Bear and bobcats These animals can be very dangerous and should only be handled by professionals. For example, there are two kinds of mountain, temperate and tropical. Thanks for your article. The smallest living member of Carnivora is the least weasel Mustela nivalis , which weighs only 25 grams 0. It was thought to be just stomach filler. Kingdom A level of classifying all living things on earth, as similar species are broken into 5 groups including plants, animals and fungi.
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The mammalian heart has four chambers, two upper atria , the receiving chambers, and two lower ventricles , the discharging chambers.
After gas exchange in the pulmonary capillaries blood vessels in the lungs , oxygen-rich blood returns to the left atrium via one of the four pulmonary veins. Blood flows nearly continuously back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle.
Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period , the left atrium will contract, pumping blood into the ventricle. The heart also requires nutrients and oxygen found in blood like other muscles, and is supplied via coronary arteries. The integumentary system is made up of three layers: The epidermis is typically 10 to 30 cells thick; its main function is to provide a waterproof layer. Its outermost cells are constantly lost; its bottommost cells are constantly dividing and pushing upward.
The middle layer, the dermis, is 15 to 40 times thicker than the epidermis. The dermis is made up of many components, such as bony structures and blood vessels. The hypodermis is made up of adipose tissue , which stores lipids and provides cushioning and insulation. The thickness of this layer varies widely from species to species; : It is a definitive characteristic of the class.
Though some mammals have very little, careful examination reveals the characteristic, often in obscure parts of their bodies. Herbivores have developed a diverse range of physical structures to facilitate the consumption of plant material. To break up intact plant tissues, mammals have developed teeth structures that reflect their feeding preferences. For instance, frugivores animals that feed primarily on fruit and herbivores that feed on soft foliage have low-crowned teeth specialized for grinding foliage and seeds.
Grazing animals that tend to eat hard, silica -rich grasses, have high-crowned teeth, which are capable of grinding tough plant tissues and do not wear down as quickly as low-crowned teeth. The stomach of Artiodactyls is divided into four sections: After the plant material is consumed, it is mixed with saliva in the rumen and reticulum and separates into solid and liquid material.
The solids lump together to form a bolus or cud , and is regurgitated. When the bolus enters the mouth, the fluid is squeezed out with the tongue and swallowed again.
Ingested food passes to the rumen and reticulum where cellulytic microbes bacteria , protozoa and fungi produce cellulase , which is needed to break down the cellulose in plants. The caecum is either absent or short and simple, and the large intestine is not sacculated or much wider than the small intestine.
The mammalian excretory system involves many components. Like most other land animals, mammals are ureotelic , and convert ammonia into urea , which is done by the liver as part of the urea cycle.
Only the mammalian kidney has a bean shape, although there are some exceptions, such as the multilobed reniculate kidneys of pinnipeds, cetaceans and bears. In the embryo, the embryonic cloaca divides into a posterior region that becomes part of the anus, and an anterior region that has different fates depending on the sex of the individual: As in all other tetrapods, mammals have a larynx that can quickly open and close to produce sounds, and a supralaryngeal vocal tract which filters this sound.
The lungs and surrounding musculature provide the air stream and pressure required to phonate. The larynx controls the pitch and volume of sound, but the strength the lungs exert to exhale also contributes to volume. More primitive mammals, such as the echidna, can only hiss, as sound is achieved solely through exhaling through a partially closed larynx.
Other mammals phonate using vocal folds , as opposed to the vocal cords seen in birds and reptiles. The movement or tenseness of the vocal folds can result in many sounds such as purring and screaming. Mammals can change the position of the larynx, allowing them to breathe through the nose while swallowing through the mouth, and to form both oral and nasal sounds; nasal sounds, such as a dog whine, are generally soft sounds, and oral sounds, such as a dog bark, are generally loud.
Some mammals have a large larynx and thus a low-pitched voice, namely the hammer-headed bat Hypsignathus monstrosus where the larynx can take up the entirety of the thoracic cavity while pushing the lungs, heart, and trachea into the abdomen. Ultrasound is inaudible to birds and reptiles, which might have been important during the Mesozoic, when birds and reptiles were the dominant predators.
