Question

Hair occurs in all mammals except those of
A) Chiroptera
B) Rodentia
C) Cetacea
D) Primates

Answer 1

The presence of hair is one of the defining characteristic features of mammals, but some mammals are adapted to a different environment and they lack hair.

Complete answer:
Hair in mammals is very important in the conservation of body heat in mammals by insulating the body from cold. Cetaceans are aquatic mammals that include dolphins, whales, etc. Since they are adapted to the aquatic environment and they have blubber (A thick layer of fat) that helps the whales and other aquatic mammals to conserve body heat and therefore, they do not show the presence of hairs. Cetaceans show a smooth and hairless body.

Option(A): Chiroptera refers to a bat which is a mammal but it shows the presence of hair, Therefore this is an incorrect option.

Option(B): Rodentia is an order which includes rodents like a hamster, rats, beavers, pedetes, etc and these rodents also have hair on their body surface, Therefore this is an incorrect option.

Option(C): Cetaceans include aquatic mammals like dolphins and whales and they have a smooth body without hairs.These animals do not need hair to survive as they have the ability to keep themselves warm because of the presence of a thick layer of fat which is present below the skin. This thick layer of fat is known as blubber. Therefore this is the correct option.

Option(D): Primates include monkeys, tarsiers, apes, humans, etc. Primates also show the presence of hairs, Therefore this is an incorrect option.

Additional information:
Dolphins also show some small hairs known as whiskers around the snout but only in the womb and they lose it when they are born but Amazon river dolphins are known to keep these whiskers up to adulthood that acts as sensors which helps dolphins in capturing prey in the river.

Therefore the correct answer is option ‘C’.

Note: The hairless body helps the cetaceans to swim easily in the water as the hairless body comparatively exerts a lower drag.
-The smallest cetacean: vaquita
-The largest cetacean: Blue whale