Shark

Sharks make up a family of elasmobranch fishes. They also have about five to seven slits on the side of their head for their gills. Their pectoral fins are not fused to their heads.

Experts believe that there are over 500 species grouped into 8 living orders. Some of the common species include salmon, tiger, great white, whale, and bull sharks.

Incredible Shark Facts

• Boneless creatures: Sharks are fish that do not have any bones at all. Instead, their body is primarily made of cartilage, which is the same material that the human nose and ears are made from.
• Good eyesight: They have pretty good eyesight, which means that they can also see clearly in dimly lit areas.
• Sandpaper texture: The skin of these fish often feels like sandpaper. This is because their skin has small, tooth-like structures.
• Immobility trance: These fish can become immobile when flipped upside down.
• Ancient fishes: Sharks are ancient fish, and scientists believe that these fish have been around for more than 450 million years.
• Land sharks: One species of shark — the epaulette shark — has evolved the ability to walk on land over small distances.
• Sixth Sense: Sharks have long been thought to have a sixth sense.

Evolution and Origins

Sharks are some of the most ancient groups of fish species on the planet. They have a rich history that dates back over 400 million years. They belong to the class of Chondrichthyes. This class also includes sting rays and chimaeras. These types of animals are characterized by their cartilaginous skeletons. They have five to seven gills, and they do not have a swim bladder.

The earliest known shark appeared in the oceans during the Silurian period. This was about 420 million years ago. These primitive sharks were small and had dorsal fins covered in very sharp scales.

Over time, sharks have evolved to become more diverse and complex beings. This includes their different body shapes and diets. Some important evolutionary sharks include the great white and the mako shark.

Classification and Scientific Name

Sharks belong to the superorder Selachimorpha. These fish belong to the kingdom Animalia and phylum Chordata. Their class is Chondrichthyes.

Selachimorpha comes from a combination of ancient Greek words, sélakhos and the suffix -morpha. Sélakhos means “cartilaginous fish.” However, the word can be broken down even further to the root “sélas,” which means “light” or “glow.” These pre-Greek origins are likely due to the phosphorescent light that some of these sharks have.

Within the Selachimorpha superorder, eight orders are still alive, which include Squatiniformes, Pristiophoriformes, Squaliformes, Carcharhiniformes, Lamniformes, Orectolobiformes, Heterodontiformes, and Hexanchiformes. Four orders of these fish have gone extinct, but there are still over 500 different species alive today.

Different Species

Even with four different orders extinct, the fish still manages to have quite a few variations. Some of these species have no anal fin, while others do. Everything from the positioning of the mouth to the length of their snout can differentiate between other species.

Some of the most notable types of sharks include:

• Great white shark (Carcharodon carcharias): Perhaps the most popular and well-known, the Great White can reach lengths of about 20 feet. Plus, these fish can reside in the ocean for 30 years, swimming along coastal waters.
• Cookiecutter Shark: The cookiecutter shark takes its name because it leaves a cookie-shaped bite hole in its predators. These sharks have the largest teeth relative to their body size of any shark species at any location. Like all sharks, it loses its teeth and grows new ones throughout its life.
• Ragged-tooth shark (Carcharias taurus): These sharks stand out for an interesting reason — they gulp air. Much like a mammal would, this species will hold onto the air in its stomach so that it can stay in the same place. Their dagger-like teeth are lined along two rows on both their top and bottom jaw, though they actually lose up to three teeth daily. Even with their ferocious appearance, they are fairly harmless if left alone.
• Bull shark (Carcharhinus Leucas): Primarily residing in freshwater areas, the bull shark will seek out shallow areas. They have special glands that provide them with the salt that their bodies need, allowing them to journey where they need to go for food.
• Tiger shark (Galeocerdo cuvier): These sharks can grow as long as 18 feet, and they are pretty easy to identify with their vertical stripes and spots. They will live in both shallow and deep waters, and their jaws are powerful enough to break apart the shell of a sea turtle.
• Salmon shark (Lamna ditropis): Salmon sharks can be very dangerous to humans. At about 6.5 feet long (at their shortest), they typically live in the northern region of the Pacific Ocean. They are able to regulate their own stomach temperature, though this feature is rare amongst sharks in general. They’re considered one of the fastest sharks in the world.
• Nurse Shark (Ginglymostoma cirratum): These sharks don’t pose any threat to humans unless they are disturbed. In fact, many people swim right by these sharks without ever knowing they were there.
• Horn Shark (Heterodontus francisci): The horn shark moves by pushing itself along the bottom with its strong fins. This shark is very sensitive to light. It spends almost all its life hidden in crevices, shadows, or dark waters.
• Goblin Shark (Mitsukurina owstoni): The Goblin Shark, which is sometimes referred to as a living fossil, is a type of shark that is found in the deep sea. This unique-looking shark is easily identified by its long snout, protruding jaws, and semitranslucent skin. Goblin Sharks have been found in all three of the major oceans. Because they live so deep under the water, there are still a lot of unknowns about this creature.
• Greenland Shark (Somniosus microcephalus): This shark has the longest lifespan of any vertebrate. The Greenland shark, called eqalussuaq by the Inuit people, is famous for living to a great age. Biologists believe that this large, slow fish can live to be half a millennium old. Its longevity probably has something to do with the fact that it does everything slowly. It swims slowly. It reproduces slowly. It catches prey by sneaking up on them when they’re asleep and then attacking.
• Grey Reef Shark (Carcharhinus amblyrhynchos): Grey reef sharks are voracious marine predators that prefer shallow waters and are among the most common sharks found in coral reef habitats throughout the Indo-Pacific region.
• Basking Shark (Cetorhinus maximus): These sharks tend to swim with their big mouth hanging wide open, which can be intimidating to divers who don’t know better.
• Hammerhead Shark: Hammerhead sharks are best known for their long, rectangular heads. They tend to swim at an angle to decrease drag and increase their swimming efficiency.
• Frilled Shark (Chlamydoselachus anguineus): Frilled Sharks got their name from the six rows of gills on their throat that look like ruffled collars.

Appearance

These fish have a cylindrical shape and tapered edges. This body structure allows them to smoothly sail through deep waters in search of their prey. However, the length of their body and even their snout can be different from species to species.

Sharks are usually 19 to 23 feet long, which is at least 3 times the height of the average human. While the smallest species is less than 7.9 inches long, the largest one is about 39.4 feet long. Sharks usually have a body weight of around 1,500 to 4,000 pounds. However, some can also weigh about 5,500 pounds. Sharks are an animal that never stops growing, so larger sharks are generally very old.

These fish are naturally colored to be able to camouflage and blend with their surroundings, typically to catch the prey easily. The dorsal side of their body is darker than the ventral side. Therefore, when seen from above, the body of the shark would usually blend with the dark atmosphere of the ocean.

Distribution, Population, and Habitat

Sharks, along with their sister group of rays, have, over millions of years, adapted to living in a wide range of habitats. While some of them live in shallow and coastal regions, others live in deep waters. Some others are found in the open oceans or on the ocean floors.

Even though these large fish are found in several places around the world, they are mostly and most commonly found in the water around the USA and Australia. There are only a few species (i.e., the bull shark and the river shark) that live in freshwater areas, but the highest number are found in the waters of New South Wales in Australia. They can also be found in the Indian Ocean, near Brazil, and even as locally as North Carolina.

According to experts, there are over 500 recognized living shark species around the world, grouped into 8 living orders.

Predators and Prey

As big as these fish may be, most people believe that this fish has no natural predators, but they would be incorrect. Both killer whales and sperm whales will consume smaller shark breeds as their nourishment, but they also consume their fair share of animals in the sea.