This private channel is used by some rodents in, for example, mother-to-pup communication, and by bats when echolocating. Toothed whales also use echolocation, but, as opposed to the vocal membrane that extends upward from the vocal folds, they have a melon to manipulate sounds. Some mammals, namely the primates, have air sacs attached to the larynx, which may function to lower the resonances or increase the volume of sound. The vocal production system is controlled by the cranial nerve nuclei in the brain, and supplied by the recurrent laryngeal nerve and the superior laryngeal nerve , branches of the vagus nerve.
The vocal tract is supplied by the hypoglossal nerve and facial nerves. Electrical stimulation of the periaqueductal gray PEG region of the mammalian midbrain elicit vocalizations.
The ability to learn new vocalizations is only exemplified in humans, seals, cetaceans, elephants and possibly bats; in humans, this is the result of a direct connection between the motor cortex , which controls movement, and the motor neurons in the spinal cord. The fur of mammals has many uses protection, sensory purposes, waterproofing, and camouflage, with the primary usage being thermoregulation.
Mammalian coats are colored for a variety of reasons, the major selective pressures including camouflage , sexual selection , communication and physiological processes such as temperature regulation. Camouflage is a powerful influence in a large number of mammals, as it helps to conceal individuals from predators or prey.
Mammals with a darker colored coat can absorb more heat from solar radiation, and stay warmer, and some smaller mammals, such as voles , have darker fur in the winter. The white, pigmentless fur of arctic mammals, such as the polar bear, may reflect more solar radiation directly onto the skin. The ancestral condition for mammal reproduction is the birthing of relatively undeveloped, either through direct vivipary or a short period as soft-shelled eggs.
This is likely due to the fact that the torso could not expand due to the presence of epipubic bones. The oldest demonstration of this reproductive style is with Kayentatherium , which produced undeveloped perinates , but at much higher litter sizes than any modern mammal, 38 specimens.
In male placentals, the penis is used both for urination and copulation. Depending on the species, an erection may be fueled by blood flow into vascular, spongy tissue or by muscular action.
A penis may be contained in a sheath when not erect, and some placentals also have a penis bone baculum. Marsupials typically have forked penises while the monotreme penis generally has four heads with only two functioning. The testes of most mammals descend into the scrotum which is typically posterior to the penis but is often anterior in marsupials. Female mammals generally have a clitoris , labia majora and labia minora on the outside, while the internal system contains paired oviducts , uteri , cervices and a vagina.
Marsupials have two lateral vaginas and a medial vagina. The "vagina" of monotremes is better understood as a "urogenital sinus". The uterine systems of placental mammals can vary between a duplex, were there are two uteri and cervices which open into the vagina, a bipartite, were two uterine horns have a single cervix that connects to the vagina, a bicornuate, which consists where two uterine horns that are connected distally but separate medially creating a Y-shape, and a simplex, which has a single uterus.
Most mammals are viviparous , giving birth to live young. However, the five species of monotreme, the platypus and the four species of echidna, lay eggs. The monotremes have a sex determination system different from that of most other mammals. Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses.
Marsupials have a short gestation period, typically shorter than its estrous cycle and gives birth to an undeveloped newborn that then undergoes further development; in many species, this takes place within a pouch-like sac, the marsupium , located in the front of the mother's abdomen.
This is the plesiomorphic condition among viviparous mammals; the presence of epipubic bones in all non-placental mammals prevents the expansion of the torso needed for full pregnancy. The mammary glands of mammals are specialized to produce milk, the primary source of nutrition for newborns. The monotremes branched early from other mammals and do not have the nipples seen in most mammals, but they do have mammary glands.
The young lick the milk from a mammary patch on the mother's belly. Nearly all mammals are endothermic "warm-blooded". Most mammals also have hair to help keep them warm. Like birds, mammals can forage or hunt in weather and climates too cold for ectothermic "cold-blooded" reptiles and insects. Endothermy requires plenty of food energy, so mammals eat more food per unit of body weight than most reptiles.
