Mammal Characteristics:
1. Vertebrates
2. Mammals are endothermic
3. Mammals have hair - sweat glands, sebaceous glands, scent glands
4. Mammalian heart has four chambers
5. Diaphragm that aids the lungs in breathing
6. 4 different types of teeth: incisors - bite and cut, bicuspids - shear and shred, molars - grind and crush, canines - grip, puncture
7. Mammals have a single lower jaw bone
8. Viviparous - females carry and nourish the young inside their bodies
9. Females secrete milk from mammary glands to feed newborn
10. Mammals have highly developed brains
Marsupials: there are more than 260 species of mammals that are marsupials. Most species live in Australia, New Guinea, and Tansania. The only wild marsupial that lives in the United States is the opossum. Marsupials live in a variety of environments including forests, deserts, and meadows. The largest marsupial is the kangaroo, and the smallest marsupial is the marsupial mouse - which is shorter than four inches. Marsupials give birth to offspring that are physically undeveloped, and spend their first weeks or months in their mother's pouch, where they are fed and kept. Most marsupials are herbivores (plant-eating) and nocturnal (more active at night than the day.)
Koala - Koalas are Australian marsupials that almost look like a teddy bear. They have soft, thick fur; a large, hairless nose; round ears; and no tail. Their fur is gray or brown on their back and white on its belly. They measure from 25-30 inches and weigh 15-30 pounds. They have sharp, curved claws; long toes; and a strong grip. They almost always dwell in trees and come down only to move to another one. They are usually active at night. These herbivores eat the leaves of eucalyptus trees, where they receive the liquids they need. Wild koalas do not drink.
Monotremes: are mammals that lay eggs, and have only one external opening, called a cloaca, through which all waste matter and reproductive substances pass. (The word monotreme means "one opening.") Because it lays eggs and some of its bones are like those of living reptiles and fossilised mammal-like reptiles, the monotreme is sometimes referred to as "primitive", and even a "furred reptile". But overall it is much more mammalian than reptilian. Besides the Echidna (aka - the spiny anteater), the only other living Monotreme is the Duck-Billed Platypus. Both are native to Australia and Tasmania.
Echidna - vary in color, the predominant shades being black or dark brown, but "blonde" are also not uncommon. Echidna are exceedingly long-lived for their size. One captive Echidna is documented to have lived at least 49 years. Compared to say, a cat, which is of similar mass, this is simply ancient. This is another sign of the essential difference of Echidna's from other mammals. Echidnas are rather solitary in their habits generally, but are also mutually tolerant. In situations where there is a shortage of shelter, numbers of echidnas have been found sharing the same hole or cranny with no apparent strife. In captivity, Echidnas have been found to observe simple "rules of the road" whereby smaller echidnas will get out of the way of larger echidnas. Many sources on Echidnas describe them as nocturnal, this is not correct. Studies have found that Echidna activity levels vary with temperature, not light levels. Echidnas are most active when the temperature is 60 and 68 degrees Farenheit. This means in the hot summer, they will operate mainly at night, but other times of the year may be active during the day. Echidnas are famous for their method of escaping danger. While echidnas do not build borrows to live in (except for the raising of young), they are excellent diggers. If caught in an exposed position, an echdinas will dig very rapidly straight down. In seconds, all that is showing is a small tuft of spines along the back. Echidnas eat ants and termites, thus the name spiny anteater. They do this with their remarkable tongues. Echidna tongues are 6 inches long and oval in cross section, they can shoot out of the tiny mouth with lightening speed and be bent in U-shapes to follow ant tunnels. The tongue is coated with a sticky secretion. Prey sticks to the tongue, and then is removed in the mouth by spines, which line the roof. The Echidna has no teeth; food is ground up with special hard pads on the back of the tongue and top of the mouth. Echidnas prefer termites to ants, both because of a higher food and fat content, and less tendency to bite in self-defense. They also tend to prefer the queens, pupae, winged males etc. to the workers, which are more likely to fight back and have less meat on them. Echidna show remarkable sophistication in knowing when to attack ant and termite mounds. Echidnas only attack the mounds of meat ants in late winter and late in the day. Echidnas also know enough to dig on the warm northern sides of the mounds, where the queens are likely to be.
Edentates: means "without teeth", but only anteaters are totally toothless. Sloths and
armadillos have simple rootless molars that grow throughout their life. Edentates move slowly over small home ranges. They produce small precocious litters and invest much of their energy into raising young. Defense against predators is usually passive and primarily depends on camouflage. Edentates may try to flee from a predator, but they are more likely to stand their ground and strike with their sharp claws.
