1. The first sharks lived more than 400 million years ago—200 million years before the first dinosaurs. They have changed very little over the eons.^b
2. Sharks belong to a group of fish known as the elasmobranchs, or cartilaginous fishes. Rays and skates, which may have evolved from sharks, also belong to this group.^a
3. Because sharks very rarely get cancer, scientists study their cartilage in the hopes of finding a cure for the disease.ⁱ
4. Hammerhead sharks’ heads are soft at birth so they won’t jam the mothers' birth canals.^h
5. The first written account of a shark attack is found in Herodotus’ (c. 484–425 B.C.) description of hordes of “monsters” devouring the shipwrecked sailors of the Persian fleet.^f
6. When a shark eats food that it can’t digest (like a turtle shell or tin can), it can vomit by thrusting its stomach out its mouth then pulling it back in.ⁱ

Some scientists suggest women stay out of the water while menstruating

7. While blood likely does not provoke a shark to attack, a shark in the vicinity likely can detect the blood. Without any conclusive proof of how sharks might respond, some scientists suggest women stay out of the water while menstruating.^c
8. A shark’s jaw is not attached to its cranium. Because its mouth is situated on the underside of its head, a shark can temporarily dislocate its jaw and jut it forward to take a bite.^h
9. Before sandpaper was invented, people used the rough skin of sharks, called shagreen, to smooth and polish wood. Japanese warriors wrapped the skin around the handles of their swords to keep the swords from slipping out of their hands.^f
10. Sometimes when fishermen catch a shark, they will cut off its fins for soup and throw the shark back into the sea—still alive. The mutilated shark is unable to swim or breathe and eventually dies.ⁱ
11. The first pup to hatch inside the sand tiger shark mother devours its brothers and sisters until there are only two pups left, one on each side of the womb. This form of cannibalism is called oophagy.^b

Sharks tend to look scarier as they age because their new teeth are typically longer than their old teeth

12. Sharks don’t get cavities probably because they are constantly shedding teeth. Sharks have 40-45 teeth, with up to seven rows of replacement teeth behind them. When a front tooth breaks or falls out, it takes only about one day for a replacement tooth to move forward to the front row. Sharks can go through more than 30,000 teeth in a lifetime. Newer teeth are always larger, so sharks can look scarier as they age.^g
13. The first use of the word “shark” in English occurred in 1569. Previously, English sailors and fishermen used the term “sea dog” or the Spanish tiburón. It could possibly be from the German Schorck, which is a variant of Schurke (“scoundrel villain”) from shürgen (“to poke, stir”).^d
14. Even though almost equal numbers of men and women spend time in the ocean, no one knows why sharks seem to prefer to attack men. In fact, nearly 90% of shark attacks have happened to men.^b

Weird objects, such as torpedoes, have been found in shark stomachs

15. Weird things that have been found in shark stomachs include shoes, chairs, the rear half of a horse, a box of nails, a torpedo, drums, and bottles of wine.^f
16. In 1977, Happy Days' Arthur “Fonzie” Fonzarelli jumped over a penned-in shark while on water skis, giving birth to the expression “jumping the shark” to describe a desperate dramatic measure by a TV show.^f
17. There are at least 400 species of sharks that can be placed into eight groups, and new ones are being identified all the time. Of this large number, only about 30 species are known to attack humans—particularly the Great White, Tiger, Bull, Mako, and Hammerhead sharks. Most sharks are completely harmless.^f
18. Sharks do not have a single bone in their bodies.^g
19. The most bizarre feeding technique of all sharks is that of the Cookiecutter (cigar or luminous) shark. It attaches its mouth onto its victim and carves out a hunk of flesh, leaving a distinctive circular wound in its prey, like a pastry cutter. Its body has a series of holes called “photophores” that glow in the dark water. In fact, its scientific genus name is Isistius, from Isis, the Egyptian goddess of light.^g
20. The Grey Reef shark (Carcharhinus amblyrhynchos) has been called the “gangster shark” because of its highly aggressive nature.ⁱ
21. Sharks can be found in all of Earth’s oceans.^f

