Even-toed ungulate

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Even-toed ungulates
Temporal range: 55–0 Ma
Early Eocene-Holocene
Giraffe standing.jpg
Giraffe (Giraffa camelopardalis)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Eutheria
Superorder: Laurasiatheria
Order: Artiodactyla
Owen, 1848
Subclades

Artiodactyls, otherwise known as even-toed ungulates, are categorized under the order Mammalia. They are mainly herbivorous animals and, unlike the perissodactyls, are usually characterized by an even number of toes (two or four). This group includes some of the most economically important groups of mammals such as cattle, pigs, camels, goats and sheep, as well as other known animals such as giraffes, hippos, deer, or antelope. Molecular biological studies have shown that artiodactyls are probably paraphyletic with cetaceans. This means that some groups (especially the hippos) are more closely related to whales than with the other animals of this order. Modern phylogenetic systems take artiodactyls and cetaceans for common taxon of Cetartiodactyla.[1] The artiodactyls thus form a taxon, i.e., a group which, although not a closed community of descent, is characterized by common features.

Taxonomy[edit]

Anatomy[edit]

Artiodactyls have similar characteristics between each other, in particular the construction of the limbs, which are highly customized to aquatic life. As common features derived (synapomorphies) of even-toed ungulates were a special construction of the anklebone with two castors (trochlea tali proximalis and distalis) and the extended last lower premolar.[5] However, the discovery of this special anklebone has, in fossil cetaceans, has had many in the 2001 discussion about systematics rework their hunting methods.

General anatomy and fur[edit]

The mouse deer is the smallest even-toed ungulate

Artiodactyls are medium to large animals that are quadrupeds. There are two configuration types, which differ significantly in physical aspects. Porcines and hippos are characterized by a stocky body, short legs and a large head. Camels and ruminants on the other hand have a more slender build and long, thin legs. Size varies considerably. As the smallest member, the mouse deer, often reaches only 45 centimetres (18 in) in body length and a weight of 1.5 kilograms (3.3 lb). The largest members are - with up to 5 metres (16 ft) in length and 4.5 metric tons (5.0 short tons) in head weight - the hippo and - growing up to 5.5 metres (18 ft) high and 4.7 metres (15 ft) body length - the giraffe. All species display some form of sexual dimorphism: The males are consistently larger and heavier than the females, gender differences also exist in the forehead weapons, in deer usually only the males antlers, the horns of bovines are usually small or not present in the females, and the coat of Blackbucks differ between the genders in that the males coat is much darker than that of the females.

All members of this order are furry except for the nearly hairless hippos. Fur coverage vary in length and coloring depending on the habitat. Species in cooler regions can have a change of coat through. Camouflaged coat come in colors of yellow, gray, brown or black tones.

External construction of the limbs[edit]

Even-toed ungulates bear their name because they have an even number of toes (two or four) - in some peccaries the hind legs have a reduction in the number of toes to three. The central axis of a leg is between the third and fourth toe. These two middle toes are best designed. The first toe is missing in modern artiodactyls and can only be found in now extinct genera. The second and fifth toes are designed differently between species: in the hippos, they are directed forward and fully functional; for the other even-toed ungulates, they are arranged in reverse or completely reduced. For pigs and deer, piglets after the toes are still shared in soft, muddy ground and increase the contact surface. In most cases, however, they no longer touch the ground. In some groups, like the camels and giraffes, regression has progressed so far that the second and fifth toe are not even present.

When camels have only two toes present, the claws are transformed into nails. These claws are made of keratin, just like human nails, and consist initially of three parts, the plate (top and sides), the sole (bottom), and the bale (rear), which may be, however, grown in varying degrees. In general, the claws of the forelegs are wider and blunter than the hind legs and gape farther apart. Aside from camels, all even-toed ungulates put just the tip of the foremost phalanx on the ground. In camels, the horn formations on the feet to nails reduces the toes rest on an elastic pad made of connective tissue that forms a wide sole area.

Limbs[edit]

Hand skeletons of various mammals, left to right: orangutan, dog, pig, cow, tapir, horse

In the even-toed ungulates, there is a tendency to coalescence of metapodials (metacarpal - and metatarsals). For porcines and hippos, they are still isolated and coupled only by a taut connective tissue. When the camels and ruminants form a unit, the main metatarsals, merged, whose origins date from two bones often by longitudinal grooves on the front and rear side is still visible.[6]

The bones of the stylopodium (upper arm or thigh bone) and Zygopodiums (Elle and spoke or tibia and fibula) are usually elongated. The muscles of the limbs is predominantly localized rumpfnah what ensures that cloven often have very slender legs. A clavicle is never present, the scapula is very agile, his swing back and forth for added mobility with fast running.

The special construction of the legs ensures a rigid position of the lower limbs. Rotational movement of the legs are nearly impossible, but the immobility causes a higher stability when running at high speeds. In addition, many smaller artiodactyls have a very flexible body, contributing to their speed by increasing the stride length. In addition, the selection pressure to obtain high speeds with the flight of the specialized construction of the limbs increases the energy saved during slow movement, such as food intake.

Head and teeth[edit]

Many even-toed ungulates have a relatively large head. The facial skeleton is elongated and rather narrow, and the nasal bones run forward in one or two points. The frontal bone is enlarged backwards and displaces the parietal bone, which forms only part of the side of the cranium, especially in ruminants.

Horns and antlers[edit]

Outgrowths of the frontal bone characterize most forehead weapons carrier, as well such as this Gemsbok

Outgrowths of the frontal bone characterize most forehead weapons carrier, such as the Gemsbok. Four families of even-toed ungulates have end arms. The group of forehead weapons carrier, Pecora, have the musk deer and water deer but also have end unarmed members. The end weapons are mostly outgrowths of the frontal bone, which are built differently. The giraffes have bone pins, which are sheathed in hairy skin. Deer grow antlers with a peg-shaped bone structure which consists of bone and is rejected each year after the breeding season. The horns of the bovines are usually maintained for their entire life. The skin that covers the bone pins, separates horn cells that eventually form a hard sheath. The oldest horn layers are continuously moved toward the horn tip. With the exception of the four-horned antelope (and individual domestic animal breeds), all bovines have two horns. The Gabelhorn have horns that are formed similar to the bovines, except the horn sheaths are shed annually. The end weapons can serve for posturing, the battling for mating privilege and for defense. In almost all cases they are sexually dimorphic, in that females lack them.

Teeth[edit]

The canines of many artiodactyls develop into tusks
Dental formula I C P M
30–44 = 0–3 0–1 2–4 3
1–3 1 2–4 3

The dentition of artiodactyls is variable; it can, however, discern two trends. The porcine and hippos have a relatively large number of teeth (with some pigs containing 44). The dentition is more adapted to a squeezing mastication, which is the tendency for omnivores such as pigs. With camels and ruminants, the number of teeth is reduced; there is often a yawning as diastema, a designated gap in the teeth where the molars are aligned on a milled for crushing plant matter.

The incisors are often reduced in ruminants, as they are completely absent on the upper jaw, instead pressing the lower incisors against a dental plate. The canines are pronounced differently: In the porcine they are enlarged and tusk-like, and are used for digging in the ground and for defense. In ruminants, the upper canine in males of species without end arms (mouse deer, musk deer, water deer...) is enlarged and used as a weapon in the battle for the mating privilege. On the other hand, species with frontal weapons, usually, are missing the upper canine. The lower canines of ruminants resemble the incisors, so that these animals have eight uniform teeth in the front part of the lower jaw.

The molars of porcine provide a few bumps. In contrast, the camels and ruminants have bumps that are crescent-shaped melting strips reshuffled (selenodont).

Senses[edit]

In order to undertake the environmental primarily serves the sense of smell, which is very well developed as in most mammals. Even the sense of hearing is very strong; supporting this is through the mobile existing in many species external ear. Unlike many other mammals they have a poor sense of sight which is least pronounced in ruminants and camels. Above all, the motion perception is developed, stationary objects are rather not perceived. Similar to many other animals, which must be constantly mindful of predators that are eye laterally attached to the head, they have an almost complete panoramic view and the earliest possible detection of threats.

