Retrieved 15 March Likely sprainting sites, such as underneath bridges, within the m transect, can usefully be prioritised as the starting point. Ecosystem The term ecosystem is used to describe the working together of different species of animal within a particular habitat, a good example of this being the basic food chain. The full dental formula of dugongs is 2. However, it looks like Great Lakes Unflavored Beef Gelatin is not high from their amino acid comparison on the can. Keep Exploring Britannica Lystrosaurus. February 18, at
Form and function
The resulting complex of embryonic and maternal tissues is a true placenta. Placentas have been classified on the basis of the relationship between maternal and embryonic tissues.
In the simplest nondeciduate placental arrangement, the chorionic villi are in contact with uterine epithelium the inner surface layer. In advanced stages of pregnancy in rabbits , even the chorionic epithelium is eroded, and the embryonic endothelium contacts the maternal blood supply.
In no case, however, is there actual exchange of blood between mother and fetus; nutrients and gases must still pass through the walls of the fetal blood vessels. The period of intrauterine development, or gestation, varies widely among eutherians, generally depending on the size of the animal but also influenced by the number of young per litter and the condition of young at birth. The gestation period of the golden hamster is about 2 weeks, whereas that of the blue whale is 11 months and that of the African elephant 21 to 22 months.
At birth the young may be well-developed and able to move about at once precocial , or they may be blind, hairless, and essentially helpless altricial. In general, precocial young are born after a relatively long gestation period and in a small litter.
Hares and many large grazing mammals bear precocial offspring. Rabbits , carnivores , and most rodents bear altricial young. After birth young mammals are nourished by milk secreted by the mammary glands of the female.
The development of milk-producing tissue in the female mammae is triggered by conception , and the stimulation of suckling the newborn prompts copious lactation. In therians marsupials and placentals the glands open through specialized nipples. Milk consists of fat , protein especially casein , and lactose milk sugar , as well as vitamins and salts. The actual composition of milk of mammals varies widely among species.
The milk of whales and seals is some 12 times as rich in fats and 4 times as rich in protein as that of domestic cows but contains almost no sugar. Milk provides an efficient energy source for the rapid growth of young mammals; the weight at birth of some marine mammals doubles in five days. The dependence of the young mammal on its mother for nourishment has made possible a period of training. Such training permits the nongenetic transfer of information between generations.
The ability of young mammals to learn from the experience of their elders has allowed a behavioral plasticity unknown in any other group of organisms and has been a primary reason for the evolutionary success of mammals.
The possibility of training is one of the factors that has made increased brain complexity a selective advantage. Increased associational potential and memory extend the possibility of learning from experience, and the individual can make adaptive behavioral responses to environmental change. Individual response to short-term change is far more efficient than genetic response. Some types of mammals are solitary except for brief periods when the female is in estrus. Others, however, form social groups.
Such groups may be reproductive or defensive, or they may serve both functions. In those cases that have been studied in detail, a more or less strict hierarchy of dominance prevails. Within the social group , the hierarchy may be maintained through physical combat between individuals, but in many cases stereotyped patterns of behaviour evolve to displace actual combat, thereby conserving energy while maintaining the social structure see also animal behaviour , territorial behaviour , and territoriality.
A pronounced difference between sexes sexual dimorphism is frequently extreme in social mammals. In large part this is because dominant males tend to be those that are largest or best-armed. Play extends the period of maternal training and is especially important in social species, providing an opportunity to learn behaviour appropriate to the maintenance of dominance. That area covered by an individual in its general activity is frequently termed the home range. A territory is a part of the home range defended against other members of the same species.
As a generalization it may be said that territoriality is more important in the behaviour of birds than of mammals, but data for the latter are available primarily for diurnal species. This form of territorial labeling is less evident to humans than the singing or visual displays of birds.
Many mammals that do not maintain territories per se nevertheless will not permit unlimited crowding and will fight to maintain individual distance. Such mechanisms result in more economical spacing of individuals over the available habitat. Mammals may react to environmental extremes with acclimatization , compensatory behaviour, or physiological specialization. One way for a mammal to endure stressful environmental conditions is to become dormant. Dormancy is the general term that relates to the reduced metabolic activity adopted by many organisms under conditions of environmental stress.