Anteater - common name for any of four insect-eating mammals of Mexico, Central America, and South America, having a long head with a long, tubular mouth and long tongue, but no teeth. The giant anteater, weighing up to 86 lb, is the largest species of anteater. It lives in forests and swampy areas and on open plains and is mainly diurnal in areas where there are few people, and is nocturnal in densely populated areas. The coarse coat is gray, with a white-bordered black stripe on each shoulder, and the tail is long and bushy. The front claws, used to tear open termite mounds and for defense, are so long that they are tucked under, and the animal walks on its knuckles. The long tongue flicks rapidly in and out of the small mouth opening, scooping up termites or other insects on its sticky surface. Solitary habits and a low reproductive rate characterize the species. The female carries the single young on her back during its growth; in the case of the giant anteater, this can last almost one year. Other, unrelated mammals called anteaters are the aardvark, echidna, and the pangolin.
Aardvark - the head and body length 3' - 5' with a tail about 18 inches long. Adults weight up to 180 lbs. Appearance is pig-like with an elongated head and large ears that can move independently. Skin is pink/gray and thinly covered with bristle-like gray hair. Hearing and sense of smell is acute but eyesight is poor. Tongue is sticky and can reach 18" from the mouth. Front feet have 4 toes with rear feet having 5 toes, all with heavy sharp nails. Shy and primarily active at night hunting for food alone. Digs burrows up to 9' long and will dig when alarmed at a great speed. In the wild the aardvark primarily eats termites and ants.
Lagomorphs:
are small to medium-sized animals that in many ways resemble large rodents.
Currently, we recognize 80 living species of lagomorphs, placed in 2 families containing 13 genera. Native populations are found on all continents except Australia and Antarctica; they are also absent from southern South America and most islands. Humans have introduced them, however, to many areas where they were originally not native. All lagomorphs are terrestrial. They occupy a wide diversity of habitats, ranging from tropical forest to arctic tundra. All are herbivores that feed on grasses and other small plants. Lagomorphs have the ability to produce two types of fecal material, one that is wet and eaten again for further nutrient absorption, and one that is dry and discarded.
Rodents: is a mammal characterized by a pair of broad, sharp-edged, chisel-like incisor teeth that are firmly inserted in both jaws and are used in gnawing vegetation. The front surface of each incisor tooth is composed of enamel, and the hind surface is of soft dentine, which wears away during the process of gnawing so that the teeth are constantly kept sharp. Rodents have no canine teeth; a gap is present between the incisors and the grinding teeth, or molars. Most rodents are also characterized by well-developed ears. There are more species of rodents than of any other mammalian order; more than 400 genera and about 2000 species are widely distributed throughout the world. The largest of the rodents is the capybara; most other species are relatively small. Some rodents produce many litters of young each year. They dwell in various habitats: some species are aquatic, some are terrestrial, and some live in burrows in the ground. Others are arboreal, and about 35 species are flying squirrels that are semi-aerial, gliding from one tree to another. Many rodents are economically injurious, destroying crops and stored foods. Rodents such as the house mouse and the Norway and black rats sometimes carry disease. Some species, such as the muskrat and beaver, are valued for their fur; dams built by beavers help to prevent erosion. Albino strains of the mouse and rat are important in biological experimentation. The white mouse, the gerbil, and the guinea pig are popular house pets.
Beavers - semi-aquatic mammal noted for the building of dams. One species of beaver occurs in North America, the other in Eurasia. The two species differ chiefly in the shape of the nasal bones and are so much alike that some authorities consider them to be varieties of the same species. They are large rodents; the average adult beaver weighs about 16 kg (about 35 lb), but specimens as heavy as 40 kg (90 lb) have been found, and some extinct beavers were almost bear-like in size.
Cats - common name for all members of a meat-eating family of mammals, superbly adapted for their typically predatory life. All members of the family Felidae, including the domestic cat and at least 34 other species of cats, are closely similar in physical characteristics with lithe and agile soft-furred bodies, acute vision and hearing, and claws and teeth that are highly adapted for grasping and tearing.