Digestive System[edit]

Pigs have a simple sack-shaped stomach, unlike the other artiodactyls
Deer have such a multi-chambered stomach all ruminants, which is used for better utilization of the plant food

Pigs have a simple sack-shaped stomach, unlike the other even-toed ungulates.[7]

Deer have such a multi-chambered stomach, as with all ruminants, which is used for better utilization of the plant food. As an adaptation to the indigestible plant food, artiodactyls have some peculiarities of the digestive tract developed which are especially strong in ruminants. The mouth often has additional salivary glands and the oral mucosa is often heavily callused to avoid injury from hard plant parts and to allow easier transport of roughly chewed food..

The stomach of ruminants eventually divided into three or four sections: the rumen, the reticulum, the omasum and the abomasum.[7] They're classified within the ruminants particularly ethnic piglets missing the omasum, otherwise show all kinds of subordination to the same building and the same digestive way. The rumen are glands free, here roughly chewed food is decomposed by microorganisms, and promoted in small portions back into the oral cavity, where it is ruminated before it comes into the actual stomach and is further digested. (See Detailed in Article ruminants). This digestion has two advantages: firstly, can the indigestible plant food are best digested and utilized. Secondly, the duration of the actual food consumption is - especially with the unfavorable perception of the environmental posture with the head close to the ground - shortened, which is in view of the threat of predators an advantage; rumination can then take place in sheltered places.[8]

The intestine of artiodactyls, like many herbivorous mammals, is generally very long with the small intestine is heavily looped. Perrisodactyls, in contrasts, have fermentation taking place only in the intestine, with a simpler colon and less voluminous construction.

Urinary and sexual apparatus[edit]

The Japanese serow has glands in the eyes that are clearly visible

The construction of the urinary and sexual organs of cloven hoofed animals also shows some peculiarities. The penis is curved S-shape at rest and resting in a pocket under the skin on the belly. He is fibroelastisch, that is, the corpora cavernosa are developed only slight and the erection causes mainly an extension of this curvature and thus an extension, but hardly a thickening of the penis. This construction of the penis is found in a similar manner with the whales and represents a sign of the close relationship. The testicles are located in the scrotum and thus outside the abdominal cavity. The ovaries of many females make a descent (prolapse ovary) by - comparable to the testicle descent of many male mammals - and are close to the pelvic inlet at the level of the fourth lumbar vertebra. The uterus is zweihörnig formed (uterus bicornis).[9]

The number of mammary glands is variable and correlates as in all mammals about the litter size. Originally two rows of were probably teat from the armpit to the groin area available. This original arrangement is still found in some real pigs who also have the highest litter size of all cloven-hoofed animals. In most cases, however, it is come to a reduction of the number of teats, the other cloven-hoofed animals have only one or two pairs of teats. These form a in some species udder in the groin region.

Secretory glands in the skin are present in virtually all types and can be located at different places, as in the eyes, behind the horns, the neck or back, on the feet or in the anal region.

Distribution and habitat[edit]

Artiodactyls are native to almost all of the world, with the exception of Oceania - Australia, New Zealand and the many remote pacific islands, with pigs being feral. Today, the latter inhabit Africa and Asia. In America, they're relatively species-poor, particularly in South America, where only peccaries, llamas and vicunas, and capreolinae occur. Humans have introduced different artiodactyls worldwide as hunting animals among others, e.g., pigs, so these animals are found almost everywhere today, where there are people.

Artiodactyls inhabit almost all habitats, from tropical rain forests and steppes to the desert areas and high mountain regions. The greatest biodiversity prevails in open habitats such as grasslands and open forests. These animals are marked bottom dwellers, and only a few species lead a semi-aquatic, e.g., hippos. Some species have colonized the high mountains and can climb excellently.

Lifestyle[edit]

Social behavior and activity times[edit]

Artiodactyls, like impalas, live in groups, whereas others sometimes live in pairs, like giraffe

Artiodactyls often live in groups. The social behavior of even-toed ungulates varies from species to species. Generally, however, there is a tendency to merge into larger groups, but there are also solitary or in pairs. Species living in groups, often have a hierarchy, both among males and females. But some species also live in harem groups, which means that a single male gathers several females and their common offspring around and no other rivals are tolerated. In other species the females and juveniles make up for the greater part of the year on their own groups, while males are solitary or live in bachelor groups and seek the females groups only during the mating season. Many occur during mating season for fierce fighting around the mating privilege between the males, which are discharged to the end weapons.

