a) Mammals are the most advanced group of vertebrates.
b) They occur in a variety of habitats – terrestrial, aquatic and aerial.
c) The body is divided into head, trunk and tail. Trunk is divided into an upper thorax and
a lower abdomen separated by a diaphragm.
d) The exoskeleton is represented by epidermal outgrowth called hairs.
e) They are pentadactyl. Fore and hind limbs end in claws or nails.
f) Respiratory organs are a pair of lungs.
g) They are warm blooded and heart is four chambered. Aortic arch is on the left side.
h) RBC are enucleate at maturity except in camels.
i) Teeth are heterodont, embedded in sockets in jaw bones and occur in two sets during
life.
j) Nervous system is well developed with 12 pairs of cranial nerves.
k) They are generally viviparous. Both fertilization and development takes place inside
the body. A placenta is present to nourish the embryo.
l) Mammary glands are present in females secrete milk to nourish the young ones.
Ex: Platypus, Echidna, Kangaroo, Bat, Whale, Dolphins etc