Kangaroo - A kangaroo is a furry animal that can hop on its hind legs at speeds up to 40 mph. These herbivores are the largest of all marsupials. Most of them live in Australia, but some live in New Guinea. Kangaroos live in groups called mobs. Male kangaroos are known as "boomers" and baby kangaroos are known as "joeys". They stand 6-7 feet tall and weigh 100-150 pounds. They have a deer-like head and a pointed snout. They have large, upright ears that turn from front to back. They are covered with fur that varies in color. Their tails grow over 3 feet long. A kangaroo uses its tail to keep balance when hopping. Kangaroos can leap over obstacles as high as 6 feet. A kangaroo's life span is an average of 10 years, but some can live up to 20. Kangaroos usually eat grass but sometimes eat nuts. They drink water. Most kangaroos are nocturnal and live in deserts - they stay in the shade during the day. A kangaroo's few enemies include humans and dingoes (a wild Australian dog). Humans have killed kangaroos for its skin and meat. Man kills an average of 3 million kangaroos each year. Farmers dislike kangaroos because they steal food and damage grazing land. Female kangaroos may have "joeys" at any time of year, but they are normally born when the grass is green. The joey remains in its mothers pouch for 6-10 months, and stays with its mother until about 16 months. After the joey leaves the mother it has a baby, and the process continues.
Tasmanian Devil - Tasmanian devils are fierce animals that live in southwest Tasmania. They eat small mammals and reptiles and any dead animal it can find. It hunts mainly at night and spends
the day in a cave, hollow log, or other shelter. They measure 3-4 feet long, including a tail of 1 foot. It weighs between 8 and 20 pounds. Most have black fur with white markings, but some are entirely black. It looks like a small wolf. It has a bear-like shape with a large head and long, bushy tail. It is dark, which helps it blend in with the night, and has a pale throat and side patches and muzzle. The Tasmanian devil eats snakes, birds, rodents, lizards, and wallabies. It drinks water. The Tasmanian devil can survive in a variety of places from dense rain forests to open plains. Female devils give birth to an average litter of four. The devil was common in Australia until it was exterminated there because it killed a large number of livestock and poultry.
Opossum - The opossum is a member of a family of furry mammals that live in the Western Hemisphere. Opossums are the only marsupials native to North America. They live from Ontario southward into South America. There are many species of opossums (most living in Central and South America). Small opossums resemble mice. Woolly opossums have thick, soft fur. Yapok opossums have webbed feet and are good swimmers. The common opossum is the only opossum found in the United States. It grows about as big as a house cat. It has rough grayish-white hair, a long snout, dark eyes, and hairless ears. They have long tails and they can hang upside down. They have 50 sharp teeth. They hunt at night and eat just about any animal or
vegetable. 
Duck-billed Platypus - equipped with webbed feet, both front and back, as well as a horizontally flattened tail, similar to those displayed by the placental beavers, the streamlined body of the platypus is well suited for the animal's semi-aquatic mode of life. The Platypus has got a streamlined body optimized for foraging underwater. The male averages 18 inches in length and weighs about 5 pounds. Females are smaller, averaging 14 inches in length and weighing about 2 pounds. The tail is used as a stabilizer underwater. The tail also stores fat, which means a plump tail is a sign of a healthy platypus. Acutely sensitive above the water the platypus's eyes and ears lie in a furrow that closes when it is submerged. Thousands of touch-sensitive and electro-sensitive pores cover the platypus's rubbery bill. The latter can detect the electric currents generated by the muscle activity of small prey and may even be able to sense the weak electric field generated when water flows over stationary objects. The platypus has one of the mammal realm's most waterproof coats. It consists of an inner layer of fine hairs that trap air and an outer layer of longer, flat-bladed hairs, giving excellent insulation for an animal that spends up to 12 hours each day in water as cold as 32 degrees Fahrenheit. As an opportunistic predator, the Platypus feeds on all kinds of insect larvae as well as freshwater shrimp, bivalve mollusks, frogs and fish eggs. The platypus is generally regarded as nocturnal. Foraging occurs mostly between sunset and sunrise, consisting of repeated dives of between 20 and 90 seconds in duration. After successful dives, the platypus will sort and chew the captured prey. Horny buccal pads are used by the adult to grind the food. Only juveniles have teeth. While the platypus is submerged food is held in special cheek pouches. Eggs are incubated for about six to ten days. Once hatched in early November, the young is suckled by the female, which has no tits. Milk is produced in large glands under her skin, which can be up to one-third of her body's length. The milk oozes out onto a patch of fur and the young Platypus sucks it up. The Platypus is known to live for at least 12 years in the wild. 
Armadillo - "armored mammal" related to anteaters and sloths. They vary in size from the giant armadillo, which is almost 3 ft long (excluding the tail) to species only about 6 inches long when fully grown. The layer of horn (hard material derived from hair) and bony plates that protect the animal against predators is formed by the ossification of the greater part of the skin. In some species even the tail is so protected. It is nocturnal in habit and feeds on insects and worms and sometimes on carrion.
