Sharks are some of the ocean ’ s top predators. In fact, sharks and their relatives were the first gear vertebrate predators on earth .
Shark fossils date back more than 400 million years – that means sharks managed to outlive the dinosaurs, survive mass extinctions, and continue to serve an authoritative function near the top of subaqueous food chains .
After millions of years of adaptations, more than 500 species of sharks swim the planet ’ sulfur oceans today, and sharks are found in about every character of ocean habitat. So how have sharks evolved to suit their environments ?
From ancient ancestors to modern sharks
To understand how modern sharks adapted and evolved, we first have to look back through the fossil record of their ancestors .
Originating from a prison term before dinosaurs walked the earth, the earliest shark scales date back about 425 million years, and the earliest shark teeth are from the devonian Period, about 410 million years ago. And some fossils of shark-like chondrichthyans scales ( from a group of pisces including sharks, rays, and their relatives ) date as far back as 440 million years .
Because shark skeletons are made of soft cartilage, which doesn ’ triiodothyronine fossilize well, most of what scientists know about ancient sharks comes from teeth, scales and fin spine fossils. But the cartilage of early sharks would besides be similar to shark cartilage today, which distinguishes sharks from most pisces that have heavier skeletons made of bone. Having a skeletal system made of lightweight cartilage allows sharks to conserve energy and swim hanker distances .
Because shark skeletons are made of gentle cartilage, which does n’t fossilize well, most of what scientists know about ancient sharks comes from teeth, scales and five spinal column fossils .
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“ From some of the soft tissue we have found fossilized, early sharks would have had a similar body plan to most advanced day sharks, ” said Emma Bernard, pisces dodo curator at the british Natural History Museum .
That means sharks ’ bodies were tapered at both ends and the fins were in similar places, optimized to make them high-speed predators. But the size of sharks varies greatly. contemporary sharks can range from approximately 1 to 55 feet. And according to Bernard, sharks about 60 feet long ( 18 meters ) exist in the fossil commemorate .
“ The coarse thread is that they exploit different parts of the marine ecosystem, ” Bernard explained. “ So the more renaissance man an animal is the more likely it will be to adapt and survive changes in its environment, and the group as a whole will survive. ”
Wide variety of sharks and adaptations
Teeth are one beneficial example of how modern day sharks evolved in different ways. many early sharks had conic, non-serrated tooth. meanwhile, many sharks today evolved to have triangular teeth that were categoric and serrated like a steak knife, which helps them bite off chunks of prey.
But not all shark teeth are the same. Some bottom-dwelling sharks that feed on mollusks have teeth suited to grinding and cracking shells exposed. Others, such as goblin sharks ( which have a brainsick chew protrusion ), have needle-like teeth used for piercing pisces. And the biggest fish in the ocean, the filter-feeding whale shark, eats plankton and doesn ’ deoxythymidine monophosphate actually use its 300 rows of target teeth to eat .
A rare goblin shark was caught by fishermen off fleeceable Cape on the australian seashore. Goblin sharks, which are recognizable due to their large jaw proturusion, have needle-like teeth used for piercing pisces .
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“ The most interest adaptation for me, as person who studies shark feeding, is probably their tractability in diet, ” said shark development research worker Lisa Whitenack in an e-mail. “ If one prey type decreases in abundance, then they could potentially switch to something else. ”
Sharks besides have a wide variety of migration patterns. Marine conservation biologist David Shiffman said. He once saw a nanny shark stay under the lapp rock for a week .
“ But some shark migrations are thousands of miles, ” Shiffman said. “ It ’ s amazing how far they can swim and for how long. ”
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Some species travel long distances on a daily basis, yo-yo-ing from shallow to deep water to hunt. For example, the bluing shark will dive more than a thousand feet during the day but refund to the surface to spend the night .
In general, sharks and their adaptations are unmanageable to generalize .
“ They are in deep urine and shallow water, cold and warm water, even occasionally freshwater, ” said Whitenack, an Associate Professor of Biology and Geology at Allegheny College. “ When you look at ‘ sharks ’ as a group, it ’ s no wonder that they ’ ve survived multitude extinctions – chances are some small pocket of species will survive somewhere. ”
Need for speed
One way to survive in an ocean full of early predators is to be fast. so many sharks are built for accelerate .
Shark skin is made up of bantam v-shaped scales called dermal denticles, because they resemble teeth more than fish scales. These bark denticles decrease haul in the body of water and aid sharks glide more quietly .
A blue shark in the Atlantic ocean near Pico in the Azores Islands. Blue sharks can migrate on a casual basis, diving more than a thousand feet during the day but returning to the coat at night .
many sharks ’ tails, called caudally fins, are larger on peak than on the bottom, which allows the animals to swim more efficiently .
Some sharks besides have a mechanism on their caudal fins called a horizontal keel, which reduces turbulence and allows them to swim faster .
One of the fastest fish in the ocean is actually a shark – the shortfin mako – which can reach a exceed speed of about 55mph. Unlike other sharks that swim in a wavy design, mako sharks swim in a straight traffic pattern. These quick sharks besides have a face shaped like a cone to glide through the body of water more efficiently .
A sixth sense
Sharks besides have an extra sense – the ability to sense electromagnetic fields. That means they can detect the Earth ’ s magnetic field ampere well as the small electric fields that marine animals create when moving their muscles .
“ They use that for navigation, to swim in the clear ocean, and besides to find prey that ’ s buried under the backbone, ” Shiffman said. “ That ’ s why hammerheads have that human body. It ’ s like sweeping a alloy detector across the sand. ”
A dunce shark ‘s steer shape acts like sweeping a metallic element detector across the sand, using their ability to sense electromagnetic fields in order find prey that ‘s buried under the sandpaper .
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Sharks can besides detect vibrations in the water, using extra cells that run in a line along the middle of their bodies. This “ lateral line ” system allows sharks to sense ripples in the water created by their prey, meaning they can even hunt in the benighted .
Despite adaptations, sharks face threats
As a solution of these adaptations, most bombastic sharks have few natural predators apart from other sharks. But about 100 million sharks are killed each year by humans .
Movies would have you think that sharks are bloodthirsty predators that pose a threat to swimmers and surfers. But actually, people pose a much greater risk to sharks than the other means around .
The tooth and call on the carpet of a Great White Shark are displayed in Sydney, Australia. many sharks today evolved to have trilateral teeth that were directly and serrated like a steak knife, which helps them bite off chunks of raven.
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“ The biggest terror facing sharks as a group is unsustainable overfishing, ” Shiffman said. “ Some of it is shark being targeted, and some of it is shark being caught as by-catch, typically for tuna and swordfish. ”
Despite adaptations that make them great predators, sharks – and their ecosystems – are even at risk. Losing sharks due to overfishing and amateur fish can harm ecosystems and disrupt the food chain in unintended ways .
“ It ’ s important to have goodly shark populations, ” Shiffman said. “ Predators at the top of the food chain help regulate the food chain. They eat the disgusted and the unaccented, and that keeps prey populations from growing out of control condition. ”