Many artiodactyls are territorial and mark their territory, for example, with glandular secretions or urine. In addition to year-round sedentary species, there are animals that take seasonal migrations in search of better grazing places.

There are diurnal, crepuscular and nocturnal members as well as species associated with the day-night scheme which may vary depending on the season or habitat.

Diet[edit]

Most artiodactyls are herbivores whose diet range may vary depending on the nature and habitat. They often eat grasses, herbs or leaves, but can also consume other parts of plants such as tubers or fruits. Pigs, peccaries and, in a lesser extent, mouse deer, are omnivorous who supplement their diets with insects, worms and sometimes small vertebrates. Most species are dependent on a daily water intake, but some live in dry habitats; those who do, such as camels, can survive for weeks without drinking.

Reproduction and life expectancy[edit]

Many artiodactyls, like wildebeest are born with hair

Generally, even-toed ungulates have a tendency to long gestation period, smaller litter size and high level of development of the newborn. As with many other mammals, species in temperate or polar regions have a fixed mating season, while breeding can take place year-round in more tropical areas. They have a polygynous mating behavior, meaning a male so often pairs with several females, and competition will not be tolerated. The copulation is usually done by the mammals typical "ride up". In camels exclusively it is performed while lying down.

The length of the gestation period varies 4–5 months for porcine, deer, and musk deer, 6 to 10 months with hippos, deer and bovines, 10 to 13 months with camels, and 14 to 15 months with giraffes. Most deliver one or two babies, but some pigs can deliver up to ten.

The newborns are precocial and come with open eyes and, with the exception of generally hairless hippos, hairy to the world. In deer and pigs, the striped or spotted coat in juveniles disappear as they grow. The juveniles of some species spend their first weeks with their mother in a safe storage location, where others may soon run after birth and follow the herd within a few hours or days.

The life expectancy is typically 20 to 30 years, as in many mammals smaller species often have a shorter lifespan than larger species. The oldest animals like hippos, cows and camels, can reach 40 to 50 years.

Predators and parasites[edit]

Artiodactyls have different natural predators depending on their size and habitat. There are several carnivores who would prey on such mammals such as cats, dogs or bears. Other predators are, for example, crocodiles, large raptors and, for small species and young animals, giant snakes.

Parasitic infection can come around from nematodes, botflies, fleas, louse or flukes, but they have debilitating effects on them only when the infestation is severe.

Interactions with humans[edit]

Domestication[edit]

Some artiodactyls, like sheep, have been domesticated for thousands of years
Some species are used as pack animals, like Dromedary camels

Some artiodactyls, like sheep, have been domesticated for thousands of years.

Some species like the dromedary camel can be used as pack and riding animals. Artiodactyls have been hunted by primitive humans for various reasons: for meat, to process their fur into clothing, and to use their forehead weapons, bones and teeth as weapons or tools. The domestication of animals began no later than the 8,000 B.C.E. To date, humans have domesticated goats, sheep, cattle and pigs. Initially, livestock was used primarily as food suppliers, but then later, around 3,000, the animals were used for work activities.[10]

Today, artiodactyls are kept for various reasons. These are primarily for their meat, their milk (as with goat and cows) and the processing of their skin, wool or fur to leather and other clothing. They're even used for work, to ride or used as pack animals, such as the domestic cattle, the water buffalo, the yak or camels.

Two basic types of domestication were used. On one hand, the animals in different breeds were bred, which are spread throughout the world and partly differ significantly from the wild species, as with domestic cattle, domestic pigs, domestic goats and domestic sheep. Other pets have largely remained in their region of origin and, when compared with the wild species, changed little, like the reindeer, some cows (like the water buffalo, the banteng, the gaur or yak) and camels (like the dromedary, the llama or alpaca).[10]

Some are not only for food assistance, but also for sport. Such practices are not out of necessity, but for obtaining trophies, and are conducted under partly severe criticism and have driven some species, such as the Alpine ibex, or the Arabian Oryx, to the brink of extinction.