Rabbits and Hares - common name for certain small, furry mammals with long ears and short tails. Although the names rabbit and hare are often used interchangeably, in zoological classification the species called rabbits are characterized by the helplessness of their offspring, which are born naked and with closed eyes, and by their gregarious habit of living in colonies in underground burrows. (The exception is the cottontail of North America, which does not dig burrows; its nest is on the surface, usually in dense vegetation, and it is not social.) Species designated zoologically as hares are born furred and with open eyes, and the adults merely construct a simple nest and rarely live socially. Furthermore, the hare is generally larger than the rabbit and has longer ears with characteristic black markings. Both groups breed prolifically, bearing four to eight litters a year, with three to eight young in each litter, have a period of gestation lasting about a month, reach sexual maturity in about six months, and have a life span of about ten years. The chief wild rabbit of North America is the cottontail. Its name is derived from the white undersurface of its short tail, which resembles a puff of cotton. The cottontail is noted for remaining motionless to avoid notice when it senses danger. The rabbit, which swims well, also evades enemies by plunging into lakes or streams. One species of jackrabbit, the black-tailed jackrabbit, is found in the western parts of the United States and Canada. The fastest of the rabbits and hares, jackrabbits achieve speeds of about 45 mph and can bound some 15 to 20 ft in a single jump. The jackrabbit eats grasses, grains, and other vegetation including agricultural crops and young trees. It is not a burrowing animal, except for the young, which hide in burrows for defense. An adult relies on its traveling speed to escape danger. The jackrabbit usually lives in solitude except during mating season, which lasts from early spring into midsummer. Several litters are born in the season, each about six weeks after mating. Two to four young are born in each litter.
Rats - common name for any large member of a family of rodents, with dull-colored, coarse fur; long tails; large ears; and a pointed snout. Rats have extremely powerful teeth, with which they often gnaw through wooden planks to get at stores of food, and they have even been known to bite holes in lead pipes. They are usually nocturnal and live in human habitations, in forests, in deserts, and on seagoing ships. They are extremely prolific, breeding 1 to 13 times a year and producing 1 to 22 young in a litter. Most species of rats are herbivorous, but some are omnivorous.
Squirrels - common name for many rodents belonging to the same family as the woodchuck (see Marmot), chipmunk, and prairie dog. The tree and ground squirrels include about 230 species and the so-called flying squirrels include about 43 species. Squirrels range in size from the pygmy squirrels of Africa, which are about 13 cm (5 in) long, to the giant squirrels of Asia, which are about 90 cm (36 in) long. The animals are in all parts of the world except Australia. Except for the ground squirrels, the animals live mainly in trees, and their food is largely vegetable (especially nuts, seeds, and buds), although they occasionally eat insects. Their habit of storing seeds helps in the dispersion of trees and other plant forms.
Carnivores live mainly alone or in small groups and are not preyed upon except by other carnivores. A widespread group, the Carnivores have teeth adapted for grasping and tearing, highly developed physical coordination and flexibility of behavior, and extended parent-offspring bonds. The digestive system of carnivores is much less complicated than that of herbivores because it does not have to break down the cellulose in plant matter.
Dogs - generally considered the first domesticated animal. The domesticated dog (Canis familiaris) has coexisted with human beings as a working partner and household pet in all eras and cultures since the days of the cave dwellers. It is generally believed that the direct ancestor of the domestic dog is the wolf. Dogs, also called canids, have large canine teeth, long muzzles, and blunt, non-retractable claws; all but the African hunting dog have five toes on the forefeet and four toes on the hind feet. They vary in size from the tiny desert-dwelling fennec, which weighs 3.2 lbs, to the gray or timber wolf, which weighs 44 to 175 lbs. Canids are found throughout all the continents except Antarctica and in nearly every climatic zone; the arctic fox lives on ice floes and above timberlines, while the rare bush dog inhabits savannas of equatorial South America. Dogs have highly developed senses of smell and hearing, enabling them to hunt by night as well as in the daytime. They work territories, usually at a tireless trot or canter, breaking into a gallop to pursue prey. Some species of canids work primarily in relays or packs. Relay hunters, such as the African hunting dog, take turns running down hoofed animals. Wolves and hunt in packs. Dhole packs, which consist of several families and number up to 30 members, have been known to take on tigers and Himalayan bears. Few if any reports exist of unprovoked wolf or dhole attacks on humans. Dogs have territories, or home ranges, which they mark off by urine or scent posts. The range of the gray wolf varies from 7 to 5000 sq miles, whereas that of a fox may be only 2 to 20 sq miles. In more solitary dogs such as foxes, the range may depend on gender, age, and food availability. Barks, growls, yelps, whimpers, and howls are associated with different behaviors such as greeting, submission, play, or courtship. The raising or lowering of the ears or tail and the ruffling the neck hairs are also forms of communication among canids. The gestation period of most canids ranges from 50 to 70 days and occurs once a year. Dogs produce from 2 to 13 offspring, which usually are reared in a burrow. The pups are born blind, and those of some foxes are suckled for as long as ten weeks. Canids become sexually mature in one or two years. 