Physiological responses to adverse conditions include torpor , hibernation in winter , and estivation in summer. Torpor is a type of dormancy that may occur in the daily cycle or during unfavourable weather; short-term torpor is generally economical only for small mammals that can cool and warm rapidly.
The body temperature of most temperate-zone bats drops near that of the ambient air whenever the animal sleeps. The winter dormancy of bears at high latitudes is an analogous phenomenon and cannot be considered true hibernation. Strictly speaking, hibernation only occurs in warm-blooded vertebrates. True hibernation involves physiological regulation to minimize the expenditure of energy.
The body temperature is lowered, and breathing may be slowed to as low as 1 percent of the rate in an active individual. There is a corresponding slowing of circulation and typically a reduction in the peripheral blood supply. When the body temperature nears the freezing point, spontaneous arousal occurs, although other kinds of stimuli generally elicit only a very slow response.
In mammals that exhibit winter dormancy such as bears, skunks , and raccoons , arousal may be quite rapid. Hibernation has evidently originated independently in a number of mammalian lines, and the comparative physiology of this complex phenomenon is only now beginning to be understood.
Inactivity in response to adverse summer conditions heat , drought , lack of food is termed estivation. Estivation in some species is simply prolonged rest, usually in a favourable microhabitat ; in other species estivating mammals regulate their metabolism , although the effects are typically not as pronounced as in hibernation.
Behavioral response to adverse conditions may involve the selection or construction of a suitable microhabitat, such as the cool, moist burrows of desert rodents. Migration is a second kind of behavioral response.
The most obvious kind of mammalian migration is latitudinal. Many temperate-zone bats, for example, undertake extensive migrations, although other bat species hibernate near their summer foraging grounds in caves or other equable shelters during severe weather when insects are not available. Caribou Rangifer tarandus , or reindeer , migrate from the tundra to the forest edge in search of a suitable winter range, and a number of cetaceans whales , dolphins , and porpoises and pinnipeds walruses and seals undertake long migrations from polar waters to more temperate latitudes.
Gray whales , for example, migrate southward to calving grounds along the coasts of South Korea and Baja California from summer feeding grounds in the northern Pacific Ocean Okhotsk, Bering, and Chukchi seas. Of comparable extent is the dispersive feeding migration of the northern fur seal Callorhinus ursinus. Migrations of lesser extent include the elevational movements from mountains to valleys of some ungulates—the American elk Cervus elaphus canadensis , or wapiti, and bighorn sheep Ovis canadensis , for example—and the local migrations of certain bats from summer roosts to hibernation sites.
Most migratory patterns of mammals are part of a recurrent annual cycle, but the irruptive sudden emigrations of lemmings and snowshoe hares are largely acyclic responses to population pressure on food supplies.
The structure and dynamics of a population depend, among other things, on the relative lengths of these ages, the rate of recruitment of individuals either by birth or by immigration , and the rate of emigration or death. The reproductive potential of some rodents is well known; some mice are reproductively mature at four weeks of age, have gestation periods of three weeks or less, and may experience postpartum estrus, with the result that pregnancy and lactation may overlap.
Litter size, moreover, may average four or more, and breeding may occur throughout the year in favourable localities. The reproductive potential of a species is, of course, a theoretical maximum that is rarely met, inasmuch as, among other reasons, a given female typically does not reproduce throughout the year.
Growth of a population depends on the survival of individuals to reproductive age. The absolute age at sexual maturity ranges from less than 4 weeks in some rodents to some 15 years in the African bush elephant Loxodonta africana. Postreproductive individuals are rare in most mammalian populations. Survival through more than a single reproductive season is probably uncommon in many small mammals, such as mice and shrews. Larger species typically have longer life spans than do smaller kinds, but some bats are known, on the basis of banding records, to live nearly 20 years.
Many species show greater longevity in captivity than in the wild. Captive echidnas are reported to have lived more than 50 years.
Horses have been reported to live more than 60 years, and elephants have lived to more than Various cetaceans survive to more than 90 years of age, and research involving the dating of harpoons embedded in some Greenland right whales Balaena mysticetus , or bowheads, suggests that Greenland right whales can live years or more.
