Whales belong to mammals, and they also need sleep and rest. They don't need long-term continuous sleep, but are fragmented, and some are similar to human breath-holding behavior. They sleep in different positions, too. Sperm whales are vertical. Killer whales go to sleep and sleep by surfacing.

In order to adapt to the underwater environment, the whale's forelimbs evolved into fins, and its hind limbs degenerated, resulting in a horizontal caudal fin. When the nostril moves to the top of the head, it needs to be exposed to the water at regular intervals to replace oxygen. No auricle, but excellent hearing. Two branches of cetaceans, baleen whales and toothed whales, differentiated 34 million years ago.

There are about 15 species of baleen whales, with toothless mouths and curtain-like horny whales on the upper jaw, which filter krill and small fish. Because of its huge size, it is the largest animal in the world.

There are about 75 species of toothed whales. They have many teeth in their mouths and prey on fish and cephalopods. Generally speaking, the body size is smaller than that of baleen whales, and there is a big gap between different species; It has a developed sonar system, and mainly relies on the echolocation function when taking the initiative; Some species have extremely high IQs and even complex emotions.

Living habits of cetaceans:

Whales are warm-blooded animals, and their body temperature is always around 37℃, which is close to human body temperature. However, seawater is cold, especially in the Arctic, where the water temperature is often below zero.

Moreover, water absorbs heat much faster than air, so whales have a spongy thick cortex, and there is a thick layer of fat under the cortex as an insulation layer to ensure that the heat in the body is lost as little as possible. In addition, because the resistance of water is much greater than that of air, whales need more energy and physical strength to move.

Of course, there are disadvantages and advantages, because there are more food in the sea and fewer competitors, so it is easier to eat. Moreover, perhaps more importantly, although seawater has great resistance, it also has great buoyancy.

A monster like a whale, which is tens of meters long and weighs more than 100 tons, can't survive on land in any case. Needless to say, even foraging is extremely difficult to move. So it is a wise choice for the ancestors of whales to return to the water.

When swimming, whales mainly rely on the swing of their tails and tail leaves to get forward power, while their forefins are mainly used to control the direction of progress and grasp the depth of diving. The greatest thing about a whale is that it is not only the largest animal on the earth, but also a global wandering animal.

In this global migration, the polar regions are inevitable, because there are abundant food and krill, you can have a full meal for a while and store enough energy, and then you can go back to the temperate ocean for a few months' holiday.

Of course, some whales don't like to travel long distances and only rest in local waters. For example, beluga whales, narwhals and Greenland whales live in the Arctic all the year round.

Whales are divided into baleen whales and toothed whales according to their eating patterns. The upper jaw of baleen whales has a row of baleen, which acts as a filter. When they take a big bite, the water rolls the fish and shrimp into their mouths, then closes them, and the water is discharged, but the fish and shrimp are swallowed by the tongue of a whale weighing several tons. Toothed whales have sharp teeth for biting and swallowing.