Dolphins are mammals that can be found in the open seas and in river mouths. They are ideal swimmers because... their body is adapted to movement in water. The body of a dolphin is from 2 to 3.6 m, they weigh from 150 to 300 kg. They have pointed teeth, a record number of them - 272, shaped like pointed thorns. This is necessary to hold slippery prey.
Here are 10 more interesting facts about dolphins for 4th grade students that will help you learn more about these mammals. Until now, the information that we receive about them surprises and amazes, because... Not a single animal living on our planet can compare with dolphins.
Dolphin - description and photographs. What does a dolphin look like?
Some people mistakenly believe that dolphins are fish. In fact, they belong to the class of mammals and are easily recognized by their characteristic appearance. They have an elongated body, starting with an elongated head and ending with a tail. There is a long fin at the top of the body.
Upper fin of a dolphin
There are 80-100 teeth on the upper and lower jaws, slightly directed inward. The eyes are located at the level of the corners of the mouth, and have poor vision, since for dolphins this organ of touch does not play an important role even during hunting.
The body is covered with fatty enzymes that ensure easy gliding in water.
Thanks to this, they swim without encountering resistance, which allows them to develop greater speed. However, this feature leads to the fact that the dolphin's skin is constantly abraded and washed off with water. Because of this, the body is forced to continuously regenerate the upper layer of the body, based on internal reserves. Interesting fact : dolphins shed so quickly that they can completely renew the top layer of skin in an hour.
Thus, it can shed up to 24 times per day. In length, various types of these creatures can grow up to 4.5-5 meters, although most of their representatives are comparable in size to human dimensions. In color, different types are gray, blue, black and with different color pigments.
How do dolphins breathe?
Upon a detailed examination of the mammal’s body, one immediately notices that it has no gills. If in many fish the head is disconnected from the body by a cut under which the respiratory organs are hidden, then in a dolphin it is connected to it as a single whole and has no pronounced boundaries. It can be assumed that because These creatures are mammals, they should not have gills, but they also do not have nostrils at the tip of their nose. This raises a logical question: how do dolphins breathe?
Dolphin blowhole located on the back of the head
On the crown of the animal there is a blowhole - a small hole that is tightly closed with a movable lid while it is under water. When the dolphin comes to the surface, it opens and air enters. The collected oxygen is enough for the mammal for a long time, thanks to which it can swim long distances underwater. However, sooner or later he will need to surface to take another breath.
"Grey's Paradox"
He is associated with dolphins. In the 1930s, James Gray found that dolphins move at enormous speeds, at least 37 km/h. This surprised him, because... according to the laws of hydrodynamics, then they should have had 8-10 times more muscle power. Gray decided that these mammals control the streamlining of their body; their body has 8-10 times less hydrodynamic drag .
In our country, research was carried out until 1973, and the first experiments appeared confirming Gray’s statements. Most likely, Gray was mistaken about the speed of movement of dolphins, but they still know how to reduce the resistance to their movement, but not by 8 times, as the Englishman believed, but by 2 times.
Do dolphins have ears?
There are no hearing organs on the dolphin's head, just like most underwater inhabitants. But they have a highly developed inner ear, reinforced by air cushions located in the upper part of the head. This feature of the body structure works as an accurate echolocator.
Dolphins are sensitive to sound vibrations emitted by objects underwater. Thanks to them, the source of the sound is determined with incredible accuracy, and its dimensions are also recognized. They also subtly sense the wavelength that creatures and objects send in their direction. Thanks to this parameter, they can calculate the distance to the object.
Comparison of echolocation of a bat, dolphin and submarine
A reliable echolocator serves as an excellent replacement for poor eyesight. While underwater, a dolphin does not need to look around and see its surroundings. It is enough for him to feel the vibrations in the water to form a correct idea of the surroundings in his head.
“Combat” dolphins in the USA and USSR
The use of dolphins was first proposed back in the 19th century, but this idea was only realized in the 1950s. The US Navy conducted many tests involving different animals (more than 19 species). Dolphins and sea lions were sampled. They were trained to find underwater mines and destroy submarines using the kamikaze method . But the US Navy denies it has ever done anything similar. But, nevertheless, training bases exist, they have a special Marine Mammal Fleet.
The USSR established its own research center near the Black Sea in 1965, in Sevastopol. In the early 1990s, dolphins stopped being trained for military purposes. But in 2012, Ukraine continued training, and in 2014, Crimean fighting dolphins were accepted into the service of the Russian Navy.
How do dolphins sleep?
Considering that dolphins regularly need to surface to get air, they also cannot spend a lot of time on the surface, because... their delicate skin quickly dries out and becomes damaged. Things with sleep for dolphins are very interesting.
Dolphins do not sleep at all! However, every creature on Earth needs rest, so dolphins also have a period during which they rest. Their body is designed in such a way that it can turn off one of the hemispheres of the brain. Thus, while the left one is working, the right one is in hibernation, then everything happens exactly the opposite. This allows the creature to rest, gain strength, but at the same time carry out simple actions such as swimming and rising to the surface to obtain oxygen.
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