Specialization in habitat preference has been accompanied by locomotor adaptations. Terrestrial mammals have a number of modes of progression. The primitive mammalian stock walked plantigrade —that is, with the digits, bones of the midfoot, and parts of the ankle and wrist in contact with the ground.
The limbs of ambulatory mammals are typically mobile, capable of considerable rotation. Mammals modified for running are termed cursorial. The stance of cursorial species may be digitigrade the complete digits contacting the ground, as in dogs or unguligrade only tips of digits contacting the ground, as in horses.
In advanced groups limb movement is forward and backward in a single plane. This mode of locomotion is typically found in mammals living in open habitats. Jumping mammals typically have elongate, plantigrade hind feet, reduced forelimbs, and long tails.
Convergent evolution within a given adaptive mode has contributed to the ecological similarity of regional mammalian faunas. Age Of Fledgling The age of a bird when it develops wing feathers which are developed enough for the bird to fly.
Age Of Independence The age when the animal can survive without the support of its parent s. Age Of Sexual Maturity The age when an animal can mate to produce its own offspring.
Animal Animals are a multi-celled living organisms that are thought to have to developed around million years ago from single-celled marine organisms. The animals body shape generally becomes fixed once the animal reaches maturity although some species of animal undergo series metamorphosis in later life such as the caterpillar which grows wings. Most animals are generally motile which means that they are able to move in their own. Animals are also considered heterotrophs, which means that they must ingest other organisms to survive, either plant or animal organisms.
There is no way of knowing exactly how many species of animal exist as so many are found or become extinct each year. Estimates rate it at between 2 million and 50 million different species of animal on Earth. Antenna The sensory feel on the head of an arthropod.
Antennae are always present in pairs and can be sensitive to touch, taste, sound and heat. The size and shape of antennae varies widely depending on the animal species and the way in which it's antennae are used. Antler The bony growth on the head of animals such as deer. Antlers are often much large than horns, branching out as they grow. In most cases, antlers are shed and re-grown every year in connection with the breeding season.
Arboreal Locomotion Arboreal locomotion is the movement of animals in trees. In every habitat in which trees are present, animals have evolved to move in them. Some animals may only scale trees occasionally, while others are exclusively arboreal.
These habitats pose numerous mechanical challenges to animals moving through them, leading to a variety of anatomical, behavioural and ecological consequences including the evolution of sharper claws and prehensile tails.. Furthermore, many of these same principles may be applied to climbing without trees, such as on rock piles or mountains. Arthropod An arthropod is an invertebrate that has an external skeleton exoskeleton , a segmented body, and jointed leg-like attachments called appendages.
The arthropod groups includes insects, arachnids, and crustaceans. Asexual Reproduction A form of reproduction that involves just one parent, and is most common in invertebrates. Asexual reproduction means that a species can quickly multiply it's population numbers. Average Clutch Size The average number of eggs laif at once [Top]. Average Litter Size The average number of babies born at once.
Average Rainfall Year The typical amount of rain that may fall in an area in a year. Average Size The average length L or height H of the animal. Average Spawn Size The typical amount of eggs a fish may lay at once. Average Weight The average measurement of how heavy the animal is.
Baleen A fibrous substance that is found in the mouths of some species of whale, which they use to filter food particles out of the water. The baleen plates grow out of the jaw in the same way as teeth, but trap food in the mouth which the whale then swallows. Biggest Threat The largest danger to an animal, such as a predator or deforestation.
Binocular Vision When the two eyes face forwards their field of vision overlaps allowing the animal to judge depth. Biome A grouping of living organisms, including the habitat in which they are found. Bird Birds are warm blooded vertebrates that nest to lay their eggs, from which the bird offspring hatch. The birds skin is also covered in layers of feathers, to keep them warm but the feather also make the bird extremely light so it can fly without trouble.
All birds have wings and most can fly over very long distance, some species of bird migrates thousands of mile every year, while others can only fly a few feet. The penguin is one of the only birds in the world that cannot fly as their wings are too small to lift their body. There are around 10, species of bird found worldwide, although studies suggest that many more species have become extinct. The bee hummingbird is the smallest species of bird in the world growing to around 5cm, with the ostrich being the largest species of bird and growing to nearly 3m tall.
