Sharks are believed to have existed on the planet for as many as 450 million years and have most likely evolved quite a bit. Pre-historic sharks probably looked nothing like the sharks we have on our planet today.
Sharks have evolved to not have a single bone in their bodies. Instead they have a skeleton made up of cartilage, making them very flexible. Since sharks are fish, not mammals as other large sea creatures are, some sharks must remain on the move for their entire lives. Movement forces water over their gills, delivering oxygen to the blood stream. If the shark stops moving then it will suffocate and die.
These predators have a dangerous reputation, but really they keep to themselves. More than ever, their existence is threatened most by humans invading their habitats. Here are some fun facts about sharks that you might not know!