The word mammatia is demved from a latin word which means having mammary glands. They are evoived from reptiles called therapsids and they are considered as the 

most advanced vertebrates. 

There 's a great variety in size and shape. The smailest mammal is pygmy shrew having weight only about 2 gms and the largest mammal is the blue whale, which ts upto 40 meters long and with weight upto 160,000 kg. It is considered as the largest living 

organisms on the earth. 

. Human beings (Homosapiens — biological name) is also included in ctassmammalia. important Characters: 

{:-§ ‘They are warm blooded animals (Homoiotherms). They have constant body temperature which remains between 37°C - 40°C. 

(ii) They have bony skeleton and vertebral column. 

(iii) Their skin is covered by hairs Which helps to prevent the loss of heat and regulate the body temperature. 

(iv) The skin has sebaceous and sweat glands. {_ (v) They possess mammary glands which produce milk in female for nourishing the young ones. , (vi) Their + cavity is divided into upper thorax and lower abdomen by diaphragm. (vi ernal ear-pinna is present. 

(viii) Heart is completely four chambered. The oxygenated and deoxygenated bloods remain separate from each other. 

\. (ix) Respiration is by lungs. (x) Excretion is by kidneys. 

(xi) The teeth are of different types, incisors, canines, premolars and molars. So the teeth are called heterodont. They are also thecodont because they are fixed in the 

gums. (xii) They have seven cervical vertebrae in the neck region. (xiii) They are viviparous i.e. produce young ones except egg-laying mammals. 

(xix) Fertilization is internal. In most of the mammals the fertilization of egg takes place in uterus. There is a cord between mother and developing embryo, called placenta, through which food and oxygen are supplied. Mother takes care of her youngones