Blowhole The nostrils of a whale are on the top of their head, and can be pair or singular. Breaching When an animals leaps out of the water and falls back in with a splash. Breaching is often a behaviour displayed by large whales. Brood Parasite When an animal birds are common tricks another species into raising it's young.
Browsing Feeding on the leaves that are on trees, bushes and shrubs higher up rather than eating the grass and plants on the ground. Calcareous Calcareous calcium structures are shells, bones and exoskeletons that are created by many animals to provide both support and protection.
Camouflage Colours or patterns are often displayed on an animal to help it to blend into it's surroundings. Animals use camouflage to both hide and protect themselves from approaching predators but also to sure that they are not spotted by unsuspecting prey.
Canine Tooth Some mammals have canine teeth which are strong and sharply pointed teeth. Canine teeth are generally found at the front of the jaw and are used for piercing and biting prey.
Carnassial Tooth Carnivorous mammals have a carnassial tooth which is a blade-like tooth that is designed to slice through flesh. Carnivore A carnivore is an animal that only eats other animals in order to ensure its own survival. Carnivorous animals have a complex digestive system that has adapted to breaking large amounts of meat, and therefore do not need to feed as often as herbivorous and omnivorous animals.
Lions, crocodiles and sharks are all good example of animals that are carnivores. Cartilage Cartilage is a rubbery substance that helps to form part of the skeleton in vertebrates. Cellulose Cellulose is a complex carbohydrate found in plants that many animals find difficult to break down. Herbivorous grazing animals, are able to digest it with the help of micro-organisms. Chelicera Chelicerae are the first pairs of appendages of the front of an arachnids body.
Some arachnids have pincers on the end and some spiders can inject venom through them. Chordate An animal belong to the phylum Chordata, which includes all vertebrates. Chrysalis A hard and shiny case that protect insect pupa, that is often found attached to plants or buried in the soil. Circulatory System An animals circulatory system involves the animals heart, blood vessels and blood which flows around the animals body, transporting nutrients to cells that need them and removing waste products from others.
The blood is powered by the animals heart which beats on average around times a minute this obviously depends on the animal though. Class A level of classifying animals in a phylum. Classes are then sub-divided into further groups known as orders. Cloven-hoofed Animals such as deer and antelope have hooves that look like they are split in two. Cocoon A nest made by insects of woven silk, often to protect eggs or pupae. Cold Blooded Having a body temperate that is reliant on it's surroundings.
Colony A group of animals from the same species, that spend their lives together and often have individual tasks that help with the overall survival of the colony. Common Name The most widely used name for this species of animal. Compound Eye An eye that is divided up into separate compartments, each with its own set of lenses. Compound eyes are most commonly found in arthropods and can contain from a few to thousands of lenses. Conservation Status The conservation status of a species is an indicator of the likelihood of that species remaining extant either in the present day or the near future.
Many factors are taken into account when assessing the conservation status of a species: Scientifically, animals come into 9 different categories which are least concern, near threatened, conservation dependent, threatened, vulnerable, endangered, critically endangered, extinct in the wild and extinct.
A-Z Animals groups the animals into just four different categories which are least concern covering the categories least concern, near threatened and conservation dependent , threatened covering the categories threatened and vulnerable , endangered covering the categories endangered, critically endangered and extinct in the wild and extinct.
Least Concern is a category assigned to extant species which have been evaluated but do not qualify for any other category. Many common species are assigned to the least concern category but the species has to have been evaluated to be classified in the least concern category.
Near Threatened is a conservation status assigned to species that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status. As such it is important to re-evaluate Near Threatened species often or at appropriate intervals. Conservation Dependent is a category assigned to extant species that rely on conservation efforts to prevent them from being threatened from extinction.
Threatened species are any species of living organism which are vulnerable to extinction in the near future. The World Conservation Union IUCN is the main authority on threatened species, and treats threatened species not as a single category, but as a group of three categories: Vulnerable species are species which are likely to become endangered unless the circumstances threatening their survival and reproduction improve. Endangered species are a population of organisms which are at risk of becoming extinct because they are either few in numbers, or threatened by environmental changes or changes in the behaviours of their predators.
