mastication, break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with ...
to allow for proper mastication of plant material. Most of the fermentation occurs with the help of cellulolytic microorganisms within the caecum
The cecum or caecum is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body (the same side of the body as the appendix, to which it is joined). The wo ...
of the large intestine
The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in tetrapods. Water is absorbed here and the remaining waste material is stored in the rectum as feces before bein ...
. Peccaries have a complex stomach that contains four compartments. Their fore stomach has fermentation carried out by microbes and has high levels of volatile fatty acid Short-chain fatty acids (SCFAs) are fatty acids with fewer than six carbon atoms. Derived from intestinal microbial fermentation of indigestible foods, SCFAs are the main energy source of colonocytes, making them crucial to gastrointestinal health ...
; it has been proposed that their complex fore stomach is a means to slow digestive passage and increase digestive efficiency. Hippopotamuses have three-chambered stomachs and do not ruminate. They consume around of grass and other plant matter each night. They may cover distances up to to obtain food, which they digest with the help of microbes that produce cellulase. Their closest living relatives, the whales, are obligate carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
s.
Unlike other even-toed ungulates, pigs have a simple sack-shaped stomach
The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
. Some artiodactyla, such as white-tailed deer
The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...
, lack a gall bladder.
Genitourinary system
The penises of even-toed ungulates have an S-shape at rest and lie in a pocket under the skin on the belly. The corpora cavernosa are only slightly developed; and an erection mainly causes this curvature to extend, which leads to an extension, but not a thickening, of thepenis
A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...
. Cetaceans have similar penises. In some even-toed ungulates, the penis contains a structure called the ''urethral process.''
The testicle
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
s are located in the scrotum
The scrotum or scrotal sac is an anatomical male reproductive structure located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. It is present in most terrestrial male mammals. The scrotum co ...
and thus outside the abdominal cavity. The ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
of many females descend—as testicles descend of many male mammals—and are close to the pelvic inlet
The pelvic inlet or superior aperture of the pelvis is a planar surface which defines the boundary between the pelvic cavity and the abdominal cavity (or, according to some authors, between two parts of the pelvic cavity, called lesser pelvis an ...
at the level of the fourth lumbar vertebra
The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...
. The uterus
The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
has two horns ( uterus bicornis).
Other
The number ofmammary gland
A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in pri ...
s is variable and correlates, as in all mammals, with litter size. Pigs, which have the largest litter size of all even-toed ungulates, have two rows of teat
A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...
s lined from the armpit to the groin area. In most cases, however, even-toed ungulates have only one or two pairs of teats. In some species these form an udder
An udder is an organ formed of two or four mammary glands on the females of dairy animals and ruminants such as cattle, goats, and sheep. An udder is equivalent to the breast in primates and elephantine pachyderms. The udder is a single mass han ...
in the groin region.
Secretory glands in the skin are present in virtually all species and can be located in different places, such as in the eyes, behind the horns, the neck, or back, on the feet, or in the anal region.
Lifestyle
Distribution and habitat
Artiodactyls are native to almost all parts of the world, with the exception ofOceania
Oceania (, , ) is a geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern and Western hemispheres, Oceania is estimated to have a land area of and a population of around 44.5 million ...
and Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
. Humans have introduced different artiodactyls worldwide as hunting animals. Artiodactyls inhabit almost every habitat, from tropical rainforest
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equa ...
s and steppes to deserts and high mountain regions. The greatest biodiversity
Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
prevails in open habitats such as grassland
A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...
s and open forests.
Social behavior
The social behavior of even-toed ungulates varies from species to species. Generally, there is a tendency to merge into larger groups, but some live alone or in pairs. Species living in groups often have a hierarchy, both among males and females. Some species also live in harem groups, with one male, several females, and their common offspring. In other species, the females and juveniles stay together, while males are solitary or live in bachelor groups and seek out females only during mating season
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...
.
Many artiodactyls are territorial
A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal.
In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
and mark their territory, for example, with glandular secretions or urine. In addition to year-round sedentary species, there are animals that migrate seasonally.
There are diurnal, crepuscular, and nocturnal artiodactyls. Some species' pattern of wakefulness varies with season or habitat.
Reproduction and life expectancy
Generally, even-toed ungulates tend to have long gestation periods, smaller litter sizes, and more highly developed newborns. As with many other mammals, species in temperate
In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
or polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
* Polar climate, the c ...
regions have a fixed mating season
Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...
, while those in tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
areas breed year-round. They carry out polygynous mating behavior, meaning a male mates with several females and suppresses all competition.
The length of the gestation period varies from four to five months for porcine, deer, and musk deer; six to ten months for hippos, deer, and bovines; ten to thirteen months with camels; and fourteen to fifteen months with giraffes. Most deliver one or two babies, but some pigs can deliver up to ten.
The newborns are precocial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
(born relatively mature) and come with open eyes and are hairy (with the exception of the hairless hippos). Juvenile deer and pigs have striped or spotted coats; the pattern disappears as they grow older. The juveniles of some species spend their first weeks with their mother in a safe location, where others may be running and following the herd within a few hours or days.
The life expectancy is typically twenty to thirty years; as in many mammals, smaller species often have a shorter lifespan than larger species. The artiodactyls with the longest lifespans are the hippos, cows, and camels, which can live 40 to 50 years.
Predators and parasites
Artiodactyls have differentnatural predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
s depending on their size and habitat. There are several carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...
s that prey on them, including large cat
The term "big cat" is typically used to refer to any of the five living members of the genus ''Panthera'', namely the tiger, lion, jaguar, leopard, and snow leopard.
Despite enormous differences in size, various cat species are quite similar ...
s (e.g., lions) and bears. Other predators are crocodiles, wolves
The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly un ...
and dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s, large raptors, and for small species and young animals, large snake
Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more j ...
s. For cetaceans, possible predators include sharks, polar bears, and other cetaceans; in the latter is the orca, the top predator of the oceans.
Parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
include nematodes, botflies, flea
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...
s, lice, or flukes, but they have debilitating effects only when the infestation is severe.
Interactions with humans
Domestication
Artiodactyls have been hunted by primitive humans for various reasons: for meat or fur
Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
, as well as to use their bones and teeth as weapons or tools. Their domestication
Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. ...
began around 8000 BCE. To date, humans have domesticated goats, sheep, cattle, camels, llamas, alpacas, and pigs. Initially, livestock was used primarily for food, but they began being used for work activities around 3000 BCE. Clear evidence exists of antelope being used for food 2 million years ago in the Olduvai Gorge
The Olduvai Gorge or Oldupai Gorge in Tanzania is one of the most important paleoanthropological localities in the world; the many sites exposed by the gorge have proven invaluable in furthering understanding of early human evolution. A steep-si ...
, part of the Great Rift Valley
The Great Rift Valley is a series of contiguous geographic trenches, approximately in total length, that runs from Lebanon in Asia to Mozambique in Southeast Africa. While the name continues in some usages, it is rarely used in geology as it ...
. Cro-Magnons relied heavily on reindeer for food, skins, tools, and weapons; with dropping temperatures and increased reindeer numbers at the end of the Pleistocene, they became the prey of choice. Reindeer remains accounted for 94% of bones and teeth found in a cave above the river Céou
The Céou () is a long river in the Lot and Dordogne ''départements'', southwestern France. Its source is at Séniergues, southwest of Rocamadour. It flows generally northwest. It is a left tributary of the Dordogne
Dordogne ( , or ; ...
that was inhabited around 12,500 years ago.
Today, artiodactyls are kept primarily for their meat, milk, and wool
Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. ...
, fur, or hide for clothing. Domestic cattle, the water buffalo
The water buffalo (''Bubalus bubalis''), also called the domestic water buffalo or Asian water buffalo, is a large bovid originating in the Indian subcontinent and Southeast Asia. Today, it is also found in Europe, Australia, North America, So ...
, the yak, and camels are used for work, as rides, or as pack animal
A pack animal, also known as a sumpter animal or beast of burden, is an individual or type of working animal used by humans as means of transporting materials by attaching them so their weight bears on the animal's back, in contrast to draft ani ...
s.
