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Sharks, skates and rays evolved from jawless fish about 390 million years ago. Although their ancestors had bone, the shark group at some stage lost the ability to make bone, and their skeletons are made of cartilage. Cartilage is what we call "gristle" and in humans it makes the ears, nose and much of the skeletons of babies.
Sharks have no swim bladder and must swim perpetually to keep from sinking to the bottom. |
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Biological Environment > Sharks
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Note: Many facts have been simplified to make them easier to understand.
Click here to read Time Crystal, history of the Universe as sci-fi fantasy romance!
Note: Many facts have been simplified to make them easier to understand.
Click here to read Time Crystal, history of the Universe as sci-fi fantasy romance!
