Evolution of sharks

Hannah Doherty, Caitlin Felts, & Lauren McKee

Sharks have ruled the ocean for over 440 million years, but to become the kings of the ocean, they had to adapt and evolve with the oceans constant changes. Sharks evolved from the first fish, Ostracoderms, that appeared 510 million years ago. By the carboniferous period, the types of sharks were at a high. There was Stethacanthus, Xenacanthus, Helicoprion, Megalodon, Cladoselache, and many more types. But by the permian period, many of these types of sharks had become extinct. Luckily, ray finned fishes became populated, providing an easy food source for sharks, so the sharks survived the permian extinction.

In the billions of years they have been alive, sharks have survived all five large extinctions using their speed, maneuverability, and flexible jaws to prevent themselves from dying out. Although prehistoric sharks were very advanced for their time, they were very different from present day sharks. Prehistoric sharks were much bigger than modern day sharks, which is another characteristic that helped them survive mass extinctions. Other than the anal fin, modern and prehistoric sharks have the same fins, jaw placement, and vertebral column. Until sharks appeared, there had only been fishes with skeletons made of bone. During the devonian era, chondrichthyes, fishes with skeletons made of cartilage, came around and started evolving. It wasn’t until the jurassic explosion, 100 million years ago, that sharks really began to evolve into the superior predators that they are today.

Although having skeletons made entirely of cartilage sets them apart from other fish, it makes it very hard for scientists to do research on prehistoric sharks. Cartilage doesn’t fossilize like bone does, but using the shark’s teeth, scientists have discovered that sharks were around before insects, mammals, and dinosaurs. One of the greatest skills these sharks have is their ability to adapt to changes. During the Cretaceous period, the shark’s prey began to become more spread out, causing sharks to have to migrate and adapt to new areas of the ocean. In the Miocene period, sharks bodies evolved to allow them to process oxygen through their gills, allowing them to move quicker through the water. They also adapted to water temperatures decreasing in areas of the ocean where their prey was during the Pliocene period. The reason sharks are still around today is because of their remarkable ability to evolve and adapt to the situation at hand.

 

References

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Shark Evolution. (n.d.). Retrieved from Sharks-World website: http://www.sharks-world.com/shark_evolution/

Top Ten Prehistoric Sharks. (n.d). Retrieved from Prehistoric-Wildlife website: http://www.prehistoric-wildlife.com/top-tens/top-ten-prehistoric-sharks.html

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