A rare exception, the naked mole-rat produces little metabolic heat, so it is considered an operational poikilotherm. Among mammals, species maximum lifespan varies significantly for example the shrew has a lifespan of two years, whereas the oldest bowhead whale is recorded to be years. In a study by Hart and Setlow,  it was found that DNA excision repair capability increased systematically with species lifespan among seven mammalian species.
Species lifespan was observed to be robustly correlated with the capacity to recognize DNA double-strand breaks as well as the level of the DNA repair protein Ku Most vertebrates—the amphibians, the reptiles and some mammals such as humans and bears—are plantigrade , walking on the whole of the underside of the foot.
Many mammals, such as cats and dogs, are digitigrade , walking on their toes, the greater stride length allowing more speed. Digitigrade mammals are also often adept at quiet movement. This even further increases their stride length and thus their speed. Giant anteaters  and platypuses  are also knuckle-walkers.
Some mammals are bipeds , using only two limbs for locomotion, which can be seen in, for example, humans and the great apes.
Bipedal species have a larger field of vision than quadrupeds, conserve more energy and have the ability to manipulate objects with their hands, which aids in foraging.
Instead of walking, some bipeds hop, such as kangaroos and kangaroo rats. Animals will use different gaits for different speeds, terrain and situations. For example, horses show four natural gaits, the slowest horse gait is the walk , then there are three faster gaits which, from slowest to fastest, are the trot , the canter and the gallop. Animals may also have unusual gaits that are used occasionally, such as for moving sideways or backwards.
For example, the main human gaits are bipedal walking and running , but they employ many other gaits occasionally, including a four-legged crawl in tight spaces. Gaits can be grouped into categories according to their patterns of support sequence. For quadrupeds, there are three main categories: Running is considered to occur when at some points in the stride all feet are off the ground in a moment of suspension. Arboreal animals frequently have elongated limbs that help them cross gaps, reach fruit or other resources, test the firmness of support ahead and, in some cases, to brachiate swing between trees.
In the spider monkey, the tip of the tail has either a bare patch or adhesive pad, which provides increased friction. Claws can be used to interact with rough substrates and reorient the direction of forces the animal applies. This is what allows squirrels to climb tree trunks that are so large to be essentially flat from the perspective of such a small animal. However, claws can interfere with an animal's ability to grasp very small branches, as they may wrap too far around and prick the animal's own paw.
Frictional gripping is used by primates, relying upon hairless fingertips. Squeezing the branch between the fingertips generates frictional force that holds the animal's hand to the branch. However, this type of grip depends upon the angle of the frictional force, thus upon the diameter of the branch, with larger branches resulting in reduced gripping ability.
To control descent, especially down large diameter branches, some arboreal animals such as squirrels have evolved highly mobile ankle joints that permit rotating the foot into a 'reversed' posture. This allows the claws to hook into the rough surface of the bark, opposing the force of gravity. Small size provides many advantages to arboreal species: Both pitching and tipping become irrelevant, as the only method of failure would be losing their grip.
Bats are the only mammals that can truly fly. They fly through the air at a constant speed by moving their wings up and down usually with some fore-aft movement as well. Because the animal is in motion, there is some airflow relative to its body which, combined with the velocity of the wings, generates a faster airflow moving over the wing. This generates a lift force vector pointing forwards and upwards, and a drag force vector pointing rearwards and upwards.
The upwards components of these counteract gravity, keeping the body in the air, while the forward component provides thrust to counteract both the drag from the wing and from the body as a whole. The wings of bats are much thinner and consist of more bones than that of birds, allowing bats to maneuver more accurately and fly with more lift and less drag.
