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Class Mammalia: Characteristics, Classification, Examples, Practice Problems and FAQs

Class Mammalia: Characteristics, Classification, Examples, Practice Problems and FAQs

We all belong to the Animal Kingdom and you all know that there are a number of varieties of organisms present in this particular Kingdom. The main difference between the members of the Kingdom Plantae and Animalia is that the members of the Animal Kingdom show locomotion. You know that they possess various types of organs depending on the species to perform this particular activity like flagella, pseudopodia, cilia, limbs etc.

Tetrapoda is a superclass belonging to the Gnathostomata division of the subphylum Vertebrata under the phylum Chordata. We all are chordates. Tetrapoda (tetra- four, podus- foot), as the name suggests, includes animals bearing four limbs for locomotion.

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GIF: Superclass Tetrapoda

Snakes and some amphibians which are limbless are the exceptions under this particular superclass. Tetrapoda is further classified into four classes such as class Amphibia, class Reptilia, class Aves and class Mammalia.

We belong to the class Mammalia under the superclass Tetrapoda. Can you tell me why we are called mammals? Yes we possess a pair of modified sweat glands called mammary glands in the chest region. In females these are used to nourish the young ones. Mammalia is derived from the word ‘mamma’ which means breasts. In this article we are going to discuss class Mammalia in depth.

List of contents

General characteristics of the class Mammalia

The members of the class Mammalia are the most successful and the most dominant animals in the present world. There are approximately 5700 extant species of mammals in the present world. The following are the general characteristics of class Mammalia.

Habitat

Members of class Mammalia are well-adapted to thrive in varying environmental conditions like polar areas, deserts, grasslands, dark caves, mountains, trees etc. A few of them can also live in water too. A few are adapted to aerial mode of life like bats.

Fig: Various habitats of mammals

Homoiothermic

They are warm-blooded or homeothermic, which means they can maintain their constant body temperature. This requires a high metabolic rate as they have to balance the amount of heat lost through their body surface.

Presence of mammary glands

They possess modified sweat glands called mammary glands. It is the differentiating feature of mammals. Mammary glands are the milk-producing glands which are used to feed the young ones in the females.

Fig: Mammary gland in mammals

Body form

The body is variously shaped in class Mammalia and generally divided into head, neck and trunk. Mammals possess a muscular diaphragm which divides their trunk into two major parts such as thorax and abdomen.

Fig: Body form in Class Mammalia

External features of the class Mammalia

The following are the external features in class Mammalia:

Appendages

Mammals possess a pair of pentadactyl limbs, that means they possess five toes or fingers. The digits are provided with horny claws, nails or hoofs. The limbs are used for different functions such as walking, running, jumping, burrowing, climbing, grasping, swimming or flying depending on the species.

Fig: Pentadactyl limbs

Walking

Walking in the members of the class Mammalia differs.

Walking in plantigrade mammals

Plantigrade mammals keep the heel bone on the ground and walk with the help of toes and metatarsals flat on the ground. Examples include human beings.

Fig: Walking in plantigrade mammals

Walking in digitigrade mammals

Digitigrade mammals move with the help of most of the length of their digits, but not the soles of their feet. Examples include dogs, cats etc.

Fig: Walking in digitigrade mammals

Walking in unguligrade mammals

Unguligrade mammals walk and run on the tip of digits. They excel to produce power. Examples include horses.

Fig: Walking in unguligrade mammals

Running

The best long distance runners in the entire Animal Kingdom are horses. Cheetahs are considered as the world's fastest land animal. They are capable of reaching speeds of up to 70 mph.

GIF: Running

Climbing

Mammals use claws and hands to climb. Examples include domestic cats (Felis catus), raccoons (Procyon lotor), etc.

Fig: Climbing

Swimming

Some mammals like otters and platypus, have physical adaptations for swimming. They are semi aquatic mammals. They possess webbed feet. The aquatic mammals like dolphins, manatees, whales and seals possess limbs and tails modified into flippers or fins. This helps in swimming. All aquatic mammals possess a flexible spine which also helps in swimming.

Fig: Swimming

Flying

Bats are mammals which show flying. They have many adaptations that help in flying. This includes echolocation, keen senses, reduced radius, modified pectoral girdle (at right), large humerus and ulna, high metabolic rate, clawed fingers, and a uropatagium. The uropatagium is a membrane stretched between the hindlimbs and commonly includes the tail, which helps to stabilise the bat during flight.

