Even-toed ungulate
Encyclopedia
The even-toed ungulates (Artiodactyla) are ungulate
s (hoof
ed animals) whose weight is borne about equally by the third and fourth toe
s, rather than mostly or entirely by the third as in odd-toed ungulates (perissodactyls)
such as horse
s.
Artiodactyla comes from the Greek words artios, meaning entire or even numbered, and dactylos for finger or toe. This group includes pig
s, peccaries
, hippopotamuses
, camel
s, chevrotain
s (mouse deer), deer
, giraffe
s, pronghorn
, antelope
s, sheep, goat
s, and cattle
. The group excludes whale
s even though DNA sequence data indicate that they share a common ancestor, making the group paraphyletic. The more phylogenetically accurate group is Cetartiodactyla
.
There are about 220 artiodactyl species
, including many that are of great nutritional, economic, and cultural importance to humans.
A further distinguishing feature of the group is the shape of the astragalus
(talus
), a bone in the ankle
joint, which has a double-pulley structure. This gives the foot greater flexibility.
(about 54 million years ago). In form they were rather like today's chevrotain
s: small, short-legged creatures that ate leaves
and the soft parts of plants. By the Late Eocene (46 million years ago), the three modern suborders had already developed: Suina
(the pig
group); Tylopoda
(the camel
group); and Ruminantia
(the goat
and cattle
group). Nevertheless, artiodactyls were far from dominant at that time: the odd-toed ungulate
s (ancestors of today's horse
s and rhino
s) were much more successful and far more numerous. Even-toed ungulates survived in niche roles, usually occupying marginal habitats
, and it is presumably at that time that they developed their complex digestive systems, which allowed them to survive on lower-grade food.
The appearance of grasses
during the Eocene
and their subsequent spread during the Miocene
(about 20 million years ago) saw a major change; grasses are very difficult to eat and the even-toed ungulates with their highly-developed stomach
s were better able to adapt to this coarse, low-nutrition
diet, and soon replaced the odd-toed ungulates as the dominant terrestrial
herbivore
s. Now-extinct Artiodactyla which developed during the Miocene
include the genera Ampelomeryx
, Tauromeryx, Triceromeryx
and others.
published in 2005. Currently the cetaceans and even-toed ungulates have been placed in Cetartiodactyla
as sister groups, although DNA analysis has shown cetaceans evolved from within Artiodactyla. The most recent theory into the origins of hippopotamidae suggests that hippos and whales shared a common semi-aquatic ancestor that branched off from other artiodactyls around 60 million years ago. This hypothesized ancestral group likely split into two branches around 54 million years ago. One branch would evolve into cetaceans
, possibly beginning with the proto-whale Pakicetus
from 52 million years ago with other early whale ancestors collectively known as Archaeoceti
, which eventually underwent aquatic adaptation
into the completely aquatic cetacea
ns.
The even-toed ungulates stand on an even number of toes; the group's four suborders differ in other characteristics. Suina (pigs
and peccaries
) have retained four toes of fairly equal size, have simpler molars
, short legs, and often have enlarged canine teeth that form tusk
s. Camelid
s and Ruminantia
tend to be longer-legged, to walk on only the central two toes (though the outer two may survive as rarely-used dew-claws) and to have more complex cheek teeth well-suited to grinding up tough grasses.
, although species in the suborder Suina
(pigs and peccaries) are, like their primitive ancestors, omnivores. Larger stomachs and longer intestine
s have evolved because plant food is less easily digested than meat.
Tylopoda
(camels, llamas and alpacas) and the chevrotain
s have a three-chambered stomach while the rest of Ruminantia
have four-chambered stomachs. The handicap of a heavy digestive system has increased selective pressure for limb
bone adaptations to escape predators. Most species within Suina have a simple two-chambered stomach that allows an omnivorous diet, the babirusa
, however, is a herbivore. They have extra maxillary teeth to allow proper mastication
of plant material. Most of the fermentation occurs in the caecum with the help of cellulolytic microorganism
s. Peccaries however have a complex stomach that contains four compartments. Microbial fermentation with the formation of high volatile fatty acid levels has been observed in the fore stomach, it has been proposed that their complex fore stomach is a means to slow digestive passage and increase digestive efficiency. Hippopotamus
es have a three-chambered stomach and do not ruminate, they consume grass during the night and may cover large distances (up to 20 miles) to feed. They eat around 68 kg of food each night, also relying on microbes to break down plant material with cellulase.
Rumination occurs in the ruminant
s (Ruminantia
and Tylopoda
), whereby food is regurgitated and rechewed then broken down by microbes in the stomach. After ingestion of plant material it is mixed with saliva in the rumen
and reticulum
and separates into layers of solid and liquid material. The solids lump together to form a bolus
(also known as the cud
), 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 reswallowed. The bolus is chewed slowly to completely mix it with saliva and to break down the particle size. Ingested food passes to the 'fermentation chamber' (rumen and reticulum) where it is kept in continual motion by rhythmic contractions of this organ. Cellulytic microbes (bacteria
, protozoa
, and fungi
) produce cellulase
, which is needed to break down the cellulose found in plant material. Without this mutual symbiosis
ruminants would find plant material indigestible.
and New Zealand
by humans.
s being used for food 2 million years ago in the Olduvai Gorge
, part of the Great Rift Valley
. Cro-Magnon
s 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. By around 12,500 years ago, reindeer remains accounted for 94 percent of bones and teeth found in a cave above the Céou River.
Cattle
today are the basis of a multi-billion dollar industry worldwide. The international trade in beef for 2000 was over $30 billion and represented only 23 percent of world beef production.
, from ἄρτιος, ártios, "even", and δάκτυλος, dáktylos, "finger/toe", so the name is a translation of the description "even-toed".
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s (hoof
Hoof
A hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...
ed animals) whose weight is borne about equally by the third and fourth toe
Toe
Toes are the digits 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 plantigrade; unguligrade animals are those that walk on hooves at the tips of...
s, rather than mostly or entirely by the third as in odd-toed ungulates (perissodactyls)
Odd-toed ungulate
An odd-toed ungulate is a mammal with hooves that feature an odd number of toes. Odd-toed ungulates comprise the order Perissodactyla . The middle toe on each hoof is usually larger than its neighbours...
such as horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s.
Artiodactyla comes from the Greek words artios, meaning entire or even numbered, and dactylos for finger or toe. This group includes pig
Suidae
Suidae is the biological family to which pigs belong. In addition to numerous fossil species, up to sixteen extant species are currently recognized, classified into between four and eight genera...
s, peccaries
Peccary
A peccary is a medium-sized mammal of the family Tayassuidae, or New World Pigs. Peccaries are members of the artiodactyl suborder Suina, as are the pig family and possibly the hippopotamus family...
, hippopotamuses
Hippopotamidae
Hippopotamuses are the members of the family Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.- Characteristics :...
, camel
Camel
A camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
s, chevrotain
Chevrotain
Chevrotains, also known as mouse deer, are small ungulates that make up the family Tragulidae, the only members of the infraorder Tragulina. There are 10 living species in three genera, but there are also several species only known from fossils...
s (mouse deer), deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
, giraffe
Giraffe
The giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
s, pronghorn
Pronghorn
The pronghorn is a species of artiodactyl mammal endemic to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the prong buck, pronghorn antelope, or simply antelope, as it closely resembles the true antelopes of the Old World and...
, antelope
Antelope
Antelope is a term referring to many even-toed ungulate species indigenous to various regions in Africa and Eurasia. Antelopes comprise a miscellaneous group within the family Bovidae, encompassing those old-world species that are neither cattle, sheep, buffalo, bison, nor goats...
s, sheep, goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
s, and cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
. The group excludes whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s even though DNA sequence data indicate that they share a common ancestor, making the group paraphyletic. The more phylogenetically accurate group is Cetartiodactyla
Cetartiodactyla
Cetartiodactyla is the clade in which whales and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls...
.
