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The Human Race: It's What's for Dinner!
Sharks have had remarkable evolutionary success. The first sharks lived approximately 400 million years ago, about 200 million years before the dinosaurs. They have survived the reign of the large reptiles by another 200 million years.
The International Shark Attack File, which contains data on shark attacks from around the world, reports fewer than 100 shark attacks per year, with about 10-15 deaths each year. In comparison, about 1,000 people die from attacks by crocodiles; 1,500 from tigers, lions, and leopards; and 60,000 from snakebites.
Only about 40 of the roughly 400 species of sharks are documented attackers of humans, although another 20-30 species may occasionally attack humans. The great white shark has been implicated in more attacks than any other species. The tiger shark and bull shark are also known to be particularly dangerous. In general, however, any shark greater than 2 meters, or 6 feet, in length is potentially dangerous. Exceptions to that rule are whale sharks (the largest of the sharks), basking sharks, and megamouth sharks, all of which feed primarily on tiny plankton.
Sharks normally eat fish, sharks, rays, squid and other invertebrates, sea mammals (such as porpoises, seals, and sea lions), sea turtles, and sea birds.
Sharks have remarkable senses. They have good vision, especially up close, and are especially sensitive to motion and contrast. A shark's sense of smell and taste is remarkable, with two thirds of their brains involved in processing this information. Sharks also have specialized organs called ampullae of Lorenzini, which detect tiny electrical currents, such as those put out by active muscle contractions.
Shark attacks can be broadly categorized into the following 3 types:
* In a "hit-and-run" attack, the most common type, the shark takes a single bite and does not return for more. Experts feel this attack may be because the shark mistakes a human for its normal prey.
* In a "bump-and-bite" attack, the shark bumps the victim prior to returning for further bites.
* In a "sneak attack," the shark bites without warning, and then follows up with further attacks.
The last 2 types of attacks, though less common than the hit-and-run attack, are the source of most severe shark bite injuries and shark bite deaths.
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