Fig: Flying in bat

Burrowing

Mammals are powerful burrowers. They possess powerful short forelimbs which are adapted for digging. The digits of the forelimbs are equipped with strong claws for burrowing. Examples include gopher, mole, great gerbil and groundhog.

Fig: Burrowing

Skin

Skin of mammals possess horny epidermal skeleton of hairs that help in maintaining temperature in some mammals. The skin is glandular and possesses oil glands, wax glands, sweat glands and mammary glands.

Fig: Hair on skin

Ear pinna

Generally members of the class Mammalia possess an external ear or pinna for hearing. External ear is absent in aquatic mammals and in platypus.

Fig: External ear or pinna in mammals

Hairs on the skin

Presence of hairs on the skin helps in insulation and hence helps the mammals to thrive in cold environments. Aquatic mammals also possess hair at some point in their life.

Fig: Hairs in aquatic mammals

Sweat gland

Sweat glands are present in the epidermis of the skin in the members of the class Mammalia. Release of sweat and its evaporation leaves a cooling effect in mammals and also helps in elimination of waste products from the body.

Sebaceous glands

These glands help in keeping the skin moist by producing oily secretions.

Fig: Components of the skin

Internal features of the class Mammalia

The following are the major internal features of the class Mammalia:

Dentition

Members of the class Mammalia possess proper dentition. It is called heterodont dentition, thecodont dentition or diphyodont dentition.

Heterodont dentition

They possess heterodont dentition. That means different types of teeth with different functions present in them. It includes incisors, canines, premolars and molars.

Fig: Heterodont dentition in human beings.

Thecodont dentition

The teeth of mammals are embedded in sockets in the jaw called theca. Hence the dentition is called the thecodont dentition.

Fig: Thecodont dentition

Diphyodont dentition

Teeth of mammals are formed twice in a lifetime. This condition is referred to as diphyodont dentition. Milk teeth or deciduous teeth appear first which are later replaced by the permanent teeth.

Fig: Diphyodont dentition

Digestive system of mammals

Mammals possess a complete digestive system with two different openings, one for ingestion called mouth and the other for egestion called anus. The various parts of the gastrointestinal tract or GIT include the mouth, buccal cavity, pharynx, oesophagus or food pipe, stomach, small intestine, large intestine and anus.

Fig: Alimentary canal

Respiratory system of mammals

The respiratory systems of mammals are well developed. It possesses various organs as per the habitat.

Respiratory system of terrestrial mammals

In terrestrial mammals respiration occurs through a pair of lungs. These are spongy and elastic organs. Respiration is enhanced with the help of muscular diaphragm. A sound producing organ called larynx is also present in mammals.

GIF: Lungs

Respiratory system of aquatic mammals

In aquatic mammals respiration occurs through blowholes. Blowholes are the nostrils present on the top of the heads of certain aquatic mammals. Thus, aquatic mammals come out of the water to breathe as they cannot respire underwater.

Fig: Respiratory system of aquatic mammals

Circulatory system of mammals

Mammals have a four-chambered ventral heart which consists of two auricles and two ventricles. They possess a closed circulatory system i.e., the blood transport occurs through enclosed spaces such as blood vessels.

Fig: Human heart

Nervous system of mammals

Mammals are the most intelligent animals and have the capacity to learn. They have a well developed brain with large cerebrum and cerebellum. They possess 12 pairs of cranial nerves.

Fig: Nervous system of human beings

Sense organs of mammals

They possess well developed sense organs. This includes ears (auditory function), eyes (visual function), skin (tactile function), nose (olfactory function) and tongue (gustatory function). Eyes possess movable eyelids. Each ear consists of three parts such as the external ear, middle and inner ear. Middle ear possesses ear ossicles.

Fig: Sense organs of human beings

Skeletal system

They mainly possess bony skeletons. It provides shape and protection to the body and its parts. But some parts possess cartilages. Examples include cartilage in the ear pinna.

Fig: Skeletal system of human beings

Excretory system of mammals

They possess a pair of kidneys which are bean shaped structures. A pair of ureters helps in the transport of urine from the kidneys to the urinary bladder. Main excretory matter is urea.

Fig: Excretory system of human beings

Mode of reproduction and development of mammals

They shows sexual dimorphism and possess a well developed reproductive system.

Sexual nature

Mammals are dioecious (unisexual) in nature and shows sexual dimorphism.