There are about 220 artiodactyl species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, including many that are of great nutritional, economic, and cultural importance to humans.
A further distinguishing feature of the group is the shape of the astragalus
Talus bone
-External links:* *...
(talus
Talus
Talus may refer to:* Talus , a sloped portion of a fortified wall* Talus, California, a community in Inyo County* Talus bone, an ankle bone* Talus, fictional planet in Star Wars...
), a bone in the ankle
Ankle
The ankle joint is formed where the foot and the leg meet. The ankle, or talocrural joint, is a synovial hinge joint that connects the distal ends of the tibia and fibula in the lower limb with the proximal end of the talus bone in the foot...
joint, which has a double-pulley structure. This gives the foot greater flexibility.
Evolutionary history
As with many mammal groups, even-toed ungulates first appeared during the Early EoceneEocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
(about 54 million years ago). In form they were rather like today's chevrotain
Chevrotain
Chevrotains, also known as mouse deer, are small ungulates that make up the family Tragulidae, the only members of the infraorder Tragulina. There are 10 living species in three genera, but there are also several species only known from fossils...
s: small, short-legged creatures that ate leaves
Leaves
-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...
and the soft parts of plants. By the Late Eocene (46 million years ago), the three modern suborders had already developed: Suina
Suina
The suborder Suina are lineage of mammals that today includes the families Suidae and Tayassuidae and their fossil kin.- Classification :The suborder Suina includes Suidae and Tayassuidae...
(the pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
group); Tylopoda
Tylopoda
Tylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to Artiodactyla. They are extant in the wild in their native ranges of South America and Asia, while Australian feral camels are an introduced species. The group has a long fossil history in North America and Europe...
(the camel
Camel
A camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
group); and Ruminantia
Ruminantia
Ruminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the...
(the goat
Goat
The domestic goat is a subspecies of goat domesticated from the wild goat of southwest Asia and Eastern Europe. The goat is a member of the Bovidae family and is closely related to the sheep as both are in the goat-antelope subfamily Caprinae. There are over three hundred distinct breeds of...
and cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
group). Nevertheless, artiodactyls were far from dominant at that time: the odd-toed ungulate
Odd-toed ungulate
An odd-toed ungulate is a mammal with hooves that feature an odd number of toes. Odd-toed ungulates comprise the order Perissodactyla . The middle toe on each hoof is usually larger than its neighbours...
s (ancestors of today's horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s and rhino
Rhinoceros
Rhinoceros , also known as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa and three to southern Asia....
s) were much more successful and far more numerous. Even-toed ungulates survived in niche roles, usually occupying marginal habitats
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
, and it is presumably at that time that they developed their complex digestive systems, which allowed them to survive on lower-grade food.
The appearance of grasses
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
and their subsequent spread during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
(about 20 million years ago) saw a major change; grasses are very difficult to eat and the even-toed ungulates with their highly-developed stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
s were better able to adapt to this coarse, low-nutrition
Nutrition
Nutrition is the provision, to cells and organisms, of the materials necessary to support life. Many common health problems can be prevented or alleviated with a healthy diet....
diet, and soon replaced the odd-toed ungulates as the dominant terrestrial
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...
herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
s. Now-extinct Artiodactyla which developed during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
include the genera Ampelomeryx
Ampelomeryx
Ampelomeryx is an extinct genus of herbivorous even-toed ungulate mammal belonging to the family PalaeomerycidaeAmpelomeryx was named by Duranthon et al. . It was assigned to Palaeomerycinae by Prothero and Liter . It had frontal and occipital appendages. It was similar to Tauromeryx and...
, Tauromeryx, Triceromeryx
Triceromeryx
Triceromeryx is an extinct genus of Artiodactyla, of the family Palaeomerycidae, endemic to Europe from the early Miocene epoch, 22.4—20.0 Ma, existing for approximately .It was similar to Ampelomeryx, a herbivore.-Taxonomy:...
and others.
Classification
The following classification is based on the Spaulding et al., 2009 and the extant families recognised by Mammal Species of the WorldMammal Species of the World
Mammal Species of the World, now in its 3rd edition, is a standard reference work in zoology giving descriptions and bibliographic data for the known species of mammals.An updated Third Edition of Mammal Species of the World was published late in 2005:...
published in 2005. Currently the cetaceans and even-toed ungulates have been placed in Cetartiodactyla
Cetartiodactyla
Cetartiodactyla is the clade in which whales and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls...
as sister groups, although DNA analysis has shown cetaceans evolved from within Artiodactyla. The most recent theory into the origins of hippopotamidae suggests that hippos and whales shared a common semi-aquatic ancestor that branched off from other artiodactyls around 60 million years ago. This hypothesized ancestral group likely split into two branches around 54 million years ago. One branch would evolve into cetaceans
Evolution of cetaceans
The cetaceans are marine mammal descendants of land mammals. Their terrestrial origins are indicated by:* Their need to breathe air from the surface;* The bones of their fins, which resemble the limbs of land mammals...
, possibly beginning with the proto-whale Pakicetus
Pakicetus
Pakicetus is a genus of extinct terrestrial carnivorous mammal of the family Pakicetidae which was endemic to Pakistan from the Eocene .Pakicetus existed for approximately...
from 52 million years ago with other early whale ancestors collectively known as Archaeoceti
Archaeoceti
Archaeocetes, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to the modern cetaceans.The archaeocetes were once thought to have evolved from the mesonychids, based on dental characteristics...
, which eventually underwent aquatic adaptation
Aquatic adaptation
Several animal groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop as the animal ventures into water in order to find available food. As successive generations spend...
into the completely aquatic cetacea
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
ns.
- Order Artiodactyla/Cetartiodactyla
- Suborder TylopodaTylopodaTylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to Artiodactyla. They are extant in the wild in their native ranges of South America and Asia, while Australian feral camels are an introduced species. The group has a long fossil history in North America and Europe...
- Family †AnoplotheriidaeAnoplotheriidaeAnoplotheriidae is an extinct family of even-toed ungulates , endemic to Europe during the Eocene and Oligocene 48.6—23.030 Ma, existing for approximately . They were, most likely, all terrestrial herbivores.-Taxonomy:...
? - Family †Choeropotamidae?
- Family †Cainotheriidae
- Family †Merycoidodontidae
- Family †Agriochoeridae
- Family Camelidae: camelCamelA camel is an even-toed ungulate within the genus Camelus, bearing distinctive fatty deposits known as humps on its back. There are two species of camels: the dromedary or Arabian camel has a single hump, and the bactrian has two humps. Dromedaries are native to the dry desert areas of West Asia,...
s and llamaLlamaThe llama is a South American camelid, widely used as a meat and pack animal by Andean cultures since pre-Hispanic times....
s (6 species) - Family †OromerycidaeOromerycidaeOromerycidae is a small extinct family of artiodactyls closely related to living camels, known from the middle to late Eocene of western North America....
- Family †XiphodontidaeXiphodontidaeXiphodontidae is an extinct family of even-toed ungulates , endemic to Europe during the Eocene 40.4—33.9 Ma, existing for approximately .. They were, most likely, all terrestrial herbivores.-Taxonomy:...
- Family †Anoplotheriidae
- Suborder SuinaSuinaThe suborder Suina are lineage of mammals that today includes the families Suidae and Tayassuidae and their fossil kin.- Classification :The suborder Suina includes Suidae and Tayassuidae...
- Family SuidaeSuidaeSuidae is the biological family to which pigs belong. In addition to numerous fossil species, up to sixteen extant species are currently recognized, classified into between four and eight genera...
: pigs (19 species) - Family Tayassuidae: peccaries (4 species)
- Family †Sanitheriidae
- Family Suidae
- Suborder CetruminantiaCetruminantiaCetruminantia is a clade made up of the Cetacodontamorpha and their closest living relatives, the ruminants....
- unranked Cetancodontamorpha
- Genus †Andrewsarchus?
