21. Unlike other sharks, bull sharks can survive in fresh water, they will move between the ocean and fresh water environments frequently when they get older.
22. On average, a shark has 40-45 teeth, and there are seven rows of replacement teeth in its mouth, if the front teeth are lost, the back rowteeth will begin to take their place quickly, so sharks don’t have to worry about there are not enough teeth to use. Generally speaking, a shark’s teeth will be replaced once every two weeks, a shark will go through more than 30,000 teeth in a lifetime.
23. Some female sharks can clone themselves,it means they can give birth without males, this is called parthenogenesis.
24. Sharks have existed on Earth as early as 200 million years before the dinosaurs appeared, they have a history of over 400 million years, and sharks have changed very little in so long time.
25. Lamniformes, the mackerel sharks do not required sleep, ever.
26. Sharks do not have a swim bladder, they keep them afloat depend on their large livers.
27. Native Americans in Florida used the teeth of Great White sharks as arrowheads.
28. Some sharks are flat, such as angel sharks and the wobbegong, their flat backs make them look just like they’re part of the sea floor.
29. Sharks pups are able to survive in the harsh sea soon after birth, their mother would not stay with them to protect them, they must immediately learn to live independently and take care of themselves, fortunately, they are born with fully-fledged sets of teeth, so they can fend for themselves.
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