Fig: Sexual dimorphism in mammals

Mode of birth

They show two modes of birth as follows:

Viviparous

Most of the mammals show viviparity, that means here the mothers give birth to younger ones. Examples include human beings, cats, dogs, elephants etc.

Fig: Viviparity

Oviparous

Some mammals show oviparity, that means mothers lay eggs. Examples of oviparous forms include Duck-billed platypus, Echidna (Tachyglossidae) etc.

Fig: Platypus (Ornithorhynchus)

Type of fertilisation

The members of the class Mammalia show internal fertilisation. It is the fusion of the male gamete and female gamete inside the female body.

Type of development

They show direct development of embryos into young ones without any intervening larval stages.

Fig: Fertilisation and development in mammals

Parental care

Mammals are known for the way they protect and take care of their young ones. They feed them with their milk. They train their young ones to live.

Fig: Parental care in mammals

Classification of Mammalia

Class Mammalia is divided into three subclasses such as Prototheria, Metatheria and Eutheria.

Subclass Prototheria or monotremes

This subclass includes the egg-laying mammals. They are primitive and share characters with mammals and reptiles. Hence they are considered as the connecting link between reptiles and higher mammals. They lack external ears and the body is covered with hairs. They lack teats and the young ones lick the milk soaked hairs. The eggs are covered with calcareous shells. They are commonly found in Australia.

Fig: Duck-billed platypus (Ornithorhynchus)

Classification of monotremes

Living monotremes are classified in two families as follows:

  • Ornithorhynchidae which include the platypus family
  • Tachyglossidae which include the echidna family

Reptilian affinities of monotremes

Monotremes shows some affinities with the Class reptilia as follows:

They possess cloaca, a common chamber where the urogenital and digestive systems open. They possess vertebrae without epiphysis and with cervical ribs. Ribs are single headed in them. Body temperature is not constant. Ureters lead into a urogenital sinus in them. Corpus callosum is absent and anterior commissure is well developed. Testes are located abdominally. They are oviparous. These primitive mammals have failed to cope up with many of the evolutionary transformations which are present in higher mammals.

Avian affinities of monotremes

Monotremes shows some affinities with the Class Aves as follows:

The beak of the platypus resembles that of birds. Teeth are absent in adults. They possess webbed feet. Oil glands are present in them. The converging characters seen in them and Aves are due to the fact that monotremes possess common reptilian ancestry.

Mammalian affinities of monotremes

The prototherians are mammals as they possess the following typical mammalian

characters:

They possess hairs, oil glands, mammary glands, and sweat glands. They possess double occipital condyles. Palate or the roof of the buccal cavity is present. Presence of a typical mammalian diaphragm in the body cavity. Skull is dicondylic. Sternum is segmented. A ventral four chambered heart is present. Only the left aortic arch is present. A closed circulatory system as that of mammals present. They possess large ear ossicles. Cochlea is slightly coiled. Internal fertilisation is present. A caecum which demarcates two intestines present. Red blood cells are small, circular and non-nucleated. They possess four optic lobes or corpora quadrigemina. They possess milk glands for secreting milk.

Subclass Metatheria

They are called the pouched mammals or marsupials. They are characterised by the presence of marsupium or pouch on the belly of the females in which the young born in the immature state are kept. They are then nourished on milk produced by the mammary glands. These mammals are more common in Australia.

Fig: Marsupial

Orders under the subclass Metatheria

The following are the important orders under the subclass Metatheria:

Order Dasyuromorphia

This order includes dasyurid marsupials and marsupial carnivores. They show prolonged copulation, large testes and mate guarding. The females show long behavioural estrus. Females store sperm in the female reproductive tracts. Examples of Australian carnivorous marsupials include quolls (Dasyurus), the numbat (Myrmecobius fasciatus), dunnarts (Sminthopsis), the Tasmanian devil (Sarcophilus harrisii), and the thylacine (Thylacinus cynocephalus).

Fig: Thylacine (Thylacinus cynocephalus)

Order Didelphimorphia

Living didelphimorphia or the opossums, are a diverse group of marsupials. It includes only one family with over 60 species. All toes except the hallux have claws in them. The hallux has a nail. The tail is prehensile and usually long and scaly.

Fig: Opossum

Order Diprotodontia

Some species of this order possess a second pair of too small incisors. They lack lower canines. This arrangement is known as diprotodont dentition. Hence they got the name Diprotodontia. It is the largest extant order of marsupials, with about 155 species. Examples include the kangaroos (Macropodidae), wallabies (Notamacropus), koala (Phascolarctos cinereus), wombats (Vombatidae), and possums.