- Family †Entelodontidae
- Infraorder Cetancodonta
- Clade CetaceaCetaceaThe order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
: whales (about 90 species) - Family †RaoellidaeRaoellidaePreviously grouped with Helohyidae, Raoellidae is now a family in the Suborder Cetancodonta. It is found in Eocene of South and Southeast Asia....
- Family †DichobunidaeDichobunidaeDichobunidae is an extinct family of early even-toed hoofed mammals known from the early Eocene to late Oligocene of North America, Europe, and Asia. Dichobunidae includes some of the earliest known artiodactyls, such as Diacodexis....
- Family †Helohyidae
- Family †Cebochoeridae
- Family †AnthracotheriidaeAnthracotheriidaeAnthracotheriidae is a family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, Elomeryx, first appeared during the Middle Eocene in Asia...
- Family HippopotamidaeHippopotamidaeHippopotamuses are the members of the family Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.- Characteristics :...
: hippos (2 species)
- Clade Cetacea
- unranked RuminantiaRuminantiaRuminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the...
morpha- Infraorder TragulinaTragulinaTragulina is an infraorder of even-toed ungulates. Only the chevrotains survive to the present, including the genera Tragulus and Hyemoschus.-Taxonomy:The following is the taxonomy of the group...
- Family †Amphimerycidae
- Family †Prodremotheriidae
- Family †ProtoceratidaeProtoceratidaeProtoceratidae is an extinct family of herbivorous North American artiodactyls that lived during the Eocene through Pliocene at around 46.2—4.9 Ma., existing for approximately .-Taxonomy:...
- Family †HypertragulidaeHypertragulidaeHypertragulidae is an extinct family of even-toed ungulates , endemic to North America, Europe, and Asia during the Eocene through Miocene, living 46.2—13.6 Ma, existing for approximately ....
- Family †Praetragulidae
- Family Tragulidae: chevrotains (6 species)
- Family †Archaeomerycidae
- Family †Lophiomerycidae
- Infraorder PecoraPecoraThe Pecora is a group of hoofed mammals that comprises most of the ruminants, including cattle, sheep, goats, antelopes,deer, giraffes, and pronghorn. The only extant members of the Ruminantia that are not pecorans are the chevrotains, which lack horns and whose four-chambered stomach is less...
- Family Antilocapridae: pronghornPronghornThe pronghorn is a species of artiodactyl mammal endemic to interior western and central North America. Though not an antelope, it is often known colloquially in North America as the prong buck, pronghorn antelope, or simply antelope, as it closely resembles the true antelopes of the Old World and...
(1 species) - Family GiraffidaeGiraffidaeThe giraffids are ruminant artiodactyl mammals that share a common ancestor with deer and bovids. The biological family Giraffidae, once a diverse group spread throughout Eurasia and Africa, contains only two living members, the giraffe and the okapi. Both are confined to sub-saharan Africa: the...
: GiraffeGiraffeThe giraffe is an African even-toed ungulate mammal, the tallest of all extant land-living animal species, and the largest ruminant...
and OkapiOkapiThe okapi , Okapia johnstoni, is a giraffid artiodactyl mammal native to the Ituri Rainforest, located in the northeast of the Democratic Republic of the Congo, in Central Africa...
(2 species) - Family †ClimacoceratidaeClimacoceratidaeClimacoceratidae is a family of superficially deer-like artiodactyl ungulates that were restricted to the Miocene of Africa. They are close to the ancestry of giraffes, with some genera, such as Prolibytherium, having originally identified as being giraffes.The climacoceratids, namely, of what is...
- Family Moschidae: musk deer (7 species)
- Family †Leptomerycidae
- Family Cervidae: deerDeerDeer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
(49 species) - Family †Gelocidae
- Family †PalaeomerycidaePalaeomerycidaePalaeomerycidae is an extinct family of ruminants , probably ancestral to deer and musk deer...
- Family †Hoplitomerycidae
- Family Bovidae: cattle, goats, sheep, and antelopeAntelopeAntelope is a term referring to many even-toed ungulate species indigenous to various regions in Africa and Eurasia. Antelopes comprise a miscellaneous group within the family Bovidae, encompassing those old-world species that are neither cattle, sheep, buffalo, bison, nor goats...
