Write the characteristics of the class Mammalia.

(N/A) $\rightarrow$ Mammals are found in a variety of habitats - polar ice caps,deserts,mountains,forests,grasslands,and dark caves.
$\rightarrow$ Some of them have adapted to fly or live in water.
$\rightarrow$ The most unique mammalian characteristic is the presence of milk-producing glands (mammary glands) by which the young ones are nourished.
$\rightarrow$ They have two pairs of limbs,adapted for walking,running,climbing,burrowing,swimming,or flying.
$\rightarrow$ The skin of mammals is unique in possessing hair.
$\rightarrow$ External ears or pinnae are present.
$\rightarrow$ Different types of teeth are present in the jaw.
$\rightarrow$ The heart is four-chambered.
$\rightarrow$ They are homoiothermous (warm-blooded).
$\rightarrow$ Respiration is by lungs.
$\rightarrow$ Sexes are separate and fertilisation is internal.
$\rightarrow$ They are generally viviparous,with few exceptions,and development is direct.
$\rightarrow$ Examples: Oviparous - Ornithorhynchus (Platypus); Viviparous - Macropus (Kangaroo),Pteropus (Flying fox),Camelus (Camel),Macaca (Monkey),Rattus (Rat),Canis (Dog),Felis (Cat),Elephas (Elephant),Equus (Horse),Delphinus (Common dolphin),Balaenoptera (Blue whale),Panthera tigris (Tiger),Panthera leo (Lion).