These sensitive areas are different in bats, as each bump has a tiny hair in the center, making it even more sensitive and allowing the bat to detect and collect information about the air flowing over its wings, and to fly more efficiently by changing the shape of its wings in response. Fossorial creatures live in subterranean environments. Many fossorial mammals were classified under the, now obsolete, order Insectivora , such as shrews, hedgehogs and moles.
Fossorial mammals have a fusiform body, thickest at the shoulders and tapering off at the tail and nose. Unable to see in the dark burrows, most have degenerated eyes, but degeneration varies between species; pocket gophers , for example, are only semi-fossorial and have very small yet functional eyes, in the fully fossorial marsupial mole the eyes are degenerated and useless, talpa moles have vestigial eyes and the cape golden mole has a layer of skin covering the eyes.
External ears flaps are also very small or absent. Truly fossorial mammals have short, stout legs as strength is more important than speed to a burrowing mammal, but semi-fossorial mammals have cursorial legs. The front paws are broad and have strong claws to help in loosening dirt while excavating burrows, and the back paws have webbing, as well as claws, which aids in throwing loosened dirt backwards.
Most have large incisors to prevent dirt from flying into their mouth. Fully aquatic mammals, the cetaceans and sirenians , have lost their legs and have a tail fin to propel themselves through the water.
Flipper movement is continuous. Whales swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Their skeletal anatomy allows them to be fast swimmers.
Most species have a dorsal fin to prevent themselves from turning upside-down in the water. The forelimbs are paddle-like flippers which aid in turning and slowing. Semi-aquatic mammals, like pinnipeds, have two pairs of flippers on the front and back, the fore-flippers and hind-flippers. The elbows and ankles are enclosed within the body. In addition to their streamlined bodies, they have smooth networks of muscle bundles in their skin that may increase laminar flow and make it easier for them to slip through water.
They also lack arrector pili , so their fur can be streamlined as they swim. Many mammals communicate by vocalizing.
Vocal communication serves many purposes, including in mating rituals, as warning calls ,  to indicate food sources, and for social purposes. Males often call during mating rituals to ward off other males and to attract females, as in the roaring of lions and red deer. For example, if an alarm call signals a python, the monkeys climb into the trees, whereas the eagle alarm causes monkeys to seek a hiding place on the ground. Some of the rumbling calls are infrasonic , below the hearing range of humans, and can be heard by other elephants up to 6 miles 9.
Mammals signal by a variety of means. Many give visual anti-predator signals , as when deer and gazelle stot , honestly indicating their fit condition and their ability to escape,   or when white-tailed deer and other prey mammals flag with conspicuous tail markings when alarmed, informing the predator that it has been detected.
To maintain a high constant body temperature is energy expensive — mammals therefore need a nutritious and plentiful diet. While the earliest mammals were probably predators, different species have since adapted to meet their dietary requirements in a variety of ways. Some eat other animals — this is a carnivorous diet and includes insectivorous diets.
Other mammals, called herbivores , eat plants, which contain complex carbohydrates such as cellulose. An herbivorous diet includes subtypes such as granivory seed eating , folivory leaf eating , frugivory fruit eating , nectarivory nectar eating , gummivory gum eating and mycophagy fungus eating.
The digestive tract of an herbivore is host to bacteria that ferment these complex substances, and make them available for digestion, which are either housed in the multichambered stomach or in a large cecum. Carnivorous mammals have a simple digestive tract because the proteins , lipids and minerals found in meat require little in the way of specialized digestion.
Exceptions to this include baleen whales who also house gut flora in a multi-chambered stomach, like terrestrial herbivores.
The size of an animal is also a factor in determining diet type Allen's rule. Since small mammals have a high ratio of heat-losing surface area to heat-generating volume, they tend to have high energy requirements and a high metabolic rate.
Larger animals, on the other hand, generate more heat and less of this heat is lost. They can therefore tolerate either a slower collection process carnivores that feed on larger vertebrates or a slower digestive process herbivores. The only large insectivorous mammals are those that feed on huge colonies of insects ants or termites. Some mammals are omnivores and display varying degrees of carnivory and herbivory, generally leaning in favor of one more than the other. Since plants and meat are digested differently, there is a preference for one over the other, as in bears where some species may be mostly carnivorous and others mostly herbivorous.
