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Classification of Mammalia, Practice Problems and FAQs

Classification of Mammalia, Practice Problems and FAQs

We all are immune to a variety of diseases as we have a strong immune system in our bodies. Immunity develops as we grow and encounter various diseases in life. But even as newborns we are immune to certain diseases. Do you know how? It is because of the immunity that we receive from the colostrum. Colostrum is the first secretion that comes from the mammary glands of a mother after giving birth to the young ones. This is rich in antibodies and confers immunity and growth factors to the young ones. The presence of these mammary glands makes us humans, members of the class Mammalia.

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Fig: Giraffe feeding the young one

Release of colostrum from the mammary glands distinguishes mammals including us from the rest of the Animal Kingdom. Mammals are vertebrate animals that possess a pair of modified sweat glands called mammary glands in the chest region. Examples include monkeys, cows, dogs etc. In this world there are a variety of mammals, but how do they differ? You know there are mammals who lay eggs also. So in this article, we will discuss the classification of mammals.

Table of contents

  • Class Mammalia
  • Classification of Mammalia
  • Subclass Prototheria
  • Subclass Metatheria
  • Subclass Eutheria

Mammalia

In the Animal Kingdom, the class Mammalia possess the most successful and the most dominant animals in the current world. There are approximately 5700 extant species of mammals in the present world. These animals are well-adapted to thrive in varying environmental conditions like polar areas, deserts, grasslands, dark caves, mountains, trees etc. A few are adapted to aquatic and aerial modes of life. This class includes quadrupeds and human beings.

Classification of Mammalia

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

Subclass Prototheria

This subclass includes the primitive egg-laying mammals. They share characteristics similar to 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. Milk is secreted through the pores in the abdomen. The eggs are covered with calcareous shells and are large and yolky. They are commonly found in Australia. Presence of cloaca and egg laying habits are the major reptilian characteristics. The structure of the brain, presence of hairs, warm blooded condition and presence of diaphragm are the major mammalian characteristics. Examples include Tachyglossus (Echidna or spiny anteater), and Ornithorhynchus (Duck-billed platypus)

Classification of Prototheria

Living members are classified under the order Monotremata. It include the following two families as follows:

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

Ornithorhynchus (Duck billed platypus)

It is a semiaquatic, egg-laying mammal which 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)

Tachyglossus (Echidna)

They are called spiny anteaters. They possess a long snout and a long tongue adapted for feeding on ants and termites. They have large claws suited for digging.

Fig: Echidna

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.

Orders under the subclass Metatheria

The following are the important orders under the subclass Metatheria:

  • Order Dasyuromorphia
  • Order Didelphimorphia
  • Order Diprotodontia
  • Order Microbiotheria
  • Order Notoryctemorphia
  • Order Paucituberculata
  • Order Peramelemorphia

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

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.

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

Koala (Phascolarctos cinereus)

They are arboreal herbivorous marsupials which are native to Australia. They possess a large round head. Ears are big and furry. They possess a big black nose too. Fur is usually grey-brown in colour. They possess white hairs on the chest, ears, inner arms, and bottom. Fur is absent on the palms of paws and nose.

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).

Fig: Southern Marsupial mole

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.

Fig: Bandicoot

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

Superorders under the subclass Eutheria

The following are the important superorders under the subclass Eutheria and each suborder divided into order:

  • Superorder Afrotheria
  • Superorder Euarchontoglires
  • Superorder Laurasiatheria (Laurasiatherian mammals)
  • SuperOrder Xenarthra (Xenarthrans)

Superorder Afrotheria (Afrotherian mammals)

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

  • Order Afrosoricida
  • Order Hyracoidea
  • Order Macroscelidea
  • Order Proboscidea
  • Order Sirenia
  • Order Tubulidentata
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 and 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 and 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.

Fig: Aardvark

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
  • Order Lagomorpha
  • Order Primata
  • Order Rodentia
  • Order Scandentia
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 Primata (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: Gorilla

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

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: Kangaroo rat

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

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 (Canis lupus familiaris), cows (Bos taurus), whales (Cetartiodactyla), horses (Perissodactyla) etc.

The living orders under Superorder Laurasiatheria are as follows:

  • Order Carnivora
  • Order Cetartiodactyla
  • Order Chiroptera
  • Order Eulipotyphla
  • Order Perissodactyla
  • Order Pholidota
  • Order Artiodactyla
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 are as follows:

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

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

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)

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

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

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)

Order 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).

Family Erinaceidae (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

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

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

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: Anteater

Order Artiodactyla

Artiodactyla is an order of even-toed mammals. They walk on their toenails or unguis. Sometimes they are considered along with order Cetartiodactyla. Examples include camels.

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

Practice Problems

1. Rabbits belong to which group?

(A) Agnatha
(B) Gnathostomata
(C) Lagomorpha
(D) Prototheria

Solution: Lagomorpha is an order included in the class Mammalia. 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. Animals included in this order have jaws. Hence the correct option is (C).

Fig: Rabbit

2. Identify the aquatic mammals from the following:

(i) Balaenoptera
(ii) Equus
(iii) Delphinus
(iv) Pteropus
(v) Felis

(A) (i) and (iii) only
(B) (v) only
(C) (ii) and (iv) only
(D) (iv) and (v) only

Solution: Mammals belong to the class Mammalia under the subphylum Vertebrata. The order Cetartiodactyla possesses aquatic mammals. They have fish-like bodies with smooth, hairless skin. They lack sweat and oil glands. They possess blubber. Their forelimbs are modified into flippers. Examples include, Whale (Balaenoptera), Delphins (Dolphinus) and Porpoises (Phocoenidae). Hence the correct option is (A).

Fig: Aquatic mammals

3. Tetrapoda is a ______________.

(A) Division
(B) Superclass
(C) Class
(D) Order

Solution: Four limbed animals are categorised under the superclass Tetrapoda. It comprises the class Amphibia, Reptilia, Aves and Mammalia.

4. Most unique mammalian characteristic(s) is/are ____________.

(A) Presence of mammary glands
(B) Heart is four-chambered
(C) Presence of lungs
(D) All of the above

Solution: Mammary glands, four-chambered heart and presence of lungs are features of mammals. But mammary glands to feed the young ones is the most unique characteristic of mammals. Whereas four chambered hearts and presence of lungs is also seen in other vertebrates like birds. Thus these are not the unique mammalian characteristics. Hence the correct option is (A).

FAQs

1. What are the main 3 types of mammals?
Answer:
Mammals are classified into three subclasses like egg-laying Prototheria, marsupials or Metatheria, and placentals or Eutheria.

2. Which is the largest mammal in this world?
Answer:
The Antarctic blue whale or Balaenoptera musculus intermedia is the biggest mammal in the world. It is weighing up to 400,000 pounds (33 elephants) and 98 feet in length.

Fig: Blue whale

3. Can we call a hippo a mammal?
Answer:
Third largest living land mammals are Hippos (Hippopotamus amphibius). They come after elephants and white rhinos. They possess adaptations to live in semi-aquatic environments.

Fig: Hippopotamus amphibius

4. Which animal produces the loudest sound in the world?
Answer:
The sperm whale or Physeter macrocephalus produces the loudest sound in the world. They produce sound up to 233 decibels.

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