Sharks have lived on Earth for approximately how long?

Sharks have existed for more than 450 million years, whereas the earliest tree, lived around 350 million years ago. Not only are sharks older than trees, but they are also one of the only animals to have survived four of the five mass extinctions – now that’s impressive.

Emma Bernard, a curator of fossil fish at the Museum, says, 'Shark-like scales from the Late Ordovician have been found, but no teeth. If these were from sharks it would suggest that the earliest forms could have been toothless. Scientists are still debating if these were true sharks or shark-like animals.'

Analysis of living sharks, rays and chimaeras suggests that by around 420 million years ago, the chimaeras had already split from the rest of the group. As there are no fossils of these animals from this period of time, this is based solely on the DNA and molecular evidence of modern sharks and chimaeras. It was also around this time that the first plants invaded the land.

By the middle of the Devonian (380 million years ago), the genus Antarctilamna had appeared, looking more like eels than sharks. It is about this time that Cladoselache also evolved. This is the first group that we would recognise as sharks today, but it may well have been part of the chimaera branch, and so technically not a shark. As active predators they had torpedo-shaped bodies, forked tails and dorsal fins.   

Credit : Natural History Museum

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Where did great whites get their name?

While the shark in Jaws was inspired by a great white shark in New Jersey, the legendary fish is far less fearsome in reality. As scientific research on these elusive predators increases, their image as mindless killing machines is beginning to fade.

Found in cool, coastal waters around the world, great whites are the largest predatory fish on Earth. They grow to an average of 15 feet in length, though specimens exceeding 20 feet and weighing up to 5,000 pounds have been recorded.

They have slate-gray upper bodies to blend in with the rocky coastal sea floor, but they get their name from their white underbellies. They're streamlined, torpedo-shaped swimmers with powerful tails that can propel them through the water at speeds of up to 15 miles per hour. They can even leave the water completely, breaching like whales when attacking prey from underneath.

Credit : National Geographic

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What is the baby shark called?

Baby sharks, which are known as pups, can be born in three quite different ways. First, some sharks lay eggs. We call this oviparous. The “mommy shark” lays an egg case in a good spot and swims away. The egg case, which is sometimes called a “mermaid’s purse,” can be perfectly camouflaged to blend in with the sea floor or algae. The egg includes all of the nutrition the pup will need to grow from a fertilized embryo to a fully functioning shark pup. When the pup is ready, it emerges from the egg case and is totally independent.

Second, some sharks grow from eggs–but inside the mother shark’s body. This is called ovoviviparous. In this type of reproduction, there is no placenta to link the “mommy shark” and the “baby shark.” The shark pup gets all of its nutrition from its own egg yolk, other egg yolks, or (yikes!) from eating its fellow fertilized eggs or other pups. Ovoviviparous sharks give live birth to a fully independent pup. This is how sand tiger sharks, like the ones you can see at the Greater Cleveland Aquarium, reproduce.

And third, some sharks do have a placenta and directly support the shark embryo until it is ready to be born as a pup. This is called viviparous, and is also how humans are born. When the shark pup has matured enough, it is born and swims away. This is how sandbar sharks, which you can also see at the Aquarium, have pups.

Credit : Great clevel and aquarium 

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What kind of animal is a great white shark?

Like almost all shark species, Great White Sharks have a highly distinctive appearance with large, torpedo-shaped bodies and a pointed snout. They have very tough skin that is covered in tiny teeth called denticles that is slate-grey to black in colour on the top of their bodies which helps them to remain camouflaged into the rocky, coastal sea floors where they are most commonly found. The underside of the Great White Shark is white and is what has led to their name. Great White Sharks have powerful, crescent-shaped tail fins that help to propel them through the water at a tremendous speed, and are aided by their pectoral (side) fins that are held out in fixed wings to prevent the Great White Shark from sinking. The large and highly characteristic dorsal (back) fin of the Great White Shark is used to help them to steer through the water, along with diving and helping them to balance. One of the most characteristic features of the Great White Shark is their jaw. Their mouths are filled with up to 300 serrated, triangular teeth that are arranged in rows and are replaced continuously throughout their lives. Each tooth can grow to around 6cm in length providing Great White Sharks with a formidable bite when they are attacking their prey.

Great White Sharks are fearsome carnivores that primarily hunt large marine mammals in order to gain their nutrition. Seals, sea lions, porpoises, dolphins and smaller whales are among their most commonly hunted prey species around the world. Great White Sharks have poor eyesight in comparison to their other senses and use both their sense of smell and ability to detect vibrations caused by animals in the water to detect their prey. Once located, Great White Sharks fiercely attack with great speed and force before retreating and leaving their wounded prey to weaken before returning to feed once it is safe to do so. Although they are largely solitary, Great White Sharks can be seen in pairs or small groups to feed on a large whale carcass. In these circumstances, larger and more dominant individuals feed first with varying swimming display patterns thought to contribute to establishing their dominance hierarchy.

Credit : a-z animals

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Which internal organ helps a shark floats?

Sharks do not have a swim bladder. Instead, they have a large liver filled with oil. Because oil is less dense than water, all of this oil helps sharks float in the ocean.

Sharks have livers different from other animals. It takes up much more internal space and serves more functions than simply helping with digestion; the oil inside the liver helps sharks stay buoyant under water.

While digestion is an important function of a shark's liver, it's not the reason the liver is so big or why it's filled with oil. The oil, called squalene, is lighter than the water. A shark's body is naturally heavier than water, and he doesn't have a swim bladder to fill with air like some other fish. The oil lightens the shark's body, providing buoyancy so he won't sink. Sharks must keep swimming to push water past their gills to breathe, and buoyancy is key to keeping on the go and staying off the ocean floor. Sharks use their pectoral fins to help them change directions in the water, but without the oil, sharks would expend too much energy swimming and staying buoyant than they could replace with their food.

Credit : Pets on Mom

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