Who is the whale and what is the whale?

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Problem description stool shouting:

Why whales are not fish.

Analysis: Whales are mammals that live in the ocean. Viviparous, usually one litter per litter, feeds the calves with milk. But many people refer to them as fish, when in fact they are not fish but mammals. It is found in the world's oceans.

Whales are viviparous mammals, not fish. Calves need to be fed breast milk for a year to mature. Fish, on the other hand, are oviparous vertebrates.

Broodstock generally do not have the habit of taking care of small fish. The "fins" of the whale are actually evolved from the four limbs. Fish are not.

Whales breathe with their lungs. Fish breathe with gills Whales are homeotherms, whereas fish are ectotherms. It is not possible to distinguish a whale from a fish by the presence or absence of scales.

Whales are aquatic mammals.

In fact, although the whale looks like a fish, it is not a fish, but a class of mammals, which is similar to the situation of bats that are like birds but are not birds, and are also a class of real mammals. Unlike fish, whales are viviparous, generally giving birth to one litter per litter and one litter every two years. The pups are raised on the mother's milk.

Fish are oviparous and can lay thousands of eggs at a time, and once hatched, young fish can live independently without lactation. The whale's body temperature is constant, on average, whether in cold waters or tropical sea areas; Whereas, fish are ectotherms, and their body temperature varies with the change in ambient temperature.

Whales breathe with their lungs and need to surface frequently for ventilation. Fish, on the other hand, use their gills to absorb oxygen dissolved in the water and stay underwater. The similarity in appearance between whales and fish is due to the fact that they have been living together in the same living environment for a long time, which is a "convergence phenomenon".

Characteristics of whales:

The common feature of cetaceans is a constant body temperature, which is: ** Exposed, no body hair, only a few bristles on the tail, no sweat and sebaceous glands. The fat under the skin is thick, which maintains body temperature and reduces the body's gravity in water.

The skull is well developed, but the skull is small, the facial is large, and the forehead and maxilla are markedly elongated, forming a very long snout.

The neck is not obvious, the cervical spine is healing, and the head is directly connected to the trunk of the middle limb. The forelimbs are flake-shaped, the toes are not separated, there are no claws, and the joints of the elbows and wrists cannot move flexibly, making them suitable for swimming in water. The hind limbs are degenerate, but there are remnants of the pelvis and femur, showing fragments of bone.

The tail degenerates into fins, and the ** at the end expands horizontally to form a pair of large tail lobes, but they are not supported by bone, and the vertebrae taper gradually taper at the narrow tail trunk and finally disappear before entering the tail fin. Unlike fish, the tail fin can swing up and down and is the main organ of swimming. Some species also have dorsal fins, which are used to balance the body.

Their bones have spongy tissue, and there is more fat in the body cavity, which can increase the volume of the body, reduce the specific gravity of the body, and increase buoyancy.

Whales are cetaceans.

Whales are cetaceans, mainly divided into two categories: baleen whales and toothed whales, their nostrils are long on the top of their heads, and after a period of activity in the ocean, they need to surface to replace oxygen, and cetaceans can only produce one cub per litter, due to human overhunting, a quarter of the whale species are extinct.