Threats[edit]

Aurochs has been wiped out since the 17th century

Aurochs, the ancestral form of the domestic cattle, have been wiped out since the 17th century. The hazard level of each even-toed ungulate is different. Some species are synanthropic (such as the wild boar) and can spread their range or have been brought by humans as farm animals or runaway pets in regions where they were not indigenous to. Some artiodactyls also benefit from the fact that their predators were severely decimated as competitors of the ranchers, such as Thylacine.[11]

Conversely, many artiodactyls have declined significantly in their population, and some were even eradicated. The reasons for this is over-hunting, and, more recently though, increasing habitat destruction. Currently extinct are several gazelle species (such as the Algerian gazelle), several Malagasy Hippopotamus species, the Blue Buck and the Schomburgk's Deer. Two species, the Arabian Oryx and the Saudi Gazelle, are considered by the IUCN as extinct in the wild. 14 species are considered Critically Endangered, including Addax, the Kouprey, the red deer, Przewalski's gazelle, the Saiga, and the pygmy hog. Twenty four species are considered endangered.[12][13]

Taxonomy and phylogeny[edit]

Richard Owen coined the term "even-toed ungulate"

The classification of artiodactyls is hotly debated. The reason is that on one hand, there's a morphologically defined order, but on the other hand, the whales have evolved from them and some groups (hippos) are more closely related with these than with the other even-toed ungulates. This makes the artiodactyls in phylogenetic (defined through the tribal development) classifications - which are significant in recent times - to a paraphyletic taxon, that is a group which, although descended from a common progenitor, not all members include this as a common ancestor. Since the phylogenetic classification, by chance, only monophyletic taxa recognizes, that is, groups that are descended from a common ancestor and all descendants include this forefathers who have artiodactyl with the cetaceans as a Cetartiodactyla designated taxon are summarized. Here first is the traditional classification presented and then the phylogenetic view of even-toed ungulates are explained.

Morphological classification of Artiodactyla[edit]

Linnaeus postulated a close relationship between camels and ruminants. Henri de Blainville recognized the similar construction of the limbs of these animals with those of pigs and hippos and the British zoologist Richard Owen coined in 1848 the term "even-toed ungulates" and the scientific name Artiodactyla.

Since that time, the composition of this group was clear and was hardly ever questioned. The construction of the internal systematics (stomach and the molars) served for classification. Pigs, peccaries and hippos have molars that have well-developed roots which form early in short-term growth of the teeth, a simple stomach, digesting them directly, without rehashing. Thus they were grouped together as non-ruminants, or Porcine in the broader sense. All other even-toed ungulates have molars with a selenodontem construction (crescent-shaped melting strips) and have the ability to ruminate. Differences in the construction of the stomach could imagine that the ability of rumination has developed two independently; Therefore, the camels are not to be the actual ruminants counted, but compared with this as calluses. Inside the ruminants the primitive forehead unarmed mouse deer are compared with all other groups as end armourbearer and are classified under Pecora.

From a purely morphological point of view, therefore, the following suspected descent conditions, which were widely accepted by the end of the 20th century were:[14]

Even-toed ungulates 
 Porcine in the broader sense (Suina/Neobunodontia) 

  Porcine in the narrow sense (Suoidea)



 Hippos (Hippopotamidae)



 Selenodontia 

 Camels (Tylopoda)


 Ruminants 

 Mouse deer (Tragulidae)



 Forehead weapon carriers (Pecora)





Morphological classification of Cetacea[edit]

The mesonychid were long considered ancestors of whales

The mesonychid, carnivorous ungulates from the early Cenozoic, were long considered to be the ancestors of cetaceans. Modern cetaceans are highly accustomed sea creatures that phenotypically have little in common with other mammals - they're similar to other marine mammals such as seals and sea cows which are exclusively based on convergence. It stands to reason, however, that they must have evolved from land-dwelling mammals. The most likely candidates for the ancestors of cetaceans were long thought to be mesonychids. These were partly gigantic, carnivorous animals from the early Cenozoic (Paleocene and Eocene), who wore hooves instead of claws on their feet. Their molars were adapted to a carnivorous diet, resembling the teeth today in toothed whales, which are aligned for a fish based diet, and, unlike other mammals, have a uniform construction.

