Shark History

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Do you know how long sharks have existed? Sharks have been around for about 400 million years. There are about 450 species of sharks that have existed on the planet. That is a very long time and a lot of species of sharks! I will tell you about the different species, how long they have existed, the changes that have occurred over time, the similarities that still exist, their migration, and their closest relatives. There use to be 450 species of sharks divided into eight categories. The categories are explained in a cladogram. The first four categories in the cladogram are: nictitating (blinking) eyelids or no nictitating eyelids, mouth behind eyes or mouth in front of eyes, no fin spines or fin spines, five gills with two dorsal fins or six to seven gill slits with one dorsal fin. The next four categories are: anal fin or no anal fin, mouth at the end of snout or mouth below snout, flattened body or rounded body, and a long snout or a short snout. That seems to be a complicated way to categorise sharks, but it is very organized. Now, as more sharks are discovered or when relationships are further studied, the classifications may change Sharks have existed for a very long time. They have existed for 400 million years. When people say dinosaurs have been around the longest, they are wrong. Sharks were around 200 million years before the dinosaurs. One of the earliest known sharks that were around at that time is the Cladoselache. The Cladoselache was around about 360 million years ago and was about two meters long (seven feet). My favorite shark is the Megalodon that roamed the waters about 200 million years ago. The megalodon was a massive shark that reached up to about 16 meters long (52 feet) and had a mouth th... ... middle of paper ... ...during the winter. The sharks have some very close relatives. The closest relatives to the sharks are stingrays. The Angel Shark shows most similarities to the stingray. The flattened pectoral fins form a similar shape resulting in the looks of angel wings, hence the name angel shark. The importance of knowing about sharks and how they have evolved is that it allows knowledge. Knowing about sharks and how far they trace back allows scientists to create a timeline for classifying organisms. If we have a timeline and discover something new, then scientists can compare and do testing to see how long ago the organism had existed. Also, knowing about sharks allows us to have an idea upon what is expected in the future. If we didn’t have an idea of what has happened in the past, then how will we know what to expect in the future? We wouldn’t know what to expect.

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