Sharks
Sharks are fish that can be found all over the world, in every ocean & even some lakes & rivers. Primitive sharks are said to have evolved some 420 million years ago. True sharks have existed for over 350 million years & evolved long before the dinosaurs did. Unlike bony fish, sharks skeletons are made of cartilage, only their calcified vertebrae & teeth are preserved for the fossil record. Sharks could have up to 3,000 teeth at one time, arranged in rows. When one tooth is damaged or lost, it is replaced by another.
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