Class Mammlia

Classification of Animal Chordates of Class 11

Study of mammals is mammology.

Body distinctly divisible into head, neck, trunk and tail.

Limbs 2 pairs, pentadactyl, and variously adapted for walking, running, climbing, burrowing, swimming or flying. Hindlimbs absent in cetaceans and sirenians.

Hair-clad, mostly terrestial, air-breathing, warm-blooded, viviparous, tetrapod vertebrates.

Exoskeleton includes horny, epidermal hair, spines, scales, claws, nails, hoofs, horns, bony dermal plates, etc.

Skin richly glandular containing sweat, sebaceous (oil) and sometimes scent glands in both the sexes.

Females have mammary glands with teats.

A muscular partition, called diaphragm, separates the thoracic cavity from the abdominal cavity.

Endoskeleton of bones. Skull dicondylic. Each half of lower jaw made of a single bone, the dentary.

Alimentary canal terminates at anus, there being no cloaca except monotremes.

Teeth are of several types (heterodont), borne in sockets (thecodont) and represented by two sets (diphyodont).

Respiration always by lungs (pulmonary). Glottis protected by a epiglottis. Larynx contains vocal cords.

Heart 4-chambered with double circulation. Only the left aortic arch present. Renal portal system absent, R.B.C. small, circular and non-nucleated. Homiothermous animals.

Kidneys metanephric. Excretion is ureotelic.

Brain highly evolved. Both cerebrum and cerebellum large and convoluted. Corpora quadrigemina and Corpus callosum present. Cranial nerves 12 pairs.

Sense organs well developed. Eyes protected by lids, the upper of which is movable. External ear opening protected by a large fleshy and cartilaginous flap called pinna. Middle ear cavity with 3 ear ossicles-malleus, incus and stapes. Cochlea of internal ear spirally coiled.

Sexual dimorphism generally well marked. Male has an erectile, copulatory organ or penis. Testes commonly placed in a bag or scrotum outside abdomen.

Fertilization internal.

Except egg-laying monotremes, mammals are viviparous, giving birth to living young ones.

Parental care well developed.

Mammals show greatest intelligence among animals.

Classification

Prototheria (Monotremata) : Primitive mammals, they lay eggs, urino-genital organs open into a cloaca, mammary glands and hair are present, heart four-chambered, only left aortic arch is present and seven cervical vertebrae. e.g., Echidna (spiny ant-eater), Ornithorhynchus (duck-bill platypus).

Metatheria (Marsupilia) : They are viviparous but young ones are born in an immature stage (3 cm), abdominal pouch is present, mammary glands have teats, have two uteri and vagina, found in Australia. e.g., Macropus (kangaroo), Didelphys (opossum).

Eutheria : Placenta establishes connection between the uterus of mother and developing embryo, viviparous, brain is highly developed and has corpus callosum.

It is divided into 16 orders out of which 12 main orders are :

Edentata : Digits bear claws used for hanging from the trees, tongue is used for eating insects, no front teeth, cervical vertebrae are 6 e.g., Dasypus (armadillo), Sloth.

Pholiodata : Exoskeleton of epidermal scales formed by fused hair, teeth absent, tongue long, limbs short with five clawed digits. e.g., Scaly ant eater.

Insectivora : Teeth are small and pointed, live on insects, e.g., Erinaceus (Hedgehog).

Lagomorpha : Incisors sharp, canines absent, herbivorous, e.g., Oryctolagus (Rabbit), Lepus (Hare).

Rodentia : The upper jaw has only a single pair of incisors with enamel on the anterior surface only, e.g., Musa (Mouse), Hystrix (Porcupine), Funambulus (Squirrel).

Chiroptera : These mammals can fly, sternum has keel for attachment of muscles of flight, they hang upside down by their hind limbs, fold of skin called patagium forms wing, e.g., Pteropus (flying fox), Vespertilio (bat).

Carnivora : Jaws are powerful with three pairs of incisors and large sharp canines, e.g., Panthera tigris (tiger), Canis familiaris (dog).

Cetacea : Aquatic mammals with fish-like bodies, pinnae and scrotum are lost, hair absent, a layer of fat (blubber) is found under the skin for maintaining temperature, cervical vertebrae form a single bone of thin plate, no neck, e.g., Balaenoptera (blue whale).