Because their fins look like flowing robes, angel sharks were once called "monkfish"

22. Angel sharks were once called monkfish or bishop fish because their fins look like flowing robes.^f
23. The frilled shark, or eel shark, is called a “living fossil” because it is so much like some extinct sharks that are found preserved in rocks. Parts of its skeleton resemble those of sharks that became extinct 350 million years ago.^f
24. Portuguese sharks live at depths of 12,000 feet, which is over two miles deep.^g
25. As long as a shark’s back is mostly under water, it can swim easily. A nine-foot-long bull shark can swim in just two feet of water.^b
26. About two-thirds of shark attacks on humans have taken place in water less than six feet deep.^f
27. Most shark attacks occur less than 100 feet from the shore. Shark attacks happen all over the world, but mainly around popular beaches in North America (especially Florida and Hawaii), Australia, and South Africa.^f

More people are killed by bee stings and lightning than by shark attacks

28. More people are killed by bee stings and lightning than by shark attacks. Worldwide about 30 people die each year from shark attacks, which means a person has a one in 300 million chance of being killed by a shark. A shark attack most often occurs when a shark mistakes a person for a seal or other animal.^f
29. Sharks will often give warning signs before they attack, by arching their backs, raising their heads, and pointing their pectoral fins down.^f
30. For every human killed by a shark, humans kill two million sharks.ⁱ
31. Many species of sharks have a movable, transparent nictitating membrane that covers and protects their eyes when they are attacking and eating.^f
32. Unlike fish, sharks do not have a swim bladder to keep them afloat—for this, sharks instead have a large oil-filled liver. Sharks that spend a lot of time on the surface, such as whale and basking sharks, have a massive liver.^c
33. Shark liver oil used to be the main source of vitamin A for humans. The liver of a basking shark can weigh over 1,800 pounds and contain 600 gallons of oil.^c
34. Contrary to popular belief, the stomach is not the largest organ inside a shark’s body. The liver is the largest organ and can be 25% of the shark’s weight.^g
35. Many Greenland sharks (Somniosus microcephalus) have small parasites on their eyes that glow in dark water. Scientists think these glowing parasites attract prey into the sharks' mouths. These sharks also have poisonous flesh that must be boiled three times before eating.^a
36. A female blue shark's skin is three times thicker than a blue male’s to survive courtship bites.^a
37. In the 1980s, the efficiency of a shark was compared to that of a submarine and, weight for weight, the shark required six times less driving power. This discovery has led to remarkable new experiments for racing yachts, submarines, and bathing suits that explore “rough” rather than smooth surfaces in the water.ⁱ
38. Recent research indicates that when a shark plies surface waters (when the dorsal fin cuts through the sea’s surface), it could be detecting pressure waves associated with a struggling animal nearby.ⁱ
39. The largest fish caught with a rod and reel was a Great White shark. It weighed 2,664 pounds and was almost 17 feet long.ⁱ