Cats are regarded by many biologists as the most highly developed carnivores. Cats inhabit all continents except Antarctica and Australia. The paws are well padded; the forefeet have five toes and the hindfeet have four. All cats are digitigrade-they walk on their toes with the back part of the foot raised. The claws are long, sharp, and, with the exception of the cheetah, completely retractile-they can be drawn in so the paw can be used without scratching or ripping. In the light, the pupils of the eyes contract to vertical slits; in the dark the pupils become rounded and greatly expand to enable cats to see better. The male cat is usually longer and heavier than the female, but otherwise has about the same coloring and build. Most cats are monogamous. Offspring usually number one to six.
Raccoon - carnivorous mammal, found throughout the United States, southern Canada, and Central and South America, whose head is broad, tapering to a pointed muzzle, and whose ears are short and erect. The body is generally short and plump, with a long-haired coat of fur, and the tail is bushy. The legs are short; each foot has five toes, and the soles are naked. The animal walks on the soles of its feet with the heels touching the ground, similar to the practice of bears and humans. Raccoons are grayish-brown above and light gray beneath, with black cheek patches that narrow into a vertical stripe extending from the space between the eyes to the top of the head. The rest of the face is pale gray, with dark eyes and white whiskers. The tail is marked with six or seven brownish-black rings. A raccoon ranges in length from 2 to 3.3 ft, including its tail, which is 8 to 16 inches long. The common species found throughout the United States usually lives in trees or near ponds and streams of forests close to civilization. During the night it hunts for poultry, mice, birds' eggs, various insects, fish, and frogs. Occasionally it varies its diet with nuts and wild fruit. It is a skillful swimmer. Northern raccoons spend the winter in a den, usually high in a hollow tree, sleeping but not hibernating, and emerging during relatively warm periods. From four to six young are born in a single litter each spring, and members of the same family live and travel together for about one year. The fur of the raccoon, especially that of the northern species, has been highly valued in North America since the 17th century. Coonskin caps, and coats and robes made of the coarse but attractive fur, are still worn today. Coon hunting is practiced extensively in the southern United States. The animals are hunted at night with dogs and are usually found near swamps or streams.
Skunk - best known for the offensive odor it produces from glands on either side of the anus. The spotted skunk gives warning by standing on its front feet, and it will sometimes spray from this position, although it usually sprays after lowering its hind feet to the ground. Other species of skunks turn their backs, lift their tails, and eject a spray as far as 7 to 10 ft. Skunks give a churring sound when disturbed. They also growl and screech. Skunks vary in size, but all species have black and white coloring. The striped, or common, skunk is found everywhere in the United States, Mexico, and southern Canada. Its long fur is usually black, with a narrow white stripe on its forehead and a single (sometimes double) white stripe running from its head down its back and often onto its tail. The legs are relatively long. Skunks are omnivorous, eating small mammals, birds, eggs, and insects. They also like honey and bees. Many farmers believe that skunks keep the rodent population under control. The female produces one to ten young after a gestation of 59 to 77 days. The offspring suckle for eight to ten weeks and then follow the mother, hunting for food. Males remain solitary during the summer. Females and their young often den together-sometimes with one male-for the winter sleep, which is not a true hibernation.
Chiroptera: (Bats) is the only mammal capable of sustained flight. In all, 850 to 900 species of bats exist, far more than in any other mammalian order except the order of rodents, and bats probably exceed even rodents in total abundance. Bats occur worldwide, except in the Arctic Zone and certain remote oceanic islands. The mega-bats include the largest bats, the biggest achieves a wingspan of 5.6 ft and a body length of 16.7 in. The smallest micro-bat is only 1.1 to 1.3 inches long and weighs about 0.07 oz, making it one of the tiniest of mammals. Among living vertebrates, true flight is unique to bats and birds. Unlike most birds, however, bats are able to fly at relatively low speeds with extreme maneuverability. 