The suspected conditions can be as follows:[15][16]

Paraxonia 

 Artiodactyla


 Cete 

 Mesonychia †



 Cetacea




Research History[edit]

Molecular and morphological studies confirmed that whales are the closest living relatives of hippos

Molecular and morphological studies confirmed that cetaceans are the closest living relatives of hippos. In the 1990s, the biological systematics not only went in accordance with aspects of the build and the fossil findings, but also by means of molecular biology to develop studies. It will seek, by sequencing the DNA and RNA to obtain genetic information and compare it with the data of other living beings, to elicit the degree of relationship based on the degree of similarity notes. This method was and is used in many living things and has changed the classification of many taxa significantly. These methods were also performed between even-toed ungulates and cetaceans with the surprising result that the closest relatives of the whales and hippos are a paraphyletic group Artiodactyla.

Among the first who came to that conclusion, Dan Graur and Desmond Higgins, included a study published in 1994.[17] However, they did not recognized hippos and kept the ruminants for the sister group of whales. Subsequent studies then came to the conclusion that the hippos represent the closest living relative of whales; this was among other things based on Caseingenen,[18] SINEs,[19] fibrinogen sequences,[20] cytochrome - and rRNA sequences,[21][22][23] IRBP - and vWF gene sequences,[24] adrenergic receptors,[25] and apolipoproteins confirmed.[26] In one of these studies, the scientific names of Cetacea and Artiodactyla was established in 1997 and for the first time the name "Cetartiodactyla", proposed by Claudine Montgelard, Francois M. Catzeflis and Emmanuel Douzery, was composed.

In Pakistan, 2001, they found parts of the limb skeleton of a creature as big as a wolf, Pakicetus, and another as large as a fox, Ichthyolestes; they were two primitive cetaceans from the Eocene before about 48 million years ago. These findings not only showed that archaeocetes were land-based than previously thought to a greater extent, but clearly also referred to the special construction of the ankle bone with a double-rolled joint surface. This feature has long been considered the exclusive feature of even-toed ungulates and because it has now been discovered even in early cetaceans, the close relationship of the two groups could be assigned morphologically. In more modern cetaceans, there was a comprehensive reduction of hind limbs that made the construction of the hind legs of these animals inconclusive about possible lineages between the two. The mesonychid did not show this special construction of the talus, thus a shared lineage with cetaceans was excluded.

Although the specific construction of the talus finished a close relationship between artiodactyls and cetaceans, the question of whether the even-toed ungulates are paraphyletic is not answered. Therefore, morphological studies were conducted to support the findings of molecular biology of hippos and whales. In the arrangement of cusps of molars, the construction of the metatarsal bones and the skull support a sister group relationship between these two taxa. Whether the striking commonality, the loss of fur and the sebaceous glands is controversial.

Hippos are a geologically young group, which raises questions about their origin

The hippos are a geologically young group, which raises questions about their origin. The oldest member of cetaceans is in the early Eocene (53 million years ago approximately), whereas the oldest known hippo dates back only to the Miocene (about 15 million years ago). Because there's a 40 million year gap between whales and hippos in the fossil record, doubts have arisen. Given the relatively good fossil fund rate of even-toed ungulates, it seems unlikely that there are no remains of ancestors of hippos. Some studies declared the late emergence of hippos is that they're relatives of peccaries and split recently, but this seems unlikely because of the molecular findings. The focus of research is therefore focused on the Anthracotheriidae, one from the Eocene to Miocene which has already been described in their discovery in the 19th century as a "hippo-like". A study from 2005 showed that they have a very similar skull structure, but the hippos have a different tooth design. As a possible scenario was nevertheless believed that cetaceans and the Anthracotheriidae descended from a common ancestor and the hippos were developed from the Anthracotheriidae. A study published in a 2015 study was able to confirm this, but also revealed that the hippos, not as it was suspected, were phylogenetically much more developed, but can be derived from more original representatives of Anthracotherien. The newly introduced genus Epirigenys from eastern Africa is thus the sister group of hippos.