Fig: Koala

Order Microbiotheria

The members of this order possess short and rounded ears. The tail is long and serves as a site for storing fat to maintain the animal during hibernation. The pouch or marsupium is well developed in them. This is an Australidelphia marsupial order which possesses two families such as Microbiotheriidae and Woodburnodontidae. Examples include monito del monte (Dromiciops gliroides).

Fig: Monito del monte

Order Notoryctemorphia

This order includes the marsupial moles. They are eutherian golden moles in size, shape, and in the silky, iridescent texture and appearance of the fur. They have vestigial and functionally blind eyes which lack lens and pupil. They lack external ears or pinna. The snouts are normally covered by a horny shield. Their short and stout tails are also encased in leathery skin. The foreclaws in them are modified to miniature spades. Examples include the southern marsupial mole (Notoryctes typhlops).

Order Paucituberculata

They include the shrew opossums (Caenolestidae). They are small, shrew-like animals with small eyes, and thick, grey or grey-brown pelage. The margin of each upper lip is interrupted by a distinctive flap of skin. Their tails are long but not prehensile, and their feet are not syndactylous. Females lack a pouch.

Order Peramelemorphia

This order includes bandicoots (Peramelemorphia) and bilbies (Macrotis). All members of this order are endemic to the twin land masses of Australia-New Guinea and most have the characteristic bandicoot shape. They have a plump, arch-backed body with a long, delicately tapering snout, very large upright ears, relatively long, thin legs, and a thin tail.

Subclass Eutheria

They are the higher mammals. The young ones develop inside the uterus of the female in them. They are nourished in the uterus through a special structure called placenta and hence are called the placental mammals. They show high parental care.

Fig: Placenta in mammals

Orders under the subclass Eutheria

The following are the important orders under the subclass Eutheria:

SuperOrder Afrotheria (Afrotherian mammals)

Afrotheria is a superorder under the subclass Eutheria which contains six orders as follows:

  • Order Proboscidea (Elephants)
  • Order Sirenia (Sea cows)
  • Order Hyracoidea (Hyraxes)
  • Order Tubulidentata (Aardvark)
  • Order Macroscelidea (Elephant shrews)
  • Order Afrosoricida (Golden moles and tenrecs)

Order Afrosoricida (Tenrecs and golden moles)

This order includes the golden moles (Chrysochloridae) and tenrecs (Tenrecidae). They look like shrews, otters or hedgehogs. Their coat varies from smooth to spiny. The fur has a dirty brown colour. Most species are nocturnal and hence they have poor eyesight. Their whiskers are sensitive and able to detect very minute vibrations in the ground. This helps them in locating their prey.

Order Hyracoidea (Hyraxes)

This order includes Hyraxes. They are all small to medium-sized herbivores. They possess short legs, round ears and a bunny's tail. They normally look like rabbits and hence are called ‘rock rabbits’. Males and females are almost of the same size. They show plantigrade locomotion. The feet have rubbery pads with numerous sweat glands.This feature helps in climbing. They possess short or thick, soft fur. The upper incisors are tusk-like in males. Examples include bush hyrax (Heterohyrax brucei) and tree hyrax (Dendrohyrax).

Order Macroscelidea (Elephant-shrews)

This order includes elephant shrews (Macroscelididae). They are small animals. They possess brownish grey coats. They possess mouse-like tails and long legs which helps in jumping. Their life span varies from two and a half to four years. They possess large canine teeth. They show well camouflage.

Order Proboscidea (Elephants)

This order includes elephants (Elephantidae). They are the largest land animals. They possess padded feet with no hooves. The upper lip prolonged into proboscis or trunk in them. Elephants are herbivorous and possess massive pairs of molars on each jaw. They usually possess six pairs of molars in their lifetime that grow one after another. They have tusks that are used for defence, scrape bark off trees and dig for tubers. The upper incisors form the tusk. They possess thick skin and are called pachyderm. The skin is sensitive and needs to be kept moist and disinfected. Ears are made of thin layers of skin and a lot of blood vessels. Hence the flapping of the ears makes the blood cool. This adaptation to regulate body heat is unique to elephants. They are intelligent animals and tamed to carry logs and woods in forests and are trained to use in circuses. They include the Indian Elephant and the African elephant. Ivory and elephant’s skin are used for making precious articles.

