The even-toed ungulates (Artiodactyla) are ungulates (hoofed animals) whose weight is borne about equally by the third and fourth toes, rather than mostly or entirely by the third as in odd-toed ungulates (perissodactyls) such as horses.
Artiodactyla comes from Greek ??t??? (?rtios), "even", and d??t????, (d?ktylos), "finger/toe", so the name "even-toed" is a translation of the description .1] This group includes pigs, peccaries, hippopotamuses, camels, chevrotains (mouse deer), deer, giraffes, pronghorn, antelopes, sheep, goats, and cattle. The group excludes whales 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.[2]
Cladogram showing relations within Artiodactylamorpha
As with many mammal groups, even-toed ungulates first appeared during the Early Eocene (about 54 million years ago). In form, they were rather like
today's chevrotains: 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 ungulates (ancestors of today's horses and rhinos) 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 stomachs were better able to adapt to this coarse, low-nutrition diet, and
soon replaced the odd-toed ungulates as the dominant terrestrial herbivores. Now-extinct Artiodactyla which developed during the Miocene include the genera Ampelomeryx, Tauromeryx, Triceromeryx and others.
Classification
The following classification is based on the Spaulding et al., 2009[3] and the extant families recognised by Mammal Species of the World published in 2005.[4] 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.[5][6] This hypothesized ancestral group likely split into two branches around 54 million years ago.[7] 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 cetaceans.[8]
Giraffes necking (Giraffa camelopardalis) in Ithala Game Reserve, Northern KwaZulu Natal, South Africa.
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 tusks. Camelids 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.
The ancestors of the even-toed ungulates were omnivores that preferred plant material; now even-toed ungulates are generally herbivorous, although species in the suborder Suina (pigs and peccaries) are, like their primitive ancestors, omnivores. Larger stomachs and longer intestines have evolved because plant food is less easily digested than meat.
[10]
Tylopoda (camels, llamas and alpacas) and the chevrotains 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.[10] Most species within Suina have a simple two-chambered stomach that allows an omnivorous diet, the babirusa, however, is a herbivore.[11] 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 microorganisms. Peccaries however have a complex stomach that contains four compartments.[12] 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.[12] Hippopotamuses 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 ruminants (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.[11]
The even-toed ungulates are of more economic and cultural benefit than any other group of mammals.[10] There is clear evidence of antelopes being used for food 2 million years ago in the Olduvai Gorge, part of the Great Rift Valley.[10] 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. By around 12,500 years ago, reindeer remains accounted for 94 percent of bones and teeth found in a cave above the C?ou River.[14]
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.[15]
Jewish biblical laws of Kashrut define a cloven hoof as one of two key requirements for an animal to be capable of consideration for Kosher consumption.
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 tusks. Camelids 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.
The ancestors of the even-toed ungulates were omnivores that preferred plant material; now even-toed ungulates are generally herbivorous, although species in the suborder Suina (pigs and peccaries) are, like their primitive ancestors, omnivores. Larger stomachs and longer intestines have evolved because plant food is less easily digested than meat.[10]
Tylopoda (camels, llamas and alpacas) and the chevrotains 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.[10] Most species within Suina have a simple two-chambered stomach that allows an omnivorous diet, the babirusa, however, is a herbivore.[11] 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 microorganisms. Peccaries however have a complex stomach that contains four compartments.[12] 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.[12] Hippopotamuses 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 ruminants (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.[11]
The even-toed ungulates are of more economic and cultural benefit than any other group of mammals.[10] There is clear evidence of antelopes being used for food 2 million years ago in the Olduvai Gorge, part of the Great Rift Valley.[10] 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. By around 12,500 years ago, reindeer remains accounted for 94 percent of bones and teeth found in a cave above the C?ou River.[14]
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.[15]
Jewish biblical laws of Kashrut define a cloven hoof as one of two key requirements for an animal to be capable of consideration for Kosher consumption.
^ ab Janis, C. & Jarman, P. (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 498?499. ISBN 0-87196-871-1.
^ ab Shively, C. L. et al. (1985). "Some Aspects of the Nutritional Biology of the Collared Peccary". The Journal of Wildlife Management49 (3): 729?732. doi:10.2307/3801702. JSTOR 3801702.
^ Pough, F. W., Janis, C. M. & Heiser, J. B. (2005) [1979]. "Major Lineages of Mammals". Vertebrate Life (7th ed.). Pearson. pp. 539. ISBN 0-13-127836-3.
^ Clay, J. (2004). World Agriculture and the Environment: A Commodity-by-Commodity Guide to Impacts and Practices. Washington, D.C., USA: Island Press.
ISBN 1-55963-370-0.
