Marine mammals live in the water along with fish, with which they are sometimes confused, molluscs and crustaceans. Scientists believe that once this group of animals lived on land, but for unknown reasons, they adapted to stay in the aquatic environment.
Classification
There are two large groups of marine mammals. The first includes cetaceans and sirens, which spend their entire life from birth to death in the water and never get out on land. These are whales, dolphins, killer whales, porpoises, sperm whales. The second group is represented by pinnipeds living both on land and in the sea. These include seals, walruses, fur seals, seals, elephant seals, otters.
Features of the
When marine animals lived only on land, they had limbs. After changing their habitat, their body adapted to new conditions. So animals gradually developed fins, and their tails were modified so that they could swim and maintain balance in the water.
They retained their lungs from their ancient land ancestors. Marine mammals can stay under water for a long time. However, they are still forced to periodically rise to the surface in order to inhale the air, which contains oxygen. Like all mammals, these animals have a constant body temperature.
For marine mammals, a more or less streamlined, hydrodynamic body shape is characteristic, thanks to which they swim perfectly. Their forelimbs turned into fins, and the hind limbs disappeared in some species, like in cetaceans. In pinnipeds, they have expanded towards the edges and serve mainly for movement on land.
Cetaceans
This group of marine mammals never leaves the water element. They lead both solitary and gregarious lifestyles. A dolphin on the loose is never alone. In captivity, he may even die if left alone.
Cetaceans are carnivores. They feed on fish, squid, and small crustaceans. Some species are capable of migrating, chasing their prey for thousands of kilometers. So, killer whales hunt, uniting in large flocks. Communicating by whistling, they surround a school of fish or a school of dolphins, and then attack them.
Pinnipeds
This group of marine mammals has not fully adapted to life in the water. Their body is usually covered with fur to help keep them warm. This is also facilitated by a very thick layer of subcutaneous fat. It also serves as a source of energy in the face of food shortages.
Pinnipeds do not move as fast in water as cetaceans. However, some species are capable of speeds up to 30 km / h on the surface. Pinnipeds are very agile in water, but on land they behave awkwardly, with difficulty moving.
A large number of pinnipeds are on the verge of extinction. Since the 19th century, the number of walruses and seals has declined to dangerously low levels. They have become the target of uncontrolled hunting because of their fur and tusks. Some species have disappeared forever.