Fig: Elephant

Order Sirenia (Dugongs, manatees, and sea cows)

The forelimbs are modified into arms and are used for steering in the members of this order. The tail has been modified into a paddle used for propulsion in them. The hind limbs are small. Their skulls are modified for breathing air at the surface of the water. The teeth are highly reduced in them. They possess two teats which are located under their forelimbs. Examples include dugongs (Dugong dugon), manatees (Trichechus), and sea cows (Sirenia).

Fig: Sea cow

Order Tubulidentata (Aardvark)

The aardvark (Orycteropus afer) looks like a pig. Its body is stout with an arched back. The body is sparsely covered with coarse hairs. The front feet lack the thumb and possess four toes. The rear feet possess five toes. Each toe bears a large, robust nail which is flattened and shovel-like. It appears intermediate between a hoof and a claw and is used for digging out termites. The ears are long, and the tail is thick. The mouth is small, tubular, and used to feed termites. It possesses a thin, long, protruding tongue. They are pale yellowish grey in colour. It possesses a tough skin which helps in protection.

SuperOrder Euarchontoglires (Euarchontoglirean mammals)

Euarchontoglires is a clade and a superorder belonging to the subclass Eutheria under the class mammalia. The living members of this superorder are included under the following orders:

  • Order Dermoptera ((Flying lemurs)
  • Order Lagomorpha (Hares, pikas, and rabbits)
  • Order Primata (Primates)
  • Order Rodentia (Rodents)
  • Order Scandentia (Treeshrews)

Order Dermoptera (Flying lemurs)

This order includes the flying lemurs (Dermoptera). The members of this order glide around with the help of gliding membranes. This gliding membrane is a furred skin which extends from behind the ears outward to the digits, embracing the tail, stretching along the sides and base of the body. They are about the size of a domestic cat and possess large eyes and pointed faces. They are clumsy crawlers on the ground.

Fig: Flying lemur

Order Lagomorpha (Hares, pikas, and rabbits)

This order includes hares (Lepus), pikas (Ochotona), and rabbits (Oryctolagus cuniculus). They look like rodents and possess 4 peg-like teeth as opposed to two in rodents. They follow a vegetarian diet whereas rodents are considered as omnivores. Their teeth grow all the time.

Fig: Rabbit

Order Primates (Primates)

This order includes the primates. They possess opposable thumbs. This feature helps in grasping objects and helps in feeding. They use their limbs to escape from predators or to obtain food. They also possess binocular vision which helps in visualising the environment a lot better than other animals. They possess larger brains and colour vision. These important features help them to adapt in a better way with their surroundings. Examples include lorises (Lorisinae), lemurs (Lemuroidea), monkeys (Cercopithecidae), apes (Hominoidea), tarsiers (Tarsiidae), and humans (Homo sapiens).

Fig: Apes

Order Rodentia (Rodents)

The members of this order possess a single pair of sharp, long chisel shaped incisors in each jaw, and these incisors grow continuously throughout their life. These incisors possess thick enamel layers on the front but not on the back. This feature allows them to retain their chisel shape as they are worn down. They lack canines and this leaves a toothless space called diastema in the jaw. They possess only a few molars. Rodents have adapted to all sorts of surroundings. For example, capybaras (Hydrochoerus hydrochaeris) live in the swampy Amazon basin, Kangaroo rats (Dipodomys) live in deserts; and common rats live in our homes, fields and even the most bustling of cities. Common examples include rats (Rattus), mice (Mus musculus), beavers (Castor), squirrels (Sciuridae), guinea pigs (Cavia porcellus) and porcupines (Erethizon dorsatum).

Fig: Rat

Order Scandentia (Treeshrews)

This order includes treeshrews (Scandentia). Tree shrews look similar to squirrels. They are slender animals with long tails and soft, greyish to reddish-brown fur. The species which live on the ground are normally larger than those that live in the trees. They possess larger claws which help in digging up insects. Most of them have good binocular vision. These animals normally live in small groups and mark their territories using urine or scent glands depending on the species. They possess larger brain to body mass ratio.

SuperOrder Laurasiatheria (Laurasiatherian mammals)

Laurasiatheria is a superorder of placental mammals under the subclass Eutheria belongs to the class Mammalia. This group possess hedgehogs (Eulipotyphla), bats (Chiroptera), pangolins (Pholidotes), cats (Felis catus), dogs (Carnivora), cows (Bos taurus), whales (Cetartiodactyla), horses (Perissodactyla) etc.

Order Carnivora (Carnivores)

This order includes the flesh eating mammals. They possess sharp, well developed claws, large canines and strong jaws to capture, hold and tear the prey. They are intelligent, ferocious and bold. The structures of the skull support the large teeth. They possess relatively large brains which are encased in the heavy skull. Their digestive systems are also designed more simply than the herbivores, to absorb meat. This order possesses 12 families. Out of this 9 families live on land and the remaining 3 families are aquatic.

The various families of the order Carnivora live on land are as follows:

  • Canidae (Dogs and related species)
  • Ursidae (Bears)
  • Felidae (Cats)
  • Procyonidae (Raccoons and related species)
  • Mephitidae (Skunks and stink badgers)
  • Mustelidae (Weasels, otters, badgers, and related species)
  • Herpestidae (Mongooses)
  • Hyaenidae (Hyenas)
  • Viverridae (Civets, genets, and related species)

There are three aquatic families under the order Carnivora, which are as follows:

  • Otariidae (Sea lions and fur seals)
  • Odobenidae (Walrus)
  • Phocidae (True, or earless, seals)

Order Cetartiodactyla (Whales and dolphins)

This order includes whales (Cetacea), dolphins (Delphinidae), porpoises (Phocoenidae) etc. They are aquatic mammals with fish-like bodies. The cetaceans possess swimming abilities. They rely on modified forelimbs called flippers to get around and hindlimbs are absent. They use blubber to keep warm in the cold environments and it also provides buoyancy to the body. Blubber is a thick layer of fat present under the skin. They are large. Examples include the largest animal, the blue whale.

Fig: Blue whale (Balaenoptera)

Order Chiroptera (bats)

They are the flying placental mammals. This order includes bats, flying foxes (Pteropus) and vampire bats (Desmodontinae). The members of this order have the skin on the lateral sides of the body expanded and stretched between the digits of forelimbs and hindlimbs to form wings. They rely on echolocation to find their prey and map their surroundings.

Fig: Bat

SuperOrder Eulipotyphla (Hedgehogs, shrews, and relatives)

Eulipotyphla comprises the hedgehogs and gymnures (family Erinaceidae), the desmans, moles, and shrew-like moles (family Talpidae), solenodons (family Solenodontidae), and true shrews (family Soricidae).

Order Erinaceomorpha (Gymnures and hedgehogs)

Erinaceidae look like shrews, with long snouts and short tails. They are much larger in size. Hedgehogs (Erinaceinae) possess hair modified into sharp spines to form a protective covering over the upper body and flanks. This feature helps in defence. They possess anal scent glands. Hedgehogs are gentler and can be kept as pets.

Fig: Hedgehog

Order Soricomorpha (Shrews, moles, and relatives)

This order includes shrews (Soricidae), moles (Talpidae), and relatives. Moles are shrews which live mostly underground. Some have completely lost their eyesight. Their forelimbs are adapted for digging and swimming. Solenodons (Solenodontidae) look like large shrews with slightly longer snouts. The females have teats that are near the buttocks of the animal.

Fig: Shrew

Order Perissodactyla (Horses, rhinoceroses, and tapirs)

They are the odd toed ungulates. This order includes hoofed mammals like horses (Equus caballus), ass (Equus asinus), zebra (Equus quagga), mule (Equus mulus), rhinoceros (Rhinocerotidae) etc. They possess long limbs with a single functional digit per foot. They lack horns. They are terrestrial and fast running herbivorous mammals. They possess flat and broad incisors for cutting grasses. They do not form cud (partly digested food returned from the first stomach) like ruminants. The horses have a single functional toe on each foot (the third digit), while the Rhinos have three toes per foot. The Tapirs (Tapirus) possess four toes on the forefeet and three on the hind limb.

Fig: Zebra

Order Pholidota (Pangolins)

Pangolins resemble armadillos and anteaters. They also feed on insects. They possess long tongues, strong digging limbs, and reduced teeth. They are armoured and curl up in response to danger.

SuperOrder Xenarthra (Xenarthrans)

It is a major clade of placental mammals native to the Americas. There are 31 living species such as tree sloths, the anteaters, and armadillos present in this order. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths.

Order Cingulata (Armadillos)

This order includes armadillos (Dasypodidae). They possess poor vision. They have evolved a mechanism that helps them to roll up into a ball and stay protected behind an impressive armour shield. The armour is the skin that toughens up into overlapping scales that cover the shoulder, hips, head and the legs. The underside is the only unprotected area of the armadillo. Armadillos are able to remain underwater for short stretches of time. They have the capacity to inflate their stomach and intestines to work as ballasts to stay afloat. This adaptation also helps them to escape predators.

