Sharks are colorblind.

Like humans, sharks have rods and cones in their eyes that respond to light, but humans have three types of cones that enable color vision. In contrast, sharks lack multiple cone types, so even those with a high cone count, like the black tip shark and bull shark, can only see in black and white.

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Sharks actually have an excellent memory.

The researchers examined the memory retention abilities of juvenile gray bamboo sharks (Chiloscyllium griseum). The sharks had previously undergone training in various visual tasks, such as distinguishing shapes and optical illusions. In this study, the researchers tested the sharks for memory retention. Surprisingly, even without reinforcement, the sharks remembered what they had learned for up to 50 weeks, at which point the testing concluded.

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Sharks have no bones in their bodies.

Instead, they are made of a rubbery tissue called cartilage. That's made it more difficult for scientists to study ancient sharks, since cartilage typically doesn't preserve as well as bones do — early shark fossil records are mostly based on scales and teeth.

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