Mammalia Diversity in Living Organisms

All the animals relating to class Mammalia are termed as mammals. In the animal kingdom, one of the most developed species are mammals that are categorized under Vertebrata. Around, 5,000 species of living mammals are present on the planet and are divided into 3 sub-classes and nearly 26 orders. They are well adapted to their surroundings such as from deserts, oceans, and polar regions to rivers and rainforests, etc because of their distribution all over the world. Due to the advanced characteristics exhibited, they resemble apart from all the other animals. They are depicted by the presence of mammary glands which helps them to feed their offsprings.

[Image will be Uploaded Soon]

Main Features of Mammals

  • Sweat glands and oil glands are found on the skin.

  • All these animals are warm-blooded.

  • Their heart is divided into four chambers.

  • The tooth comes twice in these animals (Diphyodont).

  • No nucleus is found in its red blood cells (except in camel and lama). 

  • The skin of mammals has hair.

  • External ear (pinna) is present in a mammal.

Classification of Mammals

[Image will be Uploaded Soon]

The largest class in the animal kingdom is Mammalia. Several types of mammals are there which can be differentiated up into smaller mammals, larger mammals, and marine mammals, etc. Since there are different types of mammals found. So, on the basis of their reproduction, they are classified into 3 subclasses. 

  1. Eutheria

  2. Metatheria 

  3. Prototheria.


Mammals that give birth to well developed young ones or the child directly belong to the subclass Eutheria. An embryo is formed by the young ones in their mother's stomach where they grow for a particular period of time. They derive nutrition for their growth and development from the placenta of the mother. The well-known and best example of this subclass are dogs, humans, and cats. This subclass comprises of 19 orders.

Some of them are Listed Below:




moles, shrews


Flying lemurs




Hamsters, squirrel, rats


Goat, giraffes, camels


Dogs, Bears


Mammals that relate to this sub-class give birth to immature children or young ones. Hence, they jump into the pouch of their mother where they stay till they get mature.  sub-class 

For Example Kangaroos and Marsupials.

Metatheria Sub-class is Divided into 7 Orders Including 250 Species.




Marsupial moles


koalas, kangaroos




dasyurids, thylacines


South American rat opossum




New world opossum

3. Prototheria

Prototheria is also named as Monotremes. This sub-class includes egg-laying mammals. Prototheria comprises of 6 species all in a single order. 

Order:  Monotremata

Example: Duckbilled platypus, Echidna

General Classification of Mammals

[Image will be Uploaded Soon]

Even of the mammals are already classified into class or sub-class. Still, scientists have classified them on a general basis. This general classification helps in easy learning about the mammals on the basis of their class and distinguished features.




Lion, Tiger, Dog


Kangaroo, Koala


Chimpanzee, Gorilla, Monkey, Orangutan, Lemur


Squirrels, Mice, Porcupines


Whales, dolphins

Other mammals

Seals, Sea Lions, Walrus

Characteristics of Mammals

[Image will be Uploaded Soon]


  • 2 pairs of pentadactyl limbs are present. In this, each foot has either 5 or fewer toes given with horny nails, claws or hooves.

  • They are adapted variously for running, jumping, swimming, climbing, etc.

Digestive System:

  • Relatively smallmouth with movable lips.

  • True salivary glands present in the buccal cavity.

  • Different types of teeth are attained by them (Heterodont).

Respiratory System:

  • They breathe only through the lungs which are elastic and spongy.

  • In breathing, both the rib muscles and diaphragm plays a vital role for the purpose of respiration.

Circulatory System

  • The circulatory system of mammals is closed.

  • The heart pumps oxygenated blood which is transported to the several parts of the body.

  • The hepatic portal system is present while the renal portal system is not.

  • In most mammalian species, RBCs are concave, circular, and non-nucleated.

Excretory System:

  • A pair of bean-shaped kidneys are found which are metanephric.

  • They are ureotelic animals (excrete urea).

Sense Organ: 

  • With the help of internal nasal passages, the olfactory sacs open far back into the pharynx.

  • Movable lids are present in their eyes.

  • An organ of Corti is present in the internal ear and 3 bony ear ossicles (malleus, incus, and stapes) are present in the middle ear.

Fun Facts of Mammalia

  • In a mammal, the highest body temperature is of a goat (Average 39°Celsius).

  • Echidna and Duck-billed Platypus are the egg-laying mammals.

  • Atlantis of mammalian embryo help in the purpose of respiration.

  • Excretion in hemichordate takes place by the glomerulus.

  • The smallest man like Ape is Orangutan.

FAQ (Frequently Asked Questions)

1. What are the Main Orders of Placental Mammals?

  1. Artiodactyls:  These mammals have even a number of fingers in paws or claws like giraffes.

  2. Perissodactyls: They are named as ungulates (hooved). These mammals are large in size having an odd number of fingers on each paw-like rhinos.

  3. Carnivorous:  Include predators with canine teeth like lions.

  4. Cetaceans: Mammals are aquatic which lack posterior limbs like whales.

  5. Edentates:  Mammals with rare or no teeth like anteaters.

  6. Lagomorphs: Mammals are small in size with continuously growing 3 pairs of incisors teeth specialized in gnawing like rabbits.

  7. Primates: Characterized by a well-developed brain and large cranium includes humans.

2. What are the Key Characteristics of Mammals on the Basis of their Reproductive System?

  • In the adults of a male adult, testes usually descend into scrotal sacs.

  • The penis is a copulatory organ found in males.

  • Internal fertilization takes place.  Gonoducts head directly to the exterior areas.

  • Mostly viviparous animals are found that give birth directly to the young ones.

  • In the female's uterus development occurs. The embryo has amnion, chorion, and allantois.

  • For the purpose of nourishment, excretion, and respiration, the fetus is fixed by the placenta into the uterine wall.

  • After the birth of young ones, they are nourished with milk for some time.