Discovery Science: Earth Biology – Animals – Sea Mammals

Earth Science: Biology – Animals – Sea Mammals

The planet’s largest living things are the Cetacea, which include whales, dolphins, and porpoises. Cetacea and other sea mammals have exceptional sensory abilities and impressive aquatic skills.

Whales and dolphins live in all the oceans on Earth, but despite their distribution, many cetaceans are threatened by extinction. There are two groups: the toothed whales (Odontoceti) and the toothless, or baleen, whales (Mysticeti). The baleens (including blue and humpback whales) get their name from the comblike keratinous plates (baleens) they have in place of teeth.

These baleens are used to filter plankton or krill from the water. The toothed whales include dolphins, pot whales, killer whales (orcas), and narwhals. They feed mostly on fish or squid.

Cetaceans are hairless, warm-blooded creatures. Their layers of blubber (fat) help maintain their body temperature in the water. Their forelimbs have evolved into flippers used for steering, while their hind limbs have disappeared. The tail, known as a fluke, is their propellant.

They are conscious breathers, meaning that breathing is not an automatic function but one actively controlled by the animal. They can dive deeply and stay below for long periods. Whales are adapted to holding their breath, some species for 90 minutes or more. Newborn baby whales must adapt quickly.

Their initial breath comes when they reach the surface for the first time. A blue whale calf suckles underwater for about seven months and grows 110 pounds (50 kg) heavier and 1.8 inches (4.5 cm) longer every day.


Dolphins have a larger brain than humans and a fourth brain ventricle that allows them to remain mobile 24 hours a day. They relax by switching off half their brain for short periods.

The other half takes over the duties of watching for danger and controlling their swimming and breathing.


Seals and walrus are members of the Pinneped family, meaning “fin-footed mammals.” Seals can swim as fast as 28 miles per hour (35 km/h), but they spend much of their time on land and thus favor coastal habitats.

They have dense coats of body hair, which has led to them being relentlessly hunted by humans. They give birth and fight on land. In the water they use their back flippers and tail like a rudder. Seals feed primarily on fish, while the leopard seal also hunts penguins.


“WHALE SONG” is the name given to the acoustic communication between whales. Tones and tone sequences are produced, which can sometimes be heard hundreds of miles away

THE EYES OF SEALS are relatively large and, due to an increased number of rods in the retina, are suited to the low light conditions underwater.