Inner systematics[edit]

The overwhelming molecular findings and some morphological indications suggest that the even-toed ungulates are paraphyletic to the cetaceans and form with them a taxon Cetartiodactyla; the monophyly of Cetartiodactyla is well protected by a total of molecular and anatomical references. Shared modern nomenclatures divides Cetartiodactyla in five subordinate taxa that are also monophyletic, each with high probability: the camels (Tylopoda), the porcine (Suina), the ruminants (ruminant), the hippo (Ancodonta), and the whales (Cetacea).

The ruminants are likely to be more closely related to whales and hippos as with the other even-toed ungulates - this has so far only been explored by molecular biology but not investigated morphologically and is therefore controversial. The presumed lineages within Cetartiodactyla can be represented in the following cladogram:[27]

Cetartiodactyla 

Camels (Tylopoda)


 N.N. 

 Porcine (Suina)


 Cetruminantia 
 Ruminants (Ruminantia) 

 Mouse deer (Tragulidae)



 Forehead weapon carriers (Pecora)



 Cetancodonta/Whippomorpha 

 Hippos (Hippopotamidae)



 Whales (Cetacea)






Camels are now considered a sister group of artiodactyls
The pronghorn is the only extant member of Gabelhorn carriers

The camels are now considered a sister group of all other even-toed ungulates.

The pronghorn is the only extant representative of Gabelhorn carrier. The four summarized as cloven taxa Cetartiodactyla are divided into ten extant families:[28]

  • The camels (Tylopoda) comprise only one family who Camels (Camelidae). It is a species-poor group of animals that are well adapted to extreme habitats - the Camel to deserts and the llamas, vicuna, and alpaca to high mountain regions.

The porcine (Suina) are made up of two families:

    • The Porcines (Suidae) are limited to the old world. These include the wild boar and the domesticated form, the domestic pig.
    • The peccaries or peccaries (Tayassuidae) are named after glands on their belly and are indigenous to Central and South America.
  • The ruminants consist of six families:
    • The mouse deer (Tragulidae) are the smallest and most primitive even-toed-ruminants; they inhabit forests of Africa and Asia.
    • The giraffe-like (Giraffidae) are composed of two outwardly different species: the giraffe and the okapi.
    • The musk deer or musk deer (Moschidae) is a kind of stag indigenous to East Asia.
    • The Gabelhorn carrier (Antilocapridae) comprise only one species: the North America pronghorn.
    • The deer (Cervidae) are made up of about 45 species, which are characterized by a pair of antlers, worn only the males generally. They're spread across Europe, among other species, the deer, red deer, the elk and reindeer.
  • The bovines (Bovidae) are the most species-rich. Among them are the cattle, the caprine, the gazelle-like and more than antelopes designated groups.
  • The Hippos (Hippopotamidae) comprise two types, the hippo and the pygmy hippo.
  • The whales (Cetacea) comprise 72 species and two suborders: toothed whales (Odontoceti) and baleen whales (Mysticeti)

The largest systematic problem within the subordinate taxa affects ruminants. It is generally accepted that the mouse deer is the sister group of the remaining five families. The systematics is confusing within the forehead weapons carrier. Although deer, musk deer and Gabelhorn carriers have traditionally been summarized as cervids (Cervioidea), molecular studies provide different - and inconsistent - results, so that the question of phylogenetic systematics forehead weapons carrier for the time being can not be answered.

Reconstruction of Indohyus

In December 2007, Hans Thewissen, professor at the Department of Anatomy at Northeastern Ohio Universities Colleges of Medicine and Pharmacy, hypothesized an alternative family tree. According to his studies, the next of kin of early whales were an extinct group called Raoellidae and both taxa put together the sister group of the remaining artiodactyl members, including the hippo

His findings come from the study of a new skeleton of the Kashmir-region in Pakistan. It was a member of the genus Indohyus, which is assigned to the Raoellidae. Mainly due to a bony ring on temporal bone (bulla), called the involucrum, which was previously associated only with cetaceans, as well as other features of the premolars and the bone structure, the close relationship was established.[29]

Outer systematics[edit]

