Mammals are most adapted among the vertebrates and the following features explain the justify this statement.
(i) They are found in variety of habitats, i.e., polar ice caps, deserts, mountains, forests, grasslands and dark caves.
(ii) They have better developed brain. The brain bears large cerebellum and cerebrum.
(iii) The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which mammals nourish their young ones.
(iv) Mammals are homeotherms (warm blooded), i.e., they are capable of maintaining their body temperature regardless o fto the surrounding environment.
(v) They possess oil secreting glands (sebaceous glands) and sweat glands (sudoriferous glands) in the skin.
(vi) They possess two pair of limbs, that are well adapted for walking, running, climbing, burrowing, swimming and flying.
(vii) fertilisation is internal. They show viviparity with few exceptions e.g., oviparous - Ornithorhynchus (platypus) and the development is direct.
e.g., viviparous - Macropus (kangaroo), Rattus (rat), Canis (dog), Delphinus (common dolphin), Panthera ligris (tiger), etc.