A bull shark can live in both fresh and salt water

40. A bull shark can live in both salt and fresh water by regulating salt and other substances in its blood. A bull shark may have been responsible for a 1916 shark attack that happened in a creek in New Jersey. They have also been found in the Mississippi River.^g
41. The world’s most unusual shark, the megamouth (Megachasma pelagios), wasn’t discovered until 1976. Its mouth can reach up to three feet across, while the rest of the body is about 16 feet long. Only 14 megamouths have ever been seen.^h
42. The shark that lives the longest is the spiny or piked dogfish (Acanthias). They usually live up to 70 years of age, but some may live until they are 100. Dogfish sharks are named for their tendency to attack prey like a pack of wild dogs would.^g
43. Most sharks cannot pump water over the gills as most fish are able to do. They must constantly swim to force water through their mouths and over their gills. A few exceptions to this are sharks that lie flat on the bottom of the ocean, such as the angel shark (which takes in water through a hole behind its eye called a spiracle) and the nurse shark (which opens and closes its mouth to move water over its gills).^a
44. Approximately 100 million sharks are killed every year. Shark teeth are used to make necklaces; cartilage is used to make fertilizers; skin is used to make leather; liver is used to make face cream, sap, and fuel; and fins are used to make soup. The mass killing of sharks creates a negative, cascading effect in the global environment.ⁱ
45. All living creatures emit small electrical signals as they breathe or move. Some sharks, particularly hammerheads, can use electricity to help them catch their prey—they pick up very small electrical impulses through hundreds of tiny holes in their faces, called Ampullae of Lorenzini.^b
46. Sometimes sharks attack metal objects. This might be because metal gives off weak electric signals in salt water that may confuse sharks.^b
47. The smallest shark is the dwarf lantern shark, which is only seven inches long. The longest shark is the whale shark, which can grow to a whopping 50 feet long and weigh more than 40,000 pounds. These behemoths are usually gentle and get all their food by sifting small animals out of the water.^b
48. The empty egg cases of some sharks (such as the dogfish shark) that wash up on seashores are called “mermaid purses.”^h
49. Most sharks are born alive (viviparous). There are two ways a pup can grow inside the mother. In some sharks, the embryos feed on the yolk attached to their bellies. Other species have an umbilical cord that connects to a mother’s blood supply. A mother shark can give birth to up to 48 pups in one litter. The pups are usually born tail first and might rest beside their mother for a while before swimming away to fend for themselves.^h
50. Whale sharks give birth to the greatest number of pups. They can produce several hundred in a litter.^h
51. Basking sharks are pregnant for more than two years, while other sharks, such as the bonnet head shark, are pregnant for only a few months. The longest gestation period of any mammal is the elephant, at 22 months.^f
52. When it comes time to give birth, the female shark loses her appetite so she won’t be tempted to eat her own pups.^b

The blockbuster film Jaws dramatically increased shark killings

53. The 1975 movie Jaws fueled widespread fear and hatred of sharks, and the shark has been intensely hunted since. It is so endangered that many countries have taken steps to protect it. Ironically, the late Peter Benchley, the author of the book, supported shark conservation.ⁱ
54. Dreaming has been observed in bony fish, but not yet in sharks.ⁱ
55. There are some things a shark cannot eat, such as a small fish called the Moses sole and the puffer fish. When a shark bites a sole, it releases a chemical in the shark’s mouth that makes the shark release it. Scientists are trying to duplicate this chemical so it can be used to keep sharks away from people.^b
56. Sharks do not have scales. Instead their skin is covered with denticles, which give the skin its roughness. As sharks grow, the denticles fall off and are replaced by larger ones.^a
57. Native Americans in Florida used the teeth of Great White sharks as arrowheads.^f
58. A pair of shoes made of shark leather can last four times longer than shoes made with regular leather.^f
59. Some sharks—such as the Great White, Porbeagle, and Mako—have crescent-shaped tail fins and can swim very fast. Two researchers calculated a three-foot Shortfin Mako reached an amazing speed of 68 miles per hour, though generally the shark has been more reliably clocked at 46 mph. Both the Mako and the Great White can leap up out of the water.^f

The wobbegong shark blends so well into the ocean floor that it is also often called a "carpet shark"

60. Some sharks, like the wobbegong and angel sharks, are so flat that they look like they're part of the sea floor.^h
61. Discovered in Japan in 1898, the goblin shark has a long snout, beady eyes, and pink-gray flabby skin. Some scientists call it “Frankenshark” because it looks so ugly. Its bizarre beak may be a step in evolution toward something like a saw shark or hammerhead shark.^g
62. Hearing is probably the best of all of a shark’s senses. Some sharks can hear prey in the water from 3,000 feet away. They are better at detecting low frequency sounds, so they can’t detect the high-frequency sounds dolphins make.ⁱ