Threats
The endangerment level of each even-toed ungulate is different. Some species are synanthropic
A synanthrope (from the Greek σύν ''syn'', "together with" + ἄνθρωπος ''anthropos'', "man") is a member of a species of wild animal or plant that lives near, and benefits from, an association with human beings and the somewhat artific ...
(such as the wild boar
The wild boar (''Sus scrofa''), also known as the wild swine, common wild pig, Eurasian wild pig, or simply wild pig, is a suid native to much of Eurasia and North Africa, and has been introduced to the Americas and Oceania. The species is ...
) and have spread into areas that they are not indigenous to, either having been brought as farm animals or having run away as people's pets. Some artiodactyls also benefit from the fact that their predators (e.g. the Tasmanian tiger
The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was captured in 1930 in Tasma ...
) were severely decimated by ranchers, who saw them as competition.
Conversely, many artiodactyls have declined significantly in numbers, and some have even gone extinct, largely due to over-hunting
Hunting is the human practice of seeking, pursuing, capturing, or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest food (i.e. meat) and useful animal products (fur/ hide, bone/tusks, horn/ antler ...
, and, more recently, habitat destruction
Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat becomes incapable of supporting its native species. The organisms that previously inhabited the site are displaced or dead, thereby ...
. Extinct species include several gazelles, the aurochs, the Malagasy hippopotamus, the bluebuck
The bluebuck (Afrikaans: bloubok ) or blue antelope (''Hippotragus leucophaeus'') is an extinct species of antelope that lived in South Africa until around 1800. It was smaller than the other two species in its genus ''Hippotragus,'' the roan ...
, and Schomburgk's deer
The Schomburgk's deer (''Rucervus schomburgki'') is an extinct species of deer once endemic to central Thailand. It was described by Edward Blyth in 1863 and named after Sir Robert H. Schomburgk, who was the British consul in Bangkok from 1857 t ...
. Two species, the Scimitar-horned oryx
The scimitar oryx (''Oryx dammah''), also known as the scimitar-horned oryx and the Sahara oryx, is a ''Oryx'' species that was once widespread across North Africa. In 2000, it was declared extinct in the wild on the IUCN Red List.
A captive br ...
and Père David's deer, are extinct in the wild. Fourteen species are considered critically endangered, including the addax
The addax (''Addax nasomaculatus''), also known as the white antelope and the screwhorn antelope, is an antelope native to the Sahara Desert. The only member of the genus ''Addax'', it was first described scientifically by Henri de Blainvil ...
, the kouprey
The kouprey (''Bos sauveli''), also known as forest ox is a forest-dwelling, wild bovine species native to Southeast Asia. A young male was sent to the Paris Zoological Park in 1937 and was described by the French zoologist Achille Urbain who ...
, the Bactrian camel
The Bactrian camel (''Camelus bactrianus''), also known as the Mongolian camel or domestic Bactrian camel, is a large even-toed ungulate native to the steppes of Central Asia. It has two humps on its back, in contrast to the single-humped dro ...
, Przewalski's gazelle
Przewalski's gazelle (''Procapra przewalskii'') is a member of the family Bovidae, and in the wild, is found only in China. Once widespread, its range has declined to six populations near Qinghai Lake. The gazelle was named after Nikolai Przheva ...
, the saiga
The saiga antelope (, ''Saiga tatarica''), or saiga, is a critically endangered antelope which during antiquity inhabited a vast area of the Eurasian steppe spanning the foothills of the Carpathian Mountains in the northwest and Caucasus in t ...
, and the pygmy hog
The pygmy hog (''Porcula salvania'') is the rarest species of pig in the world today, and is the only species in the genus ''Porcula''. It is also the smallest species of pig in the world, with its piglets being small enough to fit in one's pock ...
. Twenty-four species are considered endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
.
See also
*References
External links
Ungulate Taxonomy: A new perspective from Groves and Grubb (2011)
{{DEFAULTSORT:Even-Toed Ungulate Extant Ypresian first appearances