The dentition of hypocarnivores consists of dull, triangular carnassial teeth meant for grinding food. Hypercarnivores, however, have conical teeth and sharp carnassials meant for slashing, and in some cases strong jaws for bone-crushing, as in the case of hyenas , allowing them to consume bones; some extinct groups, notably the Machairodontinae , had saber-shaped canines. Some physiological carnivores consume plant matter and some physiological herbivores consume meat.
From a behavioral aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy. Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous. Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not seemingly complement their classification.
Many mammals, in the absence of sufficient food requirements in an environment, suppress their metabolism and conserve energy in a process known as hibernation. In intelligent mammals, such as primates, the cerebrum is larger relative to the rest of the brain. Intelligence itself is not easy to define, but indications of intelligence include the ability to learn, matched with behavioral flexibility.
Rats , for example, are considered to be highly intelligent, as they can learn and perform new tasks, an ability that may be important when they first colonize a fresh habitat.
In some mammals, food gathering appears to be related to intelligence: Tool use by animals may indicate different levels of learning and cognition. Brain size was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalisation quotient that can be used as another indication of animal intelligence.
Self-awareness appears to be a sign of abstract thinking. Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning.
The traditional method for measuring this is the mirror test , which determines if an animal possesses the ability of self-recognition. Eusociality is the highest level of social organization.
These societies have an overlap of adult generations, the division of reproductive labor and cooperative caring of young. Usually insects, such as bees , ants and termites, have eusocial behavior, but it is demonstrated in two rodent species: Presociality is when animals exhibit more than just sexual interactions with members of the same species, but fall short of qualifying as eusocial.
That is, presocial animals can display communal living, cooperative care of young, or primitive division of reproductive labor, but they do not display all of the three essential traits of eusocial animals. The number of vertebrae in the tail part may vary a lot. Ribs are fixed to the thoracic vertebrae. They are also used as a great protection. Lungs consist of many small alveoli - this rapidly increases their inner surface. Diaphragm is between the thorax and the abdominal part. It also participates in breathing and is an inevitable inhaling muscle.
The heart is made of four completely separated parts. There are two atriums and two ventricles. Deoxygenated blood flows through the right heart whereas the oxygenated blood flows through the left heart. So there are two separated blood circulations. The blood circulation starts in the right atrium and then the blood flows into the right ventricle. From the right ventricle the blood flows into the lungs where it is oxygenated. Consequently it flows into the left atrium and then into the left ventricle.
From the left ventricle the oxygenated blood flows into the entire body to all organs. There it gives inevitable oxygen to tissues and last but not least the deoxygenated blood comes through veins into the right atrium.
And in the right atrium it starts all over again. Mammals have got a constant body temperature, they are endothermic. They also do have sweat glands which enable them to cool themselves. The alimentary canal starts with a mouth with teeth. Teeth have got different shape and different functions too.
A food comes through the pharynx and esophagus into the stomach gaster. Chemical digestion starts in stomach and is finished in duodenum, jejunum and ileum. Pancreas and gall bladder participate in digestion. Gall helps to digest fat and pancreatic enzymes proteins and sugars. Intestunum tenue duodenum, jejunum and ileum participates apart from digestion in resorption too.
The concentration of indigestible food takes place in colon. Only water is digested there. The alimentary canal ends as an anus. Mammals have got pair of kidneys, which excrete toxic and abundant fluid. They are placed in the lumbar area on the both sides. Nervous system is extraordinary developed. The frontal part has got the most impact over other brain parts. For details on the anatomy and physiology for specific digestive systems, see digestive system, human , and digestive system, invertebrate.
In order to sustain themselves, all organisms must obtain nutrients from the environment. Some nutrients serve as raw materials for the synthesis of cellular material; others e. Not all nutrients, however, are in a form suitable for immediate use by an organism; some must undergo physical and chemical changes before they can serve as energy or cell substance. Through the act of eating, or ingestion, nutrients are taken from the environment. Many nutrient molecules are so large and complex that they must be split into smaller molecules before they can be used by the organism.
