Toothed whales, such as the sperm w

Toothed whales, such as the sperm whale, possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Only in larger whales, where the cementum is worn away on the tip of the tooth, does enamel show.

Instead of teeth, baleen whales have a row of baleen plates on the upper side of their jaws that resemble the teeth of a comb.

Ears
The whale ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance matcher between the outside air's low impedance and the cochlear fluid's high impedance. However, in aquatic mammals, such as whales, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, whales receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.The whale ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.