The wing is a thin, fleshy membrane supported near its leading edge by the greatly elongated bones of the forelimb and second finger, and toward the tip and rear by the even more attenuated third, fourth, and fifth fingers. By contrast, mega-bats use vision rather than acoustics for orientation. Only one genus has evolved an echolocation mechanism, involving the emission of audible "clicks," and it is used only when the bats fly in darkness. The eyes of mega-bats are also relatively larger than those of micro-bats. No bat is blind, however, and even echolocating micro-bats may use gross visual landmarks for homing during flight. With a few exceptions, all micro-bats are nocturnal. During the day they may rest in a variety of roosting places, such as caves, crevices, hollow trees, foliage, hiding places beneath rocks or bark, and in buildings. They may even roost in exposed situations; certain larger mega-bats hang upside down in enormous aggregations from tree branches. Nocturnality gives bats many advantages, such as greatly reduced competition for insects and other food items, substantial freedom from attack, and protection from overheating and dehydration, to which bats are especially liable because of their enormous skin area relative to their size. A few species of bats live solitarily, but most are gregarious. Aggregation during the day may vary from small groups consisting of a single male and a dozen or more females to enormous assemblages numbering many thousands or even millions of individuals. Aggregations of members of specific species may show seasonal variation and sexual segregation in varying combinations. Mixed-species associations of a casual sort are common among bats using protected shelters such as caves. Most bats are insectivorous and are able to catch their prey in flight or to seek out stationary insects on foliage or other surfaces. Most mega-bats are fruit eaters. Still others in both groups consume flower parts or extract the nectar from flowering plants by means of greatly elongated tongues, aiding cross-pollination of the plants in the process. Some of the larger leaf-nosed bats as well as members of one Eurasian family are carnivorous or omnivorous; they attack small amphibians, lizards, birds, mice, and even other bats, in addition to consuming insects and fruit. The true vampire bats of the American Tropics, which subsist entirely on blood freshly drawn from small wounds inflicted on mostly warm-blooded prey such as fowl, cattle, horses, swine, and occasionally human beings. At least three species of bats supplement their diets with small fish, which are caught as the flying bats drag their enlarged feet and claws just beneath the water surface. Copulation occurs prior to hibernation, and sperm are retained within the females throughout the hibernation period. Fertilization occurs when the egg is released from the ovary after the bats arouse in the spring. This is called delayed fertilization. The abundance of bats despite their low individual reproductive performances is attributable not only to the survival value of their habits but also to their remarkable longevity. The record is a specimen recovered 31 years after it was initially marked and released in New England.
Perissodactlyl: any member of the three families of hoofed mammals-the horses, tapirs, and rhinoceroses. The term is derived from Greek words meaning "odd-toed," as contrasted with the artiodactyl order of even-toed hoofed mammals.
When ungulates are cornered by predators, hooves are used as a means of counterattack. Using their height as an advantage, ungulates such as horses and zebras rear up and strike downward with their well-muscled legs, and the hard hooves can cut deep wounds into animal flesh. In the case of domesticated horses, the hoof is further protected by the addition of a horse shoe, which is nailed to the lower end of the unguis and also helps prevent the hoof from splitting. Horses, donkeys, and zebras have a single solid hoof on each foot. Other ungulates, such as tapirs and rhinoceroses, have three toes on each foot, and each toe is covered by a separate hoof. In cattle, deer, sheep, camels, and antelope, each foot has two toes, each with its own hoof. Since the hooves on each foot are separated by a narrow space between the toes, animals with hooves divided into two or more parts are commonly called cloven-hoofed, which means "divided hoof."
Artiodactlyl: (Greek artios, "even"; dactylos, "finger" or "toe"), any member of the order of hoofed mammals, including cattle, pigs, goats, giraffes, camels, deer, antelopes, and hippopotamuses. All artiodactyls, with the exception of the collared and white-clipped peccaries, have an even number of toes on each foot. A majority of species in the order are native to Africa, but they are well represented in North and South America, Europe, and Asia. Australia has no native artiodactyls. 
All members of the order support their weight on the tips of the third and fourth toes. Their remote ancestors had five toes. Through evolutionary modification, the first toe has disappeared completely, and the second and fifth toes are only vestigial (nonfunctional) remnants. These small appendages are located higher up on the foot than the terminal toes on which the animals stand. The vestigial toes, sometimes called dewclaws, serve no purpose except in pigs and caribou, preventing these animals from sinking into soft ground. Each of the two large, supporting toes of artiodactyls terminates in a hoof. The deceptive appearance of these two hooves gave rise to the biblical term cloven hoof, which suggests erroneously that the two hooves derive from a single large hoof. The hippopotamus, unique among artiodactyls, has four toes of equal size and width. Artiodactyls feed almost exclusively on vegetation, except for pigs, which also feed on eggs, small reptiles, worms, and carrion. Although artiodactyls lack upper incisors, and most species lack upper canine teeth, they have a pad in the upper jaw against which the lower teeth can operate. Artiodactyls rely mainly on speed and keen senses to protect themselves from predators even though most males have horns or antlers.
