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  • The Coenozoic era is the “Golden era of Mammals”.
  • Study of mammals is known as Mammalogy.
  • It includes animals which have mammary glands/breast.

Detailed explanation:

General characteristics of class Amphibia

Habit and habitat

  • The members of this class are cosmopolitan which means they are found in a variety of habitats such as polar ice, deserts, mountains, forest, grasslands and dark caves.
  • Some of them are also adapted to fly or live in water.


  • Body is divided into head, neck, trunk and tail.
  • Two pairs of limbs are present in the trunk.
  • Their Limbs are pentadactyl which help in swimming, walking, running etc.
  • Hind limbs are absent in some aquatic mammals.
  • The skin of mammals is unique in possessing hair.
  • Skin of mammals is thick and glandular


  • Alimentary canal is complete.
  • Anus and urogenital apertures are separate.
  • Cloaca is absent.
  • Teeth are Thecodont (embedded in bony sockets), Heterodont (different types) and mostly Diphyodont (comes twice).


  • Respiration is by one pair of lungs.
  • Larynx or sound organ is found in the neck region for the production of sound.

Circulatory system

  • Heart is four chambered.
  • Double circulatory system is present.
  • No sinus venosus.
  • Only left aortic (systemic) arch present.
  • RBCs small, circular and enucleated (except R.B.Cs of camel and llama are nucleated)


  • One pair of Metanephric kidneys are situated in the abdominal cavity.
  • They are ureotelic.

Nervous system

  • Brain is comparatively large.
  • Cerebrum and cerebellum are highly developed.
  • A special structure is present for the connection of both the cerebral hemispheres of the brain, that is called corpus - callosum. (Present only in higher mammals)
  • Cranial nerves are 12 pairs

Reproductive System

  • Reproduction is sexual.
  • They are unisexual animals.
  • Testes of males are situated outside the abdominal cavity in the scrotal sacs.
  • A distinct penis is present in males for copulation.
  • Fertilisation is internal and it takes place in fallopian tubes.
  • Most mammals are viviparous, which give birth to their young ones.
  • Some mammals are oviparous (Prototherians).


  • Development is direct.

Special adaptive features

  • Mammals are warm blooded or homeothermic or endothermic animals
  • The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished and get nutrients.
  • A horizontal diaphragm is present in between the thorax and abdomen of all the members without any exception.
  • Diaphragm helps in respiration, defaecation, micturition and parturition.
  • The skin of mammals is covered with a hairy coat.
  • Skin of mammals is thick and glandular. Many types of glands are present in the skin such as
    - Sweat glands
    - Sebaceous glands
    - Mammary glands (Mostly modified sweat glands)
  • External ear is present in the form of ear pinna.
  • Malleus, Incus and stapes are the three ear ossicles in the middle ear.
  • Embryo is attached to the uterus of the mother by placenta in higher mammals, so these animals are also called placental animals.
  • Parental care is well marked in mammals.
  • Mother feeds the child from milk secreted from her mammary glands and looks after her child.

Classification of mammalia

Living mammals are divided into two sub - classes -

1. Prototheria

  • They are considered to be the most primitive mammals which are only restricted in Australia and its neighbouring islands (Tasmania, New Guinea).
  • They possess several reptilian characters including cloaca, egg-laying.
  • Subclass prototheria includes one order Monotremata
  • Example - Ornithorhynchus, Tachyglossus/Echidna (spiny ant eater) etc

2. Theria

  • They produce young ones.
  • It is divided into two infraclasses - Metatheria and Eutheria.

(a). Metatheria

  • Females have a marsupium or brood-pouch for rearing young ones.
  • Infraclass metatheria includes one Order Marsupialia.
  • Mammals of the order Marsupialia are called marsupials or pouched mammals,
  • Example - Macropus, Didelphis (Opossum) and Phascolarctos (Koala).

(b). Eutheria

  • They are provided with true placenta, hence called placental mammals.
  • The embryos are retained in the uterus (womb) till an advanced stage.

Common examples

1. Ornithorhynchus (Duck-billed platypus) - protherian


2. Macropus (Kangaroo) - Metatherians or Marsupials



3. Pteropus (Flying fox)
4. Camelus (Camel)
5. Macaca (Monkey)
6. Rattus (Rat)
7. Canis (Dog)
8. Felis (Domestic cat)
9. Panthera leo (Lion)
10. Panthera tigris (Tiger)
11. Delphinus (Common dolphin)
12. Balaenoptera musculus - (Blue whale)
13. Elephas (Indian elephant)
14. Equus (Horse)

Frequently Asked Questions: FAQs

Q1. Which era is known as the “Golden era of mammals” ?
Ans :

  • The Coenozoic era is known as the “Golden era of mammals”.

Q2. Which is the respiratory organ in mammals ?
Ans :

  • Respiration in mammals takes place by one pair of lungs.

Q3. Which type of teeth are found in the animals belonging to class Mammalia?
Ans :

  • Teeth are Thecodont (embedded in bony sockets), Heterodont (different types) and mostly Diphyodont (comes twice).

Q4. What is the location and function of the larynx ?
Ans :

  • Larynx, also known as sound organ, is found in the neck region for the production of sound.

Q5. Which is the excretory organ of mammals ?
Ans :
Metanephric kidneys

Q6. Why Dolphin is included under class Mammalia ?
Ans :

  • The Dolphins are included under class mammalia because they have characteristics like Mammals due to the presence of mammary glands

Q7. Give examples of Protherians.
Ans :

  • Ornithorhynchus, Tachyglossus

Q8. What are the main adaptive features of the organism belonging to class Mammalia?
Ans :

The main adaptive features of the organism belonging to class Mammalia are -

  • The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished and get nutrients.
  • Mammals are warm blooded or homeothermic or endothermic animals.

Q9. Which is the connecting link between reptilia and mammalia ?
Ans :

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