Nurse sharks are probably the laziest sharks

63. Nurse sharks are probably the laziest sharks, spending much of the day resting on the sandy sea floor, sometimes stacked on top of each other. When they get hungry, they are like giant vacuum cleaners, sucking prey off the sea floor or from between rocks.^g
64. Sharks have been called “swimming noses” because their sense of smell is so good (they smell with their nostrils but don’t breath through them). Some sharks can smell one part of blood in 100 million parts of water and can tell which direction that smell is coming from.^g
65. Sharks do not have ears on the outside of their body, but rather on the inside of their heads.^b
66. Sharks have rows of small holes on the sides of their bodies called lateral line organs that are sensitive to small movements in the water...which is how they know when other fish swim near them.^f
67. Some sharks can bite hard enough to cut through a thick piece of steel. Like lions and other predators, sharks usually kill only when they are hungry, which isn’t very often. Some sharks can live a year without eating, living off the oil they stored in their bodies.^f
68. An ancient shark called Carcharodon Megalodon (“rough tooth, big tooth”) had the largest shark teeth ever found, measuring more than six inches long. Its jaws were big enough to swallow an entire car, and it was the same length as the dinosaur T-Rex. Some people believe this shark may still exist in deep water.^g
69. The largest and strongest known predatory fish in the sea, the Great White shark (also called White Death), can grow up to 30 feet long and is the only fish that lifts its head out of the water as if to investigate surface objects. Its jaw is six times stronger than a wolf’s and has about two-thirds the biting strength of a Tyrannosaurus Rex’s jaw. The Great White is responsible for 30-50% of all deadly attacks on humans.^f
70. The second-most dangerous shark in the world, the tiger shark, is sometimes called the “garbage can of the sea” because it will eat anything, including animal carcasses, tin cans, car tires, and other garbage. One was even found having a chicken coop with the remains of bones and feathers inside its stomach.^g
71. Humans stand little chance of surviving a shark attack. One of the most startling incidents of a shark attack occurred in Tasmania, Australia, in 1993. Terri Cartwright died instantly when a 15-foot Great White bit her in half as her horrified family watched from a boat. She was last seen in its mouth. Part of her leg and a piece of her wet suit were later found.^e
72. Sharks may have evolved from jawless fish, such as lampreys.^a

The thrasher shark is remarkable for its long tail, which it uses to "thrash" or stun its prey

73. The thrasher (fox, slasher, or swingle-tail) shark uses its long tail to fish. Its tail can be half the length of its whole body—up to 10 feet. It uses its tail like a bat or whip that either smacks or stuns its prey.^f
74. Sharks may use the Earth’s magnetic field with special organs that act as a compass to navigate the oceans.^f
75. Until the nineteenth century, some inhabitants of the islands in the South Pacific considered sharks to be gods and offered human sacrifices to them.^f
76. In Borneo, to stop babies from crying, the saw from a sawfish shark is covered in cloth and hung over the cradle.^f
77. Solomon Islanders believed that when people died, their ghosts inhabited the bodies of sharks.^h
78. Shipwrecked sailors or ditched airman may sometimes use what is called a shark screen bag that disguises the person's shape and keeps telltale scents from reaching cruising sharks.^f
79. Although there are about 400 different types of sharks, fewer than 20% of them are larger than adult humans.^h
80. While the ostrich lays the largest eggs on land, the whale shark lays the largest eggs in the world. An egg from a whale shark measuring 14 inches in diameter was found in the Gulf of Mexico in 1953.^h

-- Posted March 11, 2009

References

^a Bright, Michael. 2002. Sharks. London: The Natural History Museum, London.

^b Crawford, Dean. Shark. London: Reaktion Books, Ltd.

^c eMedicineHealth. “Shark Bite—Prevention.” February 27, 2009. Accessed: February 27, 2009.

^d Etymology Online. “Online Etymological Dictionary.” Accessed February 26, 2009.

^e MacCormick, Alex. 1998. Shark Attacks: Terrifying True Accounts of Shark Attacks Worldwide. New York: Macmillan.

^f MacQuitty, Miranda. 1992. Shark. New York: Dorling Kindersley Book.

^g ---. 2002. Sharks and Other Scary Sea Creatures. New York: Dorling Kindersley Limited.

^h Pope, Joyce. 2002. 1001 Facts about Sharks. New York: DK Publishing.