Shark

Sharks live in the sea. Some are very big. The whale shark is the largest fish.

Other sharks are very small.

Sharks have a special body. Their bones are made of cartilage. This is soft and bendy. It helps them stay light.

Sharks have many teeth. They lose teeth all the time. New teeth grow to take their place.

Their skin has tiny scales. These scales protect their skin. They also help sharks swim fast.

Many sharks are at the top of the food chain. They are great hunters in the ocean.

Sharks are a group of fish that live in the sea. They come in many different sizes. The whale shark is the largest fish in the world.

It can grow very long. Other sharks are quite small. The dwarf lanternshark is only about 40 centimeters long.

Sharks have a unique body. Instead of hard bone, they have a skeleton made of cartilage. Cartilage is a flexible and durable material. It is much lighter than bone. This helps sharks save power when they swim.

Their skin is covered in tiny scales called dermal denticles. These scales protect their skin from damage. They also help the shark swim through water more easily. Some sharks have patterns on their skin for camouflage. This helps them hide from prey.

Sharks also have many rows of teeth. They are constantly replaced throughout their lives. A shark might lose 30,000 teeth or more!

New teeth move forward like a conveyor belt to take the place of old ones.

Sharks are a fascinating group of fish found in all the world's seas. They belong to a group called elasmobranchs. These fish are different from most others because they have skeletons made of cartilage.

This material is flexible and very durable. It is also much lighter than bone. This lightness helps sharks save energy while they swim. Because they lack a rib cage, they would be crushed by their own weight on land.

How a shark works involves many clever body parts. Their skin is covered in tiny scales called dermal denticles. These scales protect the skin and help the shark move through water smoothly. Sharks also have many rows of replaceable teeth. These teeth move forward like a conveyor belt. A single shark might lose over 30,000 teeth in its life!

The shape of the teeth depends on what the shark eats.

Sharks have a very long history on our planet.

Some fossilized shark-like scales are as old as 458 million years. The earliest confirmed modern sharks appeared during the Early Jurassic period.

One of the oldest known members was a shark named Agaleus. Other shark-like creatures, called hybodonts, were very common in the Triassic and Early Jurassic. Over time, modern sharks grew and became more diverse. They eventually replaced the older groups of shark-like fish.

There are more than 500 different species of sharks today.

They come in many different sizes and shapes. The whale shark is the largest fish in the world.

It can grow to be about 12 meters long. On the other end, the dwarf lanternshark is only about 40 centimeters long. Some sharks are apex predators, meaning they are at the top of the food chain. Examples include the great white shark and the hammerhead shark. Others, like the basking shark, eat tiny plankton.

Sharks are closely linked to the ocean life you might see in books.

They are related to rays and skates, which are also cartilaginous fish. While most sharks live in salt water, some can live in fresh water. The bull shark and the Ganges shark are examples of this. Humans have a complex relationship with sharks too. People catch them for meat and fins. Since 1970, shark populations have dropped by 71% due to activities like overfishing.

Sharks are a diverse group of cartilaginous fishes belonging to the division Selachii.

Unlike most bony fish, sharks are characterized by a ribless endoskeleton made of cartilage. This flexible and durable material is about half the density of bone. This lightness helps sharks save energy during swimming. However, because they lack a rib cage, sharks can be crushed by their own weight on land. They are part of the subclass Elasmobranchii, which also includes rays and skates.

Modern sharks are considered the sister group to the Batomorphi, which includes those rays and skates.

The anatomy of a shark is built for efficient movement and hunting.

Their skin is covered in placoid scales, also called dermal denticles. These tiny structures improve fluid dynamics by reducing turbulence as the shark swims. They also provide a protective layer against damage and parasites. Many sharks have a dermal corset made of flexible collagenous fibers. This helical network acts like an outer skeleton to support swimming muscles. Some species use pigmented denticles to create patterns like spots or stripes for camouflage.

A shark's feeding mechanism is highly specialized through its teeth and jaws.

Teeth are not fixed to the jaw but are embedded in the gums. They grow in multiple rows that move forward like a conveyor belt. A single shark may lose more than 30,000 teeth during its lifetime. The replacement rate varies from every 8 to 10 days to several months. Tooth shape is determined by diet. For example, those eating mollusks have flat teeth for crushing. Fish-eaters have needle-like teeth for gripping. Predators of mammals have triangular, serrated teeth for cutting.

Sharks have a deep evolutionary history spanning hundreds of millions of years.

Some fossilized scales date back to the Late Ordovician, about 458 to 444 million years ago. The oldest total-group chondrichthyans, called acanthodians, appeared in the Early Silurian. Shark-like creatures such as Cladoselache first appeared in the Devonian Period. The earliest confirmed modern sharks, known as Selachii, appear in the Early Jurassic. One of the oldest members was a species called Agaleus. During the Jurassic, true sharks underwent great diversification and replaced the previously dominant hybodonts.

There is an incredible range of sizes and lifestyles among the 500 known species. The whale shark is the largest fish in the world, reaching approximately 12 meters in length.

In contrast, the deep-sea dwarf lanternshark is only about 40 centimeters long. Many sharks are apex predators at the top of the food chain. This group includes the great white shark, tiger shark, and hammerhead shark.

Other species, like the basking shark, are planktivores that filter-feed on tiny organisms. Most sharks live in the ocean, but the bull shark and Ganges shark can live in freshwater.

Sharks are organized into many different biological orders.

The order Carcharhiniformes includes ground sharks like the hammerhead and bull shark. These sharks often have an elongated snout and a nictitating membrane to protect their eyes. The Lamniformes, or mackerel sharks, include the great white and the extinct giant megalodon.

Some orders have very unique shapes, such as the sawsharks of the order Pristiophoriformes. These sharks possess an elongated, toothed snout used for slashing prey. Other groups include the flattened angel sharks and the snake-like frilled sharks.

Human activity has a significant impact on modern shark populations.

Many sharks are caught for their meat or their fins. Since 1970, shark populations have been reduced by 71%. This decline is largely due to overfishing and the practice of shark finning. Understanding the biology and history of these animals helps us see their importance to the ocean. Sharks serve as vital components of marine ecosystems, maintaining the balance of the food web through their roles as both predators and filter-feeders.