On this day, 27 years ago, November 14, 1998 (September 26, 1998, the lunar calendar), experts said that the rare species of the baiji dolphin would become extinct within 20 years. Scientific name: Lipotesvexillifer(Miller, 1918) Chineseeriverdolphin Baiji dolphin (báijītún), a national first-class protected animal, also known as white dolphin, baiji dolphin, and white flag. Vertebrate phylum, Mammalia, Cetaceans, Odontocetus. Originally belonging to the freshwater dolphin family, in the late 1970s, based on the suggestion of Professor Zhou Kaiya, a China scientist, the Baiji dolphin family was established separately. The only species in the Baiji genus of the family Baiji in the cetaceans. Freshwater toothed cetaceans, a specialty of China, are distributed in the middle and lower reaches of the Yangtze River. It is also found in Dongting Lake, Poyang Lake, and Qiantang River. The body is spindle shaped, with a body length of 1.5 to 2.5 meters and a weight of up to 230 kilograms; The snout is beak-shaped, narrow and long, with the tip of the snout slightly upward; the top of the forehead is significantly raised; the eyes are small and located below the corner of the mouth; the ear foramen are extremely small and shaped like a needle of a needle and located below the back of the eye; the dorsal fin is a low isosceles triangle, located in the middle of the back and slightly back; The flippers are wide and the ends are round and blunt, and the trailing edge of the caudal fin is concave in a crescent shape; the back is gray or blue-gray, the ventral surface is white, the dorsal fin, the back of the flippers, and the caudal fin are all gray or bluish-gray. When breathing, the head comes out of the water first, the spray is not high, and the caudal fin does not come out of the water. Baiji dolphins are good at diving, but they are easily injured and killed by the propellers of motor boats. Usually activities in pairs. Eat fish and use long beaks to catch benthic fish. Baiji dolphins mainly live in the middle and lower reaches of the Yangtze River and the connected waters of Dongting Lake, Poyang Lake, Qiantang River and other waters. They are usually paired or more than 10 dolphins together and prefer to move in places with deep water and rapid currents. They like to live in groups, especially during the spring mating season, when the herd behavior is more obvious. Each group generally has 2-6 heads. It has a wide range of activities, but it has high requirements on hydrological conditions. It often stays in a fixed area for a period of time, and then moves to another area after the hydrological conditions change. Eat fish. Baiji dolphins breed once every two years, with one cub per child and a body length of about 80 centimeters at birth. The body color of the newborn larvae is slightly darker, and the adult Baiji dolphin generally has a light bluish-gray back and a clean white belly, which is especially bright under the sun. The upper and lower sides of the horizontally extending fins and caudal fins are the same color as the back and ventral sides respectively, and this color distribution coincides with the color of the environment. When looking down from the water surface, it is difficult to distinguish between the bluish-gray color on the back and the river water; when looking up from the water bottom, the white abdomen and the strong light reflected by the water surface are similar in color and it is difficult to detect. This gives the baiji dolphins a natural hidden barrier when escaping from enemies and approaching prey. Baiji dolphins can live for more than 30 years. Females generally reach sexual maturity at the age of 6 and males are 4 years old. Adult baiji porpoise is in estrus twice a year, from March to May and from August to October. The pregnancy lasts for 10 to 11 months, with one child per child and occasionally two children. In the wild, the male to female ratio of adult Baiji dolphins is 1:1, but the pregnancy rate of female animals is generally only 30%, and the natural reproduction rate is very low. The Baiji dolphin is a carnivore with about 130 sharp teeth in its mouth, which are homotypic teeth. They often swim to shallow waters on the shore during the morning and dusk to hunt. They generally devour whole freshwater fish with a body length of less than 6.5 centimeters, and also eat a small amount of aquatic plants and insects. When breathing, the head comes out of the water first, and then all comes out of the water. After swimming on the water surface for 2 meters, it reenters the water. Baiji dolphins have almost zero vision and rely on echolocation to understand environmental changes. They have extensive scientific research value in biology, bionics and physiology. However, Baiji dolphins are naturally timid and easily scared. They are generally far away from ships and difficult to approach. In addition, their population is small and their range of activity is vast, so research on Baiji dolphins in the wild is very limited. Baiji dolphin's skin is smooth and delicate and full of a special elasticity. The principle is the same as the elastic nylon fabric used in competitive swimming clothing, which can reduce the turbulence generated around the body when swimming rapidly in the water. Its caudal fin is flatly divided into two forks, the pectoral fins on both sides are flat palm-shaped, and the dorsal fin is triangular. These four fins provide the Baiji dolphin with excellent control over direction and balance when swimming in the water. Coupled with its smooth and highly elastic skin and streamlined body, the Baiji dolphin can swim at a speed of 60 kilometers per hour while avoiding danger. Normally it maintains a swimming speed of 10 to 15 kilometers per hour. The Baiji dolphin has lived in the turbid water of the Yangtze River for a long time, so its vision and hearing have been seriously degraded. In the water, it mainly transmits sonar to receive signals to identify objects. The upper respiratory tract of the Baiji dolphin has three pairs of unique air sacs and a throat shaped like a goose's head. However, because it lives in water and relies on water to make sounds, it does not have the vocal cords needed by land animals to make sounds in the air. Using special hydrophones, you can hear dozens of different sounds such as "dada" and "quack" made by the baiji dolphin. Baiji dolphins often make two sounds in pairs. After making the sound, they will quietly wait for the echo to identify the distance and size of the obstacle that generated the echo and consider whether to swim towards the target. It will emit a new pair of sounds shortly after receiving the echo, and then wait for the echo for a while. After receiving the second echo, it can analyze the direction and speed of the target's swimming. This is how the Baiji dolphin performs echolocation like artificial sonar. With this unique sonar system, it can often capture food in the mud at the bottom of the river, and can also emit high-frequency sound waves that are inaudible to the human ear to communicate with companions more than ten kilometers away. The brain surface area of Baiji dolphins is larger than that of dolphins, and the brain weighs about 0.5% of the total. Among them, a male dolphin weighing 95 kilograms on average has a brain weight of 470 grams. This weight is close to the brain weight of gorillas and chimpanzees, and some scholars even believe that the baiji is smarter than gibbons and chimpanzees.