About Sharks
Sharks are the most fascinating of creatures. They have been around far longer than humans and have an undeservedly bad reputation. They live all over the world, mostly in salt water, and actually do not like to eat humans.
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History
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Sharks are one of the oldest species on Earth. Fossils of shark teeth have been dated to 400 million years ago, while modern sharks are thought to have emerged 100 million years ago. Sharks were swimming in the oceans before any vertebrates or plants existed on solid ground. One shark that existed about 370 million years ago, Cladoselache, lived in the area that now makes up Ohio, Kentucky and Tennessee. Back then, this area was not solid land but a shallow ocean, and it covered most of what is now the North American continent.
Types
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There are close to 500 different species of sharks, and they are classified into eight different types.
Hexanchiformes include cow sharks and frilled shark. Squaliformes include the bramble sharks, dogfish and roughsharks, and the prickly shark. Pristiophoriformes are sharks with one particular distinction: They have an extra-long nose, as well as sharp teeth that they use to slash fish before eating them. Squatiniformes are the Angel Sharks. They are often confused with stingrays and skates. Heterodontiformes are bullhead or horn sharks. Orectolobiformes include zebra sharks, nurse sharks, wobbegongs and the whale shark. Carcharhiniformes include the blue, tiger, bull, grey reef, blacktip reef, Caribbean reef, blacktail reef, whitetip reef, oceanic whitetip sharks, houndsharks, catsharks and hammerhead sharks. Lamniformes include the goblin shark, basking shark, megamouth shark, thresher shark, shortfin and longfin mako shark, and Great White shark.
The smallest shark is the Dwarf Lantern Shark, at 7 inches, and the largest is the Whale Shark, at 30 feet long.
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Features
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A shark does not have bones. The entire skeleton is made up of cartilage. If a shark loses one of its teeth, there is another one waiting to take its place.
Sharks are fish, and they get their oxygen from the water, with enters their body through gills behind their head. Sharks have to be constantly swimming in order to breathe. If they sleep for a long time, they will sink. (One exception to the rule is the Nurse Shark.) Most sharks will live to be between 20 and 30 years old, but the Whale Shark holds the record at about 100 years.
Sharks have a keen sense of smell and hearing. Their sight is not as well-developed, and varies by species.
Food
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Some species, like the Whale Shark, only feed on plankton, squid and small fish. Sharks like the Great White eat fish and marine mammals like seals. Sharks that live on the bottom of the ocean eat mollusks and crustaceans.
Misconceptions
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Sharks are thought to be solitary creatures, but only a few of them are. Most live in large schools, sometimes with other species of sharks. Sharks are thought to be dangerous to humans, but only four out of the hundreds of different species have been known to attack humans--probably because they mistook the human for a seal or other prey. Humans simply do not taste good to sharks.
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