Question

Which of the following is an egg-laying mammal?
A. Kangaroo
B. Whale
C. Bat
D. Platypus

Answer 1

Hint: Egg- laying mammals are the animals which lay eggs but have several other characteristics that resemble the mammals . They do not give birth to young one means they are the only oviparous mammals among other viviparous mammals.

Complete answer:
Platypus are categorized under the group of mammals because they possess various characteristic that resemble mammals such as :
They have hairs on their skin to provide them protection.
They have sweat glands under skin for regulating their body temperature and ionic balance.
They have milk producing mammary glands as other Mammals that provide nourishment to their new born. These glands are present in both male and female.
They have seven cervical vertebrae and 12 pairs of cranial nerves as other mammals.
They have claws which are used for digging.
They have Webbed feet.
They flap a beaver-like tail.
On other hand, Kangaroo are pouched mammals. They don’t lay eggs, their young one is born in an immature state. Gestation period shows complete development in the abdominal pouch or marsupium. So option (A) can’t be the answer.
Whales are aquatic placental marine animals. They give birth to their young one and produce milk which they squirt down to the throat of the baby by muscular contractions of the mother. Their baby is delivered with foetus positioned for tail first delivery. So option (B) is not the answer.
Bats are true flying mammals. They can produce milk for their young ones and they do not lay eggs but give birth to young. Young bats born are called pups. So option ( C) is not correct for the answer either.
The correct answer is (D) i.e. Platypus

Note: Mammals originated from reptiles in the Triassic period of Mesozoic era.