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Super Class Tetrapoda
Animals having four limbs or descended from four-limbed ancestors.
The transition from aquatic to terrestrial living is clearly indicated in the Class Amphibia. They are the rst vertebrates to live on land with dual adaptation to live in aquatic and land environments. is double life is expressed as amphibious. The body is divisible into head and trunk. In frogs, hind limbs have webbed feet. The skin is moist and glandular usually without scales. Respiration is e ected by gills, skin, bucco-pharynx and lungs. The heart is three chambered with two auricles and a single ventricle. Sexes are separate. Fertilization is mostly external and the larva is a tadpole which metamorphoses into an adult.
Reptilia represents the first class of vertebrates that is fully adapted for life on dry land. It is covered with an exoskeleton of horny imbricate epidermal scales. Skin glands are absent. Respiration is through lungs. The heart is three chambered with an exemption of crocodiles with four chambered. Sexes are separate. Fertilization is internal. Eggs are covered with an outer shell.
Birds (Aves) are the first homeothermic vertebrates with spindle shaped body which is divisible into four distinct regions namely head, neck, trunk and tail. They have two pairs of limbs, in that forelimbs are modified as wings. The hind limbs are adapted for walking and running. The feet are covered with scales, while the body is covered with feathers. A horny beak is present. Alimentary canal is provided with crop and gizzard. Respiration is through spongy lungs. Air sacs are present to make the bird light weight. The bones are filled with air, so they are called pneumatic bones. Their eggs are yolk laden and covered by hard calcareous shell.
Have you observed different shapes of birdâ€™s beak? Do you know the purpose of this modification?
This is a successful group of animals called mammals that adapt themselves readily to new situations and to new food habits. The integument is provided with epidermal hairs, sweat, sebaceous and scent glands. Mammary glands are the modified integumentary glands. The external ear or the pinna is present in most of the mammals. The heart is four chambered. Testes lie outside the body cavity, enclosed in scrotal sacs. Eggs are small with little or no yolk. Fertilization is always internal. They give birth to young ones and feed their young with milk. Placenta is a characteristic feature.
Can you identify these mammals? Do you see them near your home? If you wish to see many of them which place will you visit?
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