Hog, domesticated mammal, of the swine family, extensively raised in almost every part of the world as a food animal. The terms hog, swine, and pig are often used interchangeably for these animals. They were introduced into the Americas by Christopher Columbus and the Spanish explorers, and present-day feral razorbacks (pigs that escaped to the wild) are probably descended from those animals. Wild hogs develop tusk (extended canines), but the tusk of farm hogs are clipped to control aggresive and dangerous behavior. Well adapted for the production of meat because they grow and mature rapidly, 
the pork produced by these animals is used in sausage, ribs, pork chops, bologna, salami, just to name a few. Hogs have a short gestation period of about 114 days, and they produce large numbers of young each time they give birth. They are omnivorous and can scavenge a wide range of foods-perhaps one of the reasons they were first domesticated. As food sources, they convert cereal grains and legumes such as soybeans into meat. Other than meat, products from swine include leather (pigskin) for luggage and gloves, and bristles for brushes. For centuries they have also been used as a primary source of edible fat. In the United States until the mid-1920s, they were bred for the production of large amounts of lard. Swine in other countries such as England, however, were bred for the production of lean meat and were called bacon-type hogs. Modern swine are intermediate between these two types and are known as meat-type hogs. As the demand for fats has decreased, the meat-type hogs have been developed to resemble the bacon type more closely. Hogs are the most intelligent of the domesticated animals, and have an anatomy that is close enough to humans that they are sometimes called horizontal humans. Hogs often grunt as a method of communication, but squeal whenever they become excited.
Deer, common name for certain hoofed, artiodactyl mammals, usually characterized by bony, often branching antlers that are shed and regenerated annually. The animals are ruminants, or cud chewers, and have a four-chambered stomach. Nearly all deer have a facial gland, in front of each eye, that contains a strongly scented substance, or pheromone, used to mark its home range. The males, which are known as bucks or stags, of many species open these glands wide when angry or excited. Females are called does and the offspring are known as fawns. Unlike the hollow, permanent horns of other ruminants, the antlers of deer are solid and bony. Except in the caribou (reindeer), antlers form only on males and their growth is controlled by the male sex hormone. Antlers are used to slash territorial markings on trees or bushes, to make threatening displays, and to combat other males. Usually the fighting is stylized and harmless, but occasionally males of large species lock antlers and die of exhaustion or starvation. Deer forage on twigs, leaves, bark, and buds of bushes and saplings and on grasses and other plants, feeding most actively at twilight. Musk, which comes from a gland on the abdomen of the musk deer, is used in medicines and perfumes. Deerskin is used for shoes, boots, and gloves, and antlers are made into buttons and knife handles. Deer are hunted for sport and for their meat, which is called venison.
Ox, plural, oxen, domesticated cow or bull used for agricultural work as a draft animal (an animal that pulls a cart or wagon) or as a pack animal (an animal that carries cargo on its back). Male oxen are typically castrated (sexually neutered by the removal of testes) to produce a larger, stronger, and more docile animal.
Cattle, common term for the domesticated herbivorous mammals that are of great importance to humans because of the meat, milk, leather, glue, gelatin, and other items of commerce they yield. Sexually mature males are called bulls, males that have had their reproductive organs removed are called steers. Females are called cows, while female calves are called heifers. Modern cattle are divided into two species: breeds of dairy and beef cattle. They have paired, hollow, unbranched horns that do not shed. Certain species of hornless cattle are bred and known as polled cattle. Dairy cattle are those breeds that have been developed primarily to produce milk, and beef cattle have been bred and selected primarily for the production of meat. A female cannot produce milk until after she has given birth to a calf. Bovine Somatotropin (BST), is a protein hormone that stimulates milk yields. It is produced in the pituitary gland of lactating dairy cows and can be manufactured in the laboratory. Artificial BST is used by farmers to boost natural milk yields. It is injected under the cow's skin at regular intervals to extend the peak milk production period. Butter, solidified milk fat, especially cow's milk, used principally as a food item. In the manufacture of butter, the cream is skimmed from the milk or separated mechanically. It is then placed in a churn, and the butter is coagulated by agitation. The crude butter is then worked (or kneaded) and is washed with water to remove as much of the milk curd and other non fatty components of the cream as possible.
