鲨鱼的资料（英文）

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解决时间 2021-01-29 12:38

提问者网友：wodetian
2021-01-29 02:59

鲨鱼的资料（英文）

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五星知识达人网友：神也偏爱
2021-01-29 04:20

How long have sharks existed?

Fossil records indicate that ancestors of modern sharks swam the seas over 400 million years ago, making them older than dinosaurs! They are considered to be the first vertebrate with a complete jaw. Throughout time sharks have changed very little.

What is an "elasmobranch"? Elasmobranchs are a closely related group of fishes, differing from bony fishes by having cartilaginous skeletons and five or more gill slits on each side of the head. In contrast, bony fishes have bony skeletons and a single gill cover. Elasmobranchs include sharks, rays, and skates.

Do sharks have bones?

No, sharks and all other fishes belonging to the class Chondrichthyes lack true bone, but rather have cartilaginous skeletons.

How long do sharks live?

While longevity data are not available for many sharks, maximum ages do vary by species. Some sharks like the smooth dogfish (Mustelus canis) may only live 16 years, while others such as the porbeagle shark, (Lamna nasus) may live as long as 46 years. Whale sharks (Rhincodon typus) the largest fish in the world may live over 100 years.

What does a shark's skin feel like?

Shark skin feels exactly like sandpaper because it is made up of tiny teeth-like structures called placoid scales, also known as dermal denticles. These scales point towards the tail and helps to reduce friction from surrounding water when the shark swims. Because of this, if someone rubbed the skin from the head towards the tail, it would feel very smooth. In the opposite direction it feels very rough like sandpaper. As the shark grows, the placoid scales do not increase in size, but rather the shark grows more scales. The silky shark (Carcharhinus falciformis) has small scales giving it a "silky" feel to the touch.

Do sharks sleep?

It was once believed that all sharks had to swim constantly in order to breathe and could not sleep for more than a few minutes at a time. Oxygen-rich water flows through the gills during movement allowing the shark to breathe. While some species of sharks do need to swim constantly, this is not true for all sharks. Some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest. Sharks do not sleep like humans do, but instead have active and restful periods.

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1楼网友：怙棘
2021-01-29 06:24

In some form, sharks have been around for about 400 million years. Even before dinosaurs roamed the earth, sharks hunted through the oceans! They're such good survivors that they've had little need to evolve in the last 150 million years. These ancient predators fascinate adults and children alike. Sharks have the most powerful jaws on the planet. Unlike most animals' jaws, both the sharks' upper and lower jaws move. A shark bites with it's lower jaw first and then its upper. It tosses its head back and forth to tear loose a piece of meat which it swallows whole. Each type of shark has a different shaped tooth depending on their diet (the shark in the photo is a great white -- you can tell he's a carnivore just by looking at those sharp, pointy teeth!). A shark may grow and use over 20,000 teeth in its lifetime! Normally, sharks eat alone. But sometimes one feeding shark attracts others. They swim up as quickly as possible and all begin to try to get a piece of the prey. They bite wildly at anything that gets in their way -- even each other. The great white shark rarely partakes in feeding frenzies. Almost all sharks are "carnivores" or meat eaters. They live on a diet of fish and sea mammals (like dolphins and seals) and even such prey as turtles and seagulls. Sharks even eat other sharks. For example, a tiger shark might eat a bull shark, a bull shark might eat a blacktip shark and a blacktip shark might eat a dogfish shark! The teeth of the carnivores are sharp and pointy. Their skeleton is made of cartilage instead of bone, which allows greater flexibility. Their skin is made of denticles instead of ordinary fish scales. The denticles are constructed like hard, sharp teeth and help to protect the shark from injury. Not all sharks are fierce carnivores. Some are quite harmless. Oddly enough, the most harmless sharks tend to be the largest! The basking shark, the whale shark and the megamouth sharks all fit this description. These huge sharks eat plankton, a tiny shrimp-like creature found in the ocean. To do this, they swim forward with their mouths wide open. "Gill rakers" at the back of their throat strain the tiny food from the water. Think sharks are dangerous? The most dangerous sharks are the Great White shark, the Tiger shark, the Hammerhead shark, the Mako shark and the Bull shark. On average, there are only about 100 shark attacks each year and only 10 of those result in a human death. You should check it out from their perspective, though! People kill thousands of sharks in a year for sport and for food. Shark skins are used to make products like any other leather would be. Up until the 1950's, shark livers were used as a vitamin A supplement. Shark fin soup and shark steaks are both eaten in many countries (Mako, seen in the top photo, is the most popular in the United States). Baby sharks are called pups. Just like there are many types of sharks, there are also different ways that sharks come into this world. There are three ways that sharks are born: eggs are laid (like birds) eggs hatch inside the mother and then are born pups sharks grow inside the mother (like humans) Sharks can have from 1 to 100 babies at a time, depending on the type of shark. The ones with pups that grow inside the mother have fewer babies at a time than sharks that lay eggs outside the body. Sharks do not care for their babies after they are born, but they do search for a safe place where they can lay their eggs or give birth. One of the reasons that sharks are such successful predators is that they have such super senses. Two-thirds of a shark's brain is dedicated to its keenest sense -- smell. Some sharks have eyes similar to a cat. A mirror-like layer in their eyes allows them to see better in the water. This allows the shark to hunt in clear seas or murky water. To top it off, sharks have a few unusual senses. For instance, they are able to feel vibrations in the water using a line of canals that go from its head to its tail. Called a "lateral line", these canals are filled with water and contain sensory cells with hairs growing out of them. These hairs move when the water vibrates and alerts the shark to potential prey. Sharks also have a sensory organ called the "ampullae of Lorenzini" which they use to "feel" the electrical field coming from its prey.

