skeleton on display at the
Museum of Osteology Apart from cetaceans, artiodactyls are generally
quadrupeds. Two major body types are known: suinids and hippopotamuses are characterized by a stocky body, short legs, and a large head; camels and ruminants, though, have a more slender build and lanky legs. Size varies considerably; the smallest member, the mouse deer, often reaches a body length of only and a weight of . The largest member, the hippopotamus, can grow up to in length and weigh , and the giraffe can grow to be tall and in body length. All even-toed ungulates display some form of
sexual dimorphism: the males are consistently larger and heavier than the females. In the majority of deer species, only the males grow antlers, and the horns of
bovines are usually small or not present in females. Male
Indian antelopes have a much darker coat than females. In cetaceans the two forelimbs have evolved into flippers, and the hind legs lost to external view; the largest cetaceans, up to long, are considerably larger than any other artiodactyls. Almost all even-toed ungulates have fur, with the exception being the nearly hairless hippopotamus. Fur varies in length and coloration depending on the habitat. Species in cooler regions can shed their coat in summer. Camouflaged coats come in colors of yellow, gray, brown, or black tones. Cetaceans are largely hairless, apart from a few small facial
whiskers. These claws consist of three parts: the plate (top and sides), the sole (bottom), and the bale (rear). In general, the claws of the forelegs are wider and blunter than those of the hind legs, and they are farther apart. Aside from camels, all even-toed ungulates put just the tip of the foremost
phalanx on the ground. ,
dog,
pig,
cow,
tapir, and
horse. Highlighted are the even-toed ungulates pig and cow. In even-toed ungulates, the bones of the stylopodium (upper arm or thigh bone) and
zygopodiums (tibia and fibula) are usually elongated. The muscles of the limbs are predominantly localized, which ensures that artiodactyls often have very slender legs. A
clavicle is never present, and the
scapula is very agile and swings back and forth for added mobility when running. The special construction of the legs causes the legs to be unable to rotate, which allows for greater stability when running at high speeds. In addition, many smaller artiodactyls have a very flexible body, contributing to their speed by increasing their stride length.
Head Many even-toed ungulates have a relatively large head. The skull is elongated and rather narrow; the
frontal bone is enlarged near the back and displaces the
parietal bone, which forms only part of the side of the cranium (especially in ruminants).
Horns and antlers and its horns.|alt=A gemsbok, a type of antelope Four families of even-toed ungulates have cranial appendages. These
Pecora (with the exception of the
musk deer), have one of four types of cranial appendages: true horns,
antlers,
ossicones, or
pronghorns.
True horns have a bone core that is covered in a permanent sheath of keratin, and are found only in the
bovids.
Antlers are bony structures that are shed and replaced each year; they are found in deer (members of the family
Cervidae). They grow from a permanent outgrowth of the frontal bone called the pedicle and can be branched, as in the
white-tailed deer (
Odocoileus virginianus), or palmate, as in the
moose (
Alces alces).
Ossicones are permanent bone structures that fuse to the frontal or parietal bones during an animal's life and are found only in the
Giraffidae.
Pronghorns, while similar to horns in that they have keratinous sheaths covering permanent bone cores, are deciduous. All these cranial appendages can serve for posturing, battling for mating privilege, and for defense. In almost all cases, they are sexually dimorphic, and are often found only on the males. One exception is the species
Rangifer tarandus, known as
reindeer in Europe or caribou in North America, where both sexes can grow antlers yearly, though the females' antlers are typically smaller and not always present.
Teeth of Suina (here, a
babirusa pig) develop into
tusks.|alt=A babirusa with elongated lower canines that curve up, forming tusks. There are two trends in terms of teeth within Artiodactyla. The Suina and hippopotamuses have a relatively large number of teeth (with some pigs having 44); their dentition is more adapted to a squeezing
mastication, which is characteristic of
omnivores. Camels and ruminants have fewer teeth; there is often a yawning
diastema, a designated gap in the teeth where the molars are aligned for crushing plant matter. The
incisors are often reduced in ruminants, and are completely absent in the
upper jaw. The canines are enlarged and tusk-like in the Suina, and are used for digging in the ground and for defense. In ruminants, the males' upper canines are enlarged and used as a weapon in certain species (mouse deer, musk deer,
water deer); species with frontal weapons are usually missing the upper canines. The lower canines of ruminants resemble the incisors, so that these animals have eight uniform teeth in the frontal part of the
lower jaw. The molars of porcine have only a few bumps. In contrast, camels and ruminants have bumps that are crescent-shaped cusps (
selenodont). Artiodactyl teeth exhibit significant intraspecific variation, with the width of the M3 and M3 and the length of the M1 and M1 being the most common variations in their molars. Their
premolar rows also show variation, as those teeth are prone to replication, rotation, and absence.
Senses Artiodactyls have a well-developed sense of smell and sense of hearing. Unlike many other mammals, they have a poor sense of sight, and find moving objects much easier to see than stationary ones. Similar to many other prey animals, their eyes are on the sides of the head, giving them an almost panoramic view.
Digestive system , have a simple sack-shaped stomach. The
ruminants (Ruminantia) ruminate their food, regurgitating and re-chewing it. Ruminants' mouths often have additional
salivary glands, and the
oral mucosa is often heavily calloused to avoid injury from hard plant parts and to allow easier transport of roughly chewed food. Their stomachs are divided into three to four sections: the
rumen, the
reticulum, the
omasum, and the
abomasum. After the food is ingested, it is mixed with saliva in the
rumen and
reticulum and separates into layers of solid versus 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 re-swallowed. The bolus is chewed slowly to completely mix it with saliva and to break it down. Ingested food passes to the "fermentation chamber" (rumen and reticulum), where it is kept in continual motion by rhythmic contractions. Cellulytic
microbes (
bacteria,
protozoa, and
fungi) produce
cellulase, which is needed to break down the cellulose found in plant material. s,
deer have such a multi-chambered stomach, which is used for better digestion of plant food.
Tylopoda (camels, llamas, and alpacas) and
chevrotains have three-chambered stomachs, while the rest of
Ruminantia have four-chambered stomachs. The handicap of a heavy digestive system has increased selective pressure towards limbs that allow the animal to quickly escape predators.
Genitourinary system The penises of even-toed ungulates have an S-shape at rest and lie in a pocket under the skin on the belly. The
corpora cavernosa are only slightly developed; and an
erection mainly causes this curvature to extend, which leads to an extension, but not a thickening, of the
penis. Cetaceans have similar penises. or
penile vermiform appendix. The
testicles are located in the
scrotum and thus outside the
abdominal cavity. The
ovaries of many females descend as the testicles descend of many male mammals, and are close to the
pelvic inlet at the level of the fourth
lumbar vertebra. The
uterus has two horns (
uterus bicornis).
Other has glands in the eyes that are clearly visible.|alt=Two Japanese serows (goat-antelopes) sit together. The number of
mammary glands is variable and correlates, as in all mammals, with
litter size. Pigs, which have the largest litter size of all even-toed ungulates, have two rows of
teats lined from the armpit to the groin area. In most cases, however, even-toed ungulates have only one or two pairs of teats. In some species these form an
udder in the groin region.
Secretory glands in the skin are present in virtually all species and can be located in different places, such as in the eyes, behind the horns, the neck, or back, on the feet, or in the anal region. Artiodactyls have a
carotid rete heat exchange that enables them, unlike perissodactyls which lack one, to regulate their brain temperature independently of their bodies. It has been argued that its presence explains the greater success of artiodactyls compared to perissodactyls in being able to adapt to diverse environments from the Arctic Circle to deserts and tropical savannahs. ==Lifestyle==