Order Pilosa (Sloths and anteaters)

This order includes sloths (Folivora) and anteaters (Vermilingua). Anteaters are specialised to eat ants and termites. Their jaws have become longer snouts, teeth have receded and tongues have become longer for this purpose. These animals have very strong forelimbs which help them to dig up termites nests or ant hills. These forelimbs also help in defence against its most common predators, the jaguars. The sloths are specialised in eating leaves. Their canine teeth have receded and they possess growing peg-like molars. They are known to use their claws when threatened.

Fig: Sloth

Common examples of mammals

The following are the common mammals:

Ornithorhynchus (Duck billed platypus)

It is a semiaquatic, egg-laying mammal. It is considered endemic to Eastern Australia and Tasmania. They possess a streamlined body with a bill and broad flat tail. They also possess short limbs with webbed feet. They have a dark brown to reddish brown fur with light brown or silver underfur.

Fig: Platypus (Ornithorhynchus)

Monkey (Macaca)

They are commonly considered as the tree-living simians. They show a high degree of social behaviour and parental care. They possess a tail which helps in balancing by coiling around the trees and branches. They live in forests, on plains, or among cliffs and rocky terrains. They are omnivorous, and possess large cheek pouches in which they can carry extra food.

Fig: Monkey

Flying fox (Pteropus)

They are large fruit eating (frugivorous) bats. Their fur is woolly and it is golden on the head, neck and shoulders. They are nocturnal and can be seen hanging upside down with the branches of trees during day time.

Fig: Flying fox (Pteropus)

Camel (Camelus)

They are called the ‘ships of the desert’ as they are adapted to move fast in the deserts. They possess at least one hump on their backs. They are even toed ungulates. They have long limbs with two functional digits per foot. Their feet are broad and large. They are terrestrial and fast running and herbivorous animals. They possess long curved necks. They possess four teats. The hump on their back allows them to withstand the heat of the sun. They possess double eyelashes which shield them from sandstorms. They possess large flat feet with protective pads. They are able to withstand high temperatures without sweating.

Fig: Camel

Cat (Felis)

All species of Felis have high and wide skulls. They possess short jaws and narrow ears with short tufts. They have a strong and flexible body with sharp teeth, and retractable claws adapted to kill the small prey. They have night vision and possess a keen sense of smell.

Fig: Cat

Elephant (Elephantidae)

They are the largest land animals. They possess padded feet. They possess thick and loose skin with scanty hair. They possess a trunk or proboscis. The canines are absent and two upper incisors are very long and called tusks. They are herbivorous mammals. At present only two species of elephants are present like the Indian elephant and the African elephant.

Fig: Elephant

Horse (Equus)

They are the odd toed ungulates. They have long limbs with a single functional digit per foot. They lack horns. They are terrestrial, fast running and herbivorous. They have flat and broad incisors for grazing and they do not form cud like ruminants.

Fig: Horse

Blue whale (Balaenoptera)

They are the largest animals in the world and measure about 30 m in length. They are filter feeders and feed on planktons or fishes. They come to the water surface for breathing as they are lung breathing animals. They are hunted by poachers for blubber.

Fig: Blue whale

Dolphin (Delphinus)

They are highly intelligent animals. They feed on fishes and show a great sense of social behaviour. They possess a smooth and rubbery skin. The skin is coloured in a mixture of black, white, and grey. They possess two flippers on their sides and a triangular fin on the back. They have an insulating layer of blubber beneath the skin. They can easily learn to imitate and perform feats.

Fig: Dolphin

Rat (Rattus)

They possess sharp long chisel shaped incisors in each jaw which helps in gnawing. They lack canines which leaves a toothless space called diastema in the jaw. They possess many teats. They possess abdominal testes. They are destructive and destroy crops, stored food grains etc. They are also responsible for spreading plague.

Fig: Rat

Lion (Panthera leo)

They possess strong, compact bodies and powerful forelegs. Their coats are yellow-gold in colour. Adult males possess shaggy manes that range in colour from blond to reddish-brown to black. The colour and length of the mane is determined by genetics, age, and hormones.

Fig: Lion

Tiger (Panthera tigris)

They possess a muscular body with strong forelimbs. The head is large and the tail is about half the length of the body. The pelage coloration of the body varies between shades of orange with a white underside and distinctive vertical black stripes. The pattern stripes are unique in each individual.

