Mammalia Diversity In Living Organisms


The animal kingdom is large and extremely diverse. Classifying them is necessary to know and understand in spite of their large size. Classification allows an easier understanding of the complexity, evolution patterns, and interrelationships among animals. Primarily animals are classified based on the presence or absence of vertebral column.Vertebrates are those having a vertebral column and invertebrates are with no vertebral column.

Invertebrate phyla include Porifera, Cnidaria, Ctenophora, Platyhelminthes, Nematoda, Annelida, Arthropoda, and Echinodermata. Vertebrate phyla include Phylum Pisces, Amphibia, Reptilia, Aves and Mammalia. Members of phylum Mammalia are called mammals and are the most advanced members of the animal kingdom.

Characteristics of Mammals

Mammals are the most evolved animal members with distinguished abilities to adapt to different climatic regions and hence are distributed widely on the globe. They have distinct characteristics that make them a large separate group of study.

  • The foremost characteristic of mammals is that they give birth to young ones and feed them with milk produced by female adults.

  • The presence of special mammary glands avails them to produce milk.

  • They are endothermic vertebrates (warm-blooded) and are capable of maintaining a constant internal body temperature irrespective of the surrounding environmental conditions.

  • The body is covered by fur or hair to adapt to the surrounding environments. Skin is thick with underlying sweat and sebaceous glands.

  • The head, neck, trunk and tail make a body. Bodies have a pair of forelimbs and a pair of hind limbs that are adapted with unique structures for easy adaptation to surroundings.

  • The presence of a diaphragm between the thorax and abdomen facilitates respiration, micturition and defecation.

  • Mammalian teeth are thecodont (embedded in the bony sockets), heterodont (different shaped tooth in a row) and diphyodont (temporary milk set of teeth replaced by permanent set).

  • The larynx is a sound-producing organ located in the neck region.

  • The presence of pair of lungs facilitates respiration.

  • They have three middle ear bones that facilitate good hearing ability.

  • Two articulatory condyles attach the dicondylic skull bearing a single lower jaw to the body.

  • The brain is complex and large with the cerebrum, cerebellum, and medulla. It has a special thinking centre called the neocortex.

  • Twelve pairs of cranial nerves are present.

  • The circulatory system has a four-chambered heart with double circulation.

Classification of Mammals

Mammalian members are around 5,500 living species. Mammals are classified into Eutheria, Metatheria and Prototheria based on their reproduction.

Subclass Eutheria

  • Eutherian mammals bear developing young ones inside their womb.

  • The placenta carries nutrients and wastes into and from the developing baby inside the womb.

  • Eutherians are also called placental mammals.

  • Examples are cows, tigers, monkeys, camels, foxes, dogs etc.

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Subclass Metatheria

  • They give birth to an incompletely developed young one.

  • Female adults bear a brood pouch called marsupium to carry their underdeveloped young ones till they attain maturity.

  • Metatherians are also called pouched mammals.

  • Examples are kangaroos, opossums, bandicoots, and koalas.

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Subclass Prototheria

  • They are primitive egg-laying mammals.

  • Prototherians resemble reptiles in some characteristics like the presence of cloaca and egg laying ability.

  • They are also called monotremes.

  • Examples are spiny ant eater and duck-billed platypus.

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General Classification of Mammals

Mammalian body weight ranges from grams to several tonnes in weight. The body size ranges from a few inches to several feet in length. Mammals inhabit different habitats like terrestrial, aquatic, polar, aerial, and underground. They adopt different lifestyles like gliding, swimming, running, burrowing, climbing, flying, etc. Their wide distribution in various environments makes them commonly encountered animals by mankind. For an easy understanding, mammals are classified on a general basis of their behavioural and physical characteristics and grouped together.

Some of those groups and the member animals are listed below −

  • Herbivore − Cows, goats, elephants, deer, giraffes, etc.

  • Carnivores − Tigers, lions, foxes, etc.

  • Insectivores − Moles, moon rats, hedgehogs, etc.

  • Marsupials − Kangaroos, koalas, etc.

  • Primates − Apes, gorillas, chimpanzees, monkeys, etc.

  • Cetaceans − Porpoises, whales, dolphins, etc.

  • Rodents − Rats, squirrels, etc.

  • Sirenians − Manatees, dugongs, etc.

  • Flying mammals or chiropterans − bats.

Interesting Facts about Mammals

  • Mammalian young ones are fed milk by female adults and are under parental care. Protection from predators as well as environmental factors along with survival training is a part of parental care.

  • Only after the young ones are capable of an independent life do they opt for it. Showing a high level of parental care is an interesting feature in mammals.

  • Mammalian young ones do not have teeth at birth and they grow them with age.

  • Although their teeth are heterodont, each species have specially adapted teeth to fit their feeding habits. Carnivores have specialised teeth for tearing flesh while herbivores have teeth for cutting and chewing grasses.

  • Mammals have brains with intelligence and are capable of living in social groups based on the species. Dolphins, chimpanzees and humans are the most intelligent in the animal kingdom.

  • Mammalian members have special adaptations to live in diverse habitats. Some species are flying mammals, some are burrowing, some are swimming and so on.


Mammals are a large group of animals with extreme diversity. They are complex and the most advanced of the members of the animal kingdom. They are endothermic animals widely distributed around the globe. The main aspect of mammals that set them apart from other animals is that they possess mammary glands to feed their young ones. Mammals are again of 3 types namely placental, pouched and primitive egg-laying mammals. The presence of the diaphragm, neocortex in the brain, and larynx are the special characteristics of mammals. Apart from the general characteristics, they have specialised adaptations that allow their survival in their respective niches.


Q1. What is the function of the placenta in placental mammals?

Ans: Placental mammals reproduce through sexual mode and carry on internal fertilisation. The embryo develops inside the mother's uterus called the womb. The placenta carries nutrients to the growing embryo.

Q2. Name some homologous structures in mammals.

Ans: Wings of bats, forelimbs of cats, whale's flippers and human arms are homologous structures. Although the function and purpose they serve vary, their basic anatomy is the same.

Q3. What are fossorial mammals?

Ans: Fossorial mammals are those mammals having special adaptations to inhabit sub-terrain environments. They primarily inhabit the underground burrows but are not solely confined to those habitats. They have long claws on the powerful forelimbs that help them dig and loosen the soil. The bodies have tapered ends which help fossorial mammals to enter and leave the underground holes.

Q4. What is the purpose of the pouch in marsupials?

Ans: Marsupials have a folded skin called a pouch or marsupium. The metatherians or the pouched mammals give birth to the underdeveloped fetus which grows into a juvenile inside the pouch.

Q5. What dental adaptation do carnivores have with respect to nutrition?

Ans: Carnivores like tigers and lions have special long and pointed front teeth called canines that help them tear the flesh of their prey.