This process of breaking down food into molecular particles of usable size and content is called digestion. Unusable components are expelled from the organism by a process called egestion, or excretion. Some plants, many microorganisms, and all animals perform these three functions—ingestion, digestion, and egestion often grouped under the term alimentation —but, as expected, the details differ considerably from group to group.
The problems associated with nutrient intake and processing differ greatly depending on whether the organism is autotrophic or heterotrophic. Autotrophic organisms can manufacture the large energy-rich organic compounds necessary for life from simple inorganic raw materials; consequently, they require only simple nutrients from the environment.
By contrast, heterotrophic organisms cannot manufacture complex organic compounds from simple inorganic ones, and so they must obtain preformed organic molecules directly from the environment. During the process of photosynthesis , plants use light energy to synthesize organic materials from carbon dioxide and water. Both compounds can be absorbed easily across the membranes of cells—in a typical land plant, carbon dioxide is absorbed from the air by leaf cells, and water is absorbed from the soil by root cells—and used directly in photosynthesis; i.
The only other nutrients needed by most green plants are minerals such as nitrogen , phosphorus , and potassium , which also can be absorbed directly and require no digestion.
Heterotrophy characterizes all animals, most microorganisms, and plants and plantlike organisms e. These organisms must ingest organic nutrients—carbohydrates, proteins, and fats—and, by digestion, rearrange them into a form suitable for their own particular needs. The main source of fatty acids in the diet is triglycerides, generically called fats. In humans, fat constitutes an important part of the diet, and in some countries it can contribute as much as 45 percent of energy intake.
As already explained, the nutrients obtained by most green plants are small inorganic molecules that can move with relative ease across cell membranes. Heterotrophic organisms such as bacteria and fungi , which require organic nutrients yet lack adaptations for ingesting bulk food, also rely on direct absorption of small nutrient molecules. Molecules of carbohydrates , proteins , or lipids , however, are too large and complex to move easily across cell membranes.
Bacteria and fungi circumvent this by secreting digestive enzymes onto the food material; these enzymes catalyze the splitting of the large molecules into smaller units that are then absorbed into the cells. In other words, the bacteria and fungi perform extracellular digestion—digestion outside cells—before ingesting the food. This is often referred to as osmotrophic nutrition. Like bacteria, protozoans are unicellular organisms, but their method of feeding is quite different.
They ingest relatively large particles of food and carry out intracellular digestion digestion inside cells through a method of feeding called phagotrophic nutrition. Many protozoans also are osmotrophic to a lesser degree. Other protozoans, such as paramecia , pinch off food vacuoles from the end of a prominent oral groove into which food particles are drawn by the beating of numerous small hairlike projections called cilia.
In still other cases of phagotrophic nutrition, tiny particles of food adhere to the membranous surface of the cell, which then folds inward and is pinched off as a vacuole; this process is called pinocytosis.
The food particles contained in vacuoles formed through phagocytosis or pinocytosis have not entered the cell in the fullest sense until they have been digested into molecules able to cross the membrane of the vacuole and become incorporated into the cellular substance. This is accomplished by enzyme-containing organelles called lysosomes , which fuse with the vacuoles and convert food into simpler compounds see figure. Most multicellular animals possess some sort of digestive cavity—a chamber opening to the exterior via a mouth —in which digestion takes place.
The higher animals, including the vertebrates, have more elaborate digestive tracts, or alimentary canals , through which food passes.
In all of these systems large particles of food are broken down to units of more manageable size within the cavity before being taken into cells and reassembled or assimilated as cellular substance. The enzymatic splitting of large and complex molecules into smaller ones is effective only if the enzyme molecules come into direct contact with the molecules of the material they are to digest.
In animals that ingest very large pieces of food, only the molecules at the surface are exposed to the digestive enzymes.