Many nations have laws offering protection to conservation reliant species: Only a few of the many species at risk of extinction actually make it to the lists and obtain legal protection. Many more species become extinct, or potentially will become extinct, without gaining public notice. Critically Endangered species are organisms that are of an extremely high risk of becoming extinct in the wild or completely extinct in the immediate future. Extinct in the Wild is a conservation status assigned to species where the only known living members are being kept in captivity or as a naturalized population outside it's historic and natural range.
Extinct species no longer exist anywhere on Earth. The moment of extinction is generally considered to be the death of the last individual of that species. Cryptic Colouration An animal uses certain colours and markings in order to make itself invisible in its surroundings. Delayed Implantation In some mammals, there can be a delay between when the egg is fertilised and when the embryo begins to develop. Deposit Feeder An animal that feeds on small particles of organic matter that have drifted down to and settle on the bottom.
Detritivore An animals that feeds on dead plant and animal matter. Distinctive Features Characteristics unique to the animal [Top]. Diurnal If an animal is diurnal it means that the animal tends to sleep during the dark, night hours and wakes up to hunt when the sun rises in the morning.
Humans, bears and horses are considered to be diurnal animals. Domesticated An animal that lives with humans or is looked after by them. Dorsal Fin Large fin on the back of marine animals such as fish, sharks, whales and dolphins.
Echinoderm Echinoderms are spiny-skinned invertebrates that are found on the ocean floor. Echinoderms are armoured animals that have a hard internal skeleton endoskeleton made up of plates and spines. Echinoderms are slow-moving creatures that have a water-vascular system which pumps water through the body.
Echinoderms also have small jaws that are supported by the water-vascular system and tube feet which they use to attach to objects for protection, as well as to obtain food. Echinoderms generally have radial symmetry and most can regenerate lost limbs. Four types of uterus are generally recognized among placentals, based on the relationship of the uterine horns branches. A duplex uterus characterizes rodents and rabbits ; the uterine horns are completely separated and have separate cervices opening into the vagina.
Carnivores have a bipartite uterus, in which the horns are largely separate but enter the vagina by a single cervix. In the bicornate uterus, typical of many ungulates , the horns are distinct for less than half their length; the lower part of the uterus is a common chamber, the body. Higher primates have a simplex uterus in which there is no separation between the horns and thus a single chamber. The female reproductive tract of marsupials is termed didelphous; the vagina is paired, as are oviducts and uteri.
In primitive marsupials there are paired vaginae lateral to the ureters. Monotremes have paired uteri and oviducts, which empty into a urogenital sinus cavity as fluid wastes do. The sinus passes into the cloaca , a common receptacle for reproductive and excretory products. In mammals, as in birds , the right and left ventricles of the heart are completely separated, so that pulmonary lung and systemic body circulations are completely independent.
Oxygenated blood arrives in the left atrium from the lungs and passes to the left ventricle , whence it is forced through the aorta to the systemic circulation. Deoxygenated blood from the tissues returns to the right atrium via a large vein , the vena cava , and is pumped to the pulmonary capillary bed through the pulmonary artery. Among vertebrates contraction of the heart is myogenic, or generated by muscle; rhythm is inherent in all cardiac muscle, but in myogenic hearts the pacemaker is derived from cardiac tissue.
The pacemaker in mammals and also in birds is an oblong mass of specialized cells called the sinoatrial node , located in the right atrium near the junction with the venae cavae. A wave of excitation spreads from this node to the atrioventricular node, which is located in the right atrium near the base of the interatrial septum. From this point excitation is conducted along the atrioventricular bundle bundle of His and enters the main mass of cardiac tissue along fine branches, the Purkinje fibres.
Homeostatic, or stable, control of the heart by neuroendocrine or other agents is mediated through the intrinsic control network of the heart. Blood leaves the left ventricle through the aorta. The mammalian aorta is an unpaired structure derived from the left fourth aortic arch of the primitive vertebrate.
Birds, on the other hand, retain the right fourth arch. The circulatory system forms a complex communication and distribution network to all physiologically active tissues of the body. A constant, copious supply of oxygen is required for sustaining the active, heat-producing endothermous physiology of the higher vertebrates see also endotherm.
The efficiency of the four-chambered heart is important to this function. Oxygen is transported by specialized red blood cells, or erythrocytes , as in all vertebrates. Packaging the oxygen-bearing pigment hemoglobin in erythrocytes keeps the viscosity of the blood minimal and thereby allows efficient circulation while limiting the mechanical load on the heart.