What Sharks Eat

Sharks have no qualms about consuming their relatives, as larger sharks will consume other species as well. All of them are carnivores, which means that they will only eat other animals for their nourishment. Most sharks enjoy a balanced diet of dolphins, seals, turtles, and even seagulls. They seek out other fish and sea mammals as well.

What Eats Sharks

As stated above, these fish face the threat of other sharks coming after them as food. Apart from their own species, the amount of fat and protein that they offer makes them ideal for the diet of an orca whale or a sperm whale. In fact, these orcas, also known as killer whales, are apex predators, and even the largest sharks cannot hunt them.

Reproduction and Lifespan

These fish do not reproduce like other fish. Generally speaking, fish lay eggs, and while some species of shark do lay eggs, many others use internal reproduction, much in the same way that mammals do. There are three ways that sharks are known to reproduce.

The first is oviparity; in other words, egg-laying. These sharks produce eggs that are encased in a tough, leathery-like egg case. Female sharks will spend plenty of time laying their eggs to ensure they are secured in safe place for a 6- to 9-month incubation period. Different species’ eggs will have varied features such as curled tendrils, horns, or sticky mucus filaments that help the egg case attach to a substrate, which could be anything from the seabed or reef to seaweed. Embryos develop in these egg cases, which provide protection and all that growing sharks need during the incubation period. The sharks born this way emerge as miniature versions of adults. A few examples of shark species that reproduce in this way are catsharks, horn sharks, and swell sharks.

Ovoviviparity is the second way that sharks reproduce. In this scenario, female sharks do not lay their eggs but carry them inside their bodies until they hatch, at which point the females will give birth. While in utero, these sharks receive their nourishment from eating yolk sac—either their own or another’s. Mako sharks, porbeagles, and sand tiger sharks reproduce in this way. Interestingly, after hatching, not all pups are immediately born. In fact, some will stay in their mother’s uterus where they may engage in intrauterine cannibalism. The lesser but far more common form is oophagy, in which these sharks will feed on tiny, unfertilized eggs. Sand tiger sharks (Carcharias taurus) are the only shark species to be observed participating in the more extreme form of intrauterine cannibalism: adelphophagy, which is the eating of other embryos (i.e., their siblings).

Live birth, or viviparity, is the third method of shark reproduction. Like mammals, a true placenta connects the embryo to the mother’s bloodstream for nutrients. Baby sharks develop inside their mother’s body; however, when born, unlike mammals, these shark pups are immediately independent and do not rely on their parents to fend for them. Some examples of species that reproduce viviparously are lemon sharks and blue sharks. This is the same method used by mammals.

Male sharks have two organs that are attached to their anal fins for the purpose of reproduction. When mating, a male shark will insert one of them into the female’s cloaca. During insertion, sperm is transferred from the male to the female. The sperm then fertilizes the eggs inside the female.

Asexual reproduction, or parthenogenesis, has been seen, albeit rarely, in a few shark species in captivity, notably zebra sharks. In such cases, females reproduce without males, producing offspring that are genetically similar to the mother (essentially clones). Little is known or understood about why this happens or how.

Though the exact amount of time varies by species, these fish species are well-known for having long gestations. Great whites, for example, are estimated to carry their eggs (they are ovoviviparous) for 11-18 months, which is significantly less than the 24 months that spiny dogfish shark, also ovoviviparous, are pregnant. Spiny dogfish sharks have the longest-known gestation period. Other shark species’ gestations are as short as five or six months, such as with bonnethead sharks.

The lifespan of sharks varies widely by species; many live 20 to 30 years, but some, like great white sharks, can live up to 70 years, and the Greenland shark can live for several centuries (it is believed).

Fishing and Cooking

Most of these fish are fished out for commercial purposes. They are cooked widely, especially in the United States. Due to their body weight, they are a good meat source for humans.

People love eating shark steaks, which are prepared using a wide variety of spices and are later cooked in oil before being savored by humans.

CORRECTION: This article was updated on December 29, 2025, to clarify the different ways in which sharks reproduce.