2楼网友：毛毛
2021-01-29 05:41

what is a shark? sharks are a type of fish. sharks are amazing fish that have been around since long before the dinosaurs existed. they live in waters all over the world, in every ocean, and even in some rivers and lakes. unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. sharks also have no swim bladder (unlike bony fish). ________________________________________ major differences between sharks and bony fish attribute sharks bony fish skeleton cartilage only bones and cartilage swimming can only swim forward. can swim forwards and backwards buoyancy (floating) large oily liver gas-filled swim bladder gills gill slits but no gill cover covered gill slits reproduction eggs fertilized in female's body. eggs usually fertilized in the water. skin rough, sandpaper-like placoid scales slippery, overlapping scales size a scuba diver above a whale shark. the whale shark is the largest fish in the world; the basking shark is the second largest fish. there are many different species of sharks that range in size from the size of a person's hand to bigger than a bus. fully-grown sharks range in size from 7 inches (18 cm) long (the spined pygmy shark), up to 50 feet (15 m) long (the whale shark). most sharks are intermediate in size, and are about the same size as people, 5-7 feet (1.5-2.1 m) long. half of the 368 shark species are under 39 inches (1 m) long. ________________________________________ body shapes sharks have a variety of body shapes. most sharks have streamlined, torpedo-shaped bodies that glide easily through the water. some bottom-dwelling sharks (e.g. the angelshark) have flattened bodies that allow them to hide in the sand of the ocean bed. some sharks have an elongated body shape (e.g., cookiecutter sharks and wobbegongs). sawsharks have elongated snouts, thresher sharks have a tremendously elongated upper tail fin which they use to stun prey, and hammerheads have extraordinarily wide heads. the goblin shark has a large, pointed protuberance on its head; its purpose is unknown. ________________________________________ varieties of sharks there are about 368 different species of sharks, which are divided into 30 families. these different families of sharks are very different in the way they look, live, and eat. they have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. some types of shark are very rare (like the great white shark and the megamouth) and some are quite common (like the dogfish shark and bull shark). sharks belong to the group of cartilagenous fish, the elasmobranchii, that includes the sharks, rays, and skates. there are over 350 different species of sharks. the spiny dogfish shark is the most common shark.

3楼网友：一叶十三刺
2021-01-29 04:47

Out of all the species walking, flying, slithering or swimming, there aren't many who have been around as long, survived as well, or come in so many shapes and kinds as the shark. The earliest evidences of sharks are isolated spines, teeth and scales that appeared about 430 million years ago in the Silurian Period, known as the "Age of Fishes". Sharks have a sleek, streamlined design which helps them swim without using up a lot of energy.They certainly need to conserve their energy because they never really sleep and most of them never stop swimming. Some sharks are fierce predators, and would be happy to eat you if they encountered you. Almost any shark six feet or longer is a potential danger, but three species have been identified repeatedly in attacks: the Great White Shark, the Tiger Shark and the Bull Shark . All three live world wide, reach large sizes and eat large prey such as marine mammals or sea turtles. But most sharks never grow longer than five feet and never even see anyone with legs and arms anyway. People kill thousands more sharks every year than sharks kill people. Sharks take about as long to mature as we do. Some of them become adults in their teens. A mother shark carries her babies inside her body while they develop, sometimes for more than a year. Even so, some sharks are born inside an egg which they have to crack open. They spend early portions of their lives in nursery grounds. Some of the advantages sharks have over people is that they keep growing new teeth, they don't have breakable bones, and they are not prone to get cancer. Sometimes sharks are referred to as swimming computers because of the six senses which they possess: vision, hearing, vibration, smell, taste and electro-perception.

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