Question

External ears are characteristic of
A. Birds
B. Mammals
C. Birds and Mammals
D. Mammals and Reptiles

Answer 1

Hint: External ears the organs of hearing for the organisms they are present in. the external ear forms a part of the outer ear and functions to channelize the sound vibrations towards the eardrum. It is of various shapes and sizes.

Complete answer:
The external ear is also known as the pinna. It is a characteristic of the mammals. The pinna is a cartilaginous structure present on the head and is covered with skin. The external ears of varying shapes and sizes in mammals. For example, the elephants have large pinna and the cetaceans lack pinna. The primary function of pinna is to perceive sound vibrations and subsequently focus it on the eardrum. However, other functions of the pinna have also been observed, like elephants flap their external ears when the climate is very hot, indicating that it might be a mechanism to lower the body temperature. Again rabbits that inhabit colder regions have shorter pinna than those living in hotter climates. These examples indicate that the external ears might play a role in regulating body temperatures in these groups of animals.
The external ears of reptiles are either reduced or absent. If present, it is covered by a flap of skin or scaly skin. However, the inner and outer ear of reptiles are well developed and aid in hearing primarily earth-borne sounds. Crocodiles and geckos have a well developed auditory system and their hearing ability is as good as the mammals.
Birds, like reptiles, primarily lack external ears. Their outer ears are simple openings concealed beneath the feathers and located behind the eyes. The openings are concealed in order to protect them from air turbulence during flight. The middle ear and inner ear are well developed. Birds like owls have specialized hearing ability and can pinpoint the location from where the sound is coming. This helps them to hunt.
Hence, to conclude, external ears are present in mammals only.

Hence, the correct answer is option (B).

Note: External ears are present only in mammals. They are soft bony structures present on either side of the head. External ears are connected to the middle ear with the help of the ear canal. They help the mammals to perceive sound vibrations and focus it into the middle ear, which in turn carries it to the eardrum of the inner ear and helps in hearing.