Question

A mammal lacking pinna is
A. Platypus
B. Whale
C. Seal
D. All of the above

Answer 1

Hint: Mammals usually contain the external part of the ear that is auricle or pinna except the most primitive mammals. The mammals which lay eggs have no pinna ears. Pinna is the visible external part of the ear that receives sound waves and transfers them to the auditory canal. In some of the animals instead of pinna they have small openings towards the outside.

Complete answer:
Platypus belongs to the order monothematic which is egg laying animals. They are mostly found in lakes of eastern Australia. They occur in a wide range of habitats that range from tropical to cool temperate. Platypus has a little ear canal but has little pinna development. Platypus lacks in pinna due to this reason its hearing ability is very low.
Whales are not egg laying mammals but they have some adaptations for underwater hearing. Cetaceans do not contain external pinna. They have Eustachian tubes, no pinnae, and no air filled external canals. Soft tissues help in conducting sound to the ear. The ear canals of the whales are not opened to the outside. They have special structures in their jawbones to help them in hearing.
Members of family Phocaea or true seals do not have pinnae. Due to this reason their hearing ability is not strong, depending on the situation. True seals or Harp seals are also known as earless seals. They have tiny holes in the side of their head. They have such adaptation to provide them hearing ability in water. Seals ears are designed in such a way so that they can work both underwater and above the surface. This also works as an advantage for them. They pick up the direction of hearing.
As we have discussed above some of the members of the whales and seals lack in pinna but platypus is the only one who completely lacks pinna.

So we have reached the conclusion that platypus is the correct answer.

Note: Pinna plays a very important role in hearing ability of animals. It is the first outer part of the ear. Egg laying mammal’s spiny anteater or Echidna lacks in pinna. Eyes of the platypus are tilted up to scan the predator as they have acute hearing ability. Functioning of the ear does not only affect the hearing ability but also helps in spatial awareness and balance.