Cetartiodactyla is classified within the higher mammals to the superiority of the Laurasiatheria filed, a mammalian group named after their putative origin in the extinct continent Laurasia. Which major groups within the Laurasiatheria the Cetartiodactyla are more closely related is still unresolved, however, the previously proposed set of ungulates is not a natural group. Various molecular studies can recognize different possible lineages: After a hypothesis Cetartiodactyla, together with the perissodactyls and ferae (pangolins and carnivores) a common taxon Fereuungulata - remains being unclear whether the odd-toed ungulates are more closely related to Cetartiodactyla or ferae. Another recently drawn up hypothesis contrast summarizes Perissodactyla, ferae and bats to a taxon pegasoferae together and sees Cetartiodactyla as its sister group.[30]

Evolution[edit]

The oldest fossils of even-toed ungulates dates back to the early Eocene (about 55 million years ago). Since these findings almost simultaneously appeared in Europe, Asia and North America, it is very difficult to determine the origin of artiodactyls accurately. These ancient creatures are classified in the group Dichobunoidea - their best-known and best-preserved member is Diacodexis from the family Diacodexeidae.[31] These are small (as small as a hare) animals with a slim build, long thin legs and a long tail. The hind legs were much longer than the front legs. The early to middle Eocene saw the emergence of the ancestors of most of today's mammals. The phylogeny of even-toed ungulates proceeded relatively uniformly and unspectacular, giant or bizarre animals (such as those in the perissodactyls originated), are hardly known in this group.[2]

The earliest whales evolved in the early Eocene (53 million years ago approximately) and have believed to have developed in the Indian subcontinent. From then on, they hit, due to the aquatic life, their own lineage.[32]

Entelodonts were stocky animals with a large head, which was characterized by bony bumps on the lower jaw

Two formerly widespread, but now extinct groups, of even-toed ungulates were Entelodont and Anthracotheriidae. The Entelodont existed from the middle Eocene to the early Miocene in Eurasia 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. Anthracotheriidae had a large, porcine build, with short legs and a remarkably elongated muzzle. This group appeared in the Middle Eocene and spread throughout Eurasia, Africa and North America. They lived up until the Pliocene. Anthracotheriidae were probably the ancestors of hippos, and, likewise, they probably led a similar aquatic lifestyle. The hippos even appeared in the Late Miocene and occupied Africa and Asia - they never got to the Americas.[2]

The camels (Tylopoda) were, during large parts of the Cenozoic, limited to North America; early forms like Cainotheriidae occupied Europe. Among the North American camels included groups like the stocky, short-legged Merycoidodontidae which was equipped with frontal weapons. This 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 America into Eurasia. North American variety have become extinct for reasons unknown around 10,000 years ago.

Members of the porcine (Suina) have been around since the Eocene. In the late Eocene or Oligocene, the two still existing families who were the ancestors of pigs always remained restricted to Eurasia and Africa and the peccaries, which became extinct in the Old World, exist today only in America.

Sivatherium were a group of giraffes with deer-like forehead weapons

The cattle and giraffe (Sivatherium) were a group consisting of the giraffes with deer-like forehead weapons. The ruminants are designed with many early forms. These early forms, which are classified as Tragulina, lived up to the Miocene in Africa, Eurasia and North America, and then died out, except for the mouse deer. In the Oligocene or Miocene, the other members, the majority remained confined to the Old World, developed. Within the giraffes (Giraffidae), emerging alongside the existing species, developed the stag-like end weapons. The deer (Cervidae) developed numerous species, but remained rather limited to Eurasia. Bovines and deer arrived relatively late in North America, however, the group with Gabelhorn carriers spread with numerous species, of which today only one species, the pronghorn, survived.[2]

South America was settled by the even-toed ungulates only in Pliocene some three million years ago when the land bridge at the Isthmus of Panama concluded. With peccaries, llamas and deceit deer, the South American artiodactyls, compared to the other continents, has remained poor in species. Among the mass extinction of mega-fauna at the end of the Pleistocene, the even-toed ungulates were less affected than other groups of mammals. One reason for this is that the larger members resided in Africa and there, unlike the other continents, at that time wasn't affected as much.

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