Question

All mammals are viviparous, but lower mammals are?

Answer 1

Hint: Mammals belong to kingdom Animalia and the class mammalia. Their distribution is worldwide. Viviparous are those organisms which give birth to young ones and the development of offspring is inside the mother’s body. Oviparous are those organisms which lay eggs and hence the development of offspring is outside the mother’s body.

Complete answer:
Mammals are characterized by following features:
Presence of hair or fur on the body, this helps them to maintain their body temperature and also provides protection to them.
Mammary glands, these glands produce milk in females which will help them for feeding their offspring.
Three middle ear bones (maleus, incus and stapes), help in the passage of sound waves from outer to inner ear.
Mammals are also endothermic meaning they do not get affected by the external environment, they can easily regulate their body temperature.
Majority of mammals are viviparous, which means they give birth to young ones.
But there are exceptions to this viviparous character. Few of the lower mammals are oviparous in nature that means they lay eggs. The duck-billed platypus and the spiny anteater are the examples of mammals having oviparous nature.
Both animals possess other characteristics of mammals but the only exception is viviparous nature.

So, all mammals are viviparous, but lower mammals are oviparous.

Note:
The spiny anteater possesses a long tongue which helps them to catch the ants and it produces several eggs and keeps them in pouch until they are hatched. Platypus appears as a duck and the whole body is covered with fur and has webbed feet. Few characters of platypus resemble reptiles like oviparous nature, endoskeleton features etc.