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You might not know these
sleek, swift swimmers as well as you think. There are more than 370 species
of sharks, and about half of them are less than
3 feet long when fully grown. Sharks have
a keen sense of smell. Scientists
estimate that scent detection makes up about 70 percent of a shark's
total brain activity! Some sharks,
such as the reef and bull shark, have
color vision that attracts them
to bright orange and yellow shades.
Shark-savvy scuba divers avoid these colors,
calling them "yum-yum yellow." The inside of
a shark's jaw has many rows of teeth.
These rows usually lie flat until
the first tooth in front falls out. It
is then replaced by another tooth popping forward
to replace it, as if on a conveyor
belt. This process of
teeth replacement continues throughout a shark's life, so it has a
lifetime supply of chompers! Sharks do
not chew their food. Instead, they
swallow their bites whole.A big meal, such as a sea lion or turtle, may fill up a shark
for over a month. Cartilage, the tough,
flexible material that makes up a shark's
skeleton, is used both for cancer research and as
a possible skin replacement for burn victims. Experts say that only half a
dozen types of sharksare very dangerous. Most are shy and
harmless, avoiding people and other large
animals when possible. People kill over a hundred million sharks per year. Shark
skins are used to create strong
leather. Some sharks are eaten for their meat or in shark
fin soup, while others are used for fertilizer. |
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