General Facts About Sharks
A shark is an amazing fish that lives mostly in oceans. They have no bones, and their skeleton is made of cartilage. They are different sizes which range from the size of your hand to the size of a school bus! There are over 368 different types of sharks which are divided into 8 orders and 30 different families. Sharks go back some 400 million years as shown by fossil records. These records show that sharks were the first fully jawed vertebrates. Sharks have survived at least four global extinctions which knocked 80% of the planet's mega --fauna into extinction. Sharks still live today in essentially the same shape, form, and structure as they were millions of years ago.
Egg fertilization occurs in the female shark's body. The reproductive organ of a male shark is called the pelvic clasper. The male shark has two pelvic claspers. The male shark holds the female shark by biting the female with its mouth and uses the pelvic claspers to fertilize eggs in the female shark. Sperm from the male shark is deposited in a chamber called the cloaca.
When eggs are fertilized, a protective case is created over them. The egg cases have distinctive shapes. This happens for 90% of sharks. About 10% of sharks, like the hammerhead shark, do not have this protective case. The embryo is connected to the mother's uterus by an umbilical cord just like mammals.
30% of sharks lay their eggs and leave. The sharks develop and are born fully independent. In 60% of sharks the embryo develop and hatch inside the shark. In 10% of sharks, the shark gives birth to live pups (baby sharks are called pups) like mammals.
Most sharks eat the same things. Some of these are fish, squid, and octopuses. Some are so small they have to eat plankton, while others eat other sharks, including their own babies. Big sharks will eat anything, even trash. Once a suit of armor was found in a Great White Shark! Sharks do not normally eat people. Shark attacks rarely ever happen.
Sharks' ecosystems are quite varied. Some sharks live in fresh water while others live in salt water. Sharks can be found in tropical waters around the world, as well as icy waters. Sharks live in all depths of water.