The mammalian erythrocyte is a highly evolved structure; its discoid, biconcave shape allows maximal surface area per unit volume. When mature and functional, mammalian red blood cells are enucleate lacking a nucleus. Closely coupled with the circulatory system is the ventilatory breathing apparatus, the lungs and associated structures.
Ventilation in mammals is unique. The lungs themselves are less efficient than those of birds, for air movement consists of an ebb and flow, rather than a one-way circuit, so a residual volume of air always remains that cannot be expired. Ventilation in mammals is by means of a negative pressure pump made possible by the evolution of a definitive thoracic cavity with a diaphragm.
The diaphragm is a unique composite structure consisting of 1 the transverse septum a wall that primitively separates the heart from the general viscera ; 2 pleuroperitoneal folds from the body wall; 3 mesenteric folds; and 4 axial muscles inserting on a central tendon, or diaphragmatic aponeurosis. The lungs lie in separate airtight compartments called pleural cavities, separated by the mediastinum.
As the size of the pleural cavity is increased, the lung is expanded and air flows in passively. Enlargement of the pleural cavity is produced by contraction of the diaphragm or by elevation of the ribs.
The relaxed diaphragm domes upward, but when contracted it stretches flat. Expiration is an active movement brought about by contraction of abdominal muscles against the viscera. Air typically enters the respiratory passages through the nostrils, where it may be warmed and moistened. It passes above the bony palate and the soft palate and enters the pharynx. In the pharynx the passages for air and food cross.
Air enters the trachea , which divides at the level of the lungs into primary bronchi. A characteristic feature of the trachea of many mammals is the larynx.
Vocal cords stretch across the larynx and are vibrated by forced expiration to produce sound. The laryngeal apparatus may be greatly modified for the production of complex vocalizations.
In some groups—for example, howler monkeys —the hyoid apparatus is incorporated into the sound -producing organ, as a resonating chamber. The nervous system and the endocrine system are closely related to one another in their function, for both serve to coordinate activity. The endocrine glands of mammals generally have more complex regulatory functions than do those of lower vertebrates. This is particularly true of the pituitary gland , which supplies hormones that regulate the reproductive cycle.
Follicle-stimulating hormone FSH initiates the maturation of the ovarian follicle. Luteinizing hormone LH mediates the formation of the corpus luteum from the follicle following ovulation. Prolactin , also a product of the anterior pituitary, stimulates the secretion of milk. Control of the pituitary glands is partially by means of neurohumours from the hypothalamus , a part of the forebrain in contact with the pituitary gland by nervous and circulatory pathways. The hypothalamus is of the utmost importance in mammals, for it integrates stimuli from both internal and external environments, channeling signals to higher centres or into autonomic pathways.
The cerebellum of vertebrates is at the anterior end of the hindbrain. Its function is to coordinate motor activities and to maintain posture. In most mammals the cerebellum is highly developed, and its surface may be convoluted to increase its area. In the vertebrate ancestors of mammals, the cerebral hemispheres were centres for the reception of olfactory stimuli see also smell. Vertebrate evolution has favoured an increasing importance of these lobes in the integration of stimuli.
In vertebrate evolution the gray matter of the cerebrum has moved from a primitive internal position in the hemispheres to a superficial position. The superficial gray matter is termed the pallium. The paleopallium of amphibians has become the olfactory lobes of the higher vertebrates ; the dorsolateral surface, or archipallium, has become the mammalian hippocampus. The great neural advance of the mammals lies in the elaboration of the neopallium, which makes up the bulk of the cerebrum.
By contrast, the highest centre in the avian brain is the corpus striatum, an evolutionary product of the basal nuclei of the amphibian brain. Therefore, the bulk of complex behaviour of birds is instinctive. The surface of the neopallium tends in some mammals to be greatly expanded by convoluting, forming folds gyri between deep grooves sulci. We welcome suggested improvements to any of our articles.
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Form and function Skin and hair The skin of mammals is constructed of two layers, a superficial nonvascular epidermis and an inner layer, the dermis , or corium. Page 2 of 3. Next page Evolution and classification.
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