(135 species)
- Family Antilocapridae: pronghorn
- Infraorder Tragulina
- unranked Cetancodontamorpha
- Suborder Tylopoda
Anatomy, physiology and morphology
PIGS
PIGS is a four letter acronym that can stand for:* PIGS , Phosphatidylinositol glycan anchor biosynthesis, class S, a human gene* PIGS , the economies of Portugal, Italy , Greece and Spain...
and peccaries
Peccary
A peccary is a medium-sized mammal of the family Tayassuidae, or New World Pigs. Peccaries are members of the artiodactyl suborder Suina, as are the pig family and possibly the hippopotamus family...
) have retained four toes of fairly equal size, have simpler molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
, short legs, and often have enlarged canine teeth that form tusk
Tusk
Tusks are elongated, continuously growing front teeth, usually but not always in pairs, that protrude well beyond the mouth of certain mammal species. They are most commonly canines, as with warthogs, wild boar, and walruses, or, in the case of elephants and narwhals, elongated incisors...
s. Camelid
Camelid
Camelids are members of the biological family Camelidae, the only living family in the suborder Tylopoda. Dromedaries, Bactrian Camels, llamas, alpacas, vicuñas, and guanacos are in this group....
s and Ruminantia
Ruminantia
Ruminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the...
tend to be longer-legged, to walk on only the central two toes (though the outer two may survive as rarely-used dew-claws) and to have more complex cheek teeth well-suited to grinding up tough grasses.
Diet and feeding
The ancestors of the even-toed ungulates were omnivores that preferred plant material; now even-toed ungulates are generally herbivorousHerbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, although species in the suborder Suina
Suina
The suborder Suina are lineage of mammals that today includes the families Suidae and Tayassuidae and their fossil kin.- Classification :The suborder Suina includes Suidae and Tayassuidae...
(pigs and peccaries) are, like their primitive ancestors, omnivores. Larger stomachs and longer intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s have evolved because plant food is less easily digested than meat.
Tylopoda
Tylopoda
Tylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to Artiodactyla. They are extant in the wild in their native ranges of South America and Asia, while Australian feral camels are an introduced species. The group has a long fossil history in North America and Europe...
(camels, llamas and alpacas) and the chevrotain
Chevrotain
Chevrotains, also known as mouse deer, are small ungulates that make up the family Tragulidae, the only members of the infraorder Tragulina. There are 10 living species in three genera, but there are also several species only known from fossils...
s have a three-chambered stomach while the rest of Ruminantia
Ruminantia
Ruminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the...
have four-chambered stomachs. The handicap of a heavy digestive system has increased selective pressure for limb
Limb (anatomy)
A limb is a jointed, or prehensile , appendage of the human or other animal body....
bone adaptations to escape predators. Most species within Suina have a simple two-chambered stomach that allows an omnivorous diet, the babirusa
Babirusa
The North Sulawesi babirusa, Babyrousa celebensis, is a pig-like animal native to northern Sulawesi and the nearby Lembeh Islands in Indonesia. It has two pairs of large tusks composed of enlarged canine teeth. The canines in the maxilla penetrate the top of the snout, curving back toward the...
, however, is a herbivore. They have extra maxillary teeth to allow proper mastication
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
of plant material. Most of the fermentation occurs in the caecum with the help of cellulolytic microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s. Peccaries however have a complex stomach that contains four compartments. Microbial fermentation with the formation of high volatile fatty acid levels has been observed in the fore stomach, it has been proposed that their complex fore stomach is a means to slow digestive passage and increase digestive efficiency. Hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
es have a three-chambered stomach and do not ruminate, they consume grass during the night and may cover large distances (up to 20 miles) to feed. They eat around 68 kg of food each night, also relying on microbes to break down plant material with cellulase.