Fig: Tiger

Dog (Canis)

The canines are prominent in dogs. They possess uniform teeth. Dogs show high variability in weight and height. The smallest known adult dog was a Yorkshire Terrier. The heaviest dog was an English Mastiff named Zorba.

Fig: Dog

Kangaroo (Macropus)

Kangaroos possess short hair and powerful hind legs. They have small forelimbs and big feet. They possess a long tail also. They have good hearing and keen eyesight. The colour of the coat varies which depends on the species. Their fur coats can be grey, red, or light to dark brown. The muscular tail present is used for balance when hopping.

Fig: Kangaroo

Practice Problems

  1. Identify the order of 'Horse' from the options given below?

(a) Perissodactyla

(c ) Ferus

(b) Caballus

(d) Equidae

Solution: The members of the Order Perissodactyla are odd-toed hoofed mammals. Some examples of mammals belonging to this order are horses, rhinos, mules, tapirs, etc. Hence the correct option is ‘a’. The taxonomic classification of horse is as follows :

  • Kingdom - Animalia
  • Phylum - Chordata
  • Class - Mammalia
  • Order - Perissodactyla
  • Family - Equidae
  • Genus - Equus
  • Species - Equus ferus
  • Subspecies - Equus ferus caballus

Fig: Horse

  1. Identify the correct combination of aquatic mammals from the options given below?
  1. Seals, Dolphins and Trygon
  2. Dolphins, Whales, Seals

(c) Whales, Trygon and Seals

(d) Dolphins, Seals and Sharks

Solution: Mammals are animals belonging to class Mammalia of phylum Chordata. Some of the characteristics of mammals are as follows:

  • Presence of modified sweat glands called mammary glands to feed the young ones.
  • Most mammals give birth to their young ones, exceptions include duck-billed platypus and Echidna.
  • Mammals possess body hairs.
  • These are warm-blooded animals or homeotherms.
  • They have a four chambered ventral heart.
  • They breathe through their lungs.
  • They possess a muscular sheath called a diaphragm which separates the thoracic and abdominal cavities.

Dolphins, whales, and seals are warm-blooded aquatic mammals that live in water. They possess mammary glands and their forelimbs are modified into flippers for swimming. They breathe through their lungs and give birth to their young ones. Hence the correct option is ‘b’.

Fig: Aquatic mammals

  1. Mention two similarities between Aves and Mammalia?

Answer: Class Aves and class Mammalia belong to the superclass Tetrapoda of the division Gnathostomata under the Kingdom Animalia. They belong to the phylum Chordata and subphylum Vertebrata. Both possess four chambered ventral hearts and are warm-blooded or homeotherms. That means they maintain a constant body temperature.

  1. Organisms that give birth to young ones are commonly called ______________.

(A) Oviparous

(B) Ovoviviparous

(C) Viviparous

(D) Both B and C

Solution: Animals are of three types based on the mode of reproduction as follows:

  • Oviparous
  • Viviparous
  • Ovoviviparous

Oviparous are those animals that lay eggs which hatch out into young ones. Examples include hens.

Fig: Hen

Those animals that give birth to young ones are known as viviparous animals. Examples include leopards.

Fig: Leopard

In some animals heavily yolked eggs will be retained in the body of the mother and the young one developed inside the maternal body. This type of animal is called ovoviviparous. Examples include most of the sharks.

Fig: Shark

FAQs

  1. Do humans belong to the class Mammalia?

Answer: Class Mammalia include humans and all other animals that possess a pair of modified sweat glands called mammary glands. Human beings are warm-blooded or homeothermic vertebrates with hair. The females use the mammary glands to feed their young ones with milk. They possess a more well-developed brain.

  1. Can we say that humans are still evolving?

Answer: Evolution is considered as a process of gradual change which takes place over many generations. This results in slow change of some of their physical characteristics. The changes occurring in evolution include the ability to adjust with their environment and more subtle, genetic changes. We can say that humans are still evolving.

  1. Who is considered as the king of animals in the world?

Answer: Lions (Panthera leo) are considered as the king of animals in the world. They are also called 'the king of beasts.

Fig: Lion

  1. Which is considered as the smallest mammal?

The bumblebee bat (Craseonycteris thonglongyai), is considered as the smallest mammal in the world. It weighs just 2 grams and measures 1 to 1.3 inches in length. It is about the size of a large bumblebee.

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