​Sharks are the first vertebrates that had jaws.

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The earliest Shark was dated to be over 420 million years old. At this time, on land there was only desert; no trees had managed to establish themselves yet, there were no mammals, bird or reptiles.

The Sharks at that time looked a bit different than modern sharks do. Some scientists believe, that some of the first shark life forms had scales like bony fish. Many of the early sharks are belived to have lived in freshwater lakes.

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The majority of the modern sharks can be traced back to about 100 million years ago. They largely have remained unchanged ever since then. Then again, they didn't have to as they are a successful biological model shaped by evolution.