Rumination occurs in the ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
s (Ruminantia
Ruminantia
Ruminantia includes many of the well-known large grazing or browsing mammals: among them cattle, goats, sheep, deer, and antelope. All members of the Ruminantia are ruminants: they digest food in two steps, chewing and swallowing in the normal way to begin with, and then regurgitating the...
and Tylopoda
Tylopoda
Tylopoda is a suborder of terrestrial herbivorous even-toed ungulates belonging to Artiodactyla. They are extant in the wild in their native ranges of South America and Asia, while Australian feral camels are an introduced species. The group has a long fossil history in North America and Europe...
), whereby food is regurgitated and rechewed then broken down by microbes in the stomach. After ingestion of plant material it is mixed with saliva in the rumen
Rumen
The rumen, also known as a paunch, forms the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. It serves as the primary site for microbial fermentation of ingested feed...
and reticulum
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...
and separates into layers of solid and liquid material. The solids lump together to form a bolus
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
(also known as the cud
Cud
Cud is a portion of food that returns from a ruminant's stomach in the mouth to be chewed for the second time. More accurately, it is a bolus of semi-degraded food regurgitated from the reticulorumen of a ruminant. Cud is produced during the physical digestive process of rumination, or "chewing the...
), this is regurgitated by reticular contractions while the glottis
Glottis
The glottis is defined as the combination of the vocal folds and the space in between the folds .-Function:...
is closed. When the bolus enters the mouth, the fluid is squeezed out with the tongue and reswallowed. The bolus is chewed slowly to completely mix it with saliva and to break down the particle size. Ingested food passes to the 'fermentation chamber' (rumen and reticulum) where it is kept in continual motion by rhythmic contractions of this organ. Cellulytic microbes (bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
, and fungi
Fungus
A fungus is a member of a large 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, Fungi, which is separate from plants, animals, and bacteria...
) produce cellulase
Cellulase
400px|thumb|right|alt = Colored dice with checkered background|Ribbon representation of the Streptomyces lividans beta-1,4-endoglucanase catalytic domain - an example from the family 12 glycoside hydrolases...
, which is needed to break down the cellulose found in plant material. Without this mutual symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
ruminants would find plant material indigestible.
Habitat and distribution
Even-toed ungulates are found on every continent but Antarctica; they were introduced to AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
by humans.
Relationship with humans
The even-toed ungulates are of more economic and cultural benefit than any other group of mammals. There is clear evidence of antelopeAntelope
Antelope is a term referring to many even-toed ungulate species indigenous to various regions in Africa and Eurasia. Antelopes comprise a miscellaneous group within the family Bovidae, encompassing those old-world species that are neither cattle, sheep, buffalo, bison, nor goats...
s being used for food 2 million years ago in the Olduvai Gorge
Olduvai Gorge
The Olduvai Gorge is a steep-sided ravine in the Great Rift Valley that stretches through eastern Africa. It is in the eastern Serengeti Plains in northern Tanzania and is about long. It is located 45 km from the Laetoli archaeological site...
, part of the Great Rift Valley
Great Rift Valley
The Great Rift Valley is a name given in the late 19th century by British explorer John Walter Gregory to the continuous geographic trench, approximately in length, that runs from northern Syria in Southwest Asia to central Mozambique in South East Africa...
. Cro-Magnon
Cro-Magnon
The Cro-Magnon were the first early modern humans of the European Upper Paleolithic. The earliest known remains of Cro-Magnon-like humans are radiometrically dated to 35,000 years before present....
s relied heavily on reindeer for food, skins, tools and weapons; with dropping temperatures and increased reindeer numbers at the end of the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, they became the prey of choice. By around 12,500 years ago, reindeer remains accounted for 94 percent of bones and teeth found in a cave above the Céou River.
Cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
today are the basis of a multi-billion dollar industry worldwide. The international trade in beef for 2000 was over $30 billion and represented only 23 percent of world beef production.
Etymology
Artiodactyl is GreekGreek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, from ἄρτιος, ártios, "even", and δάκτυλος, dáktylos, "finger/toe", so the name is a translation of the description "even-toed".