Strange sense of smell
According to the investigation of fossils and the calculation of scientists, sharks have lived on the ground for about1.800 million years. They existed more than 300 million years ago, and their appearance has not changed much so far, which shows that their viability is extremely strong. However, its character is extremely fierce. No wonder people have great prejudice against it and think it is so primitive and stupid. In fact, sharks not only have a highly developed brain, but also can store information in the center of the brain with the help of electromagnetic fields and send information directly to the motor nervous system. And rely on a keen sense of smell to maintain all life activities. So the sense of smell is more important and mysterious to sharks.
Sharks are particularly sensitive to the smell of seawater, especially to the smell of blood, low-frequency vibration or a small amount of bleeding caused by irregular swimming of injured fish, which can attract them far away, even exceeding the sense of smell of land dogs. You can smell the fishy smell of flesh and blood with the concentration of 1ppm (one in a million) in the water. Japanese scientists have found that even if only 1 g amino acid is dissolved in 1 10,000 tons of seawater, sharks can detect the smell and gather together. For example, after giving birth, a female shark can swim back to her birthplace with the smell even if she roams thousands of miles in the sea. A shark with a length of 1 meter has dense olfactory nerve endings of 4,842 square centimeters, such as a man-eating shark with a length of 5-7 meters. Its sensitive sense of smell can smell the blood of injured people and marine animals several kilometers away.
More interestingly, sharks can also distinguish their children according to various smells, distinguish enemies from friends, maintain group contact, and meet male and female sharks to lay eggs and sperm. Because sharks have a keen sense of smell, they can easily smell their own fear or disgust. Sharks can also detect the smell of L- hydroxyalanine, a human secretion with a content of 80 billion in seawater. It is said that there was once a professional shark catcher. In the later shark catching, the shark never caught his hook again, but other fishermen in the same fishing ground caught more sharks instead. Why are sharks afraid that this shark catcher can
Where are the hands? According to the research of ichthyologists, shark catchers once suffered from skin diseases, so the fingerprints left on fishing rods contain this L- hydroxyalanine. When sharks smell this smell, they will naturally stay away from him, which is why they don't take the bait.
Unique teeth
As we all know, sharks have many unique ecology in marine life. Besides a keen sense of smell, sharks rarely get sick and die. The tooth structure of sharks is another unique ecology. Anyone who is familiar with sharks knows that its teeth are like a sharp knife, which can easily bite off a cable the thickness of a finger. Such as the devil shark, has a long, pointed nose and sharp teeth. The teeth of different kinds of sharks are almost different in size, shape and function. Therefore, ichthyologists can judge which order, genus and family sharks belong to only by the shape and size of their teeth.
Surprisingly, shark's teeth are not fixed in a row like other animals in the ocean, but there are 5-6 rows. Except for the outermost row of teeth, the other rows are "supine", just like the tiles on the roof. Once the outermost tooth falls off, the inner row of teeth will move forward immediately to make up for the hole position that replaces the fallen tooth. At the same time, the larger teeth of sharks will constantly replace the smaller teeth during their growth. So sharks often have to change tens of thousands of teeth in their lifetime. According to statistics, a shark needs to replace more than 20,000 teeth in 10 years. Its teeth are not only strong.
Strong and extremely sharp. For example, some sharks have sharp teeth like razors, so they can be used to cut food. Some teeth are serrated and can be used to tear food; Other teeth are flat mortar-shaped, which can be used to crush food shells and bones. It seems that Indians in North America use shark teeth as shaving tools. But what is terrible is that when they compete for each other's food, sharks often indiscriminately, and even their own children, shark cubs, are not spared and are completely eaten; When a shark struggles to be accidentally injured by other sharks, the injured shark will be unlucky, and other brothers of the same clan will gang up and attack it until it is completely swallowed up; still
What is even more frightening is that a shark can give birth to more than 10 sharks in one fetus, and the highest number can reach more than 80. These sharks actually kill each other in their mother's womb. People once found the belly of a tiger shark on the Atlantic coast, and made an autopsy to conclude that the womb of the mother shark has become a battlefield, which is unprecedented in any animal.
The reason why sharks change their teeth like this is not only related to their cruelty, but also to their different tooth shapes. Because the biting force of sharks can be said to be the most powerful of all animals in the ocean. Someone once used a metal bite device hidden in bait to measure the bite force of an 8-foot-long shark. The results show that the bite force is as high as 0/8 ton per square inch/kloc. Therefore, it is not surprising that some merchant ships recorded in their nautical diaries that their propellers were bent by sharks and their hulls were bitten by sharks. The shape of shark teeth is very strange. For example, the tooth edge of a man-eating shark is serrated and triangular; Great blue shark's teeth are big and sharp; And whales
Although sharks are huge, their teeth are as short as needles; Conodont shark's teeth are conical, long and sharp; The teeth of long-tailed sharks are flat and angular; The teeth of basking sharks are very small, as many as rice grains; Tiger sharks have wide mortar-shaped teeth and so on. As mentioned above, the diversity of shark teeth is closely related to its ecological feeding habits.