Proboscidea: the elephant is the largest living land mammal. There are two species the African and Asian elephants. The elephant derives its name from it rather large proboscis (nose). The proboscis is actually a combination of the upper lip and nose. It is used to convey grasses, leaves, and water to the mouth. It is also used in communication and smell. By means of finger-like projections on the end of the trunk and by the sucking action of the nostrils, elephants can pick up and examine small objects. Most elephants have two large tusks that are actually extended incisors. The tusks, which are embedded in the skull, are used for deriving food as well as defense purposes. As humans are right and left handed, elephants are right and left tusked. One tusk is used more often than the other and wears away at a faster rate. Present day elephants consume as much as 450 lbs of food and over 50 gallons of water per day. Elephants generally feed to during the mornings and night and rest during the day. The African elephant is easily distinguished from its Asian counterpart by its size. The largest of the elephants, it can stand nearly 13 feet tall and weigh almost 15,000 lbs. Elephants walk at about 4 mph, but run at speeds up to 25 mph. They are capable of swimming and love to recreate in water. The ears of an elephant are extremely large and fan as means of circulating air to cool the body. The elephant's eyesight is poor forcing it to rely upon hearing and smell as a defense mechanism. Female elephants are gregarious and live in herds of up to 15-20 members and are led by a leader known as the matriarch. When migrating, they generally trek in single file lines. The gestation period of an elephant is typically around two years in length. Calves suckle from their mother for a period of five years before being weaned.
Pinnipedia: or meat-eating marine mammal that has fins (used for propulsion) instead of feet. The word Pinnipedia comes from two Latin words: pinna, a feather or wing, and pedis, a foot. Pinnipeds have four limbs modified to use as flippers and a streamlined body. This is enough to identify any mammal as a member of the order. All pinnipeds have a body form adapted for life and locomotion in water, which is modified from the basic mammalian body form designed for terrestrial habitat. Pinnipeds find their food in the sea but are still tied to land because they must birth and suckle their young on shore.
Eared seals - They have long, flexible necks and small external ears. They have hind flippers that can be turned forward, enabling them to support the body, and they use all four limbs for land travel. They comprise two groups: the sea lions and the fur seals. The sea lions are the larger of the eared seals. Adult males attain a length of 12 ft and a maximum weight of 2400 lbs. Males are known as bulls and can have a harem consisting of up to 40 females. The commercially important fur seals closely resemble the sea lions anatomically but differ in that they have a rich, silky undercoat of fur. Eared seals can dive for as long 5-10 minutes. Pinniped's blood contains three and a half more times the oxygen-carrying cells, hemoglobin, than man's blood.
True Seals - lack external ears and have shorter, relatively inflexible necks and undeveloped forelimbs; the forelimbs, however, do bear claws used for crawling up rocks and ice floes. The hind limbs do not flex forward and are stroked vertically in swimming like the tail of a dolphin. True seals are better adapted to life in water than are the longer-limbed eared seals, but on land they progress laboriously by wriggling and hunching the entire body. True seals can dive for as long as 35 minutes. Elephant seals are so called for their trunk-like proboscis (nose) and great size. They were once numerous, but the oil obtained from their blubber, or fat, was found to be of high commercial value (lamp oil, cosmetics, etc.) and they were hunted almost to extinction. Survivors of large herds of two species still exist. The northern elephant seal, once common in the waters of southern California, attains a length of 22 ft, and a single animal has yielded as much as much as 200 gallons of oil.
Walrus - Like eared seals, walruses can turn their hind limbs forward and thus use all four limbs in moving when ashore. Walruses range from 8.9 to 11.7 ft in length and weigh 1,800 to 3,700 lb males are larger than females. Both the male and female have massive bodies with thick, wrinkled, hairy skin that becomes nearly hairless with age. Both have relatively small heads with no external ears; a fold of skin marks the location of the ear. They have broad, bristled muzzles; and enormously elongated upper canine teeth forming heavy tusks. The tusks, about about 3 ft long in some males, are used as weapons in fighting and as hooks in climbing on the ice. Although it was once thought that the tusks were also used to rake the ocean bottom for mollusks and shellfish, which constitute the principal food of the walrus, it is now believed that the sensitive whiskers and fleshy snout play a primary role in detecting and removing prey from the ocean floor. Walruses are gentle unless attacked; the whole herd will come to the defense of a member in danger. Polar bears are the chief natural predator of the walrus, and humans hunt the animal for its valuable ivory tusks and for its flesh and blubber.