Artiodactyla or even-toed ungulates : They walk on tips of their digits (unguligrade), stomach is complicated with several chambers (Ruminants or cud chewing) where bacteria digest cellulose, herbivorous, e.g., Giraffe, Camelus (camel), Capra (goat), sheep.

Perissodactyla or odd-toed ungulates : Incisors are present in both jaws but canines are found only in males, stomach is simple, no gall bladder, they walk on the tips of their digits but have an odd number of toes, e.g., Equus (horse), Rhinoceros, zebra, ass, donkey, tapir.

Proboscidea : Testes are internal, the nose and upper lip form a long trunk or proboscis, two upper incisors are elongated to form tusks of solid ivory, canines and pre-molars absent, three molars in each jaw but only one is functional, e.g., Elephas (Elephant), mammoths & mastodons are extinct elephants.

Primates : Clavicles well-developed, a large cranium, very intelligent, pentadactyl limbs with locomotion on palms, testes lie in scrotal sacs, two thoracic mammae, e.g., Gorilla, Homo sapiens (man), Macaca (monkey), Pan (chimpanzee).

POINTS TO REMEMBER

Man remains plantigrade at rest or during locomotion. Uses only the toes for running, thus is called sub-plantigrade.

Colour of human skin is yellow to orange due to carotene pigment in cells of stratum corneum and subdermal fat cells. Melanin is found in melanocytes.

In man sweat glands are absent at lip borders, clitoris, glans penis, nail beds, under surface of prepuce.

Sweat or sudoriferous glands secrete sweat. Sweat comprises of 95% water and 5% metabolic waste.

Spiny ant eater, scaly ant eaters, cetaceans, sirenians and some edentates do not possess sweat glands.

Tusks of elephants are two incisors of upper jaw which constantly grow throughout life.

Primates such as monkeys, man, apes, etc., acquired 3-dimensional vision due to their most evolved motor understanding of visual sensation.

Deer, amongst vertebrates, proportionate to their body size, possess largest eyes.

Carnassial Teeth. Special shearing teeth in carnivores for cracking bones–4th premolar of upper jaw and first molar of lower jaw.

Milk Producing Male Mammal. Spiny Ant Eater/Echidna.

Monotreme. With a single aperture of cloaca for urinogenital and digestive tracts.

Largest Land Animal. Loxodonta africana/African Elephant. Height 3.5 m and weight 7 tonnes.

Tallest Land Animal/Mammal. Giraffe, upto 6m.

Zebra Stripes. Stripes of no two zebras are alike.

Fastest Mammals. Acinonyx jubatus/(Cheetah) (extinct from India but present in Africa). Speed upto
100 km/hr.

Smallest Mammals. Previously Pigmy water shrew. Now Hog nose bat.

Slowest Terrestrial Mammal. 3-toed sloth/Bradypus, 100-150 m/hr.

Slowest Aquatic Mammal. Sea Otter/ 10 km/hr.

Longest Gestation Period in Mammal. 609 days/20 months in Elephas maximus.

Shortest Gestation Period in Mammal. Opossum. 12–13 days.

Horn. Matted hair in Rhino. Antlers are solid, shed and regrown every year.

Tiger. Panthera tigris is National animal of India (declared in 1973).

Marsupials are found mainly in Australia except few marsupials like American opossum.

Rabbit is digitgrade because it moves on digits.

Plantigrade mammals are those whose palm and sole touch the ground when moving from one place to another e.g., bears and certain insectivores.

Unguligrade mammals are those whose tips of one or two fingers and toes only remain in contact with the ground, both at rest and locomotion. These are fastest running terrestrial mammals e.g., horses, deers, cows donkeys etc.

Hides are prepared from dermis of animals skin.

Seals and whales have scanty hair because heat insulation is done by blubber.

Horns of rhinoceros, scales of scaly ant eater and spines of porcupine are derivatives of hair.

Retina of owls, shrews, hedge hog, rodents, bats etc. contains only rods (suitable for nocturnal habit).

Retina of fowls, squirrels contains only cones (suitable for diurnal habit).

Scrotum of mammals contains testes, in most of the mammals; this is a thermostatic chamber for testes and lies outside the abdominal cavity because sperms can not develop at body cavity temperature.

In insectivores, tubulidentates, chiroptera and rodentia scrotum is formed only during breeding season, later move to abdominal cavity e.g., bat, otter.

Insectivores, Edentates, Proboscidians (Elephants), Cetaceans (whales) always have their testes inside the body cavity.

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