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There are several hundred species of sharks, ranging
in size from less than ten inches to over 50 feet. These amazing animals
have a fierce reputation, but fascinating biology. Here we'll explore
some things that define sharks.
Until the 16th century, sharks were known to mariners as “sea dogs”.
Sharks even eat other sharks.
For example, a tiger shark might eat a bull shark, a bull shark might
eat a blacktip shark and a blacktip shark might eat a dogfish shark!
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And though sharks kill only a few people each year, media coverage and
movie portrayals of attacks have marked sharks as voracious killing
machines.
Their size, power, and great, toothy jaws fill us with fear and
fascination.
However, the term “shark” has also been used for extinct members of the
subclassElasmobranchii outside the Selachimorpha, such asCladoselache
and Xenacanthus.
The etymology of the word “shark” is uncertain.
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The teeth of the carnivores are sharp and pointy.
Sharks have prowled Earth’s seas, essentially unchanged, for 400 million
years.
Almost all sharks are “carnivores” or meat eaters.
Modern sharks are classified within the cladeSelachimorpha and are the
sister group to the rays.
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Their skeleton is made of cartilage instead of bone, which allows
greater flexibility.
Sharks are a group of fish characterized by acartilaginous skeleton,
five to seven gill slits on the sides of the head, and pectoral fins
that are not fused to the head.
One theory is that it derives from the Yucatec Maya wordxok, pronounced
‘shok’.
They live on a diet of fish and sea mammals (like dolphins and seals)
and even such prey as turtles and seagulls.
Their skin is made of denticles instead of ordinary fish scales. |