The order $Cetacea$ includes:

The tusk of an elephant is an enormously enlarged:

$A$: The duck-billed platypus and the spiny ant-eater,both are egg-laying animals yet are grouped under mammals.
$R$: Both of them have seven cervical vertebrae and mammary glands without teats.

$A$ fat called blubber could be obtained from

In which of the following organisms are turbinal bones found in the nasal passage?

Both birds and bats can fly. Bats differ from birds due to the presence of: