Sharks, known as sharks, sharks, and sharks in ancient times, are behemoths in the ocean, so they are known as "wolves of the sea." The nostrils of sharks are located in front of the mouth on the ventral surface of the head. Some have an oronasal groove, which is connected between the corners of the nose and mouth. The folds of the olfactory sac increase the contact area with the external environment. Sharks are cartilaginous fish and do not have a swim bladder. They mainly rely on their large liver to regulate their ups and downs. According to fossil surveys and scientists’ calculations, it is known that sharks have lived on the ground for about 180 million years. They existed more than 300 million years ago, and their appearance has not changed much to this day. This shows that they have extremely strong survivability and are known as the “hunters of the ocean.” ".

Edit the classification of sharks in this paragraph

Phylum Chordata, subphylum Vertebrates, class Fish, class Chondrichthyes, subclass Elasmobranchia, superorder Pleurospora

According to the 1971 Russ classification system, it is divided downwards

Hexabranchia: 1st order of the Chondrichthyes. There are only about 4 species in 1 family and 3 genera in the family Hexagillidae. There are 3 genera and 3 species in China. The structure is original. There are 6 to 7 gill openings. The eyes have no nictitating membrane or folds. There are blowholes. One dorsal fin, no spines, positioned posteriorly, with anal fin; the axial bone of the pectoral fin extends to the front edge of the fin, and the front fin cartilage has no radial rays. The segmentation of the spine is incomplete, but the vertebral bodies are somewhat calcified, and the notochord is partially or not constricted. 1 kiss cartilage.

The order Porphyra: The order Porphyra, also known as the order Mackerel, is the largest order in the superorder Pleurospora. Including most modern species. There are 5 pairs of gill openings. 2 dorsal fins, spineless, with anal fin. The eyes have no nictitating membrane or folds. The vertebral body has radial calcification areas, and there are 4 non-calcification areas without calcification spoke invasion. In the maxillolingual joint type, the maxilla is connected to the skull only by ligaments. It is considered to be more harmful to humans than other sharks, and is also known as the man-eating shark and the white death shark. Distributed in tropical and temperate zones of all oceans, it generally lives in open ocean areas, but often enters inland waters. They are notorious for sometimes fatal attacks on swimmers, divers, surfers, and even small boats in unprovoked situations. It eats a lot, and its food includes fish, turtles, seabirds, sea lions, debris discarded from ships, etc.

The white shark has a heavy body, a crescent-shaped tail, and large, triangular teeth with serrated edges. It is dangerous because of its large size and aggressive nature. The specimen weighed 3,300 kilograms (7,300 pounds) and was approximately 6.4 meters (21 feet) long. The length of a shark can reach up to 11 meters (36 feet). Generally, the body is gray, light blue or light brown, and the abdomen is light white. The dorsal and abdominal body colors are clearly defined, and the larger ones are lighter in color.

The fame and prestige enjoyed by the great white shark is unparalleled anywhere in the world. As one of the largest marine carnivores, the great white shark has a unique and cool color, black eyes, vicious teeth and jaws, which not only makes it the most easily identifiable shark in the world, but also makes it one of the most recognizable sharks in the world for decades. Decorative cover "character".

The great white shark is one of the most widespread sharks due to its unusual ability to maintain a body temperature higher than its surroundings, which allows it to survive in very cold waters. You can live comfortably here. Although it is rare to see it in most coastal areas, it is often encountered by fishing and diving boats.

Tiger sharks: an order in the class Elasmobranchia of the class Chondrichthyes. There are only 1 family, 1 genus and 8 species. The body is thick and short, and the head is nearly square. The snout is short and blunt, the eyes are small, oval, and positioned upward. The nostrils have a nasal groove. The mouth is flat and horizontal, with well-developed upper and lower lip folds. The upper and lower jaw teeth are of the same shape, and the front and back teeth of each jaw are shaped differently. The front teeth are thin and pointed, with 3 to 5 tooth heads; the rear teeth are flat and molar-like. The blowhole is small and located behind and below the eye.

Carcharhinales: 1st order of the Chondrichthyes. 2 dorsal fins, no spines. With anal fin. There are 5 gill openings. Maxillolingual joint type. 3 kissing cartilages. The eyes have nictitating folds or membranes. The vertebral body has radial calcified areas, and calcified spokes invade four non-calcified areas. The spiral valves of the intestine are spiral or scroll-shaped. There are more than 200 species in 4 suborders, 7 families, 49 genera in the world. China has more than 60 species in 4 suborders, 4 families, 23 genera, and is the group with the most genera and species among cartilaginous fishes in China.

Squalia: an order in the subclass Elasmobranchia of the class Chondrichthyes. There are 87 species in 3 families, 21 genera. 2 dorsal fins, with or without hard spines; anal fin missing. There are 5 gill openings, and the vertebral body is annular or multi-annular.

1 kiss cartilage. Mainly distributed in warm water, cold water areas or deep sea areas around the world.

Carcharhinidae: an order of the Chondrichthyes. This order has only one family, the family Carcharhinidae, and a genus, the genus Carcharhini, with about 13 species. The body is flat; the snout is short and wide; the pectoral fins are wide and extend to the head side like free sleeves, so it was formerly known as the sleeve shark, and is commonly known as angel fish or monk fish in the West; the eyes are superior; the mouth is wide and sub-anterior; the upper teeth and lower jaw are the same shape , slender single-tooth head shape; nostrils in front; 5 gill openings, wide, extending to the ventral surface; 2 dorsal fins, no hard spines.

Whisker sharks: Belonging to the subclass Elasmobranchi, divided into the spotted sharks, the long tail sharks, the long tail sharks, the long tail sharks, the rheumatoid sharks, the leopard sharks and the whale sharks division.

Sharks are considered by some to be the most ferocious animals in the ocean. Whale sharks feed on small marine creatures, similar to baleen whales. Due to certain similarities in food, after a long period of biological evolution, they look very similar to baleen whales. This is called "convergent evolution." So the name "whale shark" was a no-brainer. The whale shark is, of course, the largest living shark and the largest known fish.

Edit this paragraph Characteristics of sharks

Sharks have hard bodies, well-developed muscles, and are spindle-shaped to varying degrees. The snout part varies depending on the species, ranging from pointed, such as mako sharks and great white sharks, to large and round, such as tiger sharks and broad tiger sharks with flat heads. The vertically upward tail (caudal fin) is roughly crescent-shaped, and the upper part of the caudal fin of most species is much larger than the lower part.

When sharks swim, they mainly rely on the movement of their bodies like snakes and the swinging of their tail fins like oars to propel themselves forward. Stability and control are mainly achieved through the use of a more or less vertical dorsal fin and horizontally maneuverable pectoral fins. Most sharks cannot move backwards, so they can easily become entangled in an obstacle like a gillnet, and once trapped, have difficulty extricating themselves. Sharks don't have swim bladders, so the animal's specific gravity is determined primarily by the amount of oil stored in its liver. Sharks are slightly denser than water, which means that if they are not actively swimming, they will sink to the bottom of the ocean. They swim very fast, but can only maintain high speeds for short periods of time. Talking about why sharks don’t have swim bladders, this is related to a legend: a long time ago, God created fish, and sharks were just a small fish. One day God suddenly thought of the contribution of fish and wanted to reward all fish with a swim bladder. But the naughty little shark was playing, and when the little shark knew it, God had left. The little shark can only keep swimming, swimming and swimming. The more you swim, the stronger you become. Thousands of years later, God came to inspect and found that the strongest shark felt strange. He treated every fish fairly! Why are only sharks like this? He asked the shark why, and the shark replied: "Because my ancestor did not receive your gift, so he could only keep swimming, and the more he swam, the stronger he became!"

There are 5 on each side of the shark. ~7 gill slits (unlike the carp we usually buy from the market, which has a pair of gill covers protecting the gills). When swimming, seawater is sucked in through the half-open mouth and flows out through the gill slits for gas exchange. A shark swimming with its mouth open does look scary, but can you prevent it from breathing? A few shark species can rest on the ocean floor to breathe.

Edit this section about shark research

Marine biologists at the University of Hawaii said they have obtained first-hand evidence that sharks can detect changes in the Earth's magnetic field. This discovery provides new evidence that marine fish have an internal "compass" system to guide them in their direction.

This latest research result was published in the Journal of the Royal Academy of Sciences in the United Kingdom. Carl Meyer, a marine biologist at the University of Hawaii, and his colleagues designed and planned the experiment. They trained six sandbar sharks and one hammerhead shark in an artificial magnetic field environment. This artificial magnetic field environment is a 7-meter-diameter water tank with a layer of copper cables wrapped around it. Whenever food is put into the water tank, the cable switch is turned on to simulate the magnetic field environment.

After six weeks of training, no matter when the cable switch was turned on, even if no food was put into the tank, the sharks would still gather in the usual feeding area.

This reaction proves that they sense the presence of a magnetic field.

Before scientists conducted this experiment, the strange habits of some sharks had already led scientists to speculate that sharks might have this special ability. Tiger sharks and blue sharks can swim long distances directly in the ocean, which is impossible if they rely solely on their sense of smell. Hammerhead sharks often congregate near undersea mountain ranges, areas where the Earth's magnetic field changes.

The next step in scientists' research is to understand how sharks detect the Earth's magnetic field and how sensitive they are to magnetic field induction. Not long ago, scientists have known that other animals have the ability to detect magnetic fields. Researchers at the University of North Carolina in the United States have proven through experiments that pigeons have tiny magnetic particles in their upper beaks, which can help pigeons fly long distances.

Edit this paragraph Sharks and anti-cancer

In the past 20 years, the shark fin trade in the market has become more and more popular, and millions of sharks are slaughtered every year. At least 10 new shark species have been added to the International Union for Conservation of Nature's "2004 Endangered Species List," including great white sharks, New England sharks and Gulf of Mexico whitenose sharks. An important reason why sharks are hunted in large numbers is that people have accepted the false propaganda that shark cartilage (including the famous "shark fin") can fight cancer.

According to a recent report by the Russian News Network, Gary Ostrander, a professor at the Department of Biology and Comparative Medicine at Johns Hopkins University in the United States, pointed out in a newly released research report that sharks also Will get cancer. At the same time, eating shark cartilage has no obvious effect on treating cancer.

Professor Gary Ostrander believes that the current trend of eating shark cartilage is just a victory of "pseudoscience" through marketing. He said that eating shark cartilage is not only useless for treating patients, but also causes great harm to the shark population - patients often blindly believe in the efficacy of these cartilages and refuse other treatments, and large-scale hunting activities have caused a decline in the number of sharks. Decline rapidly.

Shark was once considered an insulator against cancer, and its cartilage powder was promoted as a cancer cure.

As early as 1983, two biochemistry doctors from the Massachusetts Institute of Technology, Ann Lee and Robert Lange, published an article in the famous American "Science" magazine stating that dogfish in shark cartilage Alkene has a blocking effect on the angiogenesis of cancer cells and has been proven to inhibit the growth of cancer cells.

In 1993, the American CBS TV station's "60 Minutes" program invited Dr. William Lance, author of "Sharks Don't Get Cancer", to discuss the research results that shark cartilage can fight cancer. Several terminal cancer patients The program stated that after taking shark cartilage capsules for a few weeks, the symptoms were relieved.

Since then, claims that shark cartilage fights cancer have spread widely through books, articles, websites and vendors. Subsequently, the pharmaceutical company launched a pill made from shark connective fiber tissue on the market, claiming that this shark pill is a "good medicine for treating cancer", creating a market for shark cartilage products with annual sales of more than 50 million US dollars. One of the largest shark cartilage manufacturers is Dr. William's son.

In 1994, the U.S. Food and Drug Administration (FDA) officially approved the use of shark cartilage products to prevent and treat cancer. As a result, shark cartilage products have become a hot spot in the health care product market, and their influence has spread all over the world.

In China, shark cartilage products and restaurants selling shark soup were once very popular.

In the late 1990s, the claim that shark cartilage powder can fight cancer spread to China. At that time, there were two main categories of shark cartilage products on the market: one was physically processed bone powder of shark cartilage, and the other was active extracts extracted by chemical methods.

In addition to vigorously promoting the number of "active ingredients" in anti-cancer, the former also claimed that the fineness of grinding bone powder must be more than 200 mesh in order to be absorbed by the human body. The finer the better. It is said that the fineness of some products in the United States has reached 300 mesh, which greatly improves the extent to which the active ingredient active egg in bone meal can be absorbed by the human body.

The latter claimed that two angiogenesis inhibitory factors with anti-tumor functions were purified and extracted from the very complex shark cartilage tissue, and shark chondroitin capsules and shark cartilage were made based on these ingredients. powder and other series of anti-cancer drugs. This drug was once very popular in the Chinese market.

Because sharks have this unique anti-cancer function, there is also a "crush" on eating sharks in society. Especially restaurants in Hong Kong and Guangzhou boil shark cartilage into a soup and sell it, which is called "Shark Cartilage Laohuo Soup" has various varieties. These restaurants claim that in addition to its anti-cancer and anti-cancer effects, this soup also has the effects of nourishing the skin, beautifying the body, strengthening the muscles and bones, and replenishing the spleen and stomach. As a result, there is an endless stream of people eating it.

Recent research suggests that sharks themselves can develop cancer.

Recent studies have shown that sharks themselves are susceptible to a variety of cancers, including cancers of cartilage tissue. Professor Gary Ostrander*** listed 40 examples of sharks suffering from tumors in his research report, overturning the previous statement that sharks do not develop cancer.

American scientist John Hasbarger also pointed out at the 91st Annual Meeting of the American Anti-Cancer Society that sharks can develop cancer. Haasbarger, a scholar at the National Cancer Institute, discovered 50 types of cancer in cartilaginous fish, 23 of which came from various sharks, and some of them grew directly in cartilage.

It is worth noting that Dr. William Lance, author of "Sharks Don't Get Cancer" (he can be regarded as the father of "shark therapy") recently admitted that sharks do in fact will get cancer, and confessed to the outside world that his conclusion that shark cartilage extract can treat cancer was only based on the results of a very limited number of experiments.

Clinical experiments have proven that shark cartilage powder has no cancer treatment effect.

In fact, so far, clinical trials on the anti-cancer effect of shark cartilage powder have proven to be ineffective. Danish scholars presented a study report to the European Breast Cancer Conference saying they found that women who took so-called "alternative anti-cancer drugs" made from shark cartilage did not get any benefit from the drug.

Danish researchers used shark cartilage extract to conduct a trial on 17 patients with terminal breast cancer. They gave 17 patients a considerable amount of shark pills, taking 24 pills a day.

Three months later, 15 of the 17 patients' cancer continued to progress. Another patient initially showed signs of improvement but later discovered he had developed a new tumor in his brain.

In addition, in another clinical trial, more than 50 patients suffering from breast cancer, lung cancer, prostate cancer, colorectal cancer, etc., all had no symptoms after using purified shark cartilage protein. There was a noticeable improvement. Moreover, according to research conducted by the National Institutes of Health, because the protein molecules of shark cartilage are too large to be easily absorbed by the intestines, even if they are absorbed, they will be broken down and destroyed.

Healthy foods named after shark cartilage have no effect on cancer at all.

Not long ago, the U.S. Food and Drug Administration filed a lawsuit against William and his son's laboratory and manufacturing plant, demanding that they stop promoting unsubstantiated and false advertising that "shark cartilage products can fight cancer" .

The U.S. Federal Trade Commission also ruled that any false promotion of shark cartilage products is prohibited unless supported by relevant scientific evidence. The William Lance Laboratory must pay a judgment fee of US$1 million, of which US$450,000 will be handed over to the National Cancer Center and the William Lance Laboratory to jointly conduct a large-scale clinical trial of shark cartilage to find out the truth.

Scientists believe that various health foods named after shark cartilage have no obvious effect on cancer.

Shark’s fin’s anti-cancer effect is a new version of the unscientific saying that “you will get what you eat”. To take a step back, even if sharks do not suffer from certain cancers that humans suffer from, it does not mean that shark products can treat human cancers.

For example, cats and horses do not get prostate cancer, and research shows that even eating the prostate of cats and horses does not prevent prostate cancer.

Moreover, sharks can develop cancer, so consumers who want to eat expensive shark bone meal to fight cancer should think twice. Medical experts believe that most health foods advertised as "anti-cancer" are nothing more than "hope." What consumers really need to look forward to is technological progress, not superstition in commercial advertisements.

Edit this paragraph Shark's Sleep

In the past, it was generally believed that sharks never sleep. According to the Florida Museum of Natural History, whitetip sharks, tiger sharks and great white sharks actually sleep. They sleep during the day and come out at night. Other species, such as nurse sharks, have spiracles that force water through their gills, providing a steady supply of oxygen-rich water that they can breathe while stationary. The central test signal generator, the organ that controls swimming, is located in the spinal cord and allows sharks to swim unconsciously. But because fish don't have eyelids, it's impossible to tell whether a shark is sleeping.

Edit this paragraph Shark Reproduction

Like most animals, sharks reproduce sexually. Shark mating behavior is complex, and male and female shark species have very different pre-mating routines. Behavioral patterns such as swimming together, biting and color changes are unique. Sharks such as basking sharks use complex swarming behaviors, the purpose of which is not yet understood.

The egg sac of the short-nosed spiny shark is often called the "mermaid's purse".

After the male and female sharks mate successfully and the eggs in the female shark are fertilized, the fertilized eggs of this species of shark will continue to develop in one of the following three ways:

Oviparous sharks lay eggs with thick sheaths that allow them to cling to rocks or seaweed and ward off predators. The eggs hatch after a few days or weeks, and the shark leaves the young to survive on their own. Most egg sheaths are broad rectangular in shape, and some, such as the "mermaid purses" laid by dogfish, often wash up on beaches.

Sharks give birth to young, which are nourished in the female shark's uterus through the placenta or a secretion called uterine fluid. Viviparity ensures that the young are well nurtured during their growth period and therefore able to survive in the harsh sea immediately after birth.

Sharks also nurse embryos inside their bodies and then give birth to live young, but they cannot provide any direct nutrition to their offspring. Instead, the gestating shark relies on the eggs' yolk sac for sustenance. Some species of sharks, such as the mako shark, use the "oophagy" method, in which the mother shark lays a string of small, unfertilized eggs, which are eaten by the growing embryos.

1. Oviparous: generally used by large sharks. Shark eggs are very large and have a good supply of nutrients. The discharged eggs are wrapped in a flat cushion-shaped sheath, which is added around the egg as it passes through the fallopian tube. The outer skin of the sheath will harden after entering the water. There is a short and hollow in each corner of the sheath. A horn through which seawater can enter, allowing the eggs to obtain oxygen. There is a limited number of ovulations each time. The eggs are bag-shaped or spiral-shaped and are fixed in coral reefs, seafloor plants or rock crevices after being laid. The empty egg sacs of spiny sharks that wash up on the coast are nicknamed "mermaid's little purses."

2. Ovoviviparous (non-placental viviparous): The fertilized egg develops in the uterus and uses the yolk sac or the eggs discharged from the ovary into the uterus as the source of nutrition. The placenta does not form in the uterus. Except for the whale shark, which can give birth to more than 300 tails at a time, the others can only give birth to dozens of tails at a time, and the least is the fox shark (thresher shark), which only gives birth to two tails at a time.

3. Viviparous (placental viviparous): The fertilized egg enclosed by a horny shell develops in the uterus. The nutrients required for growth are obtained from the yolk sac and placenta. The young shark is not produced until it is almost fully formed. Each time Dozens of tails are produced. Most sharks in the ocean are viviparous. Most sharks reproduce seasonally every year, and some large sharks reproduce every other year. The gestation period of most sharks lasts 8 to 9 months, and the gestation period of dogfish is even as long as 24 months. Generally speaking, larger sharks produce more baby sharks at a time, and the opposite is true for smaller sharks. Sharks also grow extremely slowly and are not sexually mature until they are 5 to 10 years old.

Edit this paragraph about shark fun

There are many types of sharks, and there are at least 350 species in the world's oceans. Sharks, known as sharks, sharks, and sharks in ancient times, are behemoths in the ocean, so they are known as "wolves of the sea." Sharks are carnivorous and so ferocious that even the whale, the "King of the Sea," has to stay away from it. Its greedy and ferocious nature when feeding has left a terrible image on people. Therefore, when it comes to sharks, people often feel that they are talking about it. Sharks are better at catching food than tigers. They can make full use of their unique sense of smell to detect the direction and location of food, while tigers only use their eyes and nose to find food.

Peculiar sense of smell. According to fossil surveys and scientists’ calculations, it is known that sharks have lived on the ground for about 180 million years. They existed more than 300 million years ago, and their appearance has not changed much to this day, indicating that they The survivability is extremely strong. But it has an extremely ferocious personality. No wonder people have a big prejudice against it, thinking it is so primitive and stupid. In fact, sharks not only have highly developed brains, but can navigate with the help of electromagnetic fields and store information in the center of the brain. parts, and can directly send information to the motor nervous system; and maintain all life activities with its sensitive sense of smell. Therefore, the sense of smell is even more important and mysterious to sharks.

Sharks are particularly sensitive to smells in seawater, especially the smell of blood. The low-frequency vibrations or small amounts of bleeding emitted by injured and injured fishes can attract them from a distance, and even Can exceed the sense of smell of land dogs. It can smell the smell of flesh and blood at a concentration of 1ppm (one part per million) in the water. Japanese scientists found that even if only 1 gram of amino acid is dissolved in 10,000 tons of seawater, sharks can detect the smell and gather together. For example, after a female shark gives birth, she can swim back to her birthplace following the scent even after roaming thousands of miles in the sea. A 1 meter long shark has a nasal cavity densely covered with olfactory nerve endings covering an area of ??up to 4842 square centimeters. For example, a 5 to 7 meter long man-eating shark has a keen sense of smell that can smell the blood of injured people and marine animals several kilometers away. .

What is even more interesting is that sharks can also identify their own children based on various smells, distinguish enemies from friends, keep themselves in constant contact with the group, and can meet male and female sharks to lay eggs and ejaculate. Since sharks have an extremely sensitive sense of smell, they can easily pick out odors that scare or disgust them. Sharks can also smell the smell of L-hydroxyalanine, a human secretion with a content of 80 billion parts in sea water. It is said that there was once an expert shark fisher. Later, when he fished for sharks, sharks always failed to catch his hook, while other fishermen in the same fishing ground caught more sharks. Why are sharks afraid of this expert shark fisherman? According to research by ichthyologists, it was found that the shark fishing expert had suffered from skin diseases, so the fingerprints left on the fishing rod contained a relatively high amount of this kind of L-hydroxyalanine. When the shark smells this smell, it will naturally retreat from it. This is why it doesn't take the bait.

Unique Teeth People know that sharks have many unique ecologies among marine life. In addition to its keen sense of smell and the fact that it rarely gets sick or dies, the shark's tooth structure is another unique feature of its ecology. Anyone familiar with sharks knows that its teeth are like sharp knives and can easily bite through cables as thick as fingers. Like the devil shark, it has a long and pointed snout and sharp teeth. Different species of sharks have almost different tooth sizes, shapes, and functions. Therefore, ichthyologists can determine which order, genus, and family a shark belongs to simply by looking at the shape and size of its teeth.

What is surprising is that the teeth of sharks are not a permanent row like other animals in the ocean, but have 5 to 6 rows. Except for the outermost row of teeth, they really function as teeth. In addition, the remaining rows are "lying on their backs" for backup, just like the tiles on the roof covering each other. Once a tooth in the outermost layer falls off, the teeth in the inner row will immediately fall off. Moves forward to fill the cavity that replaced the missing tooth. At the same time, larger teeth continue to replace smaller teeth as the shark grows. As a result, sharks often replace tens of thousands of teeth during their lifetime.

According to statistics, a shark needs to replace more than 20,000 teeth in 10 years. Its teeth are not only strong and powerful, but also extremely sharp. For example, some sharks have teeth as sharp as razors, which can be used to cut food; some have serrated teeth, which can be used to tear food; and some have flat molar-shaped teeth, which can be used to crush food. Shells and bones etc. It seems that the Indians of North America used shark teeth as shaving tools. But the scary thing is that when they are competing for food with each other, sharks often act indiscriminately, even their own children, the shark cubs, and eat them all; when a shark is accidentally injured by another shark and dies When struggling, the injured shark will be unlucky. Other brothers of the same clan will also attack it in groups until it is completely devoured. What is even more terrifying is that sharks are viviparous and can give birth to more than 10 babies in one litter. There are up to more than 80 shark cubs. These shark cubs actually kill each other in their mother's womb. People once found a tiger shark in the belly of a tiger shark on the Atlantic coast. After an autopsy, they came to the conclusion: the mother's womb killed each other. It has become a battlefield, which has never been seen before in any animal.

The reason why sharks change their teeth in this way is not only related to their brutality and fighting nature, but also to the different shapes of their teeth. Because the bite of sharks can be said to be the most powerful among all animals in the ocean. Someone once used a metal bite force device hidden in the bait to measure the bite force of an 8-foot-long shark. The measurement results showed that the bite pressure was as high as 18 tons per square inch. Therefore, it is not surprising that some merchant ships recorded accidents in their sailing diaries in which the ship's propeller was bent and the hull was bitten by sharks. Shark teeth are very strangely shaped. For example, the teeth of the man-eating shark have finely serrated edges and are triangular in shape; the teeth of the blue shark are large and sharp; and although the whale shark has a huge body, its teeth are as short and thin as needles; the teeth of the cone-toothed shark are cone-shaped. And long and pointed; the thresher shark's teeth are flat and horn-shaped; the basking shark's teeth are both small and numerous like rice grains; the tiger shark's teeth are wide and mortar-shaped, etc. The reason why sharks have various tooth shapes is closely related to their ecological feeding habits as mentioned above.

In a sense, the whole body of sharks is made of teeth. The structure of the shield scales covering its body is similar to that of teeth, so it can be called skin teeth. Sharks have hundreds of teeth that can be moved, so sharks don't have to worry about running out of teeth, so they have great attack power.

The great white shark is by far the most powerful shark in the ocean, dominating with its powerful teeth.

In the ditch at the bottom or in the sparkling waves of the sea, sharks always gather in the ocean world. There are currently 315 named shark species, but new sharks are constantly being discovered. In terms of size, the gigantic whale shark feeds on plankton enough to dwarf a bus, and the dwarf pygmy spiny shark isn't much bigger than your cell phone.

Fossil records show that the ancestors of sharks have roamed the oceans for more than 400 million years, which is obviously longer than the dinosaurs. They are the overlords in the field of survival; their perfect body structure and hunting skills ensure that they can adapt to various marine environments. Their aerodynamic bodies are packed with highly sensitive nerve endings, helping them detect and capture prey easily and efficiently. They can smell blood up to 4 kilometers away. Their eyesight is excellent even in dim light, and they also have natural magic weapons like the ampullae of Lorenz. The gel-filled tubes surrounding the shark's snout pick up electrical impulses from all living things.

Sharks come in all shapes and sizes, and they are adept at using this design to evolve to hunt their prey. The flat-bodied angel shark is a perfect master of camouflage, hiding among the seabed and waiting for unexpected prey. The strangely twisted hammerhead sharks may only be seen in science fiction movies, but their wide eyes undoubtedly enhance their field of vision and are conducive to hunting.

The most terrifying shark is the cigar-shaped Brazilian Dharma shark. Although it is only as small as a kitten, it dares to attack large prey such as dolphins and tuna. Its weapon is to bite the prey with its powerful jaws and forcefully pull off the meat.

Sometimes it bites too deep and cannot loosen its teeth, resulting in the prey being swallowed alive, skin and flesh. Hey - who told each animal to have its own food chain?

Let's go back to the 1970s. The overnight sensation "The Gate of Hell" triggered the world's excessive panic about a special species - the great white shark. However, the little-known blue shark has killed more humans than its movie-star cousin. Blue sharks are one of the few shark species that can adapt to freshwater and swim in inland rivers. They often lurk in dark waters and attack and kill local fishermen or swimmers along the river.

Human beings are fascinated by sharks, sometimes mistaking them for stupid serial killers that roam the oceans all year round and devour anything that moves. Facts have shown that most shark attacks are responses to harassment by humans, and of the countless attacks around the world, only a handful are fatal. In the United States, soda machines are said to kill more people than shark attacks; frustrated customers often slam soda machines, causing them to rebound and knock over the user.

Sharks are very healthy animals. It is this abundant energy that also allows it to occupy a place in current scientific research. Scientists have long investigated why they are among the species with the lowest rates of cancer in nature. At the same time, their ability to self-heal wounds is also world-class. Perhaps we can learn more about shark physiology that could transform human health in the future.

In December 2000, US President Bill Clinton issued a presidential decree banning shark finning in US waters. Almost 100 million sharks are hunted every year - either as delicacies for ruthless consumers, as unlucky eggs in fishing nets, or even lost in fishing entertainment. Many shark species are endangered because their slow reproduction rate cannot keep up with their slaughter. Sharks play a unique role in the marine food chain and play a vital role in maintaining the balance of our marine ecosystems. Fifteen million years ago, the legendary ancestor of sharks, the "Megalodon", was already swimming in the Cretaceous oceans. Humans must work hard to ensure that this diverse species still swims our oceans millions of years from now.