Antilocapridae is a family of artiodactyls endemic to North America. Their closest extant relatives are the giraffids. Only one species, the pronghorn (Antilocapra americana), is living today; all other members of the family are extinct. The living pronghorn is a small ruminant mammal resembling an antelope. It bears small, forked horns. [more]
Camelids are members of the biological family Camelidae, the only living family in the suborder Tylopoda. dromedaries, Bactrian camels, llamas, alpacas, vicu?as, and guanacos are in this group. [more]
Deer (singular and plural) are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, mule deer such as black-tailed deer, elk, moose, red deer, reindeer (caribou), fallow deer, roe deer and chital. Male deer of all species (except the Chinese water deer) and also female reindeer grow and shed new antlers each year. In this they differ from permanently horned animals such as antelope; these are in the same order as deer and may bear a superficial resemblance. The musk deer of Asia and water chevrotain (or mouse deer) of tropical African and Asian forests are not usually regarded as true deer and form their own families, Moschidae and Tragulidae, respectively. [more]
Entelodonts, sometimes nicknamed hell pigs or terminator pigs, is an extinct family of pig-like omnivores endemic to forests and plains of North America, Europe, and Asia from the middle Eocene to early Miocene epochs (37.2?16.3 mya), existing for approximately 20.9 million years. [more]
The 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 giraffe to the open savannas, and the okapi to the dense rainforest of the Congo. The two species look very different on first sight, but share a number of common features, including a long, dark-colored tongue, lobed canine teeth, and horns covered in skin, called "ossicones". [more]
Hypertragulidae is an extinct family of even-toed ungulates (order Artiodactyla), endemic to North America, Europe, and Asia during the Eocene through Miocene, living 46.2?13.6 Ma, existing for approximately 32.6 million years. [more]
Oreodonts, sometimes called prehistoric "ruminating hogs," were a family of cud-chewing plant-eater with a short face and tusk-like canine teeth. As their name implies, some of the better known forms were generally hog-like, and the group was once thought to be a member of Suina, the pigs, peccaries and their ancestors, though recent work indicate they were more closely related to camels. The scientific name means Mountain teeth and refer to the appearance of the molars. Most oreodonts were sheep-sized, though some genera grew to the size of cattle. They were heavy bodied, with short four-toed hooves. Unlike any modern ruminant, they had long tails. [more]
Musk deer are artiodactyls of the genus Moschus, the only genus of family Moschidae. They are more primitive than the cervids, or true deer, in not having antlers or facial glands, in having only a single pair of teats, and in possessing a gall bladder, a caudal gland, a pair of tusk-like teeth and?of particular economic importance to humans?a musk gland. Moschids live mainly in forested and alpine scrub habitats in the mountains of southern Asia, notably Himalayas. Moschids are entirely Asian in their present distribution, being extinct in Europe where the earliest musk deer are known from Oligocene deposits. [more]
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. The family includes the domestic pig, Sus scrofa domesticus or Sus domesticus, in addition to numerous species of wild pig, such as the babirusa Babyrousa babyrussa and the warthog Phacochoerus aethiopicus. All suids are native to the Old World, ranging from Asia and its islands, to Europe, and Africa. [more]
Tayassuidae
A peccary (plural peccaries; also javelina and skunk pig; Portuguese javali and Spanish jabal?, sajino or pecar?) 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 (Suidae) and possibly the hippopotamus family (Hippopotamidae). They are found in the southwestern area of North America and throughout Central and South America. Peccaries usually measure between 90 and 130 centimetres (3.0 and 4.3 ft) in length, and a full-grown adult usually weighs between about 20 to 40 kilograms (44 to 88 lb). The word ?peccary? is derived from the Carib word pakira or paquira. [more]
Tragulidae
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 (extant) species in three genera, but there are also several species only known from fossils. The extant species are found in forests in South and Southeast Asia, with a single species in the rainforests of Central and West Africa. They are solitary or live in pairs, and feed almost exclusively on plant material. Depending on exact species, the Asian species weigh between 0.7 and 8.0 kilograms (1.5 and 18 lb), and the smallest species are also the smallest ungulates in the world. The African chevrotain is considerably larger at 7?16 kilograms (15?35 lb). [more]
^ ab Janis, C. & Jarman, P. (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 498?499. ISBN 0-87196-871-1.
^ ab Shively, C. L. et al. (1985). "Some Aspects of the Nutritional Biology of the Collared Peccary". The Journal of Wildlife Management49 (3): 729?732. doi:10.2307/3801702. JSTOR 3801702.
^ Pough, F. W., Janis, C. M. & Heiser, J. B. (2005) [1979]. "Major Lineages of Mammals". Vertebrate Life (7th ed.). Pearson. pp. 539. ISBN 0-13-127836-3.
^ Clay, J. (2004). World Agriculture and the Environment: A Commodity-by-Commodity Guide to Impacts and Practices. Washington, D.C., USA: Island Press. ISBN 1-55963-370-0.
^ Boisserie, Jean-Renaud; Fabrice Lihoreau and Michel Brunet (February 2005). "The position of Hippopotamidae within Cetartiodactyla". Proceedings of the National Academy of Sciences102 (5): 1537-1541. Retrieved on 2007-06-09.
